Electrophysiologic Properties of Isolated Preparations of Human Atrial Myocardium

The electrophysiologic properties of human atrium were studied with intracellular microelectrodes in 22 preparations of human right atrial tissue obtained at the time of corrective open heart surgery. Two types of fibers were identified: the first had electrical characteristics typical of atrial contractile cells and the second those of atrial specialized fibers. Automaticity developed only in the latter type of cell. In 36 impalements of specialized atrial fibers, resting membrane potential was — 86 ± 5 mv (mean±SD), transmembrane action potential amplitude was 102 ± 12 mv, transmembrane action potential overshoot was 16 ± 4 mv. Similar results were obtained in 49 impalements of contractile fibers. Conduction velocity measured 0.28-0.33 m/sec in contractile fibers and 0.41-0.45 m/sec in specialized atrial fibers. Action potential duration of specialized atrial fibers was linearly related to the basic cycle length between 200 and 1000 msec. At cycle lengths greater than 1000 msec the increase in action potential duration was no longer linear. There was a decrease of 58 m