HMB 381
Standard operating procedure for ECG - SOP 11
Risk Assessment of standard ECG trace
As the procedure only involves placing electrodes on the surface of the subjects skin, the risk to the tester and subject is minimal. The only discomfort to the subject may occur if the skin is abraded or shaved prior to placement of the electrodes. If shaved the razors have to be placed in a yellow sharps containers for disposal and the sand paper and used electrodes in the biohazard bag.
The ECG equipment must be tagged and tested on an annual basis.
The Measurement of Heart Rate by ECG
Introduction
The electrocardiogram (ECG) depicts the pattern of electrical activity across the myocardium recorded by an electrocardiograph. As the wave of depolarisation travels throughout the heart, electrical currents spread through the highly conductive body fluids for monitoring by electrodes placed on the skin’s surface. Standard markings on the ECG paper allow time interval and voltage measurements during ECG propagation.
Preparation of the Subject
The following three electrode sites are recommended:
1. The negative (or Right Arm; white) electrode is placed just beneath the sternal notch in the midclavicular line, right side.
2. The positive (or Left Arm; black) electrode is placed in the fifth inter-costal space, midclavicular line, left side.
3. The earth (or Right Leg; green) electrode is placed just beneath the sternal notch in the midclavicular line, left side.
Standard ECG Tracing
Figure A shows the standard R-R method. The R-R interval dictates the time between successive R waves. An approximate heart rate in beats per minute (bpm) can be determined by dividing 1500 (60 s x 25 mm/s) by the number of mm between adjacent R waves. In the example, heart rate equals 125 bpm, since 12 mm occurs between two successive R waves.
Another method (Figure C), often used with irregular heart rates, counts the number of complete R-R intervals in a 6-second ECG strip multiplied by 10. In this example, six complete R-to-R intervals occur in six seconds; this equals a heart rate of 60 bpm (6 x 10 = 60).
Recording the ECG
Make sure the subject's cable is connected to the machine. The cable connects on the left hand side. Double-check the following:
1. Paper speed set at 25 mm/sec
2. Filters are on
3. Amplitude or sensitivity set at 1cm/mV
4. Lead 1 has been selected.
If the machine has been stopped (i.e. "START" button light is not glowing) no response will be noticed. Turn the "RESET" switch off and the pen should move in time with the subject's heartbeat. To obtain a trace press the "START" button.
Let the paper run and obtain at least 10 ECG complexes. (You need at least seven to derive heart rate.)