What is the clinical evidence from this study?

Study design: Cohort. Population: Cardiovascular mortality risk (n=1839). Intervention: Increased PCA ratio (>90th percentile) vs. PCA ratio ≤90th percentile. Primary outcome: Cardiovascular mortality (HR 3.68, 95% CI 1.54-8.83, p=0.043).

February 12, 2002

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

Key Result

An increased PCA ratio of the T-wave loop (>90th percentile) was associated with a 3.68-fold increased risk of cardiovascular mortality in women and a 2.77-fold increased risk in men.

Study Design

Type

Cohort (n=1,839)

Structured PICO

Does principal component analysis of the T-wave vector loop predict cardiovascular mortality better than QT interval dispersion in American Indians?

Population

1,839 American Indian participants in the first Strong Heart Study examination followed for a mean of 3.7 years to assess predictors of cardiovascular mortality.

Exposure

Principal component analysis (PCA) of the T-wave vector loop (PCA ratio)

Comparator

QT interval dispersion (QTd)

Outcome

Cardiovascular (CV) mortalityhard clinical

Abnormalities of repolarization measured by PCA of the T-wave loop predict cardiovascular death in both men and women, outperforming QT dispersion which only predicted risk in women.

Main Result

Hazard Ratio: 3.68 (95% CI 1.54–8.83)

p-value: p=0.043

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 (chi2=7.8, P=0.0053) and men (chi2=9.5, P=0.0021). In contrast, increased QTd was a significant predictor of CV mortality in women (chi2=30.6, P90th 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.