Superiority of transesophageal echocardiography in detecting aortic arch atheromatous disease: identification of patients at increased risk of stroke during cardiac surgery

Neurologic complications of vascular surgery

Technological advances in the management of cardiovascular disorders have resulted in an expansion of eligibility criteria for treatment, as well as an increased demand for improved outcomes. Neurologic complications after coronary artery bypass surgery, particularly stroke and cognitive dysfunction, substantially increase mortality, strain health care resources, and reduce the clinical effectiveness of the procedure. Carotid endarterectomy can be both the optimum stroke preventative strategy as well as a cause of stroke. The trend toward minimally invasive endovascular procedures, which has provided non-surgical options for both coronary and cerebral vascular occlusive lesions, is slowly being compared to conventional surgical and medical therapies. The identification of risk factors and mechanisms of adverse cerebral outcomes of these myriad vascular procedures is essential in improving their clinical effectiveness and patient applicability.

Mobile atheroma of the aortic arch is an underestimated source of embolization

BACKGROUND

Mobile atheroma are associated with increased perioperative strokes in patients undergoing coronary artery bypass surgery. Peripheral embolization is an additional risk. Transesophageal echocardiography (TEE) accurately identifies mobile atheroma. Recent reports have discussed the possible influence of anticoagulant therapy in promoting peripheral cholesterol embolization.

METHODS

Fourteen patients with mobile atheroma were treated with anticoagulation. A review of literature reporting results and complications of anticoagulation in the treatment of this condition was compared with our recent experience.

RESULTS

Between 1994 and 1996, 14 patients with peripheral embolization and mobile atheroma confirmed by TEE were anticoagulated. Clinical follow-up between 6 to 30 months has demonstrated no further evidence of systemic embolization since anticoagulation. Furthermore, repeat TEE in 3 of 14 patients no longer visualized mobile atheroma.

CONCLUSIONS

Mobile atheroma are recognized sources for embolization. Patients with generalized atherosclerosis should be screened for this condition in cases of systemic embolization. Anticoagulation may have therapeutic considerations in the management of this condition.

Aortic atheroma is related to outcome but not numbers of emboli during coronary bypass

BACKGROUND

The relation between aortic atheroma severity and stroke after coronary artery bypass grafting is established. The relation between atheroma severity and other outcome measures or numbers of emboli has not been determined.

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 m any emboli may be nonatheromatous in nature.

Perioperative Stroke, Encephalopathy, and Central Nervous System Dysfunction

The leading cause of mortality in adult populations throughout the world is atherosclerosis, which results in cardiovascular and cerebrovascular complications and consumes substantive health care resources. The impact of atherosclerosis on patients undergoing surgery is also considerable, given the multiple stresses occurring during, and especially following, the surgical procedures, thereby precipitating vascular morbidity. Perioperative cerebrovascular morbidity and mortality occur in approximately 10% of the 600,000 patients who undergo cardiac surgery annually, consuming approximately $13 billion, which is expended on in-hospital, intensive care unit (ICU), and long-term specialized care for these neurological complications of stroke, encephalopathy, and cognitive dysfunction. Furthermore, risk of these outcomes will continue to increase as the surgical population ages. Principal among the etiologies of focal stroke and encephalopathy appear to be perioperative hypotension and precipitation of macroemboli and microemboli. As a result, new detection techniques for these events have been instituted, including (1) continuous hemodynamic monitoring, for detection of hypotensive episodes; (2) transesophageal echocardiography, for detection of aortic atherosclerosis, a potential source for emboli; and (3) transcranial Doppler sonography, for detection of cerebral emboli, as well as determination of cerebral blood flow. Recent large-scale multicenter studies have identified risk factors and indices for perioperative central nervous system (CNS) morbidity. Regarding therapy, a number of pharmacological approaches are currently under consideration; principal among these approaches are agents that can modulate the excitotoxic response, including glutamate receptor antagonists (NMDA, AMPA, metabotrophic), calcium channel blockers, free radical scavengers, and agents that modify the inflammatory white cell response. Although a number of laboratory, animal, and smaller clinical trials have been conducted, only one large-scale multicenter program to date has been conducted to assess the efficacy of adenosine modulation. These data, collected in more than 4,000 patients undergoing cardiac surgery, suggest that in addition to mitigation of myocardial injury, stroke also may be modulated by enhancing adenosine concentration in the area of cerebral ischemia. However, these preliminary findings must be validated in appropriately powered clinical trials. Finally, postoperative stroke and encephalopathy consume substantive resources, resulting in prolonged length-of-stay (17 days in-hospital 10 days for patients suffering Q-wavc infarction, vs 7 days for patients having no adverse outcome) and prolonged length-of-stay in the ICU following surgery (5 vs 3 vs 2 days, respectively). Hospital costs increase by approximately 3- to 4-fold in patients who suffer CNS outcomes following surgery. In conclusion, perioperative CNS morbidity and mortality is a critical problem that affects a substantial portion of the surgical population and consumes considerable health care resources. Over the next several years, attention must be focused on this important problem, and clinical and research resources should be redirected toward the solution of perioperative CNS morbidity.

Significantly reduced incidence of stroke during coronary artery bypass grafting using transesophageal echocardiography

OBJECTIVE

Protruding atheromas of thoracic aorta have been identified as a source of systemic emboli and a major cause of stroke following cardiac surgery. This prospective study used transesophageal echocardiography (TEE) to identify atherosclerosis of thoracic aorta intraoperatively. The influence of risk factors was studied. Finally the impact of modifying surgical technique on the outcome was evaluated.

METHODS

Seven-hundred and ninety-two patients undergoing coronary artery bypass grafting (CABG) were evaluated with TEE. Depending on the location and extent of thoracic aortic disease various surgical modifications were carried out, e.g. hypothermic circulatory arrest with aortic arch atherectomy, CABG on beating heart and others. The stroke rate in this group of patients was determined and analysed.

RESULTS

Of the 114 patients with grade II and III atheromas of aortic arch and ascending aorta in whom surgical modifications were done, none had stroke. The overall stroke rate in the study group was 0.76%, six patients had stroke. Stepwise logistic regression identified age, diabetes, serum triglycerides and VLDL as important risk factors. Associated carotid artery disease and calcium on chest X-ray (CXR) were identified as important predictors of disease.

CONCLUSIONS

Intraoperative TEE is an invaluable modality for evaluating the thoracic aorta. There is significant reduction in stroke rate following identification of atheromas and modification of surgical technique.

Adverse cerebral outcomes after coronary bypass surgery. Multicenter Study of Perioperative Ischemia Research Group and the Ischemia Research and Education Foundation Investigators

BACKGROUND

Acute changes in cerebral function after elective coronary bypass surgery is a difficult clinical problem. We carried out a multicenter study to determine the incidence and predictors of -- and the use of resources associated with -- perioperative adverse neurologic events, including cerebral injury.

METHODS

In a prospective study, we evaluated 2108 patients from 24 U.S. institutions for two general categories of neurologic outcome: type I (focal injury, or stupor or coma at discharge) and type II (deterioration in intellectual function, memory deficit, or seizures).

RESULTS

Adverse cerebral outcomes occurred in 129 patients (6.1 percent). A total of 3.1 percent had type I neurologic outcomes (8 died of cerebral injury, 55 had nonfatal strokes, 2 had transient ischemic attacks, and 1 had stupor), and 3.0 percent had type II outcomes (55 had deterioration of intellectual function and 8 had seizures). Patients with adverse cerebral outcomes had higher in-hospital mortality (21 percent of patients with type I outcomes died, vs. 10 percent of those with type II and 2 percent of those with no adverse cerebral outcome; P<0.001 for all comparisons), longer hospitalization (25 days with type I outcomes, 21 days with type II, and 10 days with no adverse outcome; P<0.001), and a higher rate of discharge to facilities for intermediate- or long-term care (69 percent, 39 percent, and 10 percent ; P<0.001). Predictors of type I outcomes were proximal aortic atherosclerosis, a history of neurologic disease, and older age; predictors of type II outcomes were older age, systolic hypertension on admission, pulmonary disease, and excessive consumption of alcohol.

CONCLUSIONS

Adverse cerebral outcomes after coronary bypass surgery are relatively common and serious; they are associated with substantial increases in mortality, length of hospitalization, and use of intermediate- or long-term care facilities. New diagnostic and therapeutic strategies must be developed to lessen such injury.

Severity of aortic atheromatous disease diagnosed by transesophageal echocardiography predicts stroke and other outcomes associated with coronary artery surgery: a prospective study

Advanced atheromatous disease of the thoracic aorta identified by transesophageal echocardiography (TEE) is a major risk factor for perioperative stroke. This study investigated whether varying degrees of atherosclerosis of the descending aorta, as assessed by TEE, are an independent predictor of cardiac and neurologic outcome in patients undergoing coronary artery bypass grafting (CABG). Intraoperative TEE of the descending aorta was performed on 189 of 248 patients participating in a randomized controlled trial of low (50-60 mm Hg) or high (80-100 mm Hg) mean arterial pressure during cardiopulmonary bypass for elective CABG. Aortic atheromatous disease was graded from I to V in order of increasing severity by observers blinded to outcome. Measured outcomes were death, stroke, and major cardiac events assessed at 1 wk and 6 mo. Nine of the 189 patients with TEE examinations had perioperative strokes by 1 wk. At 1 wk, no strokes had occurred in the 123 patients with atheroma Grades I or II, while the 1-wk stroke rate was 5.5% (2/36), 10.5% (2/19), and 45.5% (5/11) for Grades III, IV, and V, respectively (Fisher's exact test, P = 0.00001). For 6-mo outcome, advancing aortic atheroma grade was a univariate predictor of stroke (P = 0.00001) and death (P = 0.03). By 6 mo there were one additional stroke, three additional deaths, and one additional major cardiac event. Atheromatous disease of the descending aorta was a strong predictor of stroke and death after CABG. TEE determination of atheroma grade is a critical element in the management of patients undergoing CABG surgery.

High reproducibility in the interpretation of intraoperative transesophageal echocardiographic evaluation of aortic atheromatous disease

Intraoperative decisions are often based on interpretation of results from transesophageal echocardiography (TEE). One such area is the intraoperative evaluation of atheromatous disease of the thoracic aorta and subsequent classification or grading. These grading schemes are predictive of stroke after cardiac surgery. Since intraoperative strategies may be modified based on this TEE aortic atheroma grading, assessment of the interobserver variability of TEE findings between observers is essential. Forty TEE videotape segments imaging three portions of the thoracic aorta (ascending, arch, descending) were selected from 189 reports of a larger cohort. Three independent, blinded observers, experienced in TEE, evaluated these examinations for atheroma severity. If a TEE segment had insufficient data, "uninterpretable" was recorded. Weighted kappa coefficients of agreement were calculated on the three data sets. Mean weighted kappa coefficients for the three observers A, B, and C were 0.69, 0.74, and 0.72, for the ascending, arch, and descending aorta segments, respectively, representing excellent agreement. We have demonstrated uniformly high agreement for interpretation of TEE, which indicates the excellent reproducibility of TEE grading and stratification of aortic atheroma. Reproducibility within and across specialties and institutions is essential for widespread application of TEE for evaluation of the thoracic aorta.

Coronary artery disease in the geriatric population

The elderly represent an increasingly important and challenging subset of the population of patients with ischemic heart disease. They are more likely to have comorbid conditions, atypical presentations, and unfavorable outcomes than their younger counterparts. Some of these findings are undoubtedly related to the structural and functional changes in the cardiovascular system associated with aging. The available data suggest that standard pharmacologic, thrombolytic, and definitive revascularization techniques have important roles in the therapy of geriatric patients but have been underused.

Aortic atheromatosis and risks of cerebral embolization

With the advent of transesophageal echocardiography, aortic atheromatosis has emerged as an important source of cerebral embolization. Mobile atheromatous plaque in the ascending aorta and aortic arch has been shown to constitute a strong and independent risk factor in patients with stroke. In patients undergoing coronary bypass surgery, it is the single most important contributing factor to perioperative neurologic morbidity. Emboli originating in the heart, aorta, and proximal cerebral vasculature have been observed intraoperatively in patients undergoing coronary bypass surgery, especially when aortic clamps are released. The constitution of these emboli is unclear, although an indeterminate fraction undoubtedly represents dislodged atheromatous material. The impact of such embolization in terms of neurologic outcome is currently under investigation. Prevention of embolization from mobile aortic atheroma in patients undergoing cardiac surgery may require modification of surgical technique. Secondary prevention in patients with a history of embolization can only be determined once the natural history of such lesions is established.

Adverse neurologic events: risks of intracardiac versus extracardiac surgery

Intracardiac operations such as valve replacements have typically carried a higher risk (4.2% to 13%) of overt central nervous system outcome, compared with coronary artery bypass grafting (CABG) procedures (0.6% to 5.2%). This is likely owing to the increased risk of macroembolization of air or particulate matter from the surgical field during intracardiac surgery. The periods of highest risk for emboli are during aortic cannulation and especially during release of aortic clamps and weaning from bypass. The number of embolic events measured with transcranial Doppler is significantly higher in patients undergoing valve surgery compared with coronary surgery, particularly during cardiac ejection and immediately after bypass. However, there is current evidence that neurologic risk is increasing in patients undergoing CABG owing to the tendency to operate on older patients with more severe aortic atherosclerosis and cerebrovascular disease. Patients having an intracardiac procedure combined with a CABG procedure may be at particularly high risk for adverse neurologic outcome. For all cardiac surgical patients, there is some cause for optimism in that risk may be minimized by improved assessment (e.g., intraoperative transesophageal or epiaortic echocardiographic scanning of the ascending aorta to identify patients at risk) and monitoring (e.g., detection of embolic phenomena, using transesophageal echocardiography or transcranial Doppler technology). Furthermore, in the future, development and testing of more ideal cerebroprotective drugs may allow amelioration of neurologic injury, either by pretreating all patients at risk, or possibly even by delaying treatment until after the suspected occurrence of an insult.

The role of CPB management in neurobehavioral outcomes after cardiac surgery

Recent developments in techniques for managing cardiopulmonary bypass are outlined with a view toward interventions aimed at decreasing the incidence of perioperative central nervous system dysfunction and overt stroke. Recent reports assessing central nervous system dysfunction after hypothermic and normothermic cardiopulmonary bypass are reviewed and critiqued along with data assessing techniques for cerebral protection during hypothermic circulatory arrest. Controversy surrounding optimal pH management is explored along with a proposal that pH-stat may be most satisfactory to ensure better brain cooling where circulatory arrest is anticipated, whereas alpha-stat may avoid cerebral hyperemia and thus decrease the cerebral embolic load during moderate hypothermic cardiopulmonary bypass. Newer developments in cerebral monitoring techniques are also reviewed.

Effect of cannula length on aortic arch flow: protection of the atheromatous aortic arch

Atheromatous disease in the transverse aortic arch is associated with an increased incidence of perioperative stroke. In addition, tissue erosion in the aortic arch is caused by the high-velocity jet emerging from an aortic cannula during cardiopulmonary bypass (CPB), termed the "sandblast effect". To quantify this phenomenon, flow in the aortic arch was measured intraoperatively by epiaortic ultrasonography in 18 patients undergoing CPB. All were cannulated in the ascending aorta, 10 with a short (1.5 cm) cannula and 8 with a long (7.0 cm) cannula. The peak forward aortic flow velocities (mean +/- standard deviation) measured on the caudal luminal surface of the aortic arch were 0.80 +/- 0.23 m/s off CPB and 2.42 +/- 0.69 m/s on CPB (p < 0.001) for the short cannula and 0.53 +/- 0.20 m/s off CPB and 0.18 m/s on CPB for the long cannula. Thus, during CPB the peak forward aortic flow velocity with the short cannula was significantly greater (p < 0.001) than before CPB, whereas the long cannula produced a lower peak forward aortic flow velocity during CPB. Furthermore, Doppler examination revealed severe turbulence in the aortic arch in all patients with a short cannula. No arch turbulence, however, was seen in 7 patients with a long cannula, and only mild turbulence appeared in the remaining patient with a long cannula. These results show that use of a long aortic cannula results in a significant decrease in peak forward aortic flow velocity and turbulence in the aortic arch during CPB, which may reduce the risk of erosion or disruption of existing atheroma and ensuing embolic complications.