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Heart Valve Class Action Dismissed on Merits

Victor Lewin - Wednesday, August 15, 2012

A medical product liability class action was recently dismissed following a lengthy 138-day trial. The trial spanned over two years, from 2010 to 2011. The length and complication of the trial in reflected in the length of the detailed decision.

The plaintiff and class members each had implanted mechanical prosthetic heart valves and annuloplasty rings with Silzone, which is a proprietary term for a coating comprising layers of titanium, palladium and an outer layer of metallic silver. This was applied to the polyester sewing cuff that surgeons use to attach a prosthetic heart valve to heart tissue. Silver is known as an antimicrobial in medicine and the Silzone coating was designed to inhibit the growth of the bacteria that can cause endocarditis, an infection that is a serious complication of heart valve surgery.

The medical products were implanted in Canadian patients between September 1997 and January 21, 2000, when the defendants issued a worldwide recall of all Silzone-coated products. At that time, an ongoing randomized clinical trial called 'AVERT' revealed a small, but statistically significant increase in explants due to a medical complication known as paravalvular leak (PVL) in patients who had received a Silzone implant.

It was alleged that the Defendants designed and manufactured the products such that they were unsafe for use. It was not disputed that the silver within the product can be poisonous to human cells. However, at the time that Silzone was developed, the silver had been shown to be effective against bacteria and safe to use in applications such as wound dressings, sutures and catheters.

A few Canadian hospitals stopped using Silzone-coated devices in the year preceding the recall and in November 1999, the United Kingdom Medical Devices Agency (MDA) issued an Advice Notice to physicians warning about possible thromboembolic complications.

The MDA took no other action, but within days of this notice, Australian and New Zealand regulators withdrew approvals for Silzone products in those countries. Health Canada and the United States Food and Drug Administration (FDA), as well as the Data Safety Monitoring Board (DSMB) for the AVERT clinical trial, were well-informed about this, but they did not express concerns about the safety of the valve or take any action.

The claim against the defendants was based in negligence. The evidence focused mainly on two of its major elements: breach of duty causing injury and cause. The trial examined the defendants' conduct in designing, testing and marketing the Silzone valve and considered whether Silzone has an adverse effect on tissue healing and whether the risk of medical complications is greater for patients with Silzone valves.

The plaintiffs needed to establish, on a balance of probabilities, a "but for" negligent act or omission linking the defendants' conduct to a class-wide injury in order to move the claims of each class member forward to individual hearings.

They tried to show that the defendants failed to reasonably evaluate the utility and safety of Silzone before introducing it to the market and then failed in their duty to warn of its risks. A theme was that the Silzone valve was rushed to market in view of the pending expiry of the patent for the defendants' successful bileaflet valve.

The plaintiffs advanced the theory that Silzone is a toxic substance that interferes with the cells involved in tissue healing and impairs the body's ability to properly incorporate the Silzone device into the heart, thereby causing or contributing to a variety of serious medical complications for Silzone patients.

As medical complications can occur with all prosthetic heart valves, the trial judge focused on whether that heart valve puts patients at a materially increased risk of experiencing one or more of these complications. The defendants did not dispute that Silzone probably materially increased the risk of PVL for some patients for some period of time post implant. The explanation for this is unclear.

However, the Court found that there was insufficient evidence to conclude that Silzone increased the risk of the other medical complications that were in issue. The judge found that the plaintiffs did not succeed in proving that Silzone has an adverse effect on tissue healing.

Although there is a high duty of care imposed on a medical device manufacturer, the plaintiffs did not establish that the defendants failed to exercise a reasonable degree of care in the pre-market design and testing or in the post-market surveillance of Silzone-coated products that would be expected of a reasonable and prudent prosthetic heart valve manufacturer in similar circumstances.

These findings, based primarily on a lack of evidence, led to the conclusion that the action must be dismissed.

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