14 June 2010 - Increased heart rate (HR) variability during sleep, measured using 24-hour ambulatory blood pressure monitoring (ABPM), increases the risk for incident cardiovascular disease (CVD) in Type 2 (T2) diabetics, report researchers in the journal Hypertension Research. "There is an increasing body of evidence that ambulatory BP is a better predictor of future CVD than clinic BP in hypertensive patients," write Kazuo Eguchi, MD (Jichi Medical University, Tochigi, Japan) and colleagues.
As both hypertension and T2 diabetes increase CVD risk, the researchers tested the efficacy of 24-hour ABPM for predicting incident CVD (stroke, fatal or nonfatal myocardial infarction [MI], or sudden cardiac death) in a group of 200 T2 diabetics, both with and without hypertension, and a group of 257 hypertensive individuals without diabetes. The mean age of both groups was 66.9 years.
All the participants underwent 24-hour ABPM at baseline. They were then followed up for 67 months for incident CVD. The researchers measured the standard deviation (SD) of HR, the root-mean-square of successive differences (RMSSD) of HR, and assessed systolic blood pressure (SBP)-HR relationships evaluated by slope and coefficients of correlation between SBP and HR.
In total, there were 34 CVD events during follow-up. HR variability while awake was reduced in diabetics compared with non-diabetics, whereas variability while asleep was similar between the two groups. Multivariate analysis showed that increased SD of sleep HR, RMSSD of sleep HR, slope of SBP-HR, and correlation coefficient of SBP-HR in diabetics increased the risk for incident CVD 1.29-, 1.28-, 5.67-, and 8.04-fold, respectively.
No significant associations between heart rate variability and incident CVD were seen in the non-diabetics with hypertension.
"These results suggest that the evaluation of HR variability can be an additional risk marker of CVD, probably reflecting the early signs of diabetic and non-diabetic cardiac autonomic neuropathy," conclude the authors.