[The vulnerability of the right atrium. II. Correlations between vulnerability and the atrial refractory periods...

The vulnerability of the right atrium to single electrical stimuli was investigated in 100 non-selected patients. According to the response pattern to extrasystolic stimulation of the right atrium during the relative refractory period, the patients could be divided in 3 groups: Group A: no signs of vulnerability. Group B: 1 to 5 additional atrial extrasystoles after the premature atrial stimulus. Group C: runs of atrial flutter or fibrillation for at least 8 s. The 3 groups were compared with respect to the duration of the effective and relative refractory period of the right atrium. From group A to group C the effective refractory period showed a tendency to shorten, while the relative refractory period showed a tendency to prolong. These results are interpreted as supporting a reentry as the underlying mechanism of the here described atrial vulnerability.