• AF/flutter
  • AF: irregular without P waves
  • Atrial flutter: saw-tooth baseline (fluttering P waves) – may be regular with 2:1, 3:1 or 4:1 block, or irregular with variable block
• Supraventricular tachycardias
  • Atrial tachycardia: regular with abnormal P waves
  • AV nodal re-entry tachycardia/AV re-entry tachycardia: regular, usually without discernible P waves
• VT: regular, organised wavy line (broad complex tachycardia is VT until proven otherwise) – MAY BE PULSED VT OR PULSELESS VT
• Polymorphic VT (Torsades de pointes): VT with varying amplitude
• VF: random wavy line with no discernible P waves or QRS complexes – NO PULSE!
• Asystole: flat line – NO PULSE!
• Atrial ectopic: narrow QRS ± preceding abnormal P wave (resets the P wave cycle)
• Ventricular ectopic: abnormal broad QRS at abnormal time (usually followed by compensatory pause)
• Ventricular bigeminy (regular ventricular ectopics): abnormal premature ventricular complexes after every normal complex

• Infarction: ST-elevation (first change), T wave inversion, pathological Q waves (signify full thickness MI and develop 8-12 hours after ST-elevation if myocardium is not reperfused)
• STEMI criteria: ST-elevation in >2 small squares in 2 adjacent chest leads or ST-elevation > 1 small square in 2 adjacent limb leads or new LBBB
• Ischemia: ST-depression, new T wave inversion
• Posterior (wall of LV) infarction: dominant R wave in V1/2 with horizontal ST-depression V1-3.
• Previous infarcts: T wave inversion (persists weeks to months), pathological Q waves (permanent)

• Left ventricular hypertrophy: left axis deviation, dominant S wave in V1, tall R wave (>5 big squares in V5/6), T wave inversion in lateral leads. Sokolow-Lyon voltage criteria: S depth in V1 + tallest R wave height in V5/6 = >7 big squares.
• Right ventricular hypertrophy: right axis deviation, dominant R wave in V1, dominant S wave in V5/6, T wave inversion in right/inferior chest leads (V1-3, II, III, aVF)

• Any of the three conduction paths after the bundle of His can become blocked
  • Right bundle branch → RBBB pattern
  • Anterior fascicle of left bundle branch (i.e. left anterior hemiblock) → marked left axis deviation
  • Posterior fascicle of left bundle branch (i.e. left posterior hemiblock; rare) → marked right axis deviation
• Bifascicular block is RBBB + left anterior/posterior hemiblock → RBBB + left/right axis deviation
• Trifascicular block is RBBB + left anterior
  • ‘Incomplete’ may be either of these patterns:
    • Fixed block of 2 fascicles + delayed conduction in remaining fascicle = bifascicular block + 1st/2nd degree heart block
    • Fixed block of 1 fascicle + intermittent failure of other 2 = RBBB + alternating left anterior/posterior hemiblock
  • ‘Complete’ → complete heart block (escape rhythm shows signs of bifascicular block)

NB: bifascicular block with 1st degree heart block is the most common pattern referred to as ‘trifascicular block’.

• Hyperkalaemia: wide flat P waves, wide bizarre QRS, tall tented T waves
• Hypokalaemia: prolonged PR, depressed ST, flattened/inverted T waves, prominent U wave
• Hypercalcaemia: short QT interval
• Hypocalcaemia: prolonged QT interval

• Wolff-Parkinson-White syndrome: slurred upstroke into the QRS complex (delta wave), short PR interval, QRS complexes may be slightly broad, dominant R wave in V1 (if accessory pathway is left-sided, i.e. type A)/dominant S wave in V1 (if accessory pathway is right-sided, i.e. type B)
• Hypertrophic cardiomyopathy: left ventricular hypertrophy signs + dramatic T wave inversion in lateral leads (maximal in V4 rather than V6)

• PE – possible changes: tachycardia, right axis deviation, RA enlargement (i.e. P pulmonale), RBBB, RV dilation (i.e. dominant R in V1), RV strain (i.e. T wave inversion in right chest and inferior leads). NB: the ‘classical’ S1Q3T3 pattern (prominent S wave in lead I, and Q wave and inverted T wave in lead III) is uncommon.
• Pericarditis: PR depression, saddle-shaped ST-elevation