How does a normal heart beat?

The heart is a hollow muscular organ – approximately the size of your clenched fist – that beats 40 million times per year (between 60 and 100 beats per minute). The heart's pumping action is controlled by its electrical system, which gives rise to the heart rhythm.

Normal cardiac rhythm results from electrical impulses that begin in a special group of cells that form the sinoatrial (SA) node, also called the sinus node. Located in the right upper chamber of the heart, sinus node cells act as the heart's natural pacemaker. Impulses spread from the sinus node to the right and left atria (the upper chambers of the heart), causing them to contract at the same time. The impulses then travel to the AV (atrioventricular) node, the region that manages impulse traffic from the atria to the ventricles (the lower chambers of the heart). Here, impulses are slowed slightly to give the atria time to contract before the signal reaches the ventricles. From the AV node, the impulses travel through a system of specialized heart tissue. Located in the wall that separates the two ventricles, this conducting system splits to form the right and left bundle branches that travel to the respective ventricles. Via this conducting pathway, powerful electrical "jump-start" signals are delivered to the ventricular muscle of the heart. In the healthy heart, these impulses travel at the same speed so that the two ventricles contract at the same time, and oxygen-rich blood from the lungs is pumped throughout the body.

What is Ventricular tachycardia?

Ventricular tachycardia is a rapid, regular heart rhythm that originates in the lower chambers of the heart. Ventricular fibrillation is an abnormal heart rhythm that is disorganized and irregular.

Causes

These conditions occur most commonly in people who have damaged heart muscle or coronary artery disease (blockages in the arteries that supply the heart). In the US, the most common cause of damage to the heart muscle is heart attack. Other potential causes include valve disease or cardiomyopathy. Less commonly, some patients can develop ventricular tachycardia or fibrillation due to electrical abnormalities in a structurally normal heart.

Regardless of the cause, the end result is the same.

What are the symptoms of ventricular fibrillation and ventricular tachycardia?

These include fainting without warning and even sudden death. In the cases of ventricular tachycardia, sometimes patients feel palpitations, chest pain, shortness of breath, or sweating.

What are the risks of ventricular fibrillation and ventricular tachycardia?

Both ventricular tachycardia and ventricular fibrillation are usually life-threatening arrhythmias. Rapid heart rates of the lower heart chambers prevent them from having adequate time to fill with blood. As a result, the heart does not pump effectively; the heart muscle, brain, and other parts of the body do not get adequate blood supply, which can result in fainting and even loss of life. Some patients with a structurally normal heart can have a more benign form of ventricular tachycardia.

How are ventricular fibrillation and ventricular tachycardia diagnosed?

Tests to determine those at risk for ventricular tachycardia or fibrillation include:

• Echocardiogram
• Stress test
• Holter monitoring
• T-wave alternans testing
• Cardiac electrophysiology study

How are ventricular fibrillation and ventricular tachycardia treated?

The implantable cardioverter defibrillator (ICD) has proven to be extremely effective in detecting and terminating ventricular tachycardia and fibrillation. This electronic device, which is usually implanted under the skin just below the collarbone, monitors heart rhythm constantly. The ICD has the ability to detect ventricular tachycardia and fibrillation and can deliver an electrical impulse to regulate a heart rhythm that is too fast. ICDs implanted today also function as pacemakers that can prevent the heart from beating too slowly.

In patients with heart disease, medications alone are less effective in the treatment of these types of arrhythmia.

Catheter ablation is occasionally used in conjunction with ICDs in patients who experience multiple episodes of ventricular tachycardia.