Morbidity and mortality associated with transient ischemic attack (TIA).

Transient ischemic attack (TIA) is defined as "an episode of focal loss of brain function attributed to ischemia that lasts less than 24 hours, is localized to a portion of the brain supplied by one vascular system, has no persistent deficit, and is not attributable to any other cause." Most TIAs are caused by small thromboemboli that originate in atheromatous areas in neck vessels or the heart. Other mechanisms include nonatherosclerotic vascular diseases, mitral valve prolapse, hematologic diseases, and abnormal blood pressure fluctuations. Even in series of fully investigated cases, there remains a group in which no cause can be found. The great majority of TIAs are extremely brief. In one series, 24% ended within 5 minutes, 39% in 15 minutes, 50% in 30 minutes, and 60% in 1 hour.