10.3 Antiarrhythmics for Tachycardia with Pulse

Where Drugs Fit After Electricity and Expert Judgment

Antiarrhythmic medications for tachycardia with a pulse sit in a different mental box from cardiac arrest drugs. In arrest (Chapter 8), the priorities are CPR, defibrillation for VF/pVT, and epinephrine timing. Antiarrhythmics for refractory shockable arrest are given in a bolus context during CPR. In perfusing VT or other stable/near-stable wide-complex rhythms, the goals shift to terminating or suppressing the arrhythmia without crashing blood pressure, often with controlled infusions and continuous monitoring—preferably under expert consultation.

Before any infusion:

1. Confirm a pulse is present.
2. Decide stable vs unstable. Unstable → synchronized cardioversion first (Section 10.1), not a 20-minute drug prep.
3. Support ABCs; pads remain on the chest.
4. Correct obvious reversible causes when feasible (electrolytes, toxins, hypoxia).
5. Call for pediatric cardiology / critical care / EP help early.

Drugs buy time and may convert rhythm; they do not replace airway support, electricity when indicated, or diagnosis of the underlying disease (myocarditis, channelopathy, congenital heart disease, drug toxicity).

Arrest bolus vs pulse-present infusion — the amiodarone distinction

Amiodarone 5 mg/kg IV/IO appears in both worlds, but how you give it changes with context:

On the exam, if the vignette says VT with a pulse and asks for amiodarone dosing concept, answer 5 mg/kg and recognize infusion/over-time administration—not “push it like epinephrine in asystole.” Exact infusion durations can vary by protocol and formulation; PALS-level mastery is the dose number + pulse-present vs arrest technique distinction.

Core Agents for Perfusing VT (Exam-Level)

Amiodarone

• Dose teaching point: 5 mg/kg IV/IO
• Use case: Ventricular arrhythmias / wide-complex VT pathways when drugs are indicated
• Pulse-present key: give over time (infusion), monitor BP and rhythm continuously
• Risks: hypotension, bradycardia, further arrhythmias; long half-life complicates stacking other agents
• May be repeated per protocol/expert guidance up to cumulative limits taught in provider materials—do not invent unlimited redosing on your own

Procainamide

• Role: Alternative antiarrhythmic for stable/perfusing VT or certain supraventricular scenarios in expert hands
• Why alternatives exist: Some rhythms or patient factors favor procainamide over amiodarone (and vice versa); local protocols and cardiology preference matter
• Practical exam point: Know that procainamide is an accepted alternative where used—not that every learner must memorize every adult milligram-per-minute chart for the PALS written exam
• Cautions: Hypotension, QRS widening, proarrhythmia; infusion requires monitoring; avoid casual combination with amiodarone

Lidocaine

• Role: Another option in ventricular arrhythmia algorithms (including some arrest and peri-arrest pathways depending on guideline/protocol generation and local practice)
• Exam framing: If a question lists lidocaine among antiarrhythmic choices for VT, recognize it as a legitimate class option, while still applying the stable/unstable and pulse/pulseless branches first
• Cautions: CNS toxicity (seizures, altered mentation) at high levels; dose adjustments in low cardiac output states per protocol

Comparison snapshot

Do not stack antiarrhythmics casually

Giving amiodarone and procainamide together (or piling multiple agents without expertise) increases risk of:

• Severe hypotension
• Proarrhythmia (including bradycardia, heart block, or degeneration to VF)
• Inability to tell which drug caused deterioration
• Delayed electricity or expert care while “one more drug” is mixed

Preferred pattern: choose one pharmacologic strategy under protocol/expert guidance, reassess, and escalate to cardioversion if the child becomes unstable or the rhythm is refractory. If the first agent fails and the child remains stable enough, expert consultation—not reflexive dual loading—should drive the next agent.

Contrast: Adenosine for SVT vs Antiarrhythmics for VT

Mixing these pathways is one of the most common pharmacology errors on resuscitation exams.

Adenosine pathway (Chapter 9 reminder)

• Rhythm: Regular, monomorphic, narrow-complex SVT (reentry involving AV node)
• Stability: Used when the child is stable enough for a chemical attempt (or as part of the standard stable pathway); unstable SVT → cardioversion
• Dose: 0.1 mg/kg rapid IV/IO push + flush, then 0.2 mg/kg if needed (common teaching maxima 6 mg / 12 mg)
• Technique: Speed matters more than ceremony—ultrashort half-life
• Not for: Irregular wide-complex tachycardia, known pre-excited AF, or as a substitute for defibrillation in pVT

VT / wide-complex antiarrhythmic pathway (this section)

• Rhythm: Presumed or confirmed VT / selected wide-complex rhythms with pulse
• Stability: Unstable → electricity first; stable → expert + single-agent strategy
• Amiodarone teaching dose: 5 mg/kg IV/IO over time for perfusing VT
• Alternatives: Procainamide, lidocaine per protocol
• Not interchangeable with adenosine as a first-line “rate reset” for VT

Practical monitoring while infusions run

• Continuous ECG; watch for conversion, QRS widening, bradycardia, or degeneration to VF
• Frequent blood pressure; be ready to stop the infusion and support perfusion
• Defibrillator charged conceptually “one button away”—know the next energy if the child crashes
• Document times, doses, and rhythm strips
• After conversion: search etiology, consider ICU/cardiology admission, avoid premature removal of pads

Clinical scenarios (synthesis)

Scenario A — Perfusing VT, stable enough for meds: A 9-year-old is alert with acceptable blood pressure and a regular wide tachycardia thought to be monomorphic VT. Pads are applied. Cardiology recommends amiodarone. You administer amiodarone 5 mg/kg IV over the protocol infusion interval, monitor BP, and do not simultaneously start procainamide. If hypotension and poor perfusion develop, you stop the infusion mindset and move to synchronized cardioversion.

Scenario B — Unstable—do not hide behind drugs: A toddler with wide-complex tachycardia is limp and hypotensive with weak pulses. Drawing amiodarone is fine in parallel, but the first rhythm-specific therapy is synchronized cardioversion at 0.5–1 J/kg, not waiting for the infusion to finish.

Scenario C — Wrong drug class: A nurse suggests adenosine 0.1 mg/kg for irregular wide-complex tachycardia in an adolescent with possible WPW. You stop that plan: avoid adenosine in irregular wide / pre-excitation concerns; support ABCs, get expert help, and cardiovert if unstable.

Scenario D — Arrest vs pulse contrast: During CPR for refractory pVT, amiodarone may be given as an arrest bolus of 5 mg/kg. After ROSC, ongoing infusions and expert management differ from the code-bolus context—do not confuse the two on test items that carefully specify “with a pulse” vs “pulseless.”

Exam traps

Bottom line for 10.3: For tachycardia with a pulse, match the drug to the rhythm class: adenosine for appropriate narrow SVT, amiodarone 5 mg/kg over time (or procainamide/lidocaine alternatives) for perfusing VT, magnesium in torsades context, expert consultation, no casual stacking, and cardioversion first whenever cardiopulmonary compromise appears. Link Chapters 8–10: arrest boluses and defibrillation when pulseless; synchronized shocks and careful infusions when a pulse remains.