What is the initial step in managing a 6-year-old male with a history of congenital heart disease repair, presenting with sudden lethargy, palpitations, and tachycardia, with an electrocardiogram (ECG) showing a wide QRS complex and regular rhythm at 250 beats per minute (bpm)?

Management of Wide QRS Tachycardia in a Hemodynamically Unstable Pediatric Patient with Congenital Heart Disease

Synchronized cardioversion is the initial step for this 6-year-old with hemodynamic instability (lethargy, pallor, delayed capillary refill) and wide QRS tachycardia at 250 bpm. 1

Immediate Management Algorithm

Step 1: Recognize Hemodynamic Instability

This patient demonstrates clear signs of hemodynamic compromise:

• Lethargy indicates inadequate cerebral perfusion 1
• Pallor with delayed capillary refill signals poor peripheral perfusion 1
• Heart rate of 250 bpm in a 6-year-old is critically elevated 1

Step 2: Perform Synchronized Cardioversion

The ACC/AHA/HRS guidelines explicitly recommend synchronized cardioversion as Class I (highest level) for acute treatment in patients with supraventricular tachycardia who are hemodynamically unstable. 1 This recommendation applies directly to pediatric patients with congenital heart disease, as the guideline specifically addresses this population 1

• Start with 100-200 joules for initial cardioversion 2
• Provide appropriate sedation if the patient is conscious 2
• Have full resuscitation equipment immediately available 2

Step 3: Why NOT Medications First?

IV propranolol (Option A) is contraindicated in hemodynamically unstable patients because:

• Beta-blockers can worsen hypotension and shock 1
• They are only reasonable (Class IIa) for stable junctional tachycardia, not unstable wide QRS tachycardia 1

IV amiodarone (Option B) is inappropriate as initial therapy because:

• While amiodarone has a role in pediatric arrhythmias, it is not first-line for hemodynamically unstable patients 1
• The guideline reserves amiodarone for rate control strategies or as adjunctive therapy, not emergency stabilization 1
• Delaying cardioversion to administer medications increases risk of cardiovascular collapse 1

Critical Context for Congenital Heart Disease

This patient's history of congenital heart disease repair is highly relevant:

• Post-surgical patients are at high risk for atrial reentry tachycardia, ventricular tachycardia, and junctional ectopic tachycardia 1, 3, 4
• Wide QRS tachycardia at 250 bpm in this population could represent ventricular tachycardia or supraventricular tachycardia with aberrancy 1, 3
• Regardless of the specific mechanism, hemodynamic instability mandates immediate cardioversion 1, 2

Post-Cardioversion Management

After successful cardioversion:

1. Anticoagulation assessment - ACHD patients with atrial tachyarrhythmias require antithrombotic therapy similar to atrial fibrillation protocols 1

2. Evaluate underlying hemodynamics - Development of arrhythmias in ACHD often indicates progressive hemodynamic changes requiring assessment for residual structural defects 1

3. Consider maintenance antiarrhythmic therapy - Beta-blockers, amiodarone, or other agents may be needed to prevent recurrence, but only after hemodynamic stability is achieved 1

4. Electrophysiology consultation - ACHD patients with recurrent tachyarrhythmias may benefit from catheter ablation, though success rates are lower (70-85%) than in structurally normal hearts 1, 4

Common Pitfalls to Avoid

• Never delay cardioversion to attempt pharmacologic conversion in hemodynamically unstable patients 1, 2
• Do not use flecainide in post-surgical CHD patients due to increased risk of sudden cardiac death 1
• Avoid assuming narrow complex tachycardia - wide QRS in pediatric CHD can represent multiple mechanisms, all requiring urgent cardioversion when unstable 1, 3
• Remember that junctional ectopic tachycardia post-cardiac surgery in children has high mortality if uncontrolled, making aggressive management essential 1

The answer is C - synchronized cardioversion.