Supraventricular Tachycardia

Question 1

What is supraventricular tachycardia caused by?

Answer 1

electrical signal re-entering the atria from the ventricles.
Once the signal is back in the atria, it again travels through the atrioventricular node to the ventricles, causing another ventricular contraction.
This causes a self-perpetuating electrical loop without an endpoint, resulting in narrow complex tachycardia.

Question 2

What length of QRS is seen in SVT?

Answer 2

Narrow complex tachycardia
<0.12s
<3 small squares

Question 3

What does SVT look like?

Answer 3

QRS complex immediately followed by a T wave and so on
P waves are buried in the T waves

Question 4

What does atrial fibrillation look like?

Answer 4

Absent p waves
Irregularly irregular

Question 5

What does atrial flutter look like?

Answer 5

Sawtooth
Atrial rate around 300bpm

Question 6

When can SVT cause a broad complex tachycardia?

Answer 6

When patient also has a bundle branch block

Question 7

What are the 3 main types of SVT?

Answer 7

AVNRT
AVRT
Atrial tachycardia

Question 8

What is AVNRT?

Answer 8

• Atrioventricular nodal re-entrant tachycardia (AVNRT) = is where the re-entry point is back through the atrioventricular node.

Question 9

What is AVRT?

Answer 9

• Atrioventricular re-entrant tachycardia (AVRT) = is where the re-entry point is an accessory pathway.
○ An additional electrical pathway, somewhere between the atria and the ventricles, lets electricity back through from the ventricles to the atria.

Question 10

What is atrial tachycardia SVT?

Answer 10

• Atrial tachycardia = is where the electrical signal originates in the atria somewhere other than the sinoatrial node.
○ This is not caused by a signal re-entering from the ventricles but from abnormally generated electrical activity in the atria.
○ Ectopic atrial activity
○ Atrial rate >100bpm

Question 11

What is wolf Parkinson white syndrome?

Answer 11

• Wolff-Parkinson-White syndrome (WPW) is caused by an extra electrical pathway connecting the atria and ventricles.

Question 12

What is the extra pathway in wolf Parkinson white syndrome called?

Answer 12

Bundle of Kent

Question 13

What ecg changes are seen in wolf Parkinson white syndrome?

Answer 13

• Short PR interval, less than 0.12 seconds
• Wide QRS complex, greater than 0.12 seconds
• Delta wave = slurred upstroke of the QRS complex
○ It is caused by the electricity prematurely entering the ventricles through the accessory pathway.

Question 14

What is the management of Wolff Parkinson white syndrome?

Answer 14

Radio frequency ablation of the accessory pathway

Question 15

Why are most anti-arrhythmic drugs e.g. beta blockers, CCB, digoxin contra-indicated in Wolff Parkinson white syndrome?

Answer 15

increase this risk by reducing conduction through the AV node and promoting conduction through the accessory pathway.

Question 16

What is the stepwise management of SVT? (4)

Answer 16

a. Step 1: Vagal manoeuvres
b. Step 2: Adenosine
c. Step 3: Verapamil or a beta blocker
d. Step 4: Synchronised DC cardioversion

Question 17

What is the usual management for patients with Wolff Parkinson white syndrome who develop atrial fibrillation or flutter?

Answer 17

Procainamide (if stable)
Electrical cardioversion (if unstable)

Question 18

What is the action of vagal manoeuvres?

Answer 18

• Vagal manoeuvres stimulate the vagus nerve, increasing the activity in the parasympathetic nervous system.
• This can slow the conduction of electrical activity in the heart, terminating an episode of supraventricular tachycardia.

Question 19

What are 3 types of vagal manoeuvres?

Answer 19

Valsalva manoeuvres
Carotid sinus massage
Diving reflex

Question 20

What is done in a valsalva manoeuvre?

Answer 20

• Valsalva manoeuvres involve increasing the intrathoracic pressure.
○ This can be achieved by having the patient blow hard against resistance, for example, blowing into a 10ml syringe for 10-15 seconds.

Question 21

What is the action of adenosine?

Answer 21

• Adenosine works by slowing cardiac conduction, primarily through the AV node.
It interrupts the AV node or accessory pathway during SVT and “resets” it to sinus rhythm

Question 22

How is adenosine given?

Answer 22

○ It needs to be given as a rapid bolus to ensure it reaches the heart with enough impact to interrupt the pathway for a short period.

Question 23

What do patients need to be warned of when being given adenosine?

Answer 23

○ It will often cause a brief period of asystole or bradycardia that can be scary for the patient and doctor. However, it metabolises quickly, and sinus rhythm will return.

Question 24

When is adenosine avoided? (6)

Answer 24

• Asthma
• COPD
• Heart failure
• Heart block
• Severe hypotension
Potential atrial arrhythmia with underlying pre-excitation

Question 25

How does synchronised dc cardioversion work?

Answer 25

• A defibrillator machine monitors the electrical signal, particularly identifying the R waves.
• An electric shock is synchronised with a ventricular contraction, at the R wave on the ECG.
• If successful, the shock will be followed by sinus rhythm.

Question 26

Why is synchronised cardioversion used in patients with a pulse rather than unsynchronised?

Answer 26

Avoid shocking during a t wave
○ Delivering a shock during a T wave can result in ventricular fibrillation and, subsequently, cardiac arrest.

Question 27

How is paroxysmal SVT managed? (2)

Answer 27

• Radiofrequency ablation
• Long-term medication (e.g., beta blockers, calcium channel blockers or amiodarone)

Question 28

How does radio frequency ablation work?

Answer 28

radiofrequency ablation (heat) is applied to burn the abnormal electrical pathway.
• This leaves scar tissue that does not conduct electrical activity.
• Destroying the abnormal electrical pathway aims to remove the source of the arrhythmia.

Question 29

What arrhythmias can be permanently resolved with radio frequency ablation? (4)

Answer 29

○ Atrial fibrillation
○ Atrial flutter
○ Supraventricular tachycardias
○ Wolff-Parkinson-White syndrome