Tachycardia is a faster than normal heart rate caused by your heart producing rapid electrical signals. It can seriously disrupt normal heart function, causing stroke, sudden cardiac arrest or death.
Symptoms: dizziness, shortness of breath, lightheadedness, rapid pulse rate, palpitations, chest pain, fainting.
Bradycardia is a slower than normal heart rate. It is dangerous when the heart doesn't pump enough oxygen-rich blood to the brain and other organs. For some people, though, a slow resting heart rate is normal and not a health problem.
Symptoms: near-fainting or fainting, dizziness, weakness, fatigue, shortness of breath, chest pains, disturbed sleep, confusion or memory impairment, easily tiring during physical activity.
Atrial fibrillation is an irregular and often rapid heart rate resulting from the atria beating out of coordination with the ventricles. It may be caused by changes in the heart as a result of heart disease or high blood pressure. Episodes may be occasional or chronic.
Symptoms: palpitations, decreased blood pressure, shortness of breath, fatigue, weakness, confusion, lightheadedness, chest pain.
Atrial fibrillation isn't usually life-threatening but should be treated as a medical emergency because it can lead to complications, including stroke.
In ventricular fibrillation, your heart beats with rapid, erratic electrical impulses, causing the ventricles to stop pumping blood. Blood pressure plummets and fainting occurs. Your pulse and breathing may stop almost at once. Immediate medical attention is critical.
Symptoms may start approximately an hour before your heart goes into ventricular fibrillation and you faint. They include: chest pain, rapid heartbeat, dizziness, nausea, shortness of breath.
Brugada syndrome is a life-threatening inherited disease characterized by ventricular fibrillation. The abnormality can be detected with an electrocardiogram test. People with this disease may have recurrent fainting spells and may die within a few minutes of the attack if the heart is not reset. If someone in your family has Brugada syndrome, everyone else in the family should be screened.
For more information on arrhythmias visit Mayo Clinic, the National Library of Medicine or go to HealthKey.com's Heart Health page.