 A. non-diagnostic i.e., low or intermediate probability ventilationperfusion lung scan B. non-diagnostic i.e., subsegmental defects or technically inadequate study helical CT scan Cardiac arrest: documented or presumed ventricular fibrillation, sustained ventricular tachycardia, asystole, or pulseless electrical activity requiring cardiopulmonary resuscitation, pharmacological therapy, or cardiac defibrillation. 