Electrophysiologic properties and response to pharmacologic agents of fibers from diseased human atria

We used standard microelectrode techniques to record action potentials of human right atrial fibers obtained during cardiac surgery, and correlated these potentials with clinical and preoperative ECG data. Human atrial fibers were classified as follows: Group A (ten patients) had a maximum diastolic potential (MDP) of -71.4 +/- 5.1mV (mean +/- SD), and action potentials that were primarily fast responses. These atria were normal or slightly dilated. In group B (12 patients) MDP was 50.3 +/- 5.7 mV; action potentials were slow responses and the atria were moderately to markedly dilated. Atrial arrhythmias occurred in four group B and no group A patients. The ECG revealed a signficant difference (P less than 0.005) in P wave duration: group A, 89 +/- 3.0 msec; group B, 111 +/- 6.0 msec. Verapamil, 0.1 mg/L, markedly depressed only the action potential plateau of group A. Procainamide 1-100 mg/L had equivalent effects on fibers of both groups A and B, effects which were small at dosages of less than 40 mg/L. Procainamide did not depress slow response automaticity, but verapamil (0.1-1 mg/L) did.