Good Collateral Flow May Justify Expanding Endovascular Stroke Treatment Window

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In patients with good collateral pial circulation in the brain, clinicians may be able to further extend the time window for endovascular treatment in stroke patients beyond that of subjects with poor collateral flow. Results of a consecutive patient series were published online September 29, 2011, ahead of print in Stroke.

Researchers led by Marc Ribo, MD, PhD, of Hospital Vall d’Hebron (Barcelona, Spain), looked at collateral pial circulation in 61 acute stroke patients who received endovascular treatment after persistent occlusion of the internal carotid artery or middle cerebral artery. Collateral scores were assigned based on anatomic extent at initial angiography (grades < 3 = good; 3-5 = poor).

Good collateral pial flow on the brain’s surface sustains the penumbra before recanalization, and is thought to offset infarct growth, reduce hemorrhagic transformation, and even support a higher degree of recanalization. In the study, patients were divided according to good (n = 21) and bad (n = 40) collateral circulation.

Better Outcomes with Good Collateral Flow

The duration of the procedure was no different between patients with good vs. poor collateral flow (94 vs. 100 min; P = 0.701), nor was total ischemic time in those who achieved recanalization (361 minutes in patients with good collateral flow vs. 314 in patients with poor flow; P = 0.32). Among patients with good collateral flow, rates of recanalization were higher while National Institutes of Health Stroke Scale (NIHSS) scores on discharge and infarct volume were lower compared with patients with poor flow (table 1). Median baseline NIHSS was 18.

Table 1. Periprocedural Outcomes Based on Collateral Pial Circulation

In patients with poor collateral circulation, receiver operating characteristic curve analysis determined a total ischemic time window of 5 hours until the start of recanalization (sensitivity 67%, specificity 75%), within which better clinical outcomes were predicted (total ischemic time < 5 hrs: 66.7% vs. total ischemic time > 5 hrs: 25%; P = 0.05). However, among patients with good collateral flow, no time cutoff could be determined.

While clinical improvement was similar for patients recanalized within 5 hours regardless of the status of collateral pial circulation (60% with poor collateral flow vs. 85.7% with good collateral flow; P = 0.35), rates were threefold higher after 5 hours only in patients with good collateral circulation.

Likewise, while infarct size was similar between groups within 5 hours (145 mL with poor collateral flow vs. 93 mL with good collateral flow: P = 0.56), this endpoint was sevenfold lower after delayed recanalization in patients with good collateral circulation. And at 3 months, more patients with good collateral flow had modified Rankin Scale scores less than 2, showing no significant disability (66.7% vs. 15.6%; P = 0.002), driven by the difference after delayed recanalization (table 2).

Table 2. Outcomes After 5 Hours of Total Ischemic Time

After adjusting for age, baseline NIHSS, and occlusion location, total ischemic time less than 5 hours proved to be an independent predictor of clinical improvement in patients with poor collateral pial circulation (OR 6.6; 95% CI 1.01-44.3; P = 0.05), but not in patients with good collateral flow. In addition, after adjusting for the same factors, good collateral circulation was an independent predictor of clinical improvement (OR 12.5; 95% CI 1.6-74.8; P = 0.016).

“The presence of good [collateral pial circulation] predicts a better clinical response to intra-arterial treatment beyond 5 hours from symptom onset,” Dr. Ribo and colleagues conclude. “In patients with stroke receiving endovascular treatment, identification of good [collateral flow] may help physicians when considering expanding the therapeutic time window.”

The authors note that the different outcomes as the time window for recanalization increased in the 2 groups may reflect an accelerated progression of the ischemic penumbra into irreversible infarct due to insufficient collateral flow. They point out that in many cases of endovascular treatment for acute stroke, procedures may last several hours if recanalization is not promptly achieved, in which case the decision to continue or end recanalization efforts often is solely based on time from symptom onset.

Angiography May Help Time-Based Decision

“This decision may deny the benefit of recanalization to some patients with still viable ischemic penumbra,” the study authors assert. “Angiographic assessment of collateral pial circulation may be rapidly performed during endovascular procedures. The information about the presence or lack of good collateral flow… may be used to tailor the therapeutic window in each patient.”

In an e-mail communication with TCTMD, Dr. Ribo explained that the study results help explain the inter-individual variability seen in response to reperfusion therapies for acute stroke. “Some patients in which reperfusion is achieved after 3 hours from symptom onset will not recover and develop a large infarction, whereas others that are reperfused up to 6 or 8 hours later will experience a dramatic recovery,” he said. “Study of collateral flow can help identify these groups.”

Dr. Ribo noted that if pial collateral circulation is well developed, it can work as a natural bypass when a major vessel such as the middle cerebral artery is occluded. “Our work will encourage physicians to grade the collateral circulation in the angiograms during endovascular reperfusion procedures,” he said.

Dr. Ribo estimated that 5% to 8% of US stroke patients receive endovascular treatments, and that the currently accepted window within which clinicians are comfortable performing such procedures after symptom onset is 6 to 8 hours. “Our findings could open the door to widen the window in some patients up to 10 to 12 hours or more,” he said, noting that at his institution, clinicians are using pial collateral flow to do just that in appropriately selected patients.

Study Details

In the study, interventionalists tried to achieve recanalization with repeated local 3- to 5-mg tPA injections or mechanical clot disruption with a guidewire and/or the Merci, Solitaire, or Trevo clot retrievers. Procedures were terminated when recanalization was achieved, or at 6 to 8 hours from symptom onset.

Source:

Ribo M, Flores A, Rubiera M, et al. Extending the time window for endovascular procedures according to collateral pial circulation. Stroke. 2011; Epub ahead of print.

Disclosures:

• Dr. Ribo reports receiving a grant from the Spanish Ministry of Science.

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