Indian Pacing Electrophysiol. J.

   ISSN  0972-6292

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Indian Pacing Electrophysiol. J. 2002;2(3):92

Arrhythmia Quiz 2- Answer

Arrhythmia Diagnosis Following an ICD Shock: Part II 

Roy M. John, MD, PhD, FRCP


          4: a left ventricular tachycardia is appropriately terminated by the ICD


            There is no evidence for a supraventricular arrhythmia. Two separate series of electrograms are seen in the atrial channel. The ones that occur in concert with the larger component of the ventricular electrogram are due to oversensing of right ventricular electrograms by the atrial channel. Isolated true atrial electrograms are seen occurring separately and totally dissociated from the ventricular rhythm (see arrows in figure 2). Hence the oversensing is in the atrial channel, not the ventricular channel. Atrioventricular dissociation is present confirming that the arrhythmia shown in the ventricular channel is a ventricular tachycardia.

            A slow ventricular tachycardia at a cycle length of 460 msec (rate 130 bpm) is present.  The arrhythmia is double counted by the ICD because of separate electrograms sensed from the left ventricle (smaller component designated LV EGM in Figure 2) and the right ventricle (larger component designated RV EGM in Figure2 and corresponding to the oversensed electrograms in the atrial channel). The double-counting results in detection in the VF zone and a 24 joule ICD shock that terminates the tachycardia. Note that the left ventricular electrograms precedes the RV electrograms indicating a left ventricular origin of the ventricular tachycardia.

            In ICD systems that incorporate biventricular pacing, lack of univentricular sensing capability, as in this case, will lead to double counting and ICD shocks for slow ventricular arrhythmias. The newer generation cardiac resynchronization ICDs will overcome this issue by limiting sensing to the right ventricular channel.

Figure 2:

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