9.3 Stable SVT: Vagal Maneuvers & Adenosine

Stable vs Unstable: The First Branch of Tachycardia Care

Once you have identified narrow-complex SVT (Section 9.2), ask whether cardiopulmonary compromise is present. Signs of compromise include hypotension for age, acutely altered mental status, signs of shock (poor pulses, delayed refill, mottling), and acute heart-failure features (rales, hepatomegaly, severe respiratory distress from pulmonary edema). If compromise is present, this is unstable tachycardia—prioritize synchronized cardioversion (Chapter 10) rather than prolonged vagal/adenosine delays.

If cardiopulmonary compromise is absent, the child is managed on the stable SVT pathway:

1. Support ABCs; oxygen if needed; continuous ECG monitoring; defibrillator/pads available.
2. Obtain IV/IO access (preferably a large proximal vein for adenosine delivery).
3. Attempt vagal maneuvers while preparing adenosine.
4. Give adenosine as rapid push with flush if vagal maneuvers fail.
5. Reassess rhythm and perfusion continuously; escalate if the child becomes unstable.

"Stable" is a moment-to-moment label. Infants in SVT for many hours can look deceptively quiet while sliding into cardiogenic shock—reassess after every intervention.

Team setup before drugs

• Continuous monitor and printed/recorded rhythm strip capability
• Airway equipment and oxygen ready
• Defibrillator with pediatric capabilities at the bedside (pads sized/placed appropriately)
• Two-syringe or stopcock setup for adenosine + flush
• Clear role assignment: medication, airway, documentation, team lead

Vagal Maneuvers in Children

Vagal maneuvers increase parasympathetic tone at the AV node, briefly slowing or blocking conduction enough to interrupt many reentrant SVT circuits.

Infants: ice to the face (diving reflex)

For infants, the classic PALS teaching maneuver is application of a bag of ice mixed with water (or a frozen cold pack protected to avoid frostbite injury) over the face—especially the forehead, eyes, and bridge of the nose—for a brief period (commonly taught around 10–15 seconds or until conversion, without obstructing the airway or covering the nose/mouth in a way that prevents breathing). This stimulates the diving reflex, producing a strong vagal surge.

Critical safety points:

• Do not occlude the airway or plunge the infant’s head underwater.
• Protect the skin; do not apply dry ice or leave ice in place for prolonged periods.
• Monitor ECG continuously; be ready for conversion, pauses, or deterioration.
• Ocular pressure as a vagal technique is not recommended in modern pediatric teaching because of injury risk—prefer ice-to-face per current PALS instruction.

Older children: Valsalva

For a cooperative older child, teach a Valsalva maneuver: bear down as if having a bowel movement, or blow against resistance (for example, into a syringe or occluded straw) for about 10–15 seconds. Some settings use a modified Valsalva (strain then passive leg raise) when age and cooperation allow—follow local protocol and PALS instructor guidance.

Carotid sinus massage is not a routine pediatric first-line teaching maneuver the way some adult pathways discuss it; stick to ice-to-face and Valsalva for exam-level answers unless a specific expert protocol says otherwise.

If vagal maneuvers convert the rhythm, monitor for recurrence, search for triggers, and arrange appropriate follow-up. If they fail, proceed immediately to adenosine without prolonged repeated attempts that delay definitive drug therapy.

Adenosine: Dose, Technique, and Documentation

Adenosine is an ultrashort-acting AV nodal blocker. Its plasma half-life is only seconds, so administration technique is as important as the milligram number. A correctly calculated dose given slowly into a distal IV may never reach the heart in effective concentration.

Dosing (PALS teaching)

Give via a rapid IV/IO push as close to the central circulation as practical (proximal IV preferred), then immediately follow with a rapid saline flush to propel the drug into the central circulation. Elevate the extremity when using a peripheral IV if that is your system’s technique. Use a stopcock or two-syringe method so there is zero delay between drug and flush.

What to expect and how to document

• Record a continuous rhythm strip before, during, and after the dose—this documents conversion, reveals atrial activity during block, and provides medico-legal/clinical clarity.
• Brief asystole, pauses, or escape beats for a few seconds are expected; warn the team and (when appropriate) the child/family that a transient "flatline" can appear on the monitor and then recover.
• Side effects are usually short-lived: flushing, chest discomfort, dyspnea, sense of dread.
• If SVT terminates, monitor for recurrence; if it does not, give the second dose promptly per algorithm timing.
• If the strip shows that the rhythm was actually something else (e.g., atrial flutter with transient slowing), use that diagnostic information and consult experts—do not blindly stack unrelated antiarrhythmics.

Access and "failed adenosine" troubleshooting

Before declaring adenosine a failure:

• Confirm the dose was weight-based and within max teaching limits.
• Confirm rapid push + immediate flush technique.
• Prefer a more proximal IV or IO route if the first attempt used a tiny distal vein with sluggish flow.
• Reconfirm the rhythm is still SVT and the child remains on the stable pathway.

If the child develops cardiopulmonary compromise at any time, abandon a prolonged chemical pathway and move to synchronized cardioversion.

2025 Note: IV Sotalol as an Advanced, Not First-Line, Option

Under 2025 AHA pediatric advanced life support guidance, IV sotalol may be considered for SVT with cardiopulmonary compromise that is unresponsive to vagal maneuvers, adenosine, and synchronized cardioversion when expert consultation is not available. Frame this carefully for the exam:

• It is not first-line therapy for stable SVT.
• It does not replace vagal maneuvers or adenosine in the standard stable pathway.
• It does not replace synchronized cardioversion for the unstable child.
• It is an advanced refractory option after the standard sequence fails and expert help is unavailable—know that it exists, know its place late in the algorithm, and prioritize the high-yield basics (vagal → adenosine dosing/technique → cardioversion when unstable).

Expert consultation (pediatric cardiology/electrophysiology/critical care) remains preferred whenever reachable for refractory arrhythmias.

Clinical scenario (synthesis)

A 4-year-old with known SVT presents alert, with strong pulses, normal blood pressure for age, and a regular narrow tachycardia at 220/min without clear P waves. Cardiopulmonary compromise is absent. You place pads, start oxygen as needed, and coach a Valsalva—no conversion. You give adenosine 0.1 mg/kg rapid IV push with immediate flush while recording the strip; a brief pause is followed by sinus rhythm. If SVT had persisted, you would give 0.2 mg/kg next. If the child had instead arrived pale, hypotensive, and poorly responsive, you would prioritize synchronized cardioversion, not a long adenosine delay. If after vagal attempts, adenosine, and cardioversion the compromised SVT still persisted and no specialist were available, you would recognize that 2025 guidance allows consideration of IV sotalol as an advanced option—while still seeking expert care as soon as possible.

Memorize the 0.1 → 0.2 mg/kg rapid-push sequence, infant ice-to-face vagal technique, and the stable-versus-unstable branch, and you will handle the majority of PALS narrow-complex SVT items correctly.