Mode of spontaneous onset and termination of supraventricular tachyarrhythmias

ECG tracings from 16 patients with spontaneous onset and/or termination of supraventricular tachyarrhythmias (SVTA) were studied. Of these recordings, 13 were made with a special technique which gives a high resolution of the atrial waves. At the onset of SVTA, the first atrial wave invariably had an aberrant configuration. The coupling index (coupling interval (P-1P) preceding cycle length) was 0.05 or less in 9 of 16 cases but more than 0.60 in 4 cases. In the 5 cases of onset of atrial fibrillation, the intervals between the first few atrial waves corresponded to a frequency of 300-350 per minute. Acceleration of the atrial activity occurred within the first 30 seconds. At the termination of SVTA, no successive modification of the atrial activity was found. The termination often did not occur at or shortly after a QRS complex. It is concluded that a premature atrial beat--even a single one--with a short coupling interval may well intiate a circus-movement SVTA, while an ectopic atrial beat with a long coupling interval apparently must be followed by repeated rapid discharges from the ectopic focus in order for SVTA to ensue. The functional conditions of the atria may then determine which kind of SVTA eventually results.