A person can suffer a heart attack only three days after a knee replacement (or other joint replacement) surgery.

Just HOW does this happen?

You may already be aware that knee and hip replacement surgery greatly increases the risk of a heart attack – not long-term, but in the early postop period.

This can be pretty darn scary to someone about to undergo such an operation.

In a study led by Yuqing Zhang, D.Sc., of Boston University School of Medicine, risk of heart attack was significantly higher in those who’d had knee replacement surgery in the month following, when compared to a non-surgical control group.

The study results (Arthritis & Rheumatology, 2015) show that patients with osteoarthritis “who have total knee or total hip replacement surgery are at increased risk of heart attack in the immediate postoperative period,” points out Dr. Zhang.

Okay, so you know this as a fact. But WHY is this? HOW does it happen?

Why a Knee Replacement Surgery Ups Heart Attack Risk

People over 60 are at greatest risk. Any major surgery raises heart attack risk. A Denmark study of 95,000 patients showed that:

• Compared to same-age/gender adults who didn’t have joint replacement, those who had knee replacement were 30 times more likely to have a heart attack—within two weeks of the surgery. (Archives of Internal Medicine, 2012)

Reason #1. Loss of hemodynamic balance. This means disruption of blood flow during surgery which can harm the heart.

Reason #2. The patient has comorbidities: body mass greater than 30; pre-existing heart rhythm disorder; pre-existing heart disease or congestive heart failure; use of NSAIDS.

Two more risk factors are revision knee (or hip) surgery and having the operation on both knees at the same time. (Basilico et al, Arthritis & Rheumatology, 2008)

Reason #3. The patient’s body is not used to trauma. Now here is where we get a layperson’s explanation, but it really makes a lot of sense…

Heart Attack Soon after Knee Replacement Caused by Shock to a Weak Body

Suppose we have a person over 60 who has never worked out. He’s sedentary. No dumbbell presses, barbell squats, kettlebell swings, deadlifts, hill sprints, sled pulls or rigorous hiking in his lifestyle.

His body is not used to getting hit hard. His body is not trained to take a hit.

When you kill it at the gym, you subject your body to trauma. Do this repeatedly, consistently over time, and you toughen up your body.

You teach it to deal with trauma. It learns to constructively respond to trauma. The trauma is the strenuous workout – you know, the kind that pummels you but at the same time makes you feel incredible.

Now imagine this very same body undergoing a knee replacement. Joint replacement surgery is serious trauma to the body.

Though it’s not the same kind of trauma as a hardcore gym workout, it’s still trauma – a major hit – all the same. The highly fit body is USED to trauma.

The body “thinks” that the knee (or hip) replacement surgery is just another gym workout. The cardiovascular system is not shocked at this hit.

There’s no surprise. It’s been there many times before (the gym). The body doesn’t know that this time, though, the trauma is from a surgery rather than numerous intense weightlifting sets or staircase dashes holding weights.

All the body know is that, “Hey, it’s THIS again. I can handle this; been there, done that, many times! Noooo problem!”

The deconditioned, out of shape, weak body (even if the patient doesn’t smoke) does not know what to make of the surgical trauma.

It’s shocked, overwhelmed, thrown for a loop. It freaks out. A heart attack occurs:

• “What IS this? What’s going on?”
• “What’s happening to me? How do I handle this?!”
• “What do I DO? I’ve had no practice at dealing with trauma! Help!”
• Heart attack

This is why one of the reasons you should work out intensely is to prepare your body for future surgery – any surgery, be in knee replacement or a repair of injuries from a car accident. A “shocked” body is more likely to suffer a heart attack.

Top image: Shutterstock/ArtFamily