In-hospital cardiac arrest (IHCA) occurs in two groups of patients that differ in pathophysiology and underlying cardiac rhythm (Table 6.1):

• Ventricular fibrillation/pulseless ventricular tachycardia (VF/pVT) (∼25% total). This is typically due to myocardial ischaemia or primary cardiac disease.
• Pulseless electrical activity (PEA) (∼50% total) or asystole (∼25% total), usually as the result of prolonged hypoxia, hypotension or other severe metabolic derangement from non-cardiac disease. For this second group of patients, better outcomes may be achieved by earlier recognition, diagnosis and treatment of critical illness (Chapter 1), so that progression to cardiac arrest is forestalled.