Arrhythmias – pathophysiology, presentation and investigation

Question 1

What is normal sinus rhythm (NSR)?

Answer 1

Regular rhythm from the SA node
Rate: 60-100 bpm
P wave before every QRS
PR interval: 120-200ms

Question 2

What are the types of heart block?

Answer 2

1️⃣ 1st-degree → Prolonged PR interval (>200ms), all P waves conducted
2️⃣ 2nd-degree Mobitz I (Wenckebach) → PR interval gradually lengthens until a QRS drops
3️⃣ 2nd-degree Mobitz II → Fixed PR interval, but intermittent QRS drops (more dangerous)
4️⃣ 3rd-degree (Complete HB) → No association between P waves and QRS, requires pacemaker

Question 3

What is atrial fibrillation (AF)?

Answer 3

Irregularly irregular rhythm

No P waves, fibrillatory baseline

Narrow QRS, chaotic atrial activity

Risk of stroke (clots in left atrial appendage)

Question 4

What are the symptoms of atrial fibrillation?

Answer 4

Palpitations

Fatigue

Breathlessness

Dizziness

Asymptomatic (common in elderly)

Question 5

What is atrial flutter?

Answer 5

Re-entrant circuit in the atria

Sawtooth P waves (best seen in II, III, aVF)

2:1, 3:1 conduction (e.g., 2 flutter waves per QRS)

Often progresses to AF

Question 6

What is supraventricular tachycardia (SVT)?

Answer 6

Narrow-complex tachycardia (>150 bpm)

Sudden onset & termination

No P waves or retrograde P waves

Can use vagal maneuvers or adenosine to terminate

Question 7

What is Wolff-Parkinson-White (WPW) Syndrome?

Answer 7

Accessory pathway (Bundle of Kent) → pre-excitation

Short PR interval (<120ms), delta wave, wide QRS

Can cause AVRT (orthodromic/antidromic re-entry tachycardia)

Avoid AV nodal blockers (risk of VF)

Question 8

What is ventricular tachycardia (VT)?

Answer 8

Wide QRS tachycardia (>100 bpm)

Monomorphic (same QRS) or polymorphic (e.g., Torsades de Pointes)

Risk of progression to ventricular fibrillation (VF)

Question 9

What is ventricular fibrillation (VF)?

Answer 9

Chaotic electrical activity

No cardiac output → Cardiac arrest

Defibrillation required ASAP

Question 10

What is sinus tachycardia vs. bradycardia?

Answer 10

Sinus tachycardia: HR >100 bpm, normal P waves

Sinus bradycardia: HR <60 bpm, normal P waves

Causes: Exercise, fever, medications, autonomic tone changes

Question 11

What is sinus arrest?

Answer 11

Failure of SA node → transient pause in heartbeat

May cause syncope

Can require a pacemaker

Question 12

What is the difference between atrial and ventricular ectopic beats?

Answer 12

Atrial ectopics (PACs) → Premature P wave, narrow QRS

Ventricular ectopics (PVCs) → No P wave, wide QRS

Question 13

What is the prevalence of atrial fibrillation?

Answer 13

1-2% of the population

Increases with age, hypertension, heart disease

Question 14

How is atrial fibrillation treated?

Answer 14

🔹 Rate control (Beta-blockers, diltiazem, digoxin)
🔹 Rhythm control (Amiodarone, Flecainide, Cardioversion)
🔹 Anticoagulation (DOACs, Warfarin if CHADS-VASC >1)
🔹 Ablation therapy (for symptomatic or refractory AF)

Question 15

When is electrical cardioversion indicated in AF?

Answer 15

Haemodynamically unstable AF (emergency)

Persistent symptomatic AF despite rate control

If AF duration <48 hours (low clot risk)

If >48 hours, anticoagulation needed first

Question 16

Mnemonic for Types of Heart Block

Answer 16

🛑 “If the R is far from P, then you have a FIRST DEGREE”
🛑 “Longer, longer, longer, drop – then you have a WENCKEBACH”
🛑 “If some Ps don’t get through, then you have MOBITZ II”
🛑 “If Ps and Qs don’t agree, then you have a THIRD DEGREE”