Arrhythmias – Supraventricular Tachycardia (SVT) – AVRT and AVNRT Flashcards
What does AVRT stand for?
Atrioventricular Re-entrant/Reciprocating Tachycardia
What is AVRT?
a form of supraventricular tachycardia which presents in patients as occasional brief episodes of rapid heart contractions
What is the rate of AVRT when there is rapid heart contractions?
150 – 250bpm
What is AVRT caused by?
by the presence of abnormal accessory pathways that allow the impulse to travel in a loop between the atria/ventricles
What is the onset of AVRT usually triggered by?
- premature atrial contractions (PAC) or premature ventricular contractions (PVC)
- This leads to tachycardia
What is the most common type of AVRT?
Wolff-Parkinson White syndrome (WPW)
What accessory pathway does Wolff-Parkinson White syndrome (WPW) form?
bundle of Kent
What are the 2 types of AVRT?
- Orthodromic AVRT
- Antidromic AVRT
What is Orthodromic AVRT?
The impulse travels down the normal AV pathway and returns up the accessory pathway
What is Antidromic AVRT?
The impulse travels down the accessory pathway and returns up the normal AV pathway
Which type of AVRT is more common?
Orthodromic AVRT
Which type of AVRT is less common?
Antidromic AVRT
but tends to result in wide QRS complex
What is the investigation for AVRT?
ECG
What is seen on ECG for AVRT?
Slurred delta waves (WPW specific), short PR interval, Tachycardia, and narrow QRS
What does AVNRT stand for?
Atrioventricular Nodal Reentrant Tachycardia
What is AVNRT?
- is a form of SVT where the reentrant circuit is within the atrioventricular node
- This is one of the most common paroxysmal SVTs
What is the pathophysiology for AVNRT?
- In a normal heart, the AV node delays the transmission of the signal before allowing it to pass through to the ventricles
- In AVNRT, a reentrant circuit forms involving pathways within the AV node and the signal circulates, leading to rapid and regular tachycardia
What is AVNRT triggered by?
a premature atrial contraction (PAC)
What are the 2 types of AVNRT?
- Slow-Fast AVNRT
- Fast-Slow AVNRT
What is slow-fast AVNRT?
The impulse travels slowly through the slow pathway and quickly through the fast pathway during the reentrant
What is fast-slow AVNRT?
The impulse travels quickly through the slow pathway and slowly through the fast pathway during the reentrant
What is the investigation for AVNRT?
ECG
What is seen on ECG for AVNRT?
Absence of P waves as they are buried in the QRS Complex
What are the symptoms for AVRT and AVNRT?
Palpitations
Tachycardia
Chest discomfort
Dizziness
Syncope
What is the first treatment for AVRT and AVNRT in young patients?
first, try Carotid massage (due to the risk of emboli in older patients)
Otherwise what is the treatment in AVRT and AVNRT?
work down the list till effective:
- Valsalva manoeuvre
- Adenosine
- Beta blocker or verapamil
If all fails:
- Synchronised DC shock
