In patients with idiopathic pulmonary fibrosis (IPF), our objectives were to identify
predictors of abnormal heart rate recovery (HRR) at 1 min after completion of a 6-min
walk test (6MWT) [HRR1] and 2 min after completion of a 6MWT (HRR2), and to determine
whether abnormal HRR predicts mortality.
From 2003 to 2008, we identified IPF patients who had been evaluated at our center
(n = 76) with a pulmonary physiologic examination and the 6MWT. We used logistic regression
to identify predictors of abnormal HRR, the product-limit method to compare survival
in the sample stratified on HRR, and Cox proportional hazards analysis to estimate
the prognostic capability of abnormal HRR.
Cutoff values were 13 beats for abnormal HRR1 and 22 beats for HRR2. In a multivariable
model, predictors of abnormal HRR1 were diffusing capacity of the lung for carbon
monoxide (odds ratio [OR], 0.4 per 10% predicted; 95% confidence interval [CI], 0.2
to 0.7; p = 0.003), change in heart rate from baseline to maximum (OR, 0.9; 95% CI,
0.8 to 0.97; p = 0.01), and having a right ventricular systolic pressure > 35 mm Hg
as determined by transthoracic echocardiogram (OR, 12.7; 95% CI, 2.0 to 79.7; p =
0.01). Subjects with an abnormal HRR had significantly worse survival than subjects
with a normal HRR (for HRR1, p = 0.0007 [log-rank test]; for HRR2, p = 0.03 [log-rank
test]); these results held for the subgroup of 30 subjects without resting pulmonary
hypertension (HRR1, p = 0.04 [log-rank test]). Among several candidate variables,
abnormal HRR1 appeared to be the most potent predictor of mortality (hazard ratio,
5.2; 95% CI, 1.8 to 15.2; p = 0.004).
Abnormal HRR after 6MWT predicts mortality in IPF patients. Research is needed to
confirm these findings prospectively and to examine the mechanisms of HRR in IPF patients.