At rest, your heart normally beats between 60 and 80 times a minute. Exercise, mental or emotional stress, and some illnesses can cause your heart rate to accelerate. A heart rate over 100 beats per minute is called tachycardia. A tachycardia can be a normal adaptation to certain conditions (for example exercise) or, can occur inappropriately, and is then called a tachyarrhythmia.

Warning: This information should not be used as a substitute to consultation from a physician.

Atrial fibrillation (AF) : In AF the electrical activity of the atria becomes very rapid and irregular, and the pumping action of the atria is lost. The rapid beating of the atria can also cause the ventricles to contract very rapidly and irregularly. This rapid beating of the ventricles can cause fatigue, lightheadedness, shortness of breath, or other manifestations of abnormal heart function.

 
AF is usually treated with medications that restore and maintain a normal rhythm, or, if that fails, that prevent the ventricles from beating too fast. Blood-thinning medicines are also usually given to prevent blood clots from forming in the left atrium, which can break off, migrate and cause strokes or other major complications.

 
Ventricular tachycardia (VT) : In VT, a rapid heart rhythm originates in the ventricles instead of the SA node. The heart pumps less blood with each beat and, since the rhythm usually starts very suddenly, the cardiac output suddenly falls, and less blood reaches your brain and other organs. Although it is occasionally well tolerated, most patients feel quite ill, become lightheaded, faint, or lose consciousness. For most patients, VT is dangerous if not properly treated, particularly because it may cause loss of consciousness or evolve toward ventricular fibrillation.

Ventricular fibrillation (VF) : In VF, the electrical activity of the ventricles is very rapid and disorganized. Little or no blood is pumped, and, unless VF is rapidly terminated, it is invariably fatal. This type of event is also called a cardiac arrest. Loss of consciousness occurs within a few seconds of onset of VF, which rarely stops spontaneously. The only means to restore a normal rhythm is by the delivery of an electric shock, known as defibrillation. This can be given by doctors or emergency medical personnel using paddles held on the outside of the chest (external defibrillation), or automatically by an implanted device called a cardioverter defibrillator (ICD). VT and VF have several causes, the most common of which are 1) scarring of the heart muscle due to a previous heart attack, and 2) occlusion of a coronary artery causing the death (and later scarring) of a part of the heart muscle. This is also known as a myocardial infarction or a “heart attack”. A cardiac arrest is rarely preceded by prolonged warning signs or symptoms. In order to survive a cardiac arrest, an external or internal shock must be delivered within minutes (preferably within seconds) of the onset of VF.

When someone has suffered a cardiac arrest due to VT or VF, attempts will be made to treat the condition which caused it (for example prevent another heart attack by performing angioplasty or coronary bypass surgery). If, despite treatment, the patient remains at high risk of another cardiac arrest or of recurrent VT, the implantation of an ICD is usually recommended. At first sign of VF or VT, the ICD paces or shocks the heart back to a normal rhythm.

Warning: This information should not be used as a substitute to consultation from a physician