Syncope and paroxysmal atrioventricular block

Abstract

Current literature reveals three types of paroxysmal atrioventricular block (AVB) that can cause syncope:Intrinsic paroxysmal atrioventricular block is due to an intrinsic disease of the AV conduction system; this type of “cardiac syncope” is also called Stokes-Adams attack;Extrinsic vagal paroxysmal atrioventricular block is linked to the effect of the parasympathetic nervous system on cardiac conduction and is one of the mechanisms involved in “reflex syncope.”Extrinsic idiopathic paroxysmal atrioventricular block is associated with low levels of endogenous adenosine and is supposed to be one of the mechanisms involved in “low-adenosine syncope.”These three types of paroxysmal AVB present different clinical and electrocardiographic features. Additionally, the efficacy of cardiac pacing and theophylline therapy to prevent syncopal recurrences is also different for these three types of AVB.

What is the mechanism of paroxysmal atrioventricular block in a patient with recurrent syncope?

“…The prevalence is not known and the condition itself remains under‐recognized as it is often difficult to document. Three major types of paroxysmal AV block have been identified: vagally mediated, intrinsic (Phase 4), and idiopathic …”

“…Pacemaker implantation has high efficacy in intrinsic and idiopathic paroxysmal AV block with <5% recurrence of syncope . A single‐chamber implantation may be considered in idiopathic subtype in view of intermittent requirement of pacing.…”

Atrial pacing‐induced paroxysmal atrioventricular block: Concealed conduction or phase 3 block or intrahisian reentry?

“…The PAVB is relatively rare, and due to its transient nature, it is often under‐recognized . Current literature reveals three types of PAVB as associated with syncope (a) intrinsic PAVB (Stokes‐Adams attack type “cardiac syncope”), (b) extrinsic vagal PAVB (“reflex syncope”), and (c) extrinsic idiopathic PAVB (“low‐adenosine syncope”) . Vagally mediated PAVB must be differentiated from bradycardia‐dependent PAVB (BD‐PAVB), because BD‐PAVB may progress to persistent AVB and require pacemaker placement .…”

“…Current literature reveals three types of PAVB as associated with syncope (a) intrinsic PAVB (Stokes‐Adams attack type “cardiac syncope”), (b) extrinsic vagal PAVB (“reflex syncope”), and (c) extrinsic idiopathic PAVB (“low‐adenosine syncope”) . Vagally mediated PAVB must be differentiated from bradycardia‐dependent PAVB (BD‐PAVB), because BD‐PAVB may progress to persistent AVB and require pacemaker placement . Whereas the depression of both sinus and AV node conduction must be present to diagnose vagally mediated PAVB, BD‐PAVB will typically demonstrate unchanged P‐P intervals and constant PR intervals .…”

“…Vagally mediated PAVB must be differentiated from bradycardia‐dependent PAVB (BD‐PAVB), because BD‐PAVB may progress to persistent AVB and require pacemaker placement . Whereas the depression of both sinus and AV node conduction must be present to diagnose vagally mediated PAVB, BD‐PAVB will typically demonstrate unchanged P‐P intervals and constant PR intervals . Therefore, the sinus acceleration during AV block is a feature that differentiates PAVB from parasympathetically mediated AV block .…”