Atrial excitability and conduction in patients with interatrial conduction defects.

Prolongation of P-wave duration is an accepted indicator of an interatrial conduction disturbance and may predispose patients to atrial arrhythmias. This study was performed to monitor electrophysiologic characteristics of the atria in patients with a prolonged P-wave duration. Atrial excitability and conduction times were compared in 7 patients with a P-wave duration of less than 115 ms (Group I), and 13 patients with a duration of greater than of equal to 115 ms (Group II). In contrast of the Group I patients, most of the 13 patients in Group II had atrial arrhythmias, including sinus nodal dysfunction (3 patients) and a history of atrial fibrillation or ectopic atrial tachycardia (6 patients). Electrophysiologic differences between the 2 groups included a higher late diastolic threshold in Group II (0.8 +/- 0.2 mA versus 1.3 +/- 0.2 mA; p less than 0.005), and a greater increase in intraatrial conduction time (5 +/- 10 ms versus 30 +/- 20 ms; p less than 0.005) and interatrial conduction time (5 +/- 15 ms versus 30 +/- 15 ms; p less than 0.05) of early premature responses. There were no differences between the 2 groups in refractory periods, shape of the strength interval curve, or conduction times of premature responses occurring late in diastole. These abnormalities in conduction time and excitability found in patients with a prolonged P-wave duration may predispose to the initiation of certain atrial tachyarrhythmias.