ECG abnormalities

Sinus tachycardia

• Rate >100
• Causes
• Anaemia
• Anxiety
• Exercise
• Pain
• Sepsis
• Hypovolaemia
• Heart failure
• Pulmonary embolism
• Pregnancy
• Thyrotoxicosis
• Beri beri
• CO2 retention
• Autonomic neuropathy
• Sympathomimetics e.g. caffeine, adrenaline, and nicotine

Sinus bradycardia

• Rate <60
• Causes
• Physical fitness
• Vasovagal attacks
• Sick sinus syndrome
• Acute MI (inferior most likely)
• Hypothyroidism
• Hypothermia
• Increased intracranial pressure
• Cholestasis
• Drugs e.g. Beta blockers, digoxin, amiodarone, verapamil

 AF

• Causes
• IHD
• Thyrotoxicosis
• Hypertension

1st and 2nd degree (Mobitz I/II) heart block

• Causes
• Normal variant
• Athletes
• Sick sinus syndrome
• IHD
• Acute carditis
• Drugs (digoxin, Beta-blockers)

3rd degree complete heart block

• Causes
• Idiopathic (fibrosis)
• Congenital
• IHD
• Aortic valve calcification
• Cardiac surgery/trauma
• Digoxin toxicity
• Infiltration (abscesses, granulomas, tumours, parasites)

Q waves

• Pathological Q waves are usually >0.04s wide and >2mm deep
• Causes
• Infarction
• Acute MI

ST elevation

• Causes
• Normal variant (high take-off)
• Acute MI
• Prinzmetal's angina
• Acute pericarditis (saddle-shaped)
• Left ventricular aneurysm

ST depression

• Causes
• Normal variant (upward sloping)
• Digoxin (downward sloping)
• Ischaemic (horizontal)
• Angina
• Acute posterior MI

T inversion

• V1-V3
• Normal (Blacks and children)
• Right bundle branch block (RBBB)
• Pulmonary embolism
• V2-V5
• Subendocardial MI
• HCM
• Subarachnoid haemorrhage
• Lithium
• V4-V6 and aVL
• Ischaemia
• LVH
• Left bundle branch block (LBBB)

Myocardial infarction

• Within hours, the T wave may become peaked and ST segments may begin to rise
• Within 24 hours, the T wave inverts, as ST segment elevation begins to resolve
• ST elevation rarely persists, unless a left ventricular aneurysm develops
• T wave inversion may or may not persist
• Within a few days, pathological Q waves begin to form
• Q waves usually persist, but may resolve in 10%
• The leads affected reflect the site of the infarct
• Inferior (II, III, aVF)
• Anteroseptal (V1-V4)
• Anterolateral (V4-V6, I, aVL)
• Posterior (V1-V2, tall R)
• Subendocardial (No Q waves, ST and T changes present)

Pulmonary embolism

• Sinus tachycardia is commonest
• There may be RAD, RBBB, right ventricular strain pattern (R-axis deviation, dominant R wave and T wave inversion/ST depression in V1 and V2, leads II, III and aVF may show similar changes)
• Rarely, the 'SIQIIITIII' pattern occurs: deep S waves in I, pathological Q waves in III, inverted T waves in III

Metabolic abnormalities

• 'Digoxin effect': ST depression and inverted T wave in V5-6 (reversed tick)
• In digoxin toxicity, ANY arrhythmia can occur (ventricular ectopics and nodal bradycardia are common)
• Hyperkalaemia: Tall, tented T wave, widened QRS, absent P waves, 'sine wave' appearance
• Hypokalaemia: Small T waves, prominent U waves
• Hypercalcaemia: Short QT interval
• Hypocalcaemia: Long QT interval, small T waves