Impact of changing activation sequence on bipolar electrogram amplitude for voltage mapping of left ventricular infarcts causing ventricular tachycardia

Introduction: Wavefront direction is a determinant of bipolar electrogram amplitude that could influence identification of low amplitude regions indicating infarction or scar. Methods: To assess the importance of activation sequence on electrogram amplitude 11 patients with prior infarction and ventricular tachycardia were studied. At 819 left ventricular sites bipolar electrograms were recorded during atrial pacing and ventricular pacing, followed by unipolar pacing with a stimulus of 10 mA at 2 ms. Sites with a pacing threshold > 10 mA were designated electrically unexcitable scar. Results: Areas of low voltage (less than or equal to 1.5 mV) were present in all patients. Atrial paced and ventricular paced electrogram amplitudes were strongly correlated ( r = 0.77; p< 0.0001). Changing the activation sequence ( from atrial pacing to ventricular pacing) produced a > 50% change in electrogram amplitude at 28% of sites and a > 100% change at 10% of sites, but only 8% of sites had an electrogram amplitude classified as abnormal (= 1.5 mV) with one activation sequence and normal (> 1.5 mV) with the other activation sequence. Electrically unexcitable scar ( 6% of sites) was associated with lower electrogram amplitude but could not be reliably identified based on electrogram amplitude alone for either activation sequence. Conclusion: Voltage maps created with bipolar recordings using these methods should be relatively robust depictions of abnormal ventricular regions despite variable catheter orientation and activation sequences that might be produced by different rhythms.