Acute ischemic stroke treatment, part 1: patient selection "the 50% barrier and the capillary index score"

Abstract

The current strategy for intra-arterial treatment (IAT) of acute ischemic stroke focuses on minimizing time from ictus to revascularization and maximizing revascularization. Employing this strategy has yet to lead to improved rates of successful outcomes. However, the collateral blood supply likely plays a significant role in maintaining viable brain tissue during ischemia. Based on our prior work, we believe that only approximately 50% of patients are genetically predisposed to have sufficient collaterals for a good outcome following treatment, a concept we call the 50% barrier. The Capillary Index Score (CIS) has been developed as a tool to identify patients with a sufficient collateral blood supply to maintain tissue viability prior to treatment. Patients with a favorable CIS (f CIS) may be able to achieve a good outcome with IAT beyond an arbitrary time window. The CIS is incorporated into a proposed patient treatment algorithm. For patients suffering from a large stroke without aphasia, a non-enhanced head CT should be followed by CT angiography (CTA). For patients without signs of stroke mimics or visible signs of structural changes due to large irreversible ischemia, CTA can help confirm the vascular occlusion and location. The CIS can be obtained from a diagnostic cerebral angiogram, with IAT offered to patients categorized as f CIS.

Keywords: acute ischemic stroke; capillary index score; intra-arterial treatment; patient selection; revascularization; stroke outcome; the 50% barrier.

Figures

Figure 1

Depth of ischemia and time to irreversible cerebral damage: time to irreversible cerebral damage depends on the depth of ischemia, which depends on the pial collateral supply to the ischemic territory. Since different patients have different collaterals, the depth of ischemia will vary among patients, as will the time available for therapy to salvage the tissue (16).

Figure 2

Logarithmic time curve: the infarction threshold distinguishing between reversible and irreversible ischemia as a function of rCBF and time from ictus. Time window here is an approximation. The vertical lines are an approximation and have not yet been validated (20).

Figure 3

Calculating the capillary index score (CIS). A frontal view of normal diagnostic cerebral angiogram. The territory of the middle cerebral artery (MCA) is being used as an example of an ischemic territory. The ischemic territory is divided into three equal sections; each section is given a 1 if it exhibits capillary blush, or a 0 if no capillary blush is present. The CIS is the sum of these three numbers. CIS can range from a score of 0 to 3 (20, 61).

Figure 4

CIS = 0. In this patient with proximal left middle cerebral artery occlusion, we can calculate the CIS from this injection only since the only other potential collateral to the MCA territory is from the left posterior cerebral artery (PCA), which is filled in the injection through the posterior communicating artery (Pcom, arrow). If we divide the ischemic territory (Lt MCA territory) into three sections, none of these sections exhibit a capillary blush, late in the venous phase; therefore, the CIS = 0.

Figure 5

CIS = 1. (A) Occlusion of intracranial right ICA. (B) Injection of the left ICA demonstrates absence of the Acom; hence, no cross filling to the right hemisphere from this injection (ischemic territory = right middle and right anterior carotid arteries). (C) Injection of the right vertebral artery demonstrates partial opacification of the temporal and parietal lobes through the right PCA via pial collaterals. (D) Delayed combined venous phase of the left internal carotid and right vertebral showing only one-third of the ischemic territory (right middle cerebral and interior cerebral arteries) territory demonstrates capillary blush. CIS = 1.

Figure 6

CIS = 2. (A) Occlusion of the left ICA. (B) Injection of the right ICA demonstrates filling of the left ACA territory through the Acom with partial opacification of the fronto–parietal lobes via pial collaterals. (C) Injection of the left vertebral artery demonstrates partial opacification of the left temporal lobes via pial collaterals. (D) Delayed venous phase of the right ICA and left vertebral showing approximately two-third of the ischemic territory (left middle MCA) to demonstrate capillary blush.

Figure 7

CIS = 3. (A) Injection of the left ICA demonstrates occlusion of proximal left MCA (ischemic territory = left MCA) with partial opacification of the left fronto-parietal lobes via pial collaterals of the left ACA. (B) Injection of the left vertebral artery demonstrates partial opacification of the left temporal lobes via pial collaterals. (C) Delayed venous phase of the left ICA and the left vertebral artery. All the ischemic territory (left MCA) demonstrates capillary blush. CIS = 3.

Figure 8

Vascular occlusion and ischemic territory. This patient has occlusion of the right ICA and a congenital absence of the anterior and posterior communicating arteries (Acom, Pcom). The resulting ischemic territory is the right MCA and ICA. (A) Frontal view of the injection of the right common carotid artery demonstrating no intracranial capillary blush. (B) Frontal view of the injection of the left common carotid artery demonstrating no collateral flow to the right hemisphere through the interior cerebral artery. (C) Frontal view of the injection of the right vertebral artery demonstrating no collateral flow to the right interior carotid artery territory.

Figure 9

Vascular occlusion and ischemic territory. This patient has occlusion of the left internal carotid artery (ICA), but has a well-developed anterior communicating artery (Acom). The resulting ischemic territory is only the left MCA territory.

Figure 10

Proposed patient selection algorithm for AIS.