Normal standards for computer-ECG programs for prognostically and diagnostically important ECG variables derived from a large ethnically diverse female cohort: The Women's Health Initiative (WHI)

Abstract

BackgroundSubstantial new information has emerged recently about the prognostic value for a variety of new ECG variables. The objective of the present study was to establish reference standards for these novel risk predictors in a large, ethnically diverse cohort of healthy women from the Women's Health Initiative (WHI) study. Methods and ResultsThe study population consisted of 36,299 healthy women. Racial differences in rate-adjusted QT end (QTea) and QT peak (QTpa) intervals as linear functions of RR were small, leading to the conclusion that 450 and 390ms are applicable as thresholds for prolonged and shortened QTea and similarly, 365 and 295ms for prolonged and shortened QTpa, respectively. As a threshold for increased dispersion of global repolarization (TpeakTend interval), 110ms was established for white and Hispanic women and 120ms for African-American and Asian women. ST elevation and depression values for the monitoring leads of each person with limb electrodes at Mason-Likar positions and chest leads at level of V1 and V2 were first computed from standard leads using lead transformation coefficients derived from 892 body surface maps, and subsequently normal standards were determined for the monitoring leads, including vessel-specific bipolar left anterior descending, left circumflex artery and right coronary artery leads. The results support the choice 150μV as a tentative threshold for abnormal ST-onset elevation for all monitoring leads. Body mass index (BMI) had a profound effect on Cornell voltage and Sokolow–Lyon voltage in all racial groups and their utility for left ventricular hypertrophy classification remains open. ConclusionsCommon thresholds for all racial groups are applicable for QTea, and QTpa intervals and ST elevation. Race-specific normal standards are required for many other ECG parameters.