Non-Ischemic Perfusion Defects due to Delayed Arrival of Contrast Material on Stress Perfusion Cardiac Magnetic Resonance Imaging after Coronary Artery Bypass Graft Surgery
A 50-year-old man visited our hospital for a 3 month-follow-up examination after coronary bypass graft surgery. In this surgery a left internal thoracic artery (LITA) graft to the distal left anterior descending artery (LAD), and a right saphenous venous Y graft from the LITA to the diagonal branch and posterior descending artery (PDA) was performed through sequential anastomosis. The cardiac adenosine stress perfusion MR imaging revealed two perfusion defects at the mid-anterior and mid-inferior walls (, Movies I, II). One perfusion defect at the mid-anterior wall was reversible on rest perfusion images. However, the other perfusion defect at the mid-inferior wallwas persistent on rest perfusion images. But later it disappeared on both stress and rest perfusion images. On the myocardial single-photon emission computed tomography, the inferior wall showed a mild degree of perfusion decrease which was considered as due to the diaphragmatic attenuation effect rather than an ischemic perfusion defect while the mid-anterior wall showed a reversible perfusion defect indicating a reversible ischemia (). On cine images no regional wall motion abnormalities and on late gadolinium enhancement images no delayed myocardial enhancement were observed.\nSignal time curve analyses at stress and rest perfusion MR were performed at three different regions: normal myocardium at the mid-lateral wall and two perfusion defects at the mid-anterior and mid-inferior walls (). From the data, the perfusion index and ratio index of each region were calculated using a previously described method (). In brief, a smooth-fit corrected signal-time curve within the time window of the first pass was analyzed using the gamma-variate function after subtraction of the baseline signal intensity (SI) value from the mean SI of each region. The time window of the first pass was determined from the SI curve of the left ventricular cavity. The time window of the first pass in the myocardium at the same level as the left ventricular cavity was determined by shifting the time window determined from the left ventricular cavity to when the SI in the myocardium started to rise. The maximal upslope indicating the perfusion index was computed from the peak value of the time derivatives of the fit function in the myocardial region, normalized by the maximal upslope in the left ventricular cavity. The ratio index, widely accepted to represent myocardial perfusion reserve, was defined as the ratio of maximal upslope at stress to that at rest (). To calculate perfusion parameters an in-house software was developed using MATLAB 2012a (MathWorks, Natick, MA, USA).\nThe corrected signal-time curves demonstrated that the maximal upslope of the anterior wall decreased from 0.089 during rest to 0.022 during stress perfusion with a ratio index of 0.25, indicating typical reversible ischemia (). In contrast, the maximal upslope of the mid-inferior wall was similar to that of normal myocardium during stress and rest perfusion. But the time to delivery and time to peak enhancement were delayed 7 seconds on both stress and rest images approximately (). The maximal upslope of the mid-lateral wall increased with a ratio index by 1.10 from 0.094 during rest perfusion to 0.104 during stress perfusion. Also for the mid-inferior wall the maximal upslope increased with a ratio index by 1.10 from 0.079 during rest to 0.087 during stress perfusion (). Coronary angiography revealed a focal tight stenosis at the anastomosis site between the right saphenous venous graft and diagonal branch, limiting the flow to the diagonal branch. With this can be explained the reversible ischemia at the apical to the mid-anterior wall on perfusion MRI. However, there was no significant stenosis at the right saphenous venous graft to the PDA. The contrast delivery in the right saphenous venous graft was slightly delayed compared to the LITA to distal LAD graft. It may indicate that the early perfusion defect at the mid-inferior wall was a result of delayed contrast media delivery due to the wide and long pathway of the bypass graft (). Six-month follow-up images showed still a persistent perfusion defect without significant stenosis of the saphenous venous Y graft in the mid-inferior myocardial wall ().