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 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)