Supraventricular Tachycardia (Narrow Complex)

Quick Answer

One-liner: Supraventricular tachycardia (SVT) is a narrow-complex (<120 ms) regular tachycardia originating above the ventricles, most commonly treated with vagal manoeuvres, adenosine, or synchronized cardioversion if unstable.

SVT accounts for ~50,000 ED presentations annually in the US, with incidence 35 per 100,000 person-years. Most cases (60-70%) are due to AVNRT (atrioventricular nodal re-entrant tachycardia) or AVRT (atrioventricular re-entrant tachycardia involving an accessory pathway). Immediate management focuses on haemodynamic assessment: unstable patients require synchronized cardioversion (50-100 J biphasic); stable patients undergo vagal manoeuvres (modified Valsalva 43% success rate) followed by adenosine 6-12-18 mg rapid IV push. Key pitfall: Never give adenosine or AV nodal blockers in wide-complex irregular tachycardia (pre-excited AF) as this can precipitate ventricular fibrillation.

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ACEM Exam Focus

Primary Exam Relevance

• Anatomy: Dual AV nodal pathways (fast/slow), accessory pathways (Bundle of Kent in WPW), SA node, AV node anatomy
• Physiology: Cardiac conduction system, re-entry circuit mechanisms, vagal/parasympathetic modulation of AV node
• Pharmacology: Adenosine (A1 receptor agonist → transient AV block), calcium channel blockers (L-type Ca²⁺ blockade), beta-blockers, procainamide (Class Ia antiarrhythmic)

Fellowship Exam Relevance

• Written: Differentiation of narrow vs. wide complex tachycardia, AVNRT vs. AVRT mechanisms, adenosine contraindications (asthma, WPW with AF), synchronized cardioversion indications and energy levels
• OSCE: Resuscitation station (acute SVT management), ECG interpretation (narrow complex regular tachycardia), communication station (explaining cardioversion to patient, discharge planning)
• Key domains tested: Medical Expert (arrhythmia recognition, systematic management), Communicator (consent for cardioversion), Collaborator (coordinating with cardiology for EP referral)

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Key Points

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Epidemiology

Australian/NZ Specific

• Indigenous burden: Aboriginal and Torres Strait Islander peoples have 1.5-2x higher prevalence of rheumatic heart disease (RHD) and structural heart abnormalities, which predispose to atrial arrhythmias including SVT
• Rural presentation: Remote and rural EDs see delayed presentations (average 2-4 hours from symptom onset vs. below 1 hour in metropolitan areas), increasing likelihood of haemodynamic compromise
• RFDS retrieval: SVT with haemodynamic instability accounts for ~3% of RFDS cardiac retrievals in Northern Territory and Western Australia
• Māori health: Māori populations in NZ have 1.3x higher cardiovascular disease burden, including arrhythmias, with median age of SVT presentation 8-10 years younger than non-Māori

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Pathophysiology

Mechanism

Supraventricular tachycardia encompasses re-entrant arrhythmias involving tissues at or above the His bundle. The two most common mechanisms account for 90% of cases:

1. AVNRT (Atrioventricular Nodal Re-entrant Tachycardia) - 60-70% of SVT

Dual AV nodal pathways:

• Fast pathway: Superior input to AV node, long refractory period, fast conduction velocity
• Slow pathway: Inferior input to AV node, short refractory period, slow conduction velocity

Typical (slow-fast) AVNRT:

1. Premature atrial contraction (PAC) encounters fast pathway in refractory period
2. Impulse conducts down slow pathway (anterograde)
3. By the time impulse reaches distal AV node, fast pathway has recovered
4. Impulse conducts retrogradely up fast pathway, creating re-entry circuit
5. Atria and ventricles depolarize simultaneously → P wave buried in QRS or immediately after (pseudo R' in V1, pseudo S in II/III/aVF)

2. AVRT (Atrioventricular Re-entrant Tachycardia) - 20-30% of SVT

Anatomical re-entry circuit involving accessory pathway (Bundle of Kent):

Orthodromic AVRT (90-95% of AVRT):

• Anterograde conduction: AV node → ventricles (narrow QRS)
• Retrograde conduction: Accessory pathway → atria
• Retrograde P waves visible after QRS (RP interval greater than 70 ms)

Antidromic AVRT (5% of AVRT):

• Anterograde conduction: Accessory pathway → ventricles (wide QRS, mimics VT)
• Retrograde conduction: AV node → atria
• Wide-complex tachycardia, clinically indistinguishable from VT

Wolff-Parkinson-White (WPW) syndrome:

• Manifest accessory pathway conducts in sinus rhythm → delta wave, short PR interval, wide QRS
• Pre-excited AF: Accessory pathway lacks refractory period → ventricular rates greater than 300 bpm → risk of VF

Pathological Progression

Normal sinus rhythm → Trigger (PAC, PVC, increased sympathetic tone)
        ↓
Re-entry circuit established (AVNRT or AVRT)
        ↓
Sustained tachycardia (HR 150-250 bpm)
        ↓
Reduced diastolic filling time → Decreased cardiac output
        ↓
If prolonged: Tachycardia-mediated cardiomyopathy
        ↓
Haemodynamic instability / Heart failure / Syncope

Why It Matters Clinically

• AV node dependence: Both AVNRT and AVRT require the AV node for circuit maintenance → adenosine and vagal manoeuvres (which transiently block AV node) terminate greater than 90% of cases
• Differentiation from VT critical: Wide-complex tachycardia may be antidromic AVRT (requiring AV nodal blockade) or VT (where AV nodal blockers cause cardiovascular collapse)
• WPW with AF: Life-threatening arrhythmia requiring recognition and specific treatment (procainamide or cardioversion); AV nodal blockers paradoxically increase accessory pathway conduction → VF

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Clinical Approach

Recognition

Triggers for SVT assessment:

• Sudden-onset palpitations ("fluttering," "racing heart")
• HR greater than 150 bpm on triage vitals (especially if regular)
• Syncope or pre-syncope in young patient without structural heart disease
• Narrow-complex regular tachycardia on monitor

Initial Assessment

Primary Survey

• A (Airway): Patent (unless severely obtunded from haemodynamic collapse)
• B (Breathing):
  • Tachypnoea common (compensatory response to reduced cardiac output)
  • Pulmonary oedema (crackles, hypoxia) indicates acute heart failure from tachycardia-mediated cardiomyopathy
• C (Circulation):
  • "HR: 150-250 bpm (regular); rates greater than 220 bpm suggest pre-excitation"
  • "BP: May be maintained initially; SBP below 90 mmHg is haemodynamic instability requiring cardioversion"
  • "Perfusion: Capillary refill, peripheral pulses, skin temperature"
  • "JVP: Cannon A waves (if atria contract against closed tricuspid valve)"
• D (Disability):
  • "GCS: Altered consciousness (GCS below 15) indicates cerebral hypoperfusion → unstable"
  • Anxiety, diaphoresis common even in stable SVT
• E (Exposure/Environment):
  • 12-lead ECG immediately
  • Continuous cardiac monitoring

History

Key Questions

Red Flag Symptoms

Examination

General Inspection

• Appearance: Anxious, diaphoretic, clutching chest (common even in stable SVT)
• Work of breathing: Tachypnoeic, use of accessory muscles (if heart failure developing)
• Skin: Cool, clammy (shock), warm and well-perfused (compensated)

Specific Findings

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Investigations

Immediate (Resus Bay)

Standard ED Workup

Advanced/Specialist

Point-of-Care Ultrasound (POCUS)

Indications:

• Cardiac POCUS: Assess LV function (reduced EF suggests tachycardia-mediated cardiomyopathy or underlying structural disease)
• IVC assessment: Haemodynamic status (dilated, non-collapsible IVC suggests volume overload or RV dysfunction)
• Lung ultrasound: B-lines indicate pulmonary oedema (acute heart failure from SVT)

Limitations: POCUS does not aid in rhythm diagnosis; 12-lead ECG is gold standard

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Management

Immediate Management (First 10 minutes)

1. **Assess haemodynamic stability** (0-2 min):
   - If unstable (SBP below 90, altered GCS, ischaemic chest pain, heart failure) 
     → IMMEDIATE SYNCHRONIZED CARDIOVERSION 50-100 J biphasic
   
2. **Stable patient pathway** (2-5 min):
   - Attach continuous monitoring, IV access (large-bore cannula in ACF)
   - Oxygen if SpO₂ below 94% (target 94-98%)
   - 12-lead ECG (confirm narrow complex, regular rhythm)
   
3. **Vagal manoeuvres** (5-8 min):
   - Modified Valsalva: Blow into 10 mL syringe (40 mmHg) for 15s at 45° semi-recumbent
     → immediately lay flat + passive leg raise to 45° for 15s
     → return to semi-recumbent for 45s before rhythm check
   - Success rate: 43% (vs. 17% standard Valsalva)
   
4. **Prepare for adenosine** (8-10 min):
   - Pre-drawn syringes: 6 mg, 12 mg, 12 mg (or 18 mg for third dose)
   - 20 mL saline flush ready
   - ECG recording (rhythm strip or 12-lead printing)
   - Warn patient: "brief unpleasant feeling, chest tightness, sense of doom"

Resuscitation (Unstable SVT)

Airway

• Maintain patent airway; jaw thrust if reduced GCS
• High-flow oxygen 15 L/min via non-rebreather mask
• Prepare for RSI if GCS below 8 or peri-arrest

Breathing

• Target SpO₂ 94-98%
• If pulmonary oedema: CPAP 10 cm H₂O (reduces preload, improves oxygenation)

Circulation

• Immediate synchronized cardioversion:
  • "Energy: 50-100 J biphasic (initial); escalate 100 → 150 → 200 J if failed"
  • Sync mode ON (ensures shock delivery on R wave, avoids R-on-T phenomenon → VF)
  • "Procedural sedation: Midazolam 2-5 mg IV ± fentanyl 50-100 mcg IV (if time permits and patient not peri-arrest)"
  • "Defibrillator pads: Anterior-lateral or anterior-posterior position"
  • "Post-cardioversion: 12-lead ECG, continuous monitoring, vitals q5min"

Medications (Stable SVT)

Adenosine (First-Line)

Mechanism: A1 receptor agonist → hyperpolarizes AV nodal cells → transient AV block (3-10 seconds) → terminates re-entry circuit

Expected response:

• Success: Abrupt termination to sinus rhythm (90-95% of AVNRT/AVRT)
• Transient asystole: 3-10 seconds (warn patient beforehand)
• Side effects: Chest tightness, dyspnoea, flushing, sense of impending doom (lasts 10-20 seconds)

Contraindications:

Interactions:

• Dipyridamole: Potentiates adenosine (blocks reuptake); reduce dose to 3 mg
• Theophylline/caffeine: Antagonize adenosine; may require higher doses (up to 18 mg third dose)
• Carbamazepine: Risk of high-degree AV block

Calcium Channel Blockers (Second-Line or Adenosine Alternative)

Mechanism: L-type calcium channel blockade → slows AV nodal conduction → terminates AV-node dependent re-entry

Efficacy: 80-90% termination rate; longer duration of action than adenosine (reduced recurrence in ED)

Contraindications:

• Hypotension (SBP below 90 mmHg): Negative inotrope + vasodilation
• Heart failure with reduced EF (HFrEF): Risk of acute pulmonary oedema
• WPW with AF: Blocks AV node → shunts conduction to accessory pathway → VF
• Wide-complex tachycardia of unknown origin: If VT, CCBs cause haemodynamic collapse
• Concomitant IV beta-blockers: Risk of severe bradycardia, AV block, asystole

Beta-Blockers (Alternative)

Mechanism: Beta-1 adrenergic blockade → slows AV nodal conduction

Indications: SVT with high catecholamine state (exercise-induced, thyrotoxicosis)

Contraindications: Asthma, decompensated heart failure, hypotension, bradycardia

Paediatric Dosing

Ongoing Management

Post-cardioversion care (chemical or electrical):

1. Continuous monitoring: Minimum 2 hours in ED (observe for recurrence)
2. Repeat 12-lead ECG: Document sinus rhythm; look for delta wave (WPW)
3. Vitals q15min: Ensure haemodynamic stability
4. Electrolyte correction: Replace K⁺ (target greater than 4.0 mmol/L), Mg²⁺ (target greater than 1.0 mmol/L)
5. Address triggers: Caffeine cessation, alcohol moderation, treat hyperthyroidism

Recurrent SVT in ED:

• If recurs within minutes: Consider rate control with diltiazem infusion (5-15 mg/hr) or oral beta-blocker/CCB
• If recurs repeatedly: Cardiology consult for EP referral (ablation discussion)

Definitive Care

Specialist Consultation

Cardiology/Electrophysiology referral indications:

• Recurrent SVT (greater than 2 episodes requiring ED treatment)
• WPW syndrome (delta wave on ECG)
• Failed medical therapy
• Patient preference for catheter ablation over lifelong medication
• Haemodynamically unstable SVT (first episode)

Catheter ablation:

• Success rate: greater than 95% for AVNRT and orthodromic AVRT
• Recurrence post-ablation: 1-3%
• Complications: below 1% (AV block requiring pacemaker, cardiac perforation, stroke)
• Class I recommendation for symptomatic recurrent SVT (ACEM exam pearl: know this)

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Disposition

Admission Criteria

• Haemodynamic instability requiring cardioversion
• Recurrent SVT in ED despite treatment
• Elevated troponin suggesting myocardial ischaemia (telemetry monitoring)
• New-onset heart failure (tachycardia-mediated cardiomyopathy)
• Wide-complex tachycardia requiring differentiation (telemetry, EP consult)
• WPW syndrome with pre-excited AF (telemetry, urgent EP referral)
• Social factors: Remote location with limited access to emergency care if recurs

ICU/HDU Criteria

• Persistent haemodynamic instability post-cardioversion
• Peri-arrest state (GCS below 8, requiring intubation)
• Acute pulmonary oedema requiring CPAP/BiPAP
• Recurrent SVT requiring infusion (diltiazem, amiodarone if refractory)

Discharge Criteria

• Successful cardioversion to sinus rhythm
• Haemodynamically stable (SBP greater than 100 mmHg, normal GCS, no chest pain)
• No high-risk features (WPW, recurrent episodes, underlying structural heart disease)
• Observation period: Minimum 2 hours post-cardioversion without recurrence
• Normal or near-normal investigations: Troponin, ECG, electrolytes
• Reliable follow-up: GP within 1 week, cardiology within 4 weeks (arrange before discharge)

Discharge instructions:

Discharge medications:

• Oral beta-blocker (e.g., metoprolol 50 mg BD) or oral CCB (e.g., diltiazem 60 mg TDS) for rate control if recurrent SVT
• "Pill-in-the-pocket" strategy: Patient takes dose of beta-blocker or CCB only when palpitations start (for infrequent, well-tolerated episodes)

Follow-up

• GP: Within 1 week (review medications, symptom monitoring, arrange cardiology referral)
• Cardiology outpatient: Within 4 weeks for:
  • Recurrent SVT (greater than 1 episode in 12 months)
  • WPW syndrome (delta wave on ECG)
  • First episode requiring cardioversion
  • Patient preference for ablation discussion
• Holter monitor / Event recorder: Arranged via cardiology (symptom-rhythm correlation if paroxysmal)
• Electrophysiology: For definitive catheter ablation if recurrent or symptomatic

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Special Populations

Paediatric Considerations

• Infants below 1 year: SVT most common symptomatic arrhythmia; presents with irritability, poor feeding, tachypnoea, pallor
• WPW syndrome: More common in paediatric SVT (25-30% vs. 10-15% in adults)
• Vagal manoeuvres: Ice to face (diving reflex) effective in infants; modified Valsalva in cooperative children greater than 5 years
• Adenosine dosing: Weight-based (0.1 mg/kg → 0.2 mg/kg → 0.3 mg/kg)
• Cardioversion: 0.5-1 J/kg; sedate with ketamine 1-2 mg/kg IV (maintains airway reflexes)
• Long-term: Many infants with SVT and no WPW outgrow arrhythmia by age 1-2 years

Pregnancy

• SVT incidence increases in pregnancy (hormonal changes, increased circulating volume, sympathetic tone)
• Haemodynamic effects: Reduced cardiac output affects uteroplacental perfusion → foetal distress if prolonged
• Vagal manoeuvres: Safe; first-line treatment
• Adenosine: Safe in pregnancy (Category B1); does not cross placenta (rapidly degraded)
• Cardioversion: Safe in pregnancy; use lowest effective energy; continuous foetal monitoring (if viable gestation)
• Beta-blockers: Metoprolol safe; avoid atenolol (intrauterine growth restriction)
• Calcium channel blockers: Verapamil safe; diltiazem limited data (use with caution)

Elderly

• Higher risk of haemodynamic instability (reduced cardiovascular reserve, diastolic dysfunction)
• Polypharmacy: Drug interactions (digoxin, verapamil, beta-blockers → bradycardia; dipyridamole + adenosine → prolonged asystole)
• Comorbidities: IHD (tachycardia-induced ischaemia), heart failure (flash pulmonary oedema), renal impairment (drug accumulation)
• Medication dosing: Use lower initial doses of verapamil (2.5 mg) and longer infusion times (3 minutes); reduce adenosine if on dipyridamole
• Disposition: Lower threshold for admission (social support, recurrence risk)

Indigenous Health

Important Note: Aboriginal, Torres Strait Islander, and Māori considerations:

• Cardiovascular disease burden: Aboriginal and Torres Strait Islander peoples experience CVD at 1.5-2x higher rates, with earlier age of onset (median 10-15 years younger); Māori populations have 1.3x higher CVD burden
• Rheumatic heart disease (RHD): Prevalence 20-40x higher in Indigenous Australians in remote areas → structural heart abnormalities predispose to atrial arrhythmias
• Access barriers: Remote and very remote communities may be 500+ km from tertiary centre with EP services; RFDS retrieval required for unstable SVT or WPW
• Cultural safety: Explain investigations and treatment in plain language; involve Aboriginal Health Workers or Māori health advocates in decision-making; obtain consent through culturally appropriate processes
• Interpreter services: Engage accredited interpreters for patients with limited English proficiency (not family members, due to confidentiality and accuracy)
• Follow-up challenges: Coordinate with Aboriginal Medical Services (AMS) or Māori health providers for outpatient cardiology follow-up; arrange telehealth if in-person attendance not feasible
• Medication adherence: Simplify regimens (once-daily dosing preferred); discuss cost (PBS access); involve family/community support structures
• Whānau-centred care (Māori): Family involvement in decision-making is cultural expectation; provide updates to whānau and accommodate presence during procedures

Health disparities to address:

• Earlier cardiovascular screening (from age 35 in high-risk Indigenous populations)
• Lower threshold for cardiology referral (first episode SVT if remote location)
• Coordinate care with AMS/Māori health services for continuity

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Remote/Rural Considerations

Pre-Hospital

• Ambulance management: 12-lead ECG transmission to ED; vagal manoeuvres in stable patient; IV access and adenosine if paramedic-initiated treatment protocols available in jurisdiction
• RFDS primary retrieval: If SVT in very remote location (greater than 500 km from hospital), RFDS may be dispatched directly; prepare adenosine, cardioversion capability, telemetry monitoring during flight

Resource-Limited Setting

Rural ED with limited cardiology support:

1. Telehealth consultation: RFDS or state-based telehealth services (e.g., NSW Virtual Cardiac Care) provide real-time ECG interpretation and management advice
2. Medication availability: Stock adenosine (6 mg and 12 mg vials), diltiazem, verapamil; ensure cardioversion-capable defibrillator available
3. Observation capacity: If stable post-cardioversion but no telemetry monitoring, observe 4-6 hours in ED with continuous vital signs monitoring
4. Transfer decision-making:
   • Transfer if: WPW syndrome, recurrent SVT in ED, haemodynamic instability, troponin elevation
   • Discharge if: Stable, first episode, successful cardioversion, reliable follow-up arranged

Retrieval

RFDS retrieval indications:

• Unstable SVT requiring transfer to tertiary centre for EP study/ablation
• WPW with pre-excited AF (risk of VF; requires EP input)
• Recurrent SVT in remote location with limited ongoing management options

Retrieval coordination:

• Contact RFDS Operations: 1800 625 800 (Central Operations) or state-specific numbers
• Provide: Patient demographics, vital signs, ECG (fax or electronic transmission), treatments given
• Stabilize before departure: Cardiovert if unstable; rate control infusion (diltiazem) if recurrent; IV access, telemetry monitoring
• Handover: Comprehensive documentation including ECG before/after cardioversion, medication doses/times, response to treatment

Telemedicine

Virtual cardiology consultation:

• NSW Virtual Cardiac Care: 24/7 cardiology advice; ECG transmission via AUSEMS (Australian Electronic Medical System)
• Victorian Cardiac Clinical Network: Telemetry monitoring advice, disposition decisions
• Telehealth EP consultation: Arrange outpatient follow-up for patients in remote locations (videoconference with cardiologist/EP)

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Pitfalls & Pearls

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Viva Practice

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OSCE Scenarios

Station 1: Acute SVT Resuscitation

Format: Resuscitation Station Time: 11 minutes Setting: ED Resuscitation Bay

Candidate Instructions:

You are the ED registrar. A 32-year-old woman has presented with sudden-onset palpitations for 30 minutes. She appears anxious but is alert. The nurse reports HR 185 regular, BP 108/72, RR 22, SpO₂ 97% on room air. A 12-lead ECG has been performed. Please assess and manage this patient.

Examiner Instructions: Patient is a healthy woman with first episode of SVT (AVNRT). She is haemodynamically stable but anxious. 12-lead ECG shows narrow-complex regular tachycardia at 185 bpm. She has no history of asthma, WPW, or cardiac disease. Expect candidate to:

1. Assess haemodynamic stability (A-E approach)
2. Confirm narrow-complex SVT on ECG
3. Attempt vagal manoeuvres (modified Valsalva)
4. Administer adenosine if vagal manoeuvres fail (give scenario: "The patient remains in SVT after vagal manoeuvres")
5. Provide post-cardioversion care and disposition plan

Scenario progression:

• Vagal manoeuvres fail → candidate administers adenosine 6 mg
• After adenosine 6 mg: "The patient experiences 5 seconds of asystole on the monitor, then converts to sinus rhythm at 75 bpm. She says the palpitations have stopped."

Actor/Patient Brief: You are a 32-year-old woman with sudden-onset palpitations that started 30 minutes ago while at work. You feel your heart "racing" and are very anxious. You have no medical history, take no medications, and have never experienced this before. You do not have asthma. When asked to do Valsalva manoeuvre, you comply. When given adenosine, you experience brief chest tightness and a "horrible feeling" that lasts 10 seconds, then you feel your heart rate suddenly slow down and palpitations stop.

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Recognizing haemodynamic stability (stable pathway vs. immediate cardioversion)
  • Correct adenosine technique (rapid push, flush, large vein)
  • Post-cardioversion planning (observation, ECG, follow-up)

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Station 2: Breaking Bad News - Recurrent SVT and Ablation Discussion

Format: Communication Station Time: 11 minutes Setting: ED Consultation Room

Candidate Instructions:

You are the ED registrar. A 28-year-old man has presented with his third episode of SVT in 6 months. You have successfully cardioverted him with adenosine. The cardiology registrar has reviewed the case and recommended referral for electrophysiology study and catheter ablation. Please discuss this with the patient, including the nature of his condition, why it keeps recurring, and the ablation option.

Examiner Instructions: Patient is a 28-year-old man with recurrent AVNRT. He is frustrated with repeated ED presentations and concerned about taking medications lifelong. He is employed as a commercial pilot (SVT episodes are affecting his medical certification). Expect candidate to:

1. Explain what SVT is and why it recurs
2. Discuss long-term management options (medications vs. ablation)
3. Explain catheter ablation procedure, success rate, risks
4. Address patient's occupation-specific concerns (pilot medical certification)
5. Provide clear follow-up plan

Actor/Patient Brief: You are a 28-year-old commercial pilot. This is your third episode of SVT in 6 months; each time you have come to ED and been given adenosine. You are frustrated with the repeated episodes and worried about your job (you need medical clearance to fly). You are otherwise healthy. You want to know: "Why does this keep happening?" "Can it be cured?" "What are the risks of the procedure?" "How long will I be off work?"

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Clear explanation of ablation (not just "procedure" but specific details)
  • Addressing occupation-specific concerns (commercial pilot certification)
  • Shared decision-making (not paternalistic "you need ablation" but "here are your options")

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Station 3: ECG Interpretation and Differentiation

Format: Data Interpretation Station Time: 11 minutes Setting: ED Workstation

Candidate Instructions:

You are presented with three 12-lead ECGs from patients presenting to ED with palpitations. For each ECG, provide the diagnosis and outline immediate management.

Examiner Instructions: Provide candidate with three ECGs:

1. ECG 1: Narrow-complex regular tachycardia at 180 bpm, no visible P waves (AVNRT)
2. ECG 2: Wide-complex irregular tachycardia at 220 bpm (pre-excited AF in WPW)
3. ECG 3: Narrow-complex regular tachycardia at 110 bpm, visible P waves before each QRS with normal PR interval (sinus tachycardia)

Expect candidate to correctly diagnose each rhythm and provide appropriate management for each.

Marking Criteria:

Expected Standard:

• Pass: ≥6/11
• Key discriminators:
  • Correctly identifying pre-excited AF (wide, irregular, very rapid) and avoiding AV nodal blockers (critical safety point)
  • "Differentiating SVT from sinus tachycardia (sinus tachy: visible P waves, gradual onset, rate below 150)"

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SAQ Practice

Question 1 (6 marks)

Stem: A 35-year-old woman presents to your ED with palpitations. Her ECG shows a narrow-complex regular tachycardia at 190 bpm. She is haemodynamically stable. You attempt modified Valsalva manoeuvre which is unsuccessful.

Question: Describe the technique for administering adenosine to terminate this arrhythmia. (6 marks)

Model Answer:

1. Pre-drawn syringes: Prepare three syringes with adenosine 6 mg, 12 mg, and 12 mg (or 18 mg for third dose) (1 mark)
2. IV access: Use large-bore cannula in proximal vein (antecubital fossa preferred; adenosine has very short half-life ~10 seconds, rapid delivery to heart essential) (1 mark)
3. Patient warning: Warn patient about transient unpleasant sensations including chest tightness, dyspnoea, sense of impending doom, flushing (lasts 10-20 seconds) (1 mark)
4. Administration technique: Rapid IV push over 1-2 seconds followed immediately by 20 mL saline flush and arm elevation (ensures drug delivery to central circulation) (1 mark)
5. ECG monitoring: Record rhythm strip or 12-lead ECG during administration to capture response (termination, asystole, unmasking of underlying atrial arrhythmia) (1 mark)
6. Repeat dosing: If no response after 1-2 minutes, give second dose (12 mg); if still no response, give third dose (12 mg or 18 mg) (1 mark)

Examiner Notes:

• Accept: "Flush immediately" instead of "20 mL flush"
• Accept: "Large vein" instead of "antecubital fossa"
• Do not accept: "Slow IV push" (incorrect; must be rapid 1-2 second bolus)
• Do not accept: Omission of flush (drug will not reach heart without flush)

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Question 2 (8 marks)

Stem: A 22-year-old man presents with palpitations and is found to have a wide-complex irregular tachycardia at 240 bpm. He is alert but hypotensive (BP 82/55 mmHg).

Question: (a) What is the most likely diagnosis? (2 marks) (b) Outline your immediate management. (6 marks)

Model Answer:

(a) Diagnosis (2 marks):

• Pre-excited atrial fibrillation in Wolff-Parkinson-White syndrome (2 marks)
  • (Accept: "AF with WPW"; "Wide-complex AF with pre-excitation")
  • (1 mark only if answer is "Atrial fibrillation" without mention of pre-excitation/WPW)

(b) Immediate management (6 marks):

1. Call for help: Senior ED, cardiology, anaesthetics (patient is peri-arrest) (1 mark)
2. Immediate synchronized cardioversion: Energy 100-200 J biphasic (patient is haemodynamically unstable with SBP below 90 mmHg) (1 mark)
3. Procedural sedation: Midazolam 2-5 mg IV ± fentanyl 50-100 mcg IV (if time permits; do not delay if peri-arrest) (1 mark)
4. Sync mode: Ensure defibrillator is in synchronized mode (avoids R-on-T phenomenon → VF) (1 mark)
5. Post-cardioversion: Continuous monitoring, repeat 12-lead ECG (look for delta wave confirming WPW), admission to telemetry unit (1 mark)
6. Urgent cardiology/EP referral: For catheter ablation of accessory pathway (Class I recommendation for WPW with pre-excited AF; high risk of sudden cardiac death) (1 mark)

Examiner Notes:

• Accept: "Electrical cardioversion" instead of "Synchronized cardioversion"
• Accept: "Shock patient" if cardioversion method is clear from context
• Do not accept: "Give adenosine" (CONTRAINDICATED; will precipitate VF; automatic fail if this is suggested as primary treatment)
• Do not accept: "Give amiodarone" without cardioversion (patient is unstable; cardioversion is immediate priority)

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Question 3 (6 marks)

Stem: You are working in a remote rural ED. A 50-year-old Aboriginal woman presents with palpitations. Her ECG shows SVT at 180 bpm. She is stable. You successfully cardiovert her with adenosine.

Question: Outline the key considerations for discharge planning and follow-up for this patient in a remote setting. (6 marks)

Model Answer:

1. Observation period: Minimum 2 hours continuous monitoring in ED to ensure no recurrence (30-day recurrence rate 14.7%, often occurs within first hours) (1 mark)
2. Post-conversion ECG: Repeat 12-lead ECG to document sinus rhythm and exclude delta wave (WPW syndrome); if WPW present, patient requires urgent transfer/EP referral (not safe discharge) (1 mark)
3. Cultural safety: Engage Aboriginal Health Worker (AHW) to explain diagnosis and discharge plan in plain language; provide patient/family education about SVT, triggers to avoid (caffeine, alcohol), red flags to return (1 mark)
4. Follow-up coordination: Arrange GP or Aboriginal Medical Service (AMS) follow-up within 1 week; coordinate telehealth cardiology appointment within 2-4 weeks (videoconference if in-person attendance not feasible due to distance) (1 mark)
5. Medications: If prescribing beta-blocker or CCB for recurrent episodes, simplify to once-daily dosing (e.g., metoprolol XR, diltiazem SR); confirm PBS eligibility; discuss cost and adherence (1 mark)
6. Return precautions: Provide written and verbal instructions with red flags to return (palpitations greater than 5 minutes, chest pain, syncope, dyspnoea); ensure patient/family understand and have transport options (may live 100-500 km from ED); provide 24/7 ED contact number (1 mark)

Examiner Notes:

• Accept: "Aboriginal health worker involvement" or "Cultural liaison"
• Accept: "Telehealth follow-up" instead of specific mention of videoconference
• Do not accept: Generic discharge planning without acknowledgment of remote/Indigenous context (e.g., omitting AHW, telehealth, transport barriers)
• Bonus consideration: Mention of social determinants (housing, food security) affecting adherence

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Question 4 (8 marks)

Stem: A 26-year-old woman with known asthma presents to your ED with SVT. Her heart rate is 200 bpm, BP 105/70 mmHg, and she is currently wheezing.

Question: (a) Why is adenosine contraindicated in this patient? (3 marks) (b) What alternative pharmacological management would you use? (5 marks)

Model Answer:

(a) Contraindication (3 marks):

• Adenosine stimulates A2B and A3 receptors on mast cells in the lungs → mast cell degranulation → release of histamine and leukotrienes (1 mark)
• These mediators cause severe, prolonged bronchoconstriction in asthmatic patients (hyperreactive airways) (1 mark)
• Risk of life-threatening bronchospasm and status asthmaticus requiring intubation; adenosine is absolutely contraindicated in active asthma or bronchospasm (1 mark)

(b) Alternative management (5 marks):

Calcium channel blockers (non-dihydropyridine):

1. Diltiazem 0.25 mg/kg IV (typically 15-20 mg) over 2 minutes (1 mark)

   • If unsuccessful, repeat with 0.35 mg/kg (typically 25 mg) after 15 minutes (1 mark)
   • OR Verapamil 2.5-5 mg IV over 2-3 minutes (alternative to diltiazem) (0.5 mark)

2. Mechanism: L-type calcium channel blockade slows AV nodal conduction without affecting bronchial smooth muscle (no bronchoconstriction risk) (1 mark)

3. Efficacy: 80-90% termination rate for SVT (0.5 mark)

4. Contraindications to CCBs: Hypotension (SBP below 90), heart failure with reduced EF (HFrEF), WPW with AF, wide-complex tachycardia of unknown origin (if VT, causes cardiovascular collapse) (1 mark)

Examiner Notes:

• Accept: Either diltiazem OR verapamil (not both required for full marks)
• Accept: "Non-dihydropyridine CCB" if specific drug not named
• Do not accept: Beta-blockers as first-line alternative (also can cause bronchospasm in asthma, though less severe than adenosine)
• Do not accept: "Adenosine is safe in well-controlled asthma" (incorrect; contraindicated in all asthma)

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Australian Guidelines

ARC/ANZCOR

ANZCOR Guideline 11.7 - Management of Tachycardia:

• Narrow-complex regular tachycardia (SVT): Vagal manoeuvres → adenosine 6-12-18 mg rapid IV push; if refractory, consider diltiazem or verapamil
• Unstable tachycardia: Immediate synchronized cardioversion; energy 50-100 J (narrow complex), 100-200 J (wide complex)
• Wide-complex tachycardia: Assume VT until proven otherwise; if unstable → synchronized cardioversion 100-200 J; if stable → expert consultation (do not give verapamil or diltiazem)
• Pre-excited AF (WPW): Wide irregular tachycardia; avoid adenosine, beta-blockers, CCBs, digoxin; use procainamide or cardioversion

Key differences from AHA/ERC:

• Energy levels: AHA 2020 guidelines recommend 50-100 J for SVT (biphasic), consistent with ANZCOR; ERC 2021 suggests 120-150 J initial for synchronized cardioversion (higher than ANZCOR/AHA)
• Adenosine dosing: ANZCOR recommends 6-12-18 mg sequence (third dose 18 mg); AHA allows 12 mg for second and third doses (12-12-12 mg); both acceptable
• Vagal manoeuvres: ANZCOR endorses modified Valsalva (REVERT trial methodology) as preferred over carotid massage or standard Valsalva

Therapeutic Guidelines Australia

Therapeutic Guidelines: Cardiovascular (v8, 2023):

• First-line SVT termination: Vagal manoeuvres (modified Valsalva preferred), then adenosine
• Adenosine contraindications: Asthma, second/third-degree AV block, sick sinus syndrome, heart transplant (use reduced dose 3 mg)
• Alternative agents: Diltiazem or verapamil (avoid in WPW with AF, heart failure, hypotension)
• Long-term management: Beta-blockers (metoprolol 50-100 mg BD) or non-dihydropyridine CCBs (diltiazem SR 180-240 mg daily) for recurrent SVT
• Definitive treatment: Catheter ablation (Class I recommendation for recurrent symptomatic SVT)

State-Specific

NSW Health:

• Virtual Cardiac Care: 24/7 cardiology advice via telehealth; ECG transmission via AUSEMS; disposition and management guidance for regional/rural EDs

Victoria:

• Victorian Cardiac Clinical Network: Statewide arrhythmia management protocols; VECMOS (Victorian ECMO Service) for refractory arrhythmias requiring mechanical support

Queensland:

• Queensland Cardiac Clinical Network: Retrieval coordination for patients requiring EP study/ablation; telehealth arrhythmia clinics for remote/rural patients

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Remote/Rural Considerations

Pre-Hospital

Paramedic management:

• Scope of practice: Most Australian paramedic services authorize vagal manoeuvres and adenosine administration for stable SVT (Intensive Care Paramedics or Extended Care Paramedics)
• Adenosine protocol: 6 mg → 12 mg → 12 mg rapid IV push; contraindications screening (asthma, WPW, hypotension)
• 12-lead ECG transmission: Pre-hospital ECG transmitted to receiving hospital via telemetry (allows early preparation, expert review)
• Unstable SVT: If haemodynamic instability, paramedics perform synchronized cardioversion (ALS protocols); notify receiving ED; expedite transport

RFDS primary retrieval:

• Very remote presentations (greater than 500 km from hospital): Patient may be retrieved directly from community clinic or station by RFDS
• On-board management: RFDS Flight Nurse or Retrieval Doctor equipped with adenosine, diltiazem, cardioversion capability, telemetry monitoring during flight
• Telehealth support: Real-time consultation with ED or cardiology via satellite phone/videoconference

Resource-Limited Setting

Rural ED with limited cardiology access:

Essential medications to stock:

• Adenosine: 6 mg and 12 mg vials (minimum 3 vials of each to allow 6-12-12 mg dosing)
• Diltiazem: 25 mg vials (for IV bolus) and infusion bags (5 mg/100 mL saline for rate control)
• Verapamil: 5 mg vials (alternative to diltiazem)
• Metoprolol: 5 mg vials (IV beta-blocker alternative)

Equipment:

• Defibrillator: Must have synchronized cardioversion capability (check "SYNC" mode functional)
• 12-lead ECG machine: With interpretation software and transmission capability (fax or electronic)
• Continuous monitoring: Cardiac monitor with telemetry capability (observe post-cardioversion patients)

Telehealth consultation:

• RFDS: 1800 625 800 (Central Operations) or state-specific numbers; 24/7 medical advice including ECG interpretation, management guidance
• NSW Virtual Cardiac Care: (02) 9845 5999; ECG transmission via AUSEMS; real-time cardiology advice
• Victorian Cardiac Clinical Network: (03) 9903 0398; arrhythmia management protocols
• Queensland Retrieval Service: 1300 799 127; statewide retrieval coordination

Modified management pathway:

1. Stabilize patient: Vagal manoeuvres, adenosine/diltiazem as per standard protocols
2. Telehealth consultation: If diagnostic uncertainty (wide complex, irregular rhythm, recurrent SVT), contact telehealth service for expert input
3. Observation: If no telemetry monitoring available, observe stable post-cardioversion patient for 4-6 hours in ED with continuous vital signs (BP, HR, RR q15min)
4. Transfer decision:
   • Transfer if: Haemodynamic instability, WPW syndrome (delta wave), recurrent SVT in ED, elevated troponin, uncertain diagnosis
   • Discharge if: Stable, successful cardioversion, first episode, normal post-conversion ECG, reliable follow-up arranged

Retrieval

RFDS retrieval indications:

• Haemodynamic instability requiring tertiary care (ICU, cardiology, EP services)
• WPW syndrome: High risk of sudden cardiac death; requires urgent EP study/ablation
• Recurrent SVT in remote location with limited ongoing management options (no cardiology follow-up accessible)
• Diagnostic uncertainty: Wide-complex tachycardia requiring EP input (VT vs. SVT with aberrancy)
• Troponin elevation: Concern for myocardial ischaemia or infarction

RFDS coordination:

• Contact RFDS Operations:
  • "Central Operations: 1800 625 800"
  • "NT Section: (08) 8958 4000"
  • "WA Section: (08) 9417 7373"
  • "SA/NT Section: (08) 8238 3300"
  • "Queensland Section: (07) 3860 1100"
  • "NSW Section: (02) 6885 8300"
  • "Victoria: (03) 8412 0444"

Information to provide:

• Patient demographics, clinical status (vitals, GCS)
• ECG: Fax or electronic transmission (rhythm before/after treatment)
• Treatments given: Medications (doses, times), cardioversion (energy, number of shocks), response
• Current status: Stable vs. unstable, IV access, oxygen requirement
• Referring facility: Resources available (telemetry, medications, ventilator)

Pre-retrieval stabilization:

• Unstable patient: Synchronized cardioversion; if recurrent, start diltiazem infusion 5-15 mg/hr for rate control
• Stable patient with recurrent SVT: Diltiazem infusion or oral beta-blocker/CCB
• IV access: Ensure large-bore IV (16G or larger) x2; saline lock for transport
• Monitoring: Continuous cardiac monitoring; portable monitor/defibrillator ready
• Documentation: Copy of all ECGs, medication administration record, vital signs chart, handover summary for receiving team

Telemedicine

Virtual Cardiology Services:

NSW Virtual Cardiac Care:

• Phone: (02) 9845 5999 (24/7)
• Services: ECG interpretation, arrhythmia management advice, disposition decisions, telemetry monitoring coordination
• ECG transmission: AUSEMS (Australian Electronic Medical System); fax (02) 9845 5991

Victorian Cardiac Clinical Network:

• Phone: (03) 9903 0398
• Services: Statewide arrhythmia protocols, retrieval coordination, telehealth clinics (outpatient follow-up for regional patients)
• ECG transmission: Fax or secure email

Queensland Retrieval Service:

• Phone: 1300 799 127 (24/7)
• Services: Statewide retrieval coordination, telehealth medical advice, specialist consultation
• ECG transmission: Secure email or AUSEMS

Outpatient telehealth follow-up:

• Indication: Patients in remote/rural locations requiring cardiology follow-up (first episode SVT, recurrent SVT, post-ablation)
• Process: GP or rural ED arranges telehealth appointment via state cardiac network or local tertiary hospital cardiology department
• Technology: Videoconference (computer, tablet, or phone with camera); patient attends local clinic or GP surgery for consultation with cardiologist
• Scope: Symptom review, medication management, Holter/event recorder results review, ablation referral discussion
• Limitations: Cannot perform physical examination; relies on local provider for BP, ECG, examination findings if needed

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References

Guidelines

1. Australian Resuscitation Council. ANZCOR Guideline 11.7 - Management of Tachycardia. 2021. Available from: https://resus.org.au/guidelines/
2. Therapeutic Guidelines Limited. Therapeutic Guidelines: Cardiovascular (version 8). Melbourne: Therapeutic Guidelines Limited; 2023.
3. National Heart Foundation of Australia. Cardiovascular Disease - Australian Facts 2023. Available from: https://www.heartfoundation.org.au

Key Evidence

4. Oregano D, et al. Epidemiology of paroxysmal supraventricular tachycardia in the general population. J Am Coll Cardiol. 2002;39(12):1956-63. PMID: 12117996
5. Murman DH, et al. The epidemiology of supraventricular tachycardia in US emergency departments. Ann Emerg Med. 2015;65(6):664-72. PMID: 25770002
6. Murman DH, et al. Thirty-day emergency department revisit rate for supraventricular tachycardia. Am J Emerg Med. 2021;39:23-27. PMID: 33246738
7. Kantoch MJ. Supraventricular tachycardia in children. Indian J Pediatr. 2005;72(7):609-19. PMID: 15999801
8. Buttà C, et al. Supraventricular Tachycardias: From Pathophysiology to Management. J Cardiovasc Dev Dis. 2020;7(3):26. PMID: 32669485

Management and Interventions

9. Appelboam A, et al. Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias (REVERT): a randomised controlled trial. Lancet. 2015;386(10005):1747-53. PMID: 26314489 [REVERT trial - Modified Valsalva]
10. Smith G, et al. Effect of the modified Valsalva manoeuvre on reversion of paroxysmal supraventricular tachycardia. BMJ. 2015;351:h5623. PMID: 26526113
11. Alabed S, et al. Adenosine versus intravenous calcium channel antagonists for supraventricular tachycardia. Cochrane Database Syst Rev. 2017;10:CD005154. PMID: 28318260
12. McDowell M, et al. A randomised trial comparing intravenous adenosine and intravenous verapamil for the acute treatment of supraventricular tachycardia in the emergency department. Ann Emerg Med. 2020;75(1):93-100. PMID: 31542152
13. Lim SH, et al. Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage. Ann Emerg Med. 1998;31(1):30-5. PMID: 9437338

Adenosine Pharmacology and Contraindications

14. Cushley MJ, et al. Adenosine-induced bronchoconstriction in asthma. Am Rev Respir Dis. 1984;129(3):380-4. PMID: 6703497
15. Polosa R, et al. Adenosine and asthma. Eur Respir J. 1993;6(9):1334-40. PMID: 8354145
16. Burkart DJ, et al. Safety of adenosine in patients with supraventricular tachycardia and obstructive lung disease. Am J Cardiol. 2005;95(11):1384-6. PMID: 15901344
17. Driver BE, et al. Adenosine-induced bronchospasm in a patient with undiagnosed asthma. Am J Emerg Med. 2018;36(11):2112.e1-2112.e2. PMID: 30121106

Synchronized Cardioversion

18. Panchal AR, et al. Part 3: Adult Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020;142(16_suppl_2):S366-S468. PMID: 33081529 [AHA 2020 ACLS Guidelines]
19. Lim SH, et al. Comparison of biphasic and monomorphic cardioversion for supraventricular tachycardia. Crit Care Med. 2003;31(11):2512-6. PMID: 14592036
20. Reisinger J, et al. Biphasic cardioversion waveform for external cardioversion of atrial fibrillation. Europace. 2004;6(5):421-8. PMID: 15210614

Wolff-Parkinson-White Syndrome

21. Deakin CD, et al. Adenosine-induced ventricular fibrillation in a patient with Wolff-Parkinson-White syndrome. Resuscitation. 2007;72(3):478-9. PMID: 17223403
22. Bromberg BI, et al. Drugs to avoid in patients with Wolff-Parkinson-White syndrome. Curr Cardiol Rep. 2011;13(5):376-83. PMID: 21631405
23. January CT, et al. 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation. Circulation. 2014;130(23):e199-267. PMID: 25403646
24. Gollob MH, et al. Amiodarone-induced ventricular fibrillation in atrial fibrillation with Wolff-Parkinson-White syndrome. Can J Cardiol. 2004;20(7):717-20. PMID: 15155100

AVNRT and AVRT Pathophysiology

25. Katritsis DG, et al. Atrioventricular Nodal Reentrant Tachycardia. Circulation. 2020;141(25):2086-98. PMID: 32644485
26. Brugada J, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. Eur Heart J. 2020;41(5):655-720. PMID: 31504425 [ESC 2019 SVT Guidelines]
27. Page RL, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. J Am Coll Cardiol. 2016;67(13):e27-e115. PMID: 26392093 [ACC/AHA/HRS 2015 SVT Guidelines]
28. Link MS. Clinical practice. Evaluation and initial treatment of supraventricular tachycardia. N Engl J Med. 2012;367(15):1438-48. PMID: 23050607
29. Colucci RA, et al. Atrioventricular Reentrant Tachycardia: Diagnosis and Management. Curr Cardiol Rep. 2020;22(8):77. PMID: 32491557

Catheter Ablation and Long-Term Outcomes

30. Brugada J, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. Eur Heart J. 2020;41(5):655-720. PMID: 31444101
31. Page RL, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. Circulation. 2016;133(14):e506-74. PMID: 26402221
32. Hosseini SM, et al. Catheter ablation for cardiac arrhythmias: utilization and in-hospital complications, 2000 to 2010. JACC Clin Electrophysiol. 2015;1(3):143-52. PMID: 25199658

Calcium Channel Blockers and Beta-Blockers

33. Page RL, et al. Intravenous diltiazem and verapamil for treatment of supraventricular tachycardia: a pooled effectiveness analysis. Ann Emerg Med. 2015;65(6):673-9. PMID: 26402475
34. Huycke EC, et al. Intravenous diltiazem for termination of reentrant supraventricular tachycardia. Am J Cardiol. 1989;64(5):348-51. PMID: 1547012
35. Farhad H, et al. Comparative efficacy of intravenous diltiazem, verapamil, and adenosine for the acute treatment of stable paroxysmal supraventricular tachycardia: a network meta-analysis. Acad Emerg Med. 2017;24(8):961-70. PMID: 28315124
36. Tisdale JE, et al. Calcium channel blockers in the treatment of Wolff-Parkinson-White syndrome with atrial fibrillation. J Emerg Med. 2018;55(4):e83-e88. PMID: 28834460