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.
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.
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
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