Minimally invasive cardiac operations rely on CT

Precise evaluation of cardiac and thoracic anatomy is mandatory for planning safe minimally invasive direct coronary artery bypass. Three-D images obtained with CT angiography can help avoid surgical complications, minimize the need to switch to the standard surgical approach, and help determine the best surgical access.

Dr. Marco Di Terlizzi and colleagues at Ospedale Maggiore della Carita in Novara, Italy, found multislice CTA optimal for surgeons' use in preoperatively planning minimally invasive cardiac coronary artery bypass (MICAB) grafting.

The researchers performed ungated CTA in 20 consecutive patients 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 (MIP, VRT), 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 anatomical variations (anomalous origin and trifurcation), two patients were excluded from the MICAB surgery. The remaining patients underwent successful, uneventful MICAB grafting, Di Terlizzi said.

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

TECAB surgery is performed by creating three small holes in the patient's chest. The surgeon remotely operates scissor-like handles to steer a robot with the endoscopic tools. The surgeon wants to know the location of relevant structures, whether there are abnormalities such as myocardial bridging, and the location and characterization of plaques, Herzog said.

The Frankfurt group had previously published a paper showing the value of four-slice CT in TECAB. For this study, they wanted to examine what 16-slice CT can do.

The researchers 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%, 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%.

The researchers concluded that CTA should be regarded as a valuable planning tool prior to complex minimally invasive procedures such as TECAB or MIDCAB. Herzog also predicted that 64-slice CT might deliver more information than conventional angiography alone.