The heart pumps blood, nutrients and oxygen throughout the body. The sinus node, a group of specialized cells in the top right chamber of the heart, generates electrical impulses that travel through the heart muscle causing it to contract. The sinus node helps to maintain a normal resting heart rate, defined as 60 to 100 beats per minute, according to MayoClinic.com. Abnormalities in cardiac rhythm, known as arrhythmia, occur when the heart beats too slowly or too quickly.
Supraventricular Tachycardia
Tachycardia is a condition of an increased heart rate. The term supraventricular indicates that the arrhythmia begins in the atria, the upper chambers of the heart. Those with supraventricular tachycardia experience a heart rate of greater than 150 beats per minute. The American Heart Association reports that supraventricular tachycardia is the most common type of arrhythmia in young adults.
Supraventricular tachycardia produces heart palpitations that feel like fluttering or a racing heart. Other symptoms include shortness of breath, chest pain, lightheadedness and dizziness. Episodes last from a few seconds to several hours, according to the American Heart Association Journal.
Atrial Tachycardia
Atrial tachycardia, also referred to as atrial fibrillation, occurs when the electrical impulses cause the atria to fibrillate, or flutter, contracting too fast and creating an irregular pattern. Atrial fibrillation affects more than 2 million people in the United States, according to the National Heart Lung and Blood Institute. This condition often occurs following surgery, which causes the atria to enlarge, or as a result of leaky valves between the atria and ventricle---lower heart chamber. Symptoms include dizziness, lightheadedness and fainting caused by a lack of blood flow, and therefore oxygen, to the brain.
Ventricular Tachycardia
Ventricular tachycardia originates in the lower chambers of the heart. Usually caused by heart disease, ventricular tachycardia is a serious condition that requires medical treatment, as described by the American Heart Association. The symptoms of lightheadedness, dizziness and fainting are often severe.
Sinus Node Dysfunction
Damage to the sinus node, such as from surgery, can cause it to function improperly resulting in a slow heart beat. A heart that beats too slowly cannot pump enough oxygenated blood to the vital organs including the brain. This causes the symptoms of dizziness and fainting. A sinus node dysfunction also inhibits the heart from increasing the heart rate during times of need, such as during exercise.
Atrioventricular Block
The electrical impulses travel from the sinus node in the right atria across the atrioventricular node, called the AV node, into the ventricle. If the AV node becomes damaged, the electrical signal may be partially or completely blocked, interrupting the electrical conduction and interfering with contractions resulting in an abnormal heart rhythm.
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