Significance of electron-beam tomography in the evaluation of the patency of aortocoronary bypasses

Abstract

Electron beam tomography (EBT) permits acquisition of images with high spatial and temporal resolution. The value of EBT and other imaging modalities for the depiction of patent coronary artery bypass grafts (ACVB, IMA) are compared to coronary angiography and an overview of current results is given. Graft patency can be evaluated with indirect methods stress, such as echocardiography, radionuclide ventriculography, myocardial scintigraphy, positron-emission tomography (PET) and direct imaging modalities, such as Doppler/2D echocardiography, EBT, spiral computed tomography (SCT) and magnetic resonance angiography (MRA). With indirect methods graft patency can be evaluated with sensitivity of 64-100% and specificity of 73-100%. EBT and SCT are equivalent in sensitivity (= 94%) in the assessment of open venous grafts and specificity is up to 100%, but EBT is superior in the diagnosis of patent IMA grafts (sensitivity 100% vs 89%). Visualization of high-grade venous bypass stenosis seems possible with EBT. MRA with gradient echo technique is highly accurate in the assessment of patent venous grafts (sensitivity 77-93%) but has limited value in the evaluation of IMAs (sensitivity = 53%). Promising are ultrafast 3D-MRA methods which permit high accuracy (sensitivity = 94-96%) in assessing venous and arterial grafts. Indirect imaging methods cannot differentiate between an occluded bypass, progression of coronary artery disease and myocardial infarction. EBT and SCT are equivalent in the diagnosis of open and occluded venous grafts, but EBT is superior in the assessment of patent IMA grafts. Visualization of high-grade venous bypass stenosis seems possible with EBT. MRA techniques, especially ultrafast 3D-MR methods, are highly accurate in the assessment of patent venous and arterial grafts but are still limited to scientific research.