Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension caused by old blood clots in the lungs (pulmonary embolism). In most patients who have suffered a blood clot, blood thinners are enough to restore blood flow to the lungs, improving breathing and exercise tolerance, and preventing development of pulmonary hypertension.
However, a minority of patients will not respond adequately to blood thinners, and may develop CTEPH. In these patients, problems arise not only from lung segments being obstructed by clots, but because seemingly healthy blood vessels (supplying uninvolved lung segments) may develop progressive narrowing, similar to pulmonary arterial hypertension (PAH).
Importantly, patients may develop CTEPH without any history of a blood clot. It is also possible for CTEPH to develop from multiple small clots over a long period of time, as opposed to one or two large blood clots.