Phase-4 paroxysmal atrioventricular block in sarcoidosis

Atrioventricular Block Reproduced during Atrial Threshold Testing: What Is the Mechanism?

“…The most common type of conduction defect is a right bundle branch block . It can also be seen in patients with a normal QRS and has been reported in pediatric populations, patients with sarcoidosis, and scleroderma …”

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

“…Indeed, the precise mechanism for the occurrence of PAVB remains speculative but is thought to be the result of retrograde CC into the abnormal His‐Purkinje system (HPS). It is often triggered and initiated by atrial, His, or ventricular premature beats that initiate the pause or by suppression of AV conduction , , . As the author stated, a barrage of non‐conducted atrial impulses may result in long ventricular pauses and PAVB, and potentially unfavorable clinical consequences such as syncope .…”

“…Block of the first atrial impulse creates CC that perpetuates for several cycles. Some authors also speculated that this response is related to phase 3 or 4 AV block . Phase 4 AV block occurs mostly in the diseased HPS, whereas phase 3 AV block is a normal physiological phenomenon (physiological or functional block) and can occur in the normal HPS after a conducted atrial premature depolarization or at the beginning of a supraventricular tachycardia .…”

“…Phase 4 AV block occurs mostly in the diseased HPS, whereas phase 3 AV block is a normal physiological phenomenon (physiological or functional block) and can occur in the normal HPS after a conducted atrial premature depolarization or at the beginning of a supraventricular tachycardia . However, the mechanism remains unsettled with phase 3 block ( voltage‐dependent or tachycardia‐dependent PAVB [TD‐PAVB] ), phase 4 block ( pause‐dependent or BD‐PAVB as associated with a phase‐4 enhanced automaticity ), and the CC all proposed . Indeed, we recently encountered a 33‐years‐old woman with regular palpitations and exercise induced‐dizziness and presented it at electrophysiology (EP) rounds section .…”

“…It is often triggered and initiated by atrial, His, or ventricular premature beats that initiate the pause or by suppression of AV conduction. 2,5,6 As the author stated, a barrage of non-conducted atrial impulses may result in long ventricular pauses and PAVB, and potentially unfavorable clinical consequences such as syncope. 1 Block of the first atrial impulse creates CC that perpetuates for several cycles.…”