Bradyarrhythmias

Sinus bradycardia

•    Causes: high vagal tone (athletes), hypothyroidism, hypothermia, beta-blockers

•    Usually asymptomatic; may cause dizziness, syncope if severe

Atrioventricular (AV) block

•    1st degree: PR >200 ms, all P waves conducted

•    2nd degree Mobitz I (Wenckebach): progressive PR prolongation → dropped beat

•    2nd degree Mobitz II: dropped beats without PR prolongation → higher risk of CHB

•    Complete heart block (CHB)

o    Atria and ventricles beat independently

o    Ventricular escape rhythm (regular, slow ~30–40 bpm)

o    Cannon "a" waves (atria contract against closed AV valve)

Atrial arrhythmias

Atrial fibrillation (AF)

•    ECG: irregularly irregular, no P waves, fibrillatory baseline

•    Risk factors: HTN, valvular disease (especially mitral), hyperthyroidism

•    Stroke risk: CHA₂DS₂-VASc score

•    Management:

o    Rate control (beta-blocker, diltiazem)

o    Rhythm control (if symptomatic, younger)

o    Anticoagulation per stroke risk

Atrial flutter

•    ECG: sawtooth flutter waves, atrial rate ~300; often 2:1 block → ~150 bpm

•    Management: rate control, anticoagulation, consider ablation (curative)

Ventricular arrhythmias

Ventricular tachycardia (VT)

•    Broad complex tachycardia (>120 ms)

•    Monomorphic (scar-related) vs polymorphic (torsades, ischaemia)

•    Haemodynamically unstable → immediate DC cardioversion

•    Antiarrhythmics: amiodarone, lidocaine

Ventricular fibrillation (VF)

•    Chaotic, no cardiac output → cardiac arrest

•    Immediate defibrillation (unsynchronised DC shock)

Long QT Syndrome

•    QTc >450 ms (men), >470 ms (women)

•    Causes:

o    Congenital (e.g., Romano-Ward)

o    Drugs: macrolides, quinolones, antipsychotics, amiodarone, sotalol

o    Electrolytes: low K⁺, Mg²⁺, Ca²⁺

•    Risk of torsades de pointes → polymorphic VT

Device therapy

Permanent pacemaker

•    Indications:

o    Symptomatic bradycardia

o    High-grade AV block (Mobitz II or CHB)

Implantable cardioverter-defibrillator (ICD)

•    Indications:

o    Secondary prevention (survivors of VT/VF arrest)

o    Primary prevention in severe LV dysfunction (EF ≤35%) with high arrhythmic risk

Cardiac resynchronisation therapy (CRT)

•    Biventricular pacing for heart failure

•    Indications:

o    LVEF ≤35%

o    QRS ≥120 ms (esp. LBBB morphology)

o    Symptomatic despite medical therapy

Extra Revision Pearls

•    Mobitz I clue → progressively lengthening PR, usually benign

•    Mobitz II clue → sudden drop without warning → pacemaker indicated

•    CHA₂DS₂-VASc ≥2 → anticoagulate (AF)

•    Broad complex tachycardia = VT until proven otherwise

•    Torsades clue → polymorphic VT with pause-dependent initiation

•    Cannon ‘a’ waves → CHB classic sign

•    AF in hyperthyroidism → always check TSH