Arrhythmias

Question 1

What is AVNRT?

Answer 1

Atrioventricular nodal reentrant tachycardia. Essentially impulse reaches the AV node where it splits into a slow and fast pathway - the slow pathway has a short refractory period while the fast has a long refractory period. The impulses rejoin in the bundle of His and then travel to the ventricles.

However, in the case of a premature/extra beat, anterograde conduction starts to occur down the slow pathway with retrograde conduction in the fast pathway leading to a constantly stimulated loop forming in the AV node.

Question 2

What are ECG features of AVNRT?

Answer 2

Tachycardia (150-200 bpm)
Narrow QRS complex
Regular rhythm
P waves not visible

Question 3

How is AVNRT treated?

Answer 3

If unstable: electrical cardioversion
If stable: 1st line is vagal manoeuvres followed by adenosine and then calcium channel blockers/beta blockers

Adenosine 6mg over 2 seconds IV, then 12mg 1-2 mins later (with constant cardiac monitoring) and then 12mg 1-2 mins later.

Chronic management is catheter ablation of accessory pathway.

Question 4

What is AVRT?

Answer 4

Atrioventricular re-entry tachycardia - accessory pathway is outside the AV node. Can be antidromic/orthodromic but orthodromic is more popular.

Question 5

Describe ECG changes in AVRT

Answer 5

Orthodromic - Narrow QRS complex, tachycardia, regular rhythm
Antidromic - Broad QRS complex, tachycardia, regular rhythm

Question 6

Describe Wolff-Parkinson White syndrome

Answer 6

An accessory bundle known as the Bundle of Kent exists resulting in impulse bypassing AV node, leading to pre-excitation of ventricles. Hence, no delay between atrial and ventricular contraction.

Question 7

What does an ECG of WPW show?

Answer 7

Delta waves (slow-rising QRS post P-wave) - shortened PR interval + widened QRS

Question 8

What are the symptoms of WPW?

Answer 8

Syncope, light headedness and palpitations

Question 9

What is the treatment for WPW?

Answer 9

If unstable: electrical cardioversion
If stable: vagal manouevres, adenosine, catheter ablation of accessory pathway

Question 10

How is atrial fibrillation classified?

Answer 10

1. Haemodynamic stability
2. Onset and duration: paroxysmal? new onset? persistent? long standing? permanent?

Question 11

How is atrial fibrillation managed?

Answer 11

If not haemodynamically stable, immediate synchronised electrical cardioversion.

If stable and onset has occured LESS than 48 hours ago, focus on rate control (preferred to rhythm as it also allows alleviation of symptoms) and TOE to check for thrombus in LA. Anticoagulate for 3 weeks depending on CHAD VASc score and if no thrombus found, cardiovert.

If stable and onset has occured MORE than 48 hours ago:
Option 1: If rate >110bpm, rate control through CCB/BB or 2nd line digoxin.
Option 2: Rhythm control with amiodarone, flecanide and ibutilide or synchronised electrical cardioversion.

Question 12

What is the CHADS VASc score?

Answer 12

Calculates stroke risk for patients with atrial fibrillation

C - Congestive heart failure
H - Hypertension
A - Age over or equal to 75
D - Diabetes
S - Stroke/TIA Hx
V - Vascular disease
A - Age 65-74
S - Sex (Female)