The Heart's Electrical Sequence The synchronized electrical sequence of the heart is initiated by the SA node, the heart's natural pacemaker. The firing of the SA node sends out an electrical impulse via its neurons to the right atrium, left atrium, and AV node simultaneously. Since the right atrium is closer to the SA node, it depolarizes first, resulting in pumping action by the right atrium before the left atrium. At the AV node, the impulse is delayed to allow for the ventricles to fill up with blood. After the delay, the AV node sends the impulse to the Bundle of His and the Purkinje fibers. This triggers the contraction of the ventricles to send blood either to the lungs or out to the body. Component of the electrical sequence Association in the heart P Wave Firing of the SA node and depolarization of the atria. PR Interval Delay of the electrical impulse at the AV node and the depolarization of the atrium. QRS Complex Ventricular depolarization Q-wave = first negative deflection R-wave = first positive deflection S-wave = second negative deflecton ST Segment The beginning of ventricular repolarization. Should be isoelectric (flat at baseline). T Wave Ventricular repolarization. Electrocardiograms

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Electrocardiograms The electocardiogram or ECG is a major diagnostic tool for the assessment of the health of the heart. It is a measurement taken at the surface of the skin which reflects the electrical phenomena in the heart when the SA node triggers the electrical sequence that controls heart action. Vector Electrocardiograms	Index Bioelectricty
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Vector Electrocardiograms The electocardiograph or ECG is a major diagnostic tool for the assessment of the health of the heart.	Index Bioelectricty
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