Recent Topics in Obstetrical Ultrasound in Japan—Fetal Tachyarrhythmia and Bradyarrhythmia

Fetal arrhythmia is frequently found in daily clinical practice. Extrasystole is the most common type of fetal arrhythmia, which is mostly benign and transient. Meanwhile, bradyarrhythmia and tachyarrhythmia are problematic as they cause fetal heart failure. Fetal tachyarrhythmias include supraventricular tachycardia (SVT), atrial flutter (AFL), and ventricular tachycardia (VT). Supraventricular tachycardia are the most commonly reported type of fetal tachyarrhythmia whose mechanisms are classified into AV re-entrant tachycardia (AVRT), AV nodal re-entrant tachycardia (AVNRT), and intra-atrial re-entrant tachycardia (IART). Fetal therapy is performed in cases where extending the gestation period is required. For the fetal therapy of SVT, the classification by VA intervals is used. In 2019, a Japanese prospective study has proposed a protocol of fetal therapy for supraventricular tachyarrhythmia. The efficacy of fetal therapy was 90% (n = 44/49) overall. In fetal bradyarrhythmias, a ventricular rate of <55 bpm is defined as a risk for hydrops fetalis. A prospective study of hydroxychloroquine is currently being conducted in Japan as its prophylactic efficacy was found. An accurate diagnosis is needed to provide appropriate treatment. The recent advancement of ultrasound equipment has enabled higher-resolution imaging than conventional equipment with high temporal and spatial resolutions. In our research, a template matching technique is employed to track tissue architecture in which the speckle pattern is moved to the most similar orientation. With this technique, we estimated the timings of the P and R waves. The reproducibility of such detection for fetuses is currently insufficient. There is still room to be improved.