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March 2000
Approaches to the Prevention of Perioperative Myocardial Ischemia
Warltier DC, Pagel PS, Kersten JR.
Anesthesiology. 2000;92:53-9.
Commentary by Katherine Grichnik, M.D.
Return to the Current Literature Review Front Page
[ see abstract below ]
This is a brief review of approaches to the prevention of myocardial ischemia which examines established methods and presents potential future therapeutic agents. The authors point out that the anesthesiologist can often implement pharmacologic and anesthetic interventions to improve perioperative outcomes in patients with CAD undergoing surgical procedures. Myocardial oxygen supply and demand are nicely reviewed, and anesthesiologists are advised to make an aggressive attempt to favorably alter this balance, much as one would monitor for ischemia in a patient with known or suspected CAD. Known effective medical interventions are also reviewed. The most well-established intervention which has been shown to reduce morbidity and mortality is beta-adrenergic blockade, which is currently recommended by the American College of Physicians. Beta-adrenergic blockade should be titrated to individual patient response with consideration of individual co-morbidities such as bronchospastic lung disease. Alpha2 adrenergic blockade is also discussed. These drugs reduce central nervous system activity but with unpredictable declines in heart rate and vasomotor tone. Alpha2 blocking agents should be very useful in prevention of myocardial ischemia, but large scale, adequately powered trials have yet to conclusively document this effect. Nitrates have been documented to be useful to treat myocardial ischemia, however the prophylactic use of nitrates to prevent ischemia has not been conclusively proven to be effective. Further, if nitrates are used in the face of hypovolemia, detrimental reductions in coronary perfusion pressure can occur. Similarly, calcium channel antagonists have not been proven to prevent myocardial ischemia when used prophylactically.
Some of the new drugs on the horizon may act to improve myocardial oxygen supply and demand balance while others may directly protect the myocardium from injury. These drugs may alter myocardial oxygen demand at the cellular or mitochondrial level, independent of systemic and coronary hemodynamic state. As a caution, the article states that most of the data about these newer agents has been collected in people with severe CAD; the results must be extrapolated for use in patients with less severe CAD. These therapies are presented in a compact table within the article.
A short section on the selection of anesthetic technique is also covered. Neither regional nor general anesthesia has been proven to be more advantageous for people with CAD. There is also a discussion of possible cardioprotective effects of volatile anesthetics in experimental animals. These agents may enhance the functional recovery of stunned myocardium and reduce the extent of myocardial infarction after brief and prolonged coronary artery occlusion followed by reperfusion. Similarly morphine and other opioid agonists may have cardioprotective effects in vitro. Other beneficial effects of regional
blockade such as reduction in hypercoagulability and thrombotic events are also discussed.
The importance of preventing and treating myocardial ischemia in the postoperative period is also a topic discussed in the article. Proinflammatory responses, release of cytokines, hypercoagulability, diminished fibrinolytic activity, endothelial dysfunction and atherosclerotic plaque instability are all postulated as causes. The role of adequate analgesia and control of sympathetic responses is also considered.
In summary, this is a short, concise, easy to read article which should remind us of our duty to try to PREVENT adverse cardiac events. It also presents some less commonly known information about new agents for the treatment of ischemia, the possible role of volatile agents as cardioprotective agents and possible causes for ischemia in the perioperative period.
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ABSTRACT
Approaches to the prevention of perioperative myocardial ischemia
Warltier DC, Pagel PS, Kersten JR.
SOURCE:
Anesthesiology.
2000 Jan;92(1):253-9
ABSTRACT:
Goals for the perioperative management of patients with coronary artery disease include:
Prevent increases in sympathetic nervous system activity: reduce anxiety preoperatively; prevent stress response and release of catecholamines by appropriate use of opioids or volatile anesthetics and beta-adrenoceptor antagonists; beta-blocker therapy should be initiated before and continued during and after the surgical procedure.
Decrease heart rate: reduction in heart rate increases oxygen supply to ischemic myocardium and reduces oxygen demand; the use of beta-blockers is the most effective means to reduce or attenuate deleterious increases in heart rate.
Preserve coronary perfusion pressure: decreases in diastolic arterial pressure in the presence of severe coronary artery stenoses will lead to decreases in blood flow; preservation of perfusion pressure by administration of fluid or phenylephrine or a reduction in anesthetic concentration may be critical.
Decrease myocardial contractility: reduces myocardial oxygen demand and can be accomplished with beta-adrenoceptor antagonists or volatile anesthetics.
Precondition myocardium against stunning and infarction: in the future, this may accomplished by stimulating the adenosine triphosphate- dependent potassium channel with agents such as volatile anesthetics and opioid delta1-receptor agonists.
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