Simultaneous recording of pulsed‐wave Doppler signals in innominate vein and transverse aortic arch: new technique to evaluate atrioventricular conduction and fetal heart rhythm

Abnormalities of fetal heart rhythm account for approximately 10–20% of referrals to fetal cardiologists1. Echocardiography is the most widely used perinatal tool to assess fetal heart rhythm and differentiate pathological heart rhythm abnormalities from benign rhythms. Fetal cardiac rhythm is most commonly analyzed by measuring the mechanical equivalent of underlying electrical events using M-mode and pulsed spectral Doppler2, 3. Simultaneous pulsed Doppler recordings of the flow profile in the superior vena cava (SVC) and the ascending aorta (AAo) has been shown to be more accurate than M-mode for precise atrioventricular (AV) and ventriculoatrial time measurements4. The SVC/AAo Doppler technique is performed with the fetus in a sagittal plane. A-wave reversal in the SVC represents atrial systole and antegrade flow in the AAo represents ventricular systole, with the two together defining the AV relationship5. However, numerous factors can influence the success of this Doppler technique. Reliable sampling of the low-velocity SVC atrial systolic flow and simultaneous AAo Doppler signal requires an optimal angle of insonation and low wall-motion filter. If the angle of insonation is not close to 0° or if the wall filter is set too high, the A-wave in the SVC may not be discernible, particularly in arrhythmias in which the venous A-wave might be hidden within the arterial Doppler signal. To improve the performance of fetal rhythm interrogation, we modified the SVC/AAo sampling method by simultaneously recording pulsed-wave Doppler signals in the innominate vein (InnV) and transverse aortic arch (Ao) from an axial view of the fetal thorax. Using a four-chamber view in a horizontal position, the InnV can be identified easily by sweeping cephalad to the three-vessels and trachea view. In this view, the InnV is located immediately superior to the transverse arch and can be positioned parallel to the ultrasound beam. This allows for clear and precise spectral Doppler sampling of the venous A-wave signal. Widening of the Doppler sample volume allows for simultaneous recording of blood velocities in both the InnV and the Ao (Figure 1). The advantage of the InnV/Ao method is a near 0° angle of insonation of the InnV, which optimizes visualization of the retrograde atrial systolic flow. Figure 2 demonstrates fetal bradycardia detected using the InnV/Ao method and Figure S1 demonstrates other fetal arrhythmias. To our knowledge, simultaneous Doppler recordings of the InnV and Ao in an axial plane to assess fetal cardiac arrhythmia has not been described previously. We consider the InnV/Ao Doppler technique to be a feasible and precise method of fetal heart rhythm assessment which can be performed routinely in the clinical setting. Figure S1 Simultaneous recordings of innominate vein (InnV) and transverse aortic arch (Ao) in fetal irregular rhythm (a,b) and tachycardia (c–f). (a) Isolated conducted premature atrial contraction (A′). (b) Ventricular bigeminy with premature ventricular contraction every other beat. In contrast to premature atrial beats, ventricular signal occurs prior to atrial signal (A). (c) 1:1 reciprocating supraventricular tachycardia (SVT) with short ventriculoatrial (VA) interval (VA interval, 103 ms; atrioventricular (AV) interval, 160 ms). Ventricular rate is regular with R–R interval of 260 ms. (d) 1:1 reciprocating SVT with long VA interval (VA interval, 190 ms; AV interval, 130 ms). Ventricular rate is regular with R–R interval of 321 ms. (e) Atrial flutter with 2:1 AV conduction. Atrial rate is regular (A–A interval, 128 ms) and the R–R interval is 256 ms. (f) Junctional ectopic tachycardia with simultaneous depolarization of A and ventricular systole (V). V′, premature ventricular contraction. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.