Sick sinus syndrome: the role of hypervagotonia.
A 58-year-old man with persistent symptomatic sinus bradycardia (52 beats/min) showed a markedly prolonged postpacing pause (3240 msec) after atrial pacing at a cycle of 840 msec. In addition, Wenckebach block occurred following atrial pacing at a cycle length of 700 msec. After atropine (2 mg) postpacing pauses returned to normal value and type 1 second-degree AV block completely reversed to 1:1 AV conduction until paced rates greater than 140/min. It may be that in some patients marked and persistent vagal overactivity may predispose to "intrinsic" sinus node dysfunction; in later stages, sinus node function may paradoxically result unaffected by changes in autonomic tone.
D006327:Heart Block / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012804:Sick Sinus Syndrome / Q000503:physiopathology*; D014630:Vagus Nerve / Q000503:physiopathology*