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Understanding EKGs. Vectors. A vector has direction A vector has magnitude Vectors can be added or summated. Vector A. Vector B. Resultant Vector. A + B. EKG 2. EKG 3. Normal Waves of the EKG. P wave – atrial depolarization T a wave – atrial repolarization
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Vectors • A vector has direction • A vector has magnitude • Vectors can be added or summated
Vector A Vector B Resultant Vector A + B
Normal Waves of the EKG • P wave – atrial depolarization • Ta wave – atrial repolarization • Q wave – initial negative deflection from ventricular depolarization • R wave – first positive deflection from ventricular depolarization • S wave – first negative deflection following the R
Normal Waves Con’td • R’ wave – second positive deflection • S’ wave – second negative deflection following R • T wave – ventricular repolarization
P Wave Characteristics • Duration is < 0.12 seconds • Amplitude is < 4 mm • Contour is normally gently rounded, not notched or peaked • Normally upright in I, II, aVF • Inverted in aVR
QRS Characteristics • Normal duration is < 0.11 seconds • Amplitude (R or S wave) is > 5 mm and < 30 mm • Dominantly positive in I, II, aVF • Dominantly negative in aVR
T Wave Characteristics • Same polarity as dominant wave of QRS • Positive in I, II, aVF • Inverted in aVR • Asymmetrical, ascending more slowly than descending
Segments and Intervals of the EKG • P-R Interval • From beginning of P to beginning of QRS • Measures time taken by impulse to travel from SA node to ventricular fibers • Normal duration 0.12-0.20 seconds • ST Segment • From end of QRS to beginning of T • Should be isoelectric (on baseline)