▪Objective: To examine the natural history of preexcitation occurring on the routine electrocardiogram (ECG).
▪Design: A longitudinal cohort study of 3983 originally healthy men followed prospectively for 40 years.
▪Setting: Free-living (community-dwelling) study members residing predominantly in Canada.
▪Participants: Nineteen male study members with preexcitation occurring during routine examination in the 40-year follow-up of the Manitoba Follow-up Study.
▪Measurements: Routinely requested clinical examinations and ECGs, supplemented by information supplied by the study member or his physician.
▪Main Results: Ten study members were found to have preexcitation at enrollment, for a prevalence of 2.5 per 1000 (95% Cl, 1.2 to 4.6). A delta wave was first detected during follow-up in an additional nine study members. Seventeen of 19 study members did not have the delta wave at some later time, and preexcitation was intermittently present in most of these members. Over time there was a loss of preexcitation, with 15 of 19 study members no longer exhibiting a delta wave by the end of follow-up. Five of 11 study members with symptoms had physician confirmation of an arrhythmia. Fourteen study members remain alive, and none of the five deaths was attributed to preexcitation.
▪Conclusions: Preexcitation found on routine ECG in our originally healthy male study group did not confer excess morbidity or mortality, even in those study members who developed symptomatic arrhythmias. Most preexcitation was intermittent and disappeared over time.