Use of Imaging to Select Patients for Late Window Endovascular Therapy

Gregory W. Albers, MD

Stroke. 2018;49(9):2256-2260.

Estimating the Ischemic Penumbra With CTP

Positron emission tomography scan and Xenon CBF studies, as well as clinical trials, have demonstrated that in acute stroke patients, the T_max >6 seconds perfusion parameter can estimate tissue that is likely to be critically hypoperfused (CBF <20 mL/100 g per minute) and is at high risk for progressing to infarction if reperfusion is not obtained.^[8–10] The mismatch between the T_max >6 seconds volume and the ischemic core volume was used to estimate the volume of salvageable tissue in DEFUSE 3.

It is important to be aware that the T_max maps are sensitive to delayed contrast arrival, and in some circumstances, delayed arrival does not imply critical hypoperfusion. For example, in a patient with a chronic carotid occlusion, T_max delays may be present despite normal CBF, cerebral blood volume (CBV), and mean transit times.

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Table 1. Key Imaging-Based Inclusion Criterial for DEFUSE 3 and DAWN
	DEFUSE 3	DAWN
Ischemic core volume	≤70 mL	≤20 mL if age >80
		≤30 mL if age <80 and NIHSS 10–20
		≤50 mL if age <80 and NIHSS >20
Mismatch volume	≥15 mL and a mismatch ratio of ≥1.8	Not required
Vessel occlusion	M1 or ICA (cervical and intracranial)	M1 or ICA (intracranial and cervical if stent not anticipated to be required)

DAWN indicates Triage of Wake-up and Late Presenting Strokes Undergoing Neurointervention With Trevo); DEFUSE 3, Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke 3; ICA, internal carotid artery; M1, the first segment of the middle cerebral artery; and NIHSS, National Institutes of Health Stroke Scale.

Table 2. MRI Versus CTP in Early and Late Window Thrombectomy Studies
Study	N	90-d mRS 0–2	90-d mRS 0–2	Absolute
Study	N	Control (%)	Thrombectomy (%)	Benefit (%)
SWIFT PRIME*
MRI	34	33	63	30
CTP	139	40	60	20
DEFUSE 3†
MRI	49	19	61	42
CTP	133	16	39	23
DAWN
MRI	83	35‡		NA
CTP	123	29‡		NA

CTP indicates computed tomography perfusion; DAWN, Triage of Wake-up and Late Presenting Strokes Undergoing Neurointervention With Trevo; DEFUSE 3, Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke 3; MRI, magnetic resonance imaging; mRS, modified Rankin Scale; and SWIFT PRIME, Solitaire With the Intention for Thrombectomy as Primary Endovascular Treatment for Acute Ischemic Stroke.
*SWIFT PRIME was an early window (<6 hours) study.
†CTP and MRI groups had statistically significant treatment effects on the studies primary outcome.
‡DAWN reported pooled data for the thrombectomy and control arms for the MRI and CTP subgroups.