Supraventricular Tachycardia

Question 1

What is supra ventricular tachycardia?

Answer 1

a regular narrow-complex tachycardia (> 100 bpm) with no p waves + a supraventricular origin.
Refers to:
Atrioventricular Nodal Re-entry Tachycardia (AVNRT)
Atrioventricular Re-entry Tachycardia (AVRT)
(though AF technically counts as a type of SVT)

Question 2

What is the aetiological cause of Atrioventricular Nodal Re-entry Tachycardia?

Answer 2

A localised re-entry circuit forms around the AV node

Question 3

What is the aetiological cause of Atrioventricular Re-entry Tachycardia?

Answer 3

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

Question 4

List 5 risk factors for SVT

Answer 4

Nicotine  
Alcohol  
Caffeine  
Previous MI  
Digoxin toxicity

Question 5

Give 2 epidemiological facts on SVT

Answer 5

VERY common

F > M

Question 6

List 6 symptoms of SVT

Answer 6

Syncope  
Palpitations  
Light-headedness  
Fatigue
Chest discomfort
Dyspnoea

Question 7

Describe the nature of symptoms in SVT

Answer 7

May have minimal Sx or may present with syncope
Sx vary depending on rate + duration of SVT
Abrupt onset + termination of Sx

Question 8

What are the signs of SVT?

Answer 8

AVNRT: tachycardia

AVRT (Wolff-Parkinson-White): Tachycardia + Secondary cardiomyopathy (S3 gallop, RV heave, displaced apex beat)

Question 9

How do you differentiate between AVNRT and AVRT on ECG?

Answer 9

Once SVT has been terminated + normal rate + rhythm are re-established:
AVNRT: appears normal
AVRT: delta-waves (slurred upstroke of the QRS complex)

Question 10

Other than an ECG what investigations should be carried out in SVT?

Answer 10

Cardiac Enzymes: Exclude MI (esp if there is chest pain)
Electrolytes: can cause arrhythmia
TFTs: can cause arrhythmia
Digoxin Level: digoxin toxicity can cause arrhythmia
Echocardiogram: check for structural heart disease

Question 11

How do you manage a patient with SVT if haemodynamically unstable?

Answer 11

DC Cardioversion

Question 12

How do you manage a patient with SVT if haemodynamically stable?

Answer 12

Vagal manouevres + chemical cardioversion
Vagal manoeuvres (e.g. Valsalva, carotid massage)
Carotid massage could dislodge atherosclerotic plaques, so only performed in young
If Vagal manoeuvres fail:
Adenosine 6 mg bolus
CI in ASTHMA (can cause bronchospasm)
Can give verapamil 2.5 - 5 mg if unsuccessful/ adenosine CI
Alternatives: atenolol, amiodarone

Question 13

How do you manage a patient if unresponsive to chemical cardioversion or tachycardia > 250 bpm or adverse signs (low BP, heart failure, low consciousness)

Answer 13

Sedate + synchronised DC cardioversion

Amiodarone

Question 14

Describe the ongoing management of SVT

Answer 14

AVNRT:
Radiofrequency ablation of slow pathway
B-blockers
Alternatives: fleicanide, propafenone, verapamil
AVRT:
Radiofrequency ablation
Sinus Tachycardia:
Exclude secondary cause (e.g. hyperthyroidism)
B-blocker or rate-limiting CCB

Question 15

List 4 complications of SVT

Answer 15

Haemodynamic collapse
DVT
Systemic embolism
Cardiac tamponade

Question 16

Describe the prognosis in SVT

Answer 16

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

Question 17

What is the half life of adenosine? Thus how should it be administered?

Answer 17

8-10s
Infused via a large-calibre cannula

Question 18

In which patients should adenosine be avoided?

Answer 18

Asthmatics
(Possible bronchospasm)

Question 19

List 3 side effects of adenosine

Answer 19

Chest pain
Bronchospasm
Transient flushing

Question 20

How can adenosine increase ventricular rate?

Answer 20

Can enhance conduction down accessory pathways e.g. WPW syndrome