Acute ischemic stroke (AIS) is defined as permanent brain injury secondary to disruption of blood flow. The incidence of AIS is approximately 700,000 per year, with about 61,000 deaths.¹ Although care of the patient with AIS begins with the public (recognition) and EMS (expeditious transport), the formal evaluation and treatment of AIS occur in the emergency department.² The only approved acute pharmacologic intervention for AIS, intravenous alteplase (rTPA), is unique in the emergency department because of its extremely narrow temporal window and strict contraindications.³ It has been estimated that just 3%-8% of eligible patients with AIS receive rTPA.⁴ Because of the potential for benefit from this therapy for AIS, the emergency physician must be competent in clinical recognition, rapid initial management, and specialist consultation early in the diagnostic and treatment process.

Pathogenesis and Etiology

Anything that disrupts the flow of blood to the brain may cause a stroke. Common causes include large vessel atherosclerosis, small vessel disease, and cardioembolic events. More rare causes of stroke include arterial dissection, vasculopathies, hypercoagulable states, hematologic conditions that increase blood viscosity, and septic emboli. Up to 40% of all strokes are cryptogenic.⁵

When blood flow to areas of the brain is reduced, neurons begin to die via direct starvation from lack of glucose, failure of ATP production, membrane depolarization, rises in intra­cellular calcium, and free radical production. Rising synaptic glutamate concentrations also promote elevations in intracellular calcium ­levels. Membranes degrade, mitochondria break down, and the cellular cyto­skeleton fails.⁶

As with other emergency diagnoses that focus on arterial obstruction, such as acute myocardial infarction and gonadal torsion, “time is tissue.”⁷ Saver quantified this concept with respect to AIS: Every minute of large-vessel brain ischemia results in the death of 1.9 million neurons and 14 billion synapses. Furthermore, the rate of tissue loss in AIS compared with the normal neuronal decline of aging suggests that brain is “aging” 3 weeks for every minute of ischemia and 3.6 years for every hour.⁸

Diagnosis

Prompt diagnosis of stroke is essential because of the time-sensitive nature of the only available emergent drug treatment. The National Institute of Neurologic Disorders and Stroke (NINDS) rTPA study group trial showed in 1995 that in a population of 624 patients with AIS, intravenous alteplase administered within 3 hours of the onset of stroke symptoms resulted in better 3-month outcomes than did placebo.⁷