Tachycardia is a condition in which the heart beats abnormally fast--more than 100 beats per minute. It is caused by abnormal electrical impulses sent from just above the lower chambers of the heart--called supraventricular tachycardia--or from the ventricles--called ventricular tachycardia. While in many cases the cause is unknown, tachycardia may be caused by cardiovascular disease, stimulants, certain medications or other underlying medical conditions.
Cardiovascular Problems
A number of problems related to the heart and circulation of blood can lead to tachycardia.
Genetic heart defects, abnormalities in individual heart cells, chronic high blood pressure, structural abnormalities in the heart's valves, dysfunction of the sinus node which normally serves as a natural pacemaker for the heart, heart muscle damage called cardiomyopathy, heart disease and atherosclerosis--a thickening of artery walls caused by a buildup of fat and cholesterol--may all cause rapid heart rate, according to the Mayo Clinic.
Stimulants
Substances that stimulate the nervous system can lead to an abnormally fast heart rate. According to the Mayo Clinic, tobacco, alcohol, caffeine and illicit drugs such as cocaine may all cause tachycardia.
Even changes in posture--such as moving from a sitting to a standing position--exercise or emotional excitement can stimulate the heart to beat abnormally fast, usually for a brief period of time before returning to normal, according to the American Heart Association.
Medications
According to the American Heart Association, some people may have adverse reactions to medications used to control certain heart conditions. For example, digitalis and digitoxin are drugs commonly used to treat congestive heart failure and abnormal heart rhythms that may cause toxic reactions that lead to tachycardia in some people. Sympathomimetic amines--medications such as epinephrine, norepinephrine and dopamine used to stimulate the nervous system in those who have suffered a heart attack or who have low blood pressure--may also cause tachycardia.
Electrical Impulse Problems
Tachycardia is caused by abnormal electrical impulses stimulating the heart to beat too rapidly. According to the Mayo Clinic, these problems may be congenital, or present at birth. Abnormal electrical pathways caused by a genetic defect can cause intermittent tachycardia from a young age. Electrolyte imbalances in the body, including too much or too little of potassium, calcium, sodium and other minerals necessary for proper conduction of electrical impulses of the heart, may also cause tachycardia.
Health Conditions
A number of underlying medical conditions can cause tachycardia. According to the Mayo Clinic, overproduction of thyroid hormone associated with hyperthyroidism, emphysema and other lung diseases can all cause abnormally rapid heart rate.
According to the American Heart Association, sarcoidosis--a disease in which clumps of inflammatory cells form in any number of the body's organs, including the lungs, eyes or lymph nodes--can also interfere with normal electrical conduction of the heart.
