Neonatal bradycardia.
Heart rate monitoring has become a ubiquitous part of fetal and neonatal assessment, and has made detection of bradycardia in the fetal and neonatal periods a frequent occurrence. Evaluation of a fetus or neonate with bradycardia requires an understanding of the mechanisms of bradycardia as well as the cardiac and non-cardiac causes of bradycardia. The mechanisms of bradycardia include sinus bradycardia, abnormalities of sinus node function and abnormalities of atrioventricular conduction. In the instances where sinus bradycardia is pathologic, it usually results from non-cardiac disease. Sinus node dysfunction is rare early in life but can arise from surgical interventions, congenital heart disease, or endovascular manipulations. Abnormalities of atrioventricular conduction have a similar etiology but are more common than sinus node disease. Atrioventricular nodal disease can also result from maternal collagen vascular disease, even in the absence of symptoms in the mother. In these cases, epidemiological issues such as heart block in subsequent pregnancies and the maternal risk of developing symptomatic collagen vascular disease become important. The approach to treatment and long-term prognosis for bradycardia in the neonate is highly dependent on the underlying etiology and on the presence of concurrent factors such as structural heart disease.