MIRACLE researchers comment on implant
Early in November, John Messenger, MD, medical director of cardiovascular services at Long Beach (CA) Memorial Medical Center, implanted Minneapolis-based Medtronic’s cardiac resynchronization device as part of the Multicenter InSync Randomized Clinical Evaluation (MIRACLE), a parallel study to the MIRACLE ICD trial. He says there are always technical problems in a new arena, but he started putting in coronary sinus pacemakers in 1975, so getting into the coronary sinus was not difficult for him.
"Many people involved in these studies are electrophysiologists who are very familiar with the coronary sinus, and they place leads there all the time," he says. "But others have not had the practice that we have had putting leads in the coronary sinus. Skill levels across the country vary from zero to excellent. Unlike going to the right ventricle, which is basically very easy, this is a challenge and requires planning and luck."
What does luck have to do with it? "The anatomy of the patient has a lot to do with it," he explains. "The final placement of the lead in the ideal position — high left lateral wall — is easy if you’re lucky enough to get a patient with a nice vein at that site. If the patient doesn’t, you have to go somewhere else on the left ventricle."
John Boehmer, MD, medical director of the Heart Failure Center and the heart transplant program at the Hershey (PA) Medical Center has implanted Minneapolis-based Guidant’s Contak in patients. He says he has had two cases that were problematic: In one, the middle cardiac vein corkscrewed so the surgeons had trouble getting the wire through it. "We ended up using the great cardiac vein. In the other difficult case, staying in the coronary sinus was the problem."
Under what circumstances will this procedure improve the condition of a patient, and how long will that effect remain active? "Those questions remain unanswered at this point," says Messenger, "but my gut feeling is, the procedure will dramatically improve a patient and that improvement will continue. As patients improve, the dramatic changes go away and their conditions becomes the norm." He predicts a success rate of 90% for the device he implanted.
"When we make a heart better, it tends to get smaller, and that results in a very good improvement from a physiological standpoint," Messenger explains. "The volumes of the heart diminish — the actual physical volumes — so it takes less biochemical work to generate the same cardiac output. If my goal is for a heart to generate five liters per minute cardiac forward flow, and we do it with a heart that is 400 cc to 500 cc in diameter, it doesn’t take much to do that even with an [ejection fraction] of 10%. We achieve that output by heart rate, the ability to squeeze, and the volume of the heart. That’s 50 cc forward flow — 50 cc times a heart rate of a hundred is 5 liters a minute. The average cardiac output is 4.5 liters to 5.5 liters per minute in all humans."
Messenger says the success of these pacing-resync devices will depend on the development of better catheters, and that problem is well on its way to being solved. "In left ventricular pacing, the technical development of the electrodes and the ability to get them into the coronary sinus go hand in hand. I think we’re still early in the development of that. There’s lots more to come."
He says the procedure is not that extraordinarily expensive or dangerous to the patient. "No physician is going to stop helping people get better. If we are able to show that we can reduce hospital returns, the devices will more than pay for themselves five times over. And the quality of life of patients will be truly improved. The ifs’ are what we’re trying to answer with this program."