Intravenous tPA is the only FDA-approved (since 1996) medication for the management of acute ischemic stroke. tPA is a thrombolytic agent that breaks down the fibrin that binds clots together. When administered to a patient having an acute ischemic stroke, tPA has been demonstrated to reduce long-term disability. The mechanism of this action is the lysis of the clot or clots that restrict blood flow the brain during an ischemic stroke and the restoration of blood flow before brain tissue is infarcted (dead). FDA guidelines state that tPA must be administered within three hours after a patient was last known to be stroke symptom-free [a/k/a last known well time or LKW]. Hospitals implement systems to facilitate the rapid evaluation and management of stroke patients so that tPA can be administered within this time frame. An extended window of 4.5 hours is often used in clinical practice based on trial data but this time frame has not been approved by the FDA. When a patient’s stroke symptoms completely resolve, the LKW time resets, i.e., the clock restarts for the eligibility of tPA.
When a hospital does not have sufficient staffing to provide around-the-clock vascular (stroke) neurology expertise to its ED, teleneurology programs may be contracted to fill the gap. In this arrangement, a teleneurology consultant provides expert advice about acute stroke management including the eligibility and appropriateness of tPA administration.
tPA carries a significant risk of bleeding. Because of this risk, eligibility is carefully assessed to avoid exposing patients to the risks of tPA administration if they are unlikely to benefit. It is for this reason that tPA is usually withheld when stroke symptoms have completely resolved.
Sometimes symptoms do not persist, i.e., are transient. Transient stroke symptoms are called a transient ischemic attack (TIA). A diagnosis of TIA implies that there is no ongoing stroke and, therefore, there is no indication for the administration of tPA.
Critically, a stuttering or fluctuating ischemic stroke is a stroke with symptoms that relapse and remit (wax and wane) in the same pattern over hours or days. Stuttering strokes are often lacunar in origin. Lacunar strokes are caused by occlusion of small penetrating arteries in the deep structures of the brain. Lacunar strokes often cause fluctuating hemiparesis, heminumbness, hemiataxia (clumsiness on one side of the body), and/or slurred speech.
Stroke, Intravenous tPA, and Last Known Well (LKW) Time medical expert witness specialties include vascular surgery, interventional radiology, and vascular neurology.