Arrhythmia is the term used for an irregularity or rapidity of the heartbeat or an abnormal heart rhythm. The patient experiences the sensation as stronger, more forceful, or rapid heartbeats, or skipping of beats; this sensation is commonly called palpitations. The sinus node, a very small group of specialized cells, is located in the upper right corner of the heart (see Fig. 1). The node is about 30 x 3 mm thick. Through its genetic code and the influx
and efflux of sodium and potassium into its cells, this natural pacemaker spontaneously fires infinitesimal elec¬trical discharges that are conducted through electric cable¬like bundles to the atria and ventricles causing the heart muscle to contract about 70 times a minute. The sinoatrial (SA) node’s spontaneous depolarization and repolarization provides a unique and miraculous automatic pacemaker stimulus that activates the atria and atrioventricular (AV) node, which conducts the activation current down the bundle branches to activate the ventricular muscle mass. Cardiac cells outside the SA node normally do not exhibit spontaneous depolarization. The SA discharge rate, usually 50–100 beats per minute, is under autonomic, neural, chemical, and hormonal influence. The rate slows or gets faster depending on the needs of the body. The sinus node is like a powerful generator and has complete control of the heart rate.

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