Human atrial repolarization: effects of sinus rate, pacing and drugs on the surface electrocardiogram

Objectives We studied the effects of rate and some cardioactive drugs on the atrial surface electrocardiogram (ECG). Background In atrioventricular block, atrial surface ECG is unmasked. The effect of rate alone permits detection of the effect of other exogenous stimulations such as drugs in the presence of rate alterations. Methods High fidelity, high gain ECG leads I, II and III were recorded from 51 patients with heart block. Durations of P and T waves and the total PT interval were measured from nonconducted atrial events. Results No relationship was found between sinus cycle length and PTa, P or T in 31 patients. In 20 patients, progressively decreasing the atrial pacing cycle length from 853 ms to 381 ms resulted in linear reduction of the PT interval from 444 to 291 ms (rho = 0.76, slope = 0.24). This was largely due to shortening of Ta. linear rate correction formul was derived: corrected PT = PT − 0.24 (PP − 1000). Atropine (0.02 mg/kg) shortened the PP interval (p < 0.001) and the PT interval (p < 0.01). Propranolol (0.1 mg/kg) prolonged the PP interval (p < 0.001) but did not alter the PT interval. Neither disopyramide (2.0 mg/kg) nor flecainide acetate (2.0 mg/kg) altered the PP interval, but both prolonged the PT interval (p < 0.001). This was largely due to P wave lengthening after flecainide (p < 0.001) and to T prolongation after disopyramide (p < 0.001). Conclusions In heart block, PTa, P and T waves can be measured reliably. The effects of pacing and some antiarrhythmic drugs on the atrial myocardium are similar to those known at the ventricular level.