Low heart rate variability is associated with future arrhythmic events in hypertension

Abstract Background/Introduction Cardiac autonomic dysfunction and target organ damage are associated with increased cardiovascular mortality and arrhythmias. Purpose The aim of the study was to investigate the effect of heart rate variability (HRV) and markers of target organ damage in the prognosis of future arrhythmic events. Methods We studied 292 untreated at baseline hypertensives (mean age 53±13, 153 males). Cardiac autonomic function was evaluated by analysis of short-term HRV measures over 24-h using 24-h ambulatory blood pressure monitoring and the standard deviation of the measurements. Echocardiography was also performed and left ventricular mass index (LVMI) was estimated with the Demereux formula. Aortic stiffness was assessed with carotid-femoral pulse wave velocity (cfPWV) and wave reflections with aortic augmentation index corrected for heart rate (Alx@75). Patients were followed up for a median period of 13 years. The primary endpoint was a composite of atrial/ventricular tachycardias, symptomatic multiple premature ventricular contractions, second and third-degree heart blocks and pacemaker/defibrillator placement. Results In comparison without events, patients with the primary endpoint (n=37, 13%) had lower 24-h daytime HRV (9.6 beats per minute vs. 11.1 beats per minute, p=0.005), higher systolic blood pressure (168 mmHg vs. 163 mmHg, p=0.003), higher cfPWV (8.4 m/s vs. 7.7 m/s, p=0.005), higher LVMI (133 g/m2 vs. 122 g/m2, p=0.002) and higher AIx@75 (29.0% vs. 26.3%, p=0.043). In further analysis, receiver operating characteristic (ROC) curves were generated to evaluate the ability of HRV, cfPWV, LVMI and AIx@75 to discriminate subjects with arrhythmic events. The area under the curve (AUC) and 95% CIs of the ROC curves were AUC=0.35 (95% CI: 0.26–0.44, p=0.003) for HRV, AUC=0.64 (95% CI: 0.54–0.73, P<0.006) for cfPWV, AUC=0.67 (95% CI: 0.58–0.75, P=0.001) for LVMI and AUC=0.55 (95% CI: 0.47–0.64, P=0.298) for AIx@75 (Figure). In Cox regression analysis, only HRV was associated with increased risk of arrhythmic events (Hazard ratio per 1 unit =0.87, 95% Confidence intervals 0.76 to 0.995, p=0.043) when adjusted for age, gender, cfPWV, LVMI and AIx@75. ROC curves of HRV & target organ damage Conclusions Low heart rate variability is associated with increased risk of future arrhythmic events suggesting an early sympathovagal imbalance that could lead to future events in hypertension.