Feasibility of Real-Time Myocardial Contrast Echocardiography to Detect Cardiac Allograft Vasculopathy in Pediatric Heart Transplant Recipients

Background: Cardiac allograft vasculopathy (CAV) is an important adverse prognostic factor for pediatric heart transplant (HT) recipients. Invasive coronary angiography (ICA) is the gold standard for CAV detection but lacks sensitivity for early microvascular changes and cumulative radiation exposure is of concern. Real-time myocardial contrast echocardiography (RTMCE) using ultrasound enhancing (contrast) agents performed during dobutamine stress echocardiography (DSE) can assess myocardial function, perfusion, and microvascular integrity. The objective of this study was to determine the safety and feasibility of RTMCE during DSE to detect CAV in a pediatric HT population. Methods: HT patients 10-21 years of age were recruited to undergo DSE with RTMCE to determine technical feasibility, test tolerability and adverse event rate, and detection of perfusion defects compared with ICA-detected CAV. Thirty-six patients from two centers were enrolled, with a mean age 13.5 ± 4.3 years; 21 (58%) were male. Wall motion and myocardial perfusion were qualitatively assessed and compared with ICA findings of CAV. Myocardial blood flow (MBF) at rest and peak stress was quantified, and myocardial blood flow reserve (MBFR) was defined as the ratio of peak to rest MBF. Results: Five (14%) patients had CAV by ICA, two with obstructive disease and three with mild CAV. Real-time myocardial contrast echocardiography was feasible in 32 (89%) patients. Three patients had wall motion defects, including one with a mixed defect and two with fixed defects. A perfusion abnormality was present in five patients, two of whom had obstructive CAV and one with mild CAV. Sensitivity and specificity of RTMCE for CAV detection were 60% and 94%, respectively, and diagnostic accuracy was 89%. MBFR assessment was feasible in 20 (63%) patients. The mean MBFR was 3.4 ± 0.7. Patients with CAV had lower MBFR than those without (2.0 ± 0.2 vs 3.7 ± 0.8; P < .01). There were no serious adverse events related to RTMCE. Conclusions: Dobutamine stress RTMCE appears to be safe and feasible for the assessment of CAV in pediatric HT recipients. Further assessment is warranted to determine whether this noninvasive technique could provide a reliable alternative to ICA.