Lecture 6.2 - Interpretation of ECG.pdf

ECG tracing: ◦The x-axis measure time (s) ‣ Small box = 0.04s ‣ Large box = 0.2s ‣ 5 large boxes = 1s ‣ 300 large boxes = 1 minute ◦The y-axis measures voltage (mV) ‣ Small box = 0.1mV ‣ Large box = 0.5mV Assessing the rhythm...

ECG tracing: ◦The x-axis measure time (s) ‣ Small box = 0.04s ‣ Large box = 0.2s ‣ 5 large boxes = 1s ‣ 300 large boxes = 1 minute ◦The y-axis measures voltage (mV) ‣ Small box = 0.1mV ‣ Large box = 0.5mV Assessing the rhythm and rate: ◦Normal sinus rhythm (constant heart rate): ‣ Heart rate between 60-100 bpm ‣ Assessed by presence of p-waves ‣ Every p wave is followed by QRS and vice versa ‣ R-R interval constant: regular rhythm (if not: irregular rhythm) ◦Determining heart rate: ‣ 300 method (if rhythm is regular) 300 large squares = 1 minute Count large squares (n) between consecutive P (atrial rate) or R (ventricular) wave 300 divided by n ‣ 6 times method (if rhythm is irregular) Obtain 10 second strip Count P (atrial) or R (ventricular) waves and multiply by 6 Wave characteristics: ◦p- wave: Less than 3 small boxes (0.12s) ◦PR interval: 3-5 small boxes (0.12-2s) ◦QRS complex: less than 3 small boxes (0.12s) ◦T wave: upright (T wave that is not upright could be caused by MI) ◦ST segment: isoelectric ◦QT interval: should be less than half of the preceding R-R interval Axis - the rotation of the heart in the frontal plane: ◦Normally between -30 to +90 degrees ◦Look for QRS being +ve or –ve in leads I, II and avF ◦+ve in lead I and aVF: Normal ◦–ve in lead I and +ve in aVF: Right axis deviation (RAD) - right ventricular hypertrophy ◦+ve in lead I and –ve in aVF: normal if lead II is +ve ◦+ve in lead I and –ve in aVF: LAD if lead II is –ve - left ventricular hypertrophy ◦-ve in lead I, II and avF: extreme axis deviation (EAD) - ventricular tachycardia, which can lead to ventricular fibrillation, and later death  ECG examples: