3.3 Neonatal Dysrhythmias and Cardioversion

3.3 Neonatal Dysrhythmias and Cardioversion

Quick Answer: SVT is the most common neonatal tachyarrhythmia. Distinguish it from sinus tachycardia with rate and variability clues (SVT is often abrupt and commonly faster than about 220 bpm with little change when you stimulate the infant). Stable SVT: brief ice to the face with airway caution, then adenosine via rapid flush. Unstable SVT: synchronized cardioversion. Bradycardia is hypoxia until proven otherwise—airway and ventilation before atropine or pacing, following NRP logic. Complete heart block, long QT, and VT/VF are less common but testable. Confirm lead placement so you do not cardiovert artifact.

Dysrhythmias are a cardiovascular leaf on the Neonatal CCRN Test Plan (exams on and after November 12, 2025; cardiovascular domain 10%). OpenExamPrep independent teaching treats them as a nursing-action list: identify the true rhythm, decide stable versus unstable, then apply vagal, pharmacologic, or electrical cardioversion in the right order. Congenital heart surgery can add postoperative junctional ectopic tachycardia; that context belongs with the surgery chapter, but the same stable-versus-unstable logic still applies.

Start with the paper: is it real?

Before you name a rhythm, prove the ECG is the infant’s electrical activity.

Lead placement. Right arm (RA) and left arm (LA) on the correct shoulders or trunk positions, left leg (LL) on the left lower limb or flank, right leg (RL) as ground, and a precordial lead (often V1) if you are recording a diagnostic tracing. In the NICU, limb leads often sit on the trunk to spare tiny limbs—consistency matters more than adult wrist ritual, but RA/LA reversal will invert P and QRS and can mimic dextrocardia or ischemia. Label the tracing with lead positions when the diagnosis is high-stakes.

Loose electrodes, 60-Hz interference from incubators and warmers, patting, hiccups, and bubbling CPAP create artifact. Artifact usually shows an intact QRS marching through, or a tracing that does not match the pulse oximeter pulse and the femoral pulse. Always confirm with pulse, heart tones, and arterial waveform if an arterial line exists. A monitor rate of 280 with a palpable rate of 140 is artifact or double-counting, not an invitation to shock.

If the infant is pulseless with VT/VF morphology, that is a defibrillation (unsynchronized) pathway, not synchronized cardioversion. Pulseless arrest follows NRP/PALS-style unit protocols. VT/VF is rare in neonates compared with asphyxial bradycardia; do not let an adult ACLS reflex skip ventilation.

Common non-crisis findings

Premature atrial contractions are common and often benign in otherwise well newborns, including after caffeine. Blocked PACs can create pauses that look like sinus bradycardia or AV block until you hunt for hidden P waves in the T wave. Isolated premature ventricular contractions deserve a look at electrolytes and lines sitting in the ventricle, but a few PVCs in a pink infant are not automatic amiodarone. Document, assess perfusion, and escalate when ectopy is frequent, polymorphic, or coupled with poor output.

Sinus tachycardia versus SVT

Sinus tachycardia is a response: fever, pain, anemia, hypovolemia, inotropes, seizures, hyperthyroidism, or high-output runoff. Clues:

• Rate often elevated but, in many term infants, still below about 220 bpm (preterm infants may have a slightly different ceiling; use the stem).
• Beat-to-beat and minute-to-minute variability; the rate rises when you stimulate and falls when the infant settles.
• Visible P waves with a stable PR relationship and an axis appropriate for age.

Supraventricular tachycardia (SVT), most often AV re-entry via an accessory pathway in this age group:

• Often abrupt onset and offset.
• Commonly 220–300 bpm in neonates.
• Little variability with stimulation; the infant stays locked.
• P waves absent, retrograde, or buried; QRS usually narrow.
• May present with heart failure if it has been incessant for hours (tachycardia-induced cardiomyopathy—see the failure section).

Worked contrast: a crying 3 kg infant at 190 bpm with clear P waves who drops to 160 when swaddled is sinus tachycardia. An infant at 270 bpm, gray, with no P waves and a rate that does not blink when you stimulate is SVT until proven otherwise.

Atrial flutter appears in some neonates (especially with CHD or after surgery) as a sawtooth atrial rate with variable conduction. Adenosine may reveal flutter waves without converting the atrium. That is diagnostic, not proof that the nurse gave it wrong, if the flush technique was correct. Unstable flutter still follows the synchronized-cardioversion path.

Stable versus unstable SVT

Unstable means shock, severe poor perfusion, collapse, or acute heart failure from the rate. Do not wait for a textbook blood pressure if the infant is gray and barely pulsatile.

Stable means the infant is perfusing enough that you have seconds to a few minutes for a vagal maneuver and adenosine, with the defibrillator already in the room. Stable is not an excuse to leave the bedside for supplies.

Vagal maneuver: ice to the face

A bag of ice (or iced cloth) applied to the face—diving reflex—can interrupt AV re-entry. Cautions that exams love:

• Do not occlude the airway or pack ice over the nose and mouth.
• Keep the pass brief (often taught around 10–15 seconds, not minutes).
• Use extra caution in very preterm infants (skin injury, apnea, bradycardia).
• Do not use eyeball pressure.
• Have airway equipment ready; vagal success can be followed by a pause.

If ice fails or is inappropriate, move to adenosine without delay. Ice is a nursing action, not a substitute for electricity in a crashing infant.

Adenosine: pharmacologic cardioversion

Adenosine blocks the AV node briefly. Because the half-life is seconds, technique is the drug:

• Best through a right-arm or proximal IV with a stopcock and an immediate saline flush
• Record a continuous rhythm strip
• Warn that a pause, flushing, or brief asystole can occur
• If it does nothing, ask whether it truly reached the heart as a bolus

Typical pediatric/PALS-style dosing (0.1 mg/kg then 0.2 mg/kg in many protocols) is used in NICUs; this guide does not present those numbers as an AACN-published table. Repeat dosing and expert consultation follow unit protocol when the infant remains stable. If the infant becomes unstable, stop the adenosine debate and cardiovert.

Other antiarrhythmics (procainamide, beta blockade, rare amiodarone use) appear under specialist direction after adenosine fails in a still-stable infant. They are not the first-line independent nursing action the way ice, adenosine, and sync shock are.

Synchronized cardioversion: mechanical/electrical cardioversion

Synchronized cardioversion times the shock to the QRS to avoid an R-on-T event. It is the testable mechanical cardioversion for unstable SVT and for some unstable atrial flutter. Setup:

• Sedation if it will not delay a crashing infant
• Pads sized for a neonate; anterior-posterior placement is common on tiny chests
• SYNC on; confirm flags mark QRS complexes, not T waves or artifact
• Energy per current PALS-style pediatric dosing used in your unit (commonly a low joule/kg starting dose). Follow the stem if numbers are given; do not freeze the exam to one unpublished AACN joule table
• Recheck rhythm and perfusion after the shock

Unsynchronized defibrillation is for pulseless VF/pulseless VT, not for a perfusing SVT. Shocking a monitor full of artifact because nobody felt a pulse is a preventable disaster.

Bradycardia, complete heart block, and the NRP order of operations

Neonatal bradycardia is airway and oxygenation first. Under NRP logic, HR under 100 with poor breathing gets ventilation; HR under 60 despite effective ventilation gets chest compressions and then epinephrine. Atropine and pacing are not the opening moves for asphyxial bradycardia. If a question offers atropine before opening the airway, it is wrong.

Complete (third-degree) heart block: P waves march independently of a slow QRS. Causes: maternal anti-Ro/La antibodies (acquired–congenital overlap in the previous section), structural CHD (l-TGA, heterotaxy—CHD chapter), postoperative AV-node injury. Compensated infants may look surprisingly well at a rate in the 50s–70s; hydrops and heart failure mean they are not compensated. Support: maintain temperature and glucose, avoid further AV-block drugs, consider isoproterenol or low-dose epinephrine as a chemical bridge, and prepare for pacing (transcutaneous as a bridge, then temporary or permanent epicardial or transvenous strategies in a capable center).

Long QT, VT, and VF (conceptual)

Long QT (congenital syndromes or acquired from drugs and electrolytes—macrolides, some antiarrhythmics, 5-HT3 antagonists in susceptible infants, hypokalemia, hypocalcemia, hypomagnesemia) predisposes to polymorphic VT (torsades). Nursing actions: review the medication list, replete electrolytes, avoid unnecessary QT-prolonging drugs, and treat torsades with magnesium per protocol. A long QT on a sinus strip after conversion from SVT should change the discharge medication review.

VT/VF are uncommon primary neonatal rhythms. When they occur, think congenital channelopathy, myocarditis, ischemia, a catheter irritating the ventricle, or hyperkalemia (a sine-wave can mimic a wide rhythm). Pulseless → unsynchronized defibrillation and NRP/PALS-style CPR. Pulse-present unstable VT → synchronized cardioversion. Do not give adenosine as the primary therapy for a shocky wide-complex rhythm.

After conversion

Search for Wolff–Parkinson–White (delta wave) on a sinus strip, fever, electrolyte derangement, and CHD. Incessant SVT causes secondary heart failure; after conversion the infant may still need failure support. Document strips with clocks, mark adenosine and shock times, and keep the family informed during a terrifying monitor event. Facilitation of learning for parents is a professional-caring skill; here it means explaining that the ice bag and the brief pause after adenosine were treatments, not accidents.

Pharmacologic cardioversion (adenosine) and mechanical/electrical cardioversion (synchronized shock) are the Test Plan-style nursing actions. Ice is a vagal maneuver that sits in front of adenosine for selected stable infants. Independent practice items: /practice/ccrn-neonatal. Adult and pediatric CCRN rhythm chapters (/study-guides/ccrn, /study-guides/ccrn-pediatric) use similar adenosine and sync-shock logic with different rate cutoffs and access devices.