The age-related risks of central nervous system (CNS) morbidity appear to increase exponentially relative to cardiovascular risk. In a prospective 2,000-patient survey, investigators found that the stroke rate was 1% in patients less than 65 years of age. The stroke rate was 9%, however, in patients over 75 years of age. There was no age-dependent trend in incidence of low cardiac output or perioperative myocardial infarction.

There is some evidence that on-pump bypass results in significant physiologic changes versus off-pump procedures. In a small, prospective study, assessors demonstrated a 5% increase in brain water content in patients who underwent conventional coronary bypass with pump. This probably reflects an increase in inflammatory mediators. No such change occurred in patients undergoing beating heart procedures.

Several years ago, Dr. Murkin's group reported a study suggesting that beating heart surgery resulted in less neurocognitive dysfunction versus conventional bypass. However, there were significant differences in patient and procedural characteristics. Investigators said further studies would be needed to confirm the initial findings.

More recently, some prospective randomized trials have begun to appear. Van Dijk et al. reported on a relatively young population (mean age 61 years), of which 142 were randomized to conventional and 139 to off-pump procedures. They were unable to show a significant difference in cognitive decline at 3 or 12 months postoperatively. However, there was some evidence that cognitive function (learning) was better preserved in the beating heart patients.

A group from Hawaii (Lee et al.) undertook a small (n = 60) prospective randomized trial using a battery of cognitive testing and positron emission tomography (PET) scanning. They detected significantly more cerebral emboli in the conventional bypass group. There were no significant differences in cognitive dysfunction, but the beating heart group had significantly better performance upon repeat cognitive testing in the postoperative period.

A group from the United Kingdom (Zamvar et al.) undertook a prospective randomized trial in 60 patients with triple vessel coronary disease. In the off-pump group, there was use of a partial occlusion clamp. Cognitive performance was significantly better in beating heart group at both 1 and 10 weeks postoperatively. The conventional bypass group had a significantly higher incidence of deterioration in one or more of their cognitive tests.

Aortic instrumentation clearly confounds the neurocognitive results in bypass procedure studies, Dr. Murkin said. In one study of conventional bypass (Ura et al.) there was a 2.1% incidence of overt neurologic events. There was also a 3.4% incidence of new aortic lesions directly related to extent of atherosclerotic change in the ascending aorta. Patients having an atheroma greater than 4 mm had a 33% chance of having significant intimal damage. Investigators found 10 patients had severe intimal tears or flaps. Of these, 6 were related to clamping and 4 were due to cannulation. In this group, there was a 30% stroke rate.

In a retrospective review (Calafiore et al.) of 2,800 conventional and 2,000 beating heart procedures, the overall clinical stroke rate was 1%. Approx 500 beating heart procedures involved the use of a partial aortic occlusion clamp. Patients in this subgroup had the same stroke incidence as patients undergoing conventional bypass procedures.

Taken together, these studies suggest that beating heart procedures may offer better neurologic outcomes. However, these procedures thus far have generally been associated with less complete myocardial revascularization. The lower stroke rate appears to be primarily the result of less aortic instrumentation. Use of partial aortic clamping significantly decreases the benefit of off-pump surgery. These differences in cognitive outcomes are subtle, and appear to be greatest in older patients, or those who are sicker.