Ventricular arrhythmias occur in the lower chambers of the heart, called the ventricles. Supraventricular arrhythmias occur in the area above the ventricles, usually in the upper chambers of the heart, called the atria. The irregular beats can either be too slow (bradycardia) or too fast (tachycardia).
Bradycardia
Bradycardia is a very slow heart rate of less than 60 beats per minute. It happens when the electrical impulse that signals the heart to contract is not formed in your heart’s natural pacemaker, the sinoatrial node (SA node), or is not sent to the heart’s lower chambers (the ventricles) through the proper channels.
Bradycardia most often affects elderly people, but it may affect even the very young. It may be caused by one of two sources: The central nervous system does not signal that the heart needs to pump more, or the SA node may be damaged. This damage might be related to heart disease, aging, inherited or congenital defects, or it might be caused by certain medicines—including those used to control arrhythmias and high blood pressure.
Tachycardia
Tachycardia is a very fast heart rate of more than 100 beats per minute. The many forms of tachycardia depend on where the fast heart rate begins. If it begins in the ventricles, it is called ventricular tachycardia. If it begins above the ventricles, it is called supraventricular tachycardia.
Ventricular Arrhythmias
Ventricular Tachycardia
Ventricular tachycardia is a condition in which the SA node no longer controls the beating of the ventricles. Instead, other areas along the lower electrical pathway take over the pacemaking role. Since the new signal does not move through your heart muscle along the regular route, the heart muscle does not beat normally. Your heartbeat quickens, and you feel as if your heart is “skipping beats.” This rhythm may cause severe shortness of breath, dizziness, or fainting (syncope).
Ventricular Fibrillation
The most serious arrhythmia is ventricular fibrillation, which is an uncontrolled, irregular beat. Instead of one misplaced beat from the ventricles, you may have several impulses that begin at the same time from different locations—all telling the heart to beat. The result is a much faster, chaotic heartbeat that sometimes reaches 300 beats a minute. This chaotic heartbeat means very little blood is pumped from the heart to the brain and body and can result in fainting. Medical attention is needed right away. If cardiopulmonary resuscitation (CPR) can be started, or if electrical energy is used to “shock” the heart back to a normal rhythm, then the heart may not be too damaged. About 220,000 deaths from heart attacks each year are thought to be caused by ventricular fibrillation. People who have heart disease or a history of heart attack have the highest risk of ventricular fibrillation.