Night heart rate variability identifies cardiovascular risk in community dwelling people with uncomplicated type 2 diabetes mellitus

Abstract

Abstract Introduction Low Heart rate variability (HRV) reflects cardiac autonomic neuropathy, associated with increased cardiovascular mortality in type 2 diabetes (T2DM) patients. Measuring HRV is challenged by environmental noise, mental stress and physical activity during the day-time. Thus, measuring night-time HRV during sleep may be a better tool to predict cardiovascular (CV) events in low risk T2DM patients without previous cardiovascular disease. Methods Copenhagen Holter Study included 678 community dwelling subjects aged 55–75 years free of previous cardiovascular disease. Day- and night-time HRV were available for 653. The population included 133 well-controlled T2DM patients (mean HbA1c 7.2%). Median follow- up was 14.4 years. HRV is defined as standard deviation for the mean value of normal-to-normal complexes (SDNN). Night-time HRV measurements were pre-defined from 2:00 to 2:15 AM. CV events were defined as CV death, myocardial infarction, stroke, or coronary revascularization. Results The rate of CV events was 17 and 31 per 1000 patient-year in patients without and with T2DM, respectively (p=0.015). Night-time SDNN was inversely associated with CV events in T2DM patients with a HR of 0.74 (0.61–0.89), P=0.001, for each 10 ms increment in SDNN, after adjustment for sex, age, LDL, smoking, systolic BP, glucose, CRP and NT pro-BNP (table 1). Twenty-four-hours HRV was not associated with cardiovascular events (table 1). Conventional risk factors had an AUC of 0.704 (95% CI 0.602–0.806) to predict CV events in T2DM. Prediction was improved by the addition of night-time SDNN; AUC 0.765 (95% CI 0.669–0.862), P=0.037, but not by CRP or NT-proBNP (Figure 1). In subjects with well-controlled T2DM and night-time SDNN ≤30 ms, the 10-year risk of CV death and CV even-rate were 12% and 45%, respectively. This allocates these T2DM patients in a “very high-risk” group, and more aggressive targets for blood-pressure and lipids according to the current guidelines. Conclusion Reduced night-time HRV associates with increased risk of CV events in persons with well-controlled T2DM. We observed improved risk prediction of cardiovascular events in T2DM by night-time HRV, which may have therapeutic consequences. Figure 1. ROC Curve Funding Acknowledgement Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): Danish Heart Foundation