Myocardial Perfusion Imaging After Coronary Artery Bypass Surgery Using Cardiovascular Magnetic Resonance

Abstract

Background-Absolute quantification of perfusion with cardiovascular magnetic resonance has not previously been applied in patients with coronary artery bypass grafting (CABG). Owing to increased contrast bolus dispersion due to the greater distance of travel through a bypass graft, this approach may result in systematic underestimation of myocardial blood flow (MBF). As resting MBF remains normal in segments supplied by noncritical coronary stenosis (Ͻ85%), measurement of perfusion in such territories may be utilized to reveal systematic error in the quantification of MBF. The objective of this study was to test whether absolute quantification of perfusion with cardiovascular magnetic resonance systematically underestimates MBF in segments subtended by bypass grafts. Methods and Results-The study population comprised 28 patients undergoing elective CABG for treatment of multivessel coronary artery disease. Eligible patients had angiographic evidence of at least 1 myocardial segment subtended by a noncritically stenosed coronary artery (Ͻ85%). Subjects were studied at 1.5 T, with evaluation of resting MBF using model-independent deconvolution. Analyses were confined to myocardial segments subtended by native coronary arteries with Ͻ85% stenosis at baseline, and MBF was compared in grafted and ungrafted segments before and after revascularization. A total of 249 segments were subtended by coronary arteries with Ͻ85% stenosis at baseline. After revascularization, there was no significant difference in MBF in ungrafted (0.82Ϯ0.19 mL/min/g) versus grafted segments (0.82Ϯ0.15 mL/min/g, Pϭ0.57). In the latter, MBF after revascularization did not change significantly from baseline (0.86Ϯ0.20 mL/min/g, Pϭ0.82). Conclusions-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. (Circ Cardiovasc Imaging. 2011;4:312-318.)

Perfusion MRI at rest in subacute and chronic myocardial infarct

“…The parameter v e reflects the tissue distribution volume fraction (leakage space) of the contrast agent. An estimate for F (rBF) can be directly measured from the tissue residue function derived from AIF deconvolution (9)(10)(11). Myocardial perfusion MRI studies have indicated reduced flow in MI tissue, assessed through a variety of different perfusion parameters (12)(13)(14)(15).…”

Use of quantitative cardiovascular magnetic resonance myocardial perfusion mapping for characterization of ischemia in patients with left internal mammary coronary artery bypass grafts

“…A concern with the use of any first pass perfusion imaging technique in patients with CABG is the increased transit delay in the dynamic contrast delivery to tissue through long graft conduits [ 23 ]. Using model-independent deconvolution analysis, Arnold et al [ 8 ], demonstrated that in the context of rest perfusion, despite a short delay associated with contrast arrival and the resulting increased contrast dispersion particularly involving the internal mammary arterial graft, estimation of MBF was not systematically underestimated in graft subtended myocardial territories. Similarly, using semiquantitative perfusion parameters Kelle et al [ 9 ] showed that grafted and native vessel myocardium shared similar contrast kinetics, despite a short delay in contrast arrival in grafted territories.…”

“…Fourthly, our technical analysis specifically considered the arterial time delay of contrast through the LIMA graft conduit, and did not consider additional dispersion or broadening of the arterial input function. Although the effect of long conduits such as the LIMA graft on contrast dispersion was previously thought to be small [ 8 ], its impact on absolute MBF estimation warrants further evaluation.…”

“…Graft length is of particular concern for any non-invasive test that relies on first pass perfusion using an intravenous contrast medium. Post CABG, the increased length of graft conduits plausibly results in a prolonged contrast transit time (arterial time delay), potentially distorting the first pass kinetics of the contrast bolus and the subsequent estimation of myocardial blood flow in graft-subtended territories [ 8 ]. This is often proposed as an explanation for the presence of perfusion defects in the LIMA territory, although evidence to support this is lacking.…”

Residual Ischemia After Revascularization in Multivessel Coronary Artery Disease

“…23 Absolute myocardial blood flow (MBF) in mL/min per gram was calculated for each myocardial segment by model-independent deconvolution of myocardial signal intensity curves with the arterial input measured at the basal level. 24,25 Segments with hyperemic MBF below 1.8 mL/min per gram were classified as ischemic. 26 Ischemia burden was defined as the percentage of segments with ischemia.…”