![]() ![]() 8 The three most common fetal tachyarrhythmias aside from premature atrial contractions (PACs) are supraventricular (re-entrant) tachycardia (SVT), atrial flutter (AF), and ventricular tachycardia (VT). It is important to exclude fetal distress (with loss of beat-to-beat variability) and chorioamnionitis (with maternal fever), which may cause fetal heart rates up to 200bpm. 13,14 Fetal Tachyarrhythmiasįetal tachycardias may have several causes. 10,12 Fetal magnetocardiography uses the magnetic field generated by electrical activity of the fetal heart for more precise delineation of fetal rhythms. 8,10,11 Similarly pulsed Doppler can be used to identify fetal rhythms by assessing intracardiac flow patterns. ![]() A cursor placed through both the fetal atrium and ventricle allows the timing of atrial and ventricular contractions to be determined and premature beats to be identified. Other non-invasive approaches include two-dimensional (2-D) fetal echocardiography, to exclude structural cardiac defects, and M-mode ultrasonography, which depicts cardiac motion as a function of time. External acquisition of fetal electrocardiography is currently not available. 2 Once an arrhythmia is detected by auscultation, additional evaluation is indicated. Less than 10% of fetal arrhythmia analyses are found to have sustained tachyarrhythmias or bradyarrhythmias. 8,9Īpproximately 50% of fetuses referred for evaluation of fetal arrhythmias are in normal sinus rhythm, with the vast majority having isolated supraventricular systoles. 8 Transient slowing of the fetal heart rate with immediate return to normal rates is common in mid-trimester when patients lie supine, caused by normal variable-type fetal heart rate decelerations, and does not need further cardiac evaluation.This isolated physiological slowing of the heart must be differentiated from persistent bradycardia, which does require expedited evaluation. Abrupt changes, especially if the rate is over 200bpm, are more often associated with pathological tachycardias. Gradual onset and cessation are associated with normal fetal accelerations, especially with a rate below 200bpm. 1,4 If a fetal tachycardia is heard, the referring practitioner should attempt to determine its rate and characteristics. Generally the mother is asymptomatic and has not appreciated any decreased fetal activity. 1,7įetal arrhythmias are often first noted on auscultation during routine maternal prenatal examinations once heart tones are appreciated around 10-12 weeks. 5,6 Heart rates less than 100bpm are classified as bradycardia, and rates greater than 180bpm are identified as tachycardia. 4 Normal fetal heart rates range from 120-160bpm at 30 weeks' gestation and 110-150bpm at term. ![]() Almost all arrhythmias fall into one of three categories: irregular, tachycardic, or bradycardic. 2,3 Fetal Arrhythmiasįetal arrhythmias are noted in only 1-2% of all pregnancies and can be categorized by rate and regularity. Irregularities of fetal and neonatal cardiac rhythm commonly occur and rarely have serious consequences however, it is important to realize that sustained tachycardias and bradycardias can lead to heart failure and hydrops fetalis. 1 The innate physiological properties of the fetal and neonatal myocardium make it more vulnerable to these high or low ventricular rates. They include both tachycardias and bradycardias. Fetal and neonatal arrhythmias are diverse in type and severity. ![]()
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