Heavy Burden of Residual Thrombus After Thrombectomy Signals Worse Primary PCI Results

Among patients with STEMI undergoing aspiration thrombectomy before primary PCI, those with the most residual thrombus before stenting have poorer microvascular function and greater myocardial damage, a retrospective analysis shows. The findings may help provide an explanation for the failure of recent trials to show a benefit of routine thrombectomy in this setting.

“Aspiration thrombectomy can no longer be recommended as a routine strategy in patients with STEMI,” lead author Takumi Higuma, MD, PhD (Hirosaki University, Japan), and colleagues write in a study published in the October 10, 2016, issue of JACC: Cardiovascular Interventions. “However, our results strongly indicate that a more thorough removal of thrombus is beneficial to patients with large thrombus burden, which can be achieved by more effective aspiration thrombectomy devices with effective antithrombotic therapy.”

The view of aspiration thrombectomy has changed substantially in recent years. Earlier studies suggested that routine use led to better primary PCI results, with the TAPAS trial demonstrating improved myocardial blush grade and reduced 1-year cardiac mortality. Those results supported a guideline recommendation for routine thrombectomy and subsequently sparked regular use at most centers.

Momentum shifted with publication of the TASTE and TOTAL trials, both of which showed that routine thrombectomy failed to reduce mortality compared with standard PCI alone. Moreover, stroke risk was higher among TOTAL participants who had thrombus removed. Those findings supported a new class III recommendation (indicating no benefit) against routine use of thrombectomy.

But whether more effective thrombus aspiration can improve outcomes remains an open question that would require additional trials using newer devices, commented Sanjit Jolly, MD, MSc, of McMaster University (Hamilton, Canada), who was a principal investigator of the TOTAL trial.

“I think the caveat is that they would need to target only the highest-risk subset, those patients with the highest thrombus burden,” Jolly told TCTMD. “I think it’s unlikely to be of benefit in every single patient.”

No Reflow Common With More Residual Thrombus

Higuma and colleagues performed a retrospective analysis of 109 patients who underwent aspiration thrombectomy followed by stenting at Hirosaki University Hospital within 24 hours of STEMI onset. Optical coherence tomography (OCT) was performed after thrombectomy in all patients.

Patients in the top third according to the amount of residual thrombus after thrombectomy were more likely to have myocardial no reflow (44.4% vs 16.7%; P = 0.001), defined as a TIMI flow grade no higher than 2 or TIMI flow grade 3 with a myocardial blush grade of 1 or lower on the final angiogram. The relationship remained after accounting for baseline TIMI flow (OR 3.12; 95% CI 1.01-9.66), “indicating the significance of residual thrombus burden on clinical outcomes,” the authors say.

Patients in the highest tertile of residual thrombus also showed greater myocardial damage as measured by peak creatinine kinase MB (391 vs 90 IU/L; P = 0.002).

The investigators did not evaluate clinical outcomes, but they note that the no reflow phenomenon has been associated with both short- and long-term mortality in patients undergoing primary PCI.

Thrombectomy Remains a Treatment Option

Jolly noted that prior studies conducted before thrombectomy was widely used identified a relationship between higher thrombus burden and worse primary PCI outcomes. The current study is unique, he said, in that it demonstrates the same association using a sensitive measure (OCT) in a group of patients who all underwent thrombus aspiration.

There remains a question, however, about whether thrombus burden is a risk marker or a cause of the poorer results, he said. The findings of Higuma et al complement those from TOTAL “in providing more detailed data that perhaps we need better devices and perhaps we need to target a specific subset of the population, not everyone,” Jolly said.

In an accompanying editorial, Eric Powers, MD (Medical University of South Carolina, Charleston), questions why the recent trials contradicted the earlier positive studies.

“In addition to the possibility that thrombus removal is not beneficial, several other possible explanations for the absence of benefit observed in these trials should be considered,” he says.

“Treated arteries may have contained only a small thrombus burden, as observed in the optical coherence tomography substudy of TOTAL,” he writes. “Perhaps infarction was nearly complete when PCI was performed, limiting the possible benefit of any intervention including thrombectomy. In addition, outcome in both thrombectomy and control groups was excellent in studies failing to demonstrate benefit of thrombectomy, perhaps making the demonstration of benefit more difficult.”

The current analysis suggests that inadequate thrombectomy could be to blame, Powers says, adding that the potential benefit of removing thrombus is still an area open to further study.

“In the meantime,” he concludes, “I expect that most interventional cardiologists will continue to consider thrombectomy as a treatment option for patients with STEMI.”

Sources:

• Higuma T, Soeda T, Yamada M, et al. Does residual thrombus after aspiration thrombectomy affect the outcome of primary PCI in patients with ST-segment elevation myocardial infarction? An optical coherence tomography study. J Am Coll Cardiol Intv. 2016;9:2002-2011.
• Powers ER. Aspiration thrombectomy: the possible importance of effective thrombus removal and minimal residual thrombus burden. J Am Coll Cardiol Intv. 2016;9:2012-2013.

Related Stories:

• Thrombectomy Results Underwhelming in AMI Patients
• TOTAL: Use of Routine Thrombectomy in Primary PCI Takes Another Blow
• TOTAL Substudy: Routine Thrombectomy Again Tied to Strokes, Major Disabilities