As you’ve already ready, premature atrial contractions (PACs), abnormal early heartbeats that originate in the upper chambers of the heart, are frequently seen in utero, especially during the second trimester. They can persist into the third trimester, but often go away during that time or soon after birth. Bigeminy, for our othe r readers, means that every other beat is premature. There are two issues that can become concerning here. The first is what the underlying heart rate and ventricular function of the heart is. Frequent PACs, even as much as bigeminy, don’t cause problems UNLESS they are causing the heart rate to be too slow for the baby’s needs. This can manifest in congestive heart failure, or a form of what is called hydrops. So, the important questions here are whether the baby has a structurally normal heart and also if the ventricles, the pumping chambers, are working adequately. The second issue is that sometimes PACs can lead to supraventricular tachycardia, an abnormal sustained fast heart rate, which can also lead to problems, especially if it is sustained for a long period of time. Often, we do not know the reason for PACs, though sometimes we do see a structure inside the right atrium called the Eustachian valve, a normal structure, that can be larger than usual. It can be floppy and smack against the wall of the atrium during the normal cardiac cycle, which can cause these early beats.
Without knowing much more about the baby’s heart or the mother’s medical condition, it is difficult to be able to say much more about this. A pediatric cardiologist who specializes in fetal cardiology would be an appropriate person to evaluate mother and baby at this time. A fetal echocardiogram can be performed, which is a detailed cardiac ultrasound of the baby’s heart. Your sister can look for a center that has this available and is, hopefully, relatively close to home.