Faculty Spotlight: Scot Merrick, MD
Dr. Scot Merrick, a UCSF cardiac surgeon and chief of the Division of Cardiothoracic Surgery, spent many years on the crew team in high school and college. “In my opinion, rowing is one of the ultimate team sports,” he said. “You can’t go fast if you have one person slowing you down. If everyone is committed to going fast, watch out.
“Cardiac surgery is not a lot different,” he said. “It’s a team sport. And that’s what translates into good outcomes.”
Dr. Merrick’s current teammates include outstanding surgical nurses, cardiac anesthesiologists, ICU nurses, ward nurses, the Division of Cardiology, and many others. Together they provide superior care before, during and after surgery, oftentimes to patients with complex conditions who have been referred from other centers all over California.
A cardiothoracic surgeon, Dr. Merrick used to perform most of the adult heart and lung operations at UCSF, and now focuses on a wide range of adult cardiac surgeries, including bypass surgery, surgery of the aorta and its branches, and removing tumors of the heart. He specializes in fixing problems with the four heart valves, which may need repair or replacement due to a birth defect, complications from rheumatic fever or infection, or other reasons. Almost all valve procedures require open heart surgery, which involves administering general anesthesia, making an incision in the chest, temporarily stopping the patient’s heart, and putting the patient on a heart-lung machine to ensure that all parts of the body receive adequate oxygen during the surgery.
Mitral Valve Prolapse
One of the most common conditions that Dr. Merrick treats is myxomatous valve, also called mitral valve prolapse or floppy valve. It occurs when the mitral valve fails to close properly. “In my opinion, and in most valve surgeons’ opinions, you should be able to repair those valves almost 100% of the time,” said Dr. Merrick, who is internationally renowned for his skill in complex mitral valve repair. “The mitral valve is a very forgiving structure. If you can eliminate the prolapse and maintain the symmetry of the valve, it’s almost always going to work. If you can fix your own valve, you’re better off than having an artificial valve put in, because you preserve the normal anatomy and retain the most efficient function.”
The mitral valve is a parachute-like structure, with two leaflets that are connected to the inside of the heart by a number of cords. The most common problem occurs when leaflet tissue becomes stretched or excess tissue develops, creating a gap between the two leaflets through which blood can flow backwards. “You just take a V-shaped wedge of the excess leaflet tissue out, and you sew the two edges back together,” said Dr. Merrick. “You basically eliminate the redundancy, and the prolapse that occurs along with that.”
Another cause of mitral valve prolapse occurs when one of the cords stretches or breaks, leaving a portion of the leaflet unsupported and causing blood to leak. While some surgeons use artificial suture material to repair this problem, Dr. Merrick has honed the ability to reposition some of the patient’s own cords to fix the prolapse. Most people have about 20 to 30 cords for each leaflet. “The beauty of the mitral valve is, there are quite a number of these cords that aren’t necessary for the structural integrity of the valve,” said Merrick. “In many cases, you can remove the attachment of those cords to the leaflet and move them around, without removing their attachment to the origin inside the heart.”
Dr. Merrick carefully chooses a cord from an area of the leaflet that is already well supported, snips the end connected to the leaflet, then stitches it onto the area of the leaflet that needs support. In some cases, when the cord is elongated but not torn, Dr. Merrick shortens the cord to the correct length.
When repairing the mitral valve, Dr. Merrick almost always fixes an accompanying problem. Over time, a leaky valve can cause the left ventricle to expand. This stretches the perimeter of the area where the mitral valve’s leaflets are attached, called the annulus. It becomes a vicious cycle: the leaking stretches the annulus, which in turn causes even more leaking.
To correct this, Dr. Merrick sews on an annuloplasty ring. “The ring is calibrated to some very specific anatomic landmarks,” said Dr. Merrick. “You measure the height of the leaflets, and the ring is calibrated to that size. It restores the annulus to the correct size, and the leaflets will come right back together.”
The original annuloplasty rings were made of metal, with cloth covering the outside so they could be stitched on. Dr. Merrick tends to use the latest model, made of more flexible material. It functions like an elastic belt, restoring the annulus to its proper dimensions while flexing with the movement of the heartbeat. Even though the ventricle may remain enlarged, it is not problematic. “As long as you eliminate the leak, the pattern of blood flow through the heart is restored to normal,” said Dr. Merrick.
The Power of Imaging
Dr. Merrick noted that landmark studies from the Mayo Clinic in the 1980s demonstrated that patients in need of mitral valve surgery experienced better outcomes when they were referred for surgery before they developed heart failure. At UCSF, Dr. Merrick works closely with his colleagues in the Division of Cardiology to develop an accurate diagnosis and create a customized treatment plan for each patient, including the best time for surgery.
“The big thing in mitral valve surgery that’s occurred in my lifetime is the introduction and perfection of echocardiography,” said Dr. Merrick. An echocardiogram is an ultrasound of the heart, which provides a wealth of information about the anatomy of the heart and patterns of blood flow.
“It is the gold standard, not only for making a diagnosis, but mapping out what operation you can do,” said Merrick. “The echo is a spectacular way to look at the anatomy of the valve. It shows how it moves, how it works, and where it doesn’t close properly. You can tell, based on what segment of the leaflet is not working properly, where the anatomy is going to be faulty. I’d say 95 percent of the time, you know before you even make the incision exactly what you’re going to do.”
UCSF also has the advantage of using the most advanced imaging equipment, and having experts in performing and analyzing echocardiograms. “The people who do echocardiography here – Drs. Nelson Schiller, Elyse Foster – they’re just phenomenally good,” said Dr. Merrick. “They do perfect echoes. It’s great, because they can really sit down and help you understand the anatomy.”
Aortic Valve Replacement Surgery
Another common valve procedure that Dr. Merrick performs is aortic valve replacement surgery. Sometimes, a patient’s aortic valve may not have formed properly before birth, or may wear out over time. In other cases, patients develop a heart infection like endocarditis, in which bacteria attack the aortic valve tissue. Sometimes this can cause the valve to leak, and may eventually require open heart surgery.
To perform an aortic valve replacement, Dr. Merrick cuts out the defective valve with scissors, and stitches in a replacement valve. There are two main types of valves. Mechanical valves are made of material like carbon fiber and are very long-lasting, but require patients to take blood thinners for life to prevent clots from forming on the device. Tissue valves are made from a pig heart valve or the lining that surrounds a cow’s heart. They do not require patients to take blood thinners, but do wear out after 10 to 15 years. Dr. Merrick is reluctant to recommend a tissue valve for young people, because they calcify more quickly and wear out even faster – in about eight to 10 years.
“When someone is in need of surgery, it’s tough to figure out what kind of valve you’d want, especially if you’re in the 40 to 50 age range,” said Dr. Merrick. “You may still be really active and do athletic things, and you wouldn’t want to be on a blood thinner. But at the same time, you’d prefer not to have more surgery when you’re in your 60s or 70s, when your risk may be higher.”
Occasionally, a patient with extensive infections inside the heart may be a good candidate for a human valve. This is obtained the same way any donor tissue is procured, such as a kidney or liver, and has the advantage of being very resistant to infection. (Whether tissue valves come from animals or humans, they are specially treated so that the immunologically active proteins on their surface are denatured, so that recipients do not need to take immunosuppressant drugs to prevent rejection of their new valves.)
Dr. Merrick also occasionally performs surgery on the pulmonary valve, which is located between the right ventricle and the artery which carries deoxygenated blood to the lungs. This valve rarely malfunctions, but may require surgical treatment for patients with a congenital heart defect such as tetralogy of Fallot.
The tricuspid valve, located between the right atrium and right ventricle, also sometimes requires surgery. “Even though it’s the most accessible valve on the heart, it’s probably the most unpredictable,” said Dr. Merrick. Many factors can contribute to a leaky tricuspid valve, including blockages in the lungs. Alternatively, a leaky mitral valve can cause blood to back up in the lungs, which in turn elevates pressure in the right side of the heart and can cause the tricuspid valve to leak – similar to a freeway accident causing traffic to back up for miles behind it. “If you’re operating on a leaky tricuspid valve, the key thing is to know what caused the high pressures,” said Dr. Merrick.
Looking to the Future
Dr. Merrick noted that there are new surgical procedures on the horizon. For example, a recent trial tested the use of a percutaneous valve to replace a malfunctioning aortic valve. Instead of requiring open heart surgery and a heart-lung machine, doctors use technology similar to that employed in cardiac catheterization. They make a small cut to gain access to a major blood vessel, such as the femoral artery in the groin area, then thread a compressed pig valve surrounded by a mesh metal housing through a patient’s arteries. When the valve is threaded into the heart, a balloon is inflated to open up the calcified valve, and then the compressed pig valve is deployed to expand to its full size – a bit like opening an umbrella. The irregular, hardened calcified surface actually provides an ideal framework for the expandable metal housing of the percutaneous valve to grab on to.
Currently, the only candidates for this less invasive procedure are older patients with aortic stenosis, a condition in which the aortic valve is calcified and has difficulty closing properly. “It works, and it certainly works better than nothing,” said Dr. Merrick. “But there are problems with it. It’s a new technology, and it’s not perfect yet. … It’s a hot topic right now.” The technique has been used in Europe, and approval in the United States is anticipated within the next year. Dr. Merrick said that if the procedure is approved, UCSF would like begin offering it to a select group of patients, most of whom are not candidates for traditional surgery due to age or other factors.
Another innovation is robotic surgery for mitral valve surgery, which uses a robot to make multiple small incisions on the side of the chest. The procedure takes longer than traditional open surgery, and the results are close to those achieved by traditional surgery, but not quite as good, said Dr. Merrick. This approach still requires the heart-lung machine, but the incisions are smaller and more cosmetically pleasing than traditional surgery.
“I always am reluctant to use the term ‘minimally invasive surgery,’ because any time you’re on the heart-lung machine, that’s invasive, in my opinion,” said Dr. Merrick. “In fact, most surgery is invasive. The size of the incision is what you’re varying. For almost all valve surgery at this point in time, you have to use the heart-lung machine. It’s the morbidity of the heart-lung machine that people are trying to get away from, by doing percutaneous valves, for example.”
Dr. Merrick noted that the results for traditional surgery keep improving – for example, operative mortality for elective aortic valve replacement has dropped from about 7 percent to less than 3 percent, while the heart-lung machine continues to get safer each year, and artificial valve technology continues to improve. It will take decades to learn how percutaneous valve surgery compares with traditional valve surgery in the long run, said Dr. Merrick.
For the foreseeable future, some conditions will still require traditional open heart surgery. For example, to treat infection on valves, a surgeon must remove the infected tissue, similar to removing an abscess on a person’s skin; this requires a level of precision that is only possible with open surgery.
Leading the Team
Dr. Merrick grew up in Seattle, where he rowed in four- and eight-man shells in high school and college. Dr. Merrick still keeps a boat up in Puget Sound, and returns once or twice a month to row. He also sails in the Bay Area on his 23-foot long sailboat.
During medical school at the University of Washington, he thought he would become a cardiologist, but changed course when he started doing research in a cardiac surgery laboratory. “It was hard work, but I loved it,” he said. He came to UCSF for his residency training, working with Dr. Paul Ebert, then chair of the Department of Surgery and a world-famous heart surgeon. After his residency, Dr. Merrick joined the UCSF faculty, and has been here ever since. He currently performs about 150 surgeries a year.
In addition to serving as chief of the Division of Adult Cardiothoracic Surgery, Dr. Merrick also directs the thoracic surgery residency program. He recently led efforts to expand the program from two years to three to expose residents to a wider range of rotations and procedures.
He is quick to point to his talented team of colleagues as the biggest reason for the successful outcomes of the surgeries he performs. “We’ve got great nurses in the OR who have been there a long time,” he said. “I’ve got fantastic cardiac anesthesiologists who are all fully trained in echocardiography. I’ve got a very experienced set of ICU nurses, and ward nurses who have been here almost as long as I have. And then I have a supportive group in Cardiology that are just phenomenal. I can’t claim any of that credit – that’s a credit to who comes to UCSF.”