Bradyarrhythmias

Bradyarrhythmias refer to conditions characterized by abnormally slow heart rates. Although definitions vary, most authorities consider bradycardia (brady = slow, cardia = heart) to include heart rates less than or equal to 50-55 beats/min. The most common normal slow heart rhythm is called sinus bradycardia. The normal pacemaker of the heart (the sinus or SA node) is responsible for triggering the heart to beat. The normal range of the sinus rate varies with age but is generally 45 -170 beats/min during awake periods. While asleep or very relaxed, the sinus rate may normally drop into the 30-40/min range. This is especially common in athletically well conditioned individuals. Sinus bradycardia is generally not a concern and does not require treatment unless it is associated with symptoms such as fainting or lightheadedness due to low blood pressure, or if the sinus rate fails to increase under conditions of exertion or exercise (so-called chronotropic incompetence). It is rare for sinus bradycardia to cause these symptoms, unless the sinus rate is very low, generally less than 40-45/min.

The most common causes for abnormal symptomatic bradycardias include: 1) sinus (or sinoatrial) node dysfunction, 2) atrioventricular (AV) conduction block and, 3) vasovagal episodes. Patients with vasovagal spells rarely need any special treatment, possibly only a mild medication in cases of recurrent episodes. In many patients with AV block or sinus node dysfunction the condition is caused or worsened by medications they may be taking for other heart conditions, high blood pressure, or to control fast heart rhythms (tachyarrhythmias). Therefore, treatment may involve nothing more than stopping, changing, or reducing the dosage of a medication. However, for some patients with symptomatic bradycardia (especially fainting) due to sinus node dysfunction or AV block block, implantation of a pacemaker system may be required.