Idiopathic paroxysmal atrioventricular (AV) block poses a true diagnostic challenge. What is clear about this entity is the confusion about its definition and consequently about its etiology. According to certain sources, the diagnosis of this block requires the lack of a structural cardiac pathology that justifies the observed manifestations and an absence of electrocardiographic disorders prior to an episode. The clinical presentation of idiopathic paroxysmal AV block does not differ from that of another cardiogenic syncope or of a vasovagal syncope with a significant cardioinhibitory component. With respect to the mechanism that explains this block, it has been postulated that patients with low basal adenosine levels exhibit hyperaffinity of the A2 receptors of the AV node. Variations in plasma adenosine levels may favor episodes of paroxysmal AV block. The diagnosis of this block is complex and can require years to determine. Routine electrophysiological examination of these patients is not cost effective due to the low sensitivity and specificity of this approach. Numerous groups have supported the use of an implantable loop recorder to substantiate AV block paroxysms and assess their clinical correlations. Permanent stimulation devices are utilized to reduce syncopal recurrence.
Keywords: Adenosine Plasma Level; Atrioventricular Block Idiopathic; Syncope.