Introduction: Heart rate turbulence is a powerful de novo risk predictor for patients surviving acute myocardial infarction. However, little is known about its underlying physiologic mechanism. Methods and Results: Hypothesizing that heart rate turbulence is barorceptor reflex related, we studied heart rate and blood pressure fluctuations at rest and after systematically introduced ventricular premature beats in 16 patients without structural heart disease (10 men and 6 women; mean age 45 ± 17 years) before and after sequential sympathetic (esmolol 4-mg bolus followed by 120 μg/kg/min intravenously), parasympathetic (atropine 0.04 mg/kg intravenously), and combined autonomic blockade (esmolol plus atropine). Turbulence onset (%) and turbulence slope (msec/beat) were averaged from 10 respective ventricular premature beats. Spontaneous baroreflex sensitivity (msec/mmHg) was calculated from 5 minutes of sinus rhythm recording. The results showed that turbulence slope decreased after atropine (0.71 ± 0.50 msec/beat vs 5.17 ± 3.96 msec/beat at baseline; P < 0.01) and combined autonomic blockade (1.23 ± 1.02 msec/beat; P < 0.01) but was unchanged after esmolol (4.53 ± 3.30 msec/beat; P > 0.05). Turbulence onset increased after atropine (0.32% ± 0.35% vs -0.45 ± 0.94 at baseline; P < 0.05) and combined sympathetic and parasympathetic blockade (0.58% ± 0.86%; P < 0.05) but was unchanged after esmolol (-0.62% ± 1.33%; P > 0.05). Turbulence slope was positively correlated with baroreflex sensitivity at baseline (r = 0.78, P < 0.01) and after esmolol (r = 0.8, P < 0.01), but dissociated after atropine (r = 0.16, P > 0.05) and combined autonomic blockade (r = 0.31, P > 0.05). Turbulence onset was negatively correlated with baroreflex sensitivity at baseline (r = -0.61, P < 0.05), after esmolol (r = -0.80, P < 0.01), and after atropine (r = -0.53, P < 0.05). Conclusion: Heart rate turbulence of turbulence onset and turbulence slope is critically vagal dependent and highly correlated with spontaneous baroreflex sensitivity, which underscores its clinical importance in cardiovascular risk stratification.
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