The heart has a natural pacemaker that regulates the rate of the heart, it is in the upper part of the atrium and is a collection of specialised electrical cells known as the sino atrial (SA) node it generates a number of sparks per minute each spark travels across the electrical pathway and stimulates the muscle wall of the four chambers of the heart.
The SA node fires each electrical impulses that travel through the right and left atrium, this electrical activity cause the two upper chambers of the heart to contract, this electrical activity can be recorded as a P wave on a ECG, the electrical impulse then moves to an area called the AS (artio-ventricular) node, this node is above the ventricles, the electrical impulse is held for a brief period, This delay allows the right and left atrium to continue emptying the blood into the two ventricles, this delay is recorded as a PR interval, the AV node acts as a relay station delaying stimulation of the ventricles long enough to allow the two atrium to empty after this delay. The electrical impulse travels through both ventricles ( via specialised electrical pathways known as left and right bundle branches). The electrically stimulated ventricles contract and blood is pumped into the pulmonary artery and aorta, the electrical activity is recorded as QRS, the ventricles then recover and the electrical stimulation generates an ST segment and T wave on the ECG.
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