Quantifying fractionation and rate in human atrial fibrillation using monophasic action potentials: implications for substrate mapping

Aims To use monophasic action potentials (MAPs) to better assess the rate and the presence of fractionated electrograms during the mapping of atrial fibrillation (AF). Substrate mapping is increasingly central to AF ablation. However, traditional bipolar signals poorly represent waveform shape, making it unclear whether fractionation reflects local waveform variations, true electrogram fragmentation, or noise, and raising issues on whether their spectral dominant frequencies (DFs) accurately estimate AF rate. Methods and results In 28 patients with paroxysmal or persistent AF (left atrial diameters 44 ± 8 mm), we studied 49 epochs of right atrial MAPs during AF. We compared fractionation, spectral and time-domain AF rate estimates using MAPs and bipolar electrograms obtained by filtering the MAPs. Fractionation was overestimated in bipolar rather than MAP electrograms ( P = 0.005) and often reflected artefacts on the MAPs. Conversely, local waveform variability in the MAPs, including alternans or fractionation, was often uniform in the bipolar electrograms. The measured AF cycle length (CL) was accurately represented by the DF of the MAPs ( r = 0.73, P < 0.001) but, due to double counting, not by the DF of bipolar signals ( r = 0.29, P = 0.07). Spectral CL estimates were therefore accurate (≤20 ms from measured CL) for 77% of MAPs but for 45% of bipolar signals only. A novel autocorrelation method better estimated CL in MAPs ( r = 0.92; P < 0.001) and bipoles ( r = 0.82; P < 0.001), with 89 and 77% accuracy, respectively ( P < 0.01). Conclusion Atrial fibrillation organization and rate are better represented by MAPs, which portray fibrillatory waveform shape, than by bipolar recordings. This approach may more reliably portray electrogram variability, fragmentation, and rate for the mapping of AF substrates.