Sinus bradycardia is a slowing of the heart rate below 60 beats per minute during one sinus impulse cycle, while the pulse is clear, rhythmic and stable. Sinus rhythm may disappear (arrest).
For there are about 150 different heart rhythm disturbances or arrhythmias, which can be classified as follows: * bradycardia - a decrease in heart rate to 60 beats/min or less;
* tachycardia – increase in heart rate more than 90; * blockades (intraventricular and intraatrial);
* extrasystoles - impulses from the focus of excitation located outside the sinus and atria; extrasystolic arrhythmia - frequent extrasystoles, often pushing apart the normal RR intervals, still ending in the sinus and atria.
Sinus rhythm disturbances most often occur in middle-aged children (12-16 years old) with adynamic conditions, emotional lability, Down syndrome (Trout syndrome), porphyria and some syndromes