What are the possible causes of new‑onset bradycardia in a patient who recently experienced rhabdomyolysis?

Bradycardia After Rhabdomyolysis: Electrolyte Disturbances Are the Primary Culprit

The most likely cause of new-onset bradycardia in a patient with recent rhabdomyolysis is severe hyperkalemia, which can precipitate life-threatening cardiac arrhythmias including bradycardia and cardiac arrest. 1, 2

Immediate Life-Threatening Causes to Rule Out

Hyperkalemia (Most Critical)

• Rhabdomyolysis causes massive release of intracellular potassium into the bloodstream 1, 3
• Severe hyperkalemia is an early complication that directly causes cardiac arrhythmias and arrest 2
• This is a medical emergency requiring:
  • Immediate ECG to assess for hyperkalemic changes (peaked T waves, widened QRS, bradycardia)
  • Stat serum potassium level
  • Urgent treatment if elevated (calcium gluconate for cardiac membrane stabilization, insulin/glucose, dialysis if severe)

Other Electrolyte Abnormalities

• Hypocalcemia: Calcium shifts into damaged muscle tissue during rhabdomyolysis 3
• Hypokalemia (paradoxically, during recovery phase): Can also cause bradycardia 4
• Severe metabolic acidosis: Results from muscle breakdown and can cause sinus bradycardia 5

Secondary Reversible Causes to Consider

Per the ACC/AHA/HRS bradycardia guidelines, reversible causes must be identified and treated first before considering permanent pacing 5:

Medication-Related

• Negative chronotropic drugs: Beta blockers, calcium channel blockers, digoxin 5
• If the patient is on these medications for rhabdomyolysis-related complications (e.g., hypertension), consider dose reduction or switching to agents without chronotropic effects 5

Metabolic/Endocrine

• Hypothyroidism: Can cause clinically significant bradycardia and responds well to thyroxine replacement 5
• Severe systemic acidosis: Common in rhabdomyolysis, can cause sinus bradycardia 5

Renal Failure

• Acute kidney injury occurs in approximately 15% of rhabdomyolysis patients 2
• Uremia and associated electrolyte disturbances can contribute to bradycardia

Diagnostic Algorithm

1. Immediate labs: Potassium, calcium, magnesium, phosphate, creatinine, arterial blood gas
2. 12-lead ECG: Look for hyperkalemic changes or other conduction abnormalities
3. Review medications: Identify any negative chronotropic agents
4. Assess volume status: Severe volume depletion can contribute to bradycardia 3
5. Thyroid function tests: If other causes excluded

Critical Pitfalls to Avoid

• Do not assume bradycardia is benign in the setting of rhabdomyolysis—it may herald imminent cardiac arrest from hyperkalemia
• Do not delay treatment while waiting for lab results if ECG shows hyperkalemic changes
• Do not consider permanent pacing until all reversible causes are addressed 5
• Asymptomatic bradycardia without reversible causes does not warrant pacing 5

Treatment Priority

Direct therapy at eliminating the offending condition first 5. In rhabdomyolysis with bradycardia, this means:

• Aggressive correction of hyperkalemia if present
• Continued vigorous fluid resuscitation (the milestone of rhabdomyolysis treatment) 3, 6
• Correction of other electrolyte abnormalities
• Medication adjustment if applicable

Only after reversible causes are addressed should you consider whether the bradycardia represents intrinsic conduction system disease requiring further evaluation.