Evaluation of contrast wash-in and peak enhancement in adenosine first pass perfusion CMR in patients post bypass surgery

BACKGROUND: Adenosine first pass perfusion cardiovascular magnetic resonance (CMR) yields excellent results for the detection of significant coronary artery disease (CAD). In patients with coronary artery bypass grafts (CABG) the kinetics of a contrast bolus may by altered only due to different distances through the bypass grafts compared to native vessels, thereby possibly imitating a perfusion defect. The aim of the study was to evaluate semiquantitative perfusion parameters in order to assess possible differences in epicardial contrast kinetics in areas supplied by native coronaries and CABG, both without significant stenosis. METHODS: Twenty patients with invasive exclusion of significant CAD (control group) and 38 patients with CABG without angiographically significant (≥50%) stenosis in unbypassed coronaries or grafts were retrospectively included in the study. They underwent adenosine first pass (0.05 mmol/kg Gd-DTPA) perfusion (3 short axis views/heart beat) and late gadolinium enhancement (LGE) imaging 1 day before invasive coronary angiography. Areas perfused by native coronaries and/or the different bypasses were identified in X-ray angiography using the 16 segment model. In each of these areas upslope and maximal signal intensity (SI(max)) relative to the left ventricular parameters, time to 50% maximal signal intensity (T(SI50%max)) and time to maximal signal intensity (T(SImax)) were calculated. RESULTS: In areas perfused by coronary arteries with bypasses compared to native coronaries relative upslope and relative SI(max )did not show a significant difference. T(SI50%max )and T(SImax )in native coronaries and bypasses were 7.2s ± 1.9s vs. 7.5s ± 1.9s (p < 0.05) and 12.6s ± 3.0s vs. 13.1s ± 3.0s (p < 0.05), respectively. The delay in T(max )resulted in a significant (p < 0.05) delay of 0.5 ± 1.1 heart beats (=images) when adjusted to the heart rate. Differences in time were most pronounced in areas perfused by left internal mammary artery grafts rather than by venous CABG, but were also present between native vessel territories in patients without CAD, albeit with smaller variability. CONCLUSION: Adenosine perfusion CMR in patients post CABG may be associated with a short delay in contrast arrival. However, once the contrast is in the myocardium there is similar wash-in kinetics and peak enhancement. Therefore, since the delay is only short, the possibly differing contrast kinetics through grafts and native vessels does not seem to be a limiting factor for the accuracy of first pass adenosine perfusion in patients post CABG.