The SA node (SinoAtrial) node is the original point from which the heart receives its electrical impulse instructions. It is conducted from there through the AV (AtrioVentricular) node. The SA node is commonly called the heart's "pacemaker."
There is a conduction pathway through which the heart distributes the electrical signal throughout the cardiac muscle. That pathway is comprised of Purkinje fibers, and innervates throughout the entire heart, in all four chambers. As well, our nerve system (there are 10 cranial nerves) is an integral part of how and why the cardiac muscle's behavior is influenced by them. Further, our lifestyle and diets can influence our heart's behavior/activity.
For example, caffeine and lack of sleep can cause ectopic beats (electrical impulses originate outside the SA node). Remember, electrical stimulation of the cardiac muscle causes contraction and relaxation, also known as "beats."
While the heart may and can lose its primary point of impulse, it does have a secondary or "back-up" system, through which it may continue to receive the necessary impulses to produce circulation, yet at a significantly reduced and inefficient rate. However, those focal nodes produce an automaticity at a lower rate then the SA node, which automatically produces 60-100 beats per minute.
And, there is an entire array of problems/anomalies which the heart may suffer, including Ventricular Tachycardia, Right Bundle Branch Block, SupraVentricular Tachycardia, Atrial Flutter, Atrial Tachycardia, Wandering Atrial Pacemaker, IdioVentricular Rhythm, Accelerated Idioventricular Rhythm, Torsades de Pointes, First Degree Block, Second Degree Block Type I, Second Degree Block Type II, Complete Heart Block, Atrial Ectopic Beats, Sick Sinus Syndrome, Junctional Escape Rhythm, Ventricular Flutter, Sinus Bradycardia and Ventricular Premature Beat.
As with any electrical device, the heart can and does suffer any variety of problems and failures, including A-fib, or Atrial fibrillation. A-fib is the cessation of the atrium's ability to produce a coherent impulse which is able to be effectively transmitted to the ventricals.
Since the heart's pump or "beat" originates in the atria, the loss or "confusion" of the electrical impulse results in an effect in the ventricals, which are situated below the atrial chambers of the heart. The ventricals are affected mechanically because the atria are failing electromechanically.
The symptoms of afib can include a feeling of a "racing" heartbeat, including feelings of dread, worry, or other impending doom.
Regarding the question of whom has experienced afib, a pastor friend of mine was recently diagnosed with afib as a secondary result of another health condition. He underwent electrical cardioversion and is now healthy.
