SVT includes all tachycardias involving the atria (due to either re-entrancy or automaticity). Atrial flutter, atrial tachycardia, MAT, AF, AV node re-entrant tachycardia & AV re-entrant tachycardia. Atrial flutter, atrial tachycardia & MAT describedin Arrhythmias& _AF in Atrial Fibrillation.
AV node re-entrant tachycardia (AVNRT)
60% of SVTs
Micro re-entrant circuit in AV node.
DC cardiovert if unstable, or stable and failed pharmacological options. Otherwise:
Adenosine: 6mg (can repeat at 12mg) rapid bolus IV. SE: bronchospasm (so avoid in asthma). Theophylline blocks it. CI: post cardiac transplant (→cardiac arrest).
Verapamil: 1mg IV q5 min (don’t use β-blocker concurrently) to 15mg
β-blockers, amiodarone and flecainide may also be used
Prophylaxis: β-blockers, sotalol, verapamil, or digoxin
Bundle of Kent – accessory pathway between an atrium & ventricle, by-passing AV node
~1:1000 pop (50% symptomatic), M>F. Assoc with Ebstein’s/Tricuspid anomalies, HOCM.
Conduction down accessory pathway may be anterograde, retrograde or both.
Normal i.e. concealed WPW, if only retrograde conduction possible via accessory pathway [or if conduction is currently faster through AV node (low vagal tone)]
Else: δ wave (faster antegrade accessory conduction but slower depolarisation of ventricular myocardium compared to AV node-His → early but less steep init part of QRS), PR<120ms. Slightly QRS (>110ms), discordant ST & T changes. May show pseudo-Q or -infarction patterns (neg δ wave in inf/ant leads, prom R wave in V1-3)
Types: Type A or C – pos δ wave & R>S in V1. Type B has neg δ wave or R<S in V1-2.
Tachyarrhythmias (HR 200-300) may be generated by: