Enhanced A-V nodal conduction (Lown-Ganong-Levine syndrome) by congenitally hypoplastic A-V node

Abstract

The basic anatomical substrate of enhanced A-V nodal conduction, manifesting or not as Lown-Ganong-Levine syndrome, is still a controversial issue. We describe the case of a 34-year-old man who presented episodes of ventricular fibrillation. Electrophysiological studies showed that the AH interval was 55 ms, and increased by only 20 ms at paced cycle lengths of 300 ms; atrial pacing induced atrial fibrillation, with a shortest RR interval of 240 ms. Despite verapamil therapy, this patient died suddenly at home. Histological study disclosed a severe A-V node hypoplasia that was evidently congenital in nature; the rest of the conduction system was normal, and no accessory A-V pathways were present. We suggest that enhanced A-V nodal conduction in this patient was due to the developmental defect in the A-V node; this abnormality caused a loss of specific impulse-delaying function, and thus allowed rapid, unfiltered atrial impulses to reach the lower A-V junction and ventricles.

Overexpression of SCN5A in mouse heart mimics human syndrome of enhanced atrioventricular nodal conduction

“…In EAVNC, the P-R interval is shortened and A-V conduction time is decreased. [2][3][4][5][6] Several mechanisms have been proposed to explain short P-R intervals in EAVNC, including a partial bypass of the A-V node, an underdeveloped or anatomically small A-V node, and an anatomically normal A-V node that has rapid conduction properties either intrinsically or as a result of alterations in autonomic tone, [6][7][8][9][10][11][12] but the subject has not been resolved. A transgenic (TG) mouse with cardiacspecific overexpression of SCN5A (which encodes the cardiac sodium channel Na V 1.5) was recently developed and studied by Zhang et al 13 In this mouse model, prominent functional manifestations of overexpression of SCN5A included shortening of the P wave and the P-R interval on the surface electrocardiogram (ECG).…”

Ventricular Preexcitation in Children and Young Adults

“…Data for patient 1 have been previously reported. 8 In patient 9, who presented with right lateral WPW-type VP, transesophageal study revealed a preexcited RR interval of 240 ms; the patient refused catheter ablation and died 3 years after the last examination. None of the patients had an ECG tracing at the time of cardiac arrest.…”

“…One is a congenitally hypoplastic AV node, which created a lessened bulk of specialized tissue to delay impulse transmission from atria to ventricles. 8 The second is presence of an atrio-Hisian bundle that bypasses the AV node and transmits the activation signal directly to the His bundle. 22,23 In both substrates, the onset of atrial fibrillation may precipitate ventricular fibrillation as it occurs in the WPW syndrome.…”

Conduction System Disease

“…The AV conduction is accelerated ("enhanced AV conduction") because of a congenitally hypoplastic AV node [ 16 ] or of the existence of an anomalous pathway by passing the AV node (site of slow down) and connecting directly to the His bundle (Figs. 7.4 and 7.5 ) [ 2 -4 ].…”