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He was treated for blood clots but still felt fatigued and breathless - The Washington Post

Porter’s history of blood clots for no apparent reason, his continued shortness of breath and chest pain, along with the results of the VQ scan and other tests strongly suggested one diagnosis: chronic thromboembolic pulmonary hypertension (CTEPH). This rare form of pulmonary hypertension is caused by clots that clog arteries, forming scar tissue that adheres to blood vessels in the lungs, narrowing the vessels and impeding blood flow. Experts estimate that between 2 and 5 percent of people with blood clots will develop CTEPH, which doesn’t respond to blood thinners. But unlike other forms of pulmonary hypertension, CTEPH can be cured by a pulmonary thromboendarterectomy (PTE), a long, complex and demanding operation to remove clots. Nonsurgical treatment involves medication, but is not curative.