Déjà vu all over again for a narrow niche
An earlier study on cardiomyoplasty, sponsored by Minneapolis-based Medtronic, took a patient’s own back muscle and wrapped it around the failing heart. (See CHF Disease Management, February 1999, p. 16.) In much the same way as CardioSupport assists the heart, that technique used mechanical compression. The patient’s latissimus dorsi muscle-wrap was "trained" to respond to electric pacing, beating with the heart in an attempt to improve cardiac performance.
Citing a dwindling patient enrollment, Med-tronic ended its study. (See Circulation 1995; 91:2,314-2,318 and 1997; 96:3,665-3,671.) In testing cardiomyoplasty, investigators found that the advantage of the muscle wrap had more to do with curbing the dilation and chamber remodeling that occurs in advanced CHF than with the muscle helping the heart beat.
Reynolds M. Delgado III, MD, of the Texas Heart Institute in Houston, has seen the external pulsation device demonstrated. He says there are various ways to treat advanced heart failure with assist devices, and each has its niche of utility. "The utility of this device is very narrow, because it’s for patients who have a very acute problem."
The device poses a high risk for infection. It can only be used for a week or less, he says, because it provides a direct link to outside the body, and infection will set in after that brief time. "What we need is a similar device that can be used for many months — one we can put in and forget, one that allows mobility with no infection risk."
Delgado says that’s what the new Jarvik artificial heart will provide and that his facility will start using the Jarvik 2000 in humans in the next month. The Texas Heart Institute is the first center in the country to use the Jarvik 2000.
He says the Institute started doing the latissimus dorsi cardiomyoplasty procedure several years ago, then stopped doing it after a few years because, although it worked well in the short term, it did not in the long term.
"The technique is not an optimum solution," says Delgado. "Cardiomyoplasty used one of the skeletal muscles to help the pumping function of the heart, and skeletal muscles are not designed to continually contract for weeks and weeks. They wear out and stop working after a while. Only heart muscles are designed for that kind of continuous work."
How is the external pulsation device better than cardiomyoplasty? "Like the Jarvik, it is a device; it won’t wear down until it breaks. Theoretically, there is no limit on how long you can use a device like that," he says.
He does see another disadvantage of the CardioSupport System. "It may traumatize the outside tissues of the heart because it sits on its surface. Especially if there are delicate veins of bypass grafts there, it could disrupt those grafts when you apply this device that is pumping at high pressures."
He says he doesn’t think the system will be used to a large extent because of its narrow niche and short use potential. "But it could be helpful for people in very specific circumstances where they are literally dying within hours and minutes."
Animal studies show effectiveness
European animal studies have shown that the cuff can raise cardiac output from heart failure levels up to normal resting levels and have proven that the system is capable of sensing the EKG signal to assist the heart synchronize to its native heart rhythms.
The single-use CardioSupport System slips over the outer surface of the heart and increases cardiac output through external compression in synchronization with the normal heart rhythm. (See photo of device, above left.) The cuff is pneumatically driven and controlled by a console that keeps track of the timing and pressure of its inflation as well as monitoring the patient’s condition. Composed of biocompatible polyurethane and titanium, the cuff is flexible enough to collapse and be introduced through a standard 10 cm thoracotomy.
John Bichan, a representative of Cardio Tech-nologies, says the surgeons who participated in preclinical trials say the device can be collapsed and inserted, and the heart supported, within 15 minutes of the start of the implantation procedure. No sternotomy is required.
Mehmet C. Oz, MD, a cardiothoracic surgeon at Columbia-Presbyterian, calls this "a superb system. Avoidance of bleeding and ease of insertion are the main advantages."
The system was developed to acutely support cardiogenic shock patients regardless of cause. The clinical protocol specifies seven-day support of patients who typically have either rapidly decompensated CHF or acute myocardial infarction (AMI), or who are post-cardiotomy. CHF patients who have suddenly decompensated for reasons surrounding diet, exercise, and/or flu, cold, or pneumonia will tip over into shock, explains Bichan.
AMI patients who have developed cardiogenic shock also need acute support before their heart is able to recover. And post-cardiotomy support is still a problem for the 4% of the half million people who have open heart surgery and cannot be weaned off the heart-lung machine readily.
The system rapidly perfuses the organs, allowing the surgeon to stabilize the patient and still maintain all his surgical/interventional therapy options because the normal cardiac anatomy is kept intact. If the surgeon feels the patient requires long-term support, he can then implant an LVAD.
"Physicians aren’t burning bridges when they use this device," says Bichan. His company has received ethics committee approval for its clinical protocol from seven investigative institutions in Europe, and clinical trials are anticipated to start early next year.
No contact with the bloodstream
The system is anticipated to provide the same cardiac output in humans as LVADs at a fraction of the surgery time, invasiveness, and cost; its cost is about one-sixth of the major LVADs on the market. The main difference between the device and the DeBakey heart and Jarvik 2000 is that it does not come in contact with the bloodstream.
"Such . . . devices can potentially avoid the complications associated with currently available ventricular support devices that involve a blood/device interface," wrote Columbia University researchers.1
According to Bichan, LVADs are typically only implanted into patients who are transplant candidates, leaving out the many people who will die from cardiogenic shock.
"There is only a 1% chance that a patient who has an LVAD will not go on to heart transplant," he says.
1. Artrip JH, Wang J, Leventhal AR, et al. Hemodynamic effects of direct biventricular compression studied in isovolumic and ejecting isolated canine hearts. Circulation 1999; 99:2,177-2,184.
2. Artrip JH, Yi G-H, Levin HR, et al. Physiological and hemodynamic evaluation of nonuniform direct cardiac compression. Circulation 1999; 100:236-243.