Year-to-year variation of the orthogonal electrocardiogram and vectorcardiogram among 243 normal white males

Summary When assessing patients' serial ECG changes, the clinician implicitly compares those changes to the limits of change expected in a healthy population. Prospective epidemiological studies, too, develop their criteria from the limits of normal serial ECG changes. Surprisingly then, few studies have reported normal limits for changes between serial ECGs taken six months or longer apart, and all are based on small samples. The present study has a large sample size: 243 white middle-aged and older males, after exclusions for heart disease. Each had at least four consecutive annual examinations with ECGs. Limits of serial variability were computed for 52 measurements. The ECG measurements included durations, amplitudes, ratios, angles and spatial magnitudes. Clinical measurements included blood pressure, cholesterol, relative weight and hemoglobin. Year-to-year ECG variabilities were compared to day-to-day variabilities of the same measurements reported earlier. Year-to-year variation was virtually identical to the reported day-to-day variation in most measurements. In only two measurements was year-to-year variation over 25% greater than the reported day-to-day variation.