Can blood transfusions cause bradycardia (low heart rate)?

Blood Transfusions and Bradycardia

Blood transfusions do not directly cause bradycardia; however, they are associated with tachycardia as a common sign of transfusion reactions, and severe electrolyte disturbances from massive transfusions—particularly hypocalcemia and hyperkalemia—can precipitate cardiac arrhythmias including bradycardia and cardiac arrest. 1, 2

Typical Cardiac Response to Transfusion

Blood transfusions typically cause tachycardia, not bradycardia, as part of transfusion reactions:

• Tachycardia is a cardinal sign of transfusion reactions, including hemolytic reactions, allergic reactions, TRALI, and TACO, and should prompt immediate cessation of transfusion 1, 3
• Major hemorrhage requiring transfusion is defined by heart rate >110 beats/min, and transfusion reactions manifest with increased heart rate as a warning sign 1
• Clinical monitoring during transfusions specifically includes heart rate assessment pre-transfusion, at 15 minutes, and at completion to detect tachycardia as an adverse event 1

Mechanisms That Could Cause Bradycardia

While bradycardia is not a typical transfusion complication, specific circumstances can precipitate it:

Severe Hypocalcemia from Massive Transfusion

• Citrate in blood products chelates calcium, and each unit of RBCs or FFP contains approximately 3 grams of citrate that binds serum calcium 1
• Ionized calcium levels below 0.8 mmol/L are associated with cardiac dysrhythmias, which can include bradycardia 1
• Neonates and patients with impaired liver function are particularly vulnerable, as citrate metabolism is compromised during massive transfusion and shock states 1
• Hypocalcemia should be corrected promptly with calcium chloride (10 mL of 10% solution = 270 mg elemental calcium) rather than calcium gluconate, especially in liver dysfunction 1

Hyperkalemia-Induced Arrhythmias

• Transfusion-associated hyperkalemic cardiac arrest (TAHCA) is a rare but life-threatening complication of rapid, large-volume transfusions 1, 2
• Potassium leaks from stored RBCs into preservative fluid, particularly with prolonged storage or irradiation 1
• Risk factors include rapid transfusion rates, direct cardiac transfusions, and large-volume transfusions in neonates or small patients 1
• A case report documented ventricular fibrillation cardiac arrest following large-volume transfusion, though this represents tachyarrhythmia rather than bradycardia 2

Hypomagnesemia

• Large blood transfusions can cause hypomagnesemia, which precipitated wide-complex ventricular tachycardia and ventricular fibrillation in a documented case 2
• While this manifests as tachyarrhythmia, severe electrolyte derangements can theoretically affect cardiac conduction in multiple ways 2

Clinical Monitoring and Prevention

Monitor ionized calcium levels during massive transfusion protocols, as hypocalcemia predicts mortality and need for multiple transfusions with greater accuracy than fibrinogen, acidosis, or platelet count 1

Key monitoring parameters during transfusion:

• Heart rate, blood pressure, temperature, and respiratory rate at baseline, 15 minutes, and completion 1
• Ionized calcium levels during massive transfusion (target >0.9 mmol/L) 1
• Potassium levels with rapid or large-volume transfusions, particularly in neonates 1
• Glucose levels in neonates, as transfusions can precipitate hypoglycemia 1

Transfusion rate matters: Standard RBC transfusion should occur over 2-4 hours at 4-5 mL/kg/hour to minimize electrolyte shifts 1

Important Clinical Caveat

If bradycardia occurs during or after transfusion, consider alternative diagnoses first:

• Vasovagal response to the procedure itself
• Medication effects (beta-blockers, calcium channel blockers, digoxin)
• Underlying cardiac conduction disease
• Severe anemia correction in patients with ischemic heart disease (though this typically causes tachycardia initially) 4

The absence of tachycardia during a suspected transfusion reaction should raise concern for:

• Severe hemolytic reaction with impending cardiovascular collapse 1
• TRALI with severe hypoxemia and respiratory failure 1, 5
• Massive electrolyte derangement requiring immediate laboratory assessment 1, 2