Influence of gestational age and fetal heart rate on the fetal mechanical PR interval

Fetal PR Interval in Pregnancies with Intrahepatic Cholestasis of Pregnancy: A Case-Control Study

OBJECTIVE

 This study had three purposes: first, to explore differences in fetal cardiac function in patients with and without intrahepatic cholestasis of pregnancy (ICP) based on PR interval (the interval between the beginning of the atrial contraction and the beginning of the ventricular contraction). Second, to explore a potential correlation between PR interval and bile acid levels in pregnant women with ICP. Third, to study changes in PR interval of fetuses from pregnant women with ICP after administration of ursodeoxycholic acid (UDCA).

STUDY DESIGN

 This was a prospective observational case-control study. ICP was defined as palmar plantar pruritus of nocturnal predominance for more than 1 week associated with a total bile acid level >10 μmol/L. Control cases were women with pregnancies scheduled for induction or elective cesarean section at term.

RESULTS

 One hundred and ten women with ICP and 72 controls were included in the study. Median gestational age at inclusion was 35.9 weeks. Median PR interval was significantly longer in fetuses of women with ICP (122 vs. 102 ms, p < 0.001). There was a significant correlation between bile acid levels and PR interval (rho = 0.723, p < 0.001). In 22 fetuses, the median PR interval decreased significantly following UDCA administration (134 vs. 118 ms, p = 0.004).

CONCLUSION

 PR interval is longer in fetuses of women with ICP. PR interval was significantly correlated with bile acid levels, and administration of UDCA significantly reduced PR interval.

KEY POINTS

· Differences in fetal cardiac function in patients with and without intrahepatic cholestasis.. · PR interval and bile acid levels in pregnant women with intrahepatic cholestasis.. · Changes in PR interval of fetuses from pregnant women with ICP after use of UDCA..

Autoimmune Congenital Heart Block: A Review of Biomarkers and Management of Pregnancy

Autoimmune Congenital Heart Block (CHB) is an immune-mediated disease due to transplacental passage of circulating anti-Ro/SSA and anti-La/SSB autoantibodies. It occurs in 2% of anti-Ro/SSA-exposed pregnancies, and recurrence rate is nine times higher in subsequent pregnancies. Aim of this review is to identify biomarkers of CHB and treatment strategies. The Ro-system is constituted by two polypeptides targeted by the anti-Ro52 and anti-Ro60 autoantibodies. The central portion of Ro52 (p200), more than the full amino-acid sequence of Ro-52, is recognized to be the fine specificity of anti-Ro associated to the highest risk of cardiac damage. If anti-p200 antibody should be tested, as biomarker of CHB, over standard commercial ELISAs is still debated. Recent studies indicate that type I-Interferon (IFN) can activate fibroblasts in fetal heart. In the mother the anti-Ro/La antibodies activate the type I IFN-signature, and maternal IFN-regulated genes correlate with a similar neonatal IFN-gene expression. Evaluation of maternal IFN-signature could be used as novel biomarker of CHB. The measurement of "mechanical" PR interval with weekly fetal echocardiogram (ECHO) from 16 to at least 24 weeks of gestation is strongly recommended for CHB prenatal diagnosis. However, ECHO screening presents some limitations due to difficult identification of first-degree block and possible occurrence of a complete block from a normal rhythm in few days. Maternal administration of Hydroxychloroquine from the tenth week of gestation, modulating toll-like receptor and autoantibody-dependent type I IFN activation on the fetus, has an important role in preventing CHB in pregnant women with high risk for recurrent CHB.

Evolution of the Fetal Atrioventricular Interval from 6 to 40 Weeks of Gestation

Doppler-based methods of estimating the atrioventricular interval are commonly used as a surrogate for the electrical PR in fetuses at risk of conduction abnormalities; however, to date, normal values for the fetal atrioventricular interval and an understanding of the evolution of its components in the late first trimester are lacking. We sought to investigate changes in the fetal atrioventricular interval from the first trimester to 40 weeks gestational age, and to explore functional and electrophysiological events that potentially impact its evolution. We prospectively examined healthy pregnancies by fetal echocardiography from 6 to 40 weeks' gestational age. The atrioventricular interval, heart rate, isovolumic contraction time, and A-wave duration were measured from simultaneous ventricular inflow-outflow Doppler tracings. Regression analysis was used to examine relations with gestational age, and linear relations with heart rate were assessed by Pearson's correlation coefficient. Data were collected in 305 fetuses from 279 pregnancies. Atrioventricular interval demonstrated an inverse relation with heart rate (r = -0.45, p <0.0001), dramatically decreasing before 10 weeks and slowly increasing thereafter. Between 6 and 9 weeks, isovolumic contraction time acutely decreased approaching 0, thereafter minimally increasing to term. In contrast, from 6 weeks, the A-wave duration linearly increased through gestation, and negatively correlated with heart rate (r = -0.62, p <0.0001). In conclusion, we have established normal measures of the atrioventricular interval from 6 to 40 weeks' gestational age. Before 10 weeks, a prolonged atrioventricular interval in healthy fetuses largely reflects the lengthened isovolumic contraction time which is likely influenced by the evolution of ventricular function and afterload.

Measurement of fetal atrioventricular time intervals: A comparison of 3 spectral Doppler techniques

OBJECTIVE

To establish nomograms for fetal atrioventricular (AV) time intervals assessed by 3 different pulsed-wave Doppler techniques: left ventricular inflow and outflow tracts (LV in/out), superior vena cava and ascending aorta (SVC/AA), and pulmonary artery and pulmonary vein (PA/PV).

METHODS

A cross-sectional study was performed in 311 normal fetuses divided into 5 groups between 16 and 38 weeks. Pulsed-wave Doppler-derived AV intervals were measured by interrogation of flow in LV in/out, SVC/AA, and PA/PV. Linear regression analyses were performed to examine correlations with gestational age (GA) and fetal heart rate (FHR). Intraclass correlation coefficients for reproducibility of each method were compared.

RESULTS

Pulmonary artery and pulmonary vein revealed the longest mean AV time intervals (P < .001). The AV intervals in all methods were positively correlated with GA (R²  = 0.20-0.36; P < .001) and negatively correlated with FHR (R²  = 0.09-0.19; P < .001). The SCV/AA time intervals demonstrated the weakest influence of FHR. For LV in/out, SVC/AA, and PA/PV, intraobserver and interobserver reliability coefficients showed excellent agreements (all intraclass correlation coefficients ≥ 0.80).

CONCLUSION

All pulsed-wave Doppler-derived AV time intervals increased with advancing GA and decreased with increasing FHR. Fetal AV interval measurements can be obtained in a clinically viable fashion with excellent reproducibility.

Cardiac time intervals derived by magnetocardiography in fetuses exposed to pregnancy hypertension syndromes

OBJECTIVE

To test the hypothesis that fetuses exposed to maternal preeclampsia or chronic hypertension have deranged development of cardiac time intervals.

STUDY DESIGN

Pregnancies were divided into three groups: Intrauterine Growth Restricted (IUGR), Hypertensive, and Normal. Each group's mean fetal cardiac time intervals (P, PR, QRS and RR) derived by magnetocardiography were calculated using an analysis of covariance model's regression-adjusted estimates for a gestational age of 35 weeks.

RESULTS

We reviewed 141 recordings from 21 IUGR, 46 Hypertensive and 74 Normal patients. The IUGR, Hypertensive and Normal groups, respectively, had adjusted mean intervals in milliseconds of 66.4, 66.8 and 76.2 for P (P=0.001), 95.9, 101.6 and 109.6 for PR (P=0.002), 77.2, 78.7 and 78.7 for QRS (P=0.81) and 429.8, 429.2 and 428.5 for RR (P=0.97).

CONCLUSION

P and PR intervals are abbreviated in normotrophic fetuses exposed to maternal hypertension, suggesting shortened atrioventricular conduction times.

Finding the "PR-fect" solution: what is the best tool to measure fetal cardiac PR intervals for the detection and possible treatment of early conduction disease?

In the absence of structural heart disease, the great majority of cases with complete congenital heart block will be associated with the maternal autoantibodies directed to components of the SSA/Ro-SSB/La ribonucleoprotein complex. Usually presenting in fetal life before 26 weeks' gestation, once third-degree (complete) heart block develops, it is irreversible. Therefore, investigators over the past several years have attempted to predict which fetuses will be at risk for advanced conduction abnormalities by identifying a biomarker for less severe or incomplete disease, in this case, PR interval prolongation or first-degree atrioventricular block. In this state-of-the-art review, we critically analyze the various approaches to defining PR interval prolongation in the fetus, and then analyze several clinical trials that have attempted to address the question of whether complete heart block can be predicted and/or prevented. We find that, first and foremost, definitions of first-degree atrioventricular block vary but that the techniques themselves are all similarly valid and reliable. Nevertheless, the task of predicting those fetuses at risk, and who are therefore candidates for treatment, remains challenging. Of concern, despite anecdotal evidence, there is currently no conclusive proof that a prolonged PR interval predicts complete heart block.

Atrioventricular conduction time in fetuses assessed by Doppler echocardiography

We performed measurement of mechanical atrioventricular conduction time intervals in human fetuses assessed by Doppler echocardiography and provided reference values. We found that atrioventricular conduction time interval was prolonged with gestational age and decreased with increasing fetal heart rate. No correlation between gestational age and heart rate was found. Using normal limits established by this study, mechanical atrioventricular interval >135 ms in the 20(th) week and/or >145 ms in the 26(th) week of gestation could be suspected of having the first-degree AV block. We compared reference values with fetuses of mothers with anti-SSA Ro/SSB La autoantibodies, being in risk of isolated congenital heart block development. One of 21 fetuses of mothers with positive autoantibodies was affected by prolonged atrioventricular interval according to the established limits, with sinus rhythm after the birth.

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. Healthy mothers with sonographically normal fetuses from 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 had 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) ms 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 are influenced by GA and FHR independently, and both variables should be taken into account when evaluating fetuses at risk for congenital heart block.

FETAL BRADYCARDIA. A PRACTICAL APPROACH

Fetal bradycardia may herald fetal demise. This article highlights arrhythmic fetal bradycardia rather than bradycardia caused by perinatal distress. We briefly examine the embryonic conduction system's development and physiology and we review the classification, aetiology, evaluation, and approach to fetal bradycardia. Our aim is to provide the clinician with practical information about fetal bradycardia that enlightens causative conditions and aids management.

Assessing fetal cardiac ventricular function

Fetal echocardiography has been used primarily to identify fetuses with structural malformations of the heart. Evaluation of fetal ventricular function, however, has received minimal attention since the inception of fetal echocardiography in the early 1980s. This communication reviews the use of M-mode, B-mode and pulsed Doppler ultrasound to examine cardiac function. M-mode ultrasound is used to determine the size of the fetal heart, the end-diastolic and end-systolic dimensions of the ventricular chambers, and the thickness of the ventricular walls and the interventricular septum, and to measure the diameter of the mitral and tricuspid valves as well as the diameter of the aorta and pulmonary artery. B-mode evaluation of the fetal heart includes measurement of atrial and ventricular dimensions as well as dimensions of the outflow tracts. This modality is useful when M-mode measurements cannot be made due to fetal position. Once measurements of cardiac structures are obtained using either M-mode or B-mode ultrasound, pulsed Doppler recording of mitral valve, tricuspid valve, aortic valve and pulmonary artery waveforms can be used to compute cardiac output as well as stroke volume. In addition, pulsed Doppler can be used to evaluate diastolic and systolic cardiac functions by examining the components of each waveform.