Modification of surgical technique for ascending aortic atherosclerosis: impact on stroke reduction in coronary artery bypass grafting

Gaseous and solid cerebral microembolization during proximal aortic anastomoses in off-pump coronary surgery: the effect of an aortic side-biting clamp and two clampless devices

OBJECTIVES

Intraoperative cerebral microembolism is a cause of cerebral dysfunction after cardiac surgery, and particulate microemboli are the most damaging. Using a new-generation transcranial Doppler ultrasound, we compared the number and nature of microemboli in patients undergoing off-pump coronary artery bypass grafting during performance of proximal anastomoses with three techniques: an aortic side-biting clamp and two clampless devices (the Enclose II device [Novare Surgical Systems, Inc, Cupertino, Calif] and the Heartstring II device [Guidant Corporation, Santa Clara, Calif]) developed to obviate the need for an aortic side-biting clamp, thereby reducing the number of cerebral microemboli.

METHODS

Bilateral continuous monitoring of the middle cerebral arteries was performed with a multirange, multifrequency transcranial Doppler device that both automatically rejects artifacts online and discriminates between solid and gaseous microemboli. Recordings were continuously undertaken during performance of 66 proximal aortic anastomoses in 42 patients. Thirty-five anastomoses were performed with an aortic side-biting clamp, 20 with the Enclose device, and 11 the Hearstring device.

RESULTS

Most microemboli occurred during application/insertion and removal of each device from the ascending aorta. The median number (interquartile range) of total microemboli was 11 (6-32) during side clamping, 11 (6-15) with the Enclose device, 40 (31-48) with the Heartstring device (P < .01). The proportion of solid microemboli was significantly higher in the side-clamp group (23%) compared with 6% and 1% in the Enclose and Heartstring groups, respectively (P < .01).

CONCLUSIONS

Avoidance of aortic side clamping results in a significant reduction in the proportion of solid microemboli detected with transcranial Doppler. As solid microemboli are probably the most damaging, use of the Enclose and Heartstring devices may represent an important strategy for minimizing cerebral injury during proximal aortic anastomoses.

Initial clinical experience with the Heartstring

OBJECTIVE

The Heartstring is one of the devices that enable proximal anastomosis without clamping the aorta. We have applied the device not only to low-risk patients with normal aortas but also to high-risk patients with diseased aortas. The purpose of this study was to investigate the initial outcomes of using this device.

METHODS

The Heartstring was used on 87 patients between January and December 2004. The patients comprised 62 men and 25 women 48-86 years old (mean 68.4 +/- 8.4 years). The ascending aorta was evaluated by computed tomography (CT) scanning before surgery. If a patient's aorta was severely calcified, epiaortic echocardiography was performed. The aortas were ranked into four grades, and the preoperative patient's status were evaluated by the EuroSCORE. Angiography was performed on the third postoperative day.

RESULTS

CT scanning revealed that 74 patients had no calcification in the ascending aorta, 10 patients had scattered calcification, and 3 patients had plate-like calcification. The EuroSCORE was 6.86 +/- 1.03. We performed 93 proximal anastomoses and 149 distal anastomoses. The average distal anastomosis was 1.6 +/- 0.6 sites per graft. Of the distal anastomoses, 74.2% were to the circumflex artery territory. Postoperative coronary angiography revealed that all grafts were patent.

CONCLUSION

The Heartstring facilitates safe proximal anastomosis, even in high-risk patients. Their short-term outcome was good. The device assists in bypassing circumflex artery territory. Long-term follow-up is necessary.

Surgical management of the atherosclerotic ascending aorta: is endoaortic balloon occlusion safe?

BACKGROUND

Occlusion of the atherosclerotic ascending aorta by an endoaortic inflatable balloon has been proposed as an alternative to conventional cross-clamping to prevent injury to the vessel and distal embolization of debris. The safety and the effectiveness of endoaortic occlusion have not been documented in this setting.

METHODS

Endoaortic occlusion was employed in 52 of 2,172 consecutive patients. Surgeon's choice was based on preoperative identification of aortic calcifications or intraoperative epiaortic ultrasonographic scanning. Deaths and strokes were analyzed casewise and in aggregate.

RESULTS

In 10 patients (19.2%), the endoaortic balloon had to be replaced by the ordinary cross-clamp because of incomplete occlusion (n = 5), hindered exposure (n = 2), or balloon rupture (n = 3). In-hospital death occurred in 13 patients (25%), and stroke on awakening from anesthesia in 2 (3.8%). The death rate of patients treated by endoaortic occlusion was significantly higher compared with all other patients (4.2%, p < 0.0001) and with the expected estimate by European System for Cardiac Operative Risk Evaluation (10.5%, p = 0.05). By multivariable analysis, use of endoaortic occlusion was independently associated with in-hospital death (odds ratio = 5.609, 95% confidence interval: 2.684 to 11.719). Although the stroke rate was higher in the endoaortic occlusion group compared with all other patients, the difference was only possibly significant (3.8% versus 0.8%, p = 0.067).

CONCLUSIONS

In this series, the endoaortic occlusion was frequently ineffective, and was associated with a significantly higher risk of in-hospital death and a numerically higher risk of stroke.

Stroke and Encephalopathy After Cardiac Surgery

Background and Purpose— As a result of advances in surgical, anesthetic, and medical management, cardiac surgery can now be performed on older, sicker patients, some of whom have had prior cardiac interventions. As surgical mortality has declined in recent years, attention has focused on the complications of stroke and encephalopathy after cardiac surgery.

Summary of Review— Patients with preexisting cerebrovascular disease are at increased risk for these untoward neurological outcomes, which are associated with longer lengths of hospital stay, higher costs, and greater mortality. The mechanisms underlying these neurological events may include microemboli and hypoperfusion during surgery, and postoperative atrial fibrillation. Predictive models, based on information available before surgery, allow identification of these “high risk” patients.

Conclusion— Establishing the degree of functionally significant vascular disease of the brain before surgery should be an essential part of the preoperative evaluation, particularly when modifications in surgical technique or novel neuroprotective agents are being evaluated.

Effects of off-pump versus on-pump coronary artery bypass grafting on function and viability of circulating endothelial progenitor cells

OBJECTIVE

Off-pump coronary artery bypass grafting may result in fewer myocardial and vascular complications than on-pump. Although differences in aortic manipulations likely play a role, the systemic responses of endothelial progenitor cells to both types of operations have not been examined. We sought to examine endothelial progenitor cell characteristics after off-pump versus on-pump coronary artery bypass grafting.

METHODS

Twenty patients undergoing off-pump or on-pump coronary artery bypass grafting were prospectively enrolled and had endothelial progenitor cells isolated and cultured from their peripheral blood before and 24 hours after surgery. Endothelial progenitor cells were identified by fluorescent dual lectin/low-density lipoprotein binding. Their number, phenotype characteristics, proliferation, migratory function, and viability were determined in a blinded fashion.

RESULTS

Patient characteristics and numbers of grafts were equivalent. Endothelial progenitor cells had similar phenotypes between groups before and after surgery. Off-pump and on-pump coronary artery bypass grafting resulted in similar increases in endothelial progenitor cell numbers and showed equivalent proliferation activity. However, endothelial progenitor cell migratory function was higher in off-pump patients (25.3 +/- 5.0 vs 5.0 +/- 1.0 cells per high-powered field for off-pump vs on-pump coronary artery bypass grafting, respectively; P = .04). Postoperative endothelial progenitor cell viability adjusted for preoperative baseline was also higher after off-pump than on-pump coronary artery bypass grafting by 72.4% +/- 14.6% (P = .01). Endothelial progenitor cells of on-pump patients were less viable after surgery than before surgery, whereas the reverse was observed in off-pump patients.

CONCLUSIONS

Both on-pump and off-pump coronary artery bypass grafting elicit mobilization of endothelial progenitor cells into the peripheral blood. On-pump coronary artery bypass grafting, however, impairs the migratory function and viability of these vascular repair cells, which are conversely preserved after off-pump surgery. Further work is necessary to determine whether the function and viability of endothelial progenitor cells correlate with vascular outcomes and whether their therapeutic modulation may one day benefit coronary artery bypass grafting patients.

Hypothermic Circulatory Arrest Enables Aortic Valve Replacement in Patients With Unclampable Aorta

BACKGROUND

Atheroembolic complications associated with clamping a severely diseased ascending aorta during aortic valve replacement may result in unacceptable mortality and morbidity. Different management options include hypothermic circulatory arrest to replace the aortic valve, an aortic endarterectomy, or tube graft replacement of the aorta to allow safe application of cross-clamp before aortic valve replacement.

METHODS

From 1998 to 2004, 70 patients who underwent aortic valve replacement had an aorta that was unclampable. Median age was 76 years; 33 (47%) were women; 46 (66%) had concomitant coronary artery bypass grafting; 9 (13%) had concomitant mitral valve surgery; and 4 (6%) were reoperations. Hypothermic circulatory arrest was used to replace the aortic valve alone, to do an aortic endarterectomy, or replace the ascending aorta with a tube graft.

RESULTS

Operative mortality was 4%. There were 8 (11%) strokes and 1 (1.4%) transient ischemic attack. Statistical analysis showed no association between circulatory arrest period and occurrence of adverse cerebral events. There was no significant difference among the three groups when operative mortality and cerebral events were compared.

CONCLUSIONS

Hypothermic circulatory arrest is an important adjunct that allows aortic valve replacement to be performed with an acceptable mortality but with an increased risk of cerebral event in this high-risk and elderly group of patients.

Risk factors for late stroke after coronary artery bypass grafting

BACKGROUND

Postoperative stroke is a severe complication immediately after coronary artery bypass grafting, and it significantly deteriorates the postoperative quality of life if it occurs in the long term. It was the aim of our study to determine factors associated with the occurrence of new strokes during long-term follow-up after coronary artery bypass grafting.

METHODS

From 387 of 500 patients undergoing coronary artery bypass grafting (age, 67 years [33-84 years]; 76% male) who had intraoperative epiaortic ultrasonography for assessment of ascending aortic wall thickness, a complete follow-up regarding postoperative stroke was achieved. The median follow-up time was 52 months (9-74 months).

RESULTS

A stroke occurred in 26 (7%) of 387 patients, and the cumulative freedom from stroke was 99%, 95%, and 89% after 1, 3, and 5 years, respectively. A significantly lower freedom from stroke was present in patients with an age of 70 years or more (P = .007), preoperative unstable angina (P = .031), chronic obstructive pulmonary disease (P = .009), carotid artery disease (P < .001), preoperative history of neurologic events (P < .001), and a maximum ascending aortic wall thickness of 4 mm or more (P = .010). Multivariate analysis revealed preoperative history of neurologic events (P = .021) to be an independent risk factor.

CONCLUSION

Patients with ascending aortic atherosclerosis, older age (> or =70 years), preoperative unstable angina, chronic obstructive pulmonary disease, and carotid artery disease are at risk for late postoperative stroke after coronary artery bypass grafting. A history of neurologic events is of special predictive importance.

Atherosclerosis of the ascending aorta as a major determinant of the outcome of cardiac surgery

Epiaortic ultrasonography has high sensitivity for the detection of atherosclerosis. In several studies, the technique has identified atherosclerosis of the ascending aorta as the major risk factor for stroke after cardiac surgery. The level of risk depends on the presence, location and extent of disease when the ascending aorta is surgically manipulated. This knowledge enables clinicians to focus on the diagnostic and surgical technique and to consider the various options. Routine use of intraoperative epiaortic ultrasonography should be applied so that surgical manipulation of the ascending aorta can be reduced or, if possible, avoided in patients with atherosclerosis of the ascending aorta. Alternatively, if major manipulation such as clamping must be performed in the presence of severe atherosclerosis, the use of intra-aortic filters could be considered.

Selective Use of Off-Pump Coronary Bypass Surgery Reduces Mortality and Neurologic Morbidity Associated with High-Risk Coronary Bypass Surgery: A 400-Case Comparative Experience

The frequency of use of off-pump coronary artery bypass (CAB) surgery to surgically treat coronary artery disease has varied greatly from center to center and from surgeon to surgeon because of preference, training, and experience. We report an experience with 400 consecutive isolated CAB procedures selectively managed with on-pump or off-pump surgery, according to the perceived potential for aortic embolization or stroke as determined by clinical and imaging determinations. The off-pump CAB group (46 patients) was 7.1 years older (P < .05) and had an 11% lower ejection fraction (P < .03) than the on-pump group. There was no difference in gender, urgency of surgery, hemodynamic stability, angina class, or incidence of prior myocardial infarction. All 400 patients underwent intraoperative transesophageal echocardiography, and many underwent an epiaortic study to supplement image quality. Patients without palpable or imaged advanced aortic disease or deemed to be at clinically high risk for stroke (advanced age, prior strokes, or advanced cerebrovascular or peripheral vascular disease) underwent on-pump procedures requiring 55 minutes of aortic ischemia and 97 minutes of high-flow, high-pressure bypass on average. All others underwent off-pump procedures. The numbers of grafts per patient were similar (3.2 on-pump, 2.8 off-pump; = ns). There was no in-hospital or 30-day mortality in either group. Using the New York State risk-adjustment algorithm, we found the predicted mortality rate for the off-pump group was higher (2.24% on-pump versus 5.54% off-pump, P = .008). The postoperative length of stay was longer in the off-bypass group (3.67 days versus 4.31 days, P = .003). The frequencies of hospital readmission and perioperative complications (renal, pulmonary, infection, bleeding, cardiac, neurologic) were similar, and there were no postoperative strokes in either group. The selective use of off-pump surgery safely managed patients at higher risk for perioperative stroke and associated embolic multisystem organ failure and death. Individual surgeon and center-wide use of a selective approach is recommended as an alternative to a single-procedure nonselective approaches.

Preoperative Computed Tomography or Intraoperative Epiaortic Ultrasound for the Diagnosis of Atherosclerosis of the Ascending Aorta?

BACKGROUND

Extensive atherosclerotic disease, usually first diagnosed intraoperatively, is the most important risk factor for postoperative stroke after cardiac surgery. The aim of this study was to investigate if preoperative computed tomography (CT) is comparable with intraoperative epiaortic ultrasound to diagnose severe atherosclerosis in the ascending aorta.

METHODS

The study included 20 consecutive patients who underwent elective coronary artery bypass surgery. 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 240 segments to compare.

RESULTS

Epiaortic ultrasound detected atherosclerosis in 16.7% +/- 2.4% of the segments, a rate significantly higher than with CT ( P < or =.03). There was a low reliability between the 2 methods, indicated by kappa coefficients of 0.45 or lower.

CONCLUSIONS

The CT method is inferior to epiaortic ultrasound, today's gold standard, in diagnosing the extent and location of atherosclerosis of the ascending aorta. Other methods, possibly magnetic resonance imaging, should be considered.