[A case of sick sinus syndrome, considered to develop to atrial standstill].
A 25 year old man was admitted to our hospital because of dizziness and bradycardia. Physical examination was normal except for an irregular pulse of 90 beats/min. Chest X-ray film showed no cardiomegaly and no pulmonary congestive changes. ECG showed 2:1 or 3:1 atrial flutter on admission. After atrial flutter was terminated spontaneously, ECG revealed absent P waves, a QRS interval of 0.10 seconds, and A-V junctional rhythm with irregular R-R interval ranging from 1.20 to 2.12 seconds. At times, cardiac arrest was noted. Esophageal electrocardiogram also failed to demonstrate atrial activity while A-V junctional rhythm continued. Mitral valve echocardiogram lacked A point, and then ä waves were absent in both the right atrial and pulmonary capillary pressure recordings. Transient atrial standstill was suspected from these findings, so that electrophysiological study was performed. Right atrial electrogram revealed complete absence of atrial activity. His bundle electrogram revealed H-V prolongation [80-83 msec]. Right atrial pacing was attempted at several atrial sites, including the high lateral, middle lateral, low lateral right atrium, and low right atrial septum. Atrial activity could be elicited with stimulus strength of 3 to 5 volts. These atrial pacing thresholds were mild or moderately higher than usual. After the cessation of atrial pacing at 90 beats for two minutes, the recovery time of the first beat prolonged to 8.46 second. We considered that this case was sick sinus syndrome in young adult which revealed generalized disturbance of conduction system including the atrial muscle, and would develop to atrial standstill in the near future.