Introduction To Electrophysiology

Introduction to ELECTROPHYSIOLOGY
What Are They DOING Over There?!

Basic Principles
Electrophysiology: the study of electrical activity in the body
Three main activities in the EP lab:
EP Studies
Device Implants
Catheter Ablation

Basic Principles
Anatomy of the Cardiac Electrical System
SA Node
AV Node
His Bundle
Bundle Branches
Purkinje Fibers
*Remember: The heart has several levels of backup pacing in place.

Basic Principles

Basic Principles
Normal path of conduction
SA Node AV Node His Bundle Bundle Branches Purkinje Fibers

Basic Principles
Cardiac Action Potential

Basic Principles
Abnormal Heart Rhythms
Bradycardia
Failure to generate impulse
Failure to propagate impulse
Tachycardia
Automatic- seen in acutely ill patients
Reentry Circuits- most common (SVTs, VT)
Triggered

Basic Principles
Treatment of Arrhythmias
Drug Therapy
Class I through 5 Antiarrhythmics
Watch out for proarrhythmia!
Drug toxicity
***Only use antiarrhythmic drugs for patients with significant symptoms or life threatening arrhythmias.

Basic Principles
Non-pharmacologic Therapies
Reverse underlying cause
Example: hypokalemia
Surgery
PCI/CAB for ischemia
Devices
Pacemaker for bradycardia
Ablation
Can cure certain tachycardias

EP Studies
INTRODUCTION TO EP STUDIES
An EP study is performed by doing two things:
Recording
Pacing
That’s it! Diagnosis depends on speed of conduction through the system, direction of impulses, and any arrhythmias induced.

EP Studies
Indications for EP Study
Syncope
Palpitations
Documented tachycardia
Suspected SA or AV node disease
Risk assessment for Sudden Cardiac Death (SCD)

EP Studies
Electrode Catheters
Can use femoral, subclavian, or IJ access
Typically use 5.5 and 6 French sheaths for diagnostic studies
Similar to temporary pacing catheters, but with more electrodes near the tip
Different shapes for different areas of the heart

EP Studies

EP Studies
Electrode Catheters
A basic study will use two.
More complex studies (SVT studies) will use more.
***Multiple catheters in multiple locations can track the speed and direction of electrical impulses across the heart.

EP Studies
ECG versus EGM
Surface ECG is a total of all the electrical activity across the heart
EGM = IntracardiacElectrogram
Records only the activity of a localized area, i.e. between electrodes on the catheters
Faster sweep speed used (typically 100mm/sec)

EP Studies
IntracardiacElectrograms (EGMs)

EP Studies
IntracardiacElectrograms
These deflections represent rapid myocardial depolarization only.
Therefore, we do not see the slower conduction through the SA and AV nodes.
Remember the different action potentials of muscles cells versus nodal cells.

EP Studies
By manipulating the electrode catheters, pacing can be performed from virtually any area of the heart.
Premature impulses are delivered by the EP MD with precise timing and patterns.
This is called Programmed Stimulation.
A stimulator computer program is used to create the patterns for pacing.

EP Studies
Programmed stimulation can be used to:
Measure SA node and AV node function
Measure refractory periods of nodes and myocardium
Induce and terminate Ventricular Tachycardia
This can determine which patients receive an ICD implant.

Evaluation of SA Node
Sa Node = Pacemaker of the Heart
Comma- shaped
Located near SVC
Has sympathetic (“fight”) and parasympathetic (“flight”) innervation
*SA Node disease is the most common cause of bradycardia.

Types of SA Node Disease:
Intermittent or sustained bradycardia
Sudden SA Node arrest
Periods of bradycardia with tachycardia
Brady-Tachy Syndrome
*If significant symptoms are present, these conditions are termed Sick Sinus Syndrome.

Symptoms of SA Node Disease
Lightheadedness
Dizziness
Presyncope
Syncope

Causes of SA Node Disease:
Fibrosis
SA Nodal artery disease
Cardiac Trauma
Cardiac inflammatory/infiltrative disease
Thyroid disorders

Measurement of SA Node Function in EP Lab
Sinus node recovery time (SNRT)
Based on overdrive suppression
Sino-atrial conduction time (SACT)
Exit block

Evaluation of AV Node
AV Node = Rate Regulator of the Heart
Located on interatrial septum, near TV
Has mostly parasympathetic innervation
*AV Node disease is the second major cause of bradycardia.

The major question with AV Node disease is: “Does the patient need a pacemaker?”
This depends on:
Symptoms
Site of conduction block
Degree of conduction block

Symptoms are the same as SA Node disease:
Lightheadedness
Dizziness
Presyncope
Syncope

Site of AV Block:
General Rule:
Block located in AV Node = no PPM
Block located below AV Node = PPM

Degree of AV Block
General Rule:
If 1st Degree = no PPM
If 2nd Degree = maybe PPM
If 3rd Degree = PPM

HIS Bundle
His Bundle = Conductor to Ventricles
Compact bundle of Purkinje fibers arising after AV node
Rapid conduction through the fibrous AV skeleton
Divides into Right and Left Bundle branches
If patient has disease in His Bundle, a PPM may be indicated.

Bundle Branches
Bundle Branches = Coordinators of Ventricular Contraction
Left Bundle Branch divides into two: anterior and posterior
All end as Purkinje fibers, which rapidly spread the impulse to all ventricular muscle
Order of contraction: septum apex lateral walls base

Bundle Branches
Any delay in impulse conduction in or below the bundle branches = Interventricular Conduction Delay (ICVD)
Can disrupt normal ventricular contraction
ICVD leads to wide QRS on surface ECG
If delay is significant and leads to heart failure, Cardiac Resynchronization Therapy (CRT) may be indicated.

Bundle Branches
Take Note:
If performing a right heart cath on a patient, be prepared if they have existing LBBB:
Swan catheters may hit the Right Bundle Branch, causing Right Bundle Branch Block.
Patient would then have complete heart block and need a temporary pacing wire.

Device Therapy
Three kinds of implants in the EP Lab:
Permanent pacemakers (PPM)
Implantable Cardioverter-Defibrillators (ICDs)
Cardiac Resynchronization Therapy (CRT) devices

Device Therapy
Implanted Devices
Most are implanted in the pectoral region
Can have one, two, or three leads
Can be programmed in a variety of ways, to suit each individual patient

Device Therapy
Permanent Pacemakers
Indicationsfor use include:
Symptomatic Sinus Bradycardia
AV Conduction Disease
Cardioneurogenic Syncope
Bradycardia-induced VT
Significant Ventricular Dysfunction with wide QRS

Device Therapy
Parts of a Pacemaker
Generator- contains the circuitry, computer memory, and battery
Typical PPM weighs about an ounce (10cc)
Leads- usually inserted through venous system to heart
Can be active (screwed into heart muscle) or passive (distal tines catch onto heart tissue)

Temporary Pacers
Settings:
Rate
mA (current flow)
Sensitivity: more sensitivity = less pacing
less sensitivity = more pacing
asynchronous = pacing regardless of what heart is doing

Device Therapy
Implantable Cardioverter-Defibrillators
Indications for use include:
Sustained VT/VF
EF < or equal to 35%, Class II/III HF
Prior MI with EF < or equal to 30%, Class I HF
EF < 40, NSVT, inducible VT
Every 3 minutes someone dies from SCA in the USA.

Device Therapy
Parts of an ICD
Generator weighs more that PPM, due to addition of a capacitor
Weighs about 3 ounces (36cc)
Capacitor stores energy needed for shocks
RV lead is designed to deliver shocks to convert VT/VF- looks different from a PPM lead under fluoro

Device Therapy
Cardiac Resynchronization Therapy
Indications for use include:
Class III/IV heart failure
Dilated or ischemic cardiomyopathy
QRS interval > or equal to 120ms
EF < or equal to 35%
Vast majority of patients fitting this criteria also qualify for ICD therapy.
CRT can improve EF up to 10-15%.

Device Therapy
Parts of a CRT device
Generator weighs about
Requires placement of an LV lead in coronary sinus
Successful transvenous placement in ~95% of patients
Other 5% would need surgical placement

Cardiac Ablation
Ablation: destruction of arrhythmia- causing heart tissue
Can be curative, eliminating need for antiarrhytmic drugs or surgery
Success rates vary according to arrhythmia, with some over 90%.
Major complications occur in about 3% of patients.

Cardiac Ablation
How it works:
Ablation catheter is inserted (usually through femoral vein) to heart, along with electrode catheters for recording.
Electrical activity is recorded, and abnormal rhythms are tracked.
Ablation catheter is placed at area of arrhythmia, and energy is applied to destroy tissue.
Pt is monitored for any further signs of arrhythmia before leaving EP lab.

Cardiac Ablation
Indications for Catheter Ablation:
Symptomatic SVT due to AVNRT, WPW, unifocalatrial tachycardia, and atrial flutter.
Atrial fib with lifestyle-limiting symptoms, after inefficacy/intolerance of at least one antiarrhythmic drug.
Symptomatic VT.

Cardiac Ablation
Energy Sources:
Direct current: in the early days, the ablation catheter was connected to an external defibrillator
Greater than 250J could be delivered inside the heart, heating catheter tip to thousands of degrees Celsius
Blood was instantly vaporized, causing rise in pressure and flash of light
Created lesions up to 4cm2, with ragged edges
Only used to ablate His bundle, with 85% success rate (complications were suprisingly low).

Cardiac Ablation
Radiofrequency (RF) energy:
Most commonly used
Same as bovie machines in OR
Much lower voltage than direct current- no explosions
Creates smaller, discrete lesions
No muscle or nerve stimulation- no general anesthesia needed

Cardiac Ablation
Complications of Ablation:
Complete heart block
Cardiac perforation and tamponade
Creating MR/TR
Embolism/stroke
Pulmonary vein stenosis
Coronary artery lesions

Current challenges in EP:
Atrial Fib ablation- making it safer and more effective, with less procedure time
Optimizing CRT therapy
Getting ICD therapy to more patients who qualify

References
R. Fogoros. Electrophysiologic Testing, 4th ed.
Medtronic.com
Stiffler, J. The Diagnostic EP Study. Healthworks
www.skillstat.com
Ellenbogen and Wood. Cardiac Pacing & ICDs, 5th ed.
Eprewards.com

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Introduction To Electrophysiology

by jmlafroscia on Jul 24, 2010

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