Cardiac resynchronization therapy improves heart rate profile and heart rate variability of patients with moderate to severe heart failure

OBJECTIVES This study sought to report long-term changes of cardiac autonomic control by continuous, device-based monitoring of the standard deviation of the averages of intrinsic intervals in the 288 five-min segments of a day (SDANN) and of heart rate (HR) profile in heart failure (HF) patients treated with cardiac resynchronization therapy (CRT). BACKGROUND Data on long-term changes of time-domain parameters of heart rate variability (HRV) and of HR in highly symptomatic HF patients treated with CRT are lacking. METHODS Stored data were retrieved for 113 HF patients (New York Heart Association functional class III to TV, left ventricular ejection fraction <= 35%, QRS > 120 ms) receiving a CRT device capable of continuous assessment of HRV and HR profile. RESULTS The CRT induced a reduction of minimum HR (from 63 +/- 9 beats/min to 58 +/- 7 beats/min, p < 0.001) and mean HR (from 76 +/- 10 beats/min to 72 +/- 8 beats/min, p < 0.01) and an increase of SDANN (from 69 +/- 23 ins to 93 +/- 27 ins, p < 0.001) at three-month follow-up, which were consistent with improvement of functional capacity and structural changes. Different kinetics were observed among these parameters. The SDANN reached the plateau before minimum HR, and mean HR was the slowest parameter to change. Suboptimal left ventricular lead position was associated with no significant functional and structural improvement as well as no change or even worsening of HRV. The two-year event-free survival rate was significantly lower (62% vs. 94%, p < 0.005) in patients without any SDANN change (Delta change <= 0%) compared with patients who showed an increase in SDANN (Delta change > 0%) four weeks after CRT initiation. CONCLUSIONS Cardiac resynchronization therapy is able to significantly modi, the sympathetic-parasympathetic interaction to the heart, as defined by HR profile and HRV. Lack of HRV improvement four weeks after CRT identifies patients at higher risk for major cardiovascular events.