Essential Concepts of Electrophysiology Through Case Studies: Intracardiac EGMs : Intracardiac EGMs

by Kenneth a Ellenbogen (Editor), Roderick Tung (Editor), David Frankel (Editor)

Overview

Essential Concepts of Electrophysiology Through Case Studies: Intracardiac EGMs builds on our first book, Essential Concepts of Electrophysiology and Pacing through Case Studies, that guides the reader in developing and refining the key skill of analyzing electrophysiologic recordings.

Over 60 cases with a focus on intracardiac EGMs are presented as board exam cases and questions. Tracings are framed by a question, followed by annotated tracings, and a discussion of the correct and potential answers. Cases present a full range of difficulty from simple to advanced.

This book will provide a valuable review for a wide variety of professionals - physicians, associated professionals, nurses and technicians - preparing for certification and re-certification examinations in electrophysiology.

Product Details

ISBN-13:	9781935395331
Publisher:	Cardiotext Publishing
Publication date:	05/15/2015
Edition description:	New Edition
Pages:	338
Product dimensions:	8.50(w) x 11.00(h) x 0.70(d)

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Essential Concepts of Electrophysiology through Case Studies

Intracardiac EGMs

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By Kenneth A. Ellenbogen

Cardiotext Publishing, LLC

Copyright © 2015 Kenneth A. Ellenbogen, Roderick Tung, David S. Frankel, Prabal K. Guha, Reginald T. Ho
All rights reserved.
ISBN: 978-1-935395-33-1

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CHAPTER 1

Part 1

Electrophysiologic Concepts

Case 1.A

Question

The maneuver proves:

A) Absence of retrogradely conducting bypass tract

B) Absence of septal bypass tract

C) Presence of retrogradely conducting bypass tract

D) Presence of septal bypass tract

Answer

The correct answer is B. Parahisian pacing technique is used to determine the presence of retrograde atrial activation over a bypass tract. Pacing is carried out near the His bundle with varying output. Capture of His and right bundle results in a narrow QRS. Decrease in output results in loss of His capture, and only RV is captured (His bundle is well insulated and needs high output for capture). The changes in stimulus to atrial activation timing, atrial activation pattern, and His-to-A timing can indicate retrograde conduction over a septal pathway, AV node, or both. Readers are referred to the excellent papers referenced for a detailed description of the patterns and interpretation.

With His + RB capture (narrower QRS) the SA (135 ms) is shorter by 35 ms as compared to RV-only capture (wide QRS) (170 ms). There is no significant change in atrial activation. This indicates that the activation was conducted only over the AV node.

However, if the insertion of the bypass tract is away from the septum, changes in the atrial activation may not be apparent unless atrial activation is recorded near the site of insertion of the accessory pathway, in which case it may show fusion. Based on the findings shown in this tracing only, a septal pathway can be ruled out. In fact, a careful analysis of this tracing should lead one to suspect the possible presence of a right-sided accessory pathway. This can be discerned by the observation of the near simultaneous activation of the high right atrial electrogram with a far-field His atrial electrogram on the first and subsequent beats.

In this case, a right lateral bypass tract was present. Postablation, repeat Parahisian pacing shows changes consistent with conduction over the AV node; however, SA time was increased as compared to baseline (HB + RB capture: 133 ms, and RV capture only: 190 ms). This indicates there was fused conduction over AV node and pathway during the baseline tracing.

It should be noted that, although a rapidly conducting septal AP is excluded, a slowly conducting, decremental AP (as seen with PJRT) is not. In such a case, rapid retrograde AVN conduction could preempt slow retrograde AP conduction during both His/RV and RV-only capture.

Case 1.B

Question

An electrophysiological study was performed in a 70-year-old woman with presyncope.

This study demonstrates conduction system disease in the:

A) AV node

B) His bundle

C) Infrahisian system

D) B and C

E) All of the above

Answer

The correct answer is D. Intrahisian block is seen, with evidence of infrahisian conduction disease in the left bundle.

AV block is seen with 3:2 conduction without evidence of PR prolongation or Wenckebach behavior. The presence of a left bundle branch block with a normal PR interval increases the pretest probability that the block is infrahisian. During block, a His bundle electrogram is seen, which is supportive of this diagnosis. However, closer inspection demonstrates a split His bundle potential with block between the proximal (H1) and distal (H2) His. Note the complete absence of the H2 on the distal His electrode during block. Left bundle branch block is alleviated due to diastolic recovery from the resultant pause, and a conducted narrow QRS complex with the same HV interval (60 ms) as the conducted wide complex beat is seen. AV block in the setting of normal PR interval and narrow complex QRS is suggestive of intrahisian block.

Case 1.C

Question

What is the best explanation for the widening of the QRS complex observed during this tracing?

A) Accelerated idioventricular rhythm

B) Intermittent left bundle branch block

C) Intermittent preexcitation over a right free wall atrioventricular accessory pathway

D) Intermittent preexcitation over an atriofascicular accessory pathway

Answer

The correct answer is A. The third through eighth beats on the tracing are accelerated idioventricular rhythm (AIVR), nearly isorhythmic to the sinus rate. The third, sixth, seventh, and eighth QRS complexes (identified by stars in the second image) are marked by varying degrees of fusion between AIVR and native conduction. Importantly, the PR interval and QRS morphology vary from beat to beat. With intermittent preexcitation, the PR interval and QRS morphology tend to be constant during all preexcited beats. Further, the PR interval on the fifth and sixth beats is 40 ms, far too short for an atrial impulse to reach the ventricle. The AIVR morphology is right ventricular outflow tract, with left bundle configuration in lead V1, precordial transition at V4, and inferior axis.

Case 1.D

Question

A 71-year-old man with first-degree AV block and left bundle branch block presented with syncope. The following was observed during EP study.

What is the most likely explanation for the left bundle branch block morphology of the first QRS complex?

A) Premature ventricular contraction with concealed conduction into the His-Purkinje system

B) Conduction over an atriofascicular pathway

C) Block in the left bundle branch

D) Slowed conduction through the left bundle branch

Answer

The correct answer is D. On the first beat, conduction occurs over the right bundle branch, resulting in a left bundle branch block morphology. On the second beat, conduction occurs over both bundle branches, resulting in a narrow QRS complex. Equal delay in the right bundle branch is not a possible mechanism for narrowing of the second QRS complex, since the HV interval remains 80 ms. Rather, spontaneous recovery of conduction over the left bundle branch is the most likely explanation. On the third beat, conduction either blocks or slows severely in the right bundle branch, resulting in prolongation of the HV interval to 120 ms and right bundle branch block morphology. If the left bundle branch were actually blocked, then concurrent block in the right bundle branch would have resulted in AV block. Based on the prolongation of the HV interval and change in QRS morphologies from the 1st to 3rd complexes, we can conclude that left bundle branch conduction is delayed rather than blocked in the 1st complex.

Neither a premature ventricular contraction nor preexcitation over an atriofascicular pathway would result in a long HV interval.

Case 1.E

Question

A 55-year-old man with prior CABG/AVR (ejection fraction = 45%) was admitted with syncope.

What single best answer explains the findings on the figure?

A) Dual antegrade responses, AVNRT with phase 3 LBBB

B) Pathologic infrahisian block, phase 4 LBBB, and BBRT

C) Physiologic intranodal block, phase 4 LBBB, and BBRT

D) Phase 4 LBBB with antidromic nodofascicular reentrant tachycardia

Answer

The correct answer is C. During HRA pacing, the first stimulus captures the atrium but fails to conduct over the AV node. The ensuing pauses cause phase 4 block (pause or bradycardiadependent block) in the left bundle so that the second stimulus captures the atrium, conducts over the AV node–His–RB axis, and crosses the septum to retrogradely activate the LB and His bundle (rH) and retrogradely conceal into the AV node. Functional refractoriness in the RB after the pause prevents recurrent antegrade RB conduction. The third pacing stimulus finds the recently depolarized AV node refractory and fails to conduct to the ventricle, which with continued pacing promotes a self-perpetuating cycle of physiologic intranodal block, causing phase 4 LBBB and vice versa. This is the ideal substrate for BBRT (bottom), which was induced by a single ventricular extrastimulus (not shown). His bundle potentials precede LBBB QRS complexes with mildly prolonged HV intervals. Tachycardia terminates with retrograde block in the left bundle, causing a pause that again induces phase 4 LBBB. Bundle branch reentrant tachycardia is not reinitiated because of functional antegrade RB refractoriness following the pause. The second-to-last sinus complex finds the AV node relatively refractory and conducts to the ventricle. While dual antegrade responses can explain two His bundle electrograms for a single atrial complex, it fails to explain its occurrence with only LBBB complexes; moreover, observing both phase 3 and 4 LBBB in the same patient would be unusual. Despite LBBB, AV block during HRA pacing is functional and intranodal rather than pathologic and infrahisian. While antidromic nodo-fascicular tachycardia can produce a LBBB tachycardia with AV dissociation, His bundle potentials would occur slightly after rather than before QRS onset.

Case 1.F

Question

A 35-year-old man with GERD and nephrolithiasis underwent electrophysiologic evaluation because of rapid palpitations that occurred while the patient was power lifting.

What is the most likely diagnosis?

A) Antidromic tachycardia

B) AVNRT with a bystander preexcitation

C) Septal atrial tachycardia with RBBB aberration

D) Ventricular tachycardia

Answer

The correct answer is A. The figure shows a regular wide complex tachycardia with right bundle branch block morphology. Its morphology is consistent with a ventricular origin, and the absence of His bundle potentials preceding each QRS excludes SVT with aberration.

Rapid pacing stimuli delivered from the distal CS capture the atrium–the first of which terminates tachycardia without reaching the ventricle. The ability of an APD equivalent to terminate a wide complex tachycardia with AV block excludes VT. Furthermore, the first pacing stimulus terminates tachycardia without affecting the septal atrium. Such an AV J-refractory APD would not be able to terminate AVNRT (nor an AT that had already depolarized the septum), and therefore its ability to terminate tachycardia with AV block is diagnostic of antidromic tachycardia. In this case, antegrade conduction occurred over a left free wall AP and retrograde conduction over the AV node. Note the retrograde His bundle potentials at the onset of the ventricular electrogram ("short VH tachycardia") resulting from retrograde conduction over the left bundle (ipsilateral to the AP). Upon tachycardia termination, pacing stimuli conduct with ventricular preexcitation and a negative HV interval.

Case 1.G

Question

A 55-year-old man with pulmonary sarcoidosis presents with 2 weeks of fatigue.

Which of the following answers is the least likely to explain the findings in the figure?

A) Infrahisian AV block in the setting of RBBB/ LAFB with premature ventricular complexes arising from the left anterior fascicle

B) Infrahisian AV block in the setting of RBBB/ LPFB with ventricular escape complexes arising from the left posterior fascicle

C) Infrahisian AV block in the setting of RBBB/ LAFB with conduction during the supernormal period of the left anterior fascicle

D) Infrahisian AV block in the setting of RBBB/ LAFB with gap conduction over the left anterior fascicle

Answer

The correct answer is D. The 12-lead ECG shows sinus rhythm, high-grade AV block, and bigeminal cycles of RBBB with alternating LAFB/LPFB. His bundle recordings demonstrate block below the His bundle, but the second QRS complex (RBBB/ LPFB) is preceded by a paradoxical shortening of the HV interval. One explanation is that the second QRS complex of each cycle is a PVC arising from the LAF, resulting in a foreshortened "HV" interval. Alternatively, it is possible that the first QRS complex (RBBB/LAFB) is actually a ventricular escape complex arising from the LPF, giving the appearance of a long HV interval. By concealing into the LAF and "peeling back refractoriness" or Wedensky facilitation, the escape facilitates subsequent LAF conduction. A third explanation is that the second P wave of each cycle falls into the supernormal period of the LAF, creating RBBB/ LPFB complexes with shorter HV intervals. Evidence supporting supernormality is the observation that a nonconducted P wave (*) has a different RP relationship than conducted P waves because it falls outside the supernormal window. While gap conduction could explain unexpected LAF conduction, there is no visible conduction delay proximal to the LAF (AH and His bundle durations are constant) and the gap phenomenon would not account for the sizeable (71 ms) paradoxical shortening of the HV interval.

Case 1.H

Question

The following tracings were obtained prior to ablation of atrial flutter. A multipolar catheter is placed with its tip lateral to the right atrial isthmus. Pacing is performed from the lateral edge of the cavotricuspid isthmus. The pacing maneuver shown in this tracing demonstrates the following:

A) Pacing does not capture the circuit

B) Pacing from the exit of the circuit

C) Pacing from the central part of the circuit

D) Pacing from a bystander part of the circuit

Answer

The correct answer is A. Pacing is performed during tachycardia to determine the mechanism of the tachycardia and to determine the proximity of the ablation catheter to the tachycardia circuit.

During evaluation of atrial flutter, entrainment is carried out from the proximal and distal coronary sinus (CS) and the cavotricuspid isthmus (CTI) to broadly differentiate between a left atrial versus right atrial tachycardia. The observation that most of the tachycardia cycle length (TCL) is encompassed by the catheters shown in the figure argues strongly for a reentrant circuit (140 ms out of 189 ms). ECG morphology also suggests counterclockwise CTI-dependent atrial flutter, confirmed by the "halo" activation pattern and proximal to distal CS activation.

The proximity of the circuit to the pacing catheter is estimated by measuring the postpacing interval (PPI), which is the difference between the timing of the electrogram that is the last captured electrogram from the pacing catheter to the first subsequent electrogram on that pacing catheter after the tachycardia resumes. In general, particularly for atrial arrhythmias, it is desirable to have a PPI-TCL less than 20 ms. Pacing or entrainment (once it is shown that the tachycardia is reentrant) is then carried out from different parts of the CTI and the right atrium to determine the nature of the circuit.

Several parameters should be checked:

1. Was the tachycardia entrained? Did the tachycardia accelerate to the pacing cycle length?

2. Did the tachycardia resume at the initial cycle length and the same activation pattern/sequence?

3. Is concealed entrainment present?

In the tracing on the previous page, the tachycardia is not accelerated and there is no evidence of atrial capture; hence, the maneuver should be repeated after repositioning the catheter or pacing at a higher output.

The following image shows the outcome of repeat pacing at a higher output with better catheter contact. During this maneuver, the tachycardia is clearly accelerated to the pacing cycle length. The flutter wave morphology in lead V1 is unchanged and the atrial electrogram morphology and sequence are unchanged indicating concealed entrainment and the tachycardia continues after cessation of pacing.

The postpacing interval is 2 ms greater than the tachycardia cycle length; PPI-TCL < 20 ms indicates site of pacing is within the circuit.

The stimulus to flutter wave timing is same as the electrogram to flutter wave and is about half of the TCL. This means that the site of pacing is in the middle of the area of slow conduction (in this case, the cavotricuspid isthmus).

Case 1.I

Question

Based on the following pacing maneuver, the most likely diagnosis in this patient with recurrent wide complex tachycardia is:

A) AVNRT with a bystander accessory pathway

B) Antidromic tachycardia

C) Atriofascicular antidromic tachycardia

D) Fascicular VT

Answer

The correct answer is B. This tracing shows a wide complex tachycardia (WCT). The differential diagnosis has been previously discussed, but can be separated into ventricular tachycardia and preexcited tachycardia. This tracing shows a wide complex tachycardia with 1:1 VA relationship. The septal VA interval measured from the onset of QRS to the A electrogram on the His or proximal CS channel is ~240 ms. Septal VA interval, which is significantly greater than 70 ms, makes AVNRT with a bystander accessory pathway unlikely. (While typical AVNRT shows VA < 70 ms, other "atypical" forms of AVNRT can show septal VA intervals > 70 ms. Furthermore, while the septal VA < 70 ms or > 70 ms pertains to narrow complex tachycardias, it may not be so for preexcited tachycardias, where ventricular activation starts early over the AP compared to the HPS, resulting in a relatively longer VA interval in patients with AVNRT and a bystander pathway).

Fascicular VT has a short or negative HV interval. The His potential usually follows the QRS by 5 to 30 ms. There may be 1:1 VA conduction. Atriofascicular pathways insert into the right ventricle near the right bundle branch and produce a left bundle branch morphology.

(Continues...)

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Excerpted from Essential Concepts of Electrophysiology through Case Studies by Kenneth A. Ellenbogen. Copyright © 2015 Kenneth A. Ellenbogen, Roderick Tung, David S. Frankel, Prabal K. Guha, Reginald T. Ho. Excerpted by permission of Cardiotext Publishing, LLC.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

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Table of Contents

Contents

About the Contributors, ix,
Preface, xi,
Abbreviations, xiii,
Part 1: Electrophysiologic Concepts, 1,
Part 2: Supraventricular Tachycardia (SVT), 59,
Part 3: Atrial Fibrillation (AF), 189,
Part 4: Ventricular Tachycardia (VT), 221,
Appendix A (Cases by number, title), 319,
Appendix B (Cases by title, number), 321,