Abnormal Myocardial Strain by Strain Encoding Imaging is Prevalent in Pediatric Heart Transplant Recipients with Preserved Left Ventricular Ejection Fraction

Background: Pediatric heart transplant (PHT) recipients are at risk for long-term complications including allograft rejection and coronary artery vasculopathy. Utility of LVEF for detection of complications is limited as decrease in LVEF is often a late finding. Myocardial strain encoded imaging (SENC), a technique that utilizes high and low tuning images to produce strain maps that quantify myocardial strain in the through-plane direction, may provide a more sensitive method to detect subclinical myocardial dysfunction among PHT recipients. The purpose of this study is to evaluate myocardial dysfunction by SENC/strain analysis at rest and stress among PHT recipients undergoing stress CMR.

Methods: Retrospective review was performed of all PHT recipients who underwent regadenoson stress CMR at a single tertiary care center. Stress CMR was performed at 3T (Siemens, Skyra) using a standard regadenoson stress protocol for volumetry/function, stress imaging, and SENC at rest and stress. Strain analysis was performed using MyoStrain (Myocardial Solutions, Durham, NC). Global longitudinal strain (GLS), global circumferential strain (GCS), and “MyoHealth” (MH) score, which expresses the number of normal myocardial segments (without abnormal strain) as percentage of total myocardium, were compared to healthy controls. Abnormal strain was defined as absolute magnitude < 17%.

Results: 37 subjects (36% female) with mean age 17.9 ± 7.5 years completed 47 stress CMR studies. Resting strain analysis versus control subjects are summarized in table 1. Abnormal resting GLS was observed in 70% PHT studies. Compared to controls, PHT recipients demonstrated lower GLS (-18% vs -15%, p < 0.05) and MH scores (72% vs 52%, p < 0.05), as well as lower GCS, though GCS was preserved among PHT recipients (-21% vs -18%, p < 0.05). Among PHT recipients with abnormal GLS, LVEF remained normal with median LVEF 67% (IQR 63-70%). 16% of PHT recipients demonstrated failure to augment myocardial strain with stress. Despite inability to augment strain, resting LVEF was normal ( > 55%) in all of these subjects.

Conclusion: Myocardial strain abnormalities by SENC were prevalent in PHT recipients despite normal LVEF, with lower GLS and MH scores compared to controls. Failure to augment strain with stress was observed in subjects with no apparent evidence of LV dysfunction by LVEF. GCS remained normal in PHT recipients, suggesting relative sparing of systolic circumferential shortening but earlier involvement of longitudinal shortening. Future studies are anticipated to evaluate if abnormal strain or failure to augment strain during stress is predictive of adverse outcomes in PHT recipients.

Strain in Control Subjects versus PHT Recipients

	Controls (n=6)	Heart Transplant (n=47)	pvalue
MyoHealth	72.31 ± 22.38	52.27 ± 15.83	0.01
LV GLS	-18.08 ± 2.83	-15.10 ± 3.05	0.04
LV GCS	-20.55 ± 1.41	-17.68 ± 1.50	0.003

(GLS = global longitudinal strain, GCS = global circumferential strain)A. LV global longitudinal strain (GLS) and global circumferential strain (GCS) in PHT recipients versus controls. B. MyoHealth scores in PHT recipients versus controls. Asterisks signify statistical significance in both panels.
Polar plots of longitudinal strain in healthy control subject (A) and in PHT recipient (B). Strain values are visually represented along a color scale, with green depicting areas of abnormal strain compared to normal (blue).