Sinus bradycardia is the term for a heart rate of less than 60 beats/min and may be seen in the normal adult population. Sinus bradycardia during exercise, fever or heart failure is abnormal. Persistent rates of less than 45 beats/min are also considered abnormal, and in the absence of drugs such as digitalis, beta-blockers and calcium channel blockers, reflect abnormality in the sinus node, or pacemaker of the heart.
Sinus bradycardia can be present in otherwise normal individuals and is common in well-trained athletes and in most people during deep sleep. Sinus bradycardia may also be related to metabolic abnormalities, including hypothermia (low body temperature) and myxedema. Sinus bradycardia also may occur as a manifestation of organic heart disease, including ischemic heart disease, particularly when the sinus node is damaged, as with certain types of heart attacks and in association with severe chest pain of acute heart attack. Sinus bradycardia may also be a complication of myocardial disease in which the sinus node is damaged by scarring or infiltrative processes associated with aging as part of a degenerative conduction system process.
Sinus bradycardia without symptoms requires no treatment. If sinus bradycardia is so extreme, however, that symptoms result, such as fainting, heart failure (HF), angina and hypertension, and/or if it leads to the development of extra ventricular beats, then it should be treated, and in some instances temporary and sometimes permanent ventricular pacing is necessary.