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Home » Stent News » December 29, 2006

Collateral Circulation in the Coronary Arteries
May Be Inhibited by Drug-Eluting Stents

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December 29, 2006 -- Adding fuel to the firestorm that many thought had subsided, the January 2 issue of the Journal of the American College of Cardiology contains an article from the team at University Hospital in Bern, Switzerland that highlights yet another potential problem with drug-eluting stents.


Collateral vessels in blocked left coronary circulation
 

When a coronary artery becomes blocked, the body's natural response is to mediate the potential danger by developing "collaterals", tiny blood vessels that can supply the heart muscle with a reduced but sufficient supply of blood (and oxygen).

This collateral circulation serves as a protective "buffer", guarding against the potentially sudden and destructive cut-off of oxygen that occurs during a heart attack.

But the Swiss researchers found that drug-eluting stents seem to inhibit the growth of these collaterals. A cohort of 120 patients was chosen and divided into two groups: those patients who had received bare metal stents (BMS) and those who had received the newer drug-eluting stents (DES). Six months after implantation, all participants were studied, specifically with respect to their collateral circulation. The results were significant. The study states:

"The novel result of this study is that coronary collateral function six months after implantation of a DES is 30% to 40% lower than that obtained equally long after bare-metal-stent implantation.... Considering the salvaging effect of well-grown collaterals, a potential clinical impact of this finding is that in the presence of stent thrombosis, myocardial infarct size and thus mortality may be larger in DES than in bare-metal-stent-treated patients."

In other words, drug-eluting stents, which have been implicated in "slightly higher rates of late stent thrombosis", may also be responsible for that thrombosis (blood clot) resulting in a worse outcome because the development of collateral circulation has been inhibited: stent thrombosis is not only slightly more frequent, but 30-40% more likely to result in a heart attack..

The study does not explore the mechanisms that might be responsible and, in fact, only shows "an association" between the lack of collaterals and drug-eluting stents -- no causative factors were identified. And, of course, this study was relatively small, only 120 patients, and needs to be validated by replication. However, the clinical implications of having impaired collateral circulation may be significant for patients, no matter which type of stent is placed.

Using a simple and inexpensive technique, called "washout collaterometry", it is possible to measure collateral circulation before stents are placed. As reported by Shelley Wood in theheart.org, Dr. Bernhard Meier explains the technique. Just before stent placement, a balloon is inflated to open up the artery. Watching the injection of contrast dye for about 45 seconds reveals the existence (or absence) of collaterals. Dr. Meier continues:

"If the contrast medium is washed out within less than 10 seconds or 10 heartbeats, the collaterals will completely prevent an infarction [heart attack] in case of later stent thrombosis. If it is not washed out at all at 45 seconds, there are no collaterals to speak of, and stent thrombosis has to be avoided at all cost."

Dr. Meier added these comments when queried by Angioplasty.Org:

"Indeed, if there are no collaterals (unfortunately more common than not), the placement of a stent (conferring a thrombosis risk of about 3% over the subsequent years) and even more so the placement of a drug-eluting stent (thrombosis risk about 5%) should be carefully weighed against the risk of abrupt closure if no stent is placed). However, we have unfortunately moved way beyond the point where conditional stenting is pondered as an option."

When referring to "conditional stenting", Dr. Meier recalls the time when "Plain Old Balloon Angioplasty" (POBA) was the dominant technique, and stents were only placed in situations where it seemed beneficial. Today stents are used in virtually all angioplasty procedures, a situation characterized by Dr. Meier as "unfortunate".

Adding to the importance of collateral circulation is recent research and trials in the area of angiogenesis. For example, recent studies by Cardium Therapeutics have shown that the promotion of collateral blood vessel growth, using genetic material, can provide significant benefit for patients suffering from heart failure.

Bottom line: the lack of collaterals should definitely give pause to the interventional cardiologist when deciding to implant a stent, especially a drug-eluting stent.

In recent months, some American cardiologists have minimized the findings of their European colleagues, especially regarding drug-eluting stent problems. Angioplasty.Org would like to note that 30 years ago, it was Dr. Bernhard Meier's patient who underwent the very first coronary angioplasty -- his recounting of the first case can be seen in our video of "The First PTCA". We believe that there is no one with a longer experience in interventional cardiology than Dr. Meier, and that his observations should be taken very seriously.

 


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