To pump or not to pump?

Bypass surgery can now be carried out on a beating heart

Reviewed by Dr Kosin Thupvong, Bangkok Hospital, Bangkok, Thailand

Most major surgeries are performed with anesthesia, not just to minimize the pain that, say, yanking out an appendix would cause to someone awake and unmedicated, but also to keep the patient still while sharp objects are in the area. Imagine trying to repair the blood vessels of the heart while it continued to beat—thump, thump, thumping away as a razor-sharp scalpel is maneuvered in a small space, where a mistake can cost someone their life. Which is why, until recently, most open-heart surgery has been performed “on pump,” while the heart is no longer beating and a machine temporarily takes over the work of the heart and lungs. These days, though, surgeons leave the heart and lungs to do their jobs and “stabilize” the heart just enough to work on it. This is sometimes called “off pump” surgery. As with every situation where your chest is cut open and your heart fiddled with, there are risks and benefits to both these methods.

Bypass surgery

The heart is a pump with pipes that carry blood to it and from it, and it requires oxygen-rich blood to function. This blood flows to the heart through the coronary arteries. These arteries can become narrowed or completely clogged by plaque, causing a number of problems. If these arteries cannot be successfully treated with lifestyle changes, medications, or angioplasties, bypass surgery is often the only remaining option.

Coronary artery bypass surgery, also known as coronary artery bypass graft (with the fun acronym CABG, pronounced “cabbage”) is one of the most common heart surgeries performed all over the world. During surgery a section of a healthy vein or artery in the body of the patient is removed. This vessel is that attached above and below the damaged artery, bypassing it altogether. Blood flow then resumes in the newly grafted blood vessel, like taking a detour off the highway when traffic hasn’t budged in three hours.

On-pump bypass surgery

Traditionally medication is used to stop the heart during bypass surgery. A heart-lung machine, or a cardiopulmonary bypass machine, is attached to temporarily take over the functions of the heart and lungs, so the patient is breathing and blood continues to circulate in the body. The machine acts like a heart would, removing carbon dioxide from the blood that flows through it and sending back oxygenated blood to flow through the body. After the graft is attached the machine is turned off and the heart and lungs resume their normal functions. The heart is usually stopped for 30 to 90 minutes during a three to six-hour surgery.

Associated problems with on-pump bypass surgery include postperfusion syndrome (caused by air bubbles from the heart-lung machine that flows to the brain), hemolysis, capillary leak syndrome, and air embolism. Because the heart is without blood for a period, reintroducing blood to the tissue once the heart-lung machine is turned off can cause impairment in the function of the heart. The heart tissue can also become damaged while it is not beating. (Who knew opening up the chest and stopping the heart could be so risky?)

Off-pump bypass surgery

Off-pump bypass surgery, also known as “beating heart surgery,” was developed to counteract some of the risks associated with the traditional bypass surgery. Instead of using a heart-lung machine, off-pump surgery is performed on a beating heart that is held still with a mechanical stabilizer. Blood flow to and from the heart never stops and the lungs function normally. If the heart is never stopped, there is less risk of damage to the heart, compared with traditional bypass surgery. Patients who undergo off-pump bypass surgery usually recover more quickly.

With benefits come different risks. Off-pump bypass surgery is very difficult to perform and the learning curve is steep. It takes a long time and a lot of experience for a cardiac surgeon to become adept at working on a beating heart. Studies have also shown that in some patients, on-pump surgery reduces the risk of stroke and heart attack after the procedure. Other research has shown no difference in the long-term risks of both types of surgeries.

To pump or not to pump?

On-pump bypass surgery has been performed longer than beating heart surgery, and that in itself is a benefit of the more traditional method. Cardiac surgeons are better at on-pump bypass surgery and often feel more comfortable performing it. The risks and benefits of traditional surgery is better known. There is no doubt, though, that in time more and more bypass surgeries will probably be carried out on hearts that continue to beat. Each patient is different, with varying complications and risk levels, and the method of surgery considered must take all those factors into account.

Sources:

• http://www.uchospitals.edu/specialties/heart/services/surgery/beating-heart.html
• http://abcnews.go.com/Health/HeartFailure/beating-heart-bypass-surgery-riskier/story?id=8999797
• http://en.wikipedia.org/wiki/Off-pump_coronary_artery_bypass
• http://en.wikipedia.org/wiki/Coronary_artery_bypass_surgery

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