Identifying Concerning Fetal Heart Rate Patterns

During the labor process, a nurse is monitoring a pregnant woman experiencing uterine contractions. The patient's cervix is dilated to 6 centimeters, and she is reporting intense pressure in her lower back. The nurse knows it is essential to assess the fetal heart rate pattern to ensure the fetus is in a healthy state of well-being. Which of the following fetal heart rate patterns, observed on the electronic fetal monitor, would be most concerning to the nurse?