Bradycardia

Sinus bradycardia is any heart rhythm slower than 50 bpm, even if transient, owing to sinus node dysfunction and/or atrioventricular (AV) conduction abnormalities.

Causes include intrinsic sinus node, AV nodal, and His-Purkinje disease, or extrinsic influences, which may be reversible.

Common symptoms include syncope, fatigue, and dizziness; however, the patient may be asymptomatic.

Evaluation involves determining the association of symptoms with heart rate and an assessment of underlying cardiovascular conditions. A 12-lead ECG and/or a heart monitor are the diagnostic tests of choice.

Patients with a reversible cause may not require long-term therapy; however, patients with non-reversible causes may require an implantable pacemaker with or without a defibrillator. Urgent treatment may include temporary pacing and drug interventions.

Potentially life-threatening complications, including cardiovascular collapse and death, may occur.

While some consider bradycardia to be a heart rate <60 bpm, this is in dispute and most consider rates of <50 bpm to represent bradycardia. A study of 500 healthy people, using ECG recordings, showed the mean afternoon heart rate to be 70 bpm in men and women, with two standard deviations being 46-93 bpm in men and 51-95 bpm in women.[1]Spodick DH, Raju P, Bishop RL, et al. Operational definition of normal sinus heart rate. Am J Cardiol. 1992 May 1;69(14):1245-6. http://www.ncbi.nlm.nih.gov/pubmed/1575201?tool=bestpractice.com [2]Spodick DH. Normal sinus heart rate: sinus tachycardia and sinus bradycardia redefined. Am Heart J. 1992 Oct;124(4):1119-21. http://www.ncbi.nlm.nih.gov/pubmed/1529897?tool=bestpractice.com A slow heart rate is common under various circumstances and does not necessarily require treatment unless it causes symptoms. Nonetheless, some patients, even if asymptomatic, may require interventions to prevent life-threatening complications. This topic focuses on electrical causes of bradycardia.