Abstract 182: Early Perfusion Instability Profoundly Impacts Tissue Outcome In Acute Ischemic Stroke Patients

Abstract

Background: During the first hours after stroke onset, tissue perfusion in stroke patients may undergo a highly dynamic phase of instability. We examined the characteristics of this perfusion instability (improvement and deterioration) and its impact on tissue outcome. Methods: Mean transit time (MTT) and FLAIR maps were obtained in 45 acute stroke patients (mean NIHSS: 14; 73% received IV tPA) at 3.0 hrs (tp1), 6.4 hrs (tp2), and 1 month after onset. MTT prolongation (pMTT) was calculated as: MTT - (median MTT of the non-ischemic hemisphere). Tissue was classified into three subtypes: stable ( Methods: Mean transit time (MTT) and FLAIR maps were obtained in 45 acute stroke patients (mean NIHSS: 14; 73% received IV tPA) at 3.0 hrs (tp1), 6.4 hrs (tp2), and 1 month after onset. MTT prolongation (pMTT) was calculated as: MTT - (median MTT of the non-ischemic hemisphere). Tissue was classified into three subtypes: stable (|pMTT tp2-tp1| ≤ 2 sec), improving (pMTT tp2-tp1< -2 sec), and deteriorating (pMTT tp2-tp1>2 sec) perfusion. Percent volume was computed as: (the # of voxels of a tissue subtype/total # of voxels at a specific tp1 pMTT) for each subtype and their infarct probabilities (IP) were graphed (Fig A and B). To further evaluate perfusion change and the corresponding impact on IP, a 3D plot of IP (color axis, Fig. C) as a function of pMTT tp1 and tp2 was generated, pooling voxels from all patients. Results: Early perfusion instability (within 6.5 hrs) was observed in 70-85% of total volume at a specific tp1 pMTT (50-60% improving and 20-30% deteriorating perfusion) for a range of tp1 pMTT of 3-21 sec (Fig. A). Differences in IP were observed among the three tissue subtypes for pMTT 3-17 sec, while IPs were similar at small pMTT (< 3 sec) and large pMTT (>17 sec), (Fig. B). For pMTT of 3-17 sec, IP was highly dependent on perfusion changes at tp2 (Fig. C). For example, IP for voxels starting with pMTT of 12sec at tp1 ranged from 35-95% depending on perfusion change at tp2 (Fig. C, vertical blue line). Conclusions: Early perfusion changes profoundly impact tissue viability, especially with initial pMTT ranging from 3-17 sec (likely representing penumbral range). Acute stroke therapies may be effective not only by promoting reperfusion, but also by preventing deteriorating perfusion.