4.1 Pediatric Tachyarrhythmias: SVT, Atrial Flutter & Ventricular Tachycardia Algorithms

Pediatric Tachyarrhythmias: Diagnostic Differentiation, PALS Algorithms, and Emergency Interventions

Start with pulse, perfusion and ECG. A fixed rapid rate with abnormal P waves suggests supraventricular tachycardia (SVT). A regular wide-complex rhythm can be ventricular tachycardia (VT) or SVT with aberrancy. Treat cardiopulmonary compromise promptly and use the arrest algorithm if the pulse is lost.

Rapid assessment and algorithmic stabilization of pediatric tachyarrhythmias are core competencies for the Acute Care Pediatric Nurse Practitioner (ACPNP). Immature pediatric myocardium possesses limited stroke volume reserve; cardiac output ($CO = HR \times SV$) is heavily rate-dependent. However, extreme rates compromise diastolic filling time, reduce coronary perfusion, increase myocardial oxygen consumption, and rapidly precipitate low cardiac output syndrome, cardiogenic shock, and cardiovascular collapse.

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Electrophysiologic Mechanisms & Rhythm Classification

Tachyarrhythmias arise from three cellular mechanisms:

1. Reentry (Circus Movement): Requires two electrophysiologically distinct pathways with differing conduction velocities and refractory periods connected proximally and distally. An initiating premature beat blocks in one pathway (anterograde block) and conducts down the other, then retrogradely travels up the initially blocked limb, creating a self-sustaining loop. Reentrant tachycardias include atrioventricular reentrant tachycardia (AVRT, such as Wolff-Parkinson-White syndrome utilizing an accessory pathway), atrioventricular nodal reentrant tachycardia (AVNRT), and intra-atrial reentrant tachycardia (atrial flutter).
2. Enhanced Automaticity: Accelerated spontaneous Phase 4 depolarization of non-pacemaker cells or ectopic pacemakers exceeding the sinoatrial (SA) node firing rate. Examples include ectopic atrial tachycardia (EAT) and junctional ectopic tachycardia (JET, frequent after infant cardiac surgery).
3. Triggered Activity: Cellular depolarizations triggered by early afterdepolarizations (EADs, during Phase 2 or 3, associated with prolonged QT intervals) or delayed afterdepolarizations (DADs, during Phase 4, associated with intracellular calcium overload and digoxin toxicity). This mechanism drives Torsades de Pointes and catecholaminergic polymorphic ventricular tachycardia (CPVT).

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Differentiating SVT from Sinus Tachycardia

A critical diagnostic challenge in the pediatric emergency department and pediatric intensive care unit (PICU) is distinguishing severe sinus tachycardia from paroxysmal supraventricular tachycardia.

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Stepwise Management of Pediatric SVT

Therapeutic decision-making in pediatric SVT hinges on the patient's hemodynamic stability.

1. Hemodynamically Stable SVT

Patients with adequate end-organ perfusion (warm extremities, brisk capillary refill $\le 2\text{ seconds}$, normal blood pressure, alert baseline mental status) are managed pharmacologically and non-invasively:

Vagal maneuvers

For a monitored, stable infant, apply a cold pack or ice slurry to the face with the airway unobstructed and without pressure on the eyes. Coach an older cooperative child through a Valsalva maneuver. AHA notes limited pediatric data for the postural modification sometimes used in adults.

Adenosine

Adenosine briefly blocks conduction through the AV node, which can interrupt AV node-dependent reentry. If vagal maneuvers fail and IV/IO access is available, give $0.1\text{ mg/kg}$ as a rapid push (maximum $6\text{ mg}$) and immediately flush. If needed, repeat with $0.2\text{ mg/kg}$ (maximum $12\text{ mg}$). Record the rhythm during dosing. Brief AV block may reveal continuing atrial activity, such as flutter waves. Seek expert consultation if stable SVT persists despite initial treatment.

2. Hemodynamically Unstable SVT

Instability is defined by the presence of cardiopulmonary compromise: hypotension, acutely altered mental status, cool and mottled extremities, delayed capillary refill $>3\text{ seconds}$, or pulmonary edema.

• Electrical therapy: Start synchronized cardioversion at $0.5\text{–}1\text{ J/kg}$. Escalate to $2\text{ J/kg}$ if unsuccessful. Confirm synchronization markers on the QRS complexes. Sedate if feasible without delaying treatment. For probable narrow-complex SVT, the PALS algorithm also permits adenosine when IV/IO access is already present.
• Refractory SVT with cardiopulmonary compromise: Seek pediatric electrophysiology input. When vagal maneuvers, adenosine and synchronized cardioversion have failed and expert consultation is unavailable, 2025 PALS permits consideration of one IV antiarrhythmic: procainamide, amiodarone, or sotalol. Monitor ECG and blood pressure closely. Combining antiarrhythmics increases the risk of proarrhythmia and hemodynamic collapse.

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Atrial Flutter & Atrial Fibrillation in Pediatrics

Atrial flutter in children typically presents as an intra-atrial reentrant tachycardia (IART), most prevalent in the immediate neonatal period (structurally normal heart with immature conduction) or years following complex congenital cardiac repairs involving extensive atrial suture lines (e.g., Fontan, Mustard, Senning, or repaired ASD/total anomalous pulmonary venous return).

• ECG Findings: Characteristic rapid "sawtooth" flutter waves (F waves) seen best in inferior leads II, III, and aVF, with atrial rates between $300\text{ and }400\text{ bpm}$. The ventricular response depends on AV conduction ratios ($2:1$ conduction produces ventricular rates of $150-200\text{ bpm}$; $1:1$ conduction produces life-threatening cardiovascular collapse).
• Response to Adenosine: Adenosine does not terminate the intra-atrial circuit of atrial flutter; however, transiently blocking AV nodal conduction unmasks baseline sawtooth flutter waves, confirming the diagnosis.
• Management: Atrial flutter and atrial fibrillation are distinct rhythms. Flutter has organized atrial activation, whereas atrial fibrillation has disorganized atrial activity and typically an irregular ventricular response. Synchronized cardioversion can terminate infant atrial flutter. In postoperative or recurrent flutter, involve pediatric cardiology to select rhythm treatment and assess thromboembolic risk. See the infant atrial flutter series.

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Wide-Complex Tachycardias & Ventricular Algorithms

For the PALS decision pathway, narrow means QRS duration $\le 0.09\text{ s}$ and wide means $>0.09\text{ s}$. Wide-complex tachycardia may represent ventricular tachycardia, SVT with aberrant conduction, or antidromic SVT.

1. Wide-complex tachycardia with a pulse

• Adequate perfusion: Obtain a 12-lead ECG and continuous monitoring. Consult a pediatric rhythm expert before choosing an antiarrhythmic. With expert input, adenosine can help diagnose or treat regular, monomorphic wide-complex tachycardia. The guideline does not name a single first-line antiarrhythmic for stable wide-complex tachycardia.
• Cardiopulmonary compromise: Provide urgent synchronized cardioversion for an organized wide-complex tachycardia. Start at $0.5\text{–}1\text{ J/kg}$ and increase to $2\text{ J/kg}$ if needed. If the child becomes pulseless, check the rhythm and follow the cardiac arrest pathway.

2. Pulseless VT & Ventricular Fibrillation (PALS Cardiac Arrest Algorithm)

Pulseless VT and VF are shockable arrest rhythms requiring prompt unsynchronized defibrillation. Prioritize shocks. Give epinephrine sooner than after shock two only when rapid defibrillation is unavailable.

[Pulseless VT / Ventricular Fibrillation]
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1. Call for help, initiate high-quality CPR (100-120/min, 1/3 AP depth), attach monitor
   - If arterial line in place, target intra-arrest DBP >=25 mmHg (infants) / >=30 mmHg (children)
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2. SHOCK 1: Asynchronous Defibrillation at 2 J/kg
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3. Immediately resume CPR for 2 minutes (no advanced airway: 15:2 with 2 rescuers before puberty; 30:2 with 1 rescuer or after puberty onset)
   - Obtain IV/IO access; prepare epinephrine
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4. Rhythm Check: Persistent Shockable Rhythm?
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5. SHOCK 2: Defibrillation at 4 J/kg
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6. Immediately resume CPR for 2 minutes
   - Administer Epinephrine: 0.01 mg/kg IV/IO (0.1 mg/mL; 0.1 mL/kg; max 1 mg), repeat every 3-5 min
   - Consider advanced airway and capnography
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7. Rhythm Check: Persistent Shockable Rhythm?
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8. SHOCK 3: Defibrillation at >=4 J/kg (titrate up to max 10 J/kg or the adult maximum for the defibrillator)
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9. Immediately resume CPR for 2 minutes
   - Administer Antiarrhythmic:
     * Amiodarone: 5 mg/kg IV/IO rapid bolus (max 300 mg initially; may give up to 3 total doses, max 150 mg for each subsequent dose)
     * OR Lidocaine: 1 mg/kg IV/IO bolus
   - Identify and treat reversible causes (H's and T's)

3. Physiology-Directed CPR & Post-Cardiac Arrest (ROSC) Hemodynamic Targets (2025 AHA PALS)

The 2025 AHA PALS Guidelines strengthen physiology-directed monitoring both during chest compressions and immediately after return of spontaneous circulation (ROSC):

• Intra-Arrest Arterial Diastolic Blood Pressure (DBP) CPR Quality Targets: When continuous arterial pressure is already available during cardiac arrest, the guideline suggests considering diastolic pressure $\ge 25\text{ mmHg}$ in infants and $\ge 30\text{ mmHg}$ in children aged one year or older. Use arterial pressure alongside other CPR quality measures.
• Post-Cardiac Arrest (ROSC) Blood Pressure Targets: Post-arrest myocardial stunning and systemic ischemia-reperfusion frequently cause labile hypotension. Maintain both systolic blood pressure (SBP) and mean arterial pressure (MAP) greater than the 10th percentile for age, while actively preventing and rapidly treating drops below the 5th percentile for age (the threshold defining post-arrest hypotension) using judicious fluid administration and titrated vasoactive infusions.

4. Torsades de Pointes (Polymorphic VT)

Torsades de Pointes is a distinct form of polymorphic ventricular tachycardia characterized by continuous twisting of the QRS complexes around the isoelectric baseline. It occurs in the setting of prolonged ventricular repolarization (congenital long QT syndrome or acquired LQTS from hypokalemia, hypomagnesemia, hypocalcemia, or QT-prolonging drugs like ondansetron, macrolides, and fluoroquinolones).

• Acute management: Pulseless torsades follows the shockable arrest pathway. Give IV/IO magnesium for long-QT torsades per the pediatric resuscitation protocol, correct electrolyte abnormalities, and stop causative QT-prolonging medications. Seek specialist guidance for recurrent episodes.

AHA/AAP 2025 pediatric advanced life support guidelines · 2025 tachyarrhythmia algorithm · Pediatric arrhythmia consensus · 2025 arrest algorithm