title: Magnetophysiologic and echocardiographic comparison of blocked atrial bigeminy and 2:1 atrioventricular block in the fetus.
abstract: BACKGROUND
  Blocked atrial bigeminy (BAB) and second-degree atrioventricular block with 2:1 conduction block (2:1 AVB) both present as ventricular bradycardia and can be difficult to distinguish by echocardiography. Since the prognosis and clinical management of these rhythms are different, an accurate diagnosis is essential.
  
  
  OBJECTIVE
  To identify magnetic and mechanical heart rate and rhythm parameters that could reliably distinguish BAB from 2:1 AVB.
  
  
  METHODS
  A retrospective study of ten BAB and seven 2:1 AVB subjects was performed, using fMCG and pulsed Doppler ultrasound.
  
  
  RESULTS
  Distinguishing BAB from 2:1 AVB by using fMCG was relatively straightforward because in BAB the ectopic P wave (P') occurred early, resulting in a bigeminal (short-long) atrial rhythm. The normalized coupling interval of the ectopic beat (PP' of the blocked beat to PP of the conducted beat) was 0.29 ± 0.03. In contrast, the echocardiographic assessment of inflow-outflow gave a normalized mechanical coupling interval (AA'/AA) near 0.5, which made it difficult to distinguish BAB from 2:1 AVB. Heart rate distinguished most subjects with BAB from those with 2:1 AVB (82 ± 5.7 beats/min vs 69 ± 4.2 beats/min), but was not a completely reliable indicator. In most subjects, BAB alternated with sinus rhythm or other rhythms, resulting in complex heart rate and rhythm patterns.
  
  
  CONCLUSIONS
  Fetal BAB and 2:1 AV block can be difficult to distinguish using echocardiography because in many fetuses with BAB the mechanical rhythm does not accurately reflect the magnetic rhythm. fMCG provides a more reliable means of making a differential diagnosis.
authors.affiliation: Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin 53705, USA.
authors.forename: Delonia L
authors.initials: DL
authors.lastname: Wiggins
authors.forename: Janette F
authors.initials: JF
authors.lastname: Strasburger
authors.forename: Nina L
authors.initials: NL
authors.lastname: Gotteiner
authors.forename: Bettina
authors.initials: B
authors.lastname: Cuneo
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Wakai
mesh_terms: D054537:Atrioventricular Block / Q000175:diagnosis* / Q000503:physiopathology; D001919:Bradycardia / Q000175:diagnosis* / Q000503:physiopathology; D003937:Diagnosis, Differential; D004452:Echocardiography; D005315:Fetal Diseases / Q000175:diagnosis* / Q000503:physiopathology; D005318:Fetal Heart / Q000503:physiopathology*; D005333:Fetus; D006325:Heart Atria / Q000473:pathology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D053798:Magnetocardiography; D012189:Retrospective Studies; D018617:Ultrasonography, Doppler, Pulsed
keywords: 2-to-1 atrioventricular block; 2:1 AVB; AA; AA′; AV; AVB; Atrioventricular block; BAB; BAC; Bigeminy; Blocked atrial bigeminy; FHR; Fetal arrhythmia; Fetal magnetocardiography; PAC; PP; PP′; QTc; SVT; VSA; atrioventricular; atrioventricular block; blocked atrial bigeminy; blocked atrial couplet; corrected QT interval; fMCG; fetal heart rate; fetal magnetocardiography; interval between A waves of consecutive sinus beats; interval between P waves of consecutive sinus beats; interval from the A wave of the sinus beat to the A wave of the premature beat; interval from the P wave of the sinus beat to the P wave of the premature beat; premature atrial contraction; supraventricular tachycardia; ventriculophasic sinus arrhythmia