A simple exercise test may help predict mortality risk in patients with heart failure and help doctors to better tailor treatment strategies, according to new research from Wake Forest University Baptist Medical Center.
"This may allow doctors to better assess patient risk, and could help them determine the most appropriate plan of care based on the prognosis of the patient," said Dalane Kitzman, M.D., a professor of cardiology and senior researcher on the project.
In the current issue of the Journal of Cardiac Failure, Kitzman and colleagues report on a study involving 147 patients with congestive heart failure, which is the inability of the heart to pump enough blood to keep up with the body's demands. Congestive heart failure affects about 4.8 million Americans, with 550,000 new cases diagnosed each year. The primary symptom is shortness of breath.
The goal of the study was to evaluate a test that measures the lungs' efficiency at consuming oxygen and expiring carbon dioxide. The test has been shown to predict future hospitalizations in patients with systolic heart failure, a type in which the left chamber of the heart is too weakened to pump blood efficiently. The researchers wanted to determine if the test is also appropriate for patients with diastolic heart failure, a more recently recognized form in which the heart muscle is stiff and cannot take in enough blood with each beat.
"Although the prevalence of diastolic heart failure is increasing, we know very little about how to predict which patients are at the highest risk of death," said Kitzman.
Previous studies on predicting mortality have focused on systolic heart failure patients. The current study was the first to compare the pulmonary test in three groups: older adults with diastolic heart failure, older adults with systolic heart failure and healthy volunteers of the same age. The mean age of participants was 70.
"It is important for researchers not only to focus on potential treatments for diastolic heart failure, but to also develop the best method to assess the severity of their condition ," said Brian Moore, M.S., lead author of the study.
For the study, researchers measured pulmonary efficiency by analyzing oxygen consumption and carbon dioxide expiration during an exercise session on a stationary bicycle.
"This is an important measure in heart failure patients because it may help us to understand the cause of some of the symptoms of shortness of breath and exercise intolerance," said Moore. "The test has been previously reported as a good indicator of how serious the disease is in patients with systolic heart failure."
Previous research has shown that a test score of 34 is a threshold for increased risk of death. In the current study, patients with systolic heart failure had a mean score of 37, which suggests an increased risk of mortality. Patients with diastolic heart failure had a mean score of 34, suggesting lower risk. The group of healthy older adults had a mean score of 32.
About 45 percent of study participants with diastolic heart failure had a score greater than 34 compared to 59 percent of participants with systolic heart failure having a score that high.
The results are similar to findings in large population-based studies showing that mortality is considerably lower in diastolic heart failure compared to systolic heart failure. Combined with the new results, this suggests the exercise test can potentially predict mortality in individual patients.
"The study highlights an important physiologic principal of exercise intolerance and identifies a novel marker to assign risk," said Vinay Thohan, M.D., associate professor of cardiology and director of the heart failure service at Wake Forest Baptist. "This measure has been validated in patients with systolic heart failure and this form of testing is routinely performed for all patients who undergo evaluation for heart transplantation at our medical center. "Now, we may be able to use this test for patients with diastolic heart failure as well."
The researchers said future studies should examine whether treatments for heart failure can modify the results and reduce the risk of mortality.