MI risk heightened after total hip and knee replacement surgery

Total hip and total knee replacement procedures were associated with an increased risk for acute MI in the first 2 weeks after the operation, according to a report published in Archives of Internal Medicine.

Results of a retrospective cohort study revealed that the increased risk for MI was 25-fold during the first 2 weeks after total hip replacement and 31-fold after total knee replacement compared with matched controls.

MI risk remained elevated for 2 to 6 weeks after total hip replacement surgery (adjusted HR=5.05; 95% CI, 3.58-7.13) and then decreased to baseline levels. After total knee replacement surgery, risk did not differ from controls after the first 2 weeks.

Researchers calculated an absolute 6-week risk for MI of 0.51% for total hip replacement patients and 0.21% for total knee replacement patients.

The study included 95,227 patients in the Danish national registries who underwent either total hip or total knee replacement surgery from 1998 to 2007. Each patient was matched to three controls who had not undergone surgery. Follow-up primarily examined MI.

Additional risk factors

Arief Lalmohamed, PharmD, of Utrecht Institute for Pharmaceutical Sciences, Utrecht University, the Netherlands, told Cardiology Today that "the increased risk for MI is probably caused by direct effects of the surgery itself, as any major non-cardiac surgery is associated with hemodynamic stressors such as blood loss, arrhythmias and hypoxia, as well as indirect effects, mainly because of the stressful time before and shortly after surgery."

of Utrecht Institute for Pharmaceutical Sciences, Utrecht University, the Netherlands, told Cardiology Today that "the increased risk for MI is probably caused by direct effects of the surgery itself, as any major non-cardiac surgery is associated with hemodynamic stressors such as blood loss, arrhythmias and hypoxia, as well as indirect effects, mainly because of the stressful time before and shortly after surgery."

He said the effects are sharply diminished after 2 weeks, likely because the hemodynamic stressors are weakened by then and the stress is relieved.

Additionally, a previous MI within the 6 months before surgery further increased the risk for new MI during the first 6 weeks after total hip or knee replacement surgery. However, this association did not modify the relationship between total hip or knee replacement surgery and MI, according to the study results.

Age may also play a role, as the association between MI risk and surgery was strongest in patients aged 80 years and older, but researchers could not detect a significantly increased risk in patients aged younger than 60 years.

Assessment of risk

The researchers concluded that physicians should consider MI risk assessment during the first 6 weeks after total hip replacement surgery and the first 2 weeks after total knee replacement surgery.

"It is important to emphasize that, despite the high relative risk, in absolute numbers the risk is still low for the average patient. This may be used to reassure patients who are frightened by the high relative risk, which may not be meaningful if their baseline CV risk is low. This emphasis is particularly important because the preoperative period itself is very stressful for the patients and may further contribute to the increased risk for MI," Lalmohamed said.

On the other hand, "although there is an increased risk for MI shortly after surgery, not operating on these patients may put them at elevated risk as well," he added. 

Reference:

Lalmohamed A. Arch Intern Med. 2012;doi:10.1001/archinternmed.2012.2713.

Disclosure: Dr. Lalmohamed reports no relevant financial disclosures.