Rangaraju S, Liggins JTP, Aghaebrahim A, Streib C, Sun CH, Gupta R, et al. Pittsburgh Outcomes After Stroke Thrombectomy Score Predicts Outcomes After Endovascular Therapy for Anterior Circulation Large Vessel Occlusions. Stroke. 2014
Duy Le, MD
While there have been multiple prior models which predict outcomes prior to thrombectomies as an effort to evaluate which patients are good thrombectomy candidates; Rangaraju et al have developed a prognosis model that carves out a unique niche. Rangaraju et al developed the The Pittsburg Outcomes after Stroke Thrombectomy (POST) Scale, which evaluates how patients will do after receiving a thrombectomy in hopes of providing information to families regarding prognosis to help guide patient management.
In this retrospective validation study, data was collected from a database at Grady Memorial Hospital (GMH) in Atlanta, Georgia. 247 patients were evaluated between 2009 and 2013. These patients met the criteria as follows: they were greater than 18 years of age and underwent endovascular therapy in the anterior circulation with large vessel occlusion (type of endovascular therapy was not specified) within 8 hours of last well known time. Baseline characteristics were measured, and after multivariant regression analysis, only age, final infarct volume and presence of hemorrhage (defined as presence of PH-1 or PH-2) were deemed to be independent predictors of good outcome. They then derived the following; POST Score = Age + 0.5xFIV + 15xH. A good outcome was defined as a modified rankin score of 0-2 at 3 months. 79% of GMH patients had successful recanalization (mTICI 2b/3). The POST score was deemed an excellent predictor of good outcome when evaluated on the GMH group (area under curve = 0.85). Scores that were <60 had a 91% chance of this good outcome, whereas a score of 60-89 carried a 59% chance of having a good outcome. A score of 90-119 had a 25% chance of a good outcome, while there was only a 4% chance of a good outcome with a score of greater than or equal to 120. The POST score was then validated against two other registries; an institutional endovascular database (UPMC) and the DEFUSE-2 data set. Again, the score accurately predicted good outcomes in these registries as well. Additionally, the POST score was evaluated as a prediction model in those over 80 years of age and those who received the procedure later than 8 hours of last well known time. The general trend held true for these patients as well; a higher POST score was associated with a poorer outcome.
Some weaknesses of the study include the fact that the validating and derivative populations had significant baseline differencs. NIHSS, ASPECT score, IV-tPA, PH-1 and PH-2 rates as well as FIV were significantly different in the GMH, UMPC and DEFUSE-2 groups. UPMC patients had lower rates of IV-tPA (43.5% vs. 53% in the other two groups) and UPMC patients also had higher infarct volumes compared to the other two groups. Additionally, 20% of patients in the derivation group and 8% in the validation group were excluded due to missing data points.
The goal of this score is to help guide the management of post thrombectomy patients, as many of these patients undergo gastrostomies or tracheostomies. Surrogate decision makers often base their decision to continue vs. withdraw care depending on the likelihood of a patient achieving functional independence. While it is tempting to use the POST score as a surrogate marker in thrombectomy study patients to help dictate management; we must be careful in withdrawing care on these patients based on retrospective validation, as it may skew the results of the thrombectomy studies. To truly have a model that predicts outcome after thrombectomy, we will have to wait for a prospective validation study. And even then, we will have to await the results of this last wave of thrombectomy trials to see how applicable the POST score will ultimately be.