Can digoxin (digitalis glycoside) cause bradycardia in a 1-month-old infant?

Digoxin as a Cause of Bradycardia in a 1-Month-Old Infant

Yes, digoxin can cause bradycardia in a 1-month-old infant, and this is actually one of the earliest and most frequent manifestations of digoxin toxicity in infants. 1

Digoxin Effects on Cardiac Rhythm in Infants

• Infants react differently to digoxin than adults, with cardiac arrhythmias being the earliest sign of toxicity rather than gastrointestinal or CNS symptoms 1
• Sinus bradycardia may be a sign of impending digoxin intoxication in infants, even in the absence of first-degree heart block 1
• Any arrhythmia or alteration in cardiac conduction that develops in a child taking digoxin should be assumed to be caused by digoxin until proven otherwise 1

Clinical Presentation of Digoxin-Induced Bradycardia

• The most common arrhythmias in children on digoxin include:

  • Sinus bradycardia 1, 2
  • Conduction disturbances 1
  • Supraventricular tachyarrhythmias 1
  • Junctional (nodal) rhythm 3

• In a study of low birth weight infants treated with digoxin, 8 out of 18 infants experienced frequent episodes of bradycardia related to digoxin therapy 2

Risk Factors for Digoxin Toxicity in Infants

• Narrow therapeutic index of digoxin makes toxicity more likely 4
• Electrolyte abnormalities, particularly hypokalemia, can precipitate digoxin toxicity even with therapeutic serum levels 3
• Premature infants appear to be particularly susceptible to digoxin-related bradycardia 2
• Concomitant diuretic therapy increases risk of toxicity 5

Monitoring and Detection

• Serum digoxin levels >5 ng/ml are more likely to cause symptomatic toxicity in neonates 4
• However, toxicity can occur even with normal serum levels, especially in the presence of electrolyte disturbances 3
• ECG monitoring is essential as bradycardia and junctional rhythm may be the earliest signs of toxicity 3
• Symptoms may be delayed, with ECG abnormalities appearing more than five hours after ingestion in some cases 6

Management of Digoxin-Induced Bradycardia

• Discontinuation of digoxin is the first step in management 3
• For severe toxicity, digoxin-specific antibody Fab fragments (DigiFab®) may be required 4, 3
• Careful monitoring of electrolytes is essential, as hypokalemia may develop after Fab fragment administration 4
• Cardiac pacing may be considered if the risk of heart block is unacceptable 1

Special Considerations in Infants with Cardiac Conditions

• Digoxin is contraindicated in infants with Wolff-Parkinson-White (WPW) syndrome as it can shorten the antegrade effective refractory period of the accessory pathway 7
• In infants with WPW syndrome and supraventricular tachycardia, digoxin has been associated with sudden death 7
• For infants with congenital heart disease and left-to-right shunts, the use of digoxin remains controversial, with some studies showing benefit and others showing no improvement 7

Prevention of Digoxin Toxicity

• Lower dosing regimens are recommended to achieve serum levels of 1.1-1.7 ng/ml rather than higher levels 5
• Regular monitoring of serum electrolytes, particularly potassium 3
• Consider alternatives to digoxin in seriously ill low-birth-weight infants 2
• In infants with heart failure and hypokalemia, addition of an aldosterone antagonist like spironolactone should be considered 3