Heart attack risk balloons after surgery to fix hip or knee

Patients with osteoarthritis are vulnerable to hip and knee pain due to the wearing away of the joint’s cartilage lining. One solution is to surgically replace the faulty joints. A total of 1.8 million total hip replacement and total knee replacement surgeries are performed worldwide each year.

The surgeries are straightforward and patients are often released from the hospital within three days. But a new study finds that patients who have their hips and knees replaced have a dramatically increased risk of suffering a heart attack in the first weeks after their surgeries.

The Centers for Disease Control and Prevention estimates that roughly 785,000 Americans have their first heart attack each year and another 47,000 have a repeat attack. Someone in the U.S. has a heart attack every 34 seconds, according to the American Heart Assn.

The new study, published online Monday in Archives of International Medicine, is the first to assess the long-term risk of heart attacks after a total hip or knee replacement surgery.

The study was based on data collected by the Danish government. The study participants were drawn from a population of 5.5 million people who were tracked over nine years.

The analysis, led by Arief Lalmohamed from Utrecht University in the Netherlands, looked at 66,524 hip replacement patients and 28,703 knee replacement patients who were 18 years old or older. They were matched to patients in control groups who were of the same age and sex yet had not had the surgeries or any knee/hip problems.

Compared to patients in the control groups, patients who had a total hip replacement were 31 times more likely to have a heart attack in the first two weeks after their surgeries, the researchers found. In addition, the risk for patients who had knee replacements was 25 times greater during that two-week period.

In the hip replacement patients, the risk of heart attack remained elevated for six weeks after surgery, but for knee replacement patients this risk returned to baseline levels after only two weeks.

It should be noted that the absolute risk of nonfatal and fatal heart attack during the first six weeks was still low – 0.51% for patients who had hip replacements and 0.21% for those who had knee replacements.

The researchers found that the age of the patient and whether they’d suffered a heart attack before strongly influenced their risk of having another heart attack after surgery. For example, among patients who had their hips replaced, heart attack risk was highest in patients who were 80 years old or older; on the flip side, there was no increased risk for patients younger than 60. This trend was weaker among patients who had total knee replacements.

Additionally, if a patient had suffered a heart attack in the six months before surgery, the risk of a new heart attack quadrupled during the first six weeks after surgery but did not modify the relationship between total hip or knee replacement and heart attack.

The authors said they weren’t sure why these surgeries made patients so much more vulnerable to heart attacks, but they offered some theories. Both hip and knee replacement procedures require surgeons to cut through the femur, where bone marrow is stored. That may cause a complication called marrow embolization, which restricts blood supply to the heart and causes cardiac stress. Embolization occurs primarily in hip replacement patients, which could account for the differences in risk between hip replacement and knee replacement surgeries.

Also, the effects of anesthesia on the cardiovascular system might add to increased stress on the heart, the study authors wrote.

You can read the study online here.

In a commentary that accompanied the study, Dr. Arthur W. Wallace of UC San Francisco called on doctors to take special precautions for patients who had recent heart attacks. In preparation for surgery, these patients should be treated with beta blockers, clondine, statins, aspirin and other medications that work to reduce the risk of heart attack, he wrote. Wallace studies cardiac risks for patients just before, during and right after surgery.

The study was funded in part by GlaxoSmithKline, which makes medicines for patients with heart and circulatory disease, among other ailments.

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