Reproducibility of local activation times during intraoperative epicardial mapping.

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Abstract
The reproducibility of the measurement of local epicardial activation times using intraoperative epicardial mapping was studied in 10 patients. Two multipolar electrodes were used, 1 as a reference located on the anterior surface of the right ventricle, the other as a hand-held probe for depicting local activation times. During atrial pacing at 100 beats/min, activation times at various sites of the heart were measured consecutively using a grid system that defined 75 points on the surface of the heart. The surface of the heart was divided into 3 areas; the anterior wall of the right ventricle, the left lateral wall and the posterior wall of both ventricles. The measurements were repeated twice at the same paced atrial rate. The mean absolute differences between the 1st and 2nd measurements were calculated for each point. The earliest onset of excitation was depicted on the surface of the anterior wall of the right ventricle. The mean difference between the 1st and 2nd measurement at identical paced rates was 8 ms on the anterior wall, 6 ms on the left lateral wall and 7 ms on the posterior wall. At individual points the differences were greater (40 ms maximum). These greater differences were mainly found in the area of epicardial fat tissue in the atrioventricular groove or the sulcus interventricularis. Using a visual coordinate system, it is possible to achieve a good reproducibility of local activation times with respect to the large differences found in patients with accessory pathways or with ventricular tachycardia.