Patients presenting with severe hypertension are at risk for watershed infarcts if blood pressure is rapidly and dramatically reduced, even without frank hypotension. Blood pressure should be lowered by no more than 25% to reduce the chance of cerebral, coronary or renal ischemia.
Watershed infarcts comprise ~10% of all ischemic strokes. These infarcts are localized to borderzones between major vascular territories in the brain, and are classified as internal borderzone (IBZ) or cortical borderzone (CBZ) infarcts.
*CBZ in red, IBZ in blue.
The CBZ are located at the junctions of the distal branches of the ACA, MCA and PCA territories. CBZ infarcts are associated with small cortical infarcts that are more likely due to thromoembolism.
The IBZ are located at the junctions of the distal branches of the ACA/MCA/PCA with the deep perforating arteries (lenticulostriate, artery of Heubner, anterior choroidal artery). IBZ infarcts are more often associated with severe stenosis or occlusion in the ICA or MCA. The IBZ is more vulnerable to decreased perfusion due to the anatomic characteristics of cerebral arterioles within this area – being the most distal branches of the ICA, perfusion pressure is likely to be the lowest. Also the lenticulostriate arteries have limited collateral blood supply.
Patient admitted for hypertensive emergency, started on nicardipine drip and blood pressure lowered from 200+ to 100 systolic. Relative hypotension maintained for 2 hours. Patient became comatose thereafter. MRI showed IBZ infarcts.
Patient with aortic dissection, BP lowered from 200s with nicardipine drip. Patient became unarousable at SBP 114 where it remained for ~3 hours. MRI showed IBZ and corpus callosum infarctions. Patient never regained consciousness.
Kurowski, Donna, Michael T. Mullen, and Steven R. Messé. “Pearls & Oy-Sters: Iatrogenic Relative Hypotension Leading To Diffuse Internal Borderzone Infarctions And Coma”. Neurology 86.24 (2016): e245-e247.