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 an arrhythmia?

From time to time, everyone experiences a skipped heartbeat, palpitations, or other irregularities, most of which are not serious. Arrhythmias, or irregular heart rhythms, are disturbances in the normal beating pattern of the heart. An estimated two million Americans live with irregular heart rhythms, a condition that can grow progressively worse over time.

What are the types of arrhythmia?

Arrhythmias can cause the heart to beat too slowly or too rapidly, thereby interfering with the heart's ability to pump blood effectively.

Bradycardia is the term used to describe an abnormally slow heart rate of less than 60 beats per minute. Certain medications, pre-existing conditions such as congenital heart disease, or the degenerative process of aging can cause this condition. In some cases, slow heart rates are considered normal, for example, in a young athlete who is in peak physical condition. In fact, most people tolerate heart rates between 50 and 60 beats per minute without difficulty. A slow heart rate can be considered abnormal if it causes such problems as fainting, fatigue, and light-headedness.

Tachycardia is the term describing an abnormally rapid heart rate of more than 100 beats per minute. This condition can arise in the atria, ventricles, or in the area between the atria and ventricles.

Supraventricular Arrhythmias

An arrhythmia is defined by the area of the heart in which it occurs. Supraventricular (above the ventricles) arrhythmias occur mainly in the two upper chambers of the heart (atria). Atrial fibrillation – seen in many types of heart disease – may require lifetime treatment. Other supraventricular arrhythmias include AV nodal reentry tachycardia, atrial flutter, and Wolff-Parkinson-White (WPW) syndrome.

Ventricular Arrhythmias

The more serious abnormalities are called ventricular arrhythmias, which occur in the lower chambers (ventricles). One of the most serious ventricular arrhythmias is sustained ventricular tachycardia. This type of arrhythmia may be dangerous because the heart usually beats so rapidly that it does not have time to fill with blood. In addition, it may degenerate further into a totally disorganized electrical activity known as ventricular fibrillation, during which the heart's action is so disorganized that it quivers and does not contract, thus failing to pump blood.

How do arrhythmias occur?

In general, arrhythmias can occur:

• When a group of cells other than the sinus node starts beating rapidly, which can result in sustained tachycardia or rapid disorganized electrical activity.
• If an individual has an extra pathway for electrical conduction. This may cause the electrical impulse to follow a circular path, resulting in rapid heart rates. Variants of this circular pattern can occur in the atria, ventricles or between the chambers.
• When the normal impulse does not originate from the sinus node, or is blocked from traveling to the ventricles. This causes an abnormally slow heartbeat.

What are the symptoms of arrhythmia?

Symptoms of arrhythmias vary widely. In fact, some arrhythmias cause no symptoms at all. Many cardiac arrhythmias are temporary and benign, however, some may be life threatening and require treatment. Therefore, it is important to check with your physician if you experience recurrent symptoms or have questions about your heart rhythm. Symptoms associated with arrhythmia may include:

• Palpitations or feeling of skipped beats or fluttering
• Chest pain
• Shortness of breath
• Fainting
• Lightheadedness
• Dizziness
• Weakness or fatigue

How are arrhythmias treated?

When the arrhythmia causes symptoms, there are several different options for treatment. Your physician will choose an arrhythmia treatment based on the type of arrhythmia, the severity of symptoms being experienced, and the presence of other conditions (coronary disease, heart failure, etc.) that can affect the course of the treatment. Some treatments for arrhythmias include

Lifestyle Modification. Factors such as stress, caffeine, or alcohol can cause arrhythmias. The physician may recommend the elimination of caffeine, alcohol, or any other substances believed to be causing the problem.

Medication. There are various types of medications that may be used to treat arrhythmias. If the physician chooses to use medication, the decision of which medication to use will be determined by the type of arrhythmia, other conditions which may be present, and other medications already being taken by the patient.

Cardioversion. In this procedure, an electrical impulse is delivered to the heart through the chest to stop certain arrhythmias, such as atrial fibrillation or atrial flutter.

Ablation. This invasive procedure, performed in an electrophysiology laboratory, uses a catheter to treat the site of the arrhythmia with radiofrequency energy or freezing temperatures to disable it.

Pacemaker. A permanent pacemaker is a small device that is implanted under the skin just below the collarbone. This device sends electrical signals to start or regulate a slow heartbeat. Pacemakers are typically used for slow heart rhythms such as sinus bradycardia, sick sinus syndrome, or heart block.

Implantable Cardioverter Defibrillator. An implantable converter defibrillator (ICD) is a small device that is implanted under the skin, just below the collarbone. An ICD senses the rate of the heartbeat, and can deliver an electrical impulse to regulate a heart rate that is too fast. ICDs currently implanted can also function as pacemakers by delivering an electrical signal to regulate a heart rate that is too slow. ICDs are typically used for fast arrhythmias such as ventricular tachycardia or ventricular fibrillation.

Surgery. Surgical treatment for arrhythmias is usually done only when all other appropriate options have failed. Surgical ablation is a major surgical procedure requiring general anesthesia. Through surgical incisions, the site of the arrhythmia is located, then treated or removed in order to eliminate the arrhythmia.