Heart rate recovery one minute after a six-minute walk test predicted clinical worsening and the time to clinical worsening in patients with idiopathic pulmonary arterial hypertension (IPAH), according to a study published online Nov. 17 in the American Journal of Respiratory and Critical Care Medicine.
Omar A. Minai, MD, a staff physician in the department of pulmonary, allergy and critical care medicine at the Cleveland Clinic in Ohio, and colleagues devised the method as an easy, inexpensive alternative to complicated risk scores to predict long-term outcomes for patients with IPAH. Minai and colleagues noted that an abnormal heart rate recovery in the first minute after tests such as the six-minute walk distance (6MWD) has been shown to predict overall mortality in patients with chronic heart failure, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis. They speculated that a similar method could serve as a prognostic test in IPAH.
They enrolled 75 consecutive patients between Aug. 1, 2009, and March 31, 2010, with confirmed IPAH who had no evidence of secondary etiologies of PAH for the study. Each patient underwent a 6MWD test, modified to include heart rate at the end of the test and one minute after completion.
Their goals were to determine in patients with IPAH if heart rate recovery at one minute (HRR1) was predictive of clinical worsening and time to clinical worsening (TCW); to define a cutoff value for abnormal HRR1; and to identify potential predictors of abnormal HRR1.
They defined clinical worsening as death, lung transplantation, hospitalization for worsening PH or escalation of PH therapy. They applied a variety of statistical methods to perform their analyses.
They determined that the cutoff value for HRR1 was less than 16 beats. Patients with an HRR1 of 16 or less were more likely to experience clinical worsening in a shorter time frame compared with patients with an HRR1 of greater than 16, 6.7 months compared with 13 months, respectively. Using c-statistic and logistic regression modeling, Minai and colleagues found that HRR1 of less than 16 was a better predictive tool for clinical worsening than 6MWD alone.
They also showed that HRR1 of 16 or less was correlated with several indicators of poor prognosis of IPAH such as needing supplemental oxygen during the six-minute walk test, being classified as World Health Organization's functional Class IV, having more severe right ventricular dysfunction and pericardial effusion.
“Recent publications have questioned the ability of 6MWD to predict worsening events and survival,” the authors wrote. “Our data showed that the addition of HRR1 increased the ability of 6MWT to predict clinical worsening and TCW. The addition of HRR1 to 6MWD may therefore improve the predictive ability of the 6MW test.”
As limitations, they noted that the study was retrospective. Also, they said a lag between the baseline right heart catheterization confirming the diagnosis of PAH and the 6MWD test may have biased results. While they recommended more studies with a larger patient population, they also emphasized that the method could hold clinical usefulness.
“The strong predictive ability of HRR1 in these patients could make it a valuable new tool for measuring treatment response,” Minai said in a statement. “Further study in larger prospective studies will better define its role in both IPAH and other forms of PAH.”