ANAHEIM, CALIF. -- A laser that pierces new blood-carrying channels into ailing heart muscle is an effective new therapy for coronary artery disease patients who have exhausted all other conventional forms of treatment, according to the results of a recently completed multi-center clinical trial.
A study of 198 patients, randomized to either the new laser therapy or continued treatment with heart medicines, found that 71 percent of the patients treated with the laser showed significant decrease in chest pain (angina), compared to none of those receiving medical therapy.
The heart laser system, which uses a carbon dioxide laser, was developed by PLC Medical Systems Inc., Milford, Mass.
Results of the 12-center, Phase III clinical trial were prepared for presentation Tuesday (March 18) by Duke cardiothoracic surgeon Dr. James E. Lowe at the annual meeting of the American College of Cardiology.
The procedure, known as transmyocardial revascularization (TMR), opens new passageways in heart muscle that is still alive, but because of inadequate supply of blood, is not functioning properly.
"TMR is a promising therapy for a group of patients who have exhausted all other revascularization therapies," Lowe said. "Most patients saw a significant decrease in their angina scores after the procedure, and it appears that the benefit lasts over time. A six-month follow-up also demonstrated that patients treated with TMR displayed marked increase in blood flow to the heart.
"These patients typically have had multiple hospital admissions; they can't work or exercise and physical exertion of any kind causes crushing chest pain," Lowe said. "They are a tragic and unhappy group of patients because they are so incapacitated and in the past we could do very little for them."
Angina occurs when the heart's demand for oxygen-rich blood is not met by the coronary arteries, which are usually clogged with atherosclerotic plaques.
Patients involved in the trial had not responded to the two standard therapies for blocked or diseased coronary arteries: coronary artery bypass surgery or balloon angioplasty. In a bypass procedure, veins from the leg are used to redirect oxygen-rich blood around blockages and directly to heart muscle. In angioplasty, a tiny balloon is threaded through the arteries feeding the heart and inflated, clearing plaque blocking the artery.
During a laser procedure, surgeons gain access to the heart through a 6- to 8-inch incision in the patient's side. Once the surface of the heart is exposed, the doctors fire short pulses of laser energy into the left ventricle -- the heart's main pumping chamber -- while it is engorged with blood. A computer synchronizes the laser pulses with the pumping of the heart, and the blood in the chamber keeps the laser burst from traveling any farther.
Depending on the extent of the heart disease, the surgeons create 20 to 40 channels in the moribund heart muscle, and the holes on the heart's surface almost immediately seal themselves with clotted blood and heal over. Patients typically go home after four days in the hospital.
The study also showed that TMR might not be as effective for those patients whose heart disease has progressed to unstable angina, a severe form of angina that requires emergency hospitalization and treatment in a cardiac care unit.
After six months, 37 of the 101 patients in the medical therapy group crossed over to the TMR arm of the trial because of unstable angina.
"The mortality rate for the group that received primary TMR was 3.0 percent, while the rate for those who crossed over from the medical group was 40.0 percent," Lowe said. "For this reason, TMR should be offered only to patients before their disease progresses to unstable angina."
It is expected that the federal Food and Drug Administration (FDA) will decide later this year on whether to approve the laser for clinical use.
"At this point, we do not know exactly why this procedure works," Lowe said. "We do know that there is new capillary growth into the new channels. At Duke, we are using animal models to better understand exactly why this occurs. It appears that the new growth is somehow related to the inflammatory response to the creation of the channels. Once we figure out exactly how and why it works, we can then make it work better."
Since it takes time for the new capillaries to grow, patients usually do not begin to see major improvements until three months after the procedure, and the improvement typically continues for nine to 12 months, Lowe said.
Lowe said it is premature to consider using TMR as a routine surgical option for patients with coronary artery disease.
"Right now, the outcomes of coronary bypass are so good, and patients feel better right away, that I can't see the laser procedure supplanting it," Lowe said. "But for those who have failed all other therapies, TMR is quite promising."
In terms of cost, a typical TMR procedure ranges somewhere between angioplasty and bypass surgery.