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(Circulation. 2004;110:2097-2101.)
© 2004 American Heart Association, Inc.

Arrhythmia/Electrophysiology

Giant Fetal Magnetocardiogram P Waves in Congenital Atrioventricular Block

A Marker of Cardiovascular Compensation?

Zhimin Li, MS; Janette F. Strasburger, MD; Bettina F. Cuneo, MD; Nina L. Gotteiner, MD; Ronald T. Wakai, PhD

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

Correspondence to Dr Ronald Wakai, Department of Medical Physics, 1300 University Ave, Madison, WI 53706. E-mail rtwakai{at}facstaff.wisc.edu

Received December 19, 2003; de novo received March 15, 2004; revision received May 24, 2004; accepted May 26, 2004.

Background— Cardiogram signal amplitude is a key index of hypertrophy but has not been investigated extensively in utero. In this study, magnetocardiography was used to assess P and QRS amplitude in normal subjects and subjects with fetal arrhythmia.

Methods and Results— The study cohort consisted of 68 normal fetuses and 25 with various arrhythmias: 9 reentrant supraventricular tachycardia (SVT), 2 ventricular tachycardia (VT), 2 sinus tachycardia, 2 blocked atrial bigeminy, 2 congenital second-degree atrioventricular (AV) block, and 8 congenital complete AV block. Subjects with congenital AV block, all presenting with bradycardia, showed large QRS amplitude, exceedingly large P-wave amplitude, and long P-wave duration. The 2 subjects with VT, both with poor ventricular function, also exhibited large P waves. SVT was associated with only moderate signal amplitude elevation.

Conclusions— The data imply that AV block in utero is accompanied by hypertrophy, which is more pronounced for the atria than the ventricles. We hypothesize that the hypertrophy results from a compensatory response associated with regulation of cardiac output and is likely to be observable in other arrhythmias and disease states. Magnetocardiography may be more sensitive than fetal echocardiography for detection of atrial hypertrophy in utero.

Key Words: arrhythmia • heart block • hypertrophy • electrophysiology • tachycardia

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