Higher Rates of Mortality but Not Morbidity Follow Intracranial Mechanical Thrombectomy in the Elderly

Discussion

Recent effort to optimize patient selection for Merci thrombectomy is beginning to discriminate factors affecting outcome. Our series demonstrates that advanced age predicts overall poor outcome following Merci thrombectomy. This disadvantage is nearly entirely due to the higher rate of stroke-related death, which occurred in nearly half of all patients 80 years of age or older. Nearly all of the clinical variables used in our study incorporate death into their measurement, namely discharge NIHSS score, change in NIHSS score, and mRS score.

Most interesting, if a patient survived the stroke, the probability of good outcome by discharge did not vary according to age. By secondarily analyzing clinical outcomes in such a dichotomized fashion, we were able to account for the impact made by family influence on decisions to withdraw care due to poor prognosis. These family variations confound all analyses incorporating mortality.

Contrary to our initial expectations, the burden of decreased neuronal plasticity accompanying advanced age does not substantially impede neurologic recovery in survivors. This may be more dependent on the fact that, in select patients with salvageable tissue, the success of recanalization has a more significant impact on outcome than age. In fact, all elderly survivors with good clinical outcomes at discharge were successfully recanalized (6/6) compared with 76% of the younger cohort (19/25, P = .3).

By analyzing the stroke survivors separately, however, we significantly limited further comparison in our study by reducing the sample size. Because half of the elderly group was not further analyzed in a number of comparisons, our ability to detect intergroup differences was substantially limited in these instances. However, with nearly similar rates of good outcome among survivors, it appears that functional recovery is similar among differing age groups, even though the good outcome subgroup is composed solely of 6 elderly survivors. Larger samples are clearly needed to substantiate this finding.

These observations are somewhat comparable with findings in the similarly aged cohort receiving IA thrombolysis for acute ischemic stroke.⁷ Both groups in our study had significantly higher mortality rates by discharge (48% and 15%) than their counterparts in the IA rtPA group (18% and 10%, respectively, reported at 7 days). This finding is likely due to the presumably higher proportion of proximal occlusions in our Merci group. Alternatively, there may be some outcome effect from the greater delay in time from symptom onset to intervention in our study, 383 minutes compared with the 259 minutes average delay in our previous IA rtPA report. Similar to the current study, however, previous IA rtPA data showed that age as a dichotomous variable was not a predictor of good (mRS score, ≤2) outcome, though surviving patients were not exclusively compared in a separate analysis and disability at 90 days was the outcome measure used in the IA rtPA cohort. Preliminary analysis of the MERCI and multi MERCI cohort stratified by age has yielded similar results.¹¹

Although IA thrombolysis is a markedly different mechanism of recanalization from mechanical thrombectomy, we found a similar recanalization rate between age groups, which is consistent with previous reports of IA thrombolytic therapy.^6,7,12 Also similar to previous analyses of patients receiving IA rtPA, the rate of HT was no different between age groups,^5,6,13,14 despite the fact that increased age is an independent risk factor for HT following intravenous thrombolysis.^15,16 As with patients receiving IA thombolytics, this finding likely stems from a more rigorous patient selection process and the systemic absence of thrombolytic agents in most cases.

Although no longer significant when including stroke-related deaths, the differences in clinical outcome between the 65- and 79-year-old post hoc subgroup and those 80 years of age or older still trended in the same direction as the primary group comparisons of NIHSS score change, discharge NIHSS score, and discharge mRS score. Although this likely reflects the decrease in the size of the younger cohort from 75 to 33, the clinical outcomes in patients younger than 65 years of age may be worse than those the 65–79 years of age. For instance, younger patients are very likely treated aggressively despite large preintervention core infarct volumes and are less likely to be treated palliatively following failed intervention.

A limitation of this study is that it is a retrospective single-center observation. In addition, there were several radiographic variables that have established relationships with functional outcome that were not considered in our study, such as the angiographic collateral grade^17,18 or the final infarct core volume.^19,20 We admittedly report the AOL score, representing the final recanalization, which does not entirely reflect reperfusion. We chose the AOL scale because its definition is more constant across studies and is more applicable to the cerebral vasculature than the Thrombolysis in Myocardial Ischemia Scale, which has led to contradictory applications in past clinical trials.^21,22 Several other clinical aspects such as systolic blood pressure and temperature during the hospitalization impact overall outcome,^23–25 though they were beyond the scope of our study. Finally, because this study only compared the immediate neurologic outcomes and disability on discharge, long-term applicability is yet to be determined.

Although we have shown that older patients are more likely to die following Merci thrombectomy regardless of recanalization success, this treatment option should not be denied purely on the basis of age considerations. Approximately 38% of elderly survivors (6/16) or nearly 20% of the total number of the elderly cohort (6/31) had good functional outcomes by discharge. In our opinion, this measures well against the invariably fatal or severely disabled outcome anticipated in comparably aged patients with untreated large-vessel occlusions.

Until a randomized trial can establish whether age should be a discriminating factor for selection, thrombectomy should remain an alternative for the elderly patient, with careful consideration of all aspects of the patient's condition. Our case series suggests, though, that older age as a variable should help guide family discussions concerning patient prognosis and should be a consideration in the design of any future trial of thrombectomy for acute stroke.