Published Online
on October 4, 2004

A more recent version of this article appeared on October 12, 2004

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Submitted on December 19, 2003
Revised on May 24, 2004
Accepted on May 26, 2004

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, and 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.).

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

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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