Chronic thromboembolic pulmonary hypertension (CTEPH) is an elevation in pulmonary vascular resistance (PVR) resulting from chronic, “scarred-in” thromboembolic material partially occluding the pulmonary arteries. This vascular obstruction, over time, results in failure of the right ventricle and early mortality.
CTEPH was first characterized in an autopsy series from the Massachusetts General Hospital in 1931. On these postmortem examinations, it was noted that the affected patients had large pulmonary artery vascular obstruction, but also normal pulmonary parenchyma distal to this vascular obstruction and extensive bronchial collateral blood flow (Means J. Ann Intern Med. 1931;5:417). Although this observation set the groundwork for the theory that surgically removing the vascular obstruction to this preserved lung tissue could improve the condition of these patients, it would take until the mid-20th century until imaging and cardiac catheterization techniques allowed the recognition of the disease in real time.
CTEPH is thought to begin with an acute pulmonary embolus, but in approximately 3.4% of patients, rather than resolving over time, the thrombus will organize and incorporate into the pulmonary artery intimal layer (Simonneau G, et al. Eur Respir Rev. 2017;26:160112) A history of venous thromboembolism in a patient with persistent dyspnea should spur a screening evaluation for CTEPH; 75% of patients with CTEPH have a history of prior known acute pulmonary embolus and 56% of patients report a prior diagnosis of deep venous thrombosis. An acute pulmonary embolus will fibrinolyse early with the vast majority of the vascular obstruction resolving by the third month. Therefore, if the patient continues to report a significant exercise limitation after 3 months of therapeutic anticoagulation therapy, or has concerning physical exam signs, a workup should be pursued. The initial evaluation for CTEPH begins with a transthoracic echocardiogram (TTE) and ventilation/perfusion (V/Q) scintigraphy. A retrospective study comparing V/Q scan and multidetector CT scan revealed that V/Q scanning had a sensitivity and specificity of 97% and 95% for CTEPH, while CTPA had good specificity at 99% but only 51% sensitivity (Tunariu N, et al. J Nuc Med. 2007;48(5):680). If these are abnormal, then right-sided heart catheterization and invasive biplane digital subtraction pulmonary angiography are recommended. These studies confirm the diagnosis, grade its severity, and allow an evaluation for surgically accessible vs distal disease. Some CTEPH centers utilize additional imaging techniques, such as magnetic resonance angiography, optical resonance imaging, spectral CT scanning with iodine perfusion images, and intravascular ultrasound. These modalities and their place in the diagnostic algorithm are under investigation.
The goal of the initial evaluation process is to determine if the patient can undergo surgical pulmonary thromboendarterectomy (PTE), because in experienced hands, this procedure ensures the best long-term outcome for the patient. The first pulmonary thromboendarterectomy was performed at the University of California San Diego in 1970. Because the disease involves the intimal layer of the pulmonary artery, the surgery had to involve not just removal of the intravascular obstruction but also a pulmonary artery intimectomy. Surgical mortality rates were high in the initial experience. In 1984, a review of 85 worldwide cases reported an average mortality rate of 22%, and as high as 40% in some centers (Chitwood WR, Jr, et al. Clin Chest Med. 1984;5(3):507).