Cardiovascular: Supraventricular Tachycardia Flashcards
Is SVT the most common childhood arrhythmia?
Yes
The most common non sinus tachyarrhythmia
Describe the HR
Rapid
Between 250-300 /min
What consequences can occur?
Poor CO
Pulmonary oedema
How does it typically present?
With symptoms of HF in neonate or young infant
It is a cause of hydrops fetalis and intrauterine death
In older children: recurrent episodes of tachycardia, which often become more severe and frequent with time
SOB
Palpitations
Syncope
Dizziness
Chest pain or tightness
Progressive fatigue
Pounding of head and/or neck
Why is the term re-entry tachycardia used?
A circuit of conduction is set up, with premature activation of the atrium via an accessory pathway
There is rarely a structural heart problem, but what should be performed?
ECHO
What will the ECG show?
Narrow complex tachycardia of 250-300bpm
May be possible to discern a P wave after the QRS due to retrograde activation of the atrium via the accessory pathway
P wave before QRS may not be visible (especially AVNRT) as the atrium and ventricles contracting in very short succession
If heart failure is severe, what may be seen in ECG?
Changes suggestive of myocardial ischaemia
T wave inversion in lateral precordial leads
What types of SVT are there?
Atrio-ventricular nodal re entrant tachycardia AVNRT
Atrio-ventricular re-entrant tachycardia AVRT
Atrial tachycardia
All characterised by rapid HR that originates above ventricles
Is AVNRT of AVRT more common?
AVNRT
Describe AVNRT
2 pathways make up the loop:
Alpha pathway - slow conduction and short refractory period
Beta pathway - fast conduction and long refractory
A signal comes down from SA node, it goes down the fast pathway quicker and splits to travel to ventricles and up to meet slow pathway - they meet and cancel out and both into refractory. The alpha comes out of refractory sooner and ready for another signal. If another signal comes by, it will go down the fast pathway (blocked on beta side). The signal going down alpha pathway activates ventricle and also travels up the beta pathway and by time reaches alpha pathway again it is out of refractory = re entry loop set up that keeps going and going.
Down slow (anterograde) and up fast (retrograde) = slow-fast AVNRT (typical)
Also possible to have fast-slow AVNRT (atypical)
Describe AVRT
The electrical signal uses a separate accessory pathway to get up from the ventricles to atria - causes atria to contract before SA node sends another signal. The signal the moves back down the AV node to ventricles and back up the accessory pathway
How does the signal usually get from the atria to ventricles?
Via AV node
In terms of acute management, what can be done?
Vagal manoeuvres - valsalva, carotid sinus massage, ice to face
IV adenosine 6mg->12mg->12mg
If adenosine fails: electrical cardioversion
Who is adenosine contraindicated in?
Asthmatics - verapamil is preferable (given IV over 2 minute period)
How does adenosine work?
It induces atrioventricular blockage after rapid bolts injection. It terminates the tachycardia by breaking the re entry circuit that is set up between the AV node and the accessory pathway
Does SVT have an abrupt onset and offset?
Yes
What is the average duration of episode?
10-15 minutes but can last from seconds to hours
Is syncope common?
No
When present, is a warning sign due to significant increase in risk of sudden cardiac death
If there is haemodynamic instability (rare) what should be done first?
DC cardioversion as first treatment
Under sedation or GA
Restores normal sinus rhythm in over 95%
What are valsalva manoeuvres?
Forceful exhalation against closed airway for 15-20 sec e.g blowing into occluded straw
Head down position
When is long term management needed?
If frequency and severity of episodes impacting quality of life and functioning
What options are there for long term management?
Radio frequency ablation
Or pharmacological : beta blockers or CCBs = first line
Second line medication: flecainide, sotalol
What type of monitoring is required to identify SVT episode if patient does not present in the middle of an episode?
Ambulatory (Holter) monitoring
A normal 24-48 hour reading should not exclude SVT
What can sometimes trigger an episode?
Exercise - an increase in adrenergic tone can elicit episode in some cases