Differences in the Evolution of the Ischaemic Penumbra in the Shrsp and Wky Rat

Background and Purpose: Stroke prone spontaneously hypertensive rats (SHRSP) are a highly pertinent stroke model with increased sensitivity to focal ischaemia compared to the normotensive reference strain (WKY). Study aims were to investigate temporal changes in the ischaemic penumbra in SHRSP compared with WKY. Methods: Permanent middle cerebral artery occlusion was induced with intraluminal filament. Diffusion (DWI) and perfusion-weighted (PWI) MRI was performed from 1-6hrs post-stroke with PWI/DWI mismatch to define penumbra and thresholded Apparent Diffusion Coefficient maps to define ischaemic damage. Results: There was significantly more ischaemic damage in SHRSP than WKY from 1-6 hours post-stroke. The perfusion deficit remained unchanged in WKY (39.9±6 at 1hr, 39.6±5.3 mm at 6hrs) but, surprisingly, increased in SHRSP (43.9±9.2 at 1hr, 48.5±7.4 mm at 6hrs, P=0.01). One hour post-stroke, SHRSP had significantly less penumbra (3.4±5.8 mm) than WKY (9.7±3.8, P=0.03). In WKY, 56% of 1hr penumbra area was incorporated into ADC lesion by 6hrs, while in SHRSP the small penumbra remained static due to the temporal increase in both ADC lesion and perfusion deficit. Conclusions: Firstly, SHRSP have significantly more ischaemic damage and less penumbra than WKY within 1hr of stroke; Secondly, penumbra is recruited into the ADC abnormality over time in both strains; Thirdly, the expanding perfusion deficit in SHRSP predicts more tissue at risk of infarction. These results have important implications for management of stroke patients with pre-existing hypertension and suggest ischaemic damage could progress at a faster rate and over a longer timeframe in the presence of hypertension.