Tachycardia is defined as a heart rate faster than 100 beats per minute in adults or above the normal range for age in children and fetuses. In adults, tachycardia has many possible causes including fever, dehydration, anxiety, thyroid disorders, anemia, and cardiac arrhythmias. Echocardiography can help identify the cause and assess the impact of tachycardia on heart function. In the fetus, tachycardia (generally defined as a heart rate above 160 to 180 beats per minute sustained over time) can be detected on obstetric ultrasound and may be caused by fetal distress, maternal fever, or fetal arrhythmias. M-mode and Doppler echocardiography are used to characterize fetal arrhythmias by examining the timing relationships between atrial and ventricular contractions.
Sonography Term