Assessment of QT Interval and QT Dispersion for Prediction of All-Cause and Cardiovascular Mortality in American Indians

TLDR

Prolonged QT interval and increased QT dispersion have been proposed as surface ECG markers of ventricular arrhythmia risk and potential mortality predictors. The study evaluated QTc and QTD in 1839 American Indian participants by acquiring 250‑Hz ECGs, automatically measuring QT intervals in all 12 leads, correcting them with Bazett’s formula, and computing QTD as the difference between maximum and minimum QTc. During a 3.7‑year follow‑up, prolonged QTc and increased QTD independently predicted all‑cause and cardiovascular mortality, with QTc remaining a strong all‑cause predictor after adjustment and QTD predicting only cardiovascular death, underscoring their utility for noninvasive risk stratification.

Abstract

Background —Both a prolonged QT interval and increased QT interval dispersion (QTD) have been proposed as surface ECG markers of vulnerability to ventricular arrhythmias and potential predictors of mortality. Methods and Results —The predictive values of QT prolongation and QTD were assessed in 1839 participants in the Strong Heart Study, a prospective study of cardiovascular disease in American Indians. ECGs were acquired at 250 Hz; QT intervals were measured by computer in all 12 leads and corrected for heart rate (QTc) by use of Bazett’s formula. QTD was calculated as the difference between the maximum and minimum QTc. After a mean follow-up of 3.7±0.9 years, there were 188 deaths from all causes, including 55 cardiovascular deaths. In univariate Cox analyses, prolonged QTc and increased QTD were significant predictors of all-cause mortality (χ 2 =53.0, P <0.0001; χ 2 =11.3, P =0.0008) and cardiovascular mortality (χ 2 =14.7, P =0.0001; χ 2 =26.5, P <0.0001). In multivariate Cox regression analyses controlling for risk factors, QTc remained a strong predictor of all-cause mortality (χ 2 =16.5, P <0.0001) and a weaker predictor of cardiovascular mortality (χ 2 =5.8, P =0.016); QTD remained a significant predictor of cardiovascular mortality only (χ 2 =12.5, P =0.0004). Conclusions —These findings support the value of computerized measurements of QTc and QTD in noninvasive risk stratification and suggest that these surface ECG variables may reflect different underlying abnormalities of ventricular repolarization.