PROGNOSIS OF ARRHYTHMIC EVENTS IN HYPERTENSIVES: WHAT MAKES THE “ELECTRIC CLOCK” TICK?

Objective: Cardiac autonomic dysfunction and target organ damage have been shown to increase the risk of cardiovascular mortality and new onset arrhythmias. This study aimed to investigate the effect of heart rate variability (HRV) and target organ damage markers in the prognosis of arrhythmic events development. Design and method: A total of 292 patients (mean age 53±13 years, n=153, 52,4% males) with untreated hypertension at baseline assessment were analyzed retrospectively. Cardiac autonomic activity was assessed through a 24-h ambulatory blood pressure monitoring system and analysis of short-term 24-h HRV measures and their standard deviations. Left ventricular mass index (LVMI) was calculated using echocardiographic measurements and the Devereux formula. Aortic stiffness was quantified by carotid-femoral pulse wave velocity (cfPWV). The patients were followed-up for a median period of 13 years and were assessed for the primary endpoint of a composite of atrial/ventricular tachycardias, symptomatic multiple premature ventricular contractions, second and third-degree heart blocks, and either pacemaker or defibrillator placement. Results: Compared to those without events, patients who reached the primary endpoint (n=37, 13%) had a significantly reduced 24-hour daytime HRV (9.6 vs. 11.1 beats per minute, p=0.005), higher systolic blood pressure (168 vs. 163 mmHg, p=0.003), greater cfPWV (8.4 vs. 7.7 m/s, p=0.005) and elevated LVMI (133 vs. 122 g/m2, p=0.002). In receiver operating characteristic (ROC) curves analysis the ability of HRV, cfPWV and LVMI to identify subjects with future arrhythmic events was further evaluated. 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), AUC=0.64 (95% CI: 0.54–0.73, P<0.006) and AUC=0.67 (95% CI: 0.58–0.75, P=0.001) for HRV, cfPWV, and LVMI, respectively. In the multivariable Cox regression models, only HRV was significantly associated with an increased risk of arrhythmic outcomes (HR per 1 unit =0.87, 95% CI: 0.76-0.995, p=0.043), after adjusted for age, gender, cfPWV, and LVMI. Conclusions: A lower HRV is independently associated with an elevated risk of future arrhythmic events in hypertensive individuals, indicating an early sympatho-vagal imbalance that could predispose to future cardiovascular complications.