Mark N Rubin, MD
Yan S, Hu H, Shi Z, Zhang X, Zhang S, Liebeskind DS, and Min Lou M. Morphology of Susceptibility Vessel Sign Predicts Middle Cerebral Artery Recanalization After Intravenous Thrombolysis. Stroke. 2014

Although initial evaluation and management of stroke is typically straightforward, the dizzying array of “next steps” is matched in intensity only by the mountain of evidence that, in total, only equivocally supports any particular intervention beyond intravenous thrombolysis (IV tPA). We all just want our patients to get better, and it can be difficult if not impossible to make completely evidence-based management decisions in the timely fashion necessary for acute stroke.

All that said, stroke providers stand to benefit from the identification of biomarkers – ideally acquired during a standard clinical evaluation so as not to waste time – that inform prognosis and/or decision-making. Biomarkers of any sort would do, but there has been a focus on high-resolution neuroimaging with MRI in the hyperacute stroke setting in search of some such sign(s). This will surely continue in the era of 6-minute stroke MRI (not to be confused with the 7-minute workout), and MRI was the modality of choice for the investigators from China and the USA who contributed this biomarker study. They sought to clarify the controversy over the prognosticating value of the susceptibility vessel sign (SVS) in acute stroke.

The SVS in acute stroke, which seems to be the radiographic sign of an erythrocyte-rich or “red clot,” has been a tough nut to crack to this point. There have been conflicting studies through the years, with some showing the SVS is a predictor of recanalization and others suggesting the contrary. The SVS has all the makings of a simple, easily acquired and interpreted acute stroke biomarker, previous work suggests “red clots” are particularly amenable to tPA (at least in coronary arteries), and previous studies fail to definitively answer the question of the potential clinical use of the SVS, thus the interest in further research in this field. The investigators in this study performed a retrospective review of prospectively-collected MRI and clinical data from patients with MCA occlusions treated with tPA within 6 hours of symptom onset in order to determine potential prognostic value of the SVS.

The investigators were able to include 72 consecutive patients with acute stroke treated with IV tPA. The SVS was noted in 50/72 patients (~69%) and recanalization was only seen in 33 (~45%) patients at 24 hours. The mean clot length was ~14mm and shape irregularity was noted in 25/50 clots (50%). In brief, both SVS length and irregularity were independently associated with absence of recanalization at 24 hours. The cut-off length for prediction of recanalization was 14mm but no patients with a clot >20mm experienced recanalization.

This study suffers from a modest sample size and retrospective design, but represents the most “pure” sample of patients with SVS receiving tPA to date and an important step forward in our understanding of the SVS and its role as an acute stroke biomarker. Overall, the results suggest a long and/or irregular SVS predict absence of recanalization, something on the spectrum of “tPA failure.” There are many directions one can go with this information – and one should be cautious if considering any clinical decision-making based on these particular data – but the natural thought-leap, which the authors bring up in their discussion, is to best therapy for patients with an acute stroke and the SVS. Should a long and/or irregular clot prompt triage to the angiography suite post haste, with or without tPA, for endovascular reperfusion? Is an adjunctive antiplatelet infusion indicated in this setting? Might these be a subset of patients who benefit the most from sonothrombolysis? To parrot an oft-used phrase, further study is required. Let the hypothesis generation (and study design) begin!