Published Online
on December 9, 2002

A more recent version of this article appeared on January 21, 2003

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Submitted on August 1, 2002
Revised on September 27, 2002
Accepted on September 30, 2002

Magnetocardiographic Rhythm Patterns at Initiation and Termination of Fetal Supraventricular Tachycardia

R. T. Wakai PhD^*, J. F. Strasburger MD, Z. Li MS, B. J. Deal MD, and N. L. Gotteiner MD

From the Department of Medical Physics (R.T.W., Z.L.), University of Wisconsin-Madison, Wis; Department of Pediatrics, Division of Cardiology (J.F.S.), Children's Hospital of Wisconsin, Milwaukee, Wis; and Department of Pediatrics, Division of Cardiology (B.D., N.G.), Children's Memorial Hospital, Chicago, Ill.

^* To whom correspondence should be addressed. E-mail: rtwakai{at}wisc.edu.

Background—Using fetal magnetocardiography (fMCG), we characterize for the first time the electrophysiological patterns of initiation and termination of reentrant fetal supraventricular tachycardia (SVT), the most common form of life-threatening fetal arrhythmia.

Methods and Results—In contrast to the expectation that reentrant SVT is initiated by spontaneous premature atrial contractions (PACs) and is terminated by spontaneous block, 5 distinct patterns of initiation and 4 patterns of termination were documented, with the most common patterns of initiation involving reentrant PACs. Waveform morphology and timing, including QRS and ventriculoatrial interval, were assessed. This enabled detection of such phenomena as Wolff-Parkinson-White syndrome, QRS aberrancy, and multiple reentrant pathways that were crucial for defining the rhythm patterns. In addition, fMCG actocardiography revealed an unexpectedly strong association between fetal trunk movement and the initiation and termination of SVT, suggesting that autonomic influences play a key role.

Conclusions—This study demonstrates that the patterns of initiation and termination of fetal SVT are more diverse than is generally believed and that the most common patterns of initiation involve reentrant PACs. The ability to discern such patterns can help elucidate the underlying mechanisms and guide antiarrhythmic drug therapy. fMCG provides a noninvasive means of analyzing complex tachyarrhythmia in utero, with efficacy approaching that of postnatal electrocardiographic rhythm monitoring.

Key words: electrophysiology • arrhythmia • tachycardia

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