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The Basics of EKG

The electrocardiogram (ECG or EKG) is a diagnostic tool that is used to assess the electrical and muscular functions of the heart. The heart is an electrical pump and the heart's electrical activity can be measured by electrodes placed on the skin. The electrocardiogram measures the rate and rhythm of the heartbeat, as well as provides indirect evidence of blood flow to the heart muscle.

The ECG is a non-invasive and simple test in which patches are placed on the skin and the electrical impulses that the heart generates are detected and recorded. Four patches are placed on the limbs; one is placed on each shoulder or upper arm and one on each leg. These are called the limb leads. Then six patches are placed on the chest wall beginning just to the right of the breast bone in the shape of a semi-circle ending near the left underarm. These are called the chest leads. All these patches are connected to an ECG machine that records the tracings and prints them on a paper. In a healthy heart the Sinoatrial (SA) node initiates an electrical impulse, which then moves to the left atrium and downward through the Atrioventricular (AV) junction. From there it splits into the right and left ventricles through bundle branches that end with the Purkinje fibers. These impulses triggers depolarization of the atria and then of the ventricles, resulting in a contraction of the muscle cells in their respective areas. The EKG displays, from left to right, a small upward peak, and this are called the P wave which indicates that the atria has received an impulse to contract. After the P wave, one sees a short straight line in the middle, after this there are angled lines, which dips downward first, then shoots up, then comes back, and finally reaches the middle. These are three waves, named R, S and Q, which combined together are referred to as the QRS complex. This indicates that the ventricles have received an impulse to contract. Soon after the QRS complex you will see another upward peak, usually larger than the P wave. This is the T wave. The P wave looks at the atria and the QRS complex looks at the ventricles and the T wave evaluates the recovery stage of the ventricles while they are refilling with blood. The time it takes for electricity to travel from the SA node to the AV node is measured by the PR interval. The interval measures electrical travel time through the ventricles and the QT interval measures how long it takes for the ventricles to recover and prepare to beat again.

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