MI risk higher after total hip, knee replacement

Patients who have total hip or total knee replacement surgery are at higher risk for myocardial infarction (MI) afterward, according to a new study.

Researchers performed a retrospective cohort study using data from national registries in Denmark to compare the timing of MI in patients who had total knee or total hip replacement with that of matched controls. Patients who had a primary total knee or total hip replacement surgery from Jan. 1, 1998 through Dec. 31, 2007 were each matched by age, sex and geographic region with three controls who had not had surgery. Controls and patients were all followed for acute MI. Hazard ratios (HRs) were calculated and adjusted for disease and medication history. The study results were published online July 23 by Archives of Internal Medicine.

A total of 95,227 patients were included in the study, 66,524 who had total hip replacement and 28,703 who had total knee replacement. They were matched with 286,165 controls. Total hip patients had a mean age of 71.9 years, and 39.6% were men; total knee patients had a mean age of 67.2 years, and 37.6% were men. Within the first two weeks after surgery, total hip patients and total knee patients had a higher risk for MI compared with controls (adjusted HRs, 25.5 and 3.09, respectively). Total hip patients continued to have an elevated risk two to six weeks after surgery (adjusted HR, 5.05), but risk in total knee patients did not differ from controls after two weeks had passed. Total hip patients had an absolute six-week risk for MI of 0.51%, compared with 0.21% in total knee patients.

The authors noted that they did not have data on other risk factors for acute MI, such as body mass index and smoking; inpatient use of anticoagulant medications; or use of general anesthesia, among other limitations. However, they concluded that compared with controls, patients who undergo total hip or total knee replacement surgery have a much higher risk for acute MI within the first two postoperative weeks. “Risk assessment of [acute] MI should be considered during the first 6 weeks after THR surgery and during the first 2 weeks after TKR surgery,” the authors wrote.

An accompanying commentary pointed out that cardiac risk is higher in general after surgery and said that physicians must actively work to decrease that 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,” the commentary author wrote.