Lorenzo Guerrieri Wolf

Oxford University Hospitals NHS Trust, Oxford, ENG, United Kingdom

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Publications (4)15.96 Total impact

  • Lorenzo Guerrieri Wolf · Bikram P Choudhary · Yasir Abu-Omer · David P Taggart
    The Journal of thoracic and cardiovascular surgery 12/2008; 136(5):1392-3. DOI:10.1016/j.jtcvs.2008.07.003 · 3.99 Impact Factor
  • Lorenzo Guerrieri Wolf · Bikram P Choudhary · Yasir Abu-Omar · David P Taggart
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    ABSTRACT: 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. 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. 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. 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.
    The Journal of thoracic and cardiovascular surgery 04/2008; 135(3):512-20. DOI:10.1016/j.jtcvs.2007.07.062 · 3.99 Impact Factor
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    Lorenzo Guerrieri Wolf · Yasir Abu-Omar · Bikram P Choudhary · David Pigott · David P Taggart
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    ABSTRACT: 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. 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. 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). 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.
    The Journal of thoracic and cardiovascular surgery 02/2007; 133(2):485-93. DOI:10.1016/j.jtcvs.2006.10.002 · 3.99 Impact Factor
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    ABSTRACT: Cognitive dysfunction is common early after cardiac surgery. We previously reported that functional magnetic resonance imaging of the brain can detect subclinical changes in prefrontal cortical activation after coronary artery bypass grafting. In this study, we used functional magnetic resonance imaging to contrast perioperative prefrontal activation in patients undergoing on-pump and off-pump coronary artery bypass grafting and to relate differences to cerebral microembolic load. Functional images of the brain were acquired in 25 patients undergoing cardiac surgery (13 off-pump and 12 on-pump) before surgery and 4 weeks after surgery during performance of a verbal memory task of increasing complexity (n-back task). Continuous intraoperative transcranial Doppler scanning was performed to quantify the number of cerebral microemboli. Perioperative changes in task-associated prefrontal activation were compared between the 2 groups and were then correlated with the number of microemboli recorded during surgery. The median (interquartile range) number of detected microemboli was 35 (21-63) in the off-pump group and 254 (116-397) in the on-pump group (P < .005). Functional imaging performed before surgery demonstrated increased activity in the prefrontal regions with increasing task complexity. After surgery, there was a significant reduction in task-associated prefrontal activation in the on-pump, but not in the off-pump, group (P < .05). There was a negative correlation between the perioperative signal changes in the prefrontal region and the total number of microemboli (r = -0.63; P < .01). Patients undergoing on-pump, but not off-pump, surgery have a significant relative reduction in prefrontal activation, which correlates with intraoperative cerebral microembolic load. We hypothesize that this reduction in activation is related to subclinical functional impairments and that microembolic load is an important mechanism of perioperative cerebral insult.
    The Journal of thoracic and cardiovascular surgery 11/2006; 132(5):1119-25. DOI:10.1016/j.jtcvs.2006.04.057 · 3.99 Impact Factor

Publication Stats

73 Citations
15.96 Total Impact Points


  • 2008
    • Oxford University Hospitals NHS Trust
      • Department of Cardiothoracic Surgery
      Oxford, ENG, United Kingdom
  • 2006–2008
    • University of Oxford
      Oxford, England, United Kingdom