Supraventricular tachycardia

Question 1

Define:

Answer 1

Tachydysrhythmia arising from above the level of the Bundle of His, usually the atria or AV node.
• A regular narrow-complex tachycardia (> 100 bpm) with no p waves and a supraventricular origin.

Technically, AF and atrial flutter counts as a type of SVT
o However, SVT generally refers to:
• Atrioventricular Nodal Re-entry Tachycardia (AVNRT)
• Atrioventricular Re-entry Tachycardia (AVRT)

Question 2

Aetiology:

Answer 2

• AVNRT
o A localised re-entry circuit forms around the AV node, which conducts to the ventricles faster than normal conduction pathway.

AVRT
o This occurs when there is normal AV conduction, as well as an accessory pathway present. These form a re-entry circuit between the atria and ventricles.
o A classic example of AVRT is Wolff-Parkinson-White Syndrome, in which the accessory pathway is called Bundle of Kent. WPW Syndrome can lead to AVRT.

Question 3

Risk factors:

Answer 3

o	Nicotine 
o	Alcohol 
o	Caffeine 
o	Previous MI 
o	Digoxin toxicity

Question 4

Epidemiology:

Answer 4

• VERY COMMON

* 2 x more common in FEMALES

Question 5

symptoms:

Answer 5

Syncope
• Symptoms vary depending on rate and duration of SVT
• Palpitations
• Light-headedness
• Polyuria (due to increased atrial pressure causing ANP release)
• Abrupt onset and termination of symptoms
• Other symptoms: fatigue, chest discomfort, dyspnoea

Question 6

signs:

Answer 6

• Wolff-Parkinson-White
o Tachycardia
o Secondary cardiomyopathy (S3 gallop, RV heave, displaced apex beat)

Question 7

investigations:

Answer 7

•	ECG
o	AVNRT
	Tachycardia
	Narrow QRS 
	P waves may be buried in QRS
	Decreased PR interval
	After SVT terminated, ECG appears normal.
o	AVRT
	Narrow complex tachycardia
	Shortened PR interval
	P waves buried in QRS

24 hr ECG monitoring - will be required in patients with paroxysmal palpitations

Cardiac Enzymes
o Check for features of MI (especially if there is chest pain)

Electrolytes - can cause arrhythmia

TFTs - can cause arrhythmia

Digoxin Level - for patients on digoxin

Echocardiogram - check for structural heart disease

Question 8

Management:

Answer 8

o DC cardioversion if haemodynamically unstable

• If Haemodynamically STABLE
o Try VAGAL manoeuvres (e.g. Valsalva, carotid massage)
Note: Carotid massage could dislodge atherosclerotic plaques, so is only performed in young patients
o If vagal manoeuvres fail:
o ADENOSINE - Contraindicated in ASTHMA as it can cause bronchospasm – in asthma, use VERAPAMIL

o if still no change, IV metoprolol/ amiodarone /digoxin/synchronised DC cardiovert

If unresponsive to chemical cardioversion or tachycardia > 250 bpm or adverse signs (low BP, heart failure, low consciousness)

o AVNRT
 Radiofrequency ablation of slow pathway
 Beta-blockers
 Alternatives: fleicanide, propafenone, verapamil

AVRT
 Radiofrequency ablation
o Sinus Tachycardia

Question 9

complications:

Answer 9

• Haemodynamic collapse
• DVT
• Systemic embolism
• Cardiac tamponade

Question 10

prognosis:

Answer 10

• Dependent on the presence of underlying structural heart disease
• If structurally normal heart - GOOD PROGNOSIS
• People with pre-excitation have a small risk of sudden death