Bradycardias

Abstract

Bradycardia is defined as a heart rate slower than normal. The point at which a heart rate is normal or bradycardic varies for each age group. Two types of mechanisms are responsible for the appearance of bradycardia: those involving impulse formation and those involving impulse conduction. Of the former, sinus bradycardia and sinus standstill can slow the heart rate. Sinoatrial (SA) and atrioventricular (AV) block may produce bradycardia because these are impulse conduction defects. Atropine and isoproterenol may facilitate SA conduction, but the block itself may be drug induced. Atropine, oral vagolytics, and atrial antiarrhythmics may be useful in certain types of AV block, and permanent pacing is required for those refractory to drugs. Atrioventricular junctional escape rhythms is usually associated with sinus bradycardia, appearing when the sinus rate diminishes. The therapeutic approach to this disorder consists of treatment of the underlying bradycardia. Ventricular escape is a delayed rhythm that emerges after a very variable interval and may degenerate into ventricular tachycardia or fibrillation. Treatment of the underlying arrhythmia is also recommended.