Cardious

At Cardious, our goal is to move the aortic valve bypass graft procedure from a  procedure performed only by

AVBG Human Implant

surgeons willing and able to source needed components (off label)  and build the implant on the back table, to a predictable, easy to perform  procedure using an approved device and tool.  We will be successful when all surgeons have access to the implant and tools needed to  perform this procedure off-pump safely and with confidence.   But, until then, surgeons will, out of necessity, continue to perform this procedure using the best available but suboptimal materials and methods.

Recently, at the TCT convention in San Francisco amongst  interventional cardiologists promoting transcatheter valves as the “final solution” in AVR, Dr, James Gammie presented the  state of the art in aortic valve bypass grafting. His presentation did an excellent job explaining the features and benefits of AVBG along with his clinical results.

Compared to Standard AVR, Dr. Gammie points out that AVBG needs:

• No Aortic Cross Clamping
• No Debridement/Removal of Diseased Valve
• No Aortic Cannulation
• No CPB

Together, these all minimize embolic risk.  Also, AVBG has the following features:

• No Sternotomy
• No Cardioplegic Arrest
• No Patient-Prosthesis Mismatch
• No Heart Block

Dr. Gammie reported on his series of 31 patients, representing 7 % of his isolated AVR procedures.  Pre-op STS scores were 9.3 +/- 4.5.  Operative mortality was 26% in his first 15 pts. and 0% in his last 16 patients.  Side effects have been minimal.

Along with Dr. John Brown, Dr. Gammie has become a leading proponent of bypass grafts in the United States and has done an excellent job promoting the procedure to his colleagues.

In my last post, I argued that 40% of patients over age 70 presenting for AVR surgery  with a stenotic aortic valve will have a bicuspid shaped valve and therefore will not be eligible for a transcatheter device.  What about the 60% that have a tricuspid valve?  Are all of these candidates for a transcatheter procedure?  I don’t think so.  As it turns out,  “significant coronary artery disease” is another major contraindication/exclusion in the PARTNERS Trial and is also contraindicated in the European Guidelines.

How significant is concomitant coronary artery disease and why would it be contraindicated?

Again, based on research done by Dr. William Roberts, a cardiac pathologist who has studied aortic valves for over 40 years, over 65% of stenotic tricuspid patients also present with CAD so severe that at least one bypass graft was necessary at the time of valve surgery.  I have again taken the liberty to graph the data Dr. Roberts presented  in table format only.

This data is significant because the PARTNER Trial specifically excludes patients with CAD.  Here is the specific exclusion statement:

7. Untreated clinically significant coronary artery disease requiring revascularization.

And if a coronary stent procedure is done beforehand to alleviate a coronary obstruction, the patient is excluded from a transcatheter procedure for 6 months, effectively eliminating transcatheter as an option for most of these patients.  Here is the exclusion statement in the PARTNER Trial.

4. Any therapeutic invasive cardiac procedure performed within 30 days of the index procedure, (or 6 months if the procedure was a drug eluting coronary stent implantation)

Why are CAD patients being excluded?  Below are a few pictures that might explain the reason.  Careful examination of angiograms post implant of both a balllon expandable and a self expanding transcatheter valve show the distinct possibility of the implant obstructing the coronary ostia, not from blood flow, but from subsequent guide catheter insertion.   The last photo clearly shows an ostium with an obstructed entrance.  By implanting a transcatheter valve, the patient’s coronaries may become predictably inaccessible in the future.  I assume most cardiologists would agree this is a good reason to exclude transcatheter procedures in patients presenting with CAD.  By providing an immediate less invasive procedure, a future less invasive procedure may be forfeited.

Graphic Source, Anatomy of the Aortic Valve Complex and Its Implications

Graphic Source, Anatomy of the Aortic Valve Complex and Its Implications

In summary – if only 60% of patients over age 70 present with a stenotic tricuspid valve and 65% of these have severe CAD, that leaves only 21% of all stenotic AVR patients over age 70 eleigible for a transcatheter procedure (did I do the math right?).

My point – Transcatheter procedures will not dominate the market due to fundamental clinical restraints.  AVBG, which is agnostic to valve shape or concomitant coronary artery disease, is a logical less invasive choice for many patients.

The answer is yes.

Our device can be viewed as both complementary and directly competitive to the new class of transcatheter valves being developed by Edwards, Medtronic, and others.

It is complementary because it can be implanted in patients that present with a bicuspid shaped valve – a condition strictly contraindicated for transcatheter valve devices.  Even though only 2% of the population is born with a bicuspid shaped valve, over 40% of stenotic aortic valve patients over the age of 70 present with a bicuspid valve!

Our device is also directly competitive because, frankly, it is a better “off pump” solution even for patients presenting with a tricuspid valve.  Unlike transcatheter devices, our device:

1. Is combined with a surgeon selected “off the shelf” prosthetic heart valve with a proven long term implant history and therefore does not require substantial investment into a new class of heart valve.
2. Does not require the implantation of a pacemaker – 30% of transcatheter patients do.
3. Will not inhibit future coronary artery interventions – most transcatheter valves do.
4. Is safe, relying on minimally invasive “line of site” implant management techniques already fully established by skilled cardiac surgeons.
5. Is substantially less expensive, positioned to compete in the current healthcare environment.

James S. Gammie, M.D., Associate Professor of Surgery, Maryland Heart Center

Dr. James Gammie, a cardiac surgeon at the University of Maryland, has performed many AVBG (Aortic Valve Bypass Graft) procedures over the past few years.

Recently, Shelly Wood, a reporter for heartwire, did a story on his work in this area.  The article is titled Aortic-valve bypass: A time-tested, minimally invasive alternative to valve-replacement surgery.   I think Ms. Wood did an excellent job explaining the procedure and Dr. Gammie’s clinical experience.  Below is an excerpt from her article.

But Gammie believes that AV-bypass surgery would likely compete directly with transcatheter aortic-valve replacement and indeed has several advantages.

For one, a wide range of valve prosthetics can be used in the apicoaortic conduit-those used in Gammie et al’s study have a long track record of safety and durability, he notes. Likewise, the procedure itself, while not widely used, has proven its durability. “There are people walking around today who had this operation a quarter century ago,” Gammie points out. “So we know it’s a durable approach.”

Third, there is no disruption to the native valve and no permanent prosthetic forced over the calcified valve leaflets, thus reducing the risk of both perioperative and long-term stroke. There’s also no risk of heart block-a side effect seen following the implantation of permanent percutaneously placed devices, Gammie notes. Finally, perivalvular leak is not a potential problem, since the device does not need to be sized within the native valve. “So patient-prosthetic mismatch is not a problem,” he said.

On a more hypothetical note, Gammie said that he and his colleagues are testing whether diverting blood flow away from the calcified native valve would in itself decrease stroke rates over the long term. Preliminary analysis suggests that roughly two-thirds of the blood volume may be diverted through the conduit, a rerouting that may prove beneficial over time. “Our hypothesis, which we haven’t proven yet, is that AV bypass surgery may be ‘brain-protective,’ because of the blood flow configuration in the long term,” he speculated.