Solid and gaseous cerebral microembolization after biologic and mechanical aortic valve replacement: investigation with multirange and multifrequency transcranial Doppler ultrasound.

OBJECTIVE: Cerebral microembolization is a well-recognized phenomenon after cardiac valve replacement, but the relative proportion of solid and gaseous emboli is uncertain. Particulate microemboli are thought to be the most damaging. With the use of multifrequency transcranial Doppler ultrasound, we compared the number and nature of microemboli in recipients of biologic and mechanical aortic valve prostheses. METHODS: The middle cerebral arteries of 60 patients were monitored bilaterally with a new-generation transcranial Doppler ultrasound (Embo-Dop, DWL Elektronische Systeme GmbH, Singen, Germany) that rejects artefacts online and automatically discriminates between solid and gaseous microemboli. All recordings were performed during a 30-minute period 1 day before and at a mean of 5 days and 3 months after isolated aortic valve replacement with a biologic (30, group B) or mechanical (30, group M) prosthesis. RESULTS: The patients in group B were older, with a mean age of 70.6 +/- 9.7 years versus 55.4 +/- 9.4 years (P < .005) in the patients in group M. Biologic prosthesis recipients were all taking aspirin (no warfarin); patients with mechanical valves were well anticoagulated with warfarin both 5 days and 3 months after surgery. None of the patients had solid microemboli preoperatively. Five days postoperatively, the absolute number of cerebral microemboli was 145 and 594 for total microemboli (P = .001) and 41 and 182 for solid microemboli (P = .002) in groups B and M, respectively. At 3 months, the absolute number was 65 and 608 for total microemboli (P < .001) and 10 and 188 for solid microemboli (P < .001) in groups B and M, respectively. Solid microemboli accounted for 16% of the total microembolic load in group B compared with 31% in group M (P = .05) at 3 months. CONCLUSIONS: Solid cerebral microemboli represent approximately one third of the total cerebral microembolic load after mechanical aortic valve replacement and are detectable in the majority of such patients both 5 days and 3 months after surgery. The neurofunctional consequences of this phenomenon should be carefully assessed.

Diabetes mellitus as a predictor for radial artery vasoreactivity in patients undergoing coronary artery bypass grafting.

OBJECTIVES: Our purpose was to examine the impact of diabetes mellitus (DM) on vasoreactivity and endothelial function of radial artery (RA) grafts ex vivo. BACKGROUND: The arteriopathy associated with DM may influence the surgeon's choice of conduits for revascularization. Arterial conduits and especially the RA are prone to vasospasm in the perioperative period. METHODS: The study population consisted of 98 patients with coronary artery disease undergoing coronary artery bypass grafting by using RA grafts. The maximum contractions of RA segments induced by K+ (66 mmol/l) and clinically important vasoconstrictors such as adrenaline (5 x 10(-5) mol/l), angiotensin II (10(-6) mol/l), and prostaglandin F2alpha (PGF2alpha) (10(-6) mol/l) were recorded. Relaxation of RA rings to carbachol (10(-4) mol/l) was used as a measure of endothelial function. Multivariate analysis was then applied to determine the role of clinical characteristics on the vasomotor responses to these agents. RESULTS: Vessels from patients with DM had greater contractions in response to adrenaline (p < 0.05), angiotensin (p < 0.05), and PGF2alpha (p < 0.01) compared with non-DM vessels, despite the similar vasoconstrictions induced by high K+ (p = NS). Diabetes mellitus was also associated with smaller vasorelaxations in response to carbachol (p < 0.001). In multivariate analysis, DM was an independent predictor of RA contractions in response to adrenaline (beta [SE] 3.085 [1.410], p = 0.031), angiotensin II (beta [SE] 3.838 [1.552], p = 0.015), and PGF2alpha (beta [SE] 4.609 [1.908], p = 0.018) but not K+ (p = NS). Diabetes mellitus was also independently associated with the vasorelaxations in response to carbachol (beta [SE] -15.645 [2.622], p = 0.0001). CONCLUSIONS: Diabetes mellitus is associated with impaired endothelial function and greater contractions of RA grafts in response to all of the clinically relevant vasoconstrictors. These findings suggest that the RA of diabetic patients may be more prone to spasm in response to endogenous vasoconstrictors, an observation with important implications for surgeons' choice of conduits in this cohort of patients.

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.