Arrhythmias and Electrophysiology
Rhythm diagnosis
Pediatric arrhythmias range from benign sinus arrhythmia to fetal and neonatal supraventricular tachycardia (SVT), congenital complete heart block, and inherited channelopathies. SVT in infants is usually narrow-complex and abrupt in onset, with rates often above 220 beats/min; P waves may be hidden. Vagal maneuvers and adenosine are first-line for stable SVT. Adenosine transiently blocks the atrioventricular node and is diagnostic and therapeutic, but it can cause bronchospasm and should be used cautiously in pre-excited atrial fibrillation. Unstable patients need synchronized cardioversion.
Therapy and devices
Antiarrhythmic selection depends on mechanism: beta-blockers for long QT and catecholaminergic polymorphic ventricular tachycardia, and amiodarone or procainamide for stable ventricular tachycardia. Catheter ablation is increasingly used for accessory pathways and focal tachycardia in children, with size and risk considerations. Pacemakers are indicated for symptomatic bradycardia and congenital complete heart block; implantable defibrillators for survivors of lethal ventricular arrhythmia or high-risk channelopathy.
Traps
Do not give verapamil to infants with SVT; it can cause cardiovascular collapse. Do not treat all wide-complex tachycardia as SVT. In WPW with atrial fibrillation, avoid AV-nodal blocking drugs that may accelerate ventricular conduction. Long QT is diagnosed on rate-corrected QT, and normal QT does not exclude a channelopathy.
Worked example
A 2-month-old has a heart rate of 280 beats/min, narrow QRS, and no visible P waves. Perform vagal maneuvers; if unsuccessful, give adenosine 0.1 mg/kg rapidly. If the infant is hypotensive or has poor perfusion, use synchronized cardioversion. Rule of thumb: stable narrow-complex SVT - vagal, then adenosine; unstable - electricity.