About 2% to 6% of Americans have obstructive sleep apnea (OSA), a condition that is largely underdiagnosed but has been associated with multiple cardiovascular diseases (CVDs), including coronary heart disease (CHD) and heart failure (HF). “Although the relationship between OSA and CVD has been well defined,” says Amil M. Shah, MD, MPH, “it has been challenging for clinicians to establish a causal relationship because of the association of OSA with other risk factors.” In clinical research, elevated levels of high sensitivity troponin T (hs-TnT), a marker of myocardial injury, have been predictive of both CHD and HF in the general population. Previous studies have been conflicting as to whether there is a link between OSA severity and troponin levels, particularly after accounting for comorbidities. “The relationship between OSA severity and hs-TnT levels has not been well described in the literature,” says Dr. Shah. “More severe OSA may be associated with subclinical myocardial injury.” Understanding the relationship between OSA and CVD pathway biomarkers may help explain the association between the diseases.
Dr. Shah and colleagues had a study published in the American Journal of Respiratory and Critical Care Medicine to determine if more severe OSA, measured by the respiratory disturbance index, is associated with subclinical myocardial injury and increased myocardial wall stress. Subclinical myocardial injury was indicated by increased hs-TnT levels, while increased myocardial wall stress was indicated by elevated N-terminal pro B-type natriuretic peptide (NT-proBNP) levels. The analysis included 1,645 community-based, middle-aged and older patients who were part of the Atherosclerosis Risk in Communities and the Sleep Health studies. Participants were free of CHD and HF at baseline and underwent overnight home polysomnography. Researchers found that hs-TnT levels—but not NT-proBNP levels—were significantly associated with OSA after adjusting for 17 potential confounders, including factors such as age, gender, BMI, smoking status, hypertension, and diabetes. Participants were followed for a median of 12.4 years. “In all OSA severity categories, hs-TnT was significantly related to the risk of death or incident HF,” Dr. Shah says. “This relationship was strongest for patients who had the most severe OSA.”
According to Dr. Shah, the study is among the first to demonstrate an independent association between OSA severity and hs-TnT levels as a marker of early myocardial injury. “Our findings suggest subclinical myocardial injury may play a role in the relationship between OSA and HF,” he says. “However, further research is needed to identify the role of subclinical ischemia in OSA. In particular, prospective studies are needed to determine the best way to stratify risk in patients with OSA and whether treating OSA can reduce the risk of future cardiac events.”