- Patients with life-threatening arrhythmias (such as atrial fibrillation/flutter with hypotension, ventricular tachycardia, or ventricular fibrillation, or significant heart block that requires pacing [Type III, Type IIb]), cardiogenic shock, severe heart failure requiring high levels of inspired oxygen (FiO2 >40%), persistent chest pain despite medical or other interventions, and patients who are considered too unstable to participate for other medical reasons or complications (such as concomitant strokes, retroperitoneal hematoma, gastro-intestinal bleeding). Also excluded are patients with history of cardiac arrest during the same hospitalization.