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- HeartWire

08/06/2007 - ST-elevation MI (STEMI) patients who have a large thrombus burden on angiography are at high risk of adverse outcomes and stent thrombosis following primary PCI, according to a new study. Dr George Sianos (Thoraxcenter, Rotterdam, the Netherlands) and colleagues report their findings online July 30, 2007 in the Journal of the American College of Cardiology.

The researchers set out initially to devise a new thrombus classification system and found that they could stratify STEMI patients into one of two groups angiographically—large thrombus burden or small thrombus burden. Incidentally, one-third of the patients classified as having large thrombosis burden received thrombectomy, "and they did better clinically and experienced lower stent-thrombosis rates. This was a completely unexpected finding and it's encouraging," Sianos commented to heartwire.

Acknowledging that use of thrombectomy devices in STEMI is controversial, following studies in which it has been shown that the procedure may be harmful, Sianos is nevertheless confident that targeting the most appropriate patients [for thrombectomy] by using thrombus burden as a screening tool is the right way to go. However, he concedes that prospective randomized trials are needed to confirm these findings.

Sianos and colleagues proposed a simple angiographic thrombus classification system and retrospectively analyzed 812 consecutive patients treated with drug-eluting-stent (DES) implantation for STEMI between April 2002 and December 2004.

"Angiography is the only imaging modality that is used for decision-making during primary PCI, and it's a visual validation, so it's easy to use and it's clinically relevant," Sianos commented to heartwire.

They observed an incidence of angiographically documented stent thrombosis of 3.2% at two years but note that this probably underestimates the true incidence of stent thrombosis "because sudden deaths and repeat MIs may also be related to this complication." In addition, patients continue to present with stent thrombosis beyond the two-year time window, they say, citing recent studies showing very late DES thrombosis in STEMI patients.

They found that a large thrombus burden (two vessel diameters or greater) was an independent predictor of mortality (hazard ratio 1.76, p=0.023) and major adverse clinical events (MACE) (HR 1.88, p=0.0001). And infarct-related artery stent thrombosis was extremely high in the group with large thrombus burden compared with the one with small thrombus burden (8.2% vs 1.3% at two years, respectively; p<0.001).

"This is the first report accounting for thrombus burden," they say. "A large thrombus burden is a fundamental factor for adverse clinical outcomes because it is related to increased 30-day mortality and very high rates of infarct-related artery stent thrombosis, which account for the majority of the post-30-day MACE."

All of the patients in this study received DES for STEMI, which is the policy at Thoraxcenter, but Sianos stressed that the study "is not powered to determine whether DES should be implanted or not. But what it tells us is that if you see stent thrombosis, it's not clear whether it's related to the [specific] stent, but it is related to the thrombus burden, so we should do something for the thrombus."

After the first month following PCI, the majority of events that are happening are stent thrombosis, "and we found that thrombus burden has predictive value and that stent thrombosis is mainly observed in those with large thrombus burden, and that is very important," Sianos commented. There was also a difference in clinical outcomes in those with large vs small thrombus burden, he added.

Other significant predictors of infarct-related artery stent thrombosis were thrombectomy—which protected against thrombosis—and bifurcation stenting, which increased the risk (HR 4.06; p=0.002) and which Sianos et al note has previously been recognized as a risk factor in stable patients treated with DES. They say bifurcation stenting "should be avoided if not absolute necessary."

In their patients with large thrombus burden (n=225), rheolytic thrombectomy with the Possis Medical Inc system was performed in 59 patients and reduced infarct-related artery stent thrombosis by almost 90% (hazard ratio 0.11, p=0.03) compared with those with large thrombus burden who did not undergo thrombectomy.

Sianos stressed that it should not be deduced from these data that DES should not be used in someone with a large thrombus burden. "But if you see a large thrombus burden, use a thrombectomy device to take it out. If you don't see a large thrombus burden, you should not do thrombectomy because it might be harmful," he added.

Doctors can then choose whether to use a bare-metal stent or a drug-eluting stent, he added.

Thrombus burden did not influence the clinical antirestenotic efficacy of DES, either, the researchers note. "We know that from an efficacy point of view, DES are even better than bare-metal stents in the STEMI setting," Sianos noted. He believes that performing thrombectomy in those with a large thrombus burden will mean that those receiving DES will "perform equally from a safety point of view."

Currently, at Thoraxcenter, they still have a policy of DES for all-comers, he explained. "Our policy now is to take out a large thrombus, give a DES, and prescribe dual antiplatelet therapy for a year, and our results are getting better," he noted. But before this strategy can be extended to other institutions, "these devices should be further tested," he stressed.

He added that dual antiplatelet therapy may soon be extended for more than one year, noting that it was not used in multivariate analysis for this study because at the time it was performed the standard treatment duration was only six months.

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