PALS | Pedi Bradycardia & Tachycardia Extended

80/20 Core Need-to-Know Principles

• Cardiac Output Formula: Cardiac output equals stroke volume times heart rate ($CO = SV \times HR$)1. Because young children cannot increase stroke volume significantly, bradycardia directly drops cardiac output2.
• Leading Cause of Bradycardia: Tissue hypoxia from hypoxemia or respiratory failure is the main cause of symptomatic bradycardia1. Supporting airway, oxygenation, and ventilation is the initial priority1.
• CPR Threshold: Symptomatic bradycardia is HR < normal for age (typically <60/min) with cardiopulmonary compromise (hypotension, altered mental status, shock)3. If HR stays <60/min with poor perfusion despite ventilation, start CPR immediately3.
• QRS Classification: Tachyarrhythmias are divided by QRS width into narrow ($\le$0.09 s) and wide (>0.09 s)45. Wide QRS tachycardias are assumed to be Ventricular Tachycardia (VT) unless proven otherwise67.

Bradycardia & AV Blocks

• Etiology: Primary bradycardia stems from intrinsic pacemaker/conduction disease (congenital defects, surgery, myocarditis)1. Secondary bradycardia results from noncardiac causes (hypoxia, acidosis, hypotension, hypothermia, drugs)1.
• ECG Features: Slow rate, variable P waves, narrow/wide QRS, and potential AV dissociation2.
• AV Block Spectrum:
  • First-degree: Prolonged PR interval; asymptomatic8.
  • Second-degree Mobitz I (Wenckebach): Progressive PR prolongation until a P wave drops89.
  • Second-degree Mobitz II: Intermittent dropped P waves without PR prolongation (often 2:1 block); risks syncope89.
  • Third-degree (Complete): Complete AV dissociation with independent P waves and QRS complexes; causes fatigue and syncope89.

Tachyarrhythmias: Narrow vs. Wide Complex

• Hemodynamic Impact: Rapid rates shorten diastole, reducing stroke volume and coronary perfusion, causing heart failure and shock4.
• Sinus Tachycardia (ST) vs. SVT:
  • Sinus Tachycardia: Normal response to stress, fever, or hypovolemia5. HR <220/min in infants, <180/min in children5. Shows rate variability, normal P waves, gradual onset5more_horiz.
  • Supraventricular Tachycardia (SVT): Reentry mechanism arrhythmia11. HR $\ge$220/min in infants, $\ge$180/min in children12. Shows abrupt onset, absent/abnormal P waves, constant rate without variability6more_horiz.
• Atrial Flutter: Narrow-complex rhythm with atrial rate >300/min and sawtooth P waves10.
• Ventricular Tachycardia (VT): Wide-complex rhythm (>0.09 s), rate $\ge$120/min, AV dissociation7.
  • Monomorphic VT: Uniform QRS complexes13.
  • Polymorphic VT / Torsades de Pointes: QRS twists around baseline; linked to long QT, hypomagnesemia, hypokalemia, or drugs, deteriorating into VF713.