AVRT Flashcards
What does AVRT stand for?
Atrioventricular reentrant tachycardia
What is AVRT?
Where accessory pathways allow increased oscillations to create spontaneous palpitations
How does AVRT present?
Wolff-Parkinson-White syndrome
What are the 2 types of AVRT?
- Orthodromic AVRT
- Antidromic AVRT
What is orthodromic AVRT?
In orthodromic AVRT, anterograde conduction occurs via the AV node, resulting in a normal direction of ventricular depolarisation. This can occur in patients with a concealed pathway (AP that conducts retrograde only, not evident on sinus rhythm ECG).
What are the ECG features of orthodromic AVRT?
Rate usually 200-300 bpm
Retrograde P waves are usually visible, with a long RP interval
QRS < 120ms unless pre-existing bundle branch block, or rate-related aberrant conduction
QRS alternans: phasic variation in QRS amplitude associated with AVNT and AVRT, distinguished from electrical alternans by a normal QRS amplitude
Rate-related ischaemia is common
How can we differentiate between orthodromic AVRT and AVNRT?
In typical AVNRT, retrograde P waves occur early, so we either don’t see them (buried in QRS) or partially see them (pseudo R’ wave at terminal portion of QRS complex)
In AVRT, retrograde P waves occur later, with a long RP interval > 70 msec
What is the treatment of orthodromic AVRT?
As always, patients that are unstable due to this rhythm require urgent DC cardioversion
The anterograde portion of conduction is typically the “weak link” of the re-entry circuit. Management options in the stable patient therefore target slowing conduction through the AV node
A stepwise approach similar to AVNRT can be employed, beginning with vagal manoeuvres followed by adenosine and/or verapamil
What is antidromic AVRT?
Antidromic AVRT is rare, and makes up only 5% of tachyarrhythmias in patients with WPW. As the name suggests, it involves anterograde conduction via the AP. Retrograde conduction is usually via the AV node, but can also be via another AP. The abnormal direction of ventricular depolarisation results in a broad complex tachycardia, which can be easily mistaken for VT.
What are the ECG features of antidromic AVRT?
Rate usually 200-300 bpm
Wide QRS complexes due to abnormal ventricular depolarisation via AP
What is the treatment of antidromic AVRT?
This rhythm can be difficult to distinguish from VT, and if there is any doubt, we should presume a diagnosis of VT and treat accordingly
In stable patients, drug therapy should be targeted at the AP
Procainamide (class I) would be our first line antiarrhythmic. Ibutilide (class III) and amiodarone are second-line options, but their effectiveness is less established
DC cardioversion may still be required if drug therapy fails
