Supraventricular Tachycardia

Question 1

Definition

Answer 1

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

o AF technically 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

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

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

Presenting symptoms

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

Signs on physical examination

Answer 6

· AVNRT - normal except tachycardia

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

Question 7

Investigations (ECG)

Answer 7

o 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)

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

Question 8

Investigations (other)

Answer 8

· 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 9

Management plan (short term)

Answer 9

· If Haemodynamically UNSTABLE
o DC cardioversion

· If Haemodynamically STABLE –> vagal monouevres + chemical cardioversion
o Vagal manoeuvres (e.g. Valsalva, carotid massage)
· Carotid massage could dislodge atherosclerotic plaques, so is only performed in young patients

If Vagal manoeuvres fail:
o Adenosine 6 mg bolus (can increase to 12 mg)
· Contraindicated in ASTHMA as it can cause bronchospasm
o Can give verapamil 2.5 - 5 mg if unsuccessful/adenosine contraindicated due to asthma
o Alternatives: atenolol, amiodarone

· If unresponsive to chemical cardioversion or tachycardia > 250 bpm or adverse signs (low BP, heart failure, low consciousness)
o Sedate and synchronised DC cardioversion
o Amiodarone

Question 10

Management plan (long term)

Answer 10

· Ongoing management of SVT

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

o AVRT
· Radiofrequency ablation

o Sinus Tachycardia
· Exclude secondary cause (e.g. hyperthyroidism)
· Beta-blocker or rate-limiting CCB

Question 11

Possible complications

Answer 11

· Haemodynamic collapse

· DVT

· Systemic embolism

· Cardiac tamponade

Question 12

Prognosis

Answer 12

· 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