Prognostic value of alveolar volume in systolic heart failure: a prospective observational study

Background: Ventilatory impairment is known to occur in patients with heart failure (HF). Alveolar volume (VA) is measured by the dilution of an inert gas during a single breath-hold maneuver. Such measurement is sensitive to ventilatory disturbances. We conducted a prospective, observational study to establish the prognostic value of VA in systolic HF. Methods: We studied 260 consecutive patients who were hospitalized for systolic HF. All patients were evaluated under stable clinical conditions, before hospital discharge. Lung function studies included spirometry and determination of the lung diffusing capacity for carbon monoxide (DLCO) by the single-breath method. We also measured the cardiothoracic ratio on frontal chest radiographs, and the circulating levels of N-terminal pro-hormone of B-type natriuretic peptide (NT-proBNP). The hazard ratio (HR) of death was estimated with Cox regression, and the percentiles of survival time with Laplace regression. For survival analysis, VA was categorized as <80% (n = 135), or >=80% of the predicted value (n = 125). Results: Follow-up had a median duration of 2.7 years (interquartile range, 1.1 to 4.2 years). The crude mortality rate was 27% in the whole sample, 36% in patients with VA < 80%, and 16% in those with VA >= 80%. The HR of death was 2.3-fold higher in patients with VA <80% than in those with VA >=80% (p = 0.002). After adjusting for age, New York Heart Association class III-IV, cardiothoracic ratio >0.5, NT-proBNP, persistent atrial fibrillation, DLCO, COPD comorbidity, use of beta-blockers and angiotensin converting enzyme inhibitors, the HR decreased to 1.9 but remained statistically significant (p = 0.039). Two percent of the patients with VA < 80% died about 0.9 years earlier than those with VA >=80% (p = 0.033). The difference in survival time at the 20th percentile was 0.8 years. Conclusions: VA is a significant, independent predictor of reduced survival in patients with systolic HF.