Indian Pacing Electrophysiol. J.

   ISSN  0972-6292

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Indian Pacing Electrophysiol. J. 2001;1(1):32

Arrhythmia Quiz - Answer

Arrhythmia Diagnosis Following an ICD Shock. 

Roy M. John, MD, PhD, FRCP


            4. A pro-arrhythmic effect of ICD therapy is evident


            Stored electrograms show atrial fibrillation with rapid ventricular rates (top panel). Sufficient numbers of RR intervals meet the tachycardia detection criteria initiating a train of anti-tachycardia pacing by the ICD (after the 8th electrogram in the second panel). This provokes rapid monomorphic ventricular tachycardia (note that the electrogram morphology is different from that during atrial fibrillation) which enters the fibrillation detection zone leading to an ICD shock (after the 3rd electrogram in the 4th panel). Sinus rhythm is restored. Note the 5th and 11th electrograms in the 4th panel have different morphology from sinus rhythm electrogram following shock indicating PVCs.

             There is no evidence for ICD malfunction.  Induction of ventricular tachycardia by attempted anti-tachycardia pacing is a pro-arrhythmic effect of ICD therapy.

             The atrial arrhythmia does not appear to have been modified by anti-tachycardia pacing. Indeed, ventricular pacing would not be expected to influence atrial fibrillation. Although the final therapy with defibrillation shock was appropriate, the arrhythmia is likely to recur and the patient would be better served with therapeutic modifications. He does not appear adequately beta blocked; an increase in the dose of beta blockers or substitution of metoprolol with sotalol are appropriate in the first instance. Given, evidence for left ventricular dysfunction, he is at risk for thrombo-embolism and chronic anticoagulation should be considered. The prior history of amiodarone induced pneumonitis is a relative contra-indication to re-challenge with the drug. Early amiodarone induced pneumonitis is believed to be a hypersensitivity type response and likely to recur although there are reports of re-challenge under steroid cover.

Figure for Arrhythmia Quiz: