Timely recognition of an unfolding MH crisis can be the difference between life and death. The earliest harbinger is often an unexpected increase in end-tidal carbon dioxide (ETCO2) or a patient overbreathing the ventilator. But as the crisis unfolds, myriad symptoms manifest: from muscle rigidity and tachycardia to hyperkalemia and the onset of myoglobinuria. Laboratory tests reveal the tell-tale signs of metabolic acidosis, hyperkalemia, and evidence of rhabdomyolysis.
Recognized Arrhythmias
Tachycardia: One of the earliest signs of MH is an unexplained increase in heart rate. This rapid heartbeat can be attributed to the hypermetabolic state and the release of stress hormones in response to the crisis. Tachycardia can serve as an essential clinical indicator of MH, prompting further investigation.
Ventricular Arrhythmias: MH can progress to more severe arrhythmias, including ventricular tachycardia and ventricular fibrillation. These life-threatening rhythms can result from the profound acidosis, hyperkalemia, and catecholamine surge that occur during an MH crisis. Prompt intervention is critical to prevent cardiac arrest.
Sinus Bradycardia: In some rare cases, MH may lead to sinus bradycardia, a slower-than-normal heart rate originating from the sinoatrial (SA) node. Sinus bradycardia can be a result of increased vagal tone or impaired conduction through the SA node due to the effects of hyperkalemia and acidosis.
| Finding | Notes |
|---|---|
| Rising end-tidal CO2 | Often the earliest harbinger, along with a patient overbreathing the ventilator |
| Tachycardia | An early sign; attributed to the hypermetabolic state and stress hormone release |
| Skeletal muscle rigidity | Follows the abnormal release of ionized calcium from the sarcoplasmic reticulum |
| Ventricular arrhythmias | Ventricular tachycardia and fibrillation from profound acidosis, hyperkalemia, and catecholamine surge; prompt intervention prevents cardiac arrest |
| Sinus bradycardia | Rare; from increased vagal tone or impaired SA node conduction due to hyperkalemia and acidosis |
| Hyperkalemia | Confirmed on laboratory testing |
| Metabolic acidosis | Confirmed on laboratory testing |
| Myoglobinuria | With laboratory evidence of rhabdomyolysis |
