Supraventricular Tachycardia (SVT)

Question 1

What is this?

Answer 1

Narrow complex tachycardia, and it includes:
• Sinus tachycardia
• Atrial fibrillation
• Atrial flutter
• AVRT (AV Re-entry Tachycardia)
• AVNRT (AV Nodal Re-entry Tachycardia)

Question 2

Sinus tachycardia:
What is this usually due to?

How is it managed?

Answer 2

➊ • Exercise
• Pain, stress, anxiety
• Anaemia
• Hyperthyroidism
• Salbutamol
• Caffeine

➋ Treat the underlying cause

Question 3

AVRT: (AV Re-entry Tachycardia)
What occurs here?

What’s the most common type of this?
→ What are the types of this?

How is it managed?

Answer 3

➊ Accessory pathway is formed between the atria and ventricles, leading to pre-excitation of the ventricles, therefore a delta wave. It’s classifed into:
• Orthodromic (95%) - Impulse travels down AVN and then back up through the accessory pathway (faster pathway = narrower QRS).
• Antidromic (5%) - Impulse travels down accessory pathway and then back up through the AVN (slower pathway = broader QRS).

➋ Wolff-Parkinson-White (WPW)
→ • Type A - AP is on the left side of the heart. Creates a +ve delta wave in V1 and V2.
• Type B - AP is on the right side of the heart. Creates a -ve delta wave in V1 and V2.

➌ • As always, if unstable, DC cardiovert them
• Try vagal manouveres first
• If it fails, give AVN blocker e.g. Adenosine

Question 4

AVNRT: (AV Nodal Re-entry Tachycardia)
What is this?

What’s the most common type of this?

How is it managed?

Answer 4

➊ Accessory pathway within the AV node. Within the node, there is now both a fast and slow pathway. In normal sinus rhythm, the impulse travels down both at the same time, but the fast pathway quickly enters the slow side to cancel out that impulse, therefore preventing a re-entry circuit. But, if an ectopic atrial impulse reaches the AVN while the fast pathway is still in its refractory period, the impulse only goes down the slow pathway. This leads to a re-entry circuit.

➋ Slow-Fast AVNRT

➌ • Vagal manoeuvres
• IV Adenosine

Question 5

Wolff-Parkinson-White:
What ECG pattern is seen?

What are 2 main forms of tachyarrhythmias that can occur here?

Answer 5

➊ * Short PR interval
* Delta wave

➋ * Atrial fibrillation/flutter - Due to direct conduction from atria to ventricles via AP (bypasses the AVN)
* AVRT - Due to the formation of a re-entry circuit involving the AP and AVN. It can either be orthodromic or antidromic, based on the direction of conduction. Both usually have rates above 200 bpm.