ECG—abnormalities Sinus tachycardia: Rate >100. Causes: Anaemia, anxiety, exercise, pain, ↑ T°, sepsis, hypovolaemia, heart failure, pulmonary embolism, pregnancy, thyrotoxicosis, beri beri, CO2 retention, autonomic neuropathy, sympathomimetics, eg caffeine, adrenaline, and nicotine (may produce abrupt changes in sinus rate, or other arrhythmia). Sinus bradycardia:Rate 0.04s wide and >2mm deep. Usually as sign of infarction, and may occur within a few hours of an acute MI. ST elevation: Normal variant (high take-off), acute MI, Prinzmetal’s angina, acute pericarditis (saddle- shaped), left ventricular aneurysm. ST depression: Normal variant (upward sloping), digoxin (downward sloping), ischaemic (horizontal): angina, acute posterior MI. T inversion: In V1–V3: normal (Blacks and children), right bundle branch block (RBBB), pulmonary embolism. In V2–V5: subendocardial MI, HCM, subarachnoid haemorrhage, lithium. In V4–V6 and aVL: ischaemia, LVH, associated with left bundle branch block (LBBB). NB: ST and T wave changes are often non-specific, and must be interpreted in the light of the clinical context. Myocardial infarction: Within hours, the T wave may become peaked and ST segments may begin to rise. Within 24h, 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 (V 1–4), anterolateral (V 4–6, I, aVL), posterior (tall R and ST↓ in V 1–2). ‘Non-Q wave infarcts’ (formerly called subendocardial infarcts) have ST and T changes without Q waves. 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 V 1 and V 2. 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 V 5–6 (reversed tick). In digoxin toxicity, any arrhythmia may 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.
Posted on: Sun, 28 Sep 2014 16:05:11 +0000
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