Topic – Preparation of the patient for conduction ECG and spyrographic research Subject – Clinic

Index • Definition of ECG • Cardiac Conduction System• Reasons for Performing

ECG• Types of Leads ( 12, 15, 18

Leads)• Types of ECG (Stress ECG,

Continuous ECG• Important Clinical

Consideration• Preparation• Placement of electrodes• References

Electrocardiography  • the process of recording the electrical activity of the heart over a period

of time using electrodes placed on the skin. These electrodes detect the tiny electrical changes on the skin that arise from the heart muscle's electrophysiological pattern of depolarizing and repolarising during each heartbeat. It is a very commonly performed cardiology test.

• In a conventional 12-lead ECG, 10 electrodes are placed on the patient's limbs and on the surface of the chest. The overall magnitude of the heart's electrical potential is then measured from 12 different angles ("leads") and is recorded over a period of time (usually 10 seconds).

• In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle. The graph of voltage versus time produced by this non-invasive medical procedure is referred to as an electrocardiogram.

Theory Interpretation of the ECG is ultimately that of pattern recognition. In order to understand the patterns found, it is helpful to understand the theory of what ECGs represent. The theory is rooted in electromagnetic and boils down to the four following points:depolarization of the heart toward the positive electrode produces a positive deflectiondepolarization of the heart away from the positive electrode produces a negative deflectionrepolarisation of the heart toward the positive electrode produces a negative deflectionrepolarisation of the heart away from the positive electrode produces a positive deflectionThus, the overall direction of depolarization and repolarisation produces a vector that produces positive or negative deflection on the ECG depending on which lead it points to.

• For example, depolarizing from right to left would produce a positive deflection in lead I because the two vectors point in the same direction. In contrast, that same depolarization would produce minimal deflection in V1 and V2 because the vectors are perpendicular and this phenomenon is called isoelectric.

• Normal rhythm produces four entities — a P wave, a QRS complex, a T wave, and a U wave — that each have a fairly unique pattern.

• The P wave represents atrial depolarization.• The QRS complex represents ventricular depolarization.• The T wave represents ventricular repolarization.• The U wave represents papillary muscle repolarization.• However, the U wave is not typically seen and its absence

is generally ignored. Changes in the structure of the heart and its surroundings (including blood composition) change the patterns of these four entities.

• Finally, a full interpretation of the ECG should be performed in a methodical manner to avoid overlooking small details that may change the overall interpretation. This is similar to interpretation of radiological studies