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

Objective: Although an elevated resting heart rate is linked to higher mortality, the pathways underlying this relationship are not fully defined. One candidate mechanism is subclinical myocardial injury (SCMI), an asymptomatic form of cardiac damage indexed by a Cardiac Infarction/Injury Score (CIIS) of at least 10, which has prognostic value for adverse cardiovascular (CV) outcomes. Methods: We analyzed 7152 participants from NHANES III who underwent electrocardiogram (ECG) recording and were free of CV disease. Heart rate was categorized as bradycardia (≤50 bpm), normal (>50-<100 bpm), or tachycardia (≥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. Results: SCMI was present in 1744 (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, 2311 (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. Conclusions: These findings suggest that SCMI modestly attenuates the heart rate-mortality association, suggesting that silent myocardial damage may represent one potential intermediary pathway.