February 19th Question
Which of the following is an explanation compatible with the ECG in the Figure?
A. Sinus rhythm with first-degree atrioventricular (AV) block, bifascicular (right and left superior fascicle) block, and frequent premature junctional complexes in a pattern of bigemini
B. Sinus rhythm with aberrantly conducted (right and left superior fascicle block) premature atrial complexes in a pattern of bigemini
C. Sinus rhythm with second-degree type I AV block and rate-related bifascicular (right and left superior fascicle) aberrancy
D. Sinus rhythm with second-degree type I AV block, bifascicular (right and left superior fascicle) block, and rate-related pseudonormalization of QRS
E. Sinus rhythm with complete AV block, ventricular escape rhythm, and premature junctional (or AV nodal echo) beats in a pattern of bigemini
Answer to February 12th Question
E. Change pacing mode to DDD
The electrograms from the episode show more ventricular than atrial events consistent with ventricular tachycardia. During the episode, the near-field right ventricular electrogram shows changing morphology suggesting torsades de pointes (TdP). The susceptibility to TdP is increased with bradycardia or ventricular pauses. The marker channel shows the episode to initiate after a ventricular paced event following a pause (≈1690 ms), indicating pause-mediated TdP. The pause is because of atrioventricular (AV) block without any backup demand pacing in the ventricle. A dropped ventricular beat with a subsequent atrial event followed by ventricular paced event after 110 ms reveals atrial pacing, atrial sensing, inhibition function (AAI)–dual-chamber pacing, dual-chamber sensing, dual inhibition and tracking function (DDD) mode (Managed Ventricular Pacing mode, Medtronic, Minneapolis, MN).1 In presence of 1:1 atrioventricular conduction, the AAI-DDD algorithm operates in AAI to prevent any ventricular pacing. Occurrence of a dropped ventricular beat (AV block) triggers a backup ventricular pace output 110 ms after the next atrial event. If the ensuing atrial event is also AV blocked, the operation switches temporarily to DDD.
Increasing β-blocker (Option A) may or may not reduce risk of TdP but will increase the chances of AV block and ventricular pauses that may trigger TdP. Increasing lower limit (Option B) will shorten the overall duration of a ventricular pause but may increase the frequency of dropped ventricular beats because of increase in AV block at faster atrial rates. Amiodarone (Option C) may directly increase the risk for TdP. Catheter ablation can target critical isthmuses (of reentrant ventricular tachycardia) or triggering beats (of any ventricular arrhythmia). The role for substrate modification in suppressing polymorphic ventricular tachycardia is unclear. In this case, TdP initiates with a pause followed by ventricular paced event, and a target for ablation is not distinctly apparent (Option D). In any case, the most appropriate next step to prevent further episodes of TdP and defibrillator shocks would be to eliminate the inciting ventricular pauses by changing the pacemaker mode to DDD instead of AAI-DDD (Option E).
- © 2018 American Heart Association, Inc.