Atrial electrogram analysis: antegrade versus retrograde.

Automatic discrimination between antegrade and retrograde atrial electrograms would prevent endless loop tachycardia and contribute to tachycardia detection algorithms. We tested its feasibility by comparing antegrade and retrograde atrial electrograms in 129 patients at the time of atrial lead implantation. Only unipolar, passive-fixation, endocardial, right atrial appendage leads were included. The mean antegrade amplitude was 4.2 +/- 2.2 mV, and retrograde 2.4 +/- 1.5 mV (P less than 0.001); the mean antegrade slew rate was 2.6 +/- 2.1 mV/ms, and retrograde 1.3 +/- 1.1 mV/ms (P less than 0.001). Morphology was similar in 84 patients (65%). The antegrade amplitude exceeded the retrograde by 1.0 mV in 67%, and by 0.5 mV in 81% of patients. Morphology and slew rate contributed little to the discriminating power of amplitude alone. Thus, amplitude criteria reliably distinguish antegrade from retrograde atrial activity.