The cumulative effects of historical and physical examination findings on the prognostic value of the electrocardiogram

Abstract

The electrocardiogram has been shown in epidemiologic studies to be an independent predictor of survival. These studies have adjusted for selected covariates simultaneously. This article assesses the value of the electrocardiogram as a predictor of survival when introduced at progressive stages of the common clinical encounter. Data collected from 4,518 patients ages of 60 to 96 years with isolated systolic hypertension who were followed-up for up to 6 years as part of the Systolic Hypertension in the Elderly Project were analyzed. Survival curves and 3- and 5-year survival rates (Cox regression methods) of groups with normal and abnormal resting electrocardiograms were compared. Blocks of covariates representing demographic information, risk factors for cardiovascular disease, clinical history, and physical examination findings were added to the survival models sequentially to mimic the sequence of the common clinical encounter, and the independent significance of the electrocardiogram as a predictor of survival was assessed at each step. An abnormal electrocardiogram was associated with reduced survival when no adjustment for covariates is made. Survival was also significantly ( P < .05) different for groups with normal and abnormal electrocardiograms when demographic and risk factor variables were included in the statistical models, but not after findings from the clinical history and physical examination were added. The prognostic value of the electrocardiogram varies with the stage in the clinical encounter in which it is introduced.