Bradycardia is a form of arrhythmia characterized by the abnormal slowing of the regular sinus rhythm below 50 beats per minutes (bpm), whereas the normal rate is between 60 and 80 bpm. It can also occur from the emerging of pauses in the heart action lasting from 2 to 2.5 seconds or longer. Bradycardia is not always considered a pathological abnormality of the heart rhythm. Sometimes a natural slowing of the heart rate can be observed in athletes and elderly people. But more often this condition accompanies various heart pathologies.
A slow heart rate can be normal and healthy, or it might signal a problem with the heart’s electrical system. A slow heart rate for some people does not cause any problems; in fact, it can be a sign of optimum fitness. Athletes and healthy young adults often have heart rates of less than 60 beats a minute.
In other people, it means that the heart's natural pacemaker isn't working right or that the electrical pathways of the heart are disrupted. In severe forms of bradycardia, the heart beats so slowly that it doesn't pump enough blood to meet the body's needs. This can cause symptoms and can be life-threatening.
Despite the causes, the mechanism of bradycardia is based on:
- The decreased automatism of the sinus node (impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm, or sick sinus syndrome. That means the disturbance of the sinus node ability to generate electric impulses over 60 bpm.
- The disturbance of the cardiac conduction system. The cardiac conduction system has electrical conductors through which the impulses generated by the sinus node goes to all of the cells in myocardium, which, in turn, causes contractions of the heart. When this system is disturbed, the heart loses its ability to conduct impulses, which prevents the commands to contract. Any factors that may lead to the sick sinus syndrome or heart conduction blockage, automatically provokes bradycardia.
Depending on the causes of bradycardia this condition is divided into:
- Physiological (or functional) bradycardia. This is when the heart rate decreases because of some physiological factors (while sleeping or resting).Thus, athletes, who are in great physical shape, may have a resting heart rate of less than 60 bpm;
- Pathological bradycardia. This type of bradycardia usually accompanies the development of various disorders such as heart attack, myocarditis, thrombosis of the vessels that supply the sinus node with blood, and scaring. Pathological bradycardia may be acute (For example, a heart attack) or chronic. Acute conditions disappear once the patient recovers, whereas chronic forms remain in seniors suffering from age-related heart disorders.