Serial CMR findings in pediatric heart transplant recipients

Background: CMR has a growing role in surveillance of pediatric heart transplant recipients (PHTR). Prior studies of CMR findings in this population have largely been cross-sectional in design. We sought to evaluate longitudinal changes in CMR findings in PHTR and assess whether changes in CMR findings over time depend on clinical status, including interval events.

Methods: In a single-center, retrospective chart review, PHTR who underwent more than one CMR study between 2015 and 2025 were included. Per PHTR, the initial and most recent CMR studies were included. Patient demographics and baseline clinical history including rejection and CAV history prior to CMR 1 were collected. Interval events between CMR studies were recorded separately. PHTR were defined as low-risk if at the time of CMR 2 they had no CAV, no interval treated rejection, and no LGE (excluding cases of inferoseptal-only LGE) on CMR 1. All other PHTR were classified as high-risk (Figure). Changes in CMR parameters over time were evaluated. We also evaluated whether interval changes observed in CMR parameters differed based on clinical risk status.

Results: 52 PHTR were included, 52% female, with mean age 12.6±4.7y and time since transplant of 6.0±4.4y at time of CMR 1. Mean time between CMR studies was 3.0±1.7y. Prior to CMR 1, 33% had history of treated rejection and 6% had a CAV diagnosis. The indication for CMR 1 was surveillance in 77% (40/52) of cases. Between CMR 1 and CMR 2, 25% (13/52) had treated rejection and 14% (7/49) had an interval catheterization with new or worsened CAV. Indication for CMR 2 was surveillance in 58% (30/52), a clinical concern such as rejection in 25% (13/52), and follow-up of prior abnormal CMR finding in 17% (9/52).

There were no significant differences in RVEDVI, LVEDVI, RV or LV ejection fraction, global T1, ECV, T2 between CMR 1 and 2 (Table 1). Frequency of LGE (excluding inferoseptal-only LGE) was 8% (4/48) on CMR 1 and 15% (7/48) at CMR 2. Time between CMR studies was similar in high-risk (n=26) and low-risk patients (n=26) (3.3±1.8y vs 2.7±1.5y, p=0.218). Compared to high-risk patients, low-risk patients demonstrated an interval decrease in global T1, though this result was not statistically significant (-29.1± 55.7 vs 0.8±66.3, p=0.094). There were no significant differences in interval change in RVEDVI, LVEDVI, RV or LV ejection fraction, ECV or T2 value based on risk status (Table 2). Frequency of LGE at CMR 2 was overall similar in high risk 25% (5/25) and low risk 9% (2/23), p=0.221.

Conclusion: We describe a range of serial CMR findings in PHTR with and without heart transplant complications. Serial CMR studies demonstrated largely stable indexed ventricular volumes, ejection fractions, and parametric mapping values over a 3 year mean interval. We observed a decrease in T1 values over time in low-risk patients, which merits further study.

Table 1: CMR findings on initial and follow-up CMR in PHTR, Nf52

	CMR 1	CMR 2	p-value
RVEDVI, ml/m2, mean ± SD	74.3 ± 16.1	72.7 ± 19.1	0.446
RV EF, %, mean ± SD	55.3 ± 8.3	53.9 ± 1.1	0.277
LVEDVI, ml/m2, mean ± SD	73.4 ± 14.5	70.3 ± 16.4	0.143
LV EF, %, mean ± SD	59.1 ± 6.8	58.1 ± 5.1	0.264
LVMI, g/m2, mean ± SD	46.0 ± 9.4	45.8 ± 9.4	0.890
Global native T1, ms, mean ± SD	1049 ± 49	1034 ± 69	0.111
Global ECV, %, mean ± SD	29.6 ± 4.7	28.8 ± 5.2	0.318
Global T2, %, mean ± SD	48.7 ± 4.4	48.4 ± 4.0	0.672

Table 2: Interval change in CMR parameters according to clinical risk category

	Interval change (CMR 2 value – CMR 1 value)
	All patients (Nf52)</p>	High-risk (Nf26)</p>	Low-risk (Nf26)</p>	p-value
RVEDVI, ml/m2, mean ± SD	-1.6 ± 15.0	-4.9 ± 12.8	1.6 ± 16.4	0.122
RV EF, %, mean ± SD	-1.4 ± 8.0	-2.7 ± 10.2	-0.2 ± 7.4	0.356
LVEDVI, ml/m2, mean ± SD	-3.2 ± 15.5	-5.2 ± 14.2	-1.1 ± 16.7	0.347
LV EF, %, mean ± SD	-1.0 ± 6.6	-2.5 ± 7.0	0.4 ± 5.9	0.116
LVMI, g/m2, mean ± SD	-0.2 ± 8.3	-2.0 ± 8.9	1.7 ± 7.5	0.218
Global native T1, ms, mean ± SD	-14.4 ± 62.3	0.8 ± 66.3	-29.1 ±  55.7	0.094
Global ECV, %, mean ± SD	-0.7 ± 5.0	-0.4 ± 6.1	-1.1 ± 3.7	0.593
Global T2, %, mean ± SD	-0.3 ± 4.2	0.5 ± 4.9	-1.0 ± 3.4	0.205

Study design including patient risk classification