Author Affiliations: Department of Anesthesiology, University of California, San Francisco, and San Francisco Veterans Affairs Medical Center, San Francisco, California.
Lalmohamed et al1 used epidemiologic analysis to test the association between total hip replacement (THR) or total knee replacement (TKR) and acute myocardial infarction (AMI). Not surprisingly, during the first 2 postoperative weeks, the risk of AMI was elevated in both populations of patients undergoing THR or TKR. The risk was elevated for 6 weeks in patients undergoing THR but only for 2 weeks in those undergoing TKR. It has been previously established that patients undergoing surgical procedures have an increased risk of MI.1 The risk factors for perioperative cardiac morbidity and mortality have been established for many years, and although different studies2,3 find slightly different risk factors, there is remarkable consistency over time: age older than 60 years, coronary artery disease, peripheral vascular disease, congestive heart failure, recent MI, and the standard risk factors for coronary artery disease, including diabetes mellitus, hypertension, smoking, and hyperlipidemia. Occasionally, an investigator will suggest that one risk factor or another is no longer important, such as MI in the last 30 days, but subsequent studies will identify once again that recent MI, MI in the last 6 months, or MI in the last year remains a risk factor for subsequent MI. Epidemiologic studies are limited by the population of patients in the database. If no one performs elective surgery on a patient within 30 days of an AMI, then that variable will not be significant in epidemiologic analysis. Recent MI is still a risk factor for cardiac morbidity; it simply is not a significant risk factor identified in the study because there are no patients with that risk profile in the database. Failure to demonstrate that a risk factor is significant does not imply the risk factor is not still a clinical issue; it simply implies one could not demonstrate the effect with the database. Infrequently, a new perioperative risk factor is identified, such as erectile dysfunction.4 It is highly likely that these “new” risk factors are caused by peripheral vascular disease, which is highly associated with coronary artery disease rather than being a new independent perioperative risk factor.
The perioperative period is stressful to patients. A total of 5% to 15% of patients with cardiac risk have myocardial ischemia in the 24 hours before surgery.2,5- 7 Thinking about surgery increases cardiac risk. A total of 20% to 40% of patients at risk have an episode of myocardial ischemia in the first perioperative week. Perioperative myocardial ischemia is associated with an increased risk of short- and long-term cardiac morbidity and mortality.2,5- 8 In the present study, Lalmohamed et al1 confirmed that major surgery is a risk for AMI and the risk factors of age of 60 years or older, age of 80 years or older, male sex, previous AMI, heart failure, and cerebrovascular disease increased that risk. The age when preoperative risk begins to increase is remarkably stable at approximately 60 years of age.2,5- 8 The risk of prior MI decreased with time since the MI. There were a number of medications that also appeared to increase risk, including nonsteroidal anti-inflammatory drugs, β-blockers, potassium-sparing diuretics, organic nitrates, and antiplatelet drugs. Each of these medications is likely a surrogate marker for either older age or the presence of coronary artery disease rather than a causal risk factor. It is not surprising that patients taking β-blockers, for instance, have a higher risk of MI.9 Because β-blockers are a primary therapy for coronary artery disease, patients taking these medications have a much higher risk of having coronary artery disease.9 In epidemiologic studies, it is critical to realize that causality is difficult or impossible to establish and many factors are surrogate markers for increased preexisting risk rather than causal factors.
The present study once again confirms that the perioperative period increases cardiac risk. Physicians must go further than establishing risk factors; physicians must actively work to reduce perioperative risk. The appropriate use of preoperative β-blockers,5,6 clonidine,7 statins, and aspirin reduces perioperative cardiac risk. There is a high risk of discontinuation of therapy with anti-ischemic agents in the perioperative period, despite level I evidence for continuation, with significant cardiac morbidity from discontinuation.9 Physicians must carefully review perioperative medications and ensure they are appropriately managed in this critical perioperative period of high cardiac risk. It is important for physicians caring for patients in the perioperative period to recognize the potential for cardiac morbidity and mortality and then appropriately use the armamentarium of medical therapies we now have to reduce cardiac risk, prevent perioperative MIs, and prevent cardiac deaths. In their present study, Lalmohamed et al1 clearly reinforce the importance and significance of the cardiac risk and the need to prevent perioperative cardiac morbidity and mortality.
Correspondence: Dr Wallace, Department of Anesthesiology, San Francisco Veterans Affairs Medical Center, 4150 Clement St, San Francisco, CA 94121 (email@example.com).
Published Online: July 23, 2012. doi:10.1001 /archinternmed.2012.3776
Financial Disclosure: None reported.
Funding/Support: This work has been supported by the Northern California Institute for Research and Education and the Veterans Affairs Medical Center, San Francisco, California.
Wallace AW. Risk of Acute Myocardial Infarction in Patients With Total Hip or Knee ReplacementComment on “Timing of Acute Myocardial Infarction in Patients Undergoing Total Hip or Knee Replacement: A Nationwide Cohort Study”. Arch Intern Med. 2012;172(16):1235-1236. doi:10.1001/archinternmed.2012.3776