Medical Device Daily Washington Editor
WASHINGTON — Bad heart valves are likely to eat up a lot more of the Medicare dollar in times to come, so there is no lack of interest in this area of cardiology among researchers, as was made clear during one of Tuesday's sessions of the Transcatheter Cardiovascular Therapeutics (TCT 2008) conference here.
This session included an overview of two of the stronger candidates for a pre-market approval application (PMA) for sutureless valve, but another presenter indicated that while minimally invasive procedures for repair and replacement of heart valves have a lot going for them, they are still not at a stage of full maturity.
Discussing minimally invasive approaches to aortic valve disease, Lars Svensson, MD, director of the Center for Aortic Surgery at the Cleveland Clinic, opened by hinting at the fact that minimally invasive procedures have not quite yet come of age. "For the more complex cases, we're still doing partial sternotomy," he said.
One of the obvious apparent benefits of cutting down on the cutting up is that blood transfusions for minimally invasive approaches are "a lot less" in terms of quantity than for conventional surgical procedures, Svensson said.
One approach that induces less trauma than a full-blown open-heart surgery would commence from the patient's right side at the second, third and fourth intercostal space, which are points on the rib cage that flank the sternum. However, this approach could damage the patient's mammary artery because this artery runs down the side of the sternum right behind the ribs.
He said that using this access point "is doable," but added that it "is not a fun operation for the patient," even if it is not as traumatic as the traditional opening of the entire chest cavity.
However, Svensson also cautioned that a surgeon who cannot reliably get in and out in an hour when doing a percutaneous valve procedure should consider employing a more conventional approach due to the risk of damage to the native valve. While he didn't say it, any manufacturer that comes up with a device that can help address some of these concerns might have quite a market to fill.
"Patients are increasingly looking for a minimally invasive approach," Svensson said, but very often react negatively to the word "percutaneous," which might be the pop-culture fallout from the drug-eluting stent flap of 2006.
Svensson said an analysis of almost 2,000 patients undergoing various procedures for aortic valve repair showed substantial improvements for those undergoing minimally invasive procedures.
Survival, however, did not seem significantly enhanced because, while the raw data indicated that long-term survival is better for all patients who underwent minimally invasive procedures compared to all who had more traumatic operations, an analysis that matched sub-populations for various characteristics drove the survival score lines closer together.
Pain scores, on the other hand, are vastly different. "The majority [of patients getting minimally invasive surgery] have a significant amount of pain initially," but most of the problem disappears after a week, he said, adding that this group experienced less pain overall than controls.
As for measurements of lung output via spirometry, Svensson said patients who were put through minimally invasive surgical procedures "had significantly better function," although he could only speculate that this is because it does less damage to the chest wall and the diaphragm than a procedure that cracks open the entire rib cage.
Predictably, less-invasive procedures generated less blood loss and hence incurred less use of blood and plasma. "Length of stay [in critical-care rooms] was shorter, as was overall hospital stay," he said. In conclusion, he said minimally invasive aortic valve surgeries "had better pulmonary function, better pain scores, less product usage."
Svensson also recommended that practitioners rethink patient selection standards. "As you face more and more of these [high-risk, morbidly obese] patients, I would urge minimally invasive procedures" be used in patients who might otherwise be rejected for any sort of non-pharmacological care.
He brought this up in a discussion of the case of a 52-year-old man who was on six liters of oxygen a day and was morbidly obese and dying on admission. Svensson said he repaired the patient's aortic valve and reduced his oxygen need by two-thirds, and although the patient was not exactly hale and hearty upon discharge, he at least had a fighting chance to recover and lead a somewhat normal existence.
James Cox, MD, the inventor of the Maze-Cox procedure which was the first surgical procedure to deal effectively with defibrillation and the medical director of ATS Medical (Minneapolis), presented an update on the company's Enable sutureless aortic valve replacement. He led his presentation by commenting: "In our haste to make operations less invasive, we need to keep our eye on the ball of the quality of the valves we're implanting."
He said the ATS 3F Enable valve "has been in development for 20 years," is built on a nitinol frame, and is made with bovine cardiac tissue. "This valve is based on a tubular structure" and the maximum stress "occurs exactly where it should," where the valve seats into the heart, which is fixed in part by a single circumferential stitch. The company recently announced the first implant of the valve in a patient in North America, into a Canadian patient, in April (Medical Device Daily, April 11, 2008).
Many commercially available tissue valves suffer from stress at the other main attachment points, known as the commissural posts, but the Enable attaches to the inside of the aortic wall by means of three commissural tabs that attach with mattress sutures, Cox said, and tests indicate that "the flow pattern across these valves" indicate "no more [turbulence] than normal valves." Since turbulence is thought to be the cause of calcification, ATS feels it can avoid the use of anti-calcification agents in the Enable.
He said the design of the Enable helps preserve the aortic sinus by allowing the blood to fill in behind the valves, just as the normal heart does. Failure to allow this backfill feature creates more turbulence in the blood flow through the valve area.
Cox said that another of the unusual features of this valve is that "because the valve closes from below up, it takes the pressure off the commissure."
The nitinol frame can be folded for delivery into the body without damaging the device, he said, which is one of reasons he said "the big advantage of a valve like this is going to be in tiny roots," which are found in small patients, a group that is often left behind where new cardiovascular devices are concerned.
"The main things you're concerned about is will it migrate," Cox said, adding that out of 101 implants in Europe, there have been no cases of migration. "Two became slightly tilted, and one had to be explanted. "We don't know what the durability is," but wear testing and the optimal flow characteristic should make "durability optimal." Next up at ATS, he said, is a percutaneously introduced valve.