Electrophysiological Imaging of the Right Atrium Using a Noncontact Multielectrode Cavitary Probe: Study of Normal and Abnormal Rhythms

Cavitary electmgrams previously were measured from multiple directions simultaneously in the canine left ventricle with the use of noncontact multielectrode probes. The objective of the present study was to measure cavitary electrograms in the canine right atrium (RA) and describe the corresponding global activation sequences during normal and abnormal atrial rhythms. A 64‐electrode custom probe was inserted into the RA of six dogs. Probe position and orientation were guided by fluoroscopy. Probe unipolar electrograms were acquired simultaneously during sinus rhythm, RA pacing, and ventricular pacing, Vagally mediated atrial fibrillation (AF) was induced in four dogs. Probe electrograms were acquired during AF induced at baseline and after intravenous infusion of ibutilide (0.075 mg/kg followed by 0.075 mg/kg infusion over 10 minutes). Isochrone maps were derived from noncontact probe electrograms and were displayed on a beat‐by‐beat basis during normal and paced rhythms. During AF, maps were displayed for 10 consecutive 100‐ms windows. Isochrone maps of normal and paced beats revealed regions of early activation that were consistent with sites of wavefront initiation. During AF, multiple varying activation wavefronts were observed. At baseline, AF cycle length was 110 ± 15 ms and the number of wavefronts was 1.72 ± 0.25 per 100‐ms window. After ibutilide, AF cycle increased to 182 ± 36 ms (P = 0.018) and the number of wavefronts decreased to 0.82 ± 0.14 per 100‐ms window (P = 0.009). In conclusion, global electrophysiological imaging with a noncontact multielectrode probe delineates RA anatomy. Furthermore, images of AF activation depict multiple wandering wavefronts. Ibutilide reduces the number of these wavefronts and organizes AF.