Cardio - Tachyarrhythmias

Question 1

name 5 types of supraventricular tachycardias

Answer 1

Regular:

1. atrial tachycardia
2. atrial flutter
3. atrioventricular re-entry tachycardia (AVRT)
4. AVNRT

Irregular:
5. atrial fibrillation

Question 2

what is the pathophysiology of atrial tachycardia? how would this appear on ECG?

Answer 2

Rhythm originates within atria but outside of SAN.

ECG appearance:

i) episodes of tachycardia with atrial rates >100 bpm
ii) abnormal P wave morphology (e.g. inverted in inferior leads II, III and aVF) - must have at least 3 consecutive identical ectopic P waves

Question 3

in which pop. subset is atrial tachycardia more common?

Answer 3

females in 30s

Question 4

what is the pathophysiology of atrial flutter? how would this appear on ECG?

Answer 4

Caused by re-entry circuit in R atrium.

ECG appearance:

i) flutter waves (inverted in leads II, III and aVF if anti-clockwide re-entry circuit; positive in these leads if clockwise)
ii) atrial rate about 300 bpm (length of re-entry circuit determined by size of RA)
ii) ventricular rate determined by AV conduction ratio, most common being 2:1, resulting in ventricular rate of 150 bpm (higher degree AV blocks can occur, usually due to medications or underlying heart disease)

Question 5

what is the pathophysiology of AVRT? how would this appear on ECG?

Answer 5

Presence of accessory pathway (e.g. Bundle of Kent in WPW) enables formation of an A-V re-entry circuit causing tachyarrythmia. Can be:

• orthodromic: anterograde conduction occurs via AVN, with retrograde conduction via accessory pathway
• antidromic: anterograde conduction occurs via accessory pathway with retrograde conduction via AVN (less common)

ECG appearance (orthodromic):

i. narrow QRS complex
ii. absent P waves (may be retrograde)
iii. T wave inversion and ST segment depression common
iv. rate usually 200-300 bpm

ECG appearance (antidromic):

i. wide QRS (due to abnormal V depolarisatin)
- rate usually 200-300 bpm

Question 6

A pt presents to A and E with palpitations and syncope. ECG shows tachyarrythmia. How should they be managed?

Answer 6

Syncope is an adverse feature (also inc. shock, myocardial ischaemia and HF) suggesting unstable tacyarrythmia.

Management:

1. synchronise DC shock - up to 3 attempts
2. amiodarone 300 mg IV over 10-20 mins
3. repeat shock
4. amiodarone 900 mg over 24 hrs

Question 7

A pt presents to A and E with palpitations but no adverse features. ECG shows narrow QRS with irregular rhythm. How should they be managed?

Answer 7

Probable AF.

Management:

• rate control with B-blocker or diltiazem
• if in HF, consider digoxin or amiodarone
• assess thromboembolic risk and consider anticoagulation (warfarin or heparin)

Question 8

A pt presents to A and E with palpitations but no adverse features. ECG shows narrow QRS with regular rhythm. How should they be managed?

Answer 8

1. vagal manoeuvres
2. adenosine 6 mg rapid IV bolus
   if no effect - 12 mg
   if no effect - another 12 mg

Sinus rhythm achieved?

• yes: probable AVNRT or AVRT
• no: possible atrial flutter or atrial tachycardia - rate control with B-blocker or diltiazem

Question 9

how would you initially manage a pt presenting to A and E with unstable bradycardia?

Answer 9

1. Atropine 500 ug IV - if necessary, repeat every 3-5 mins to max dose of 3 mg.
2. If no response (or atropine is CI), initiate transcutaneous pacing.