ECG (EKG) Electrocardiogram This PowerPoint is set up as a self-tutorial. View on full-screen mode.

The ECG (EKG) A surface measurement in milliVolts on outside of cells, not an intracellular recording. Transmitted through body fluids from heart muscle to skin. Measures only electrical activity of the heart. electro = energy cardio = heart gram = to write

Watch both the electrical and mechanical events in this animation…

- + Ground electrode Measure the Electrode Difference: Recording Electrode minus Reference Electrode reference recordingI right arm and left arm

- + Ground electrode reference recordingII Measure the Electrode Difference: Recording Electrode minus Reference Electrode Right arm and left leg. Note the angle across the heart!

- + Ground electrode reference recordingIII Measure the Electrode Difference: Recording Electrode minus Reference Electrode Left arm and left leg.

- +isopotential - + Lead I: electrodes right arm = reference left arm = recording The remaining slides just focus on Lead I (note the I in the corner), but the principles can be applied to all of the leads. The machine notes that at rest both the right and left sides of the heart are positively charged. Since we use “recording minus reference” to create the ECG, a positive value minus an equally positive value is “zero”. These values are plotted directly on the line and are referred to as an isopotential wave.

- + P wave + - Lead I: SA depolarization As the SA node depolarizes, the area around it (the reference point) becomes negatively charged as does the interventricular septum and Bundle of His and Purkinji fibers. The left side is still positively charged relative to the right. Positive values minus negative values equals a series of positive values, creating the positive P wave.

isopotential Lead I: atrial depolarization and AV delay As the depolarization moves across the atria, both electrodes record negative values. Negative values minus equally negative values creates an isopotential wave.

Q wave Lead I: septal depolarization As the wave moves down the septum, the left ventricle is more negative relative to the right ventricle due to its larger mass. Negative values on the left minus positive values on the right creates the negative Q wave.

Lead I: ventricular depolarization As depolarization continues up and around the ventricles, the left side of the heart has a larger mass, the more positive values on the left minus negative values on the right creates the large positive R wave.

Lead I: full ventricular depolarization and… atrial repolarization Atrial repolarization is occurring, but is masked by the greater amount of ventricular electrical activity. As the ventricles fully depolarize, the relatively more negative values on the left minus more positive values on the right create the negative S wave.

Lead I: Depolarization is equally distributed across the heart, creating an isopotential wave. isopotential

Lead I: ventricular repolarization Repolarization occurs from the epicardium to myocardium and then endocardium. Because of the larger left ventricle’s mass, the relatively more positive values on the left minus more negative values on the right creates the positive T wave.

The average values of Lead 1 relative to the left leg produce the aVF, or augmented vector foot, lead values. -

average - The average values of Lead 2 relative to the left arm produce the aVL, or augmented vector left, lead values.

average - The average values of Lead 3 relative to the right arm produce the aVR, or augmented vector right, lead values.

The QRS axis, or Mean Electrical Ventricular Axis, can be plotted using values gained from the ECG. Follow the directions in the manual to calculate your QRS axis.

Values that fall in the “left” range can indicate left ventricle hypertrophy, pregnancy, etc. “Right” values can be associated with right ventricle hypertrophy, pulmonary issues, etc. DO NOT make rash conclusions when analyzing your QRS axis!! The QRS axis tells us the general direction of depolarization, giving us an idea of the orientation of the heart in the chest as well as the general health of the tissue. “Normal” is generally -30 o to +100 o.