Introduction

Origin of the Heart Beat and Electrocardiogram

Under physiological conditions, the sinoatrial (SA) node generates pacemaker impulses that spread to the right and left atria, converge on the atrioventricular (AV) node, and continue down the His bundle and bundle branches (right bundle branch or RBB and left bundle branch or LBB) to activate the ventricles.

Depolarization is followed by repolarization and the sequence of depolarization[activation-and-contraction[repolarization repeats itself to generate rhythmical heart beats. Under abnormal conditions, ectopic foci in the atria, the AV junction, and the ventricles can usurp pacing dominance from this node and generate ectopic beats.
The wave of depolarization and repolarization described above can be mapped on the body surface by sensing electrodes placed on the extremities and the chest wall. The resultant waveform traced on graph paper is called the electrocardiogram (ECG).

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