Clinical significance of the pre-atrial electrical activity recorded by the catheter electrode in high right atrium.

1) In canine experiment, the averaging of high right atrial electrical activity revealed the pre-A preceding the atrial deflection, which was proven to be a part of the electrical activity of sinus nodal region. 2) The pre-A was obtained in 114 (75%) of 153 clinical cases. 3) The mean pre-A interval was 18 +/- 4 msec in control group, and was prolonged in cases with sick sinus syndrome, ischemic heart disease and myocarditis. 4) The significant correlation existed between the pre-A interval and the SACT by Strauss' method (r = 0.80, p < 0.01). 5) The pre-A obtained by averaging technique is relatively simple, safe and reliable method, and is useful for evaluating the sino-atrial function.