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

Background: Substantial 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 results: The study population consisted of 36,299 healthy women. Racial differences in rate-adjusted QT end (QT(ea)) and QT peak (QT(pa)) intervals as linear functions of RR were small, leading to the conclusion that 450 and 390 ms are applicable as thresholds for prolonged and shortened QT(ea) and similarly, 365 and 295 ms for prolonged and shortened QT(pa), respectively. As a threshold for increased dispersion of global repolarization (T(peak)T(end) interval), 110 ms was established for white and Hispanic women and 120 ms 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 150 μV 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.

Conclusions: Common thresholds for all racial groups are applicable for QT(ea), and QT(pa) intervals and ST elevation. Race-specific normal standards are required for many other ECG parameters.

Keywords: Electrocardiogram; Monitoring; Normal standards; QT; ST; TpTe.

Figure 1

Mean values (in lower columns) and upper normal limits (98th percentiles, listed on top for Cornell Voltage (CV) (four columns on the left) and Sokolow-Lyon Voltage (SLV) (four columns on the right) by ethnicity. The mean values and the upper limits in black, Hispanic and Asian women differ significantly from white women and race-specific upper normal limits are necessary.

Figure 2

Mean values (lower columns) and upper normal limits (98^th percentiles, top columns) for Cornell Voltage in women by ethnic group with obesity status matched for body mass index (BMI) in white women (BMI < 23 kg/m² for lean women and BMI >32 kg/m² for obese BMI group). The limits are above the 2000 μV threshold for LVH in lean white, African-American and Asian/Pacific women but considerably below the threshold in lean Hispanic women and in obese women in all ethnic groups.

Figure 3

Normal limits (96% range) for STonset (ST_o, the J-point amplitude) in vessel-specific bipolar left anterior descending (LAD), left circumflex (LCX) and right coronary artery (RCA) leads and in chest leads V1-V6 for the combined group of women. Bipolar LAD lead is recorded from 1/2 interspace below V8 to V3, LCX from 1/2 interspace above V2 to 1/2 interspace above V8, and RCA 1 interspace above V2 (at third interspace) to left iliac crest. Electrode placements for limb leads are the same as for Mason-Likar leads and V3-V6 positions for monitoring leads are at the level of V1 and V2.