Heart Rate, Electrocardiographic Subclinical Myocardial Injury, and Long-Term Mortality

BackgroundElevated resting heart rate is associated with increased mortality, but the underlying mechanisms remain incompletely understood. Subclinical myocardial injury (SCMI), defined by a Cardiac Infarction/Injury Score (CIIS) [&ge;]10, represents silent cardiac damage that predicts poor cardiovascular (CV) outcomes and may partially explain this association. MethodsWe analyzed 7,152 participants from NHANES III who underwent ECG recording and were free of cardiovascular disease. Heart rate was categorized as bradycardia ([&le;]50 bpm), normal (>50-<100 bpm), or tachycardia ([&ge;]100 bpm). Mortality was assessed through National Death Index linkage. Logistic and Cox regression models evaluated associations with SCMI and mortality, respectively, and attenuation was assessed by change in hazard ratios after adjusting for SCMI. ResultsSCMI was present in 1,744 (24.3%) participants. Tachycardia was associated with increased odds of SCMI (adjusted OR 2.34, 95% CI 1.42-3.88). Over 13.9 years median follow-up, 2,311 (32.3%) died from all causes and 933 (13.1%) from CV causes. Tachycardia was associated with increased all-cause mortality (HR 3.58, 95% CI 2.63-4.88) and CV mortality (HR 2.05, 95% CI 1.06-3.79). Adjustment for SCMI attenuated the tachycardia-CV mortality association by 8.6% and all-cause mortality by 5%. Bradycardia was not associated with SCMI or mortality. ConclusionThese findings suggest that SCMI partially mediates the heart rate-mortality relationship and that ECG-based assessment of SCMI may enhance risk stratification in individuals with elevated resting heart rate.