Supraventricular Tachycardia — Acute Termination

Key Points

• Stability determines whether the first treatment is cardioversion or a vagal/adenosine pathway.
• Modified Valsalva is an effective first maneuver for stable regular narrow-complex SVT.
• Adenosine is given as a rapid IV push: 6 mg first, then 12 mg if needed.
• Adenosine may unmask flutter or atrial activity even when it does not terminate the rhythm.
• Do not use routine AV-nodal blockers for irregular preexcited atrial fibrillation.
• Synchronized cardioversion is recommended for unstable SVT and for refractory cases when needed.
• Capture a 12-lead ECG before and after conversion whenever this does not delay emergency treatment.
• Recurrent symptomatic AVNRT/AVRT can often be cured with catheter ablation.

Algorithm

1. Assess pulse, blood pressure, perfusion, ischemia, heart failure, and mental status.
2. If unstable because of tachycardia, perform immediate synchronized cardioversion.
3. If stable and regular narrow-complex, perform a modified Valsalva maneuver.
4. Give adenosine 6 mg rapid IV push with flush if the rhythm persists.
5. Give adenosine 12 mg if needed and appropriate.
6. Use diltiazem, verapamil, beta blocker, or synchronized cardioversion for persistent stable SVT according to ventricular function and contraindications.
7. Identify reversible triggers and evaluate for preexcitation.
8. Arrange electrophysiology referral for recurrent symptomatic episodes or patient preference for definitive ablation.

Clinical Synopsis & Reasoning

SVT typically begins and ends abruptly and produces palpitations, chest discomfort, dyspnea, lightheadedness, anxiety, or presyncope. The ventricular rate is usually regular and often 150 to 250/min. AVNRT and orthodromic AVRT are common mechanisms. Atrial flutter with 2:1 conduction can mimic regular SVT near 150/min, while sinus tachycardia generally has a physiologic trigger and gradual onset/offset. Obtain a 12-lead ECG whenever possible before conversion because the tracing can reveal preexcitation, flutter waves, or another mechanism useful for long-term treatment.

Assess hemodynamic stability before spending time on rhythm discrimination. Hypotension attributable to tachycardia, shock, acute pulmonary edema, ischemic symptoms, or altered consciousness requires immediate synchronized cardioversion. If the QRS is wide, treat the rhythm with greater caution because ventricular tachycardia or preexcited tachycardia may be present. Adenosine can be diagnostically useful in a regular monomorphic wide-complex rhythm under current ACLS guidance, but irregular or polymorphic wide-complex tachycardia should not receive routine AV-nodal blockers.

Look for triggers such as dehydration, stimulant use, hyperthyroidism, pregnancy, anemia, infection, and electrolyte disturbance, but recurrent AVNRT/AVRT often occurs without systemic illness. A history of Wolff-Parkinson-White pattern matters because preexcited atrial fibrillation requires a different treatment approach. In a patient with recurrent sudden-onset regular palpitations, electrophysiology evaluation can establish the circuit and offer curative ablation.

Treatment Strategy & Disposition

For stable regular narrow-complex SVT, perform a vagal maneuver. A modified Valsalva maneuver with strain followed by supine repositioning and passive leg raise is more effective than a simple Valsalva in many adults. If the rhythm persists, give adenosine 6 mg as a rapid IV push immediately followed by saline flush. Give 12 mg if needed for persistent SVT. The 2025 AHA adult tachyarrhythmia algorithm retains this 6 mg then 12 mg sequence.

If adenosine fails or is contraindicated and the patient remains stable, IV diltiazem, verapamil, or a beta blocker can terminate or slow AV-node-dependent tachycardia in appropriate patients. Avoid verapamil/diltiazem in significant HFrEF or hypotension. Adenosine can cause transient flushing, chest pressure, dyspnea, and a sense of impending doom, which should be explained before administration when time permits. It is used cautiously in severe reactive airway disease and can have prolonged effects with dipyridamole or transplanted hearts.

Perform synchronized cardioversion when instability develops or stable SVT persists despite appropriate vagal and pharmacologic therapy. Sedate when feasible without delaying treatment. After conversion, review the ECG for preexcitation, obtain targeted electrolytes and thyroid testing when clinically relevant, and arrange cardiology/electrophysiology follow-up. Catheter ablation is highly effective definitive therapy for recurrent symptomatic AVNRT or AVRT.

Epidemiology / Risk Factors

• Paroxysmal SVT is common across otherwise healthy adults and patients with structural heart disease.
• AVNRT is one of the most common mechanisms in adults.
• Accessory-pathway-mediated AVRT can occur in patients with or without obvious preexcitation on a resting ECG.
• Episodes are often recurrent and can significantly affect quality of life despite low mortality in structurally normal hearts.
• Catheter ablation has made long-term drug therapy unnecessary for many symptomatic patients.

Investigations

Common Doses

Pharmacology

Prognosis / Complications

• Most stable SVT episodes terminate without lasting injury.
• Prolonged rapid rates can precipitate ischemia or heart failure in susceptible patients.
• Syncope or severe instability raises concern for underlying structural disease or a different arrhythmia.
• Catheter ablation has a high success rate for common reentrant SVTs.
• Recurrence is common after ED conversion when definitive electrophysiologic therapy is not pursued.

Patient Education / Counseling

• Learn a safe vagal maneuver from the treating clinician for recurrent stable episodes.
• Call emergency services for syncope, chest pain, severe shortness of breath, or a persistent rapid rhythm with weakness.
• Avoid excessive stimulants or trigger substances when they clearly precipitate episodes.
• Keep a copy or image of an ECG captured during the episode for cardiology review when possible.
• Discuss catheter ablation if episodes are recurrent, prolonged, medication-dependent, or impair quality of life.
• Do not self-administer someone else's beta blocker or calcium-channel blocker for palpitations.

Notes

The 2025 AHA tachyarrhythmia algorithm retains the familiar stable regular-SVT sequence of vagal maneuver followed by adenosine 6 mg and then 12 mg, while emphasizing synchronized cardioversion for instability.

Long-term management is often curative rather than suppressive. Electrophysiologic mapping and catheter ablation can eliminate the reentrant pathway responsible for recurrent AVNRT or AVRT.

References

1. AHA 2025 Adult Tachyarrhythmia With a Pulse Algorithm — Link
2. AHA 2025 Adult Advanced Life Support — Link