Tachycardia is characterized by a faster than normal heart rate. A healthy adult heart normally beats 60 to 80 times a minute when a person is at rest. With tachycardia (tak-ih-KAHR-de-uh), the rate in the upper chambers or lower chambers of the heart, or both, are increased significantly and heart rate is more than 100 times a minute.
The main mechanism of tachycardia is the increase of the sinoatrial node automatism; this node normally sets the normal heart rhythm, playing the role of a pacemaker.
Depending on the causes of the increased heart rate there are two types of tachycardia:
- Physiological tachycardia – usually develops in healthy patients with normal cardiac performance. If a person feels his heart beat becoming more frequent and increasing, it is not always evidence of heart problems. Even in healthy people, tachycardia may result from the action of the physiological compensatory mechanisms in response to Adrenaline release and activation of the sympathetic nervous system due to external factors (stress, physical activity, emotional excitement, increased air temperature, use of certain drugs, strong tea, coffee or alcohol, or sudden change in body position). When the irritating factor disappears, the heart rate gradually returns to its normal value. Also, physiological tachycardia is a normal state for children and pregnant women.
- Pathologic tachycardia – the heart rate increases when a person is at rest. It should be noted that pathologic tachycardia is a symptom rather than a separate disease because it appears as evidence of various disorders. This condition may be quite dangerous as it causes the reduction in the amount of blood released and a number of various intra-cardiac hemodynamic disorders. The increased heart beat rate is accompanied by the decrease in ventricle blood filling leading to the reduced cardiac output and blood pressure, poor blood supply to all organs (including heart) and tissues as well as development of oxygen starvation. Long periods of tachycardia significantly lower the effectiveness of cardiac performance disturbing myocardial contractility, which causes the increase in the atria and ventricles volume and progression of arrhythmogenic cardiomyopathy. All these are the risk factors of coronary heart disease, angina and myocardial infarction
Depending on the source where the electrical impulses are generated they distinguish:
- Sinus tachycardia. It arises when there is an increased activity of the sinoatrial node. The characteristic feature of this tachycardia is that it starts gradually, the heart rate increases up to 120 and it shows regular sinus rhythm;
- Paroxysmal tachycardia. The pacemaker is located outside the sinoatrial node – in atria or ventricles. Usually it progresses as a rapid heart action that starts as well as stops abruptly (in paroxysms). Such paroxysms may last from several minutes and up to several days together with constantly rapid heartbeat.
Paroxysmal tachycardia is divided into three main types:
- Atrial tachycardia – electrical impulse comes from the ectopic atrial pacemaker rather than the sinoatrial node. It is characterized by a regular heart rate varying from 140 to 220 bpm;
- Junctional tachycardia – the impulse is generated in the junction of the atrium and ventricle, the atrioventricular node. The heart rate is between 100 and 140 bpm;
- Ventricular tachycardia – it develops in one of the heart ventricles, the heart rate is over 120 bpm. This is a potentially life-threatening condition and; thus, it requires immediate diagnosis and treatment.