AV node re-entry tachycardia Flashcards
What is supraventricular tachycardia?
Supraventricular Tachycardia can be used to refer to any tachycardia arising from above the bundle of His, although in clinical practice it usually refers to an AV node re-entry tachycardia (AVNRT)
What is AVNRT?
the most common form of supraventricular tachycardia, presenting as spontaneous attacks with normal QRS complexes just at a faster rate of 140-240/min
IS AVNRT more common in men or women?
women X3
What is AVNRT precipitated by?
- Caffeine
- Alcohol
- Exercise
- Drugs
- Beta-agonists
- Sympathomimetics
- Hyperthyroidism
What is slow-fast AVNRT?
During sinus rhythm, impulses travel simultaneously through both the fast and slow pathways. That which is transmitted via the fast pathway encounters the end of that of the slow, and the two are cancelled out.
If the fast pathway is in its refractory period, a premature atrial contraction will only travel via the slow pathway
By its nature, the impulse will not have fully conducted through the slow pathway by the time the fast becomes non-refractory again
The impulse will travel in a retrograde fashion, up the fast pathway
This impulse cycles around the two pathways. Its short length gives the accelerated HR
The HIS bundle is activated anterogradely
The atria are activated retrogradely
What is the pathophysiology of AVNRT?
AVNRT is caused by a re-entry within the AVN.
In most cases the re-entry is induced by a premature atrial beat reaching the AVN while some fibres are still in refractory and the other capable of conducting the impulse, re-entry may arise.
What percent of AVNRT is slow-fast?
90%
What occurs in fast-slow AVNRT?
in atypical AVNRT the fast pathway conducts the impulse in the antegrade direction while the slow pathway conducts it in the retrograde direction.
The p wave will be visible before the QRS complex. The p wave will be in retrograde in lead 2 3 and aVF and positive in lead 1.
What is the ECG findings for slow-fast AVNRT?
Because the re-entry circuit will emit impulses up to the atria and down the ventricles simultaneously, the p wave will be hidden within the QRS complex
What occurs in slow-slow AVNRT?
Both pathways are slow therefore the p-wave will occur somewhere on the ST-T segment
Give 7 presentations associated with supraventricular tachycardias (AVNRT, AVRT):
1) rapid, regular palpitations (abrupt onset and sudden termination)
2) anxiety
3) dizziness
4) dyspnoea
5) neck pulsation
6) central chest pain
7) weakness
When does AVNRT present?
AVNRT is typically paroxysmal and may occur spontaneously in patients or upon provocation with exertion, coffee, tea or alcohol.
What is the management for AVNRT?
Patients may be instructed to undertake vagal manoeuvres upon the onset of symptoms which can be effective in stopping the AVNRT. This may involve carotid sinus massage or valsalva manoeuvres, which will both stimulate the vagus nerve. Alternative strategies include:
Adenosine, beta-blockers or calcium channel blockers can suppress an AVNRT event by blocking or slowing the AV node. Other second-line therapies may include amiodarone or flecainide.
Cardioversion is rarely used on patients with AVNRT, usually when the tachycardia is refractory to other medical therapies or the tachycardia is causing haemodynamic instability (falling blood pressure, development of heart failure etc.)
Radiofrequency catheter ablation can be offered to patients with frequent attacks for whom medical therapy isn’t appropriate in the long term, and can be curative.
What treatment should be used for supraventricular tachycardias with haemodynamic instability?
emergency cardioversion
What treatment should be used for patients in supraventricular tachycardia who are haemodynamically stable?
vagal manoeuvres (to stimulate parasympathetic activity)
1) right carotid massage
2) Valsalva manoeuvre (popping ears)
3) facial immersion in cold water
