Cardiac MR measures right ventricular benefits of sleep apnea treatment

February 19, 2009

Cardiac MR can demonstrate the effects of airway pressure therapy in the hearts of patients with obstructive sleep apnea. In the first study of its kind, researchers at Ohio State University Medical Center found that it could document therapeutic benefits on structure and function to the heart’s right side.

Cardiac MR can demonstrate the effects of airway pressure therapy in the hearts of patients with obstructive sleep apnea. In the first study of its kind, researchers at Ohio State University Medical Center found that it could document therapeutic benefits on structure and function to the heart's right side.

About 18 million people in the U.S. have obstructive sleep apnea or similar sleep breathing disorders. Intermittent hypoxia produced by the condition has been linked with an elevated risk of myocardial infarction and sudden cardiac death. Patients are usually prescribed a continuous positive airway pressure (CPAP) therapy device.

Studies have shown that CPAP effectively reduces high blood pressure and other cardiovascular risk factors, but results have been mixed. At least two large international randomized trials are under way to determine if CPAP can reduce the risk of heart attack, stroke, or heart failure.

Most data on CPAP therapeutic effects on the heart address left ventricular function and volume. Little research exists on its effects on the heart's right side, however, mostly because of limitations with standard imaging modalities that are overcome with cardiac MRI, according to the recent study's principal investigator Dr. Ulysses Magalang, medical director of Ohio State's Sleep Disorders Center.

"Previous studies have employed methodologies, such as echocardiography, that are not very good in visualizing the right side of the heart, particularly in patients who are overweight," Magalang said in an interview with Diagnostic Imaging. "Of course, we also studied the left side because you can measure it, but we are more particularly interested in the right side of the heart."

Magalang and colleagues prospectively enrolled 15 patients with severe, untreated obstructive sleep apnea without comorbidities. Patients underwent 3D CMR imaging, including measurement of biventricular size and function and rest/stress myocardial perfusion at baseline and after three months of CPAP therapy. The investigators found evidence of right ventricular structural and functional improvements after CPAP therapy. Their study was published online in February in the Journal of Clinical Sleep Medicine.

Researchers found a significant decrease in the Epworth Sleepiness Scale score (p<0.0001) and significant decreases in right ventricular end-systolic and end-diastolic volumes (p<0.05) with CPAP. RV ejection fraction improvements were noted but did not reach statistical significance. CMR also measured left ventricular volume and ejection fraction, myocardial perfusion, interventricular septum thickness, and ventricular free wall. None changed significantly.

Study findings are noteworthy because subjects had no known coronary artery disease or diabetes and were relatively asymptomatic from the heart failure standpoint. In other words, patients with obstructive sleep apnea are likely to get cardiac health benefits from CPAP treatment, Magalang said.

"It's better to treat them because even if they are not symptomatic, they may already have changes in their right heart volume," he said.

The study's limitations include limited population size and selection bias. Researchers do not advocate performing CMR on a clinical basis until further studies validate these findings. CMR should be considered as only a research tool at this point since its clinical role has not yet been established. It may, however, offer a better management tool in patients with obstructive sleep apnea who have comorbid conditions, Magalang said.

"I would not advocate that patients on CPAP for obstructive sleep apnea be monitored with cardiac MRI," said Dr. James London, director of cardiac MR at the Heart & Vascular Institute of Morristown, NJ.

London agreed this study is strictly investigational and that it was too small to be considered conclusive. Findings suggesting that patients using CPAP may have positive right ventricular remodeling and that CMR can show statistically significant changes are nonetheless interesting even in a small sample size, he said.