Heart rate recovery at one minute after a six-minute walking distance (6MWD) test is highly predictive of clinical worsening and time to clinical worsening in patients with idiopathic pulmonary arterial hypertension (IPAH), according to a new study.
"Ours is the first study to show that heart rate recovery at one minute of rest (HRR1) following a 6MW test is a strong predictor of clinical worsening in IPAH patients," said Omar A. Minai, MD, staff physician in the Department of Pulmonary, Allergy, and Critical Care Medicine at the Cleveland Clinic. "Predicting long-term prognosis in these patients usually requires analysis of several pieces of data in complicated risk scores. This easily measured, cost-free biomarker may ultimately advance patient care in view of its ability to accurately predict clinical worsening even in patients receiving treatment for pulmonary hypertension."
The findings were published online ahead of print publication in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.
The study enrolled 75 patients with a diagnosis of IPAH, confirmed by right heart catheterization. Heart rate was recorded at the end of the 6MW test and then one minute after completing the test. Clinical worsening was defined as any of the end points of death, lung transplantation, hospitalization for worsening PH, or escalation of PH therapy. The cutoff value for abnormal HRR at one minute following the 6MW test was identified as 16 beats. A greater reduction in heart rate after exercise indicates a better-conditioned heart.
"Patients with HRR1 <16 were significantly more likely to have clinical worsening events and also had significantly shorter time to clinical worsening (6.7 months versus 13 months) than those patients with HRR1≥16," according to Dr. Minai. "The odds of clinical worsening were significantly greater among patients with HRR1 <16 at all time points during follow-up."
HRR1<16 was a better predictor of clinical worsening than 6MWD alone, and when added to 6MWD improved the ability of 6MWD to predict time to clinical worsening. "HRR1<16 was also associated with known predictors of poor prognosis in IPAH," Dr. Minai added. "Patients with HRR1<16 were more likely to need supplemental oxygen during the 6MW test, be in World Health Organization functional class 4, and have more severe right ventricular dysfunction and pericardial effusion."
The study had some limitations, including its retrospective design. In addition, the time lag between right heart catheterization and the 6MW test may have biased the results, because treatment may have altered baseline hemodynamic parameters.
"HRR1 is highly predictive of clinical worsening and time to clinical worsening in patients with IPAH," concludes Dr. Minai, "and is highly correlated with known indicators of poor prognosis in these patients. Clinical worsening and time to clinical worsening have been used as end-points in a number of clinical trials in patients with IPAH. The strong predictive ability of HRR1 in these patients could make it a valuable new tool for measuring treatment response. Further study in larger prospective studies will better define its role in both IPAH and other forms of PAH."