Abstract 16295: Human Epicardial Bipolar Electrograms Prolong and Reduce in Amplitude Prior to Induction of Peri-Operative Atrial Fibrillation and Are Related to Sites of High Electrogram Dominant Frequency in Sinus Rhythm

Abstract

Background: The exact trigger/substrate interactions leading to post-operative AF are unknown. Sites of high DF in sinus rhythm are proposed to harbor ‘fibrillar myocardium’ or ‘AF nests’. We studied AF inducibility related to putative upstream substrate changes by characterising epicardial electrograms (EGM) in both time and frequency domains. Method: AF naïve patients (n=14) undergoing coronary artery bypass grafting (CABG) had bipolar electrograms recorded from the lateral right atria (RA) wall with a high density spiral catheter, sampled at 1kHz. RA burst pacing at cycle lengths (CL) of 200, 500 and 1000ms was performed with any episodes of AF > 30s recorded. Electrograms were analysed using an average of 5 consecutive beats for duration, peak to peak amplitude, dominant frequency (DF) and activation time at all bipole pairs during every pacing drive train (total EGMs analysed 3430). Results: Bipolar EGM duration was significantly longer during AF (mean = 76.64ms, SD = 29.35ms) than all other CLs or NSR (p<0.0001). There was no difference between CLs but a trend to longer EGM at 200ms CL. EGM amplitude was significantly smaller during AF (mean = 0.85mV, SD = 0.51mv) vs. 500ms CL and NSR (p<0.0001) and at 200ms vs. 500ms CL (p<0.05) and NSR (p<0.0001). The EGM DF was significantly lower in AF (mean = 75.87Hz, SD = 23.63Hz) vs NSR (mean = 89.33Hz, SD = 25.99Hz) (p<0.05) but not vs. pacing CLs. Activation time was significantly prolonged at 200ms CL (mean = 29.41ms, SD = 16.23ms) vs AF and NSR (p<0.001 and 0.05 respectively). Conclusions: Human bipolar EGMs prolong and reduce in amplitude in induced peri-operative AF than in NSR or pacing. Atrial activation slows at 200ms CL, prior to initiation of AF. These changes are accompanied by high DF sites in NSR which may reveal underlying ‘AF nests’ even in non-remodelled atria. These novel peri-operative electrophysiological findings suggest upstream substrate changes which may predispose patients to post-operative AF.