In a patient with rhabdomyolysis and an anion gap of 14 who is bradycardic, what could be causing the bradycardia?

Hyperkalemia from Rhabdomyolysis is the Most Likely Cause of Bradycardia

In a patient with rhabdomyolysis presenting with bradycardia and an anion gap of 14, hyperkalemia is the primary culprit and requires immediate assessment and treatment to prevent cardiac arrest.

Primary Mechanism: Hyperkalemia-Induced Cardiac Conduction Abnormalities

Rhabdomyolysis causes massive release of intracellular potassium from damaged muscle cells into the circulation 1. This hyperkalemia directly affects cardiac conduction by:

• Depolarizing cardiac cell membranes, slowing conduction through the AV node and His-Purkinje system
• Causing progressive bradycardia that can deteriorate to complete heart block or asystole
• Creating a life-threatening emergency requiring immediate intervention

The anion gap of 14 (upper limit of normal or mildly elevated) suggests metabolic acidosis, which commonly accompanies rhabdomyolysis and further exacerbates hyperkalemia by shifting potassium extracellularly 1.

BRASH Syndrome Consideration

If this patient is on AV nodal blocking medications (beta-blockers, calcium channel blockers, digoxin, or amiodarone), consider BRASH syndrome—a synergistic, self-perpetuating cycle where:

• Hyperkalemia potentiates the bradycardic effects of AV nodal blockers
• Bradycardia causes hypotension and shock
• Hypotension worsens renal perfusion
• Acute kidney injury (common in rhabdomyolysis) prevents potassium excretion
• Rising potassium further worsens bradycardia 2, 3, 4, 5

This creates a vicious cycle that standard atropine therapy often cannot break 5.

Immediate Diagnostic Priorities

Check these labs immediately:

• Serum potassium (most critical)
• Creatinine and BUN (assess renal function)
• Creatine kinase (confirm rhabdomyolysis severity)
• Calcium, phosphate, magnesium
• Arterial blood gas (quantify metabolic acidosis)
• ECG for hyperkalemia changes (peaked T waves, widened QRS, prolonged PR interval)

Review the medication list for any AV nodal blocking agents.

Treatment Algorithm

Step 1: Cardiac Membrane Stabilization (if K+ >6.5 mEq/L or ECG changes)

• Calcium gluconate 1-2 grams IV over 2-3 minutes (or calcium chloride if central access)
• Does not lower potassium but protects the heart from arrhythmias

Step 2: Shift Potassium Intracellularly

• Regular insulin 10 units IV with dextrose 25g (if glucose >250 mg/dL, give insulin alone)
• Sodium bicarbonate if concurrent metabolic acidosis (particularly useful here given the anion gap)
• Albuterol nebulizer 10-20 mg (adjunctive)

Step 3: Remove Potassium from Body

• Aggressive IV fluid resuscitation (6-12 L in first 24 hours for rhabdomyolysis) to restore renal perfusion and promote potassium excretion 1
• Urine alkalinization with sodium bicarbonate (target urine pH 6.5-7.0) to prevent myoglobin precipitation
• Hemodialysis if life-threatening hyperkalemia, refractory acidosis, or anuric renal failure 1
• Loop diuretics (furosemide) if adequate renal function

Step 4: Address Bradycardia Directly

If bradycardia persists despite treating hyperkalemia:

• Discontinue all AV nodal blocking agents immediately 5
• Atropine 0.5-1 mg IV (may be ineffective in BRASH syndrome) 5
• Transcutaneous or transvenous pacing for hemodynamically unstable bradycardia 2
• Vasopressors/inotropes: Dopamine, epinephrine, or isoproterenol infusion for combined bradycardia and hypotension 3, 5

Critical Pitfalls to Avoid

1. Don't assume atropine will work: In hyperkalemia-induced or BRASH-related bradycardia, atropine is frequently ineffective because the problem is not vagal tone but rather direct cardiac conduction blockade 5

2. Don't delay calcium administration: If ECG shows any hyperkalemic changes (peaked T waves, widened QRS), give calcium immediately—it's cardioprotective within minutes

3. Don't forget aggressive fluid resuscitation: The cornerstone of rhabdomyolysis treatment is massive volume expansion (6-12 L/24h) to prevent acute tubular necrosis from myoglobin 1

4. Don't overlook medication reconciliation: BRASH syndrome is medication-potentiated, and stopping the offending agent is essential 3, 4, 5

5. Don't wait for "severe" hyperkalemia: Even moderate hyperkalemia (5.5-6.5 mEq/L) can cause significant bradycardia when combined with AV nodal blockers or in the setting of acidosis

Other Rhabdomyolysis Complications Contributing to Bradycardia

• Hypocalcemia (early phase): Calcium precipitates with phosphate in damaged muscle, potentially affecting cardiac conduction 1
• Severe metabolic acidosis: Independently depresses cardiac contractility and conduction
• Uremia from acute kidney injury: Can affect cardiac conduction

The combination of hyperkalemia, acidosis, and potential hypocalcemia creates a perfect storm for cardiac conduction abnormalities in rhabdomyolysis patients.