Elena Zapata-Arriaza, MD
@ElenaZaps
There is enough scientific evidence to employ endovascular treatment (EVT) for acute ischemic stroke (AIS) caused by large vessel occlusion (LVO). However, in the case of Medium Vessel Occlusion (MeVO), there are still gaps in knowledge in terms of safety and efficacy that must be clarified to indicate EVT in these occlusions. In order to determine the clinical course of acute ischemic stroke due to MeVO with and without intravenous alteplase treatment, Ospel and colleagues performed the following study.
Patients with MeVO (M2/M3/A2/A3/P2/P3 occlusion) from the INTERRSeCT and PRoveIT studies were included. Baseline characteristics and clinical outcomes were summarized using descriptive statistics. The primary outcome was a modified Rankin Scale score of 0 to 1 at 90 days. Secondary outcomes were the common odds ratio for a 1-point shift across the modified Rankin Scale and functional independence (modified Rankin Scale score 0-2). The authors compared outcomes between patients with versus without intravenous alteplase treatment and between patients who did and did not show recanalization on follow-up computed tomography angiography.
Among 258 patients with MeVO, the median baseline NIHSS was 7. A total of 72.1% patients were treated with intravenous alteplase, and in 41.8%, recanalization of the occlusion (revised arterial occlusive lesion score 2b/3) was seen on follow-up computed tomography angiography. Excellent functional outcome was achieved by 50.0%, and 67.4% patients gained functional independence, while 8.9% patients died within 90 days. Recanalization was observed in 21.4% patients who were not treated with alteplase and 47.2% patients treated with alteplase (P=0.003). Intravenous alteplase was related to ordinal mRS, but not with excellent outcome or good clinical outcome. Early recanalization (adjusted odds ratio, 2.29) was significantly associated with excellent functional outcome, while intravenous alteplase was not (adjusted odds ratio, 1.70).
There may be a generalized concept of less severe deficits in more distal vessel occlusions, excluding such occlusions from EVT in the acute phase. However, the present study reveals limitations to the previous sentence, which should make us rethink the use of mechanical thrombectomy in MeVO. First, the mean NIHSS score for these occlusions is 7, which is already considered limiting and a candidate for EVT in large published clinical trials. Secondly, the mortality rate at 3 months is 8.9%, which beats logic considering that they are distal occlusions that should not be associated with severe deficits or mortality of such a proportion. Likewise, the rate of functional independence (mRS 0-2) is 67.4% and the excellent functional outcome is 50%, which is related to the data obtained for large vessel occlusions, but insufficient again for distal occlusions. And, ultimately, early recanalization is the only independently associated variable with an excellent functional outcome. Therefore, we could argue in the light of these results that MeVO can be disabling, with significant mortality rates, and that the only thing that guarantees a good functional result, as always, is early recanalization of the vessel.
However, despite having increasingly safe and effective devices for more distal intra-arterial navigation, we must not forget that the further the occlusion is, the greater the risk of vessel perforation, because we are adding technical complexity to the procedure. The latter could explain the high mortality rate in these patients despite VTE. Likewise, we must be cautious when comparing an occlusion in P3 and equating it to an occlusion of A2, since surely the eloquence of both locations is different and therefore the risk-benefit balance is inclined differently in each case. Likewise, M2 occlusions are considered increasingly in large vessel occlusion trials and only distal segments beyond M2, included in MeVOs.
In any case, and in the absence of randomized clinical trials on the subject, it is possible that we should stop thinking about the caliber of the vessel and consider the patient’s symptoms as an inclusion criterion for EVT in patients with stroke, as long as the interventionist has experience and cathether access capabilities in such MeVOS recanalization considerations. It is exciting to see the development of more treatment options for recanalization beyond large vessel occlusions.
