R00.1

Bradycardia (R00.1): normal slow heart rate, causes, sinus node disease, AV block and pacemakers.

Bradycardia (ICD-10 R00.1) is a resting heart rate below 60 beats per minute in adults (some definitions use 50/min). It often causes no symptoms: slow rates of 40–50/min during sleep are common and normal, and well-trained athletes often have a slow resting pulse as an adaptation to training. Bradycardia matters when the heart beats too slowly to meet the body's needs, causing fatigue, weakness, dizziness or fainting. "Relative bradycardia" refers to a rate that is too slow for the person's current condition (for example during fever or bleeding) even if it is not below 60.

ICD-10 R00.1Slow heart ratePacemaker

Definition< 60 beats/min (adults)

Normal insleep, trained athletes

Main mechanismssinus node dysfunction, AV block

Long-term treatmentpacemaker if symptomatic

Figure 1. Top: normal sinus rhythm (about 70/min). Middle: sinus bradycardia (about 45/min) — each beat normal but widely spaced. Bottom: complete AV block — P waves are not conducted and a slow ventricular escape rhythm takes over.

Causes

Physiological: sleep, athletic training, high vagal tone
Sinus node dysfunction (sick sinus syndrome), often age-related
AV block of second or third degree
Medicines: beta-blockers, verapamil, diltiazem, digoxin, amiodarone, ivabradine, clonidine
Other conditions: hypothyroidism, hypothermia, high potassium, inferior myocardial infarction, raised intracranial pressure, sleep apnoea, Lyme disease, anorexia nervosa

Diagnosis and treatment

The key question is whether symptoms are caused by the slow rhythm. ECG, Holter or longer monitoring and exercise testing (does the rate rise appropriately?) are used, together with blood tests for thyroid function and electrolytes. Reversible causes are corrected first: medicines are reviewed, potassium and thyroid hormone levels normalised. Acute symptomatic bradycardia is treated with atropine, other drugs or temporary pacing. A permanent pacemaker is indicated when bradycardia due to sinus node disease or AV block causes symptoms without a reversible cause, and in high-degree AV block.

Call emergency services

for fainting, a very slow pulse with dizziness, chest pain, breathlessness or confusion.

References

Glikson M, Nielsen JC, Kronborg MB, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J. 2021;42(35):3427–3520. doi:10.1093/eurheartj/ehab364
Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628

This article is for general information and does not replace a consultation with a doctor. Diagnosis and treatment must be decided by a physician on the basis of symptoms, examination and tests.

Published on 23 March 2019