1. Myocardial infarction ECG evolution: hyperacute T waves, ST elevation/depression, Q waves, T-wave inversion, reciprocal changes, infarct localisation.
2. Arrhythmias: sinus tachycardia/bradycardia, atrial fibrillation/flutter, SVT, ventricular tachycardia/fibrillation, ectopics.
3. Heart blocks: first-degree AV block, Mobitz I and II, complete heart block, bundle branch blocks.
4. Axis deviation: normal axis, left/right axis deviation, extreme axis, rapid determination using leads I and aVF.

1. Myocardial infarction ECG evolution: hyperacute T waves, ST elevation/depression, Q waves, T-wave inversion, reciprocal changes, infarct localisation.
2. Arrhythmias: sinus tachycardia/bradycardia, atrial fibrillation/flutter, SVT, ventricular tachycardia/fibrillation, ectopics.
3. Heart blocks: first-degree AV block, Mobitz I and II, complete heart block, bundle branch blocks.
4. Axis deviation: normal axis, left/right axis deviation, extreme axis, rapid determination using leads I and aVF.

1. MI ECG changes
2. Arrhythmias
3. Heart blocks
4. Axis deviation

Arrhythmia: ECG-focused revision

Quick ECG approach

1. Rate: slow (<60/min), normal, or fast (>100/min)?
2. Regularity: regular or irregular?
3. P waves: present, absent, abnormal, or unrelated to QRS?
4. QRS width: narrow (<120 ms) or wide (≥120 ms)?

1. Sinus arrhythmias

Sinus bradycardia

• Rate <60/min
• Normal P wave before every QRS, regular rhythm
• Causes: athletes, sleep, vagal stimulation, inferior MI, hypothyroidism, drugs such as beta-blockers, verapamil/diltiazem, digoxin.

Sinus tachycardia

• Rate >100/min, often 100 to 160/min
• Normal P before each QRS, regular rhythm
• Usually a response to another condition: fever, pain, dehydration, anemia, hypoxia, anxiety, sepsis, thyrotoxicosis.
• Treat the cause, not merely the ECG rate.

Sinus arrhythmia

• Normal P-QRS relationship but cyclic variation in R-R interval, commonly with respiration.
• Usually benign, especially in young people.

2. Premature beats

Premature atrial contraction (PAC)

• Early abnormal P wave, often followed by a normal narrow QRS.
• May reset the sinus node, causing a non-compensatory pause.
• Common and often benign.

Premature ventricular contraction (PVC)

• Early, broad and bizarre QRS complex.
• No preceding P wave.
• Usually followed by a full compensatory pause.
• Can be unifocal or multifocal. Frequent PVCs, couplets, syncope, structural heart disease, or ischemia require assessment.

3. Supraventricular tachyarrhythmias

Atrial fibrillation (AF)

• Irregularly irregular R-R intervals.
• No distinct P waves.
• Fine/coarse fibrillatory baseline.
• QRS usually narrow unless aberrancy or pre-excitation exists.

• Main risks: rapid ventricular rate, heart failure exacerbation, and atrial thromboembolism/stroke.
• Management principles: assess stability, control ventricular rate or restore rhythm when appropriate, and assess need for anticoagulation.

Atrial flutter

• Regular atrial activity with saw-tooth flutter waves, best seen in II, III, aVF, often V1.
• Atrial rate often about 300/min.
• With 2:1 AV conduction, ventricular rate is often close to 150/min.
• May be regular or variable if the AV block varies.

Paroxysmal SVT: AVNRT or AVRT

• Sudden-onset, regular, narrow-complex tachycardia, often 150 to 250/min.
• P waves are absent, hidden within QRS, or retrograde just after the QRS.
• AVNRT is due to a re-entry circuit around the AV node.
• AVRT uses an accessory pathway, such as in WPW syndrome.

• Sinus tachycardia generally has gradual onset/offset and identifiable sinus P waves.
• SVT typically starts and stops abruptly.

Atrial tachycardia

• Regular narrow-complex tachycardia.
• Abnormal P-wave morphology before QRS.
• May occur with digoxin toxicity, pulmonary disease, or structural heart disease.

Multifocal atrial tachycardia (MAT)

• Irregular rhythm.
• At least 3 different P-wave morphologies.
• Variable PR intervals.
• Rate >100/min.
• Classically associated with COPD/hypoxia.

4. Ventricular arrhythmias

Ventricular tachycardia (VT)

• Three or more consecutive ventricular beats at >100/min.
• Usually broad QRS tachycardia.
• May be monomorphic or polymorphic.
• AV dissociation, capture beats, or fusion beats strongly support VT.

• Monomorphic VT: same QRS shape beat-to-beat, often due to scar-related re-entry after MI.
• Polymorphic VT: changing QRS morphology/amplitude. Consider acute ischemia or prolonged QT.
• Torsades de pointes: a polymorphic VT with apparent “twisting” QRS complexes around the baseline, associated with QT prolongation.

Ventricular fibrillation (VF)

• Chaotic, irregular waveform.
• No recognizable P waves, QRS complexes, or T waves.
• No effective cardiac output.

Asystole

• Near-flat line with no organized electrical activity.
• Confirm in more than one lead and exclude loose leads.
• Non-shockable arrest rhythm: CPR, adrenaline/epinephrine per resuscitation protocol, and treatment of reversible causes.

5. Dangerous rhythm recognition

High-yield memory points

• Irregularly irregular with absent P waves = AF.
• Saw-tooth waves = atrial flutter.
• Regular narrow fast rhythm with hidden P waves = SVT.
• Three P-wave shapes + irregular rhythm = MAT.
• Wide-complex tachycardia = VT until proven otherwise.
• Twisting polymorphic VT + long QT = torsades de pointes.
• Chaotic line with no QRS = VF.
• Pulseless VT/VF are shockable. Asystole/PEA are not shockable.