Correction of carotid augmentation index for heart rate in elderly essential hypertensives

Carotid augmentation index (AI) is used as a surrogate measure of arterial stiffness. Although arterial stiffness has been shown to either remain unch anged or increase with an increase in heart rate, AI decreases as heart rat e increases. This study aimed to quantify this confounding effect of heart rate on Al. We investigated 873 hypertensives, mean age 72 +/- 5 years, 44% men, mean b rachial blood pressure 161 +/- 21/82 +/- 11 mm Hg. Carotid artery tonometry with simultaneous continuous wave Doppler measurement of ascending aortic blood flow was performed. Al was calculated from the carotid pressure wavef orm. Waveforms were decomposed into their forward and backward components a nd the time to reflection between the maxima of the forward and backward pr essure waves was measured. Al showed a stronger (P < .001) association with ejection time (r = 0.48, P < .001) than with heart rate (r = -0.28, P < .001). Although Al is strongl y related to the time to reflection (r = -0.51, P < .001), only a weak asso ciation was seen between time to reflection and heart rate (r = 0.16, P < . 001) or ejection time (r = -0.12, P < .001), Our analysis in an elderly coh ort of patients with essential hypertension demonstrates that Al is related to the time to reflection. It also reiterates that Al is confounded by hea rt rate without any underlying heart rate-dependent change in wave reflecti on. In population-based studies the confounding effect of heart rate can po tentially be corrected. AI remains strongly (r = -0.52) related to time to reflection after correction for the effects of ejection time on AI. (C) 200 1 American Journal of Hypertension, Ltd.