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Perioperative MI - prevention with Beta blockers - role of plaque stabilization
- Praveen Kumar Neema,, Manikandan S, Sinha PK, Rathod RC (22 September 2005)
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Preoperative Revascularization to Prevent Perioperative Myocardial Infarction
- Holger K. Eltzschig, Tobias Eckle (25 June 2005)
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Praveen Kumar Neema,, Anaesthesiologist Sree Chitra Tirunal Institute for Medical Sciences and Technology,, Manikandan S, Sinha PK, Rathod RC
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Editor – We read with interest the excellent review article on Perioperative myocardial infarction – aetiology and prevention (1) and we congratulate the author for his useful review on such a difficult subject. We would like to add and share our views on the role of b–blockers in reducing perioperative cardiac morbidity. The mechanisms by which b-blockers reduces perioperative cardiac events is unclear. Myocardial O2 balance may be improved by decreases in heart rate and myocardial contractility, thus preventing myocardial ischemia, reducing the size of the infarct, or both. Beta-blockade may reduce myocardial O2 consumption by suppressing lipolysis and thus causing myocardium to metabolize more glucose in relation to free fatty acids. Beta- blockers may also increase the stability of coronary plaques or increase the threshold for ventricular fibrillation in the presence of ischemia.(2) It is well recognized that the plaque disruption is related to the inherent strength of the plaque (stable or unstable plaque). The mechanisms that stabilize the atherosclerotic plaque with the use of b-blockade are not clear. Beta-blockers are routinely used in aortic dissection to reduce the shear stress. This effect is secondary to reduction in dp/dt that is force of myocardial contraction. It is believed that the reduced force results in reduced shearing effect. The similar physical factors may be responsible for the stability of the coronary atherosclerotic plaque observed with b-blockade. The plaque can be considered an obstacle in the path of the flowing blood and is struck continuously by the constituents of the flowing blood. Apparently, the likelihood of plaque rupture depends on - the inherent strength of the plaque, the force with which the plaque is struck; and the disruptive effect of the local turbulence produced because of stenosis. The higher the force with which it is struck by the constituents of the blood or weaker the plaque, more is the possibility of its rupture. We speculate that b-adrenergic blockers by decreasing myocardial contractility reduce the kinetic energy imparted to the constituents of blood. The reduced velocity of the constituents of blood results in decreased impact on the plaque and local turbulence; and the likelihood of plaque rupture. In other words b-blockade help plaque stabilization. Reference: 1.Priebe HJ: Perioperative myocardial infarction-aetiology and prevention. Br J Anaesth 2005; 95:3-19 2.Kjekshus J, Gullestad I: Heart rate as a therapeutic target in heart failure. Eur Heart J Suppl (1) H: H64-H69; 1999 Conflict of Interest:None declared |
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Holger K. Eltzschig, Anesthesiologist Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Germany, Tobias Eckle
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With great interest, we read the excellent review article by H.-J. Priebe on perioperative myocardial infarction (1). The author states that prospective, randomized investigations on the effect of preoperative coronary revascularization on short- and long-term cardiac and overall outcome do not exist (1). In contrast, such data have meanwhile become available. In fact, a recent study randomized patients with clinically significant coronary artery disease to undergo either revascularization or no revascularization before elective major vascular surgery (2). In short, 510 patients were included to undergo either coronary-artery revascularization or no revascularization before their surgery. Of the patients assigned to preoperative coronary-artery revascularization, percutaneous coronary intervention was performed in 59 percent, and bypass surgery was performed in 41 percent. At 2.7 years after randomization, mortality in the revascularization group was 22 percent and in the no- revascularization group 23 percent (p=0.92). Within 30 days after the vascular operation, a postoperative myocardial infarction occurred in 12 percent of the revascularization group and 14 percent of the no- revascularization group (P=0.37). The authors conclude that based on these findings, a strategy of coronary-artery revascularization before elective vascular surgery is questionable. References: 1. Priebe HJ. Perioperative myocardial infarction--aetiology and prevention. Br. J. Anaesth. 2005;95(1):3-19. 2. McFalls EO, Ward HB, Moritz TE, Goldman S, Krupski WC, Littooy F, et al. Coronary-artery revascularization before elective major vascular surgery. N Engl J Med 2004;351(27):2795-804. Conflict of Interest:None declared |
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