What do ecg electrodes measure

The wave of depolarization moves across the atria, through the AV node, into the Bundle of HIS, down the Bundle Branches, and finally through the Purkinje fibers which conduct the electrical impulses throughout the ventricles.

The activity of the heart produces electrical potentials that can be measured on the surface of the skin. Using the galvanometer EKG machine , differences between electrical potentials at different sites of the body can be recorded. See illustration below:. In picture A above, the negative electrode is on the right arm and the positive electrode is on the left arm. This is lead I.

Lead I records electrical difference between the left and right arm electrodes. In picture B above, the negative electrode is on the right arm and the positive electrode is on the left leg left lower chest. This is lead II. Lead II records electrical differences between the left leg and right arm electrodes. In picture C, the negative electrode is on the left arm and the positive electrode is on the left leg left lower chest.

Picture C depicts lead III. Lead III records electrical difference between the left leg and the left arm electrodes. The other three frontal plane limb leads are called the augmented Vector leads. The Galvanometer EKG machine records potential differences and, therefore, the technique is Bipolar potential site A minus potential site B.

However, if the potential of B is zero the recorder records only the potential site A. As mentioned earlier, unipolar leads measure the electric impulses at only one point, instead of across two points, as the first three leads. With these V leads, the second site is so there is noneed to measure from two pointes, only one point is needed. The machine automatically makes the needed connection to measure the voltage from these areas. As the above illustrations point out, the six limb leads measure the electrical activity of the heart from the frontal plan.

The frontal plane only manes that the patient is in anatomical position and facing you. The six limb leads measure a copulate circle or degrees around the heart. They measure the electrical activity of the heart from every possible angle.

The reason for this is obvious. By measuring he heart from different angles, you will be able to pinpoint the location of any conduction deft in the heart.

If you refer to the previous illustration you will notice that degrees of the front of the heart are completely covered by the six limb leads. This six fontal plane leads placed across the heart form the hex axial reference system. This system is the means by which we communicate the location of the frontal plane axis. All the negative - degrees are on the superior surface of the hexaxial figure. In the future, you may wish to study in more detail the interpretation of the tracings made in each of these six leads.

These colors are not universal as two coloring standards exist for the ECG discussed below. These 3 leads monitor rhythm monitoring but doesn't reveal sufficient information on ST elevation activity. A 5-Lead ECG uses 4 limb leads and 1 chest lead.

ECG Strip Ease. Covidien Nellcor. Masimo SpO2. Philips EKG. Toco Transducers and Cables. If you need any help with your order, we're just a phone call away. Call us at Toggle main navigation. Account Cart. Additional notes on lead ECG Placement: The limb leads can also be placed on the upper arms and thighs. However, there should be uniformity in your placement.

For instance, do not attach an electrode on the right wrist and one on the left upper arm. For female patients, place leads V3-V6 under the left breast. Do not use nipples as reference points in placing electrodes for both men and women as nipple locations vary from one person to another.

Lead placement and patient positioning should be the same for subsequent ECGs on any individual patient. During the procedure, record any clinical signs e. Cardiac muscles are electrically charged at rest. The inside of the cell is negatively charged relative to the outside resting potential.

If the cardiac muscle cells are electrically stimulated, they depolarize the resting potential changes from negative to positive and contract. The electrical activity of a single cell can be registered as the action potential. As the electrical impulse spreads through the heart, the electrical field changes continually in size and direction.

The ECG is a graph of these electrical cardiac signals. The individual action potentials of the individual cardiomyocytes are averaged. The final result, which is shown on the ECG, is actually the average of billions of microscopic electrical signals. During the depolarization, sodium ions stream into the cell. Subsequently, the calcium ions stream into the cell. These calcium ions cause the actual muscular contraction. Finally the potassium ions stream out of the cell. During repolarization the ion concentration returns to its precontraction state.

On the ECG, an action potential wave coming toward the electrode is shown as a positive upwards signal. Here the ECG electrode is represented as an eye. The sinoatrial node SA node contains the fastest physiological pacemaker cells of the heart; therefore, they determine the heart rate.

First the atria depolarize and contract. After that the ventricles depolarize and contract. The electrical signal between the atria and the ventricles goes from the sinus node via the atria to the AV-node atrioventricular transition to the His bundle and subsequently to the right and left bundle branches, which end in a dense network of Purkinje fibers.

The depolarization of the heart results in an electrical force which has a direction and magnitude; an electrical vector. This vector changes every millisecond of the depolarization.

In the animation vectors for atrial depolarization, ventricular depolarization and ventricular repolarization are shown. The P wave is the result of the atrial depolarization. This depolarization starts in the SA sinoatrial node. The signal produced by pacemaker cells in the SA node is conducted to the right and left atria.

Normal atrial repolarization is not visible on the ECG but can be visible during atrial infarction and pericarditis. The QRS complex is the average of the depolarization waves of the inner endocardial and outer epicardial cardiomyocytes. As the endocardial cardiomyocytes depolarize slightly earlier than the outer layers, a typical QRS pattern occurs figure.

The T wave represents the repolarization of the ventricles. There is no cardiac muscle activity during the T wave.