Pulmonary hypertension from chronic pulmonary thromboembolism.

Pulmonary hypertension may develop whenever chronic obstruction of pulmonary arterial blood flow occurs. Although repeated pulmonary embolism is thought to be the usual underlying cause, there is little clinical evidence to support this theory. Studies of the pulmonary vascular endothelium have shown that perturbations of the normal endothelium can create a procoagulant environment, which could lead to the development of thrombosis in situ at the level of the large or smaller pulmonary vessels. Some patients develop proximal pulmonary thromboemboli, which may be the result of retrograde propagation of thrombus after an initial pulmonary embolus. Others present with unexplained pulmonary hypertension secondary to thrombotic occlusion of the pulmonary microvasculature. A perfusion lung scan will show abnormalities that should lead to correct clinical diagnosis and confirmatory evaluation. Thromboendarterectomy in selected cases provides dramatic clinical improvement in patients with proximal thromboemboli. Vasodilators may be effective in some patients with obstruction at the arteriolar level. Both groups should be treated with chronic warfarin anticoagulant therapy to protect against progression of thromboembolism.