Neal S. Parikh, MD
In this issue of Stroke, Amber Fyfe-Johnson and colleagues describe their investigation of the association between heart rate variability (HRV) and incident stroke risk in the Atherosclerosis Risk in Communities (ARIC) Study cohort.
They argue that autonomic nervous system (ANS) dysfunction, as reflected by HRV, may be associated with cardiovascular mortality, coronary heart disease, and mortality in stroke survivors. ANS dysfunction may be associated with dysregulated cerebrovascular autoregulation and blood pressure.
ARIC participants were assessed by EKG for HRV by four measures at visit 1 (1987-1989) and followed through December 31, 2011 for incident stroke by telephone ascertainment, hospital discharge diagnosis review, and state death registry review. Covariates, collected at the index visit and again at visit 4 (1996-1998), included: age, sex, race, smoking/alcohol use, physical activity, body mass index, blood pressure, blood lipids, and diabetes. Patients taking medications that modify HRV (beta-blockers, anti-arrythmics, calcium channel blockers, digoxin) and those with prevalent stroke, coronary disease, or heart failure were excluded.
Cox proportional hazards models were used to calculate hazard ratios for the relationship between each quintile of HRV measures and stroke.
Of 12,550 ARIC participants, 816 (6.5%) had stroke. Crude cumulative stroke incidence was higher in patients with the lowest HRV quintile (compared to the highest quintile). However, after adjustment for covariates, associations between HRV and stroke risk were attenuated and did not meet statistical significance. In analyses restricted to participants with diabetes, stroke risk was higher in the lowest HRV quintile, but this association was only statistically significant when testing one of four HRV measures (HR 2.0, 95% confidence interval, 1.1-4.0).
The authors conclude that there may be an association between low HRV and incident stroke in populations already at risk – patients with diabetes. Whether this association would withstand adjustment for an expanded list of cardiovascular risk factors in a modern cohort is unclear. However, the importance of identifying simple indicators of stroke risk such as HRV cannot be overstated.