Abstract 21308: Quantification of Myocardial Perfusion Following Coronary Artery Bypass Grafting using Cardiovascular Magnetic Resonance

Background: Previous studies involving visual assessment of myocardial perfusion with cardiovascular magnetic resonance (CMR) have shown reduced accuracy in patients with coronary artery bypass grafting (CABG). Absolute quantification of perfusion with CMR offers theoretical advantages, especially in multi-vessel disease. However, this Methodsology requires the definition of an arterial input function within the left ventricular blood pool, and owing to the greater distance of travel through a bypass graft, contrast bolus dispersion may Results in underestimation of myocardial blood flow (MBF). Therefore, the Objectives of this study was to test whether absolute quantification of perfusion with CMR systematically underestimates MBF in segments subtended by bypass grafts. As resting MBF remains normal in segments supplied by non-critical coronary stenosis (<85%), measurement of perfusion in such territories may be used to reveal systematic error in the quantification of MBF.

Methods: Patients referred for elective CABG who had angiographic evidence of at least one myocardial segment subtended by a non-critically stenosed coronary artery (<85%) were studied at 1.5 Tesla. First-pass perfusion imaging was performed at baseline and 4–6 months after CABG using a saturation recovery fast-gradient echo sequence and Gadolinium-DTPA bolus injections (0.04mmol/kg). Resting MBF was evaluated using model-independent deconvolution. Analyses were confined to myocardial segments subtended by native coronary arteries with <85% stenosis at baseline (on quantitative coronary angiography). MBF was compared in grafted and ungrafted segments before and after revascularization.

Results: In 28 eligible patients, a total of 249/448 segments were subtended by coronary arteries with <85% stenosis at baseline. Following revascularization, there was no significant difference in MBF in ungrafted (0.81±0.19ml/min/g) versus grafted segments (0.81±0.15ml/min/g, p=0.57), with no significant change from baseline (p=0.88).

Conclusion: Model-independent deconvolution analysis does not systematically underestimate blood flow in graft-subtended territories, justifying the use of this methodology to evaluate myocardial perfusion in patients with CABG.