Arrhythmias Flashcards
What is the most common type of tachycardia seen in children?
Narrow complex tachycardia
What is a narrow complex tachycardia?
Any arrhythmia that originates above or at the bundle of His
What is the HR in SVT?
220-300bpm
What is the clinical relevance of SVT in an individual patient related to?
- Ventricular rate
- Presence of any underlying heart disease
- Integrity of any cardiovascular reflexes
How does SVT typically present in young infants or neonates?
Symptoms of heart failure
What can SVT cause in utero?
- Hydrops fetalis
- Intrauterine demise
What might it be difficult to differentiate SVT from in the paediatric population?
Sinus tachycardia
What features might suggest a tachycardia is sinus tachycardia?
- Child may have systemic illness
- HR rarely >200bpm
- P wave upright in leads II, III< and aVF
- Beat to beat variability
- HR slows with treatment/fluid resus
What features might suggest a tachycardia is SVT?
- Previously well with no preceding systemic upset
- HR generally >220bpm
- P waves may be absent or negative in leads II, III, and aVF
- No beat to beat variability (fixed RR interval)
- Rate abruptly changes with adenosine
- Sudden onset
- May have had previous episodes
- Little change in rate with activity, crying, or breath holding
What is the probability of complete resolution of SVT dependent on?
The age of onset
What % of cases of SVT resolve when diagnosed at 1 year of age or less?
> 90%
What % of cases of SVT resolve when diagnosed after 1 year of age?
33%
What can SVT be divided into groups on the basis of?
If they arise from the atria or the atrioventricular junction
What can help in SVT?
- Carotid sinus massage
- Administration of IV adenosine
How does carotid sinus massage or administration of IV adenosine help in SVT?
It increases the atrioventricular block
Why might carotid sinus massage/administration of IV adenosine be of diagnostic value in SVT?
It allows for more accurate visualisation of the atrial activity
What type of SVT arrhythmias arise from the atria or SA node?
Atrial fibrillation or flutter
What is atrial fibrillation caused by?
Multiple re-entrant circuits triggering waves of activation in the atria
What does atrial fibrillation look like on ECG?
- Irregular baseline made up of fibrillation waves
- Absent P waves
- Conduction of atrial impulses to the ventricles is variable, resulting in irregular RR interval
What is atrial flutter caused by?
Re-entry circuit in right atrium with secondary activation of the left atrium
What is the atrial rate in atrial flutter?
About 300bpm
How does atrial flutter appear on ECG?
Saw-toothed flutter waves
What does the ventricular rate depend on in atrial flutter?
The rate of conduction through the AV node
What is the typical rate of conduction through the AV node in atrial flutter?
2:1
What is the typical ventricular rate in atrial flutter if the rate of conduction is 2:1?
150
What is the most common type of SVT seen in children?
AV re-entry tachycardia (AVRT)
What is AVRT also known as?
Accessory pathway mediated tachycardia
What % of arrhythmias occurring during infancy are AVRT?
80%
What does AVRT involve?
An electrical re-entry circuit
Describe the electrical re-entry circuit in AVRT?
The circuit proceeds down the AV node, and then up an accessory pathway outside the AV node
What kind of rhythm does AVRT produce?
A narrow complex tachycardia
What % of patients with AVRT have Wolff-Parkinson-White syndrome?
50%
How can WPW syndrome be differentiated from others with AVRT?
In WPW syndrome, even in sinus rhythm they manifest ventricular pre-excitation in the form of a delta wave on the ECG. The remainder have a ‘concealed’ pathway which is not evident on the ECG during sinus rhythm
What are the ECG features of WPW syndrome?
- Delta wave
- Shortened PR interval
- Slurred QRS upstroke
- Widened QRS
What causes the PR and QRS changes seen in WPW syndrome?
Conduction through the accessory pathway can occur before the AV node is activated
What is the result of conduction through the accessory pathway before AV node activation being possible in WPW syndrome?
It creates the potential for rapid ventricular response during atrial fibrillation
What can rapid ventricular response during atrial fibrillation result in?
Ventricular fibrillation and sudden death
What drug should not be given in WPW?
Digoxin
Why should digoxin not be given in WPW?
As it can enhance conduction through the bypass tract, whilst slowing down conduction through the AV node, and this may trigger VF
How is acute SVT managed in WPW?
Same as for patients in concealed and manifest pathways
What is recommended due to the risk of VF in WPW?
Definitive ablative therapy
