Small Clots on Replacement Aortic Valves Deserve Attention

A large study presented at last month’s American College of Cardiology meeting reported that slightly more than 1 in 10 patients with aortic valve replacements (tissue valve) had small clots on the leaflet of the new valve. The study included 890 patients.

The clots, which doctors call “subclinical thrombosis,” cannot be seen on regular echo studies; researchers used 4D CT scans.

This could be a big discovery.

One of the frontiers in cardiology is the replacement of aortic valves without open heart surgery. We call this procedure TAVR or transcatheter aortic valve replacement. Basically, the new (tissue) valve is delivered via a catheter placed in the leg artery–like a heart cath.

A few years ago, we reserved TAVR for people too sick to have open-heart surgery (SAVR–surgical aortic valve replacement). Now, TAVR is on the brink of being offered to somewhat younger and healthier patients.

I wrote a post on this new study: Small Clots in Bioprosthetic Aortic Valves Should Slow TAVR Train.

I interviewed senior author Dr. Raj R. Makkar from UCLA.

There does not seem to be much talk about this study. Mainstream media mostly ignored it. My column garnered little attention or commentary.

Here are some bullet points from the study.

• Researchers saw the small clots more often on valves placed via a transcatheter (TAVR) route than those placed via open-heart surgery (13.4% vs 3.6%).
• The study included more than eight different types of valves from different valve companies. No one valve stood out as a problem.
• Drugs that block coagulation (warfarin and the NOACs) reduced the likelihood of the clots while aspirin and other anti-platelet drugs did not.
• NOAC drugs (dabigatran, rivaroxaban and apixaban) looked to be as good as warfarin for preventing/resolving the clots.
• The presence of clots restricted leaflet motion. A course of anticoagulant drugs resolved the restricted leaflet motion. In a small number of these cases, when anticoagulants were stopped, the clots came back.
• Patients with clots had slightly higher gradients across the valve–measured by a regular echo-Doppler. These gradients are in the range we typically pass off as “normal due to a tissue valve.”
• The presence of clots associated with a higher rate of TIA (mini-stroke). Note the verb associate is not the same as cause. This sort of study cannot sort out whether the clots caused the increased rate of TIAs, or whether it was due to a play of chance. Clots did not associate with stroke or death.

In my post on theheart.org | Medscape Cardiology, I wrote a few paragraphs on why this may be a practice-changing study.

First and foremost, the great advantage of tissue valves over mechanical valves is not having to take drugs that block coagulation, such as warfarin. But… in this study, anticoagulants seemed to prevent and resolve the small clots. If these findings are confirmed, we may need to think about screening for the presence of these clots.

Screening would be a big deal because it requires a special CT scan, and most patients did not have the clots.

Second, researchers found clots more often on transcatheter valves. There are many plausible reasons why this would be, but it’s important to say this study alone cannot definitively determine which valve type (TAVR v SAVR) is more likely to have the clots.

Valve longevity is another reason this may be an important discovery. The downside tradeoff with tissue valves relative to mechanical valves is shorter longevity. Is this due to turbulent flow from restricted leaflet mobility? If anticoagulants prevent small clots and improve leaflet opening, perhaps the decreased turbulence will lessen long-term wear-and-tear? I wrote those sentences as questions intentionally. I don’t know.

This study, like all good studies, raises many questions for future study. I look forward to learning more about this issue.

This discovery also highlights the challenge of making progress in cardiology. It’s hard work. I may be wrong, but it’s likely we are in a period of slow incremental progress.

JMM