Sinus bradycardia (synonyms: sinus brachycardia; vagal bradycardia; ICD-10 R00.1: bradycardia, unspecified) is a failure to maintain the physiologic heart rate normal for the age of the patient. In adults, this is less than 40-60 beats per minute.
A generalizable threshold for relevant (sinus) bradycardia does not exist.
Sinus bradycardia is a cardiac arrhythmia that belongs to the group of pacing disorders. The reason for this is the slowing down of stimulus processing at the sinus node.
The sinus node (nodus sinuatrialis; synonyms: sinuatrial node (SA node) or Keith-Flack node) is the primary pacemaker center of the heart (= sinus rhythm). It is located in the area of the right heart ear near the suclus terminalis (depression running between the insertion of the superior and inferior vena cava).
At night, the heart rate drops and is between 45 and 55 beats per minute in many people.
Sinus bradycardia is considered physiological (without disease value) in young people as well as athletes.
To assess bradycardia, the performance of the heart must also be taken into account. For example, well-trained endurance athletes have nocturnal bradycardias of < 30-40 beats per minute (= “economization of cardiac work”), without symptoms. Cardiac patients already show symptoms of cerebral ischemia such as vertigo (dizziness) or syncope (brief unconsciousness):In the elderly (around 70 years of age), heart rates below 40 beats per minute are considered pathological, but do not require therapy as long as there are no bradycardia-related symptoms.
A sinus rhythm of 45 beats per minute should be considered atypical and in need of differential diagnosis.
The hallmark of pathological bradycardia is that the heart rate does not increase even under stress.
Pathologic (pathological) sinus bradycardia is seen in:
- Extracardiac genesis (development is independent of the heart) – e.g., hypothyroidism (hypothyroidism), hypothermia (hypothermia), vomiting, typhoid fever.
- Cardiac genesis – e.g. sick sinus syndrome (sick sinus node / the sinus node is called the body’s own pacemaker)).
Sinus bradycardia can be a symptom of many conditions (see under “Differential Diagnoses”). Note: Hyperkalemia (excess potassium) should be considered as the cause of any new-onset bradycardia.
The prevalence of sinus node disease (of cardiac origin) is 0.17% in the over-50 age group (in Germany).
Course and prognosis: Treatment of the underlying disease is paramount.
Note: In clinically heart-healthy individuals, an asymptomatic resting heart rate below 50/min appears to affect prognosis only if it is dependent on heart rate-lowering medication:
- Patients without heart rate-lowering medication: linear increase in mortality (number of deaths in a given period, relative to the number of the population in question) with heart rate:
- Group with resting heart rate <50/min: Mortality not significantly lower than in the reference group (resting heart rate: 60-69/min).
- Group with resting pulse > 80/min showed a 49% increased mortality risk, which was significant
- Patients on heart rate-lowering medication: J-shaped association between resting heart rate and mortality rate.
- Group with resting heart rate > 80/min: Mortality 255% higher than reference range.
- Group with resting pulse < 50/min: Mortality increased by 142%.