The influence of cardiac resynchronization therapy on subjective and objective parameters of sleep, and their association with the function of the autonomous nervous system

Introduction
Cardiac resynchronization therapy (CRT) was a breakthrough in the treatment of heart failure, but data regarding the effect of this therapy on numerous disorders associated with heart failure are limited.

Aim
To assess the impact of CRT on sleep breathing disorders, and to determine the relationship between the changes in the autonomous nervous system and sleep disorders after CRT.

Material and methods
The study included 55 patients with chronic heart failure stable for at least last 3 months, in New York Heart Association (NYHA) class III or IV despite optimal medical therapy, with a reduced left ventricular ejection fraction (LVEF) ≤ 35%, QRS complex duration ≥ 120 ms, and sinus rhythm. Before and 3 months after implementation of CRT echocardiography, 6-minute walk test (6MWT), polysomnography with the Pittsburgh Sleep Quality Index (PSQI) questionnaire and the Epworth Sleepiness Scale (ESS) were performed. Also baroreflex sensitivity (BRS) was evaluated.

Results
After implementation of CRT, the values of the apnea-hypopnea index (AHI), apnea index (AI), and central and mixed apnea indexes (CAI, MAI) were statistically significantly reduced. The strongest negative correlations were demonstrated for changes in CAI and changes in BRS. An improvement in sleep quality, daytime sleepiness, LVEF, NYHA class, and 6MWT was observed and was the most strongly associated with the improvement in CAI, too.

Conclusions
CRT has a beneficial effect on subjective and objective features of sleep, as well as on the function of the autonomous nervous system. In addition, patients with heart failure and coexisting central sleep apnea may benefit most from this therapy.