CTEPH, or chronic thromboembolic pulmonary hypertension, is a condition where old blood clots in the lungs don’t fully dissolve, even after months of blood-thinning treatment. The leftover clot material scars over and hardens inside the pulmonary arteries, blocking blood flow and forcing the right side of the heart to pump harder to push blood through the lungs. Over time, this elevated pressure damages the heart and, without treatment, can lead to right-sided heart failure. CTEPH is classified as Group 4 pulmonary hypertension, and it stands apart from other forms because it can sometimes be cured with surgery.
How CTEPH Develops After a Blood Clot
CTEPH begins with a pulmonary embolism, a blood clot that travels to the lungs. In most people, the body’s natural clot-dissolving processes, aided by blood thinners, clear the clot within weeks to months. In a small percentage of patients, part of the clot remains. Over time, this material transforms from a soft blood clot into a tough, fibrous obstruction made of collagen, elastin, and inflammatory cells. These chronic clots are yellow in color and develop a porous, scar-like structure that can occasionally calcify.
The blockage itself is only the starting point. When some arteries are blocked, blood is rerouted at higher speeds through the remaining open vessels. That increased flow damages the walls of those previously healthy arteries, triggering a process called vascular remodeling where even the unblocked vessels stiffen and narrow. This is why CTEPH tends to get progressively worse: the disease spreads beyond the original clot sites into smaller arteries throughout the lungs.
Roughly 3.8% of patients develop CTEPH within two years of a pulmonary embolism, based on a landmark study published in the New England Journal of Medicine. No new cases appeared after the two-year mark in that study’s follow-up period. Notably, some patients diagnosed with CTEPH have no documented history of a blood clot, which suggests that small, undetected clots may be responsible in certain cases.
The “Honeymoon Period” and Symptoms
One reason CTEPH is frequently misdiagnosed is the gap between the initial blood clot and the onset of noticeable symptoms. This interval, sometimes called the “honeymoon period,” can last months or even a couple of years. During this time, the lungs compensate for the partial blockage well enough that the person feels recovered from their original clot.
When symptoms do appear, they typically start with breathlessness during physical activity. As the condition progresses, you may notice fatigue, chest tightness, lightheadedness, or swelling in the legs and ankles. These symptoms overlap heavily with other heart and lung conditions, which contributes to delayed diagnosis. The average time from symptom onset to a correct CTEPH diagnosis is often measured in years, not months.
How CTEPH Is Diagnosed
The standard screening test is a ventilation-perfusion (V/Q) scan, which compares airflow and blood flow in different regions of the lungs. Mismatched areas, where air reaches a part of the lung but blood does not, suggest a blockage. V/Q scans are highly sensitive for CTEPH, detecting the condition in about 98% of patients who have it. CT pulmonary angiography performs similarly well at the patient level (94% sensitivity) and provides detailed anatomical images of where clots are located.
A confirmed diagnosis requires right heart catheterization, a procedure that directly measures the pressure inside the pulmonary arteries. The current threshold for pulmonary hypertension is a mean pulmonary arterial pressure above 20 mmHg, paired with elevated pulmonary vascular resistance of more than 2 Wood units. These measurements, combined with imaging that shows chronic clot material after at least three months of blood-thinning therapy, confirm CTEPH.
Surgery: The Potential Cure
The primary treatment for CTEPH is a surgery called pulmonary thromboendarterectomy (PTE). This is an open-heart procedure where a surgeon peels the organized scar tissue and clot material away from the inside walls of the pulmonary arteries. It’s a technically demanding operation performed at specialized centers, but for eligible patients, it can be life-changing.
The typical surgical candidate has significant symptoms (difficulty with everyday activities or at rest), clot material in locations that a surgeon can physically reach, and evidence of elevated lung pressures or right heart strain. Severe underlying lung diseases like emphysema or advanced interstitial lung disease generally rule out surgery, because removing the clots won’t meaningfully improve breathing in those cases. An increasing number of patients with milder symptoms are being referred for evaluation as surgical experience grows.
The results are substantial. Five-year survival after PTE is approximately 80%, and when early surgical deaths are excluded, that number rises to 86%. For comparison, patients with inoperable CTEPH who don’t receive surgery have a five-year survival of roughly 50 to 59%. Conditional on surviving the first 30 days after surgery, long-term life expectancy approaches that of the general population, with relative five-year survival reaching 94% in one Swedish study.
When Surgery Isn’t an Option
Not every patient is a candidate for PTE. The clots may be located too deep in the small branches of the pulmonary arteries for a surgeon to remove, or other health conditions may make the surgical risk too high. For these patients, two alternative approaches exist.
Balloon pulmonary angioplasty (BPA) is a catheter-based procedure where a small balloon is threaded into narrowed pulmonary arteries and inflated to widen them. It’s typically performed over multiple sessions. In patients with persistent pulmonary hypertension after surgery, BPA has been shown to reduce mean pulmonary artery pressure by about 25% and pulmonary vascular resistance by 38%. Functional improvement is significant: in one study, every patient who was in the most severe symptom categories before BPA moved to milder categories afterward.
For medication, riociguat (brand name Adempas) is the only drug specifically approved for CTEPH. It works by helping the blood vessels in the lungs relax and widen. In its pivotal clinical trial, patients taking riociguat walked an average of 39 meters farther in a six-minute walk test after 16 weeks, while the placebo group actually declined by 6 meters. That 46-meter difference translates to real improvements in daily function, like being able to walk to the mailbox or climb stairs with less breathlessness. Medication is reserved for patients who can’t undergo surgery or who still have elevated pressures after PTE.
Why Early Detection Matters
CTEPH is one of the few forms of pulmonary hypertension with a potential surgical cure, yet it remains underdiagnosed. The honeymoon period masks early disease, and the symptoms mimic more common conditions like asthma, deconditioning, or heart failure. If you’ve had a pulmonary embolism and find that your exercise tolerance hasn’t returned to normal within a few months of completing blood-thinning treatment, that persistent breathlessness is worth investigating. A V/Q scan is a straightforward, noninvasive first step that can either rule out CTEPH or set the diagnostic process in motion.