Clinical correlates and prognostic significance of the ventilatory response to exercise in chronic heart failure

Objectives. This study sought to investigate the clinical characteristics of patients with chronic heart failure and an increased ventilatory response to exercise and to examine the prognostic usefulness of this response. Background. The ventilatory response to exercise is increased in many patients with chronic heart failure and may be characterized by the regression slope relating minute ventilation to carbon dioxide output ((V) over dot E-(V) over dot CO2 slope) during exercise. Methods. One hundred seventy-three consecutive patients (155 men; mean [+/-SD] age 59.8 +/- 11.5 years; radionuclide left ventricular ejection fraction [LVEF] 28.4 +/- 14.6%) underwent cardiopulmonary exercise testing (peak oxygen consumption 18.5 +/- 7.3 ml/kg per min; (V) over dot E-(V) over dot CO2 slope 34.8 +/- 10.6) over a 2-year period. Using 1.96 standard deviations above the mean (V) over dot E-(V) over dot CO2 slope of 68 healthy age-matched subjects (mean slope 26.3 +/- 4.1), we defined a high ventilatory response to exercise as a slope >34, Results. Eighty-three patients (48%) had an increased (V) over dot E-(V) over dot CO2 slope (mean 43.1 +/- 8.9). There was a difference in age (62.2 vs. 57.3 years, p = 0.005), New York Heart Association functional class (2.9 vs, 2.1, p < 0.001), LVEF (24.7 vs. 31.9%, p = 0.0016), peak oxygen consumption (14.9 vs. 21.7 ml/kg per min, p < 0.0001) and radiographic cardiothoracic ratio (0.58 vs. 0.55, p = 0.002) between these patients and those with a normal slope. In the univariate Cox proportional hazards model, the (V) over dot E-(V) over dot CO2 slope was an important prognostic factor (p < 0.0001). In the multivariate Cox analyses using several variables (age, peak oxygen consumption, (V) over dot E-(V) over dot CO2 slope and LVEF), the (V) over dot E-(V) over dot CO2 slope gave additional prognostic information (p = 0.018) beyond peak oxygen consumption (p = 0.022). Kaplan-Meier survival curves at 18 months demonstrated a survival rate of 95% in patients with a normal (V) over dot E-(V) over dot CO2 slope compared with 69% in those with a high slope (p < 0.0001). Conclusions. A high (V) over dot E-(V) over dot CO2 slope selects patients with more severe heart failure and is an independent prognostic marker. The (V) over dot E-(V) over dot CO2 slope may be used as a supplementary index in the assessment of patients with chronic heart failure. (C) 1997 by the American College of Cardiology.