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 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 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)

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.,[object Object]

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.

Evaluation of SA Node 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.

Evaluation of SA Node Symptoms of SA Node Disease Lightheadedness Dizziness Presyncope Syncope

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

Evaluation of SA Node 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.

Evaluation of AV Node 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

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

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

Evaluation of AV Node 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

Introduction To Electrophysiology

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