Evidenced-based approach to bradyarrhythmias

Bradycardia can be caused by a wide variety of factors that affect the sinoatrial or the atrioventricular nodes. The sinus node is the main pacemaker of the heart and is extremely sensitive to autonomic influences as it is richly innervated by sympathetic and parasympathetic nerve inputs. Sinus node dysfunction is a result of various intrinsic or extrinsic causes, most commonly aging and medications. The clinical presentation can vary widely with electrocardiographic (ECG) manifestations including sinus bradycardia, sinus arrest, sinoatrial exit block, hypersensitive carotid sinus syndrome, chronotropic incompetence, and tachycardia-bradycardia syndrome. The key to the diagnosis is correlating symptoms to ECG findings. The only effective management is by pacing. The atrioventricular (AV) conduction axis has complex anatomical and physiological characteristics and the AV node is also strongly influenced by autonomic inputs. There are multiple causes of AV block divided into three ECG classifications - first-, second-, and third-degree AV block - based on the P wave to QRS complex relationship. Additional forms include 2:1, high-grade, and paroxysmal AV block which do not fit within those ECG classifications. Definitive therapy is pacemaker implantation which is indicated for treatment of symptoms with any form of AV block or an infranodal site of conduction block regardless of symptoms.