Diagnosis of fetal tachyarrhythmia at 12 weeks' gestation using spatiotemporal image correlation

Fetal therapy using transplacental antiarrhythmic drugs is effective for the management of fetal tachyarrhythmia. Measurement of ventriculoatrial (VA) and atrioventricular (AV) time intervals by fetal echocardiography is necessary in order to choose the most appropriate antiarrhythmic drug, depending on whether short- or long-VA tachycardia is present1, 2. However, accurate diagnosis of fetal arrhythmia is challenging in early pregnancy due to the small heart size3. Here, we report a case of fetal tachyarrhythmia diagnosed as short-VA tachycardia at 12 weeks' gestation using spatiotemporal image correlation (STIC). A 31-year-old woman attended our clinic at 12 weeks' gestation for first-trimester ultrasound screening. Fetal echocardiography, which is performed routinely in our clinic, showed tachyarrhythmia, with a fetal cardiac rate of 300 bpm. We examined the four-chamber view of the fetal heart using STIC and color Doppler, and analyzed the volume offline. Using STIC M-mode, we drew a line connecting the left ventricle to the right pulmonary vein of the left atrium (Figure 1a). Based on the conventional M-mode method, VA time interval of 91 ms and AV time interval of 123 ms were recorded (Figure 1b). After volume analysis using the four-dimensional STIC M-mode method with color Doppler signals, we concluded that the red color in the atrium indicated pulmonary venous backflow and the initiation of atrial contraction, while the red color in the left ventricle indicated the initiation of ventricular contraction. Using the M-mode method with color display, a VA time interval of 67 ms and an AV time interval of 145 ms were recorded, indicating a diagnosis of short-VA tachyarrhythmia (Figure 1c). The color and conventional M-mode methods demonstrated the same results; however, the color M-mode method showed the presence of contraction in the atrium and ventricle more clearly than the conventional method. On the following day, the fetal heart rate improved to sinus rhythm and the patient did not require fetal therapy thereafter. Diagnosing fetal arrhythmia in early pregnancy is difficult due to the small cardiac size and frequent fetal movement. Examination of the fetal heart using conventional two-dimensional Doppler may take time and, for safety reasons, should be avoided in early pregnancy. The STIC method has the advantages of a short acquisition time (usually less than 7.5 s), and being less affected by fetal movements. Offline analysis of STIC M-mode volumes, with or without color signals, provides a wide variety of measurements from various angles. Another advantage of the STIC method over other approaches for diagnosing fetal arrhythmia in early pregnancy is that the initiation of the atrial contraction can be depicted clearly by placing the sample point adjacent to the pulmonary vein. Our observations in this case indicate that color STIC M-mode may be a useful tool for diagnosing early fetal arrhythmia, an observation which merits investigation in larger series.