Long Thrombus Length a Greater Problem With IV tPA Than With Aspiration Thrombectomy

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Longer thrombus length has a negative impact on outcomes among patients with large-vessel occlusion (LVO) ischemic stroke, but this deleterious effect is particularly notable among patients treated with IV tPA alone, with those receiving tPA plus aspiration thrombectomy being impacted less.

The findings, from a post hoc analysis of the THERAPY trial, were published online June 8, 2017, ahead of print in Stroke.

In an independent commentary for Neurovascular Exchange, Markus Möhlenbruch, MD (University of Heidelberg, Germany), wrote via email that previous research has demonstrated that thrombus length does not negatively impact the outcome of thrombectomy using stentrievers. It is less clear, however, whether length affects the outcomes of aspiration thrombectomy.

For the THERAPY trial, 108 patients LVO stroke and a prospectively measure thrombus length ≥ 8 mm were randomized to aspiration thrombectomy plus IV tPA (alteplase) or to IV tPA alone. Overall, 28% of patients had occlusions of the internal carotid artery, 62% of the M1 artery, and 10% of the M2 artery. The new post hoc analysis, led by Albert J. Yoo, MD, PhD (Texas Stroke Institute, Dallas, TX), looked specifically at how thrombus length might interact with treatment type to influence outcomes.

Median thrombus length was 14.0 mm, with an interquartile range of 9.7-19.5 mm. Having a longer thrombus length was associated with a poorer outcome, as defined by 90-day mRS score (OR 1.24 per 5-mm increase; 95% CI 1.04-1.52; P = 0.02). The association remained significant even after adjusting for age, baseline NIHSS score, history of diabetes mellitus, and treatment allocation.

A longer thrombus length was also associated with more serious adverse events, more symptomatic hemorrhages, and increased mortality, even after adjustment for the same key outcome predictors. It was not linked with angiographic reperfusion, but procedure times were longer with longer thrombi.

Outcomes According to Thrombus Length (per 5-mm Increase)

	Adjusted OR (95% CI)	P Value
90-Day mRS	1.33 (1.09-1.66)	0.004
90-Day Serious Adverse Events	1.37 (1.09–1.81)	0.014
Symptomatic Intracranial Hemorrhage	1.33 (1.02–1.77)	0.032
90-Day Mortality	1.36 (1.06–1.77)	0.014
TICI 2b/3 (Intra-Arterial Therapy Arm)	1.34 (0.94–2.22)	0.172

Greater thrombus length was associated with a more pronounced aspiration thrombectomy treatment effect (interaction term P = 0.03), which the authors suggest might be related to a potentially stronger adverse effect of greater thrombus length on 90-day mRS among patients treated with IV tPA compared with intra-arterial therapy.

Thrombectomy Remains Treatment of Choice

Möhlenbruch is quick to point out that thrombectomy remains a preferred treatment for long thrombi, even if outcomes might be poorer than with shorter thrombi. “All recent thrombectomy trials have shown that mechanical thrombectomy improves outcome in thromboembolic stroke,” he said. “While intravenous thrombolysis has a questionable beneficial effect in long thrombi, thrombectomy still is the only therapy proven to be effective in such cases.”

What the findings do suggest, he continued, is that aspiration thrombectomy, while better than IV tPA, might not be the best endovascular approach in cases with long thrombi.

“Neurointerventionalists should not refrain from using stent retrievers instead of aspiration catheters if flow restoration cannot be achieved,” he recommended. The best way to optimize outcomes, according to Möhlenbruch, is for neurointerventionalists to be familiar with all the endovascular tools and techniques available and to understand their advantages and disadvantages, so they can match them appropriately to patients’ needs. “Hence, neurothrombectomy should only performed by physicians with expertise in neuroangiography,” he added.

Möhlenbruch identified some limitations to the study. “The authors state that occlusion level was not adjusted for because of its collinearity with thrombus length,” he pointed out. “While this is true, occlusion site still is an important factor because carotid T occlusions are generally associated with worse outcome compared to MCA occlusions. Furthermore, thrombus length in carotid T occlusions cannot be estimated as accurately as in MCA occlusions, because the proximal thrombus end cannot be appreciated easily.”

He also noted that thrombus length was measured using reformatted non-enhanced CT scans. While this technology is often sufficient, it is possible that the full length of thrombi might be underestimated if they did not appear hyperdense. Multiphase CT angiography can be more useful in these cases, he added.

Source:
Yoo AJ, Khatri P, Mocco J, et al. Impact of thrombus length on outcomes after intra-arterial aspiration thrombectomy in the THERAPY trial. Stroke. 2017;Epub ahead of print.

Disclosures:

Möhlenbruch reports no relevant conflicts of interest.
Yoo reports receiving funding for imaging core lab activities.

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