The heart is a muscle that contracts in rhythmic sequence for the duration of our lifetime. Each beat is stimulated by an electrical signal that is generated by the heart's conduction system. A normal heart beats 60 to 100 times per minute. Sometimes, a problem with the conduction system causes the heart to beat too fast, too slow, or to have an erratic or irregular beat. A test, called an electrocardiogram, or EKG, can measure and record the heart's electrical activity.
In a normal heartbeat, the heart's signal follows a specific pathway through the heart. The signal begins in the sino-atrial node, or SA node, located in the right atrium. The SA node triggers the atria to contract, pushing blood into the ventricles. The electrical signal then travels through the atrio-ventricular node, or AV node, and into the ventricles. This signal now causes the ventricles to contract, pumping blood into the lungs and body.
If the signal becomes delayed or blocked, a condition called bradycardia can develop. Bradycardia, which is more commonly called sinus bradycardia, is a type of arrhythmia in which the heart beats fewer than 60 times a minute, an abnormally slow rate.
Most people with sinus bradycardia are asymptomatic. However, in many patients, bradycardia can produce symptoms such as dizziness, weakness, or fainting. These symptoms result from a decrease in the circulation of oxygen-rich blood to the body, especially due to the decrease in bloodflow to the brain. Bradycardia can also be the result of heart disease, or it may have no identifiable cause.
Treatment for bradycardia may include medication or, in severe cases, the insertion of a pacemaker to regulate heart rhythm.