Transesophageal echocardiography and transcranial doppler monitoring in coronary surgery without cardiopulmonary bypass: preliminary results

The risk of stroke following CABG: one possible strategy to reduce it?

OBJECTIVE

Stroke remains a devastating complication of coronary artery bypass grafting (CABG): we evaluated whether a more aggressive diagnostic and therapeutic approach can reduce its incidence.

METHODS

Between January 1998 and January 2002, 1388 consecutive patients underwent isolated on pump CABG with blood cardioplegia. Among the first 627 patients (Group A), Echo-Doppler study (DS) was performed only in selected patients (58) with history of cerebrovascular disease (CVD) and/or carotid bruit; in 761 patients (Group B), DS was performed routinely. Carotid endarterectomy (CEA) was performed in 45 patients in Group A associated to CABG during cardiopulmonary bypass (CPB) and in 90 patients in Group B under local anaesthesia before CABG. Brain CT scan was performed in all cases with postoperative neurological symptoms.

RESULTS

The two groups were homogeneous for age, sex, associated diseases, history of CVD, number of graft and CPB time. There were no differences in terms of hospital mortality between Group A (22/627: 3.5%) and Group B (21/761: 2.75%); p=0.5. Postoperative stroke was observed in 24/627 (3.82%) patients of Group A and in 2/761 (0.26%) of Group B (p<0.001). Hospital mortality for stroke was higher in Group A (12/627: 1.91%) than in Group B (0/761; p<0.001) as well as the incidence of non-fatal stroke (Group A 12/627: 1.91% versus Group B 2/761: 0.26% p=0.006).

CONCLUSIONS

Preoperative DS, performed in all cases of CABG, followed by CEA under local anaesthesia in patients with critical carotid stenosis reduces the incidence of postoperative stroke.

Neuroprotection during cardiac surgery: strategies to reduce cognitive decline

Although the population receiving cardiac surgery is older and therefore more prone to cognitive deterioration, these difficulties have declined over the last ten years. It is likely that the multiple changes introduced to cardiac surgery over time have had a cumulative benefit in protecting the brain. The most likely causes of cognitive difficulties are microemboli delivered to the brain during surgery, altered cerebral perfusion and an inflammatory response. The interventions that have been implemented can be divided into those which have attempted to reduce the potential causes of damage and those aimed at reducing the impact by attempting to protect the brain. The evidence for three main types of intervention (equipment, techniques and drugs) is reviewed in this paper. Although many interventions are available only a few have shown a clear benefit. Progress in the future will require larger studies to address this multifactorial problem.

Further reduction in stroke after off-pump coronary artery bypass grafting: a 10-year experience

BACKGROUND

Perioperative stroke is a devastating complication after coronary artery bypass grafting (CABG). The reported incidence of neurologic complications after conventional CABG is 3% to 7%. With improved monitoring and surgical techniques, we have been able to achieve a drastic reduction in the stroke rate in our institution. This study evaluates the incidence of neurologic sequelae in patients who underwent off-pump CABG.

METHODS

Over a 10-year period from January 1990 to September 2000, off-pump coronary artery bypass (OPCAB) operation was performed on 2,800 patients of the 18,037 patients undergoing CABG during that time frame at the Escorts Heart Institute and Research Centre. Initially, OPCAB was performed selectively in the high-risk group of patients (atheromatous aorta, renal impairment, chronic obstructive pulmonary disease, octogenarians, etc). Lately we performed multivessel OPCABs electively in about 60% to 65% of the patients undergoing CABG. Results. Mean age of the patients was 58.0 +/- 9.91 years (range 27 to 85 years) and mean number of grafts was 2.9 per patient. Neurologic complications (stroke/transient ischemic attack) occurred in 0.14% of patients. Overall hospital mortality in OPCAB patients was 2.14%, whereas mortality from neurologic complications was 0.07%. Predicted mortality (National Society of Thoracic Surgeons Cardiac Surgery Database Risk Model for CABG) for the entire patient group was 3.86% (p < 0.001). Conclusions. Although current techniques of monitoring and surgical procedures have significantly reduced the risk of stroke from CABG, our data strongly support OPCAB as a technique to further reduce stroke after CABG, especially in the high-risk group of patients.

Beating heart surgery or conventional CABG: are neurologic outcomes different?

Although there has been much debate about the causes of neurologic complications associated with coronary artery bypass grafting (CABG), there is good evidence linking such complications with some of the pathophysiologic changes associated with use of conventional cardiopulmonary bypass (CPB). Several studies indicate that it is possible to significantly lower risk of stroke and other central nervous system (CNS) morbidity in patients undergoing CPB for CABG by application of selected techniques and equipment modifications. The resurgence of interest in coronary revascularization by using beating heart surgery (BHS) offers a unique opportunity to evaluate neurologic outcome independent of CPB. Currently, BHS would appear to significantly reduce morbidity in the elderly and to decrease the costs and resource use in coronary revascularization patients. It is hoped that by understanding the mechanisms of CNS injury associated with CABG, techniques can be developed to decrease the risk of neurologic injury associated with coronary revascularization, whether or not CPB is used. Definitive conclusions regarding outcomes after best practice CPB or BHS await large-scale, risk-stratisfied multicenter trials.

Is the number of microembolic signals related to neurologic outcome in coronary bypass surgery?

Coronary artery bypass surgery (CABG) without cardiopulmonary bypass (CPB) may potentially reduce the number of microembolic signals (MES) associated with aortic manipulation or generated by the pump circuit, resulting in a better neurologic outcome after surgery. Our aim was to compare the frequency of MES and neurologic complications in CABG with and without CPB. Twenty patients eligible to routine CABG without CPB were randomized to surgery with CPB and without CPB and continuously monitored by transcranial Doppler. Neurologic examination was performed in all patients before and after surgery. The two groups were similar with respect to demographics, risk factors, grade of aortic atheromatous disease and number of grafts. The frequency of MES in the nonCPB group was considerably lower than in CPB patients, however, we did not observe any change in the neurologic examination during the early postoperative period. Neurologic complications after CABG may be related to the size and composition of MES rather than to their absolute numbers. A large prospective multicentric randomized trial may help to elucidate this complex issue.

Inapparent hemodynamic insufficiency exacerbates ischemic damage in a rat microembolic stroke model

BACKGROUND AND PURPOSE

Patients with severe carotid artery stenosis may have more severe ischemic damage after embolic stroke than patients without this abnormality. Unilateral proximal carotid occlusion (UCO) alone typically does not induce infarction in normotensive rats. The aim of this study was to investigate whether UCO increases infarct size after microembolic, experimental stroke.

METHODS

Microembolic infarction was induced in 2 groups of Sprague-Dawley rats by injecting 2000 microspheres (50-micrometer diameter) intracranially from the external carotid artery. The common carotid artery (CCA) was either ligated just after the injection (CCA occlusion group, n=8) or left intact (CCA open group, n=8). In the control group (n=4), vehicle without microspheres was injected and the CCA was ligated. Twenty-four hours later, the brains were removed and infarct volumes measured. Perfusion-weighted imaging was used to evaluate the cerebral circulation before and after CCA occlusion with and without microsphere injection in a separate group of animals (n=16).

RESULTS

All animals in the microemboli groups survived and had only a slight hemiparesis 24 hours after occlusion. No neurological deficits were observed in the control group. Infarct volumes were 145+/-57 mm(3) in the CCA occlusion group and 45+/-26 mm(3) in the CCA open group (P <0.01). There were no infarctions detected in the control group. Perfusion-weighted imaging showed that cerebral blood flow decreased after the CCA occlusion in both experiments with and without the microsphere injection.

CONCLUSIONS

UCO alone does not induce ischemic damage, but it worsens ischemic lesion size after multiple microemboli. This is probably due to the slight cerebral perfusion insufficiency caused by UCO. These results suggest that patients with cerebral hemodynamic insufficiency, such as those with severe carotid stenosis, may have increased ischemic damage after microembolic events.

Transcranial Doppler assessment of cerebral embolic disorders

Transcranial Doppler ultrasound allows noninvasive monitoring of the large intracranial vessels. Microembolic signals (MES) have been observed under a variety of circumstances, especially in symptomatic carotid stenosis, high-risk cardiac conditions, and surgical procedures (such as carotid endarterectomy and cardiopulmonary bypass surgery). Technical considerations have presented numerous challenges to the interpretation of these signals, many of which appear to represent small emboli traveling in the blood flow. The technical aspects of these MES are discussed and their significance in relation to cerebral ischemia and its prevention are examined in some detail.