<prompt> Einthovens law -I III III -IIIIIIIIIII 0IIIIavL  <response>: Ans is a i.e., I III II o Einthovens triangle is an equilateral triangle formed by two shoulder and the pubis with the heart is in the center as moving dipole.o For convenience Eithovens triangle consider right arm RA, left arm LA, and Left leg LLQ to which electrodes are connected.o An electrode connected to all the three comers of Eithovens triangle will always be at zero potentials regardless of the direction of the cardiac vector.o Such an electrode is called the indifferent electrode or the central terminal of wiisonQ.o The indifferent electrode is connected to RA, LA and LL through high 5000 Ohm resistance.ECG Leadso An ECG is recorded by picking up potentials from two parts of the body. The two sites selected for this purpose constitue the ECG leads. Usually ECG is recoreded by 12 leads 12 lead ECG: - Three bipolar standard limb leads, three Unipolar limb leads and six unipolar chest leads.Bipolar standard limb leads or Einthovens leado Bipolar recording involves recording of potential difference between two different sites on the body using two electrodes, one serving as the reference and the other called the exploring or active electrode. These leads are:-Lead I: - Between right arm negativereference electrode and left arm positive or active or exploring electrode.LeadII: - Between right arm negative or reference electrode and left leg positive electrode.Lead III: - Between left arm negative electrode and left leg positive electrode.o The direction in wrhich positive electrode points is called the axis of lead. If the direction of the lead axis is similar to the direction of the flow of current in the heart, the recorded deflection is positive upward. Hence electrodes are arranged in such a way that most of the deflections in the ECG are positive,o Einthovens law Q: - This law states that if the electrical potential of any of the three bipolar limb leads are known at any given instant, the third one can be determined mathematically by simply summing the first two but note that the positive and negative signs of different leads must be observed when making this summation. Thus the sum of the voltages in leads I and III equals the voltage in lead IIQ.Unipolar limb leadso Unipolar recording involves recording the potential difference between an active electrode and an indifference electrode. Thus, unipolar limb leads and chest leads employ an active electrode and an indifference electrode. The indifferent electrode is connected to left arm, right arm and left leg through a very high resistance has been explained. Because of the high resistance, the indifferent electrode stays at an almost constant zero potential. Since the leads measure the potential difference between two electrodes, one of which is at constant voltage indifferent, it essentially measures the potential at the other active electrode. There are three unipolar limb leads:-o VR : Between right arm and an indifferent electrode,o VL : Between left arm and an indifferent electrode,o VF: Between left leg and an indifferent electrode.o These unipolar limb leads are not much used in practice because augmented limb leads which provide a magnified version of the same information; therefore, unipolar augmented limb leads are used. Augmented limb leads are recordings between one limb and two other limbs12, i.e., the positive active electrode is connected to one limb and the negative electrode to the other two through high resistances. This results in an increase in the voltages recorded in the ECG That is why these leads are called augmented limb leads. There are three augmented limb leads: -aVR : - Between right arm positive electrode and left arm left leg negative or refrence electrode.aVL : - Between left arm positive electrode and right arm Left leg negative electrode.aVF : - Between left leg positive electrode and right arm left arm negative electrode.Unipolar chest leadsQo These leads emply an exploring active or positive electrode on the chest and an indifferent reference or negative electrode. The indifferent electrode is connected to the right arm, left arm and left leg through high resistances. The position of chest electrode positive electrode is as follows VI - V6Q: -V1: In the right 4th intercostal space at the right border of the sternum.V2: In the left 4th intercostal space at the left border of sternum.V3: At midpoint between V2 and V4.V4: In the left 5th intercostal space in the midclavicuiar line.V5: In the left 5th intercostal space at the anterior axillary line.V6: In the left 5th intercostal space at the mid-axillary line. 