Ethnic differences in heart rate: can these be explained by conventional cardiovascular risk factors?

Objectives: South Asians worldwide have an elevated risk of coronary heart disease (CHD), only partly explicable by a higher prevalence of diabetes. Diabetes and dysglycaemia are associated with increased heart rates and abnormal cardiac sympathovagal balance, and are predictive of increased coronary mortality. This study investigated ethnic differences in heart rate, sympathovagal balance, and baroreflex sensitivity (BRS) to establish if they were explained by dysglycaemia/insulin resistance.

Methods: 84 South Asian and 83 European men (age 45-85 yrs), half with established CHD and half without proven CHD, underwent metabolic profiling and assessment of mean RR interval, heart rate variablility (HRV) and BRS.

Results: Mean resting RR interval was greater in Europeans than South Asians (1014 (149) ms vs. 936 (158) ms respectively, means (SD); P = 0.005). This corresponded to resting heart rates of 59.1 bpm for Europeans and 64.1 bpm for South Asians. No ethnic differences were detected in HRV or BRS. Insulin resistance, assessed by the homeostasis model of assessment of insulin resistance (HOMA-IR), correlated with mean RR interval (beta coefficient = -0.189, P = 0.04) and BRS (beta coefficient = -0.246, P = 0.006) and similar correlations were seen with fasting serum glucose. However, ethnic differences in mean RR interval persisted after adjustment for age, systolic BP, beta blocker use, and HOMA-IR.

Interpretation: South Asian men have higher heart rates compared with European men. This difference was not explained by measures of insulin resistance or other risk factors. This may be indicative of altered sympathovagal balance, and contribute to the greater coronary disease risk in people of South Asian ethnicity.