Fetal Doppler mechanical PR interval: correlation with fetal heart rate, gestational age and fetal sex

Objectives To establish normal fetal values for the mechanical PR interval by pulsed-wave Doppler at 16-36 weeks of gestation, and to evaluate the influence of fetal heart rate (FHR), gestational age (GA) and fetal sex. Methods Fetal mechanical PR intervals were evaluated prospectively by obstetric ultrasound examination. Health), mothers with sonographically normal fetuses front singleton pregnancies were included. Mechanical PR intervals were measured from simultaneous mitral and aortic Doppler waveforms, from the onset of left atrial contraction (mitral A-wave) to the onset of left ventricular ejection (aortic pulse wave). Simple and multiple linear regression analyses were performed to examine the correlation between PR interval and GA, FHR and fetal sex. Results We evaluated 336 fetuses at 16-36 weeks. The mean +/- SD FHR was 143.4 +/- 8.3 beats per min (bpm). The PR intervals bad a typical Gaussian distribution with a mean SD of 122.4 +/- 10.3 ms. Robust linear regression showed that the PR increased by about 0.40 ms (95% CI, 0.22-0.58) per gestational week (P < 0.001), and this relationship remained after adjustment for FHR and fetal sex. PR intervals diminished by 1.4 (95% CI, 0.75 to 2.0) ins for each 5 bpm increase in FHR (P < 0.001), independently of GA and fetal sex. No fetal sex differences were observed. Conclusions We provide normal fetal values for the mechanical PR interval at 16-36 weeks of gestation. Mechanical PR intervals in normal fetuses art,, influenced by GA and FHR independently, and both variables should be taken into account when evaluating fetuses at risk for congenital heart block. Copyright (C) 2009 ISUOG. Published by John Wiley & Sons, Ltd.