Background: The role of coronary artery bypass surgery as a key foundation in the therapy of coronary artery disease remains unchanged: in Germany in 2001, 75,537 coronary bypass procedures were performed. However, the endurance of coronary bypass grafts is limited: after 3 years, 20-30% of the bypass grafts have occluded. The myocardial infarct rate significantly increases 8 years after bypass surgery. Since the clinical outcome of the patients is closely related to the patency rate of their bypass grafts, it would be important for the patients to have the patency rate of their bypass grafts assessed on time to detect any occluded bypass grafts before the majority of the grafts become occluded. Recently, multi-slice computed tomography (MSCT) offers an attractive tool for this purpose. This paper describes our first experiences with MSCT in our cardiology practice and regards whether this new method provides relevant information for a cardiology practice.
Patients and methods: Studies were performed at the Heart Diagnostic Center in Munich with an Mx 8000 four-row spiral CT with an effective slice thickness of 1.3 mm, 120 kV at 300 mA and approximately 120 ml of contrast medium in double bolus technique. Image reconstruction was performed for 5 heart phases between 50% and 70% of the RR intervals. Thus, a total of over 1,500 slices were reconstructed. 74 patients without angina or proof of myocardial ischemia had noninvasive bypass angiography at a mean of 5 years after surgery.
Results: Of the total of 220 investigated bypass grafts, 132 were venous and 88 were arterial. 177 bypass grafts were classified as open, 42 as occluded; and one venous bypass graft was highly narrowed. Compared with cardiac catheterization, the sensitivity of the cardio-CT regarding the occlusion of a bypass graft was 100% with a specificity of 96%. The only "false positive" occlusion was a LIMA with a small lumen.
Conclusions: Our results show that noninvasive bypass angiography with the ultrafast multi-slice CT (MSCT) provides relevant information for the practicing cardiologist. Noninvasive bypass angiography with a cardio-CT predominantly aims at asymptomatic patients without proof of myocardial ischemia ("bypass check") for the detection of asymptomatic occluded bypass grafts as early as possible. In patients with asymptomatic bypass occlusion, considering a coronary or bypass intervention for prognostic reasons is an option. It is important to note that in our study in a mean of 5 years after bypass surgery almost every third patient had an unexpected bypass graft occlusion.