44 Stroke Centers and Interventional Cardiology
Stroke will affect approximately three quarters of a million Americans each year and result in nearly 150,000 deaths.1 Stroke is the third leading cause of death in the United States after heart disease and cancer and the number one cause of disability and the number one reason for rehabilitation. Over three million stroke survivors are estimated to be in the United States, a third of these being young adults with long-term disability.2 The etiologies of stroke include (1) hemorrhagic, (2) thrombotic, and (3) embolic. Embolic strokes may be from an artery to an artery or from a heart chamber (left atrium or ventricle) to an artery, particularly in patients with atrial fibrillation (AF). One of the major tenets of treatment of ischemic stroke is that “time is brain.” Variables that impact on the extent of ischemic brain injury are (1) the time from the onset of symptoms to reperfusion; (2) the presence of collateral circulation, including an intact circle of Willis; and (3) the “penumbra of viability” surrounding the infarcted brain tissue. The penumbra is the region of brain surrounding the infarct area, where the blood supply is significantly reduced but energy metabolism is maintained because of collateral flow. The viability of this area is dependent on both the severity and the duration of ischemia. If blood flow is rapidly restored, some ischemic brain tissue will be saved. For both ischemic stroke and hemorrhagic stroke, there are opportunities to minimize injury early after the onset of the stroke. This puts a premium on the rapid assessment of patients presenting with stroke (Table 44-1).3 The goals of treatment include preventing or limiting the mortality and morbidity of the acute event and preventing recurrent events. The great majority (>80%) of strokes are ischemic.4 Ischemic stroke therapy, designed to achieve reperfusion as quickly as possible and minimize further damage, consists of either intravenous (IV) thrombolysis or catheter-based reperfusion therapy, which can include intra-arterial (IA) thrombolysis, mechanical thrombectomy, or balloon angioplasty with or without stent placement.
TABLE 44-1 The Seven “D’s” of Stroke Care
New Imaging Strategies
The American Heart Association (AHA)/American Stroke Association (ASA) class I recommendation is to perform noncontrast computed tomography (CT) or magnetic resonance imaging (MRI) in patients who present within 3 hours of stroke symptom onset to exclude intracranial bleeding.2 Imaging is the cornerstone for triaging candidates for stroke therapy. The purpose of the baseline CT is to detect conditions that make the patient ineligible for thrombolysis such as subdural, subarachnoid, or parenchymal intracranial hemorrhage (ICH). CT may also detect mass lesions or hemorrhagic infarctions. There are four major goals of brain imaging in the setting of an acute stroke: (1) Most importantly, ICH must be excluded. If ICH is present, then the patient has a neurosurgical emergency, and neurosurgery needs to be involved immediately. (2) Both CT and MRI can be used to noninvasively identify intravascular thrombus. Data regarding the geographic distribution and the size of the thrombus burden can assist in deciding on IV thrombolysis, IA thrombolysis, or endovascular thrombectomy. (3) The volume of the nonviable, irreversibly infarcted brain predicts the patient’s potential for recovery. (4) The size of the penumbra—the peri-infarct zone of viable but ischemic brain tissue—can be assessed and compared with the volume of infarcted brain tissue.
Management of Physiologic Variables
Hypertension
Arterial hypertension is present in the majority of patients presenting with a stroke and is associated with a poorer outcome; however, lower blood pressure may result in decreased perfusion to the ischemic penumbra, thus extending the size of the infarction. There is a great deal of uncertainty regarding the treatment of hypertension during acute stroke. Current recommendations include lowering blood pressure to 220 mm Hg or more of systolic and 120 mm Hg or more of diastolic.5
Reperfusion Strategies
Intravenous Thrombolysis
IV administration of the thrombolytic agent—recombinant tissue-plasminogen activator (rt-PA)—is the only therapy approved by the U.S. Food and Drug Administration (FDA) for the treatment of acute ischemic stroke (Table 44-2).6 This has been shown to be an effective therapy for stroke by a recent meta-analysis of 2,775 patients treated within 6 hours of onset of stroke.7 Patients treated within 90 minutes of onset had almost a threefold increase in beneficial outcomes, dropping to 1.6-fold increase in the odds for improved outcome if patients were treated between 91 and 180 minutes. For those treated between 180 and 270 minutes, the odds ratio (OR) for benefit was 1.4 times greater compared with those given placebo. The risk of intracerebral hemorrhage was greater for the thrombolytic group (5.9%) compared with the placebo group (1.1%). The risk-to-benefit ratio for IV thrombolysis in ischemic stroke is narrow. About 11% more patients will benefit at 3 months from IV lysis, whereas 6.4% will experience ICH. Unfortunately, fewer than 10% of eligible patients with acute ischemic stroke receive reperfusion treatment in the United States.8 Seven patients are the number needed to treat (NNT) with IV lysis to achieve an excellent outcome and avoid one stroke death or dependency. For every 100 stroke patients treated with IV thrombolysis within 3 hours, 32 will have a better outcome despite the 3 who will suffer a significant intracerebral hemorrhage. At 1 year after treatment, those treated with IV lysis have a 30% increased likelihood of minimal or no disability compared with those given placebo; however, there was no difference in the mortality rate and in the rate of recurrent strokes.9 The risk of hemorrhage is increased in older patients and in patients with larger strokes, diabetes mellitus, a history of prior stroke, and thrombocytopenia. The European Cooperative Acute Stroke Study-3 (ECASS-3) tested the efficacy of extending the treatment window for intravenous thrombolysis to between 3 and 4.5 hours after stroke symptom onset. A favorable outcome occurred in 52.4% of patients assigned to rt-PA compared with 45.2% of the placebo group (OR 1.34; 95% confidence interval [CI] 1.02–1.76, P = 0.04). However, the incidence of ICH was higher in the rt-PA group (27%) compared with the placebo group (17.6%, P = 0.001). There was no difference in mortality rates between the two groups. Important exclusion criteria in this trial included a history of both stroke and diabetes mellitus, oral anticoagulation therapy regardless of international normalized ratio (INR), an NIHSS (National Institute of Health Stroke Scale) score of greater than 25, and age greater than 80 years.10 The AHA/ASA has published a science advisory with a class I, evidence level B recommendation for the administration of rt-PA to patients with ischemic stroke who present within 3 to 4.5 hours of symptom onset and meet the ECASS-3 inclusion criteria (Table 44-3).11
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