Cardiac Arrhythmia

Cardiac arrhythmia (ā-rith ́mē -ā ; a = not, rhythmos = rhythm), also called dysrhythmia, is any abnormality in the rate, regularity, or sequence of the cardiac cycle. Several common arrhythmias have been described:

• Atrial flutter occurs when the atria attempt to beat at a rate of 200 to 400 times per minute, and as a consequence literally bombard the AV node with muscle impulses. Abnormal muscle impulses flow continuously through the atrial conduction system, thus stimulating the atrial musculature and AV node over and over. This condition may persist for years, and frequently degenerates into atrial fibrillation.
• Atrial fibrillation (fı¯-bri-lā ́shūn) differs from atrial flutter in that the muscle impulses are significantly more chaotic, leading to an irregular heart rate. The ventricles respond by increasing and decreasing contraction activities, which may lead to serious disturbances in the cardiac rhythm.
• Premature ventricular contractions (PVCs) often result from stress, stimulants such as caffeine, or sleep deprivation. They occur either singly or in rapid bursts due to abnormal impulses initiated within the AV node or the ventricular conduction system. All of us experience an occasional PVC, and they are not detrimental unless they occur in great numbers. Most PVCs go unnoticed, although occasionally one is perceived as the heart “skipping a beat” and then “jumping” in the chest.

A more serious arrhythmia is ventricular fibrillation, a rapid, repetitious movement of the ventricular muscle that replaces normal contraction. This is a life-threatening condition caused by scattered impulses originating at different times and places throughout the entire myocardium. Because the contractions of a heart in fibrillation are uncoordinated, the heart does not pump blood, and blood circulation stops. This cessation of cardiac activity is called cardiac arrest.
Fibrillation almost certainly results in death unless the normal rhythmic contractions of the heart are promptly restored. To restore normal heart contractions, medical personnel apply a strong electrical shock to the skin of the chest using paddle electrodes. The electrical current passes through the chest wall to completely and immediately depolarize the entire myocardium. This procedure is analogous to pushing the reset button on a computer—and as in rebooting the computer, the hope is that when the heart begins to function again, it will work as intended.


Source : human anatomy