A rare entity, fetal ventricular tachycardia presents with a rapid ventricular rate exceeding, and occurring independently from, the atrial rate. The ventricular rate is typically over 180 beats per minute 1. Atrioventricular dissociation is characteristic; two separate pacemakers dictate the activity of the atria and ventricles, respectively.
Epidemiology
Occurs in less than 2% of fetal tachydysrhythmia cases. Associated with:
- fetal myocarditis
- long QT syndrome
- complete AV block
Radiographic features
Antenatal ultrasound - echocardiography
Features on M-mode and pulsed wave Doppler (PWD) analysis of cardiac contraction patterns which support the diagnosis of ventricular tachycardia include 3:
- rapid, regular ventricular activity
- timing of ventricular depolarization may be accurately timed by the inward excursions of the ventricular walls (M-mode), or systolic V waves (PWD)
- ventricular activity rate exceeds that of the atria
- independent, dissociated activity of atria and ventricles
- in rare instances, retrograde conduction from the ventricular pacemaker and (1:1) atrial capture may occur
- the atrial rate will then closely approximate ventricular rate
- utilization of tissue Doppler imaging may help elucidate the first structure which contracts 2