At what heart rate should therapy be initiated for beta blocker induced bradycardia?

Treatment of Beta Blocker Induced Bradycardia

Therapy for beta blocker induced bradycardia should be initiated when heart rate falls below 50 beats per minute AND is accompanied by symptoms or hemodynamic compromise. 1

Initial Assessment and Management

• Bradycardia is defined as heart rate <60 beats per minute, but clinically significant bradycardia requiring treatment typically occurs at heart rates <50 beats per minute 1
• Evaluate for symptoms of bradycardia including dizziness, lightheadedness, syncope, altered mental status, or signs of hemodynamic compromise (hypotension, shock) 1, 2
• Discontinue the beta blocker if possible and establish reliable IV access for medication administration 2
• Continuously monitor vital signs including heart rate, blood pressure, and oxygen saturation 2

Treatment Algorithm

First-line interventions (for symptomatic bradycardia):

• Glucagon: First-line therapy for symptomatic beta blocker-induced bradycardia 2, 3
  • Dosing: 3-10 mg IV bolus over 3-5 minutes, followed by infusion of 3-5 mg/hour 1, 2
  • Mechanism: Activates hepatic adenyl cyclase, bypassing beta-receptor blockade 1, 3
  • Side effects: Monitor for nausea and vomiting, which may compromise airway 1

Second-line interventions (if bradycardia persists):

• High-dose insulin therapy: Reasonable option when bradycardia persists despite glucagon 1, 2

  • Dosing: 1 unit/kg IV bolus followed by infusion of 0.5-1 units/kg/hour 1, 2
  • Concurrent dextrose administration: 0.5 g/kg bolus followed by 0.5 g/kg/hour 2
  • Monitoring: Regular glucose and potassium levels (target K+ 2.5-2.8 mEq/L) 2

• Vasopressors/inotropes: For persistent hypotension 2

  • Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV
  • Dopamine: 5-20 mcg/kg/min IV

For refractory cases:

• Calcium administration: Primarily for calcium channel blocker toxicity, but may be beneficial in combined toxicity 2

  • Calcium chloride: 1-2 g IV every 10-20 min or infusion of 0.2-0.4 mL/kg/h 2, 3

• Temporary cardiac pacing: Consider when pharmacologic therapy fails to restore adequate heart rate 2

Special Considerations

• Beta-blocker response varies significantly between patients, with 25% of patients experiencing episodes of heart rates >100 bpm despite beta-blockade 4
• First-degree heart block (PR interval >200 ms) is the most common ECG finding in symptomatic beta-blocker toxicity 5
• Acebutolol overdose may present uniquely with QTc prolongation and ventricular arrhythmias 5
• In perioperative settings, tight heart rate control (keeping HR <100 bpm) with beta-blockers is associated with reduced incidence of myocardial infarction 4
• For patients on beta-blockers for heart failure, bradycardia may actually be a key mechanism by which these agents improve left ventricular function 6

Monitoring During Treatment

• Continuous cardiac monitoring for heart rate, rhythm, and response to treatment 2
• Frequent blood pressure measurements and assessment of mental status and peripheral perfusion 2
• Regular glucose monitoring when using high-dose insulin therapy 2
• Monitor for side effects of treatment, particularly hypoglycemia and hypokalemia with insulin therapy 1, 2