Off-pump bypass surgery: Promise unfulfilled

Published: February, 2010

Traditional open-heart surgery with a heart-lung machine is still the gold standard.

Innovation doesn't always mean improvement.

That's the lesson we're learning about off-pump bypass surgery. This so-called beating heart surgery was developed in the 1990s as a novel way to reroute blood flow around cholesterol-clogged coronary arteries. But it hasn't replaced the original version, in which the heart is stopped and a machine pumps blood around the body. In fact, a major study suggests that off-pump bypass surgery doesn't quite measure up to the traditional operation.

Different approaches

A vast network of arteries delivers oxygen and nourishment to the billions of cells that make up the heart. It starts at the aorta, the main pipeline for oxygenated blood that emerges from the powerful left ventricle. The right coronary artery and left coronary artery branch off from the aorta and subdivide into progressively smaller vessels. Some hug the surface of the heart; others burrow into it.

The buildup of fatty deposits, called plaque, on the inner walls of coronary arteries can hinder blood flow. A plaque-narrowed artery may work just fine when the body is at rest. But when exercise or stress makes the heart work harder, the clogged artery may not be able to deliver as much oxygen and energy as its part of the heart needs. This causes the chest pain or pressure known as angina, or other symptoms such as shortness of breath, sudden nausea, pain in the left arm or jaw, or anxiety.

Before the 1950s, rest and symptom-stopping medications like nitroglycerine were the only remedies for angina. The invention of the heart-lung machine made a surgical fix possible. Using a small section of artery or vein taken from elsewhere in the body, a surgeon could reroute blood flow around the clogged artery. The heart-lung machine, by mechanically circulating blood around the body, allowed surgeons to temporarily stop the heart from beating. This made it much easier to sew together blood vessels as small and slippery as cooked spaghetti with thread as fine as a human hair.

Conventional bypass surgery

illustration of conventional bypass surgery

In on-pump bypass surgery, the heart is stopped and a machine circulates blood around the body. This gives the surgeon a steady, bloodless field on which to operate.

Of course, coronary artery bypass surgery isn't a magical, wave-of-the-wand cure. A small percentage of patients die during the operation or soon afterward. Some have a stroke or develop an infection. Others experience a mental fog that can last for a few weeks or longer. Some experts blamed the heart-lung pump for the apparent change in thinking skills. Others thought it might be due to clamping the aorta and connecting it to the machine, which can release small chunks of plaque into the circulation. If these settle in the brain, they can hinder blood flow to parts of the brain and slow down the nerve connections that drive thinking.

Surgeons, engineers, and inventors tinkered with all aspects of standard bypass surgery, looking for ways to make it safer. One result was beating heart surgery, which didn't require the use of the heart-lung machine. This off-pump bypass surgery begins in much the same way as a standard bypass operation, with an incision called a sternotomy that opens the breastbone and exposes the fist-sized heart muscle beneath it. But instead of stopping the heart, the surgeon applies a special tool that isolates and stabilizes only the small section of the heart around the diseased artery. As he or she bypasses the blockage with a graft, the rest of the heart keeps on beating away, circulating blood as usual. The stabilizer is moved as needed for a second, third, or even more grafts.

Off-pump bypass surgery

illustration of off-pump bypass surgery

In off-pump bypass surgery, a stabilizer immobilizes the part of the heart with the diseased coronary artery. The surgeon performs the bypass graft while the rest of the heart continues to beat and pump blood around the body.

Coming into focus

Early reports about off-pump bypass surgery were pretty positive. Short-term survival and stroke rates were much the same as they were for on-pump bypass surgery, but it seemed as though the new technique better protected the brain.

As word spread, more and more surgeons learned how to do the off-pump bypass procedure. Some believed the procedure was better, even though the early studies were a bit shaky, and there were no long-term data. Others did it to expand their repertoire or tackle a new challenge. Some hospitals jumped on the bandwagon, billing the off-pump bypass as the "executive bypass" for people who couldn't afford to slow down after the operation.

Larger, longer studies muddied the water. Some showed less loss of memory and thinking skills after off-pump bypass; others didn't. A few studies raised concern that surgeons did fewer grafts when using the off-pump technique, which could leave some blockages unfixed. A statement from the American Heart Association in 2005 called the controversy over which procedure was better "one of the most hotly debated and polarizing issues in cardiac surgery," and concluded the two procedures were generally equivalent.

The results of a large trial conducted at 18 Veterans Affairs (VA) medical centers across the country are bringing some clarity to the debate. In this trial, 2,203 veterans in need of a bypass were randomly assigned to on-pump or off-pump surgery. At 30 days after the procedure, the results were almost identical — similar numbers of deaths, strokes, cardiac arrests, cases of kidney failure, and reoperation in both groups. One key difference, though, was that 18% of the off-pump group ended up getting fewer bypass grafts than originally planned, compared with 11% of the on-pump group (New England Journal of Medicine, Nov. 5, 2009).

A year later, other important differences had emerged. In the off-pump group, 9.9% of the participants had died, had a heart attack, or needed another procedure to open or bypass a blocked coronary artery, compared to 7.4% in the on-pump group. Follow-up angiograms showed that the grafts were somewhat sturdier and tighter in the on-pump group. And there were no differences between the groups in scores on a battery of tests designed to assess memory and thinking skills.

Trial raises questions

The VA trial wasn't perfect. Critics argue that some of the surgeons doing the off-pump procedure didn't have enough experience, and the results would have been better if only surgeons who had done at least 50 or 100 operations (instead of at least 20) had been included. The study population is another problem. Although earlier studies had suggested that off-pump bypass surgery may benefit women more than men, and individuals with other illnesses in addition to coronary artery disease, the VA trial included mostly men who were younger and healthier than the average candidate for bypass surgery.

Even so, the findings give us pause about off-pump bypass surgery. It

  • may prevent a surgeon from creating grafts for all the blockages. This could leave part of the heart still starved at times for oxygen-rich blood.

  • could hinder the creation of smooth, even connections between a graft and a coronary artery. Even a small pucker in the stitching can roil blood flow, which would accelerate the formation of new plaques.

  • doesn't protect against bypass-related thinking problems (what doctors once referred to as "pump head") better than traditional bypass surgery using the heart-lung bypass machine.

What do you really need?

Off-pump bypass surgery clearly isn't better than traditional bypass surgery. When performed by equally experienced surgeons, on-pump and off-pump bypass surgery yield the same good results. That means finding an experienced surgeon, and surgical team, is an essential part of the preoperation process. "Bypass surgery is a team effort," cautions Dr. Kamal Khabbaz, chief of cardiac surgery at Harvard-affiliated Beth Israel Deaconess Medical Center. "You want to make sure that the surgeon works with a stable team and they have done this operation together many, many times."

If you have angina or other signs of a clogged coronary artery, it's a good idea to ask yourself and your doctor a few questions, says Dr. Deepak Bhatt, associate professor of medicine at Harvard Medical School and chief of cardiology for the VA Boston Healthcare System. He suggests these three for starters:

Do I really need bypass surgery? If you aren't having any symptoms of coronary artery disease, neither bypass surgery nor artery-opening angioplasty will do you much good. Medications and lifestyle changes, like more exercise and a better diet, offer a more effective way to prevent a heart attack or stroke.

What's my coronary anatomy? An angiogram showing blood flow through the coronary vessels can determine that angioplasty is the way to go or reveal that bypass is a better choice.

What's my overall risk? If you are at high risk for bypass-related problems, perhaps because you have failing kidneys or have recently had a stroke, then angioplasty might be a better option than off-pump bypass surgery. "I don't think the off-pump procedure should be thought of as a middle ground for high-risk patients," says Dr. Bhatt.

If the off-pump bypass procedure is the one your cardiac surgeon is most comfortable with, and he or she does it often with an experienced team, it's a perfectly fine choice. But there is no compelling reason to pursue this new procedure, either. For now, the old standby — which itself was once a revolutionary new technique — is still the gold standard.

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