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Background-: Prolonged duration of QRS complex in a 12-lead ECG is associated with adverse prognosis in patients with cardiac disease, but its significance is not well established in the general population. In particular, there is a paucity of data on the prognostic significance of nonspecific intraventricular conduction delay in apparently healthy subjects.

Methods and Results-: We evaluated the 12-lead ECGs of 10 899 Finnish middle-aged subjects from the general population (52% of whom were men; mean age 44 /-8.5 years) between 1966 and 1972 and followed them for 30 /-11 years. Primary end points were all-cause mortality, cardiac mortality, and arrhythmic death. Prolonged QRS duration was defined as QRS >=110 ms and intraventricular conduction delay as QRS >=110 ms, without the criteria of complete or incomplete bundle-branch block. QRS duration >=110 ms was present in 1.3% (n=147) and intraventricular conduction delay in 0.6% (n=67) of the subjects. Prolonged QRS duration predicted all-cause mortality (multivariate-adjusted relative risk [RR] 1.48; 95% confidence interval [CI] 1.22-1.81; P<0.001), cardiac mortality (RR 1.94; CI 1.44-2.63; P<0.001), and sudden arrhythmic death (RR 2.14; CI 1.38-3.33; P=0.002). Subjects with intraventricular conduction delay had increased all-cause mortality (RR 2.01; CI 1.52-2.66; P<0.001), increased cardiac mortality (RR 2.53; CI 1.64-3.90; P<0.001), and an elevated risk of arrhythmic death (RR 3.11; CI 1.74-5.54; P=0.001). Left bundle-branch block also weakly predicted arrhythmic death (P=0.04), but right bundle-branch block was not associated with increased mortality.

Conclusions-: Prolonged QRS duration in a standard 12-lead ECG is associated with increased mortality in a general population, with intraventricular conduction delay being most strongly associated with an increased risk of arrhythmic death.

(C) 2011 American Heart Association, Inc.