The primary pacemaker of the heart is the sinoatrial (SA) node. The SA node generates electrical impulses at regular intervals and with a frequency of 60 to 100 beats per minute The impulses spread rapidly through the atria and enter the atrioventricular (AV) node. After a brief delay at the AV node, the impulses propagate over the His-Purkinje system as depolarization progresses over the ventricles in an anatomically synchronous and hemodynamically effective fashion. When the conduction system malfunctions, the patient develops cardiac arrhythmias.
To prevent cardiac arrhythmias β1‑adrenergic receptor antagonists are prescribed to slow depolarization, lengthen AV conduction, reduce cardiac contractility, and slow the heart rate; calcium channel blocking agents are prescribed to slow depolarization, repolarization, and AV conduction; cardiac glycoside are prescribed to prolong the refractory period and decrease conduction velocity at the AV node. Non-pharmacological strategies include the implantation of pacemakers or ICDs. Key recommendations for practice are presented in Table 13.