| Cardiac |
| Acute coronary syndrome (most common) |
| Arrhythmia: Secondary to electrolyte disorder, acidosis, other process; abnormal conduction syndromes (eg, prolonged QT, Brugada) |
| Pericardial tamponade |
| Respiratory |
| Airway obstruction: Mucus plug, foreign body, tracheostomy decannulation |
| Asthma/COPD exacerbation |
| Pneumonia |
| Pulmonary embolus |
| Tension pneumothorax |
| Hemmorhage and hypovolemia |
| Trauma |
| Gastrointestinal bleeding |
| Abdominal aortic aneursym rupture |
| Intracranial hemorrhage |
| Profound gastrointestinal fluid loss |
| Drugs and poisons |
| Opioids |
| Beta blockers |
| Calcium-channel blockers |
| Benzodiazepines |
| Tricyclic antidepressants |
| Digoxin |
| Electrolyte disturbances |
| Potassium |
| Magnesium |
| Sepsis |
