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Rb-82 PET in Cardiac Allograft Vasculopathy
Study Questions:
Does quantification of absolute myocardial blood flow (MBF) quantification using positron emission tomography (PET) enable evaluation of diagnostically challenging diffuse epicardial and microvascular disease in cardiac allograft vasculopathy (CAV)?
Methods:
The study authors prospectively evaluated consecutive heart transplant recipients undergoing coronary angiography with multivessel intravascular ultrasound (IVUS), intracoronary hemodynamics, and rubidium 82 (Rb-82) PET (cardiac PET was performed within 1 month of angiography). They defined CAV as International Society of Heart and Lung Transplantation CAV on angiography and maximal intimal thickness ≥0.5 mm on IVUS.
Results:
Of 85 consecutive patients identified for possible coronary angiography, 47 underwent angiography and 40 patients were enrolled in the study (mean age 56 years, 4.8 years post-transplant). CAV was detected in 80% (n = 32) of patients by IVUS and 35% (n = 14) by angiography. They found that PET correlated significantly with invasive coronary flow indices: r = 0.29, rate-pressure-product adjusted myocardial flow reserve (cMFR) versus coronary flow reserve (CFR); r = 0.28, relative flow reserve versus fractional flow reserve; r = 0.37, coronary vascular resistance (CVR) versus index of microcirculatory resistance. Patients with CAV or microvascular dysfunction had reduced cMFR and stress MBF, and increased CVR. Receiver operator characteristic curves demonstrated good accuracy of PET for CAV on IVUS (area under the curve, 0.77-0.81) and optimal diagnostic cut-offs of cMFR <2.9, stress MBF <2.3, CVR >55. Combined PET assessment for CAV yielded excellent >93% sensitivity (>65% specificity) for one abnormal parameter and >96% specificity (>55% sensitivity) for two abnormal parameters.
Conclusions:
The study authors concluded that Rb-82 PET flow quantification has high diagnostic accuracy for CAV with potential for noninvasive evaluation after heart transplantation.
Perspective:
This is an important study, and if these findings are confirmed in larger randomized trials, myocardial blood quantification by PET may become the standard of care in the early detection of CAV.
Keywords: Allografts, Cardiac Surgical Procedures, Coronary Angiography, Diagnostic Imaging, Heart Failure, Heart Transplantation, Hemodynamics, Microcirculation, Myocardium, Positron-Emission Tomography, Rubidium, Standard of Care, Ultrasonography, Vascular Resistance
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