Beta-blockers and anesthetic preconditioning: friend or foe?

Abstract

To the Editor: We read with interest the recently-published article by Yu and Beattie reporting a meta-analysis investigating the effects of volatile anesthetics on morbidity and mortality in patients undergoing coronary artery bypass graft surgery.1 It was reported that volatile anesthetics do not reduce mortality compared to iv anesthesia, but reduce postoperative levels of troponin I as a marker of myocardial ischemic damage. Strikingly, patients receiving iv anesthetics had a significantly higher incidence (28%) of beta-blocker utilization compared to patients receiving volatile anesthetics. This is an extraordinarily important finding. Yu and Beattie conclude that “some myocardial protective effects of the inhalation anesthetics may have been counteracted as beta-blocker utilization was unequally distributed...”. We agree with this conclusion insofar as the disproportion of beta-blocker use may have influenced the results. However, we surmise that concurrent beta-blocker therapy inhibited the cardioprotective effects of volatile anesthetics and that the beneficial effects of the volatile anesthetics would have been even more pronounced, if no beta blockers had been used at all. This contention is derived from the fact that volatile anesthetic preconditioning is mediated by beta-adrenergic signalling. Unspecific blockade of beta-adrenergic receptors abrogates desflurane-induced preconditioning in isolated human atrial myocardium.2 Furthermore, volatile anesthetic preconditioning is abolished by concurrent blockade of beta1-adrenergic receptors by esmolol and downstream protein kinase A by the selective blocker H-89 in the rabbit heart in vivo.3 This result can also be obtained using the beta1 selective blocker metoprolol.4 Perioperative beta-blocker therapy is recommended by the American College of Cardiology/American Heart Association in cardiac high risk patients. However, evidence is emerging that the beneficial effects of perioperative beta-blocker therapy are less impressive than originally assumed.5 Patients at low cardiac risk might even be harmed by inadvertent bradycardia and hypotension.6 Thus, novel cardioprotective strategies need to be considered that are of equal benefit to low and high risk patients. Volatile anesthetic preconditioning is such a promising new strategy in perioperative cardioprotection. However, interactions with beta-blockers and other cardiovascular medications, potentially abrogating preconditioning need to be considered when anesthetic preconditioning is to be utilized for cardioprotection. The experimental data and this interesting finding of the meta-analysis suggest that volatile anesthetic preconditioning and beta-blocker therapy are incompatible cardioprotective strategies. This might, among other factors, explain the limited effects of volatile anesthetics on mortality and perioperative myocardial infarction in certain patient populations. Further studies are needed to investigate the interactions between cardiovascular medications and volatile anesthetic preconditioning.