Thrombectomy Results Underwhelming in AMI Patients

PARIS, France—Thrombectomy does little to improve flow area and often fails to completely remove thrombus when used in conjunction with primary percutaneous coronary intervention (PCI) to treat patients with ST-segment elevation myocardial infarction (STEMI). But when such therapy is used, rheolytic thrombectomy outperforms manual aspiration, according to results of 2 studies presented Wednesday, May 16, at EuroPCR 2012.

TROFI

Patrick W. Serruys, MD, PhD, of Erasmus Medical Center (Rotterdam, the Netherlands), presented results of the TROFI trial, which randomized 141 STEMI patients at 5 European centers to primary PCI with (n = 71) or without (n = 70) thrombectomy. Baseline characteristics and procedural details were similar between the groups, although there was a trend for increased glycoprotein IIb/IIIa inhibitor use in the non-thrombectomy arm (62.8% vs. 47.8%; P = 0.09) as well as increased transradial PCI (27.1% vs. 14.1%; P = 0.06). Seven percent of patients who were not initially randomized to receive thrombectomy crossed over to the thrombectomy arm.

The researchers used optical frequency domain imaging (OFDI) to determine the primary endpoint of postprocedural minimum flow area, finding the outcome was not statistically different between the groups, though there were numerical improvements in the thrombectomy arm in that and several other endpoints (table 1).

Table 1. TROFI: Postprocedural Outcomes

At 6 months, the numerical difference in minimal flow area in favor of thrombectomy persisted (6.05 mm² vs. 5.61 mm²), but the difference was still not significant (P = 0.31).

The researchers also used 6-month OFDI to analyze 49 of the patients from 3 of the centers to determine the degree of incomplete stent apposition (ISA), strut coverage, and other parameters, finding no differences in the 2 arms.

Table 2. Six-Month Outcomes

Abbreviation: ISA, incomplete stent apposition.

“We don’t know if it’s the play of chance or some confounding effect,” Dr. Serruys said regarding the similarity in minimal flow area between arms. “I was a little bit surprised to see so little difference between thrombectomy and non-thrombectomy.”

Would You Treat?

Interestingly, after completion of the trial, OFDI images were sent to the operators, who were asked to judge the necessity of further treatment based on the pictures showing minimum flow area and largest intraluminal mass area. In 38% of cases, at least 1 operator indicated there was a need for further treatment.

Commenting on the trial, panel co-chair Javier Escaned, MD, PhD, of Hospital Clínico San Carlos (Madrid, Spain), noted the numbers needed in the TAPAS trial (over 1,000 patients) to show benefit with thrombectomy compared with the small numbers in TROFI. “Immediately, you realize it will be very difficult to get in a single [study such as this] some information that will tell us what the real benefit of thrombus aspiration is in AMI,” he said. “Having said that, thrombus aspiration has been the only technique that has improved mortality in AMI in the last 10 years, and if it is guided by angiography, it is very difficult to believe that we cannot obtain any benefit.”

Dr. Serruys, though, noted that the mortality benefit shown in TAPAS was not the trial’s primary endpoint. Rather, TAPAS was powered for the surrogate endpoint of myocardial blush grade. “That monocenter study was not duplicated more than 1 or 2 times with large numbers,” Dr. Serruys said. “There were a multitude of studies with surrogates, and if you do a meta-analysis of those, the effect on mortality is reinforced. It would be interesting to rechallenge that [in a large study] with the primary endpoint of mortality.”

SMART

In a trial comparing different thrombectomy techniques, David Antoniucci, MD, of Careggi Hospital (Florence, Italy), and colleagues randomized 80 STEMI patients to primary PCI plus either rheolytic thrombectomy (n = 40) or manual aspiration (n = 40).

Baseline characteristics in the SMART (compariSon of Manual Aspiration with Rheolytic Thrombectomy in primary PCI) trial were similar between the 2 groups. Following treatment, TIMI flow grade was improved with the patients receiving rheolytic thrombectomy instead of manual aspiration (2.8 ± 0.4 vs. 2.5 ± 0.7; P = 0.04), as was TIMI thrombus grade (1.6 ± 0.9 vs. 2.4 ± 1.2; P = 0.001). Early ST-segment resolution was also numerically superior with rheolytic thrombectomy, though the difference just missed statistical significance (92% vs. 77%; P = 0.06).

On optical coherence tomography (OCT), all but 1 patient had residual thrombus after either type of thrombectomy. The primary endpoint of number of quadrants containing thrombus on OCT was improved with rheolytic thrombectomy, but not to a significant extent (53 vs. 65; P = 0.083). The same was true of maximal thrombus area (1.7 mm² with rheolytic thrombectomy vs. 2.0 mm² with manual aspiration; P = 0.092).

The only significant difference, in fact, was in the number of patients with coronary quadrants containing thrombus greater than the median value, which was lower with rheolytic thrombectomy (37% vs. 60%; P = 0.039).

Thrombus Left Behind

“With currently available devices, you cannot completely remove the thrombus in the large majority of patients,” Dr. Antoniucci concluded. “Rheolytic thrombectomy, however, is more effective at thrombus removal, as shown by differences in OCT results despite the fact that the primary endpoint was not met. But considering the totality of the results, we can say rheolytic thormbectomy is associated with better myocardial reperfusion.”

Francesco Prati, MD, of San Giovanni Hospital (Rome, Italy), commented that the data fit with his group’s experience. “We saw that about 50% of the thrombus is still there after manual aspiration,” he said. “Also, in general, this fits with the negative data from INFUSE AMI presented at [the 2012 American College of Cardiology/i2 Annual Scientific Session  in Chicago, IL].”

Dr. Escaned, though, raised another possibility that he has seen evidence of in his own research. “What you remove may be the more dangerous, friable component of the thrombus,” he said. “The idea that we had is that even when you don’t completely remove the thrombus, you at least get rid of the [worst] part of it.”

Sources:

1. Serruys PW. Six-month results of randomized study to assess the effect of thrombus aspiration on flow area in STEMI patients: An optical frequency domain imaging study (TROFI). Presented at: EuroPCR; May 16, 2012; Paris, France. 
2. Antoniucci D. CompariSon of Manual Aspiration with Rheolytic Thrombectomy in Acute Myocardial Infarction: The SMART Primary PCI Trial.Presented at: EuroPCR; May 16, 2012; Paris, France. 

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• INFUSE-AMI: Bolus Abciximab Works, Thrombus Aspiration Doesn’t for Large STEMI
• MUSTELA: Thrombectomy Use Not Associated with Smaller Infarcts at 1 Year
• Meta-Analysis: Thrombectomy Improves Reperfusion But Not Clinical Outcome in STEMI