Far-field bipolar electrograms can be unreliable for arrhythmia discrimination if changes in morphology are caused by factors like current of injury from successive shocks.
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Warrants caution relying on far-field electrograms after successive ICD shocks; case report leaves open optimal discrimination strategies.
Analysis of stored electrograms from bipolar far-field electrodes is considered to be useful in differentiating supraventricular from ventricular arrhythmias. A case of inappropriate ICD shocks for sinus tachycardia is presented whereby successive shocks caused marked widening of the ventricular electrograms. Analysis of these stored electrograms, recorded from far-field bipolar electrodes, gave the false impression of ventricular tachycardia. The widening was due to the current of injury effects, probably a consequence of the large amount of intervening myocardium between the bipoles. While analyzing recordings from far-field bipolar electrodes is generally useful, it is not always reliable, for changes in electrogram morphology, relative to baseline rhythm, may result from other factors like current of injury.
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Nayak et al. (1997) studied this question.
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