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(Circulation. 2008;117:2850-2858.)
© 2008 American Heart Association, Inc.

Arrhythmia/Electrophysiology

Accessory Atrioventricular Myocardial Connections in the Developing Human Heart

Relevance for Perinatal Supraventricular Tachycardias

Nathan D. Hahurij, MSc; Adriana C. Gittenberger-De Groot, PhD; Denise P. Kolditz, MD; Regina Bökenkamp, MD; Martin J. Schalij, MD, PhD; Robert E. Poelmann, PhD; Nico A. Blom, MD, PhD

From the Department of Pediatric Cardiology (N.D.H., R.B., N.A.B.), Department of Anatomy and Embryology (N.D.H., A.C.G.-D.G., R.E.P.), and Department of Cardiology (D.P.K., M.J.S.), Leiden University Medical Center, Leiden, Netherlands.

Correspondence to Dr Nico A. Blom, MD, Department of Pediatric Cardiology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, Netherlands. E-mail n.a.blom{at}lumc.nl

Received November 29, 2007; accepted April 7, 2008.

Background— Fetal and neonatal atrioventricular (AV) reentrant tachycardias can be life-threatening but resolve in most cases during the first year of life. The transient presence of accessory AV myocardial connections during annulus fibrosus development may explain this phenomenon.

Methods and Results— A total of 45 human embryonic, fetal, and neonatal sectioned hearts (4 to 36 weeks of development) were studied immunohistochemically. Accessory myocardial AV connections were quantified and categorized according to their specific location, and 3D reconstructions were made. Between 4 and 6 weeks of development, the atrial and ventricular myocardium was continuous at the primitive AV canal. At 6 to 10 weeks, numerous accessory myocardial AV connections were identified in the left (45%), right (35%), and septal (20%) regions of the AV junction. Most right-sided accessory connections comprised distinct myocardial strands, whereas left-sided connections consisted of larger myocardial continuities. At 10 to 20 weeks, all accessory AV connections comprised discrete myocardial strands and gradually decreased in number. The majority of accessory connections were located in the right AV junction (67%), predominantly in the lateral aspect (45%). Seventeen percent of the accessory connections were observed in the left AV junction, and 16% were observed in the septal region. 3D reconstructions of the developing AV nodal area at these stages demonstrated multiple AV node–related accessory connections. From 20 weeks until birth, and in neonatal hearts, no further accessory myocardial AV connections were observed.

Conclusions— Isolation of the AV junction is a gradual and ongoing process, and right lateral accessory myocardial AV connections in particular are commonly found at later stages of normal human cardiac development. These transitory accessory connections may act as substrate for AV reentrant tachycardias in fetuses or neonates.

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CLINICAL PERSPECTIVE

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Clinical Summaries
Circulation 2008 117: 2841-2843. [Full Text]