ARRHYTHMIAS or Irregular Heart Beats

Arrhythmias (also called dysrhythmias) are irregular heartbeats caused by damage to part of the conduction pathway, or by an ectopic focus, which is a beat generated in part of the myocardium other than the SA node.
Flutter is a very rapid but fairly regular heartbeat. In atrial flutter, the atria may contract up to 300 times per minute. Because atrial pumping is not crucial, however, blood flow to the ventricles may be maintained for a time, and flutter may not be immediately life-threatening. Ventricular flutter
is usually only a brief transition between ventricular tachycardia and fibrillation.

Fibrillation is very rapid and uncoordinated contractions. Ventricular fibrillation is a medical
emergency that must be quickly corrected to prevent death. Normal contraction of the ventricles is necessary to pump blood into the arteries, but fibrillating ventricles are not pumping, and cardiac
output decreases sharply.
Ventricular fibrillation may follow a non-fatal heart attack (myocardial infarction). Damaged cardiac muscle cells may not be able to maintain a normal state of polarization, and they depolarize spontaneously and rapidly. From this ectopic focus, impulses spread to other parts of the ventricular myocardium in a rapid and haphazard pattern, and the ventricles quiver rather than contract as a unit.

It is often possible to correct ventricular fibrillation with the use of an electrical defibrillator. This instrument delivers an electric shock to the heart, which causes the entire myocardium to depolarize and contract, then relax. If the first part of the heart to recover is the SA node (which usually has the most rapid rate of contraction), a normal heartbeat may be restored.