Supraventricular Tachycardia (SVT)

Question 1

What is the definition of SVT?

Answer 1

A regular narrow-complex tachycardia (> 100 bpm) with no p waves and a supraventricular origin.

• AF technically counts as a type of SVT
• However, SVT generally refers to:

1. Atrioventricular Nodal Re-entry Tachycardia (AVNRT)
2. Atrioventricular Re-entry Tachycardia (AVRT)

Question 2

What is the aetiology of SVT?

Answer 2

AVNRT -> A localised re-entry circuit forms around the AV node

AVRT -> A re-entry circuit forms between the atria and ventricles due to the presence of an accessory pathway (Bundle of Kent)

Question 3

What are the risk factors associated with SVT?

Answer 3

Nicotine

Alcohol

Caffeine

Previous MI

Digoxin toxicity

Question 4

What is the epidemiology of SVT?

Answer 4

VERY COMMON

2 x more common in FEMALES

Question 5

What are the presenting symptoms of SVT?

Answer 5

May have minimal symptoms or may present with syncope

Symptoms vary depending on rate and duration of SVT

Palpitations

Light-headedness

Abrupt onset and termination of symptoms

Other symptoms: fatigue, chest discomfort, dyspnoea, syncope

Question 6

What are the signs of SVT upon physical examination?

Answer 6

AVNRT - normal except tachycardia

Wolff-Parkinson-White

• Tachycardia
• Secondary cardiomyopathy (S3 gallop, RV heave, displaced apex beat)

Question 7

What are the appropriate investigations for SVT?

Answer 7

ECG

• Differentiating between AVNRT and AVRT - once the SVT has been terminated and normal rate and rhythm are re-established:
• > AVNRT - appears normal
• > AVRT - delta-waves (slurred upstroke of the QRS complex)
• 24 hr ECG monitoring - will be required in patients with paroxysmal palpitations

Cardiac Enzymes - 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

What is the management plan for SVT?

Answer 8

If Haemodynamically UNSTABLE -> DC cardioversion

If Haemodynamically STABLE –> vagal manouevres + chemical cardioversion

A)Vagal manoeuvres (e.g. Valsalva, carotid massage) -> Carotid massage could dislodge atherosclerotic plaques, so is only performed in young patients

B)If Vagal manoeuvres fail = Adenosine 6 mg bolus (can increase to 12 mg) -> Contraindicated in ASTHMA as it can cause bronchospasm

• Can give verapamil 2.5 - 5 mg if unsuccessful/adenosine contraindicated due to asthma
• Alternatives: atenolol, amiodarone

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

• Sedate and synchronised DC cardioversion
• Amiodarone

Question 9

What is an ongoing SVT managed?

Answer 9

AVNRT

• Radiofrequency ablation of slow pathway
• Beta-blockers
• Alternatives: fleicanide, propafenone, verapamil

AVRT
- Radiofrequency ablation

Sinus Tachycardia

• Exclude secondary cause (e.g. hyperthyroidism)
• Beta-blocker or rate-limiting CCB

Question 10

What are the possible complications of SVT?

Answer 10

Haemodynamic collapse

DVT

Systemic embolism

Cardiac tamponade

Question 11

What is the prognosis for patients with SVT?

Answer 11

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