Indian Pacing Electrophysiol. J.

ISSN 0972-6292

Home Page Current Issue List of Editors

Indian Pacing Electrophysiol. J. 2004;4(1):43-44  Arrhythmia Quiz 3 - Answer

Arrhythmia Diagnosis Following an ICD Shock   Download PDF 102 KB

Roy M. John, MD, PhD, FRCP

Address for correspondence: Roy M. John, MD, PhD, Section of Cardiology, Lahey Clinic  Medical Center, 41 Mall Road, Burlington, MA 01805. Email:

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.

Click here to enlarge

Click here to enlarge

Figure 1: Electrograms and markers obtained during ICD interrogation. The top and bottom panels show the onset and termination of arrhythmia respectively. In each panel, the following information is displayed from top to bottom: atrial electrogram, ventricular electrogram, atrial marker channel with cycle length and ventricular marker channel with cycle length.

Home Page Current Issue List of Editors