An arrhythmia is any type of irregular heartbeat. It may present itself as a skipped beat, a rapid or slow heart rate, or a continuous irregular heartbeat. Each year, millions of people are affected by arrhythmias, most of which can be treated and are not life-threatening. However, many arrhythmias can be very dangerous and contribute to approximately 500,000 deaths in the US each year. Early and appropriate diagnosis and treatment can help decrease the number of deaths from arrhythmias between 15 percent and 25 percent annually.
How does the heart beat?
The heart consists of four chambers, the right and left atria and the right and left ventricles. The heart beats, or contracts, because of electrical stimulation of heart muscle tissue. Electrical impulses originate in the sinus node (the heart's natural pacemaker), which is a group of special cells located in the high right atrium. The sinus node, in turn, sends the electrical signal throughout both atria to the atrioventricular (A-V) node. The A-V node transmits the signal to a group of fibers throughout the ventricles. Stimulation of muscle in the ventricle is ultimately what causes the familiar sensation of a heartbeat. A normal heart rate for an adult is between 60 beats and 100 beats per minute. In order for the heart to beat properly, the signal must follow an exact course throughout the heart.
When does an arrhythmia occur?
The heart's natural pacemaker (sinus node) usually determines the heart rate, however almost all other heart muscle is capable of assuming a pacemaker role (e.g., where the electrical impulse begins).
An arrhythmia can occur under several conditions: when a part of the heart other than the sinus node acts as the pacemaker, when the regular path for electrical conduction is altered, when the sinus node develops an abnormal rhythm, or when a patient develops heart block along the normal electrical pathway. Heart block usually occurs at the site of the atrioventricular node, prelcuding part or all of the impulse from traveling from the atria to the ventricles. The incidence of arrhythmias increases with age, occurring most frequently in middle-aged adults. People with a history of heart disease, blood chemistry imbalances, and some metabolic diseases are at a greater risk for the development of arrhythmias and their complications.