Prevalence and clinical correlates of non-Wenckebach, narrow-complex second-degree atrioventricular block detected by ambulatory ECG.

Among 113 patients with transient, narrow-complex second-degree atrioventricular (AV) block detected by ambulatory ECG, there were 20 with non-Wenckebach behavior. Based on the presence or absence of PR interval shortening after single blocked complexes, patients with narrow-complex non-Wenckebach patterns could be separated into a pseudo-Mobitz II group of 16 patients (greater than or equal to 20 msec of PR shortening after the blocked complex) and a classic Mobitz II group of four patients (constant PR interval). These groups had additional distinct ECG and clinical features. Patients with the pseudo-Mobitz II pattern had a 44% prevalence of associated Wenckebach block during the same ambulatory recording, whereas Wenckebach behavior did not occur in patients with classic Mobitz II block. Pseudo-Mobitz II block occurred at significantly longer cycle lengths (876 vs 585 msec) and with significantly longer PR intervals (225 vs 165 msec) preceding the blocked complex than did classic Mobitz II block. Syncope was the presenting symptom in 38% of patients with pseudo-Mobitz II block and in all patients with classic Mobitz II block. Patients with pseudo-Mobitz II block had a 56% prevalence of associated coronary disease and a 44% prevalence of congestive heart failure; the mortality rate was 38% in this group over 4 years of follow-up, but in all instances death was due to associated disease rather than to conduction itself. In contrast, patients with classic Mobitz II block had hypertensive or valvular disease but no evidence of coronary disease or congestive failure; all are alive with pacemakers after 3 years of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)