Heart may not fully recover after PEA blood clot surgery in CTEPH
Scarring may explain why heart does not return to normal size
The matrix around the heart’s cells does not shrink and may continue to undergo changes after pulmonary endarterectomy, or PEA, a surgery to remove blood clots from the pulmonary arteries that supply the lungs, a small study found.
Researchers suggest that fibrosis, or scarring, may explain why the heart’s size doesn’t always return to normal in people with chronic thromboembolic pulmonary hypertension (CTEPH) who undergo PEA.
Fibrosis did not seem to make the heart’s right ventricle, or RV — the heart’s chamber that propels oxygen-poor blood to the lungs — stiffer after the blood clot surgery.
However, “further investigations are needed to assess the clinical implications of residual RV [right ventricle] remodeling after PEA,” the researchers wrote.
Measuring heart parameters before, after blood clot surgery
CTEPH is a type of pulmonary hypertension. It occurs when a blood clot breaks loose and travels through the bloodstream to the lungs, where it can block blood flow and increase blood pressure.
When the blood pressure in the pulmonary arteries is too high, it makes the heart work harder to pump blood through them. This extra effort can make the right side of the heart become hypertrophic (grow bigger) and weaker.
PEA usually improves the heart’s function within months, but the organ’s size does not always return to normal. It’s unclear whether this incomplete recovery is due to expansion of the extracellular matrix that provides support to the heart’s cells or to hypertrophy of the heart itself.
To know more, a team of researchers in the Netherlands used MRI to measure a number of parameters in the heart before and six and 18 months after the blood clot surgery.
The study included 25 adults — 15 men and 10 women — who received a diagnosis of CTEPH at a mean age of 62. Nearly one-third (32%) had high blood pressure, or hypertension, and three (12%) had ischemic heart disease caused by reduced blood flow to the heart.
All underwent PEA. Mean pulmonary arterial pressure decreased significantly from 45 millimeters of mercury (mm Hg) before surgery (baseline) to 24 mm Hg six months after surgery.
The right ventricle’s mass also decreased significantly from an average of 43 grams (g) at baseline to 27 g six months after surgery. However, it did not reach the mean value of healthy individuals (22 g).
On the contrary, end-diastolic elastance, a measure of the heart’s stiffness, returned to a normal value six months after PEA, yet the change was not statistically significant.
Researchers say small sample size of patients nonetheless ‘unique’
When the researchers measured the extracellular volume fraction in the RV, they found that it had increased significantly six months after PEA, from 31% to 33.6%. The extracellular volume refers to the space outside cells.
After PEA, “extracellular matrix regression [shrinkage] is not complete in the RV as indicated by a relative smaller decrease in matrix volume compared with cellular volume,” the researchers wrote.
This was accompanied by elevated levels of biomarkers of collagen turnover. Collagen is an extracellular matrix protein that builds up during fibrosis. Collagen turnover is the process of breaking down old collagen and producing new one.
Blood levels of matrix metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), and transforming growth factor-beta (TGF-beta) were elevated at baseline and remained elevated as long as 18 months after PEA.
These findings suggest that “collagen synthesis [production] dominates over collagen breakdown,” the researchers wrote.
“Taken together, these findings suggest that even after successful PEA, diffuse interstitial [occurring between cells] fibrosis regression is not complete in the RV and signs of active collagen turnover are observed,” they added.
“Our study is limited by the relatively small sample size of patients with CTEPH,” the team noted. “Nevertheless, patients were prospectively included and followed over a time of 18 months after PEA, generating an unique data set.”