Cardiac MRI provided an effective, non-invasive means of monitoring for acute rejection episodes after heart transplantation in a prospective study.
A model combining age and the MRI parameters of global T2 and global extracellular volume fraction (ECV) was predictive of acute cardiac allograft rejection (ACAR) with an area under the curve of 0.84, according to Ryan Dolan, MD, and colleagues of Chicago’s Northwestern University reporting in JACC: Cardiovascular Imaging.
“Multiparametric CMR [cardiac MRI] is sensitive to structural changes in heart transplant recipients and shows great promise for detection of ACAR. Given its safety profile and non-invasive approach, it may be particularly well utilized when subclinical disease is suspected,” they concluded.
ACAR currently requires endomyocardial biopsy for diagnosis. Dolan and colleagues defined ACAR as anything above grade 1R on the International Society for Heart and Lung Transplantation scale.
The study was based on 58 heart transplant recipients matched to 14 controls (mean age, 47 years for both groups).
All had undergone 1.5 T cardiac MRI scanning within 3 months of biopsy. Scans were done from 1 month to 1 year after transplant in 45% of cases, in the 1-6 year range in 39%, and 7 years or more post-transplant in 17%.
ECV, as a measure of interstitial expansion (diffuse myocardial fibrosis and edema), was substantially higher in patients with active ACAR confirmed on endomyocardial biopsy — even compared with individuals with previous but resolved ACAR, according to the investigators.
On the other hand, T2 showed less sensitivity as a marker: transplant recipients with active and past ACAR alike had higher myocardial T2 compared with recipients who had no history of ACAR; this latter group, in turn, had higher T2 values than no-transplant controls.
“Even though our results suggest that ECV may be as effective or superior to T2 for detection of ACAR, it is important to note that calculation of ECV requires IV contrast, which is contraindicated in many patients, most commonly by chronic kidney disease,” Dolan’s group cautioned.
Nevertheless, the study’s findings are “intriguing,” as the observed high sensitivity of global ECV might make it “a viable screening strategy,” according to an accompanying editorial by Raymond Kwong, MD, MPH, and Yin Ge, MD, both of Brigham and Women’s Hospital in Boston.
Besides further work to improve ECV’s limited specificity, Kwong and Ge said it would take a randomized multicenter study to determine if an MRI-first strategy can become standard of care.
“Any emerging quantitative CMR applications will have to benchmark against traditional invasive investigations not only for diagnostic accuracy, but patient safety and cost effectiveness,” they commented. “CMR will also have to contend with advances in non-invasive detection of transplant rejection via gene expression profiling of circulating blood mononuclear cells.”
For the most part, however, the literature appears to support the “good” performance of parametric cardiac MRI in identifying allograft rejection, the editorialists said.
The study was funded by a grant from the National Heart, Lung, and Blood Institute.
Dolan, Kwong, and Ge reported no relevant conflicts of interest.