S surgical procedures. A major cause of perioperative

Transcription

1 Intraoperative Ultrasonic Imaging of the Ascending Aorta William G. Marshall, Jr, MD, Benico Barzilai, MD, Nicholas T. Kouchoukos, MD, and Jeffrey Saffitz, MD Divisions of Cardiothoracic Surgery and Cardiology, Washington University School of Medicine, St. Louis, Missouri Embolization of atherosclerotic material from the ascending aorta resulting from placement of cannulas or vascular clamps is a major cause of stroke during cardiac surgical procedures. In an effort to identify atherosclerotic disease of the ascending aorta which might predispose to embolization, intraoperative B-mode ultrasonography was performed in 50 patients. The aorta was imaged from the aortic annulus to the origin of the innominate artery in transverse and longitudinal views. The results were compared with visual and tactile examination of the aorta for the presence of atherosclerosis. Ultrasonic imaging demonstrated atherosclerotic disease in 29 patients (58%). Visual examination and palpation identified atherosclerosis in 12 patients (24%). The amount and location of plaque was sufficient to require a change in the site of arterial cannulation or the proximal vein graft anastomoses or the technique of cardiopulmonary perfusion in 12 of the 50 patients (24%). All 12 patients were 65 years of age or older. Palpation underestimates the presence of atherosclerotic disease in the ascending aorta. Intraoperative ultrasonography accurately identifies patients with atherosclerotic disease of the ascending aorta. This allows the surgeon to modify cannulation, perfusion, and operative techniques to reduce the risk of perioperative stroke due to the embolization of atherosclerotic debris from the ascending aorta. (Ann Thorac Surg 1989;48:33944) troke is a serious and disabling complication of cardiac S surgical procedures. A major cause of perioperative stroke is embolization of atherosclerotic material from the ascending aorta, which may result from insertion of perfusion cannulas, placement of clamps on the ascending aorta, or palpation of the ascending aorta [l]. Palpation of the aorta may identify areas of calcification or marked thickening, but may not identify lesser degrees of calcification or thickening or areas of soft, "cheesy" atheroma. In an effort to accurately identify atherosclerotic disease of the ascending aorta, a technique using intraoperative B-mode ultrasonic imaging of the ascending aorta was evaluated. Material and Methods Fifty patients undergoing cardiac surgical procedures using cardiopulmonary bypass were studied during a 9- month period (September 1987 to May 1988). The mean age of the patients was 70 years (range, 47 to 83 years) and 28 (56%) were men. The patients were not consecutive, due to equipment availability, and there was a degree of selectivity in that efforts were made to image patients felt to be at increased risk for atheroembolism. The operative procedures performed are shown in Presented at The Thirty-fifth Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, November 1CL12, Address reprint requests to Dr Kouchoukos, Department of Surgery, The Jewish Hospital at Washington University Medical Center, 216 S Kingshighway Blvd, St. Louis, MO Dr. Marshall's present address is The Watson Clinic, 1600 Lakeland Hills Blvd, Lakeland, FL Table 1. Forty-three patients had coronary artery bypass grafting, 2 patients had coronary artery bypass grafting and left ventricular aneurysmectomy, 2 patients had isolated valve replacement (one aortic, one mitral), 2 patients had ascending aorta/aortic arch replacement, and 1 patient had coronary artery bypass grafting and concomitant right carotid endarterectomy. After median sternotomy, mobilization of the internal mammary artery, if used, and suspension of the heart in a pericardial cradle, the aorta was examined visually and by palpation. The extent and location of calcification or thickening thought to be present was recorded. Ultrasonic imaging of the ascending aorta was then performed using either a Hewlett-Packard 77020A phased array system with a 5-MHz transducer with a 4-cm sonolucent standoff (Hewlett-Packard Company, Medical Products Group, Andover Division, Andover, MA), or a Medasonics 210 DX Vasculab with a 7.5-MHz transducer (Medasonics, Mountain View, CA) without a standoff. The transducer was placed in a sterile plastic sleeve containing conducting gel and placed directly on the ascending aorta. The aorta was imaged in transverse and longitudinal views from the aortic annulus to the origin of the innominate artery (Fig 1-3). The scans were recorded on standard VHS video tape and were reviewed by the surgeon and a cardiologist in the operating room. The results of the scans were compared with the visual and digital findings. Based on the results of the ultrasonic imaging, modifications of the usual cannulation and proximal graft anastomotic sites and perfusion protocols were made by the surgeon, if indicated. The operative procedures were then by The Society of Thoracic Surgeons /89/$3.50

2 340 MARSHALL ET AL INTRAOFERATIVE ULTRASOUND Ann Thorac Surg 1989:48: Table 1. Operative Procedures in the 50 Patients Procedure Patients % Coronary artery bypass grafting Coronary artery bypass grafting 2 4 and left ventricular aneurysmectomy Valve replacement 2 4 Ascending aortalaortic arch 2 4 replacement Coronary artery bypass grafting 1 2 and right carotid endarterectomy performed. The patients were evaluated postoperatively for evidence of perioperative stroke or wound infection. Results By visual and digital examination of the aorta, 38 patients (76%) were thought to have a normal aorta, and 12 B Fig 2. (A) Transverse ultrasonic imaging of the ascending aorta showing thickened aortic wall and intraluminal echogenic material (arrows).(b) Longitudinal image of the same aorta demonstrating thickened aortic wall and intraluminal echogenic material (arrows). patients (24%) were thought to have an abnormal aorta. By ultrasonic imaging, 21 patients (42%) had normal aortas and 29 patients (58%) had abnormal aortas. This included the 12 patients with an abnormal aorta by palpation and 17 patients with a normal aorta by palpation (Table 2). The intraoperative decisions resulting from detection of atherosclerotic material are shown in Table 3. Twelve of the 17 patients (71%) with a normal aorta by palpation had only small amounts of plaque or plaque located in areas that would not affect the conduct of the R " Table 2. Comparison of Palpation and Ultrasonic Imaging for Detection of Atherosclerotic Disease of the Ascending Aorta (n = 50) Palpation Scan Result Patients % Patients % Fig 1. (A) Transverse ultrasonic image of the ascending aorta demonstrating normal aortic wall and no intraluminal echogenic material. Normal (B) Longitudinal ultrasonic imaging of the ascending aorta showing normal aortic wall and no intraluminal echogenic material. Abnormal

3 Ann Thorac Surg 1989;48: MARSHALL ET AL 341 Table 3. lntraoperatiue Decisions in Patients With Abnormal Scan Palpation Palpation Normal Abnormal Total Intraoperative Decision (n = 17) (n = 12) (n = 29) Plaque insignificanthgnored Plaque detected with resulting change in cannulation/perfusion technique B Fig 3. Transverse ultrasonic image of the ascending aorta showing thickened aortic wall and large amount of intraluminal echogenic material (arrows). operation (eg, origin of the innominate artery, aortic root). Five of the 12 patients (42%) with an abnormal aorta by palpation had similar findings on ultrasonic imaging. No modifications in techniques were made in these 17 patients. The remaining 12 patients (5 with a normal aorta and 7 with an abnormal aorta by palpation) had plaque of sufficient quantity or in locations such that a change in cannulation or perfusion techniques was required. Anatomically, the atherosclerotic plaque was located in the anterior half of the circumference of the aorta in 22 of the 29 patients with abnormal scans (76%), and in all 12 of the patients in whom technical changes were made based on the scan findings. In addition, the amount of disease located posteriorly was much less than the amount located anteriorly. Plaque was more prevalent anteriorly in patients with disease located in the upper half of the ascending aorta (17118; 94%) compared with patients with disease in the lower half of the aorta (5/11; 46%). Four patients had disease involving the entire length of the ascending aorta, 2 of whom had a porcelain aorta with disease involving the entire circumference of the aorta and 2, disease located in the anterior half of the aortic circumference (Fig 4). The usual sites of insertion of the aortic cannula and the cannula for infusion of cardioplegic solution and the sites for the proximal saphenous vein graft anastomoses are shown in Figure 5. The changes in cannulation and in perfusion techniques resulting from the scan findings included relocation of the arterial or cardioplegic cannulation site in 6 patients, use of femoral cannulation in 2 patients, and use of femoral cannulation with hypothermic circulatory arrest and ascending aortic replacement or ascending aortic endarterectomy with patch aortoplasty without the use of vascular clamps (open technique) in 4 patients (Fig 6). Twelve of the 50 patients (24%) had some technical change made based on the findings of the ultrasonic imaging (Table 4). These 12 patients were 65 years of age or older, and they comprised 37% of the 27 patients in this age group (Table 5). There were no wound infections in the patients studied 13 2 ANTERIOR 11 2 LEFT Fig 4. Anatomical location of the atherosclerotic disease in the ascending aorta as documented by ultrasonic scanning. The 4 patients with near or total circumferential disease involving the entire ascending aorta were counted in the anterior, upper aorta group. TOTAL GROUP (N = 29) 1 B0 0 0 l@ 2 2 POSTERIOR UPPER AORTA (N: 18) LOWER AORTA (N ~ 1 1 )

4 342 MARSHALL ET AL Ann Thorac Surg 1989;48:33944 Table 4. Changes in Cannulation and Perfusion Techniques Change Patients % Relocation of aortic cannula 6 12 Femoral artery cannulation 2 4 Femoral artery cannulation with 4 8 profound hypothermia, total circulatory arrest, and ascending aortic replacement or patch aortoplasty Total Fig 5. Usual sites of placement of the arterial and cardioplegic cannulas and the proximal anastomoses of saphenous vein grafts. and there was one stroke (2%). This occurred in the patient who had concomitant coronary artery bypass grafting and right carotid endarterectomy. This patient had bilateral internal carotid artery stenoses greater than 95% and a normal scan of the ascending aorta. The cerebral infarct occurred in the left hemisphere, contralatera1 to the side of the endarterectomy. Comment Stroke occurring during cardiac surgical procedures using cardiopulmonary bypass has several causes. These in- +; oortoplosty - ~ Patch Plaque formot ion Fig 6. More lateral and inferior placement of the cardioplegia cannula and a longitudinal incision in a difusely atherosclerotic aorta with patch angioplasty. The vein grafts are anastornosed to the Dacron patch. The arterial cannula is placed in the femoral artery. clude air embolus from the cardiopulmonary bypass circuit, intracardiac air after cardiotomy for venting or operative procedures, intracardiac thrombus, cerebrovascular occlusive disease with resultant embolization or cerebral hypoperfusion, and embolism of atheromatous material from the ascending aorta and aortic arch [2]. Atheroemboli from the ascending aorta are usually related to the placement of cannulas for cardiopulmonary bypass or vascular instruments and have been reported to occur after palpation of the ascending aorta [l]. The incidence of stroke after cardiac surgical procedures is increased in elderly patients [3] and observational data would suggest the elderly have an increased incidence of more severe atherosclerotic disease, particularly in the ascending aorta. Complications related to the diseased ascending aorta have been demonstrated to be the primary cause of unexpected death after coronary artery bypass grafting [4]. As greater numbers of elderly patients undergo cardiac surgical procedures, the risk of neurological complications, including those resulting from embolization of atheroma from the ascending aorta, may increase. In our overall experience (unpublished data), one third of perioperative strokes are related to atherosclerotic disease of the ascending aorta. Numerous techniques have been introduced in an attempt to reduce the frequency of this complication. These include (1) placement of proximal saphenous vein graft anastomoses on the innominate or internal mammary arteries [5, 61, (2) use of an intraluminal balloon catheter rather than an aortic cross-clamp for aortic occlusion [7, 81, (3) modification of vascular instruments used to clamp Table 5. Results of Aortic Scanning According to Age (n = 50) Changes in Cannulation or Perfusion Age Patients Patients % <65 yr yr

5 Ann Thorac Surg 1989;48: MARSHALL ET AL 343 the aorta [9], (4) performance of the cardiac procedure using hypothermic fibrillatory arrest to avoid placement of clamps on the ascending aorta [lo], and (5) ascending aortic endarterectomy and patch aortoplasty or ascending aortic replacement with hypothermic circulatory arrest without the use of vascular clamps [l]. Before the problem can be managed, it must first be identified. The "egg-shell" or "porcelain" aorta can usually be identified by palpation of the aorta. However, focal or segmental areas of calcification or thickening may be present, and the surgeon cannot be certain if the soft areas can be cannulated or clamped without dislodgement of atherosclerotic debris. Identification of the aorta containing soft, friable atheroma can be even more difficult. The disease may not be palpable, and palpation may dislodge atheromatous material. Often, this type of aorta is not recognized until clamps have been placed and aortotomies made. By this time, embolization has usually already occurred. Ultrasonic imaging eliminates the need for digital palpation of the aorta, which has been implicated as a cause of atheroembolization [l]. Minimal pressure is placed on the aorta with the ultrasound probe, and in this study no neurological abnormalities related to the probe were observed. The technique is simple and rapid, adding only a few minutes to the operative procedure. Interpretation of the scans is relatively straightforward and can be done by the surgeon after an initial training period. Interpretation is very similar to that performed in the imaging of peripheral arteries, but easier because no Doppler analysis is required. Our group has extensive experience using ultrasonic techniques to detect and characterize atherosclerosis in the peripheral vessels [ll]. Thus, it was a logical extension to use B-mode imaging intraoperatively to evaluate the ascending aorta. The focal length of most commercially available ultrasonic probes prevents adequate visualization of the anterior wall of the aorta. Use of a sonolucent standoff eliminates this problem. The 5-MH.z probe provides excellent resolution of intraluminal detail, although a 7.5-MHz probe may be better. The Medasonics probe, because of the higher frequency and shorter focal length, was used without a standoff, and although this provided adequate images, use of a standoff appeared to be more optimal. The modifications in operative techniques can be relatively minimal (relocation of the arterial cannula on the ascending aorta or to the femoral artery) or extensive (hypothermic circulatory arrest with endarterectomy or graft replacement of the ascending aorta). Profound hypothermia and circulatory arrest may be associated with increased risks in the elderly patient. However, we have not found this to be the case, either among the patients in this study or in other patients undergoing ascending aortic or aortic arch replacement for aneurysmal disease. Similar findings have been reported by Culliford and associates [l]. The risk of stroke may be lower with the use of hypothermic circulatory arrest than with cannulation and clamping of the diseased aorta. The anatomical location of disease in this study differed from that reported by Tobler and Edwards [12]. They found very little disease posteriorly in the lower half of the aorta, but there were substantial amounts of plaque located posteriorly in the upper half of the aorta. In our study, no posterior plaque was found in the upper half of the aorta, and very little posterior plaque in the lower half of the aorta. Those patients requiring a technical change had disease located anteriorly with the exception of the 2 patients with circumferential disease. The smaller number of patients in our study may account for some of the differences, but the technique of evaluation (ultrasonic imaging versus gross pathological examination) is probably the major factor. Evaluation of larger numbers of patients undergoing cardiac surgical procedures will be necessary to determine the frequency of atherosclerotic disease of the ascending aorta. The incidence will likely be related to the age of the patients, and similarly, the percentage of patients requiring changes in cannulation or perfusion techniques will also be related to age. In summary, intraoperative ultrasonic imaging identifies atherosclerotic disease of the ascending aorta. It appears to be more accurate than digital palpation. It adds little time to the operative procedure and does not increase the risk of stroke or infection. When clinically significant atherosclerotic disease is present in the ascending aorta, intraoperative imaging permits the surgeon to modify cannulation, perfusion, and operative techniques to minimize the risk of stroke from atheroembolism. Use of the technique may reduce the risk of perioperative stroke in cardiac surgical patients, particularly in the elderly. Studies in larger numbers of patients or randomized trials will be necessary to determine if the technique significantly reduces the incidence of atheroembolic stroke when compared with conventional operative techniques. We thank Carla Kelley, Pat Renicke, and Becky Recar Nappier for technical assistance in the performance of the scans, and Lou Oxford for secretarial assistance in the preparation of the manuscript. References 1. Culliford AT, Colvin SB, Rohrer K, et al. The atherosclerotic ascending aorta and transverse arch: a new technique to prevent cerebral injury during bypass: experience with 13 patients. Ann Thorac Surg 1986;41: Utiey JR, Stephens DB. Prevention of major perioperative neurological dysfunction-a personal perspective. Perfusion 1986; 1 : Gardner TJ, Horneffer PJ, Masolio TA, et al. Stroke following coronary artery bypass grafting: A ten-year study. Ann Thorac Surg 1985;40: Stoney WS, Mulherin JL Jr, Alford WC Jr, et al. Unexpected death following aortocoronary bypass. Ann Thorac Surg 1976;21:52a Weinstein G, Killen DA. Innominate artery-coronary artery bypass graft in a patient with calcific aortitis. J Thorac Cardiovasc Surg 1980;79: Murphy DA, Hatcher CR. Coronary revascularization in the

6 344 MARSHALL ET AL Ann Thorac Surg 1989;48: presence of ascending aortic calcification: use of an internal mammary artery-saphenous vein composite graft. J Thorac Cardiovasc Surg 1984;87: Erath HG Jr, Stoney WS Jr. Balloon catheter occlusion of the ascending aorta. Ann Thorac Surg 1983;35: Cosgrove DM. Management of the calcified aorta: an alternative method of occlusion. Ann Thorac Surg 1983;36: Rousou JH, Engleman RM. Modified Fogarty clamp for the fragile aorta. Ann Thorac Surg 1981;32: Akins CW. Noncardioplegic myocardial preservation for coronary revascularization. J Thorac Cardiovasc Surg 1984;88: Barzilai B, Saffitz JE, Miller JG, Sobel BE. Quantitative ultrasonic characterization of the nature of atherosclerotic plaques in human aorta. Circ Res 1987;60: Tobler HG, Edwards JE. Frequency and location of atherosclerotic plaques in the ascending aorta. J Thorac Cardiovasc Surg 1988;96: Notice From the Southern Thoracic Surgical Association The Thirty-sixth Annual Meeting of the Southern Thoracic Surgical Association will be held at the Phoenician Golf and Tennis Resort, Scottsdale, AZ, November 9-11, There will be a $155 registration fee for the Scientific Session for nonmember physicians except for guest speakers, authors and coauthors on the program, and residents. There will be a $50 registration fee for attendees of the Postgraduate Course, which will be held the morning of Thursday, November 9,1989. The Postgraduate Course will provide in-depth coverage of thoracic surgical topics selected primarily as a means to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. Advance registration forms, hotel reservation cards, and details regarding transportation arrangements will be mailed to Association members. Nonmembers should write to the Secretary-Treasurer, Gordon F. Murray, MD. Gordon F. Murray, MD Secretary-Treasurer Southern Thoracic Surgical Association 1 11 East Wacker Drive Chicago, IL 60601