Medical Device Daily Contributing Writer

Research has shown that 85% to 90% of patients are cured of atrial fibrillation (AF) following the CryoMaze procedure, which uses extremely cold temperatures (cryoablation) to surgically treat AF.

The procedure was demonstrated in a live webcast from the University of Maryland Heart Center (Baltimore), using CryoCath 's (Montreal) Argon-powered cold probe to create electrical barriers in the upper chamber of the heart. By freezing the atrial tissue for a little over a minute, electrical activity is permanently blocked.

“We have taken an aggressive stance toward the treatment of atrial fibrillation in patients requiring cardiac surgery. Our approach is to perform the CryoMaze procedure on any patient with AF who needs open-heart surgery,” said James Gammie, MD, assistant professor of surgery at the University of Maryland School of Medicine , who carried out the procedure.

More than 2.5 million Americans suffer from AF and the condition results in 70,000 deaths per year, increasing with the age of the population. It is the most common abnormal heart rhythm, resulting in uncoordinated contractions of the heart. The atria, the upper chambers of the heart, contract first, followed sequentially by the ventricles, the two lower chambers.

Patients with AF are much more likely to suffer strokes – five times as likely. Roughly 15% of all strokes are due to AF. “The CryoMaze procedure is very effective in preventing these strokes,” Gammie said. “The technique returns contractibility to the left atrium. We've had no late strokes in our series of CryoMaze patients,” he said.

Gammie's patient was a 65-year-old man, who was still able to work but suffered with progressive shortness of breath, especially climbing stairs. He has been on Coumadin, a blood thinner used to prevent clot formation, for the last several years. Along with his AF, he has severe mitral valve regurgitation. The posterior leaflet of his mitral valve is prolapsed, causing enlargement of his left atrium. The patient was otherwise healthy.

The patient was under general anesthesia. A median sternotomy (chest incision) had been performed. The patient was cannulated in standard fashion and placed on a heart-lung bypass machine. With the chest open, Gammie dissected down to the left atrium. He used a laparoscope to allow the audience to view the wound closely and then initiated use of the CryoProbe.

“Now we make several sets of lesions on the outside of the right atrium with the CryoProbe,” he said. “It is argon-based and cools to a minus 140 degrees Celsius. The rapid heat removal from the tissue is due to gas expansion, like when you put your tongue on a cold window in the winter.”

After about two minutes per lesion, Gammie moved to the left side of the heart, avoiding the sinus node. He told the audience, “We try to avoid freezing the sinus node. If it is affected, about 4% of our patients will require a pacemaker.” The freezing line could be seen forming on the outside of the atrium. “Overall this adds about 30 minutes to the total time of the open heart mitral valve repair,” he said, “but it's worth taking the time because of the greatly improved overall results. And the patient can get off blood thinners.”

As the left side of the heart was approached, the surgeons used cardioplegia to stop the heart. They then freed up the left atria from the inferior vena cava. Electrosurgical energy was used to stop small bleeders.

Gammie exposed the intra-atrial groove on the roof of left atrium in preparation for use of the CryoProbe on the interior of the atria. The atrial appendage was then oversewn to prevent clot formation. “It takes us about 1.5 minutes for the first lesion inside the left atrium,” he said.

As he waited for the ice to form Gammie said, “We get a continuous line with the freeze. The line is about 5 mm to 6 mm thick right across. It looks like an ice ball.” He then used warm irrigation to allow the probe to warm.

Next, boxed lesion sets were created around the pulmonary veins. Then an isthmus lesion down to the mitral valve annulus was created. Each line took about two minutes. The malleable CryoProbe used was 10 cm in length.

“Now,” Gammie explained, “we have created a circle to electrically isolate this part of the heart using frozen radial lines out to mitral valve and left atrial appendage.” He noted while he worked, “There are multiple advantages when you perform a CryoMaze procedure at the time of other heart surgery. You get the heart back into a regular rhythm, relieving his AF symptoms and reducing the risk of stroke. At three months [post-procedure], this patient can discontinue blood thinners.”

Gammie described the history of his group of AF patients. “We've been using the CryoMaze for about four years now and find it very successful for curing atrial fib. The Maze operation to stop atrial fib is a simple-minded approach. The larger the atrium, the more likely a patient is to have AF. Cats never get atrial fib, dogs sometimes and elephants always. So we reduce the critical mass of tissue. We divide the atrium up into smaller portions. Creating electrical lines in the sand so current cannot be carried across to stimulate uncoordinated contractions.”

A variety of different energy sources have been used to create these tissue lines for electrical interference, microwave, radio frequency and high frequency ultrasound among them, Gammie said. “We use cryo because, unlike the other energy sources, cryo has advantages of safety, simplicity and lack of bleeding.”

While moving to repair the patient's mitral valve, Gammie said, “For the first few months postoperatively we see a lot of AF until about the six-month stage. We think this is probably due to atrial remodeling. After six months the AF drops off sharply. So far we have 1.5 years for our long term follow-up, but we expect this procedure to eventually mirror the old cut-and-sew technique, which is durable out to 10 years.”