A Pitfall in Using Far-Field Bipolar Electrograms in Arrhythmia Discrimination in a Patient with an Implantable Cardioverter Defibrillator

Analysis of stored electrograms from bipolar far-field electrodes is considered to be useful in differentiating supraventricular from ventricuiar arrhythmias. A case of inappropriate ICD shocks for sinus tachycardia is presented whereby successive shocks caused marked widening of the ventricuiar electrograms. Analysis of these stored electrograms, recorded from far-field bipolar electrodes, gave the false impression of ventricuiar tachycardia. The widening was due to the current of injury effects, probably a consequence of the large amount of intervening myocardium between the bipoies. While analyzing recordings from far-field bipolar electrodes is generally useful, it is not always reliable, for changes in electrogram morphoiogy, reiative to baseline rhythm, may result from other factors like current of injury.