Prognostic and pathophysiological marker for patients with chronic thromboembolic pulmonary hypertension: Usefulness of diffusing capacity for carbon monoxide at diagnosis.

BACKGROUND AND OBJECTIVE: Chronic thromboembolic pulmonary hypertension (CTEPH) is a progressive disease in some patients, despite improved treatments. Microvasculopathy has been implicated in the poor outcomes of patients with CTEPH. A reduction in the diffusing capacity for carbon monoxide (DLCO ) was previously suggested to indicate microvasculopathy in CTEPH patients; therefore, we assessed DLCO /alveolar ventilation (DLCO /VA ) as a prognostic and pathophysiological marker in CTEPH. METHODS: We performed a retrospective cohort study of 214 CTEPH patients consecutively diagnosed between 1986 and 2011. After exclusion of 24 patients because of missing DLCO data or severe obstructive impairment, the mortality rates of medically treated patients classified with normal or decreased DLCO values were compared, and prognostic factors were determined. The relationship between long-term surgical outcomes and DLCO /VA was also investigated. RESULTS: Ninety-one inoperable patients were treated medically, two of whom underwent balloon pulmonary angioplasty. Ninety-nine underwent pulmonary endarterectomy. The 5-year survival rate of medically treated patients was significantly lower in patients with decreased DLCO /VA than in those with normal values (61.4% vs 90.4%, P = 0.017). Decreased preoperative DLCO /VA was associated with a smaller percent decrease in post-operative pulmonary vascular resistance, but not with the extent of proximal thrombi; these results may support our hypothesis that DLCO reflects microvascular involvement. CONCLUSION: Decreased DLCO /VA was associated with poor outcomes of medically treated CTEPH patients; and may be useful for identifying high-risk patients, potentially leading to earlier and more appropriate interventions.