Principal Component Analysis of the T Wave and Prediction of Cardiovascular Mortality in American Indians

Abstract

Background — Increased QT interval dispersion (QTd) is a proposed ECG marker of vulnerability to ventricular arrhythmias and of cardiovascular (CV) mortality. However, principal component analysis (PCA) of the T-wave vector loop may more accurately represent repolarization abnormalities than QTd. Methods and Results — Predictive values of QTd and PCA were assessed in 1839 American Indian participants in the first Strong Heart Study examination. T-wave loop morphology was quantified by the ratio of the second to first eigenvalues of the T-wave vector by PCA (PCA ratio); QTd was quantified as the difference between maximum and minimum QT intervals. After 3.7±0.9 years mean follow-up, there were 55 CV deaths. In univariate analyses, an increased PCA ratio predicted CV mortality in women (χ 2 =7.8, P =0.0053) and men (χ 2 =9.5, P =0.0021). In contrast, increased QTd was a significant predictor of CV mortality in women (χ 2 =30.6, P <0.0001) but not in men (χ 2 =2.0, P =NS). In multivariate Cox analyses controlling for risk factors and rate-corrected QT interval, the PCA ratio remained a significant predictor of CV mortality in women (χ 2 =4.0 P =0.043) and men (χ 2 =6.4, P =0.011); QTd was a significant predictor in women only (χ 2 =11.0, P =0.0009). PCA ratios >90th percentile (32% in women and 24.6% in men) identified women with a 3.68-fold increased risk of CV mortality (95% CI, 1.54 to 8.83) and men with a 2.77-fold increased risk (95% CI, 1.18 to 6.49). Conclusions — Abnormalities of repolarization measured by PCA of the T-wave loop predict CV death in men and women, supporting use of PCA for quantifying repolarization abnormalities.