Dr. Marco Di Terlizzi and colleagues at Ospedale Maggiore della Carita in Novara, Italy, performed ungated CTA in 20 consecutive patients scheduled for minimally invasive cardiac coronary artery bypass (MICAB) grafting. The researchers sought to obtain an accurate assessment of anatomy and to estimate availability of the structures involved in the surgical procedure. They used a four-slice scanner set at 120 kVp and 300 mAs and viewed the images in the axial source view and in 3D (maximum intensity projection and volume rendering technique), using a dedicated workstation. Both internal mammary arteries were evaluated for the presence of anatomic variations, diameter, presence of wall calcifications, and distance to sternal margins.

The radiologists could visualize both internal mammary arteries in all 20 patients. Because of anatomic variations (anomalous origin and trifurcation), two patients were excluded from the surgery. The remaining patients underwent successful, uneventful MICAB grafting, Di Terlizzi said.

In another study, Dr. Christopher Herzog and colleagues at the University Clinic at Johann Wolfgang Goethe University in Frankfurt found CTA to be a beneficial preoperative tool for surgeons performing totally endoscopic coronary bypass (TECAB) procedures. TECAB is gaining favor at the Frankfurt clinic, increasing from 11 procedures in 2001 to 66 in 2004, Herzog said.

TECAB surgery is performed by creating three small holes in the patient's chest. The surgeon remotely operates scissorslike handles to steer a robot with the endoscopic tools. The surgeon seeks to know the location of relevant structures, whether there are abnormalities such as myocardial bridging, and the location and characterization of plaques. The Frankfurt researchers had previously published a paper showing the value of four-slice CT in TECAB. For this study, they examined the power of 16-slice CT.

They preoperatively evaluated 84 patients with CTA and quantitative coronary angiography (QCA). Thirty-eight patients were imaged on a four-slice scanner, and 46 were scanned on a 16-slice machine.

The assessment criteria were myocardial course of the coronary arteries, localization and degree of stenoses, and localization and quality of plaques. The investigators also sought to recommend the most suitable region for distal bypass touchdown. All findings were correlated to QCA and surgery.

Four-slice CT allowed evaluation of 79% of all segments of surgical relevance and 80% of all coronary segments. Values for 16-slice CT amounted to 87% and 89%, respectively, compared with 92% and 96% for QCA.

Both the four- and 16-slice scanners detected all calcified plaques, compared with 81% for QCA. Stenoses greater than 75% were detected by four-slice CT in 76% of cases, by 16-slice in 85%, and by QCA in 100%.

Intramyocardiac coronary segments were identified by four-slice CT in 75%, by 16-slice in 100%, and by QCA in 20%. The site of distal bypass touchdown was predicted correctly by four-slice CT in 75%, by 16-slice in 87%, and by QCA in 80%.

"CTA gives the surgeons relevant morphological information such as myocardial bridging, which appeared in about 17 patients. The 16-slice scanner detected all of them, while conventional angiography found only 25%," Herzog said. "The same goes for anastomosis, which was much better predicted with 16-row CT because we saw the calcification, which allowed us to make a better prediction."

CTA also allows for early adoption of a surgical technique, making it time-sparing, Herzog said. He concluded that CTA should be regarded as a valuable planning tool prior to minimally invasive procedures such as TECAB or MIDCAB.