Introduction: The P-wave, T-wave and QRS electrical axes are routinely reported measures on the printouts of most contemporary electrocardiograms (ECG). We sought to investigate the prognostic value of these ECG axes as predictors of mortality in the 14-year follow-up of the Bambuí cohort, a population with high prevalence of Chagas disease (ChD).
Methods: The Bambuí Study of Aging is a prospective cohort of all residents ≥60 years at study onset (1997), living in the southeastern Brazilian city of Bambuí (15,000 inhabitants). ECG axes at baseline were classified according to reference values. Participants undergo annual follow-up visits, and death certificates are tracked. Multivariable regression was performed to access the prognostic value of ECG axes for all-cause mortality, after adjustment for confounders
Results: From 1,742 qualifying city residents, 1,606 were enrolled. Mean age was 69.0±7.2 years, 39.1% were males and 557 (37.5 %) had diagnosis of ChD. Loss to follow up was 7.9% and mortality was 51.9%. Participants with and without ChD were demographically and clinically similar except that the ChD group had higher baseline B-type natriuretic peptide (BNP) levels (119 (63-206) vs. 64 (35-112) pg/dl, p<0.001). An abnormal P-wave axis was associated with a 48% (HR=1.48 (95% CI 1.16 - 1.88)) increased mortality risk in patients with ChD and 45% (HR=1.45 (CI 1.15 - 1.83)) in those without ChD after adjustments. Abnormal QRS axis was associated with a 34% (HR=1.34 (CI 1.04 - 1.73)) increased mortality risk in those with ChD, but no increased risk for those without ChD. Similarly, in the ChD group abnormal T-wave axis was associated with a 35% (HR=1.35 (CI 1.07 - 1.71)) increased mortality in the final model, but for those without ChD the variable lost significance when adjusted for BNP (HR=1.21 (CI 0.97 - 1.51)). Abnormal P-wave axis was the only ECG predictor of mortality in the total study population (HR=1.47 (CI 1.25 - 1.74).
Conclusion: In a cohort of elderly patients, abnormalities of the QRS axis and T-wave axis are associated with increased all-cause mortality in patients with ChD, and abnormal P-wave axis was the strongest predictor of mortality among the ECG-axis variables in the total study population, even after adjustment for potential confounders.