EnRythm Biomedical Design Project

THE ENRHYTHM CARDIAC PACEMAKER:
GENESIS, CURRENT MODEL, AND DESIGN
RECOMMENDATION
THE BRADY BUNCH
Gabrielle Fantich
Andrew Long
Nidhi Thite
Erik Thomas
John Wuthrich
Submitted December 11th
, 2013
for
Engineering 100.100.101
Dr. George T. Wynarsky
Dr. Elizabeth S. Hildinger
Engineering 100.100 Professors

TABLE OF CONTENTS
Foreword………………………………………………………………………………. 1
Summary………………………………………………………………………………. 1
Introduction……………………………………………………………………………. 2
Anatomy of the Heart………………………………………………………………….. 3
Blood Flow through the Heart…………………………………………………. 3
Electrical System of the Heart………………………………………………….. 3
Electrocardiogram (ECG)……………………………………………………… 3
Medical Problem: Arrhythmia………………………………………………………….. 4
Bradycardia…………………………………………………………………….. 4
Atrial Tachycardia……………………………………………………………… 4
The History of Artificial Cardiac Pacemakers…………………………………………. 4
Hopps Pacemaker-Defibrillator………………………………………………... 4
Implantable Pacemaker………………………………………………………… 5
On-Demand Pacemaker………………………………………………………… 5
Improved Battery Life…………………………………………………………... 5
Dynamic Pacemaker……………………………………………………………. 5
Dual Chamber Pacemaker……………………………………………………… 5
Microprocessor-Controlled Pacemaker………………………………………... 6
Managed Ventricular Pacing (MVP)…………………………………………... 6
Components of the EnRhythm Pacemaker……………………………………………... 6
Implantable Pulse Generator (IPG)……………………………………………. 6
Pacing Leads…………………………………………………………………… 6
Implantation of the EnRhythm Pacemaker……………………………………... 7
Function of the EnRhythm Pacemaker…………………………………………………. 7
Sensing………………………………………………………………………….. 7
Pacing…………………………………………………………………………... 8
Dual Chamber Pacing………………………………………………………….. 8
Managed Ventricular Pacing (MVP)…………………………………………... 8
Rate-Responsive Pacing………………………………………………………... 8
Reactive Atrial Antitachycardia Pacing (ATP)………………………………… 9
Cardiac Compass………………………………………………………………. 9

Materials of the EnRhythm Pacemaker………………………………………………… 9
Wire Insulation & Connector Block: Polyurethane……………………………. 9
Electrodes: Platinum Iridium Alloy……………………………………………. 10
Electrode Separation: Silicone Rubber………………………………………… 10
Implantable Pulse Generator: Grade 5 Titanium Alloy………………………... 10
Alternative Treatments for Arrhythmia………………………………………………… 11
Catheter Ablation……………………………………………………………….. 11
Electrical Cardioversion……………………………………………………….. 11
Limitations of the EnRhythm Pacemaker………………………………………………. 12
Current Pacemaker Research…………………………………………………………… 12
Leadless Pacemakers…………………………………………………………… 12
Piezoelectric-Powered Pacemakers……………………………………………. 13
Optogenetic Pacemakers……………………………………………………….. 13
Laser-Based Pacemakers………………………………………………………. 13
Design Recommendation……………………………………………………………….. 13
Components of the Proposed Design…………………………………………… 14
Function of the Proposed Design………………………………………………. 14
Benefits of the Proposed Design……………………………………………….. 14
References……………………………………………………………………………… 15
Appendix A: Pacing Modes……………………………………………………………. 20
Appendix B: Piezoelectricity…………………………………………………………… 21
Appendix C: Ultrasound………………………………………………………………... 22

Brady Bunch 1
FOREWORD
You asked our team to research a biomedical device and provide a design recommendation to
improve the device. We chose to research the Medtronic EnRhythm cardiac pacemaker. This
device treats arrhythmia, a serious heart condition causing an irregular heart rhythm. We
researched the anatomy of the heart, the medical problem of arrhythmia, and the history of
cardiac pacemakers. We also researched the components, function, and materials of the
Medtronic EnRhythm cardiac pacemaker. We then examined alternative treatments for
arrhythmia, the limitations of the EnRhythm pacemaker, and current research of pacemakers. The
purpose of this document is to present our findings and provide our design recommendation for
the Medtronic EnRhythm cardiac pacemaker.
SUMMARY
Arrhythmia is a potentially fatal heart condition resulting in an irregular heart rhythm. Cardiac
pacemakers treat arrhythmia by stimulating the heart with an electrical current. The Medtronic
EnRhythm pacemaker provides relief for patients suffering from arrhythmia.
The heart is separated into four chambers by muscular walls called septa. The top chambers are
the right and left atria, and the bottom chambers are the right and left ventricles. These chambers
contract to pump blood throughout the body. The contractions are controlled by specialized
tissues known as the sinoatrial (SA) node and the atrioventricular (AV) node, which generate
electrical signals that pass through the heart muscle. An electrocardiogram (ECG) is a test used to
monitor the heart’s electrical activity.
Arrhythmia is an abnormal beating of the heart caused by a delay or blockage of the heart’s
electrical signals. A delay or blockage occurs when the SA or AV nodes are not working properly
or when the electrical signals do not progress normally through the heart. Two types of
arrhythmia are bradycardia and atrial tachycardia. Bradycardia causes slow beating of the heart.
Atrial tachycardia causes an abnormally fast heart rhythm in the atria.
The first artificial cardiac pacemaker was introduced in 1950. It was an external device driven by
vacuum tubes. In 1958, implantable pacemakers were developed, which were more convenient
but surgically risky. In 1965, the first on-demand pacemaker was introduced, which stimulates the
heart only when necessary. Lithium-iodine batteries were introduced in 1971, making pacemakers
more reliable. Dual chamber pacemakers, introduced in 1982, have two leads: one in the right
atrium and one in the right ventricle. Dual chamber pacemakers produce more natural heartbeats
but increase the risk of congestive heart failure. The Medtronic EnRhythm pacemaker solved this
problem in 2005 through a program called Managed Ventricular Pacing (MVP).
The EnRhythm pacemaker is composed of an implantable pulse generator (IPG) and two pacing
leads. The IPG is located in the chest cavity near the heart and contains a lithium battery, internal
circuitry, and connector block. The two pacing leads are placed within the right atrium and right
ventricle and attach to the IPG through the connector block. The EnRhythm pacemaker uses
bipolar leads, which have two electrodes.
The EnRhythm pacemaker treats bradycardia and atrial tachycardia by performing two functions:
sensing and pacing. In sensing, the electrodes at the end of each lead detect the electrical signals
produced by the heart. The pacemaker circuitry analyzes these signals to determine if pacing is
necessary to correct an irregular heartbeat. In pacing, the energy from the battery is converted
into an electrical impulse, which travels through the leads to the heart tissue, causing the heart to
beat.

Brady Bunch 2
The EnRhythm pacemaker can stimulate a contraction of the atria followed closely by a
contraction of the ventricles. Managed Ventricular Pacing allows the EnRhythm pacemaker to
switch from only pacing the atria to stimulating both the atria and ventricles. The EnRhythm
pacemaker uses rate-responsive pacing to adjust a patient’s heart rate based on the patient’s
activity level. It also uses Reactive Atrial Antitachycardia Pacing (ATP), which delivers a set of
rapid impulses to the atria to treat atrial tachycardia. Cardiac Compass is a Medtronic program
that allows the EnRhythm pacemaker to store patient information that can be used by physicians
to monitor a patient’s progress and adjust their treatment plan.
The wire insulation and connector block of the IPG are made of polyurethane. Polyurethane’s
high electrical resistivity protects the body from the electrical current that passes through the
wire. The electrodes are made of a platinum iridium alloy with a high electrical conductivity that
allows the electrical current to be transmitted to the heart. Silicone rubber is used to separate the
electrodes because the rubber’s high electrical resistivity prevents current from flowing
simultaneously through the electrodes. The IPG is made out of grade 5 titanium alloy. This alloy
has a high yield strength, which makes the IPG resistant to permanent deformation, protecting its
internal components.
Two alternative treatments for arrhythmia are catheter ablation and electrical cardioversion.
Catheter ablation is a procedure in which ablation catheters (flexible tubes) are used to destroy
diseased sections of the heart that cause arrhythmia. Electrical cardioversion sends timed
electrical shocks through a patient’s chest to correct atrial tachycardia.
Limitations of the EnRhythm pacemaker include implantation risks, postoperative infections, and
allergic reactions. The electrodes of the pacemaker can cause damage to the heart tissue, the leads
can become tangled or dislodged, and the battery life is limited. Patients with pacemakers cannot
participate in full contact sports and cannot be exposed to large magnetic fields.
Medtronic is developing a miniaturized leadless pacemaker that will be implanted into the heart
using a catheter. Researchers are developing a piezoelectric material that would use energy
created by the heart’s beating to power the pacemaker. Scientists have successfully used lasers
instead of leads to pace the heart of a quail embryo. Opsins are light-sensitive proteins that can be
inserted into the heart tissue. When exposed to light, opsins cause the heart to contract.
Our design recommendation is an ultrasonic rechargeable pacemaker that converts ultrasound
waves into electrical energy. An external ultrasound transducer emits ultrasound waves to the
internal system, which converts these waves into a voltage. The internal system consists of four
components: the acoustic lens, matching layer, piezoelectric material, and backing layer. The
acoustic lens focuses the waves onto the matching layer, which then maximizes the transmission
of ultrasound waves and prevents wave reflection. The piezoelectric material, located between the
matching and backing layers, converts the mechanical energy from the ultrasound into a voltage,
which is then used to recharge the battery. The backing layer, located below the piezoelectric
material, decreases reflection by absorbing excess ultrasound waves. Our design does not alter the
implantation procedure, and the ultrasound does not interfere with the pacemaker’s internal
circuitry. Our design increases the pacemaker battery life, reduces the number of replacement
surgeries, and is safe and convenient for patients.
INTRODUCTION
Arrhythmias are problems with the rate or rhythm of the heartbeat that cause nearly 500,000
deaths in the United States each year. However, early and appropriate diagnosis and treatment of
arrhythmia decreases arrhythmia-related deaths by 15% to 25% annually [1]. Cardiac pacemakers

Brady Bunch 3
are devices used to treat arrhythmias by stimulating the heart with an electrical current [2]. The
Medtronic EnRhythm pacemaker utilizes unique programs to provide relief for patients suffering
from arrhythmias. This document will discuss the anatomy of the heart, the medical problem of
arrhythmia, the history of cardiac pacemakers, and the function and materials of the Medtronic
EnRhythm cardiac pacemaker. It will then present alternative treatments for arrhythmia, the
limitations of the EnRhythm pacemaker, and current research of pacemakers. Finally, it will
provide our design recommendation for the Medtronic EnRhythm cardiac pacemaker.
ANATOMY OF THE HEART
The heart is responsible for circulating blood throughout the human body. Blood carries nutrients
such as oxygen to the cells of the body and is responsible for removing waste products like
carbon dioxide. Without the heart to circulate nutrient-rich blood to the cells, cells would quickly
die. Therefore, a functioning heart is essential for life [2].
The human heart is a hollow specialized muscle about the size of a fist. The heart is divided into
four chambers by muscular walls called septa. As shown in Figure 1, the top chambers are the left
and right atria, and the bottom chambers are the left and right ventricles [2].
Blood Flow through the Heart
The heart’s four chambers use coordinated
contractions to pump blood throughout the
body. Deoxygenated blood enters the heart
in the right atrium. A contraction in the right
atrium pushes the blood into the right
ventricle. A ventricular contraction then
pumps the blood through the pulmonary
artery to the lungs. In the lungs, the blood is
oxygenated and carbon dioxide is removed.
The oxygenated blood then flows into the
left atrium. A second atrial contraction
forces the blood into the left ventricle,
where a final ventricular contraction pumps
the blood throughout the body. This process
repeats when the deoxygenated blood from
the body re-enters the right atrium [3].
Electrical System of the Heart
The heart’s contractions are caused by electrical impulses that travel through the heart, as shown
in Figure 1. The sinoatrial (SA) node is a specialized tissue within the right atrium that serves as
the body’s natural pacemaker. The SA node generates electrical impulses that cause the atria to
contract. These electrical signals travel along special conduction pathways to the atrioventricular
(AV) node located in the center of the heart. The AV node then creates its own electrical signal,
which results in the contraction of the ventricles. These
coordinated signals from the SA and AV nodes cause a
natural heart rhythm, with an atrial contraction followed by
a ventricular contraction [2].
Electrocardiogram (ECG)
An electrocardiogram (ECG) is a test used to monitor the
heart’s electrical activity. The electrical activity is translated
into line tracings on graph paper, as shown in Figure 2. The
Fig. 1: Structure of the heart
Adapted from: [4]
Fig. 2: ECG of the heart
Adapted from: [5]

Brady Bunch 4
first peak represents a contraction of the atria. The second peak represents a contraction of the
ventricles, and the final peak shows the ventricles returning to a resting state [5].
MEDICAL PROBLEM: ARRHYTHMIA
Arrhythmia is a problem with the rhythm or rate of the beating of the heart. The heart may beat
too slowly, too quickly, or with an abnormal rhythm. Some arrhythmias can be harmless, while
others may be life-threatening. During an arrhythmia, the heart may be incapable of pumping
enough blood to the body, causing damage to the brain, heart, and other organs [6].
Arrhythmia is caused by a delay or blockage of the electrical signals that control the heartbeat [7].
A delay or blockage occurs when the specialized nerve cells producing the electrical signals in
the SA or AV nodes are not working properly or when the electrical signals do not progress
normally through the heart [6].
Symptoms of potentially dangerous arrhythmias may include anxiety, light-headedness, fainting,
sweating, shortness of breath, or chest pain [6]. In addition, a person with arrhythmia may
experience palpitations, which are sensations in the chest or neck. Palpitations feel as if the heart
is “pounding” or has a skipped or extra beat [8].
Bradycardia
Bradycardia is a type of arrhythmia that results in
slow beating of the heart, defined as less than 60
beats per minute (bpm) [7]. Figure 3 compares the
ECGs of hearts with arrhythmias to the ECG of a
normal heart. The ECG of bradycardia shows that
a heartbeat occurs much less frequently in patients
with bradycardia than in healthy individuals.
Bradycardia can be a serious problem if the heart is
unable to pump enough oxygen-rich blood to the
organs of the body. However, people who are
physically fit can have a heart rate under 60 bpm
and be healthy. Bradycardia is caused by a failure
of the SA node to send enough electrical signals or
by a blockage or delay of electrical signals by the
AV node [9].
Atrial Tachycardia
Atrial tachycardia is a type of arrhythmia that causes fast beating of the atria [8]. A heart rate of
over 100 bpm is considered tachycardia. The ECG of atrial tachycardia in Figure 3 shows that
atrial contractions occur much more frequently in patients with atrial tachycardia than in healthy
individuals. Atrial tachycardia can be caused by AV nodal reentry. AV nodal reentry occurs when
the electrical signals pass in and around the AV node, causing the atria to keep contracting [9].
THE HISTORY OF ARTIFICIAL CARDIAC PACEMAKERS
Pacemakers have been used since the middle of the 20th century. The first pacemakers were
external units that were bulky and unreliable. Over time, improvements made pacemakers
smaller, implantable, more reliable, and longer-lasting.
Hopps Pacemaker-Defibrillator
The first pacemaker was built by John Hopps in 1950. His pacemaker was an external device
driven by vacuum tubes [13]. The vacuum tubes generated electrical impulses that traveled
Fig. 3: Comparison of ECGs
Adapted from: [10, 11, 12]

Brady Bunch 5
through wires to the atria to correct the heart’s rhythm [14].
The pacemaker was powered by a large battery known as a
mains-powered unit. As seen in Figure 4, early pacemakers
were bulky and had to be carried around in a cart.
Additionally, patients frequently experienced painful shocks
and were prone to infections [13].
Implantable Pacemaker
In 1958, pacemakers were improved when Rune Elmqvist
and Ake Sennings introduced the first fully implantable
cardiac pacemaker. This device was more convenient for
patients, but the surgeries were risky, and the battery life was
shorter than that of the external units. Additionally, the
pacemaker stimulated a heartbeat even when it was
unnecessary [15].
On-Demand Pacemaker
In 1965, the first on-demand pacemaker was introduced. On-
demand pacemakers monitor the electrical signals of the
heart. If a normal signal is detected, the pacemaker does not
stimulate the heart. Not only does this reduce patient risk, but
the decreased stimulation results in less battery usage [16].
Improved Battery Life
Researchers began focusing on improving the battery life of implantable pacemakers. In 1970, the
first nuclear-powered pacemaker was introduced, but this was quickly abandoned due to harmful
radiation. In 1971, lithium-iodine batteries were invented. These batteries made the pacemaker
significantly smaller, longer-lasting, and more reliable [17].
Dynamic Pacemaker
In 1980, the first dynamic pacemakers were introduced. These pacemakers set the heart rate
according to factors such as oxygen level, carbon dioxide level, and blood pressure. Dynamic
pacemakers are able to produce a more natural heart rhythm by adjusting heart stimulation in
response to these factors [13].
Dual Chamber Pacemaker
Dual chamber pacemakers were invented in
1982. These pacemakers use two leads
(wires) to produce a more natural heartbeat.
As shown in Figure 5, one lead is located in
the right atrium, and another lead is located
in the right ventricle. This design allows the
pacemaker to stimulate a contraction in the
atria followed closely by a contraction of the
ventricles, mimicking the natural sequence
of a healthy beating heart. However, dual
chamber pacemakers also greatly increased
the risk of congestive heart failure due to
unnecessary stimulation of the right
ventricle [18].
Fig. 5: Dual chamber pacemaker
Adapted from: [15]
Fig. 4: Early cardiac pacemaker
Image from: [13]

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Microprocessor-Controlled Pacemaker
In 1992, pacemakers utilizing microprocessors were introduced. The microprocessor stores
patient data, including blood pressure, pacing history, and oxygen levels. This data can then be
analyzed by doctors to program the pacemakers to meet the specific needs of each patient [13].
Managed Ventricular Pacing (MVP)
In 2005, Medtronic released a program called Managed Ventricular Pacing (MVP) in its
EnRhythm pacemaker. This program allows dual chamber pacemakers to switch from stimulating
both chambers of the heart to only stimulating the atria, thus reducing unnecessary stimulation of
the right ventricle [19].
COMPONENTS OF THE ENRHYTHM PACEMAKER
The EnRhythm Pacemaker is composed of an implantable pulse generator and two pacing leads.
The implantable pulse generator produces an electrical impulse, and the two leads direct the
impulse to the heart.
Implantable Pulse Generator (IPG)
The implantable pulse generator (IPG) is the device that
controls the pacemaker. It is approximately two inches
in diameter [15]. As shown in Figure 6, it is composed
of three parts: the battery, the internal circuitry, and the
connector block. The battery is a 2.8-volt lithium
battery located on the bottom of the implantable pulse
generator [20]. It has an average battery life of 8.5 to
10.5 years [15]. The second component of the
implantable pulse generator, the internal circuitry, is
located in the middle of the device. The internal
circuitry coordinates the pacemaker’s function and
allows electricity to flow from the battery to the
connector block. The final part of the implantable pulse
generator is the connector block. The connector block is
located above the internal circuitry and has two
attachment points for the pacing leads [20].
Pacing Leads
Pacing leads are thin insulated wires that direct the
artificial pulse from the implantable pulse generator to the
walls of the heart. The Medtronic EnRhythm pacemaker
has one lead in the right atrium and another lead in the
right ventricle [20]. The insulation covering the leads
protects the body from the electricity generated from the
pacemaker. The outer insulation is made of polyurethane,
shown in light blue in Figure 7. The insulation separating
the anode and cathode is made of silicone rubber, shown
in dark blue in Figure 7 [22].
The EnRhythm pacemaker uses bipolar pacing leads. Bipolar pacing leads are composed of two
electrodes: a negatively-charged anode and a positively-charged cathode. These electrodes are
made of a platinum iridium alloy [22]. As shown in Figure 7, the cathode is located at the tip of
the lead, while the anode is located just behind the cathode [20].
Fig. 6: Components of the implantable
pulse generator
Adapted from: [20]
Fig. 7: Bipolar pacing lead
Adapted from: [20]

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Implantation of the EnRhythm Pacemaker
The Medtronic EnRhythm pacemaker can be implanted with two different types of bipolar leads:
transvenous leads or epicardial leads.
As shown in Figure 8, transvenous
leads are implanted through the
veins leading to the heart. A 2.5
inch incision is made just
underneath the left clavicle
(collarbone). The leads are then
pulled through the subclavian vein
and superior vena cava into the
right chambers of the heart [23].
One of the leads is attached to the
inner wall of the right atrium, and
the other lead is attached to the
inner wall of the right ventricle.
The leads are then attached to the
connector block, and the doctor
programs the implantable pulse
generator [24]. The implantable
pulse generator is placed under the
skin at the point of the incision.
The doctor closes the incision,
completing the implantation [23].
Epicardial leads are not implanted within the heart. Instead, the leads are attached directly to the
epicardial tissue on the outer walls of the right atrium and right ventricle. This type of
implantation is less common and is used for sensitive patients, such as pediatric patients and
patients who have recently undergone heart surgery [20].
FUNCTION OF THE ENRHYTHM PACEMAKER
The EnRhythm cardiac pacemaker treats arrhythmias by delivering small electrical impulses to
the heart to correct irregular heart rhythms. The pacemaker is programmed differently to meet the
unique needs of each patient. Its primary purpose is to treat bradycardia, but it can also be
programmed to treat atrial tachycardia [15]. The
EnRhythm pacemaker treats arrhythmia by
performing two functions: sensing and pacing [2].
Sensing
The EnRhythm pacemaker senses (monitors) the
heart’s natural electrical activity in both the right
atrium and right ventricle by means of the
electrodes at the end of each lead. As shown in
Figure 9, the electrode detects the electrical
impulses that cause a natural heartbeat [18]. These
electrical signals are transmitted through the anode
in the lead to the circuitry within the pulse
generator [20]. If these signals are greater than 0.9
millivolts in the right ventricle or 0.3 millivolts in
the right atrium, then the device is able to detect the
Fig. 8: Transvenous implantation of the pacemaker
Adapted from: [25]
Fig. 9: Magnified view of electrode
sensing the heart’s electrical signals
Adapted from: [20]

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signals. If normal signals are detected, the pacemaker is said to be “inhibited”, meaning it will not
deliver a pacing pulse. If no signals are detected or the signals are too slow, the pacemaker
responds by pacing the appropriate chamber of the heart to correct the variation in the heart’s
natural rhythm [18].
Pacing
The EnRhythm pacemaker corrects
the heart’s rhythm by delivering an
electrical impulse to the heart tissue;
this process is called pacing. If an
abnormal heartbeat is detected, the
pulse generator converts the energy
from the battery into an electrical
impulse. This impulse flows through
the lead to the cathode. As shown in
Figure 10, the cathode then transmits
the impulse to the surrounding heart
tissue. This impulse replicates the
normal electrical signals of the heart,
causing the heart to beat [20]. The
electronic circuitry within the pulse
generator controls the timing and
intensity of these generated impulses
to stimulate more natural heart
rhythms [18].
Dual Chamber Pacing
The EnRhythm pacemaker is a dual chamber pacemaker, meaning it has leads in both the right
atrium and right ventricle. This allows the pacemaker to stimulate a contraction in the atria
followed closely by a contraction in the ventricles, thus mimicking the natural sequence of a
healthy beating heart [18].
Most dual chamber pacing systems run in DDD pacing mode. DDD simply means that the
pacemaker senses and paces in both the right atrium and right ventricle [26]. For more
information on pacing modes and the significance of DDD, see Appendix A. DDD pacing can
lead to severe complications because right ventricular pacing has been linked to congestive heart
failure [19]. To prevent unnecessary pacing in the right ventricle, the EnRhythm pacemaker uses
a Medtronic program called Managed Ventricular Pacing [18].
Managed Ventricular Pacing (MVP)
The EnRhythm pacemaker was the first pacemaker to use Managed Ventricular Pacing (MVP).
This program allows the pacemaker to switch from only pacing the atria to stimulating both the
atria and ventricles when ventricular pacing is necessary. Periodic tests are performed by the leads
to check that the atrioventricular (AV) node is working properly. If the AV node is not sending
electrical signals, then the ventricles also require pacing. The EnRhythm pacemaker responds to a
failed test by switching to DDD pacing mode, allowing pacing in both the atria and ventricles. If
the AV node properly sends electrical signals, the pacemaker only paces the atria [27].
Rate-Responsive Pacing
The EnRhythm pacemaker uses rate-responsive pacing, which adjusts a patient’s heart rate based
on the patient’s level of activity [2]. The accelerometer, a sensor located within the pulse
Fig. 10: Magnified view of pacing the heart
Adapted from: [20, 21]

Brady Bunch 9
generator, detects the patient’s body
motion and converts this motion into
an electrical signal. As patient
activity increases, more frequent and
larger amplitude electrical signals are
created. These signals are sent to the
pacemaker circuitry, and an
algorithm encoded in the
EnRhythm’s programming processes
the signals to determine the proper
pacing rate [28]. As shown in Figure
11, heart rhythms controlled by rate-
responsive pacing almost exactly
mimic a normal heartbeat during
various daily activities.
Reactive Atrial Antitachycardia Pacing (ATP)
The EnRhythm pacemaker can also be programmed to treat atrial tachycardia by using a
Medtronic program called Reactive Atrial Antitachycardia Pacing (ATP). If an atrial tachycardia
episode is detected, the pacemaker responds by delivering a set of rapid impulses to the atria [15].
This coordinated stimulation is designed to terminate the trapped impulse that causes atrial
tachycardia [29].
Cardiac Compass
Cardiac Compass is a Medtronic program that allows the EnRhythm pacemaker to store
information that it collects about a patient within its internal circuitry. This information is
collected for 14 months and provides clinically significant data, including the percentage of daily
pacing needed, frequency and duration of arrhythmia episodes, and physical activity of the
patient. This data can be used by physicians to monitor a patient’s progress and adjust their
treatment plan if necessary [18].
MATERIALS OF THE ENRHYTHM PACEMAKER
Each material used in the EnRhythm pacemaker has specific properties that allow the pacemaker
to function properly within the body’s environment. The materials of the EnRhythm pacemaker
that come into contact with the body are polyurethane, platinum iridium alloy, silicone rubber,
and grade 5 titanium alloy [15].
Wire Insulation & Connector Block: Polyurethane
The lead wire insulation and the casing of the
connector block of the IPG are made of
polyurethane [22]. The properties that make
polyurethane an ideal material for these
components can be seen in Table 1. The tensile
strength for polyurethane is 47 MPa, which is high
enough to prevent the wire insulation and
connector block from breaking. Polyurethane has a
low modulus of elasticity of 0.014 GPa. This
property makes the polyurethane components
flexible [30]. Polyurethane’s high electrical
resistivity value of 109
Ω-m ensures that the wire
insulation and connector block protect the body
Fig. 11: Rate-responsive pacing compared to a normal heart
rate during various daily activities
Adapted from: [2]
Table 1: Material properties of polyurethane
Material Property Value
Tensile Strength 47 MPa
Modulus of Elasticity 0.014 GPa
Electrical Resistivity 109
Ω-m
Degradation Resistance Excellent
Biocompatibility Excellent
Density 1.20 g/cm3
Table values from: [22, 30, 31, 32, 33]

Brady Bunch 10
from electrical current [31]. Polyurethane has excellent degradation resistance and excellent
biocompatibility, allowing it to withstand the body’s environment [32]. Polyurethane has a low
density of 1.20 g/cm3
, which means that both components are lightweight [33].
Electrodes: Platinum Iridium Alloy
The electrodes are made of a platinum
iridium alloy. This alloy is used because of
its specific properties listed in Table 2.
Platinum iridium alloy has a high electrical
conductivity value of 4,000,000 (Ω-m)-1
.
This high value allows the electrodes to
efficiently transfer electrical impulses to the
heart. Platinum iridium alloy also has
excellent corrosion resistance and
biocompatibility, which allow the electrodes
to function properly within the body [34].
Electrode Separation: Silicone Rubber
Silicone rubber is used to separate the anode and
cathode at the end of each lead. The material
properties that make silicone rubber suitable for
separating the electrodes are shown in Table
3. Silicone rubber has high electrical resistivity of
1012
Ω-m, which prevents current from flowing
simultaneously through both electrodes [35]. The
tensile strength for silicone rubber is 6.5 MPa, which
is sufficient to keep it from breaking. The modulus
of elasticity for silicone rubber is 0.025 GPa, which
allows the leads to be flexible for easy implantation
[36]. Silicone rubber has excellent biocompatibility,
so the lead separation is inert within the heart [37].
Implantable Pulse Generator: Grade 5 Titanium Alloy
The casing of the implantable pulse generator is made
out of grade 5 titanium alloy. Grade 5 titanium alloy
is composed primarily of titanium, aluminum, and
vanadium [38]. The properties that make grade 5
titanium alloy an ideal material for the IPG can be
seen in Table 4. Grade 5 titanium alloy has a high
yield strength value of 795 MPa, which makes the
implantable pulse generator resistant to plastic
(permanent) deformation. This property prevents any
damage to the internal components of the IPG. It has
excellent corrosion resistance and excellent
biocompatibility, allowing it to withstand the body’s
corrosive environment [39]. It has a density of 4.42
g/cm3
. This density is low in comparison to other
metals and makes the IPG relatively lightweight [40].
Table 2: Material properties of platinum iridium
alloy
Table values from: [35, 36, 37]
Table values from: [38, 39, 40]
Electrical Conductivity 4,000,000 (Ω-m)-1
Corrosion Resistance Excellent
Tensile Strength 6.5 MPa
Modulus of Elasticity 0.025 GPa
Electrical Resistivity 1012
Ω-m
Yield Strength 795 MPa
Corrosion Resistance Excellent
Density 4.4 g/cm3
Table values from: [34]
Table 3: Material properties of silicone
rubber
Table 4: Material properties of grade 5
titanium alloy

Brady Bunch 11
ALTERNATVE TREATMENTS FOR ARRHYTHMIA
Arrhythmia can be treated using several techniques. Doctors determine the appropriate treatment
based on the type and severity of the patient’s arrhythmia. Cardiac catheter ablation and electrical
cardioversion are two alternatives to cardiac pacemakers [41, 42].
Catheter Ablation
Catheter ablation is an invasive procedure that treats
arrhythmias by destroying diseased tissues [41]. A
visible dye is first inserted into the blood vessels to
provide a visual guide for the doctor. Thin flexible
tubes called ablation catheters are then inserted into
the heart through blood vessels in the arm, groin, or
neck. These catheters have electrode tips that record
the heart’s electrical activity and allow the doctor to
recognize the areas that produce irregular heart
rhythms [43]. The tips of ablation catheters are used
to transmit high-energy waves to destroy tissue cells.
Diseased tissue areas are called hot spots, seen in
Figure 12. The doctor directs the tip of the ablation
catheter to burn the area around a hot spot, creating a
scar called the ablation line [41, 43]. These scars create a barrier between the healthy heart tissue
and the diseased tissue, preventing irregular electrical signals from traveling through the heart.
The surgical procedure lasts three to six hours with a recovery time of about six hours [44].
All types of arrhythmia can be treated with catheter ablation. Unlike pacemakers, which need
periodic care and attention, catheter ablation provides a permanent cure [45]. Consequently, many
cardiologists recommend this technique. However, this procedure can be uncomfortable and
painful for patients [46].
Electrical Cardioversion
Electrical cardioversion is a procedure in which timed electrical shocks are delivered externally to
the chest to permanently correct atrial tachycardia. This process is not recommended for other
types of arrhythmias. As seen in Figure 13,
two electrode cardioversion pads are attached
to the patient’s chest. These pads contain
metallic plates surrounded by a conductive
gel. The electrode cardioversion pads are
analogous to the leads used in pacemakers.
The pads are attached via wires to a
cardioversion machine as seen in Figure
13. The electrode pads detect the electrical
signals within the heart. These signals are
sent to the cardioversion machine, which
records the heart rhythm and determines the
appropriate treatment. A doctor reviews this
information and uses the pads to manually
apply the required stimulation to correct the
irregular heart rhythm. Patients typically only
need one cardioversion procedure to correct
atrial tachycardia [42].
Fig. 12: Catheter ablation procedure
Adapted from: [44]
Fig. 13: Electrical cardioversion procedure
Adapted from: [47]

Brady Bunch 12
LIMITATIONS OF THE ENRHYTHM PACEMAKER
The limitations of the EnRhythm pacemaker include risks associated with pacemaker
implantation, restrictions on certain activities, and problems with the performance of the
pacemaker.
Complications can arise from the implantation of a pacemaker. Pacemaker implantation can result
in an infection at the surgical cut. Blood vessels or nerves can be damaged, and the lung may be
punctured, causing a collapsed lung. In addition, the patient can have an allergic reaction to the
medicine used during the surgery [48].
Patients with pacemakers should not perform certain activities. Patients should not play full-
contact sports because intense physical contact can damage the pacemaker or dislodge wires.
Additionally, patients with pacemakers should not be exposed to large magnetic fields, such as
those generated by magnetic resonance imaging (MRI) [49].
Even when patients follow all guidelines, the pacemaker does not always function properly. For
example, the electrodes can damage heart tissue, and the leads of the pacemaker can get
dislodged, tangled, or broken [50, 49].
The EnRhythm cardiac pacemaker has an average battery life of only 8.5 to 10.5 years [15].
When the battery is low, the entire implantable pulse generator must be replaced. This requires
open heart surgery, which can be dangerous for patients, especially the elderly. Additionally, the
limited battery life requires younger patients with pacemakers to have several replacement
procedures throughout their lifetime [51].
The pacemaker’s internal circuitry determines when electrical signals should be sent to the heart,
but the circuitry can malfunction. When this occurs, the pacemaker can fail to deliver enough
electrical signals or can deliver electrical signals when they are not needed. Improperly-timed or
unnecessary pacing can result in damaged heart tissue or death [49].
CURRENT PACEMAKER RESEARCH
Researchers are continually suggesting improvements for the current pacemaker design. Three of
the current research projects involving pacemakers are creating leadless pacemakers, replacing
the current lithium batteries with longer-lasting options, and using new pacing techniques that are
safer and more precise than leads.
Leadless Pacemakers
Pacemakers are being developed that do not require leads
to stimulate the heart. In 2010, Medtronic released its plans
for a leadless pacemaker that will be roughly the size of a
grain of rice, making it 1/20th
the size of the current
EnRhythm pacemaker. All of the internal components of
current pacemakers will be condensed into a small pill-like
capsule, as shown in Figure 14. Due to its small size, the
entire pacemaker can be implanted directly into the heart
and can stimulate a heartbeat by using attached electrodes
rather than leads, shown in Figure 14. The small design
also enables surgeons to use a much safer implantation
procedure. Rather than performing an open heart surgery,
doctors would be able to insert the pacemaker through the
femoral vein in the leg via a catheter in a five to ten minute
Fig. 14: Proposed Medtronic
leadless pacemaker
Adapted from: [53]

Brady Bunch 13
procedure [52, 53]. The new pacemaker will require less battery power to operate because of its
placement within the heart. The battery will only last for seven years, and once the pacemaker
runs out of power, a new device would be inserted. The inactive pacemaker would remain within
the heart [52]. Medtronic plans to make the pacemaker available to patients as early as 2014 [53].
Piezoelectric-Powered Pacemakers
Scientists could soon harness the energy from a beating heart to power pacemakers. Researchers
at the University of Michigan’s aerospace engineering department are developing a piezoelectric
material that could replace lithium batteries as a power source for pacemakers. Piezoelectric
materials generate a voltage when they are deformed due to an external force. See Appendix B
for a detailed description of piezoelectricity. The new piezoelectric material is a ceramic that
captures the vibrations caused by the heart’s beating to produce electrical energy. The material’s
shape is designed to capture heartbeat vibrations across a wide range of frequencies, and magnets
are used to amplify the electrical signals produced by the piezoelectric material [54]. These two
properties allow the device to always generate more energy than required to power the
pacemaker; less than 1/100th
of an inch of the new material has the capability to power 18
pacemakers [55]. Researchers plan to attach the material to the diaphragm, which is a muscle
located just beneath the heart in the chest cavity. The material is still in the development stage,
but if it can be successfully applied to pacemakers, the piezoelectric material will remove the
need for pacemaker replacements throughout a patient’s lifetime [56].
Optogenetic Pacemakers
Researchers at Johns Hopkins University are attempting to stimulate the heart with light through a
new technique called optogenetics. In optogenetics, researchers insert light-sensitive proteins
called opsins within the heart cells. When the opsins are exposed to light, they change the ion
balance in and outside of heart cells, causing the heart tissue to contract. The researchers suggest
that pacemaker leads could be equipped with fiber-optic cables, which would transmit light to the
heart tissue. This technique would enable more precise stimulation of the heart because only cells
injected with opsins would respond to the light, and the light would not damage the heart tissue
[57].
Laser-Based Pacemakers
Researchers have proposed using lasers instead of leads to stimulate the heart. Scientists from
Case Western Reserve University and Vanderbilt University have successfully paced the heart of
a quail embryo using a laser. The laser heats the heart tissue, opening an ion channel that causes
the heart to contract. The technique does not appear to damage heart tissue, and it requires less
energy than the current lead-based approach. Lasers also provide much more precise stimulation
than leads; a laser can stimulate a single heart cell [50].
DESIGN RECOMMENDATION
One of the biggest drawbacks of pacemakers is
their limited battery lives that require patients to
undergo frequent replacement surgeries. Our
design recommendation replaces the current
EnRhythm battery with a rechargeable lithium
battery. This new battery will be recharged using
ultrasound waves from an external ultrasound
transducer, shown in Figure 15. The new system
would significantly extend the battery life of the
EnRhythm pacemaker, reducing the number of
invasive heart surgeries for patients.
Fig. 15: Proposed ultrasound recharging
design
Adapted from: [25, 58]

Brady Bunch 14
Components of the Proposed Design
Our design recommendation consists of two parts: an external ultrasound transducer and an
internal system within the connector block of the pacemaker. The ultrasound transducer is a
device that produces ultrasound waves. Ultrasound is a type of sound wave that can pass through
body tissue [59]. For a detailed description of ultrasound, see Appendix C. The internal system
converts the applied force from the ultrasound into electrical energy. The internal system, shown
in Figure 16, has four components:
the acoustic lens, matching layer,
piezoelectric material, and backing
layer. The acoustic lens is a convex
lens placed within the polyurethane
casing of the connector block [60].
The matching layer consists of
several layers of polymers and is
located above the piezoelectric
material [59]. The piezoelectric
material is a ceramic that converts
mechanical energy into electrical
energy [61]. The backing layer is
located beneath the piezoelectric
material and is made of a set of
ceramic materials called lead
zirconate titanate (PZT) [62].
Function of the Proposed Design
The proposed design would convert the ultrasound waves into electrical energy to recharge the
pacemaker’s battery. In theory, a doctor would use the external ultrasound transducer to apply
ultrasound waves to the patient’s chest. The ultrasound waves would pass through the body tissue
and connector block to the internal system. As seen in Figure 16, the acoustic lens would focus
the waves onto the matching layer [59]. The matching layer would maximize the transmission of
the waves to the piezoelectric material by minimizing wave reflection [63]. When the waves
strike the piezoelectric material, the material would vibrate and undergo the piezoelectric effect.
The piezoelectric effect is caused by the ceramic’s ionic structure. When a force is applied, all of
the positive charges of the material collect on one side, and the negative charges collect on the
opposite side, thus producing a voltage [61]. This voltage would be sent through the wires to
recharge the pacemaker battery. The last section is the backing layer, which would absorb most of
the ultrasound that passes through the other layers [63].
Benefits of the Proposed Design
Our improvement is designed to minimize risk for patients without causing them any additional
inconvenience. Currently, the battery of the EnRhythm pacemaker only lasts 8.5 to 10.5 years.
When the battery dies, a patient must have the entire IPG replaced through an invasive surgery.
These surgeries can be dangerous and expensive, especially for the elderly. The rechargeable
batteries would extend the battery life and thus require fewer surgeries. Ultrasound waves are
used in the design because they do not damage body tissue, and the titanium casing of the IPG
blocks the ultrasound from interfering with the internal circuitry. The recharging process would
be convenient for patients. Since patients with pacemakers already regularly visit their doctor,
their pacemaker batteries could be recharged at these appointments. Our design only modifies the
internal portion of the pacemaker. Since the pacemaker retains its compact size, there would be
no additional surgical risk associated with the implantation procedure.
Fig. 16: Schematic diagram of proposed ultrasound
recharging system
Image created by Erik Thomas

Brady Bunch 15
REFERENCES
1. Arrhythmia: A patient guide. (n.d.). Health Central. Retrieved October 19, 2013, from
http://www.healthcentral.com/heart-disease/patient-guide-44628-6.html
2. Medtronic patient manual: EnRhythm pacemaker. (2009). Minneapolis, MN: Medtronic, Inc.
Retrieved October 11, 2013, from
http://manuals.medtronic.com/wcm/groups/mdtcom_sg/@emanuals
3. Cardiac anatomy & physiology. (2012). Medtronic Connect: CorePace. Minneapolis, MN:
Medtronic, Inc. Retrieved October 12, 2013, from
https://wwwp.medtronic.com/mdtConnectPortal/microsite/1581802196969/15818021969
73/1581802196978
4. Electrical conduction system of the heart. (n.d.). Phartoonz. Retrieved October 26, 2013, from
http://www.phartoonz.com/2010/09/02/electrical-conduction-system-of-the-heart/
5. The ECG made even easier. (2011). studentnursediaries. Retrieved October 16, 2013, from
http://studentnursediaries.wordpress.com/2011/06/08/the-ecg-made-even-easier/
6. What is an arrhythmia?. (2011). National Heart, Lung, and Blood Institute. Retrieved October
12, 2013, from http://www.nhlbi.nih.gov/health/health-topics/topics/arr/
7. About arrhythmia. (2012). American Heart Association. Retrieved October 13, 2013, from
http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/About-
Arrhythmia_UCM_002010_Article.jsp
8. Types of arrhythmias. (n.d.). Cleveland Clinic. Retrieved October 13, 2013, from
http://my.clevelandclinic.org/heart/disorders/electric/types.aspx
9. Supraventricular tachycardia. (n.d.). Stanford Hospital & Clinics. Retrieved October 12,
2013, from
http://stanfordhospital.org/cardiovascularhealth/arrhythmia/conditions/supraventricular-
tachycardia.html
10. Circulation. (n.d.). RRAPID homepage. Retrieved October 15, 2013, from
http://rrapid.leeds.ac.uk/ebook/05-circulation-06.html
11. Journal of pediatrics: Accuracy of interpretation of preparticipation screening
electrocardiograms. (2011). Oakwood Sports Medicine. Retrieved October 12, 2013, from
http://oakwoodsportsmedicine.com/2011/07/
12. Page, S.L. (2012). Atrial fibrillation, ventricular tachycardia, ventricular fibrilation, atrial
flutter rhythm strips EKG interpretation. Registered Nurse RN. Retrieved October 14,
2013, from http://www.registerednursern.com/wp-content/uploads/2008/11/a-fib.gif
13. Aquilina, O. (2006). A brief history of cardiac pacing. NCBI. Retrieved October 12, 2013,
from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3232561/
14. The vacuum tube. (1999). Detroit Public TV. Retrieved October 14, 2013, from
http://www.pbs.org/transistor/science/events/vacuumt.html

Brady Bunch 16
15. EnRhythm pacing system. (2010). Medtronic for Healthcare Professionals. Medtronic, Inc.
Retrieved October 12, 2013, from http://www.medtronic.com/for-healthcare-
professionals/products-therapies/cardiac-rhythm/pacemakers/enrhythm-pacing-system/
16. Castellanos, A., Lemberg, L., Jude, J., Mobin-Uddin, K., & Berkovits, B. (1968). Implantable
demand pacemaker. British Heart Journal, 30(1), 29-33. Retrieved October 13, 2013,
from the US National Library of Medicine database.
17. ARCHIVED – The pacemaker: Keeping the beat for 60 years. (2011). National Research
Council Canada. Retrieved October 13, 2013, from http://www.nrc-
cnrc.gc.ca/eng/dimensions/issue7/pacemaker.html
18. Medtronic reference manual: EnRhythm P1501DR. (2013). Minneapolis, MN: Medtronic,
Inc. Retrieved October 11, 2013, from
http://manuals.medtronic.com/wcm/groups/mdtcom_sg/@emanuals/@era/@crdm/docum
ents/documents/contrib_172163.pdf
19. Gillis AM, Pürerfellner H, Israel CW, et al. Reduction of unnecessary right ventricular
pacing due to the managed ventricular pacing (MVP) mode in patients with symptomatic
bradycardia: benefit for both sinus node disease and AV block indications. Heart Rhythm.
2005;Abstract AB21-1.
20. Basic pacing concepts. (2012). Medtronic Connect: CorePace. Minneapolis, MN: Medtronic,
74/1581802196988
21. How does a pacemaker work?. (2012). National Heart, Lung, and Blood Institute. Retrieved
October 14, 2013, from http://www.nhlbi.nih.gov/health/health-
topics/topics/pace/howdoes.html
22. Pacing leads. (2010). Medtronic for Healthcare Professionals. Retrieved October 12, 2013,
from http://www.medtronic.com/for-healthcare-professionals/products-therapies/cardiac-
rhythm/pacemakers/pacing-leads/index.htm#tab2
23. Surgery: What to expect – Implanting a pacemaker. (2010). Medtronic for Patients.
http://www.medtronic.com/patients/bradycardia/getting-a-device/surgery/index.htm
24. Chinitz, M.D., L. A., Bernstein, M.D., N. E., Aizer, M.D., A., Holmes, M.D., D. S., &
Wilbur, M.D., S. (n.d.). Pacemaker implantation. NYU Langone Medical Center Cardiac
and Vascular Institute. Retrieved October 11, 2013, from
http://cvi.med.nyu.edu/patients/treatment-technologies-surgeries/pacemaker-
implantation#C
25. Diagram of Implantation of Pacemaker. (n.d.). Retrieved October 15, 2013, from
http://www.uofmhealth.org/sites/default/files/healthwise/media/medical/hw/h9991486_0
01.jpg

Brady Bunch 17
26. Pacemaker module. (2002). University of California San Francisco School of Medicine.
http://missinglink.ucsf.edu/lm/pacemaker_module/index.htm
27. Managed Ventricular Pacing (MVP). (2013). Medtronic: Device Features. Medtronic, Inc.
Retrieved October 12, 2013, from http://www.medtronicfeatures.com/browse-
features/all/CDF_DF_M-VENTRICULAR-PACING
28. Pacemaker features. (2012). Medtronic Connect: CorePace. Minneapolis, MN: Medtronic,
74/1581802196988
29. Atrial tachyarrhythmias: A hybrid treatment approach. (2002). Medtronic Connect:
CorePace. Minneapolis, MN: Medtronic, Inc. Retrieved October 12, 2013, from
https://wwwp.medtronic.com/mdtConnectPortal/presentationtools/109/170/10836106199
54
30. Black, J., & Hastings, G. (Eds.). (1998). Handbook of Biomaterial Properties. N.p.: Springer.
31. RTP company RTP 1201-55D polyurethane thermoplastic elastomer (TPU) glass fiber 10%-
55 Shore D. (n.d.). MatWeb MATERIAL PROPERTY DATA. Retrieved November 15,
2013, from
http://www.matweb.com/search/datasheettext.aspx?matguid=70243df6826841b7b53f1fc
01f2facff
32. Di Fiore, A. (n.d.). Polyurethanes in vascular access: Clinical perspectives. Association for
Vascular Access. Retrieved November 15, 2013, from
http://www.avainfo.org/website/download.asp?id=164430
33. AdvanSource biomaterials ChronoFlex C 55D biodurable medical grade polyurethane. (n.d.).
MatWeb MATERIAL PROPERTY DATA. Retrieved November 14, 2013, from
http://www.matweb.com/search/datasheet.aspx?matguid=5d6a5b18d6484708881387e2de
0ca84b
34. 90/10 & 80/20 platinum/iridium products. (2013). H. Cross Company. Retrieved December
1, 2013, from http://hcrosscompany.com/precious/platirid.htm
35. Silicone rubber. (n.d.). MATBASE. Retrieved November 14, 2013, from
http://www.matbase.com/material-categories/natural-and-synthetic-
polymers/elastomers/material-properties-of-silicone-rubber.html#properties
36. Properties: Silicone rubber. (n.d.). Azom.com: The A to Z of Materials. Retrieved November
14, 2013, from http://www.azom.com/properties.aspx?ArticleID=920
37. Extruded material comparison chart. (n.d.). Kent Elastomer Products, Inc.. Retrieved
November 15, 2013, from http://www.kentelastomer.com/uploads/extruded-material-
comparison-chart.pdf

Brady Bunch 18
38. eFunda: Glossary: Materials: Alloys: Titanium Alloy: Wrought: Ti-6Al-4V. (n.d.). eFunda.
Retrieved November 14, 2013, from
http://www.efunda.com/glossary/materials/alloys/materials--alloys--titanium_alloy--
wrought--ti-6al-4v.cfm
39. Biomedical applications of titanium and its alloys. (2008). Biological Materials Science.
Retrieved November 15, 2013, from
http://www.meyersgroup.ucsd.edu/papers/journals/meyers%20316.pdf
40. Titanium alloys - Ti6Al4V grade 5. (2013). Azom.com: The A to Z of Materials. Retrieved
November 15, 2013, from http://www.azom.com/article.aspx?ArticleID=1547
41. Heart arrhythmias. (n.d.). University of Michigan Health System: Frankel Cardiovascular
Center. Retrieved November 14, 2013, from http://www.umcvc.org/medical-
services/abnormal-heart-rhythms
42. What is cardioversion?. (2012). National Heart, Lung, and Blood Institute. Retrieved
November 15, 2013, from http://www.nhlbi.nih.gov/health/health-topics/topics/crv/
43. What to expect during catheter ablation. (2012). National Heart, Lung, and Blood Institute.
Retrieved November 15, 2013, from http://www.nhlbi.nih.gov/health/health-
topics/topics/ablation/during.html
44. Cardiac ablation. (2010). Cardiologist. Retrieved November 15, 2013, from
http://www.cardiologist.org/cardiac-ablation/
45. Cardiac ablation procedures. (2013). University of Maryland Medical Center. Retrieved
December 6, 2013, from http://umm.edu/health/medical/ency/articles/cardiac-ablation-
procedures
46. Procedures. (n.d.). The Arrhythmia Institute. Retrieved November 16, 2013, from
http://www.arrhythmiainstitute.com/procedures/
47. Cardioversion: Electrical cardioversion. (2010). WebMD. Retrieved November 15, 2013,
from http://www.webmd.com/heart/cardioversion-low-voltage-electrical-cardioversion
48. Pacemaker risks. (2011). Medtronic: Join the Pacemakers. Retrieved November 23, 2013,
from http://www.jointhepacemakers.com/what-is-a-pacemaker/benefits-risks/index.htm
49. How will a pacemaker affect my lifestyle?. (2012). National Heart, Lung, and Blood
Institute. Retrieved November 21, 2013, from http://www.nhlbi.nih.gov/health/health-
topics/topics/pace/lifestyle.html
50. 'Laser pacemaker' controls heartbeat. (2013). Discovery News. Retrieved November 14,
2013, from http://news.discovery.com/tech/laser-heart-pacemaker.htm
51. St. Jude Medical Pediatric Pacemaker Pamphlet: Living with a pacemaker. (2011).
Minnesota, MN; St. Jude Medical. Inc. Item No. N-01052. Retrieved November 15,
2013.

Brady Bunch 19
52. Moylan, M. (2010). Medtronic developing new mini pacemaker. MPR News. Retrieved
November 14, 2013, from
http://minnesota.publicradio.org/display/web/2010/11/01/medtronic-pacemaker
53. That's mint! Pacemaker the size of a Tic Tac set to revolutionise heart treatment. (2012).
Mirror News. Retrieved November 12, 2013, from
http://www.mirror.co.uk/news/technology-science/science/heart-pacemaker-the-size-of-
a-tic-tac-758476
54. Moore, N. (2012). Heart-powered pacemaker could one day eliminate battery-replacement
surgery. ScienceDaily. Retrieved November 15, 2013, from
http://www.sciencedaily.com/releases/2012/03/120302193756.htm
55. Recinto, R. (2013). New-generation pacemaker could be powered by the heart. Yahoo! News.
Retrieved November 14, 2013, from http://news.yahoo.com/researchers-made-strides-in-
developing-heart-powered-pacemaker-173035419.html
56. D. Inman, personal communication, November 18-19, 2013.
57. Boyle, P. M., Williams, J. C., Ambrosi, C. M., Entcheva, E., & Trayanova, N. A. (2013). A
comprehensive multiscale framework for simulating optogenetics in the heart. Nature
Communications. Retrieved November 15, 2013, from
http://www.nature.com/ncomms/2013/130828/ncomms3370/full/ncomms3370.html
58. Ultrasound. (n.d.). BBC News. Retrieved November 24, 2013, from
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/radiation/ultrasound
rev3.shtml
59. Basic principle of medical ultrasonic probes (transducer). (n.d.). Nihon Dempa Kogyo Co.,
LTD. Retrieved November 28, 2013, from
http://www.ndk.com/en/sensor/ultrasonic/basic02.html
60. Zhou, Q., Hyui Cha, J., & Kirk Shung, K. (2009). Alumina/epoxy nanocomposite matching
layers for high-frequency ultrasound transducer application. National Heart, Lung, and
Blood Institute. Retrieved November 29, 2013, from
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2729565/
61. Woodford, C. (2009). Piezoelectricity. Explainthatstuff.com. Retrieved November 15, 2013,
from http://www.explainthatstuff.com/piezoelectricity.html
62. Raina, A., & Qasim. A. Transducer basics. (n.d.). http://echocardiographer.org. Retrieved
November 29, 2013, from
http://echocardiographer.org/Echo%20Physics/BasicTransducers.html
63. Characteristics of piezoelectric transducers. (n.d.). NDT Resource Center. Retrieved
November 29, 2013, from http://www.ndt-
ed.org/EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/characterist
icspt.htm
ACKNOWLEDGEMENT
The Brady Bunch would like to thank Dr. Daniel Inman for providing us with additional
information about his current research on piezoelectric-powered pacemakers.

Brady Bunch 20
APPENDIX A
Pacing Modes
Pacemakers run in different pacing modes, which are represented by the NBG code. The NBG
code is a three to five letter sequence. As Table A-1 shows, the first and second letters represent
the heart chambers that are paced and sensed, respectively. The third letter indicates how the
pacemaker responds to the sensed impulse. “I” means that the pacemaker paces the heart unless a
normal heartbeat is detected; if a normal signal is detected, the pacemaker is said to be
“inhibited” because it does not send a pacing impulse. “T” represents a triggered response and is
common for dual chamber pacemakers. A triggered response means that the pacemaker can
stimulate a contraction in the ventricles following an atrial contraction. “D” means that the
pacemaker has the capability to both inhibit and trigger an impulse. The last two letters are less
commonly used. The fourth letter indicates additional pacing features; this letter is usually “R”,
which identifies a pacemaker that uses rate-responsive pacing. The fifth letter indicates if the
device has antitachycardia features. Because very few pacemakers treat tachycardia, the fifth
letter is rarely used [1].
The NBG code can be used to determine how a pacemaker functions. For example, a pacemaker
operating in DDD pacing mode senses and paces in both chambers of the heart, and it has the
capability to inhibit and trigger an electrical impulse [1].
REFERENCES
1. Pacemaker module. (2002). University of California San Francisco School of Medicine.
http://missinglink.ucsf.edu/lm/pacemaker_module/index.htm
2. Pacemaker EP 2073891 A2. (2007). Google Patents. Retrieved October 26, 2013, from
http://www.google.com/patents/EP2073891A2
Table A-1: NBG Code
Table from: [2]

Brady Bunch 21
APPENDIX B
Piezoelectricity
Piezoelectric materials are electrically neutral under normal conditions. As seen in Figure A-1,
the material’s electrical charges are perfectly balanced and cancel out. If stress is applied and the
piezoelectric material is stretched or squeezed, some of the atoms are pushed closer together or
further apart, disrupting the balance of positive and negative charge. As shown in Figure A-2, this
causes a net electrical charge to appear throughout the whole structure; one face becomes positive
while the other becomes negative. This characteristic allows piezoelectric materials to produce
voltages when an external force is applied. Conversely, a piezoelectric material will experience
deformation when a voltage is applied [1].
REFERENCE
1. Woodford, C. (2009). Piezoelectricity. Explainthatstuff.com. Retrieved November 15, 2013,
from http://www.explainthatstuff.com/piezoelectricity.html
Fig. A-1: Piezoelectric material in neutral state
Adapted from: [1]
Fig. A-2: Piezoelectric material when force is
applied
Adapted from: [1]

Brady Bunch 22
APPENDIX C
Ultrasound
Ultrasound waves have a frequency higher than what is considered audible [1]. Wave frequency
is a measure of the amount of wavelengths that pass a given point in a fixed amount of time.
Frequency is measured in waves per second, which is known as Hertz (Hz). Medical ultrasound
waves can have a frequency from 1,000,000 to 5,000,000 Hz [1]. An ultrasound transducer uses
piezoelectric materials to send and receive ultrasound waves. When a voltage is applied through
the transducer, piezoelectric materials vibrate within the transducer. This vibration produces
sound waves that are then transmitted through the transducer. The frequency of these vibrations
determines the frequency of the sound waves that are sent into the body [2].
REFERENCES
1. Freudenrich, C. (2001). How ultrasound works. HowStuffWorks. Retrieved November 29,
2013, from http://science.howstuffworks.com/ultrasound2.htm
2. Ursu, D. (n.d.). How do ultrasound transducers work?. eHow Health. Retrieved November 29,
2013, from http://www.ehow.com/how-does_5213125_do-ultrasound-transducers-work_.html
HONOR PLEDGE
We have neither given nor received any unauthorized help on this assignment, nor have we
concealed any violation of the Honor Code.

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