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Ann Thorac Surg 1997;64:454-459
© 1997 The Society of Thoracic Surgeons
Departments of Neurology, Anesthesiology, and Cardiothoracic Surgery, Cornell University Medical College, New York, New York
Accepted for publication February 27, 1997.
| Abstract |
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Methods. Using transesophageal echocardiography, we determined the severity of atheroma in the ascending, arch, and descending aortic segments in 84 patients undergoing operations. Seventy patients were monitored using transcranial Doppler ultrasonography.
Results. The incidence of stroke was 33.3% among 9 patients with mobile plaque of the arch and 2.7% among 74 patients with nonmobile plaque (p = 0.011). Cardiac complications were not significantly related to atheroma severity in any aortic segment. Length of stay was significantly related to atheroma severity in the aortic arch (p = 0.025) and descending segment (p = 0.024). The presence of severe atheroma in both the arch and descending segments was associated with significantly longer hospital stays as compared with patients with severe atheroma in neither segment (p = 0.05). Numbers of emboli were greater in patients with severe atheroma at clamp placement, although the differences did not achieve statistical significance.
Conclusions. Aortic atheroma severity is related to stroke and to the duration of hospitalization after coronary artery bypass grafting. The lack of correlation between numbers of emboli and atheroma severity suggests that many emboli may be nonatheromatous in nature.
| Introduction |
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The advent of transesophageal echocardiography (TEE) has enabled surgeons and anesthesiologists to obtain a detailed view of the aorta during operations and to quantify atheromatous plaques according to thickness and the presence of mobile components [12]. The importance of the aorta as a source of atheroemboli and hence as a risk factor for perioperative stroke was highlighted by Katz and associates [12], who found a stroke incidence of 25% among patients with mobile plaque of the arch as opposed to only 2% of patients with nonmobile plaque. Several subsequent studies have confirmed the strong correlation between severe aortic atheroma and stroke or death [13, 14]. The relation between atheroma severity and nonneurologic indices of clinical outcome has not yet been determined.
Emboligaseous, fatty, and atheromatouscan now be detected intracranially in vivo using transcranial Doppler ultrasonography (TCD) [6, 15]. A correlation between the numbers of such emboli and aortic atheroma severity has been suggested previously, but not validated [16]. We conducted this study to determine the impact of severe aortic atheromatosis on a number of outcome variables and to define its relation to numbers of emboli.
| Material and Methods |
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Anesthesia
Morphine and lorazepam or midazolam served as premedication, and thiopental, fentanyl, and pancuronium was used for induction. Anesthesia before and after bypass was maintained with additional boluses of fentanyl and midazolam. Postoperative care was administered according to institutional standards.
Cardiopulmonary Bypass
Membrane oxygenerators were used in conjunction with nonpulsatile centrifugal pumps. All patients received anticoagulation with sodium heparin to an activated clotting time in excess of 500 seconds. A 40-µm blood filter (Ultipor; Pall Biomedical, East Hills, NY) was incorporated into the arterial perfusion line. Bypass was initiated at flow rates of 2.4 L · min-1 · m-2 at a body temperature of 37.5°C and was reduced to 1.6 L · min-1 · m-2 at 28°C. We regulated the systemic blood pressure pharmacologically using anesthetic agents and vasoconstrictors to maintain mean arterial pressures between 50 and 80 mm Hg. Operative staff were blinded to the TCD findings during the procedure.
Standard Transesophageal Echocardiography
We performed biplanar (n = 47) or monoplanar (n = 37) TEE on 84 patients after the induction of general anesthesia and endotracheal intubation and again at the end of the surgical procedure. A 5-MHz TEE probe (Acuson, Mountain View, CA) and an Acuson 128 XP system were used. All studies were recorded on standard VHS videotape and interpreted subsequently. We assessed the severity of ascending, arch, and descending aortic atheroma individually and graded each segment according to a standardized system, as follows: grade I, normal to mild intimal thickening; grade II, severe intimal thickening; grade III, atheroma protruding less that 5 mm into the lumen; grade IV, atheroma protruding 5 mm or more into the lumen; and grade V, atheroma with a mobile component [12]. The ascending segment was adequately imaged in only 75 patients, the arch in 83 patients, and the descending segment in all 84 patients. All videotapes were reviewed independently by two echocardiographers, and differences of opinion exceeding one grade were referred to a third person for arbitration.
Intraoperative Transcranial Doppler Ultrasonography Monitoring
We monitored continuously the middle cerebral artery of 70 patients from before aortic cannulation to after discontinuation of bypass using a 2-MHz pulsed-wave TCD probe (Medasonics-CDS, Fremont, CA) placed on the patient's temple at a depth of 4.5 to 6.0 cm. Embolic signals (ES) were defined as high-amplitude, unidirectional, transient signals less than 0.1 second in duration and associated with a characteristic chirping sound. Data were stored on disks and subsequently reviewed and counted manually by a single examiner. Concurrently, the number of aggregate ES were recorded by an automated counter. This number was used only during flurries of embolization too numerous to count manually. We recorded the timing of all major events and the numbers of ES occurring within 4 minutes of aortic cannulation, inception and termination of bypass, aortic clamping, and clamp release.
Neurologic Assessment
Forty-six patients were examined by a neurologist blinded to the TCD data. These patients were examined preoperatively, in the immediate postoperative period, and before discharge. Neurologic evaluation of the remaining 38 patients consisted of chart review only. Stroke was defined as focal perioperative deficit of the central nervous system persisting for more than 24 hours.
Cardiac Evaluation
All cardiac complications were determined during the hospitalization, documented by the responsible cardiologist or anesthetist, and then entered into a data base system. Patient charts and the data base were reviewed subsequently. Complications were classified as minor sustained (supraventricular arrhythmia) or major (ventricular arrhythmia, myocardial infarction, or cardiogenic shock with failure to come off bypass or requirement of intraaortic balloon pump).
Statistical Analysis
Comparison of proportions between groups was performed using
2 test or Fisher's exact test, as appropriate. Comparison of continuous quantities between groups was performed using one-way analysis of variance. When analysis of variance revealed significant differences between groups, Scheffé's post hoc test was used for pairwise comparison. All statistical analyses were performed using STATISTICA/W (version 5.0; Stat Soft, Tulsa, OK) on a PC-DOS/Windows 95 platform.
| Results |
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The mean atheroma grade for each aortic segment was not significantly higher in patients with major cardiac complications than in those with minor or no complications (Table 2
). Furthermore, the incidence of major cardiac complications was no different in patients with mobile plaque of the arch or descending aorta than in patients without (see Table 2
).
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| Comment |
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The association between aortic atheromatosis and stroke has been established previously both within and outside the context of cardiac operations [8, 1315, 19, 20]. In a prospective study involving 250 patients with stroke and 250 controls, Amarenco and colleagues [19] found protruding plaque in 14.4% of patients with stroke but in only 2% of control subjects. Plaques of all thicknesses were associated with stroke, but the association was strongest for plaques more than 4 mm thick. An even stronger association between mobile plaque and stroke has been shown in patients undergoing cardiac procedures [1214, 20]. Katz and associates [12] found a stroke incidence of 25% in patients with mobile plaque of the arch, as opposed to only 2% in those with nonmobile plaque. In another series, the stroke incidence was determined to be 45% among patients with mobile descending-segment plaque but only 3% in the remainder [14]. The association between protruding atheroma and stroke found by Amarenco and colleagues [19] was strongest for the ascending aorta when combined with the proximal arch, was much weaker for the distal arch, and was absent for descending aortic disease. In agreement with Amarenco and colleagues, we found the association between mobile plaque and stroke to be strong in the arch and weak in the descending segment. This is not surprising because atheromatous cerebral emboli emanating from the aorta can only arise from atheromatous debris in the ascending segment and proximal arch.
The relation between aortic atheroma and cardiac complications after cardiac operations has not yet been established. Although patients with major cardiac complications after cardiac procedures appeared to have slightly more atheromatous aortas, the prevalence of mobile plaques in this subgroup was not significantly higher than in patients without major complications. Similarly, Gold and co-workers [2] found a relation between aortic atheroma and major cardiac complications by combining these with stroke. One mechanism by which aortic atheroma could cause cardiac complications is intraoperative coronary atheroembolization [21, 22]. Several anecdotal reports have described such atheromatous coronary embolization from the aortic root [22], and some cases have had serious consequences [21]. Atheroemboli are also common in the coronary arteries of patients who die during coronary angioplasty, and their presence correlates with cardiac complications after the procedure [23]. Although embolization of atheromatous debris to the coronary arteries may be associated with transient or permanent cardiac ischemia, it does not seem to have as devastating an effect as atheromatous cerebral embolization.
In this study, the severity of aortic atheroma did not correlate significantly with the number of TCD-detected emboli. This finding is somewhat surprising in view of the strong relation between the severity of aortic atheroma and stroke [12, 14, 20] and suggests that a majority of emboli may be nonatheromatous. Large numbers of gaseous emboli would easily obscure the relation between the number of liberated atheromatous emboli and the amount of atheromatous deposit on the aortic wall. All types of cerebral emboli contribute to the neurologic insult. At present, however, there is no certain way using Doppler techniques to differentiate between emboli of differing constitution [24, 25]. Hence, the relative damage caused by atheromatous, gaseous, or other embolic material remains to be determined.
The outcome variables analyzed in this study correlated best with atheroma severity in the arch of the aorta. Not surprisingly, the correlation was poor in the descending segment, reflecting the fact that emboli from this segment do not enter the cerebral circulation. The lack of a relation between outcome and ascending-segment atheroma is likely artifactual and attributable to the difficulty in visualizing this segment using TEE.
The overall effect of aortic atheromatosis is clearly reflected in LOS, the "gold standard" measure of short-term procedural success. Procedural costs increase by thousands of dollars for each added day of hospitalization. The cost-effectiveness of performing preoperative TEE on all candidates for cardiac procedures in an attempt to identify those at high risk for increased LOS and multisystem complications must be judged against the increased procedural cost in those with unidentified severe aortic atheromatosis.
| Footnotes |
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| References |
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