Fetal Cardiac Function, Rhythm, and Hemodynamics
Fetal cardiac function is assessed with a combination of two-dimensional imaging, M-mode, and Doppler. Systolic function can be estimated by fractional area change or fractional shortening, ventricular ejection, and atrioventricular valve excursion; diastolic function by inflow patterns and ductus venosus waveforms. The myocardial performance (Tei) index combines isovolumetric contraction and relaxation times with ejection time, but it is angle- and load-dependent and should not be interpreted in isolation. Cardiac output is normally right-heart dominant, and combined output rises with growth. Rhythm assessment: normal fetal heart rate is about 110–160 beats/min. Sinus rhythm shows one atrial contraction before each ventricular contraction. Premature atrial contractions are common, often benign, and may produce irregular rhythm; sustained tachyarrhythmia (often >220 beats/min) suggests SVT or atrial flutter, while bradycardia (<100 beats/min) raises concern for heart block. M-mode and Doppler simultaneously compare atrial and ventricular mechanical events. Hemodynamic surveillance includes umbilical artery, middle cerebral artery, and ductus venosus Doppler, especially in growth restriction or hydrops. Traps: confusing brief irregular rhythm from PACs with sustained arrhythmia; calling a normal ductus venosus a-wave reversal abnormal; and treating a single Tei index value as diagnostic. Worked example: if atrial contractions occur at about 400/min while ventricular contractions are about 200/min, think atrial flutter with variable block rather than sinus tachycardia. Rule of thumb: rhythm diagnosis requires documenting the atrial rate, ventricular rate, and their relationship, not just the ventricular rate.