Defining Clinically Relevant Cerebral Hemorrhage After Thrombolytic Therapy for Stroke
Analysis of the National Institute of Neurological Disorders and Stroke Tissue-Type Plasminogen Activator Trials
Background and Purpose—Several definitions have been proposed to distinguish clinically relevant from incidental cerebral hemorrhagic transformation after thrombolytic therapy for acute ischemic stroke. We investigated which definition best identifies cerebral hemorrhages that alter long-term functional outcome in the National Institute of Neurological Disorders and Stroke (NINDS) tissue-type plasminogen activator (tPA) trials.
Methods—We analyzed 4 candidate hemorrhage definitions for which the NINDS tPA trials public data set had relevant data. For each, we identified tPA-treated patients having that hemorrhage type and compared their actual functional outcomes at 90 days with their predicted outcomes had they not received tPA and not had the hemorrhage. Projected outcomes without tPA were based on a 17-variable prognostic model derived from the NINDS tPA trials placebo group.
Results—Among the 312 patients treated with intravenous tPA, 33 (10.6%) experienced any radiological intracerebral hemorrhage <36 hours of treatment, 16 (5.1%) a radiological parenchymal hematoma, 20 (6.4%) a NINDS tPA trials–defined symptomatic intracerebral hemorrhage, 12 (3.8%) an European-Australian Cooperative Acute Stroke Study 2 (ECASS2)–defined symptomatic intracerebral hemorrhage, and 6 (1.9%) a modified version of the Safe Implementation of Thrombolysis in Stroke Monitoring Study (mSITS-MOST)–defined symptomatic intracerebral hemorrhage. The ECASS2 and mSITS-MOST definitions identified the largest hemorrhage-related change in 90-day modified Rankin Scale scores (2.26−0.32=1.94, P=0.0001; 2.81−0.63=2.18, P=0.0002, respectively). These definitions also distinguished the largest hemorrhage-related change in 90-day mortality (64.7%–7.6%=57.1%; P=0.0004 for ECASS2; 68.4%–19.5%=48.9%; P=0.0152 for mSITS-MOST).
Conclusions—The ECASS2 and mSITS-MOST symptomatic intracerebral hemorrhage definitions, which combine radiological features and occurrence of substantial early neurological deterioration, best identify tPA hemorrhages that alter final patient outcome.
One of the most important issues a clinician must consider when treating a patient with acute ischemic stroke with intravenous tissue-type plasminogen activator (IV tPA) is the risk of a clinically important intracerebral hemorrhage (ICH). Estimating this risk has been confounded by the various definitions of clinically important ICH proposed (Table I in the online-only Data Supplement). Some definitions consider only radiological extent of the hemorrhage. However, sometimes even large parenchymal hematomas (PHs) may occur asymptomatically and without final clinical consequence. Other definitions identify hemorrhages that produce early symptomatic worsening, based on temporal coincidence with change in neurological deficits or on relatedness by clinical judgment. However, it is challenging to delineate hemorrhages that cause early worsening, because deficit progression may arise from other causes than the ICH. Furthermore, patients who have early clinical worsening because of their hemorrhage may not have their final clinical outcome altered by the ICH.
The National Institute of Neurological Disorders and Stroke (NINDS) tPA trials were instrumental in generating data on hemorrhagic transformation after IV tPA.1 In these trials, symptomatic ICH (SICH) was defined as any hemorrhagic transformation temporally related to any worsening in neurological condition. The neurological worsening could be minor, insufficient to alter the patient’s National Institutes of Health Stroke Scale (NIHSS). In the ≈2 decades since the NINDS tPA trials, this definition of SICH was recognized as potentially overinclusive. Among the 20 cases defined as SICH in the NINDS tPA trials, there are several in which the ICH was minimal and unlikely to have altered long-term patient outcome (Figure 1).
Many processes other than ICH may cause small fluctuations in the NIHSS in a clinically stable patient, including inter-rater variability, patient fatigue, new medications, and infections. Consequently, some subsequent studies used a more stringent criterion of increase by ≥4 points on the NIHSS to define early neurological deterioration.2–6 Others advocate that pure radiological analysis of ICH should be emphasized to avoid noise introduced by the multiplicity of processes that may affect early neurological clinical course.
Which of the contending definitions of clinically important ICH to cite with patients and families is a challenge for clinicians. Taking a patient-centered perspective, the most relevant definition is the one that identifies ICH that will alter the final clinical outcome of the patient, affecting their long-term functioning. Asymptomatic or transiently symptomatic ICHs are of much less importance to patients and their families. We undertook this study to determine which definition of clinically important ICH best predicts a patient’s long-term neurological outcome.
We computationally analyzed the NINDS tPA Trials available through the public data set, which provides a record of the presence and timing of ICH and NIHSS as judged by the NINDS site investigators and central adjudicators. We included only ICH occurring within the first 36 hours of tPA administration. Twenty-four–hour NIHSS was used to determine neurological deterioration. The following candidate definitions for clinically relevant ICH were analyzed: (1) PHs, (2) the NINDS tPA trials definition of SICH, (3) the European-Australian Cooperative Acute Stroke Study 2 (ECASS2) SICH definition, and (4) a modified version of the Safe Implementation of Thrombolysis in Stroke Monitoring Study (mSITS-MOST) SICH.1–3 Because there was no distinction between PH1 and PH2 available in the public data set, the mSITS-MOST definition included all PH as opposed to only PH2 in the original definition. These 4 definitions included 1 pure radiological and 3 mixed clinical radiological (Table 1).
We tested these definitions to determine which best identified clinically relevant ICH, defined as ICH that altered long-term global disability assessed by the modified Rankin Scale (mRS) at 3 months. In a secondary analysis, we also analyzed which ICH definition best identified ICH that altered mortality at 3 months poststroke.
As described previously, a model predicting final disability outcome under supportive care based on demographic and clinical features at trial entry was developed from the 312 patients in the placebo groups of the NINDS tPA trials.7 The ordinal logistic model for 90-day mRS used the following 17 baseline variables identified in previous studies of the NINDS tPA trials and other acute ischemic stroke trials as important prognostic determinants: age, sex, pretreatment NIHSS, age–NIHSS interaction, history of hypertension, diabetes mellitus, smoking, time from onset to treatment, mean arterial pressure, pretreatment serum glucose, hyperdense artery sign on computed tomography, hypodensity on computed tomography, mass effect on computed tomography, pre-existing disability, stroke subtype, side of brain lesion, side of brain lesion–NIHSS interaction.8–12 Performance of the logistic model was evaluated with the C-statistic and maximum-rescaled R2 statistic.
Next, for each ICH definition, 2 clinical outcome distributions were compared: (1) the observed, actual 3-month mRS outcomes among those patients who experienced the defined ICH after receiving tPA, and (2) the projected 3-month mRS outcome those patients would have experienced had they not received tPA, based on the ordinal logistic regression model.
The predicted 3-month mRS values without tPA treatment were derived by entering baseline patient covariate values into the model. In the main analysis, regression imputation was used in the case of missing ordinal logistic model variables. In sensitivity analysis, only patients with complete data available were analyzed.
For each ICH definition, the 33 patients with any radiological ICH <36 hours of treatment were divided into those who fit the definition and those who did not.
The candidate definition with the largest difference (differential) in the observed minus expected mRS distribution between the 2 groups was considered the most predictive definition. That is, if Δmet is the observed minus expected mRS distribution in the group that meets the candidate definition, and Δnotmet is the observed minus expected mRS distribution in those patients with hemorrhage who do not meet the candidate definition, we defined the differential as the difference between Δmet and Δnotmet. We considered the most predictive definition to be the one that maximizes the mean differential. In other words, the criterion for the optimal definition was that patients with ICH meeting the definition had substantially worse final outcomes with tPA and ICH than they would have had without tPA, whereas patients not meeting the definition had equivalent final outcomes with tPA and ICH as they would have had without tPA.
This method to compare the change between observed mRS with tPA and predicted mRS without tPA, we think, is preferable to performing separate regression analyses for each definition, which would result in a new and possibly different expected mRS for the same person in each regression. With our method, the expected mRS with no tPA will not change for a given patient regardless of the definition of ICH used to classify that patient.
For comparison of variables across definition groups, P values for comparing categorical variables such as sex were computed using Fisher exact test. The P values for comparing continuous variables that did not follow the normal such as NIHSS were computed using the Wilcoxon rank-sum test, and the P values for comparing continuous variables that follow the normal such as age were computed with t tests (Table 2).
Differences in the observed minus expected mRS distributions were summarized using the mean difference. Mean values were used because, although mRS is an ordinal scale, the median difference is not as good a single-number summary in this data set because it does not indicate small differences/shifts in the distribution. The confidence bounds and P values for mRS mean differences were computed nonparametrically using nonparametric resampling (bootstrap) methods (Table 3; 90-day mRS). Confidence bounds and P values for mortality were computed using the exact binomial distribution and Fisher exact test (Table 3; 90-day mortality).
Among the 312 patients treated with IV tPA, 33 (10.6%) experienced any radiological ICH <36 hours of treatment, including 16 (5.1%) with a radiological PH and 17 (5.4%) with a radiological hemorrhagic infarction. Among the candidate SICH definitions, 20 (6.4%) experienced an NINDS tPA trials–defined SICH, 12 (3.8%) experienced an ECASS2-defined SICH, and 6 (1.9%) experienced an mSITS-MOST–defined SICH. The patients meeting each ICH definition are displayed graphically (Figure I in the online-only Data Supplement).
The baseline clinical characteristics of patients with PH and the 3 clinical radiographic candidate SICH categories are shown in Table 2, compared with control patients who did not receive tPA. Patients meeting the NINDS tPA trials definition were older, had higher pretreatment NIHSS scores, and more often showed mass effect compared with patients in the other groups. Mean arterial pressure was higher in patients meeting the mSITS-MOST definition.
In the prognostic model derived from the NINDS tPA trials placebo groups, the ordinal logistic model for predicted outcome had a C-statistic of 0.76 and a maximum-rescaled R2 statistic of 0.40.
The quantitative differences between actual and predicted 90-day mean mRS are shown in Table 3. The ECASS2 and mSITS-MOST definitions had the largest mRS point differentials (2.26−0.32=1.94, P=0.0001; 2.81−0.63=2.18, P=0.0002, respectively). Similar results were seen in the mortality analysis (Table 3). These same 2 definitions had the largest differentials in percent mortality (64.7%−7.6%=57.1%; P=0.0004 for ECASS2; 68.4%−19.5%=48.9%; P=0.0152 for mSITS-MOST). Sensitivity analysis confined to patients who did not have missing data revealed similar results (results not shown).
A graphical representation of the actual and predicted day 90 mRS distributions for symptomatic and asymptomatic ICH patients using the NINDS tPA trials, ECASS2, and mSITS-MOST definitions is shown in Figure 2. This visual display highlights the superiority of mSITS-MOST and ECASS2 definitions in stratifying patients. Patients with ICH meeting these definitions had the largest differences between actual and predicted outcomes, whereas patients with ICH not meeting these definitions had the smallest difference between actual and predicted outcomes.
This study of 4 candidate definitions for the most clinically relevant SICH after IV tPA in patients with acute ischemic stroke found that ECASS2 and mSITS-MOST definitions had the best performance characteristics. Patients with ICH fitting these definitions had substantial and significant differences in their actual 3-month functional outcome from their expected 3-month outcome without tPA, whereas patients not meeting these definitions had the greatest concordance of their actual 3-month function outcome with their expected 3-month outcome.
Compared with the best performing definitions, each of the other candidate definitions showed limitations. The NINDS tPA trials definition was less precise. In the patients it identified as having clinically relevant ICH, the ICH had less impact on final outcome than in the better predictor definitions. In the patients it identified as not having clinically relevant ICH, the ICH tended to have more impact on final outcome than in the better definitions. A similar lack of precision was observed with the pure radiological PH definition.
Between the 2 best performing definitions, there were differences in performance characteristics, although these did not reach statistical significance. The ECASS2 definition identified twice as many patients as having clinically relevant ICH compared with the mSITS-MOST definition (which itself is more inclusive than the standard SITS-MOST definition). This greater inclusiveness of the ECASS2 definition did not come at a cost and tended to come with greater specificity. Among patients not meeting the definitions, alterations in final outcome compared with expected outcome were nominally lower for the ECASS2 definition. If these findings became statistically significant in a larger data set, it would indicate an advantage of the ECASS2 definition over the mSITS-MOST definition in both sensitivity and specificity in detecting ICH that worsens 90-day disability and mortality.
The findings of this study are consonant with those of prior investigations. They validate the intuition of the developers of ECASS2 and SITS-MOST definitions that the NINDS tPA trials definition was overly inclusive and that more stringent classification algorithms should be formulated.13,14 This study accords with and extends the work of Strbian et al.13 In a single-center cohort of tPA-treated patients, they found the ECASS2 definition outperformed the NINDS tPA trials and SITS-MOST definitions in identifying hemorrhages, making the largest contribution to worst outcomes in both integrated discrimination improvement and receiver operating characteristic curve analysis. That both studies converge on the ECASS2 definition as best performing provides strong evidence for its utility.
This study provides insight into the population impact of ICH after IV tPA. Considering the ECASS2 definition, among 1000 patients matching the NINDS tPA trials population who are treated with IV tPA, 38 will have a potentially clinically important ICH, among whom 25 will die as a result of ICH. These adverse outcomes must be balanced against the 320 patients who will have a better outcome as a result of receiving tPA.15 For every 1 patient harmed by tPA, 10 are helped.
Our study has several limitations. Because of the constraints of the publicly available data, we could only analyze a subset of the definitions of clinically important ICH that have been proposed. We must also rely on the NINDS investigators’ judgment of the NIHSS and type of ICH. Also limited by this data set, we have no record of the exact NIHSS at the time the ICH was discovered and must use the 24-hour NIHSS as the closest surrogate. Furthermore, the public data set did not distinguish PH type 1 from PH2, did not state the lowest NIHSS between treatment and 24 hours, and did not state investigator judgment of causal relatedness between an ICH and early worsening. As a result, analysis of additional candidate definitions could not be performed, including the unmodified SITS-MOST SICH definition, the ECASS3 SICH definition, and a radiological-only PH2 definition. The sample size of patients experiencing radiological hemorrhagic transformation after IV tPA was modest, limiting the study power. More restrictive definitions of ICH (eg, mSITS-MOST) were further limited by fewer patients who met the criteria. Predictive modeling was used so that SICH could be analyzed within the context of potential clinical benefit from the administration of tPA. However, the possibility of error is inherent when comparing a calculated outcome to an actual one. The expected mRS values assuming no tPA under the logistic model assume that all relevant factors are represented correctly, and our results are tempered by the accuracy of our predictive model, which had a C-statistic of 0.76. Association is not causation, and our study of which definition identified ICH most strongly associated with worse 90-day outcome may not be identifying the ICHs actually causing worse long-term outcome.
Reperfusion therapy for acute ischemic stroke is a dynamic research arena with many ongoing studies of thrombolytics and endovascular thrombectomy techniques. It is critical to accurately quantify clinically important ICH in a standardized manner across studies. Indeed, future trials are likely to test agents specifically aimed at reducing ICH rates, requiring uniform definition of the key end point variable. To identify the subset of ICH that is most important to patients, clinicians, and society, our study supports the use of a mixed radiological clinical definition that includes patients with substantial, but not minimal, early worsening.
Sources of Funding
This article has been funded in part by the following sources: National Institutes of Health grants HL096944, AG040039, NS077378, and NS080377. The funding sources had no role in the study design; in the collection, analysis, and interpretation of data; and in the decision to submit the article for publication.
Dr Levine was previously a consultant for Genentech, serves on the Scientific Advisory Committee of PRISMS (a Genentech-funded clinical trial), and served/serves as the Independent Medical/Safety Monitor for National Institute of Neurological Disorders and Stroke–funded The Immediate Management of Stroke 3 Trial (IMS 3), Increasing Stroke Treatment Through Interventional Behavior Change Tactics (INSTINCT), Field Administration of Stroke Therapy–Magnesium Trial (FAST MAG), Combined Approach to Lysis Utilizing Eptifibatide and rt-PA in Acute Ischemic Stroke-ER (CLEAR-ER). The University of California (UC), Regents, receive funding for Dr Saver’s services as a scientific consultant regarding trial design and conduct to Covidien, CoAxia, Stryker, BrainsGate, Genervon, St Jude Medical, and Grifols. Dr Saver has served as an unpaid site investigator in multicenter trials run by Lundbeck and Covidien for which the UC Regents received payments on the basis of clinical trial contracts for the number of subjects enrolled. The UC has patent rights in retrieval devices for stroke. The other authors report no conflicts.
Guest Editor for this article was Markku Kaste, MD, PhD.
The online-only Data Supplement is available with this article at http://stroke.ahajournals.org/lookup/suppl/doi:10.1161/STROKEAHA.114.005135/-/DC1.
- Received February 19, 2014.
- Revision received June 1, 2014.
- Accepted June 23, 2014.
- © 2014 American Heart Association, Inc.
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