Electrophysiologic basis part3

Dr. Salah Atta, MDDr. Salah Atta, MDConsultant Electrophysiolgist, SBCCConsultant Electrophysiolgist, SBCC

Professor of CardiologyProfessor of Cardiology,,Assiut UniversityAssiut University..

Part3Part3, ,

How can pacing help us during EPS ?!

Ventricular Pacing:Ventricular Pacing:The RV is paced as before from the RVA and The RV is paced as before from the RVA and

the RVOT if needed, and this can show:the RVOT if needed, and this can show:-Normal sequence of retrograde activation -Normal sequence of retrograde activation

earliest at the His bundle electrogram, earliest at the His bundle electrogram, otherwise accessory pathway exists e.g if otherwise accessory pathway exists e.g if earliest in the CS.earliest in the CS.

-VA block .-VA block .-Ventricle becomes refractory to the pacing -Ventricle becomes refractory to the pacing

extra-stimulus (Ventricular refractory period).extra-stimulus (Ventricular refractory period).-Arrhythmia induction.-Arrhythmia induction.

Normal sequence of Normal sequence of retrograde retrograde activation earliest at activation earliest at the His bundle the His bundle electrogram, electrogram, otherwise accessory otherwise accessory pathway exists e.g if pathway exists e.g if earliest in the CS.earliest in the CS.

Eccenteric Retrograde Conduction

• The presnce of VA The presnce of VA dissociation during dissociation during ventricular pacing ventricular pacing excludes the excludes the presence of presence of accessory accessory atrioventricular atrioventricular pathway and proves pathway and proves successful ablation if successful ablation if it was present before it was present before the ablaation. the ablaation.

Ventricular Refractory PeriodVentricular Refractory Period

-Ventricle becomes -Ventricle becomes refractory to the refractory to the

pacing extra-pacing extra-stimulus stimulus (Ventricular (Ventricular refractory period).refractory period).

-Arrhythmia induction-Arrhythmia induction bby pacing with y pacing with extrastimulation extrastimulation indicates a re-indicates a re-entrant mechanism entrant mechanism of the induced of the induced tachycardia.tachycardia.

Example of aggressive VT indction protocolExample of aggressive VT indction protocol::

Criteria for positive or negative EPS for Criteria for positive or negative EPS for VT induction:VT induction:

• Positive: reproducible > 10 beats VT after Positive: reproducible > 10 beats VT after stimulation.stimulation.

• Negative: no VT induced during study.Negative: no VT induced during study.

• Borderline: short episodes VT (<10 beats) Borderline: short episodes VT (<10 beats) induced. induced.

Complications of EP studyThe complications associated with

diagnostic EP studies are low. Mortality is extremely rare. Complications are usually associated with catheterization and catheter manipulation rather than stimulation and the induction of arrhythmias. The reported complications include hemorrhage, venous thromboembolism (<1%), phlebitis (<1%), cardiac perforation and tamponade, and refractory ventricular fibrillation.

Complications of EP study

Most reported deaths have resulted from incessant ventricular fibrillation and have occurred in patients with severe LV dysfunction, active myocardial ischemia, or hypertrophic obstructive cardio-myopathy or because of the pro-arrhythmic effect of drugs administered during the evaluation.

Complications of EP study

Hemo-thorax and pneumothorax, recognized complications, can occur when the subclavian or internal jugular venous approaches are used. Arterial catheterization increases the associated morbidity,including vascular complications, stroke, systemic embolism, and protamine reactions.

Sinoatrial Node Function TestsSinoatrial Node Function Tests

• Sinus Node Recovery Times:Sinus Node Recovery Times:• The sinus node is the archetype of an automatic The sinus node is the archetype of an automatic

focus. Automatic rhythms are characterized by focus. Automatic rhythms are characterized by spontaneous depolarization, by overdrive spontaneous depolarization, by overdrive suppression, and by post-overdrive “warm-up” or suppression, and by post-overdrive “warm-up” or return to baseline cycle length (BCL). return to baseline cycle length (BCL).

• Pacing at rates in excess of the spontaneous Pacing at rates in excess of the spontaneous rate of an automatic focus results in temporary rate of an automatic focus results in temporary inhibition of spontaneous depolarization, with inhibition of spontaneous depolarization, with gradual return to the original cycle length over gradual return to the original cycle length over several beats following cessation of pacing. several beats following cessation of pacing.

Sinus node function testsSinus node function tests

Sinus node recovery timeSinus node recovery time : :The HRA catheter is paced faster than the The HRA catheter is paced faster than the

sinus rate by at least 30 ms for 30-60 sinus rate by at least 30 ms for 30-60 seconds, then abruptly stopped. Sinus node seconds, then abruptly stopped. Sinus node recovery time (SNRT) can be measured using recovery time (SNRT) can be measured using this way of pacing. this way of pacing. SNRT is the interval between the last paced SNRT is the interval between the last paced beat and the first returning sinus beat. beat and the first returning sinus beat. Normal range < 1500ms.Normal range < 1500ms.

Corrected SNRT=SNRT-sinus cycle length Corrected SNRT=SNRT-sinus cycle length which is normaly less than 525 ms.which is normaly less than 525 ms.

CSNRTCSNRT

• 1.1. CSNRT = SNRT-sinus cycle length. CSNRT = SNRT-sinus cycle length. This is the most common correction. This is the most common correction. Normal values have been reported from Normal values have been reported from 350 to 550 milliseconds, with 500 350 to 550 milliseconds, with 500 milliseconds being most commonly used. milliseconds being most commonly used.

• 2.2. CSNRT = X% of sinus cycle length. CSNRT = X% of sinus cycle length. Normal values range up to 160%. Normal values range up to 160%.

• 3.3. CSNRT = 1.3 (mean sinus cycle length CSNRT = 1.3 (mean sinus cycle length in milliseconds) + 101 milliseconds. in milliseconds) + 101 milliseconds.

Sinoatrial conduction Sinoatrial conduction timetime::

Two ways to calculate:Two ways to calculate:• A single paced atrial stimulus is delivered A single paced atrial stimulus is delivered

just before the next spontaneous sinus cycle, just before the next spontaneous sinus cycle, thereby resetting the sinus node. SACT is thereby resetting the sinus node. SACT is calculated from the interval between the calculated from the interval between the paced stimulus to the next sinus beat (return paced stimulus to the next sinus beat (return interval) and equals half the difference interval) and equals half the difference between the spontaneous cycle length and between the spontaneous cycle length and the return cycle length. Normal range 50-125 the return cycle length. Normal range 50-125 ms. Prolonged SACT indicates susceptibility ms. Prolonged SACT indicates susceptibility to exit block.to exit block.

• CSNRT of a single beat, if divided by 2, yields CSNRT of a single beat, if divided by 2, yields sino atrial conduction time (SACT). sino atrial conduction time (SACT).

• AV block is due to failure of conduction of the atrial impulse to ventricle in the absence of physiologic refractoriness. It is generally due to interruption of the normal conduction pathway or due to pathologic refractoriness.

Atrioventricular Conduction Atrioventricular Conduction assessmentassessment

Level of A-V block

• AV block can be proximal (above the His bundle) indicating block in the AVN or it can be intra-Hisian or it can be distal to His bundle (infra-Hisian).

• The prognosis depends on the site of the AV block.

• Block distal to His bundle implies poor prognosis and thus indicates permanent pacing.

• EPS can confirm the site of spontaneous AV block or conduction delay.

• EPS may identify indications for permanent pacemaker implantation in individuals with syncope of unknown cause.

Atrioventricular Conduction assessment

Atrioventricular Conduction assessment

• Basic conduction intervals:

Prolongation of the H-V interval > 70 msec is an indication of infra His disease and in symptomatic patient this may indicate permanent pacing in patients with 1st degree HB or BBB while A-H prolongation is not as significant.

Response to incremental atrial pacing

• As the atrial pacing rate increases, there is normally a slight increase in the intra-atrial conduction time, a progressive increase in the AV node conduction time (the AH interval), and little change in the HV interval, with block usually at the AV node level (supra His block with no His following the A).

• AV nodal function is assessed by determining the point at which 1:1 AV conduction ceases and AV nodal Wenckebach begins.

• The normal response to incremental atrial pacing at progressively faster rates is to develop a longer AH interval and, ultimately, block in the AV node.

• Most normal individuals develop Wenckebach AV block at paced atrial cycle lengths of 500 to 350 ms (heart rates of 120 to 170 beats/min).

Normal Response to atrial pacing

• Wenckebach AV block occurs at longer cycle lengths (slower pacing rates) in patients with enhanced vagal tone or under drug effects and at shorter cycle lengths (faster pacing rates) in patients with enhanced sympathetic tone as during exercise.

• In contrast to the AH interval, the HV interval

remains relatively constant during incremental atrial pacing, and block below His (infra-Hisian or intra-Hisian block) is considered pathologic at pacing cycle lengths greater than 400 ms (rates <150 beats/min).

Abnormal Response to atrial pacing

Infra-His block

What is your diagnosis?

What is this?

• In symptomatic patients:

Long HV intervals (≥70 to 100 ms) and

block below the His bundle at atrial pacing rates of less than 150 beats/min (≥ 400 ms) indicate disease in the His-Purkinje system and are associated with a relatively high incidence of subsequent complete heart block.

Indication of Permanent Pacing

Till next time InshaALLAH

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