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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- SVT = regular, narrow-complex tachycardia (HR typically 150-250 bpm). Most common types: AVNRT (~60%), AVRT (~30%), atrial tachycardia (~10%)
- Acute termination: vagal maneuvers (modified Valsalva, carotid sinus massage) first, then IV adenosine 6 mg rapid push (if no effect: 12 mg, repeat 12 mg)
- Adenosine causes brief AV block, terminates re-entrant circuits. Give via large bore IV, followed by rapid saline flush. Warn patient of transient chest tightness/flushing
- If hemodynamically unstable: synchronized cardioversion
- Long-term: catheter ablation is curative (>95% success for AVNRT/AVRT) and is first-line for recurrent SVT
Overview
Supraventricular tachycardia (SVT) is a group of arrhythmias originating at or above the AV junction, producing a regular narrow-complex tachycardia (QRS <120 ms unless aberrant conduction or pre-existing BBB). The two most common mechanisms are AVNRT (AV nodal reentrant tachycardia — dual AV nodal pathways) and AVRT (AV reentrant tachycardia — accessory pathway, as in WPW syndrome). Atrial flutter and AF are technically supraventricular but are managed differently and classified separately. SVT is common, usually benign, and highly curable with catheter ablation.
Epidemiology
Incidence ~35 per 100,000 person-years. AVNRT is more common in women (2:1). AVRT/WPW is more common in men. SVT can occur at any age but typically presents in young adults (20s-30s). WPW pattern on ECG (delta wave + short PR + wide QRS in sinus rhythm) is present in ~0.1-0.3% of the general population, but most never develop arrhythmias.
Clinical Features
Symptoms
Sudden-onset palpitations ("fluttering" or "racing heart") with abrupt offset
Lightheadedness, presyncope, or rarely syncope
Chest tightness or mild dyspnea during episode
Polyuria after episode (ANP release from atrial stretch)
Neck pounding ("frog sign" — cannon A waves from simultaneous atrial and ventricular contraction in AVNRT)
Signs
Regular tachycardia, typically 150-250 bpm
Cannon A waves in JVP (AVNRT — atria contract against closed AV valves)
Hypotension if prolonged or very fast (hemodynamic compromise)
Between episodes: examination is typically normal. In WPW: no physical findings, diagnosis is on ECG
Investigations
First-line
12-lead ECG during tachycardiaRegular narrow QRS tachycardia. No visible P waves or retrograde P waves buried in QRS (AVNRT — pseudo-R' in V1, pseudo-S in inferior leads). Short RP tachycardia with retrograde P waves (AVRT). Long RP tachycardia (atrial tachycardia, atypical AVNRT). Give adenosine diagnostically if rhythm unclear — it terminates AVNRT/AVRT or reveals atrial flutter/tachycardia by unmasking atrial activity
ECG in sinus rhythmLook for WPW pattern: short PR interval (<120 ms) + delta wave (slurred QRS upstroke) + wide QRS. This indicates an accessory pathway capable of antegrade conduction
Second-line
Ambulatory ECG monitoringHolter or event monitor if paroxysmal symptoms not captured on 12-lead
EchocardiogramAssess structural heart disease — usually normal in SVT. Consider if HF symptoms (tachycardia-mediated cardiomyopathy from incessant SVT)
Specialist
Electrophysiology study (EPS)Definitive diagnosis and cure: maps the circuit/pathway, followed by catheter ablation in the same session. Indicated for recurrent SVT or WPW with high-risk features
Management
2015 ACC/AHA/HRS SVT Guideline1
Acute termination
- If hemodynamically UNSTABLE (hypotension, AMS, severe chest pain): synchronized cardioversion
- If STABLE: vagal maneuvers first — modified Valsalva (strain in semi-recumbent then supine with passive leg raise for 15 sec — REVERT trial: 43% conversion rate), carotid sinus massage (CONTRAINDICATED if carotid bruit), ice water to face (diving reflex, especially in children)
- If vagal maneuvers fail: IV adenosine 6 mg rapid push into large proximal IV followed by 20 mL saline flush. If no effect after 1-2 min: 12 mg, can repeat 12 mg once
- Adenosine warnings: contraindicated in severe asthma/COPD (bronchospasm) and in irregular wide-complex tachycardia (may be AF + WPW — adenosine can cause VF). Use reduced dose if on dipyridamole or carbamazepine; use higher dose if on caffeine/theophylline
- If adenosine fails: IV verapamil or diltiazem (avoid if HF or WPW), or IV beta-blocker
2
WPW-specific considerations
- WPW + orthodromic AVRT (narrow complex, regular): adenosine is safe — treat like standard SVT
- WPW + antidromic AVRT (wide complex, regular): procainamide or cardioversion
- WPW + AF (irregular, wide complex): procainamide or cardioversion. NEVER give AV-nodal blockers (adenosine, BB, CCB, digoxin) — can cause VF
3
Long-term management
- Catheter ablation: first-line for recurrent SVT — curative in >95% for AVNRT and AVRT. Low complication rate
- Ablation strongly recommended for WPW with high-risk features (short refractory period, symptomatic arrhythmias, high-risk occupation)
- If ablation declined or unavailable: oral beta-blocker or CCB (verapamil/diltiazem) for rate control/prevention
- Pill-in-the-pocket: single-dose oral diltiazem + propranolol or flecainide for infrequent episodes (must trial in monitored setting first)
Complications
- Hemodynamic compromise: Hypotension, syncope — especially with very rapid rates or pre-existing heart disease
- Tachycardia-mediated cardiomyopathy: If SVT is incessant/frequent — reversible with rate/rhythm control
- SCD in WPW: Rare (~0.1-0.6%/year) but risk if accessory pathway has short refractory period and AF conducts rapidly to ventricle causing VF
USMLE Step 2 CK Exam Tips
- 1Regular narrow-complex tachycardia at 150 bpm: consider atrial flutter with 2:1 block (look for sawtooth waves). SVT is usually 160-250 bpm
- 2Adenosine: 6 mg rapid IV push with 20 mL saline flush. Terminates AVNRT/AVRT. If it only transiently slows the rate (reveals underlying rhythm) then returns = atrial flutter or atrial tachycardia
- 3Adenosine is CONTRAINDICATED in irregular wide-complex tachycardia (could be AF + WPW) and in severe asthma
- 4WPW on baseline ECG: short PR + delta wave + wide QRS in sinus rhythm. If they develop AF = irregular wide complex = procainamide or cardioversion, NEVER AV-nodal blockers
- 5Post-episode polyuria (ANP release) is a classic Step 2 CK factoid for SVT
- 6Catheter ablation is curative >95% and is first-line for recurrent SVT — always offer it
- 7Cannon A waves in the neck during SVT = AVNRT (atria contracting against closed TV/MV)
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