Roy M. John, “Arrhythmia Diagnosis Following an ICD Shock” 44
Which of the following is a true statement regarding this arrhythmia?
1. A supraventricular tachycardia is a present
2. Programming of the ICD as a two zone device with activation of the SVT discrimination
algorithm may have delayed or prevented this ICD shock
3. A ventricular tachycardia with 1:1 VA conduction is successfully terminated by the ICD
shock
4. This arrhythmia is best treated with radiofrequency ablation of the AV node
5. Separate atrial and ventricular arrhythmias are present
Answer: (5) Separate atrial and ventricular arrhythmias are present.
The initial part of the upper panel display the marker channels before electrogram
storage began. Atrial cycle lengths ranging between 230 and 290 msec are apparent at a time
when the ventricular marker channel shows sensed beats (Vs) at cycle lengths of 520 and 510
msec suggesting that an atrial arrhythmia preceded the onset of the ventricular arrhythmia. The
third ventricular event on the marker channel in the upper panel is the onset of ventricular
tachycardia. During the arrhythmia, atrial cycle lengths (250 to 270 msec) are distinctly
different from that of the ventricular cycle lengths (280 to 300msec). There is no Wenckebach
periodicity to the ventricular rhythm excluding atrio-ventricular conduction during an SVT as
the mechanism.
SVT discrimination algorithms would have classified this arrhythmia as a ventricular
arrhythmia and delivered ICD therapy.
Based on the cycle length of the atrial arrhythmia, atrial flutter is likely and any
ablative therapy should initially be targeted at eliminating flutter. RF ablation of the AV node
is an option if heart rates are excessive during the atrial arrhythmia despite AV nodal blocking
drugs or if biventricular pacing is frequently inhibited as a result of native conduction.
Atrial arrhythmias complicate ventricular tachycardia is approximately 10 to 15% of
cases. In some patients, atrial flutter or fibrillation can trigger ventricular tachycardia or
fibrillation. Control of the atrial arrhythmia is particularly important in this patient with a
biventricular pacing device. Native conduction via the AV node during atrial tachycardias is a
common reason for loss of biventricular pacing.
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 4(1): 43-44 (2004)