Supraventricular Tachycardia

Last modified: 23 June 2022, 7:11:46 AM AEST

Gems / Priorities1 / 15

Definition / diagnostic criteria2 / 15

refers to any tachydysrhythmia arising from above the level of the Bundle of His
narrow complex tachycardia
often 140-250 BPM

Classification3 / 15

Epidemiology4 / 15

1: AVNRT = atrioventricular nodal re-entrant tachycardia = most common5 / 15

re-entry circuit INSIDE the AV node
- FUNCTIONAL circuit (no discernible anatomical change)
also called "dual AV nodal physiology"
THIS is the condition often used synonymously used for "SVT" ***
5% population
commonest cause of palpitations in patients with structurally normal hearts
regular NARROW complex tachycardia

2: AVRT = atrioventricular re-entrant tachycardia6 / 15

re-entry circuit OUTSIDE the AV node
- ANATOMICAL re-entry circuit
- ie. there is accessory pathway / bypass tract
WPW = Wolf-Parkinson White syndrome
- congenital accessory pathway
- commonest cause of accessory pathway?
Other pre-excitation / AP
- Lown-Ganong-Levine (LGL) Syndrome
- Mahim-Type Pre-excitation
Direction
- Drome = "course" = Greek dromos
- Ortho = straight
- Anti = opposite
- 2a: AVRT with orthodromic reciprocating tachycardia = ORT
  - commonest = WPW = 95% of AVRT
  - ORT = orthodromic reciprocating tachycardia
    - anterograde conduction down normal / nodal (fast) pathway
    - retrograde conduction along accessory pathway
    - regular, narrow complex tachycardia
    - delta wave disappears
    - normal ECG = pre-excitation + delta wave
- 2b: AVRT with antidromic conduction = ART
  - uncommon = 5% of AVRT
  - ART = antidromic reciprocating tachycardia
    - anterograde via accessory pathway
    - retrograde conduction via AVN
    - regular, WIDE complex tachycardia

3: Accelerated junctional rhythm7 / 15

Aetiology / Causes / Risk Factors8 / 15

Pathophysiology9 / 15

ectopic focus in ATRIA or AV NODE
re-entry circuit
- slow pathway + fast pathway
- re-entrant impulse conducted retrograde via fast pathway (faster recovery from refractory period)

Symptoms / History10 / 15

Management11 / 15

O2
transient block of AVN
- vagal manoeuvre
- adenosine
- exclude pre-excitation on pre-tachycardia ECG to exclude WPW before giving
- ensure defibrillator is available
ablation of slow pathway
- 95-99% effective
vagal manoeuvres
- carotid sinus massage (CSM)
  - 30 seconds on left, then 30 seconds on right
- Valsalva manoeuvre (VM)
  - hand on abdomen, tell patient to blow out against syringe
  - inspiratory hold on ventilator
anti-arrhythmics
- adenosine
  - if HR > 200, ⬇BP, chest pain
  - requires large bore IVC in CF (closer to heart), rapid degradation
  - dose
    - 6 mg IV over 1-3 seconds, immediately followed by 20 mL NS bolus
    - paeds = 100-300 mcg/kg
  - wait 1-2 minutes
  - 2nd dose
    - adults = 12 mg
    - paeds = 200 mcg/kg
  - wait 1-2 minutes
  - 3rd dose
    - adults = repeat 12 mg
    - paeds = 300 mcg/kg
  - max dose = 30 mg
- esmolol
- digoxin
- verapamil
  - "pill in pocket" = 80 mg
- amiodarone
  - 5 mg/kg
overdrive pacing
cardioversion
- synchronised
- 0.5-1 J/kg
- then 2 J/kg

Management AVNRT = "normal SVT"12 / 15

1st line
- vagal manoeuvres
- CCB = verapamil = 5 mg IV q3min = max 15 mg
- adenosine = 6-12 mg IV bolus with flush
2nd line
- procainamide
- BB
- digoxin
- amiodarone

Management AVRT13 / 15

Anaesthetic considerations14 / 15

Pre-op
- consideration of pre-operative ablation prior to elective surgery
- avoidance of electrolyte imbalance and acid base disturbance that may increase the occurrence of premature atrial contractions
- maintenance of preoperative anti-arrhythmics
Intra-op
- rapid availability of adenosine, esmolol and verapamil
- rapid availability and familiarity with a defibrillator
Post-op

Links / References15 / 15