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(Circulation. 2008;117:1499.)
© 2008 American Heart Association, Inc.

Clinical Summaries

An extract of the first 250 words of the full text is provided, because this article has no abstract.

	Epicardium-Derived Cells in Development of Annulus Fibrosis and Persistence of Accessory Pathways

 
Atrioventricular reentrant tachycardia is a common arrhythmia in both children and adults; however, the causal mechanisms underlying the appearance of accessory pathways remain a subject of debate. During cardiogenesis, initial slow conduction over the circumferential myocardial AV continuity, which results in sequential activation of the preseptated heart, is replaced by apex-to-base conduction through the specialized AV node/His-Purkinje system in the septated heart. Concurrently, incorporation of the AV junctional myocardium in the lower atrial rim by fusion of the endocardial AV cushions and epicardial AV sulcus results in formation of the isolating annulus fibrosis. Migration of multipotent epicardium-derived cells (EPDCs) through the continuous AV junctional myocardium, ultimately reaching the endocardium-derived AV cushions, spatiotemporally correlates with annulus fibrosis formation. The AV junction has been postulated to be subject to physiological perinatal remodeling, which temporarily leaves functional small accessory pathways as anatomic substrates for spontaneously resolving neonatal AV reentrant tachycardias. Dyssynchrony in the delicate interplay between EPDCs and AV junctional cells, as shown in the EPDC-inhibited quail model in the present study, may result in marked defects in the isolating annulus fibrosis, with the persistence of large accessory pathways functionally resulting in ventricular preexcitation. We speculate that absence of EPDCs or a delay in EPDC migration results in the persistence of pathological substrates for postnatally persistent accessory pathways and AV reentrant tachycardias into childhood or adult life. See p 1508.

	Vernakalant Hydrochloride for Rapid Conversion of Atrial Fibrillation: A Phase 3, Randomized, Placebo-Controlled Trial

 
Pharmacological cardioversion often is used to restore sinus rhythm in patients with hemodynamically stable and recent-onset atrial fibrillation. However, currently available antiarrhythmic . . . [Full Text of this Article]