Association Between Thrombus Histopathology and Hemodynamic Outcomes Among Patients With Chronic Thromboembolic Pulmonary Hypertension Undergoing Pulmonary Endarterectomy.

Background: Pulmonary endarterectomy (PEA) is the treatment of choice for chronic thromboembolic pulmonary hypertension (CTEPH). Although most have normalization of pulmonary artery (PA) pressures, development of residual pulmonary hypertension (RPH) is challenging to predict.

Research question: Among patients with CTEPH undergoing PEA, is there a relationship between specimen histopathology and postoperative hemodynamics?

Study design and methods: In this single-center retrospective cohort study, patients with CTEPH who underwent PEA were classified by thrombus chronicity: organized (chronic), organizing (subacute), or mixed (combined organizing and organized). Change in mean PA pressure, pulmonary vascular resistance (PVR), and transpulmonary gradient (TPG) were examined by thrombus organization. Associations with RPH were assessed with multivariable logistic regression.

Results: A total of 163 patients were identified: 34% had organized thrombi, 17% had organizing thrombi, and 49% had mixed thrombi. Pre-PEA mean TPG and PVR were highest in the mixed group (TPG: 37 mm Hg [29-42]; PVR: 8.7 Wood units [interquartile range (IQR), 5.6-11.2]) compared with the organized (TPG: 30 mm Hg [24-38]; PVR: 6.2 Wood units [IQR, 4.2-8.8]) and organizing (TPG: 24 mm Hg [19-37]; PVR: 4.2 Wood units [IQR, 3.5-9.2]) groups (TPG: P = .05; PVR: P = .01). The adjusted change in mean PA pressure among the mixed group was -19.8 mm Hg (-21.7 to -17.8), significantly greater than -16.2 mm Hg (-18.4 to -14.1) in the organized group and -14.1 mm Hg (-17.3 to -10.9) in the organizing group (P = .004). Fifty-two patients (32%) had RPH. Mixed thrombus organization was associated with lower odds of RPH (OR, 0.35; 95% CI, 0.14-0.85; P = .02), whereas preoperative mean PA pressure (OR, 1.10; 95% CI, 1.06-1.16; P < .001) and age (OR, 1.04; 95% CI, 1.01-1.07; P = .02) were associated with higher odds of RPH.

Interpretation: Patients with mixed thrombi were less likely to have RPH, suggesting there may be an optimum time to perform PEA after the clot has mostly organized, but prior to development of irreversible small vessel disease.