Atherosclerosis of the ascending aorta as a risk factor for stroke after cardiac surgery : a study based on epiaortic ultrasound

Abstract

Postoperative stroke is a dreaded problem in cardiac surgery and atherosclerosis of the ascending aorta (AAA) is an important risk factor. The risk from calcified AAA, the extent and the topography of the disease in the development of stroke was evaluated. We also determined the most important risk factors for aortic embolization of particles with an intra-aortic filter. Moreover, we studied if conversion from a planned on-pump coronary artery bypass grafting (CABG) to off-pump coronary artery bypass (OPCAB) affected the incidence of postoperative stroke. Furthermore, we investigated if preoperative computer tomograpy (CT) was comparable with introperative epiaortic ultrasound to diagnose AAA. Finally, we evaluated the relationship between the topography of aortic atherosclerosis and the incidence of late stroke after coronary surgery.

Methods: Epiaortic ultrasound (EPI) was performed before surgical manipulation to evaluate the ascending aorta in all patients. In 921 patients the presence of calcification, location of atheroma, extent of the disease and clinical variables including postoperative stroke were recorded prospectively. In 40 consecutive patients undergoing CABG, intraaortic filters were inserted before aortic clamping and extracted after end of cardiopulmonary bypass (CPB). In 28 consecutive patients with extensive AAA, 15 patients were converted from on-pump CABG to OPCAB. Thirteen (13) patients with similar disease who underwent on-pump CABG were used as a control. In 20 patients undergoing CABG, preoperative CT evaluation of the ascending aorta was compared with intraoperative epiaortic ultrasound findings. The ascending aorta was divided into 12 segments per patient giving in total 240 segments to compare. 611 patients undergoing CABG were followed for late stroke. The extent of atherosclerotic disease in the ascending aorta and aortic arch was evaluated with EPI and transesophageal echocardiography. The mean follow-up time was 5.5±1.7 years (range 0-8 years) and covered 3358 patient-years.

Results: 26% of the patients had AAA and in 44.4% of them more than one of 12 possible segments was involved. AAA was found to be the most important predictive factor for postoperative stroke. The incidence of stroke was 1.8% in patients without, and 8.7% in patients with AAA (p<0.0001). The middle-lateral segment was found to be an independent predictive factor for postoperative stroke, with a relative risk of 26% (p=0.04) When using the intra-aortic filter, all patients had particles in the filters, in average 10.5 (SD 5.4). The most important independent risk factor for particles was number/grade of atheromas (p<0.01). When OPCAB surgery was performed, Y-grafts and the non-touch technique of the ascending aorta were used more often with than without OPCAB than in the on-pump group (47% and 73% vs. 0% and 0%, p<0.01). The incidence of stroke with OPCAB was 0% as compared with 31% in the on-pump group (p=0.03). In comparison with CT, epiaortic ultrasound detected atherosclerosis in 16.7±2.4% of the segments, which was significantly higher than with CT (p<0.03). There was a low reliability between the two methods with Kappa Coefficients of 0.45 or lower. The 5-year stroke-free survival rates for patients without aortic disease, those with less than 50% of the ascending aorta diseased and those with more than 50% affected were 95.3±0.9%, 91.8±2.1% and 65.0±14.6%, respectively (p<0.0001). The distal-left side of the ascending aorta was associated with a 5-fold increase in 5-year stroke rate.

Conclusions: Patients with AAA had an 8.7% incidence of postoperative stroke. The risk depended on presence, location and extent of AAA. Atherosclerosis is the most important risk factor for embolization of particles from the ascending aorta during CABG. OPCAB preferably without manipulation of the ascending aorta reduces the incidence of stroke in patients with severe disease of the ascending aorta. CT is inferior to EPI in diagnosing extent and location of atherosclerosis of the ascending aorta. AAA stands out as a predictor of late stroke and the extent of the disease in the distal part and lesser curvature of the ascending aorta seem to be of particular importance.