PET helps ID at-risk patients after heart transplants

PET one day may supplant invasive coronary angiography for monitoring heart transplant survivors who are at risk of developing life-threatening cardiac allograft vasculopathy (CAV), if preliminary results published online Sept. 2 hold up in larger studies.  

CAV is the leading cause of death for patients one year after a heart transplant, Brian A. McArdle, MB BCh, and colleagues at the University of Ottawa Heart Institute in Canada, wrote in Circulation: Cardiovascular Imaging. Guidelines call for screening heart transplant patients for at least five years after their operation using invasive coronary angiography.

But the modality carries risk and can’t detect the diffuse vascular injuries from CAV. Noninvasive PET, on the other hand, can quantify myocardial blood flow (MBF) and estimate MBF throughout the vascular system.  

The Ottawa team designed a prospective observational study to evaluate the prognostic value of rubidium-82 (Rb-82) PET in patients who had undergone a heart transplant. Their primary outcome was a composite of all-cause death, acute coronary syndrome and hospitalization for heart failure.  

They enrolled 140 patients using registries that tracked heart transplant patients who had undergone a rest and stress Rb-82 stress test at least 12 months after their transplant. They calculated myocardial flow reserve as a ratio of stress and rest MBF.

Based on the data, nine patients died, one had acute coronary syndrome and four were admitted to a hospital for heart failure. They found an association between baseline abnormal renal function and previous CAV and adverse outcomes. Beyond clinical factors, relative perfusion defects, mean myocardial flow reserve and mean stress MBF predicted adverse outcomes.

“While the results of this study are preliminary in nature, they demonstrate a potential role for PET with absolute flow quantification as a marker of CAV, with prediction of subsequent adverse outcome, and detection of more diffuse CAV involving both the epicardial vessels as well as the microvasculature at an earlier stage compared to other non-invasive imaging modalities,” they proposed.

McArdle et al acknowledged that not all centers may have access to PET facilities, which could crimp adoption of PET for monitoring heart transplant patients. They also recommended larger studies with long-term follow-up to confirm their findings.