Bradycardia

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 and AV nodal 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. ECG is the diagnostic test of choice.

Patients with a reversible cause may not require long-term therapy; however, patients with nonreversible 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 normal people, using ECG recordings, showed the mean afternoon heart rate to be 70 bpm in men and women, with two standard deviations being 46 to 93 bpm in men and 51 to 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.