ECG

Theory of the method

ECG

Protocol for calculating the heart rate and measuring the electrical axis

Materials:

    • electrocardiogram
  • ruler, protractor, calculator

Procedure:

A. Calculate the wave duration and amplification according to the instrument calibration

    1. wave duration (on the horizontal axis)
  1. check the speed of paper on the ecg (standard value)
  2. calculate the time required for electrical signal to pass 1 mm
    1. wave amplitude (on the vertical axis)
  3. check the amplitude of the electric potential on the ecg (standard value)
  4. calculate the voltage corresponding to 1 mm

B. Calculate the heart rate (bpm)

  1. select a RR interval
  2. measure the R-R interval in mm
  3. calculate the corresponding time required for the electrical signal to pass the distance between 2 R waves
  4. calculate the frequency of a cardiac cycle
  5. calculate the heart rate (1 minute = 60 seconds)

C. Measure the electrical axis in the case of atria depolarization (P wave)

In order to analyze the electrical axis it is enough to measure two projections of the electrical vector on standard leads I and III

In order to calculate the electrical axis, please use hexagonal reference system

1. Calculate the projections of P wave on standard leads I and III (namely, measure the area of P wave which will appear similar to a triangle)

  • Measure the period of P wave on standard lead I = base of the triangle on 0X axis
  • Measure the amplitude of P wave on standard lead I = height of the triangle on 0Y axis
  • Calculate the area of the triangle of P wave on standard lead I = (b x h)/2; b = base of the triangle, h = height of the triangle
  • Known values: 1 mm horizontally = 0.04 s; 1 mm vertically = 100 μV
  • Repeat the calculation for the P wave on standard lead III

2. Measure the electrical axis for the atria depolarization using the hexagonal reference system

  • Draw the hexagonal reference system for standard lead I, II and III
  • Select an arbitrary unit for 1 μV s
  • Draw the areas of P wave/ P vectors on the hexagonal reference system, according to your calculations
  • Rise perpendicular lines from the top of the vectors, till they are intersecting each other
  • Draw the resultant P vector
    • Measure the angle between the P wave projection on standard lead I and resultant P vector, using a protractor

3. State one – two conclusions according to your results.