Improved noninvasive assessment of coronary artery bypass grafts in an unselected patient population

In their study, Meyer and colleagues investigated the accuracy of multislice computed tomography (MSCT) in the assessment of bypass grafts following coronary artery bypass graft (CABG) surgery.¹ In the past, these scans have been unreliable in detecting stenoses in both bypass grafts and stents, thus limiting their role in the revascularized patient. Metallic stents may produce artifacts that can obscure the vessel lumen, making the diagnosis of in-stent restenosis difficult.² Earlier scanners also required large volumes of contrast media to visualize the origin of the internal mammary artery, as well as proximal and distal graft anastomoses. The presence of a tachycardia or an arrhythmia also decreased the diagnostic accuracy of these scans.

Meyer and colleagues have now demonstrated that the 64-slice scanner can improve the delineation of graft anatomy, thus increasing the ability to detect stenoses. In their study, MSCT resulted in a 97% sensitivity and a 97% specificity in the detection of graft stenoses and occlusions. The diagnostic accuracy did not differ between arterial and venous conduits. These results were obtained regardless of heart rate or arrhythmias. In addition, significantly less contrast dye was administered with this technique. It was still difficult to accurately delineate significant stenoses in smaller (0.5 mm) vessels; however, these vessels are generally not bypassable.

What, then, should be the role for the MSCT in the post-CABG surgery patient? The MSCT may be the ideal method of assessing the status of bypass grafts in patients who develop chest pain within 3 to 4 months after surgery. Patients presenting with chest pain during this time pose a difficult problem because it may be difficult to differentiate cardiac from noncardiac pain. In addition to incisional pain, these patients may also suffer from the postpericardiotomy syndrome and pleuritis. These symptoms may be difficult to differentiate from angina pain. MSCT provides an accurate and rapid method to determine the patency of bypass grafts in these patients. This would avoid an unnecessary catheterization and allow the clinician to feel more confident in treating chest pain due to noncardiac etiologies. Furthermore, the decreased contrast required for these studies minimizes the risk of further renal damage in those patients who may be still recovering from post-pump acute tubular necrosis.