PACEMAKER BASIC AND TIMING CYCLE .pptx

1. PACEMAKER BASICS AND TIMING CYCLE
DR Awadhesh sharma
Professor Cardiology
LPS Institute of cardiology,Kanpur

2. PACEMAKER CIRCUIT
Implantable pulse generator (IPG):
Battery
Circuitry
Connector(s)
Leads or wires
Cathode (negative electrode)
Anode (positive electrode)
Body tissue
IPG
Lead
Anode
Cathode

4. Stuart Allen 06
 Contains a battery that provides
the energy for sending electrical
impulses to the heart
 Houses the circuitry that
controls pacemaker operations Circuitry
Battery
The Pulse Generator

5. THE PULSE GENERATOR……
 Common battery compositions
include:
 Lithium-Iodine
 Lithium silver vanadium
oxide with carbon
monoflouride
 Starting battery voltage will
vary depending on
composition
 Longevity
 Dependent on impedance
and output
 Commonly ranges from 6-12
years

7. LEADS

8. Leads are Insulated Wires
Deliver electrical impulses from the pulse
generator to the heart
Sense cardiac depolarization
Lead

9. Lead Characterization
 Position within the heart
 Endocardial or transvenous leads
 Epicardial leads
 Fixation mechanism
 Active/Screw-in
 Passive/Tined
 Shape
 Straight
 J-shaped used in the atrium
 Polarity
 Unipolar
 Bipolar
 Insulator
 Silicone
 Polyurethane

10.  Passive fixation
The tines become lodged in the
trabeculae

11.  ACTIVE FIXATION
The helix (or screw) extends into the
endocardial tissue
Allows for lead positioning anywhere in the
heart’s chamber

12. Transvenous Leads - Fixation Mechanisms

14. CONDUCTORS -
 MP-35N – Alloy of nickel , cobalt, chromium, molybdenum
advantage – high strength and resistance to corrosion
disadvantage – high electrical resistance
 This is overcome by incorporating low resistance metals –
silver ,titanium , platinum .
 These alloy can be constructed in two ways -

15. DFT vs DBS

16.  COAXIAL LEAD VS CORADIAL LEADS SYSTEM

17. LEAD INSULATION -
POLYURETHANE –
 High tensile strength
 resistance to mechanical abrasion
 has excellent lubricity with low frictional coefficient
 Thin layer of insulation can be used so reducing overall lead
dimension
Main disadvantage – in vivo polymer degradation

18. Two mechanism –
 ESC (environmental stress cracking ) at point of
mechanical stress , at anchoring sleevs , venous entry
point
 Metal ion oxidation (MIO)- at conductor insulator
interface

20. SILICON INSULATION
 Completely inert and biostable
 More flexible – less risk of cardiac perforation
 Main disadvantage – low tensile strength susceptibility to
abrasion and tear
 So thicker layer of insulation needed which lead to bulky
design
 Cold flow phenomenon

22. Lead Insulation May Be Silicone or
Polyurethane
Advantages of Silicone-
Insulated Leads
• Inert
• Biocompatible
• Biostable
• Repairable with
medical adhesive
• Historically very
reliable
Advantages of
Polyurethane-
Insulated Leads
• Biocompatible
• High tear
strength
• Low friction
coefficient
• Smaller lead
diameter

23. Epicardial Leads
Leads applied directly to
the surface of the heart
Utilized in pediatric
patients and patients
contraindicated for
transvenous leads
Fixation mechanisms
include:
 Epicardial stab-in
 Myocardial screw-in
 Suture-on
Applied via sternotomy,
thoroscopy, or limited
thoracotomy

24.  Flows through the tip electrode
(cathode)
 Stimulates the heart
 Returns through body fluid and
tissue to the PG (anode)
A UNIPOLAR PACING SYSTEM
CONTAINS A LEAD WITH AN ELECTRODE IN THE HEART
Cathode
Anode
-
+

25. Anode
 Flows through the tip
electrode located at the
end of the lead wire
 Stimulates the heart
 Returns to the ring
electrode above the lead
tip
A BIPOLAR PACING SYSTEM
CONTAINS A LEAD WITH 2 ELECTRODES IN THE HEART
Cathode

26. Unipolar leads
 Unipolar leads have a smaller diameter than bipolar leads
 Unipolar leads exhibit larger pacing artifacts on the surface
ECG
• One electrode on the tip & one conductor coil
• Conductor coil may consist of multiple strands - (multifilar
leads)

27. Bipolar leads
 Bipolar leads are less susceptible to oversensing
noncardiac signals (myopotentials and EMI)
Coaxial Lead Design
• Circuit is tip electrode to ring electrode
• Two conductor coils (one inside the other)
• Inner layer of insulation
• Bipolar leads are typically thicker than unipolar leads

28. Unipolar Bipolar
Advantages Smaller diameter
Easier to implant
Large spike
No pocket stimulation
Less susceptible to EMI
Programming flexibility
Disadvantages Pocket stimulation
Far-field oversensing
No programming flexibility
Larger diameter
Stiffer lead body
Small spike
Higher impedance
Voltage threshold is 30%
higher

31. CHARACTERISTICS OF AN
PACEMAKER CIRCUIT:
 Voltage
 Current
 Impedance
33

32. VOLTAGE
 Voltage is the force, or “push,” that
causes electrons to move through a
circuit
 In a pacing system, voltage is:
 Measured in volts (V)
 Represented by the letter “V”
 Provided by the pacemaker battery
 Often referred to as amplitude or pulse
amplitude

33. CURRENT
 The flow of electrons in a completed
circuit
 In a pacing system, current is:
 Measured in milliamps (mA)
 Represented by the letter “I”
 Determined by the amount of electrons that
move through a circuit

34. IMPEDANCE
 The opposition to current flow
 In a pacing system, impedance is:
 Measured in ohms (W)
 Represented by the letter “R”
 The measurement of the sum of all resistance to the flow
of current
 Impedance is a function of the characteristics of the conductor
(wire), the electrode (tip), and the myocardium

35.  Impedance is the sum of all resistance to the flow of
current. The resistive factors to a pacing system
include:
• Lead conductor resistance
• The resistance to current flow from the electrode to the
myocardium
• POLARIZATION IMPEDANCE, which is the accumulation
of charges of opposite polarity in the myocardium at the
electrode-tissue interface.

36. Impedance
 Pacing lead impedance typically stated in broad ranges,
i.e. 300 to 1500 Ω
 Factors that can influence impedance
 Resistance of the conductor coils
 Tissue between anode and cathode
 The electrode/myocardial interface
 Size of the electrode’s surface area
 Size and shape of the tip electrode

37. Voltage, Current, and Impedance are
Interdependent
The interrelationship of the three components is
analogous to the flow of water through a hose
Voltage represents the force with which . . .
Current (water) is delivered through . . .
A hose, where each component represents the total
impedance:
The nozzle, representing the electrode
The tubing, representing the lead wire

38. Voltage and Current Flow
Electrical Analogies
Spigot (voltage) turned up, lots
of water flows (high current
drain)
Spigot (voltage) turned low, little flow
(low current drain)
Water pressure in system
is analogous to voltage –
providing the force to
move the current

39. Resistance and Current Flow
Electrical Analogies
• Normal resistance – friction caused by the hose and nozzle
More water discharges, but is all of it going
to the nozzle?
• High resistance – a knot results in low total current flow
• Low resistance – leaks in the hose reduce the resistance

42. POLARIZATION
 After an output pulse, positively charged particles
gather near the electrode.
 The amount of positive charge is
 Directly proportional to pulse duration
 Inversely proportional to the functional electrode
size
(i.e. smaller electrodes offer higher polarization)
Polarization effect can represent 30–40% of the total pacing
impedance As high as 70% for smooth surface, small surface area
electrodes

43. Within the electrode, current flow is due to movement of electrons
(e−).
At the electrode–tissue interface, the current flow becomes ionic &
(-) vely charged ions (Cl−, OH−) flow into the tissues toward the
anode leaving behind oppositely charged particles attracted by the
emerging electrons.
It is this capacitance effect at the electrode tissue interface, that is
the basis of polarization

48. Lead wire
fracture
Increased
resistance
High Impedance Conditions
A Fractured Conductor
 A fractured wire can cause
Impedance values to rise
 Current flow from the battery may
be too low to be effective
 Impedance values may exceed
3,000 W
Other reason for high impedance: Lead not seated properly
in pacemaker header (usually an acute problem).

49. Low Impedance Conditions
An Insulation Break
Insulation breaks can
cause impedance values
to fall
 Current drain is high and can
lead to more rapid battery
depletion
 Current can drain through
the insulation break into the
body or other lead wire, not
through myocardium
Impedance values may
be less than 300 W

50. Ohm’s Law
 Describes the relationship
between voltage, current,
and resistance
 V = I X R
 I = V / R
 R = V / I
V
I R
V
R
I
V
R
I
R
V
I =
=
=
X

51. Ohm’s law tells us:
1. If the impedance remains constant, and the voltage
decreases, the current decreases.
1. If the voltage is constant, and the impedance decreases,
the current increases.

53. Stimulation Threshold
 Pacing Voltage Threshold
 The minimum pacing voltage
 at any given pulse width
 required to consistently stimulate the heart
 outside the myocardial refractory period causing it to
contract

54. E = Energy delivered by Pulse to the Pacing
Circuit
and Cardiac Tissue
- V . I . t
I2Rt V2t/R

56.  Rheobase- (the lowest point on the curve) by definition is the lowest
voltage that results in myocardial depolarization at infinitely long
pulse duration
 Chronaxie(pulse duration time ) by definition, the chronaxie is the
threshold pulse duration at twice the rheobase voltage

58. Strength interval curve

61. Effect of Lead Design on Capture
Lead maturation
Fibrotic “capsule” develops around the electrode
following lead implantation
May gradually raise threshold
Usually no measurable effect on impedance

62. STEROID ELUTING LEADS
Steroid eluting leads reduce
the inflammatory process
Exhibit little to no acute
stimulation threshold
peaking
Leads maintain low
chronic thresholds

63. Effect of steroid on stimulation threshol

64. Evolution of Pacing Threshold
Voltage
Threshold
(V)
Observation Time (weeks)
Acute Phase
Chronic Phase
Safety Margin
6
s
4
3
2
1
0 4 8 12 16

66. INJURY CURRENT…….
 Due to pressure exerted by electrode on myocardium
 Seen in both active and passive leads(less pronounced)
 Lack of injury current – denotes poor contact / scarred myocardium
 Disappears over minutes to hours
 this may leads to high threshold soon after lead placement which
subside at end of procedure

70. Magnet mode
I. Activates magnetic reed switch
II. Model dependent behavior with magnet
I. Asynchronous pacing – most common
II. No apparent rate or rhythm change
III. Brief asynchronous pacing and then return to programmed
value
IV. Continuous or transient loss of pacing
III. Magnets will cause most DDDs to convert to DOO at about 85
with a BOL (beginning of life) battery, and to VOO at a rate of
about 65 at ERI (effective replacement interval) is reached to
conserve power.

71. The Pacing Pulse
t
Pacing Pulse
Pulse Duration (Width)
Output
Voltage
V = Pulse Amplitude in Volts (V) (say 2.5 V)
t = Pulse Duration or Width in milliseconds (ms)
(say 0.5 ms)
R = Impedance of Pacing Circuit (ohms)
(say 500 ohms)
I = V/R = Current through pacing circuit (mA)
= 2.5 V/ 500 ohms = 0.005 A = 5 mA
V
t

72. Why measure stimulation threshold?
 To enable programming stimulus voltage amplitude and
pulse width such that
 Consistent capture & Patient Safety is ensured
 Battery drain minimized, Pacemaker longevity maximized
 Good thresholds
 Ventricle - <1V @ 0.5ms
 Atrium - <1.5V @ 0.5ms

73. SENSING OF INTRINSIC HEARTBEATS
 Sensing is the ability of the pacemaker to “see” when an
intrinsic depolarization is occurring
 Pacemakers record the Intracardiac Electrogram (EGM)
by constantly recording the potential difference
between the cathode and anode
Depolarization Wave
Processed by
Device

79. Sensitivity Setting
Sensitivity settings less than 2.5 mv – High sensitivity – can lead
to oversensing
Sensitivity settings greater than 2.5 mV – Low sensitivity – can
lead to undersensing
Amplitude
(mV)
Amplitude
(mV)
Time Time
5.0
2.5
1.25
5.0
2.5
1.25

80. Undersensing . . .
 Pacemaker does not “see” the intrinsic beat, and
therefore does not respond appropriately
Intrinsic beat
not sensed
Scheduled pace
delivered
VVI / 60

81. Oversensing
 An electrical signal other than the intended P or R
wave is detected
 Pacing is inhibited
Marker channel
shows intrinsic
activity...
...though no
activity is
present

83. FUSION AND PSEUDOFUSION COMPLEX

88. TIMING CYCLE

97. VVI/60(1000msec)
? Last paced event occur later than expected

99. HYSTERESIS……
 Goal is to encourage own intrinsic activity .
 One of the cause of rate variation in paced ECG
 Hysteresis work best in patient with intrinsic rate near the
programmed base rate.

103. V
VP VP
VP
VOO TIMING
VP VP

105. V
VP VP
VP VP
VS
VVI TIMING

125. PACEMAKER MEDIATED
TACHYCARDIA
 Main trigger are –
PVC
loss of atrial capture

126. ECG- pacing at MTR
no evidence of atrial capture
retrograde P wave in inferior leads