10th March 2024

Group 4: Pulmonary vasculature obstruction

This type of pulmonary hypertension is most commonly caused by chronic thromboembolism and is also called chronic thromboembolic pulmonary hypertension (CTEPH). It occurs because of pulmonary artery obstruction and unresolved thromboembolic disease. It is paramount to distinguish this type of pulmonary hypertension from the other groups as it has a different therapeutic management.

This condition may represent the final manifestation of unresolved pulmonary embolism, but it is unclear why some patients with acute PE develop CTEPH, and others do not. Some studies suggest that an underlying hypercoagulable state may be the cause of CTEPH, but not all hypercoagulable abnormalities have been associated with the condition. There are a number of varying theories accounting for the possible pathogenesis of the disease, including one that suggests that pulmonary arteriopathy or in situ thrombosis may be the culprit. This theory is based on the fact that a substantial number of patients do not have a prior history of VTE and that most hypercoagulable states do not confer an increased risk for CTEPH.

The diagnosis of CTEPH is usually delayed due to its nonspecific clinical presentation and the low rate of CTEPH as a complication of VTE. The diagnosis is dependent upon imaging that uses contrast enhancement to identify chronic thromboembolism in the proximal or distal vasculature. Similarly to other groups of pulmonary hypertension, testing includes echocardiography, pulmonary function testing, V/Q scanning, CT pulmonary angiogram, and right heart catheterisation. The initial test of choice in this setting is a V/Q lung scan, as a normal test accurately excludes chronic thromboembolic disease with a sensitivity of 97%. Furthermore, V/Q scanning is useful in differentiating proximal large vessel obstruction from distal small vessel obstruction, as can be seen in group 1 PAH. As V/Q scan is sensitive but not specific (e.g. pulmonary artery stenosis, tumours, fibrosing mediastinitis), most patients will need a CTPA as a complementary study. CT pulmonary angiography is not performed on its own, as a negative CT scan cannot exclude the possibility of CTEPH.

Pulmonary thromboendarterectomy is the only definitive therapy for patients with CTEPH.