In patients with advanced systolic heart failure, the ability of cardiac resynchronization therapy (CRT) to lessen the severity of central sleep apnea (CSA) might result from decreased mitral regurgitation, according to a report by Czech and US researchers published in the July issue of Chest.
CSA is common among patients with stable systolic heart failure, and earlier research had shown that CSA is an independent risk factor for death in such patients, the authors note. Further, therapies typically used to treat obstructive sleep apnea do not improve long-term survival in patients with systolic heart failure.
"Our study brings new insight into the pathophysiology of central sleep apnea," Dr. Tomas Kara, of the Mayo Clinic and St. Anne's University Hospital, Brno, Czech Republic, told Reuters Health. Data from the study, he explained, suggest that by reducing mitral regurgitation, CRT may decrease the returned blood volume into the lungs and improve pulmonary circulation.
For the study, 12 patients with drug-resistant systolic heart failure, and who had already had atrial-synchronized biventricular pacemakers implanted, each spent four nights in a sleep laboratory.
The first night (night zero) was solely for familiarization with the environment. On nights one through three, patients underwent polysomnography, with the CRT in its normal mode for the first and last nights, and with the CRT function turned off for a 24-hour period that included night two. For that period, a backup right ventricular pacing rate programmed to 40 beats/min was used.
The total number of apneas (central or obstructive) or hypopneas per hour of sleep was significantly greater (p = 0.04) on night two (16.7 events per hour) than on nights one and three (13.4 and 12.1 events per hour).
Echocardiography, obtained prior to sleep on the three polysomnogram nights, showed that eight patients had mitral regurgitation, and the mitral regurgitant volume was significantly higher (p = 0.003) without than with CRT.
The mitral regurgitant volume correlated significantly with the central sleep apnea index, the investigators found.
"Mitral regurgitation is an often-underestimated phenomenon in patients who are indicated to CRT implantation," Dr. Kara commented. "Setting of stimulation in a way that leads to mitral regurgitation decrease may positively affect overall therapeutic effects of CRT and subsequently improve both clinical and economic outcomes."
Chest 2008;134:87-93
