Tachycardia - an increased heart rate
Tachycardia means an accelerated heart rate. Normal heart rate is usually between 60 and 90 beats per minutes. This means that with tachycardia, the heart rate is higher than 90 beats per minute. The sinoatrial (SA) node is responsible for the heart's function by spreading electrical impulses formed in specialized cells throughout the whole heart, in order to make the heart contract. The conduction of the impulses is ensured by the cardiac conduction system. The sinus node, and with it the heart rate, is influenced by the nervous system and certain hormones.
Causes of Tachycardia
A rapid heartbeat, tachycardia, can have a number of causes. The most common are accelerated impulse formation, impulse formation outside of the sinus node, or hormone regulation.
Accelerated Impulse Formation
If the sinus node is responsible for tachycardia by forming impulses too quickly, it is known as sinus tachycardia. The heart beats regularly, but faster than normal. This emerges during physical activity, when the body required more oxygen and nutrients and therefore blood needs to be pumped fasted in order to satisfy this need. The nervous system and released hormones support the sinus node in the heart and speed up the pumping of blood into the body. This reaction is caused by stress or excitement, when adrenaline is released. This type of tachycardia can also accompany an infection, fever or severe conditions such as hemorrhage, heart failure and shock.
Impulse Formation outside the Sinus Node
Under some circumstance, other areas in the heart form impulses causing the heart to contract. This is a dangerous condition causing an increased and irregular heart rate. There can be extra contractions in the atria and ventricles. This can be distinguished by:
- Atrial fibrillation, characterized by a chaotic electrical activity in the atria, which quiver as a result. The atria do not contract.
- Ventricular tachycardia, where there are extra contractions forming in the ventricular muscle or in the area of the conduction system.
- Ventricular fibrillation is a life-threatening condition. It is the chaotic arrangement of impulses which cause the ventricle to quiver instead of contract properly. This prevents blood from being expelled from the left ventricle into the body.
Another cause of sinus tachycardia are certain hormones. Tachycardia can accompany thyroid disorders. With hyperthyroidism, the thyroid is stimulated to function more intensively, causing an increased formation and release of thyroid hormones into the blood. These hormones influence the sinus node and if they are in excess, they cause tachycardia.
Risk Factors for Tachycardia
Risk factors for the development of tachycardia are stressful situations; where there is increased demand from the cells for oxygen and thus the heart must work faster. These do not only include sports, but stress, infection and injury as well. Tachycardia can also be caused by thyroid hormones during hyperthyroidism (increased thyroid activity). Tachycardia can occur with anemia, i.e. low iron. Other risk factors for tachycardia include heart diseases that damage the cells of the heart. These include myocardial infarction, inflammation of the myocardium, valve defects and heart failure.
Symptoms of Tachycardia
Sinus tachycardia does not cause heart diseases or other illnesses. It commonly occurs during physical stress, exercise or mental distress. On the other hand, tachycardia can accompany serious conditions and threaten the life of a patient. Tachycardia is manifested by an increased heart rate and the patient may feel heart palpitations, pressure on his or her chest and shortness of breath. The patient experiences dizziness, headaches and even a short loss of consciousness due to the lack of blood flow to the brain.
A diagnosis of tachycardia is based on a physical examination by a physician, who can detect an increased heart rate of more than 90 beats per minute. The doctor can confirm tachycardia by listening to the heart's function using a stethoscope. Last but not least, an electrocardiograph can be used for diagnosis as well. This is a painless examination where the electrical activity of the heart is monitored with the help of electrodes attached to the limbs and chest of the patient.
The treatment of tachycardia is primarily based on treating the underlying cause of this condition. In the event that tachycardia is caused by a type of arrhythmia, i.e. a disordered heart rhythm, antiarrhythmics must be administered. These are medications that interrupt the irregularity of the heart rate. If the medication is not effective, an electrical cardioversion is necessary. A cardioversion is a procedure where two electrodes coated with conductive gel are placed and an electric shock is applied, which returns the natural rhythm to the heart. If even this outpatient procedure is ineffective, a cardioverter – defibrillator needs to be implanted under the skin of the patient, which functions in the same way. If the cause of tachycardia is a thyroid disorder, it must be treated with the appropriate medications.
Preventing the development of an increased heart rate i.e. tachycardia, is done by regular participation in physical activity. The heart adapts to increased stress during exercise and ceases to react to "galloping" accelerations. It is recommended that one avoids stressful situations and sticks to a healthy, balanced life style; i.e. does no smoke and gets adequate rest and sleep. Fat intake should be limited and instead, intakes of fruits and vegetables should be increased. It is also important to schedule annual preventative exams with a physician. The exam can reveal heart disorders that could otherwise go unnoticed and can lead to sinus and ventricular tachycardia, followed by fibrillation.