To investigate if anti-Ro/SSA antibody-exposed fetuses with prolonged atrioventricular (AV) time intervals also have prolongation of the isovolumetric contraction time (ICT).
To investigate if anti-Ro/SSA antibody-exposed fetuses with prolonged atrioventricular (AV) time intervals also have prolongation of the isovolumetric contraction time (ICT).
Seventy-eight anti-Ro/SSA (including 70 anti-Ro52) antibody-exposed fetuses at risk for congenital heart block (CHB) were followed weekly, between 18 and 24 weeks of gestation, with two Doppler echocardiographic methods designed to detect signs of first-degree AV block. One of these AV time measurements, using hemodynamic events from the mitral valve and aortic outflow as indirect markers of atrial and ventricular depolarization (MV-Ao), was also used to calculate a time interval representing an early phase of systolic cardiac performance, i.e. the ICT. Two hundred and eighty-four women with normal pregnancies served as controls for AV time intervals and another 106 were used to establish an ICT reference range.
Strong positive relationships were found between ICT and MV-Ao time intervals (r = 0.91, P < 0.001), as well as between ICT and time intervals obtained from the superior vena cava and aorta (r = 0.85, P < 0.001). The ICT was estimated to contribute more than 50% of the total AV time prolongation. Abnormal AV time and ICT intervals were only seen in anti-Ro52 positive pregnancies.
The ICT is an important contributor to prolongation of AV time intervals. This observation suggests that anti-Ro52/SSA antibody-exposed fetal hearts have not only disturbed electrical conduction but also decreased mechanical performance. Moreover, our findings have implications for the interpretation of AV time intervals used for surveillance of fetuses at risk for developing CHB. Copyright © 2009 ISUOG. Published by John Wiley & Sons, Ltd.
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The link between transplacental transfer of maternal anti-Ro and anti-La autoantibodies and fetal congenital heart block (CHB) is now well established1. Maternal anti-Ro and anti-La antibodies have furthermore been suggested not only to affect the tissue of the fetal cardiac conduction system, but also to have the potential to induce a more diffuse immune reaction within the endomyocardium, leading to endocardial fibroelastosis2, end-stage heart failure and death3, 4. Endocardial fibroelastosis, or its echocardiographic presentation, with localized increases in echogenicity and thickness of the cardiac walls, with or without signs of decreased ventricular function, has also been described in rare cases of anti-Ro and anti-La antibody-exposed fetuses without CHB or with incomplete atrioventricular (AV) block2, 5, 6.
In an attempt to detect fetuses with first-degree AV block by using Doppler echocardiographic techniques, we observed that a surprisingly high proportion of anti-Ro52 antibody-exposed fetuses had AV time intervals above our normal reference range, with spontaneous normalization before or shortly after birth7. The association of prolonged AV time intervals and early signs of myocardial dysfunction (decreased fractional shortening) has been described in one anti-Ro and anti-La antibody-exposed fetus of a woman with a previous pregnancy complicated by CHB8, 9. To the best of our knowledge, no systematic attempts have been made to evaluate whether fetuses at risk for CHB also have early signs (i.e. in the absence of second or third-degree heart block) of decreased cardiac performance.
Doppler echocardiographic techniques to estimate AV time intervals use hemodynamic events as indirect markers of atrial and ventricular depolarization10–12. Hence, AV time interval measurements will be the result not only of electrical, but also of mechanical components, especially those that use the aortic outflow as a marker of ventricular activation, in which case the early systolic phase of isovolumetric contraction will be included in the measurement12. Having systematically followed a cohort of anti-Ro positive pregnant women with fetal Doppler echocardiography to detect early signs of AV block, we noticed that this early systolic time interval (the isovolumetric contraction time (ICT)) appeared to be long in some fetuses with prolonged AV time intervals (Figure 1).
The primary objective of this study was to investigate whether anti-Ro antibody-exposed fetuses with prolonged AV time intervals also had prolongation of the ICT, as an early sign of impaired cardiac function. As recent studies suggest that antibodies targeted at the 52-kd component of the Ro-antigen seem to be more likely to induce CHB than are antibodies targeted at the 60-kd component13–15, a second goal was to determine whether we could detect any differences between those anti-Ro positive pregnancies that were antibody positive and those that were antibody negative to the Ro52-antigen.
From December 1999 to March 2007, 62 women with a mean ± SD age of 31.0 ± 4.1 years were recruited to follow our protocol for the surveillance of pregnant anti-Ro52 positive women at risk for fetal CHB. Fifteen women had Sjögren's syndrome, 31 had systemic lupus erythematosus (four with secondary Sjögren's syndrome), seven had rheumatoid arthritis, seven had undifferentiated autoimmune syndrome and two were asymptomatic. All women were anti-Ro positive, but six of the 62 women studied (eight singleton pregnancies) could not be confirmed at follow-up as anti-Ro52 positive, when analyzed by ELISA and Western blot. Fifteen of the women were studied during two subsequent pregnancies and another was carrying twins. In all, 78 fetuses were followed weekly with echocardiographic examinations between 18 and 24 weeks of gestation. Fetal echocardiographic studies from 106 healthy women, with a family history of cardiac malformation and a normal pregnancy, were used to establish a normal reference range for ICT. Gestational age had been determined by ultrasound biometry before 18 weeks of gestation in both patients and controls. All women gave informed consent to participate and the study was approved by the ethics committee at Karolinska University Hospital. Some results from the first 24 anti-Ro52 positive pregnancies have been reported previously7, 16.
All echocardiographic studies were performed using an Acuson Sequoia ultrasound system with a 6C2 transducer (Siemens Medical Solutions, Ultrasound Division, Mountain View, CA, USA). After performing a structural cardiac examination, AV time intervals were measured, using previously described Doppler methods7, 11, 12. Briefly, pulsed Doppler traces showing diastolic filling through the mitral valve (MV) and left ventricular systolic ejection were recorded from a five-chamber view. From a longitudinal view, obtained by a 90° rotation from a four-chamber view in the vertical position, traces were recorded showing the retrograde venous a-wave in the superior vena cava (SVC) and the ejection wave in the ascending aorta. Until the end of year 2000, records were stored on video tape, and thereafter digitally, for later analysis. On the MV-aortic outflow recordings (Figure 1), AV time intervals were measured from the intersection of the mitral E- and A-waves to the onset of the ventricular ejection wave in the aortic outflow (MV-Ao). We also quantified an AV time interval starting with the same event but ending at the closure (click) of the MV, which is believed to represent the first mechanical sign of ventricular systole in these tracings. The difference between these two measurements (MV-Ao and MV), the ICT (Figure 1), was calculated by subtraction. AV time intervals on recordings from the SVC and aorta were measured from the beginning of the retrograde venous a-wave in the SVC to the beginning of the aortic ejection wave (SVC-Ao). All time intervals were measured on three cardiac cycles and averaged.
Statistical analysis was performed using the computer package Statistica 7.1 (StatSoft, Tulsa, OK, USA). For statistical purposes each fetus was represented by only one observation constructed from the average of the two examinations in which the highest MV-Ao time interval measurements were observed. Variables with a skewness and kurtosis within ± 1.0 were accepted as being normally distributed. Relationships between the different AV time intervals as well as heart rate (FHR) were investigated by using linear regression with F-test and plots as suggested by Bland and Altman17, 18. All fetuses were also divided into three groups (≤ 95%, > 95 to 99%, > 99%) depending on how their two highest MV-Ao time measurements compared to a 95% and a 99% reference range, based on 284 women with normal pregnancies7, 11. To compare groups we used one-way ANOVA with Tukey HSD and contrast analysis as post-hoc tests. A P-value < 0.05 was considered statistically significant.
All fetuses had structurally normal hearts of normal size, without any obvious myocardial thickening or localized echodensities. Four hundred and forty-eight fetal echocardiographic studies, originally performed to follow our 78 fetuses at risk for CHB with MV-Ao and SVC-Ao time intervals, were retrieved to analyze the MV time interval and the ICT. Recordings from the MV-aortic outflow with 1 : 1 AV conduction, and enough information to measure the MV time interval and calculate the ICT, were present in 397 examinations. By plotting these original observations, a clear trend for ICT to increase with longer MV-Ao and SVC-Ao time intervals was demonstrated (Figure 2). The plots also suggested that the longer time intervals were observed exclusively in pregnancies of anti-Ro52 positive women.
As expected from this preliminary analysis, a significant positive relationship with excellent correlation was demonstrated between ICT and MV-Ao time intervals (y = − 56 + 0.73x, Sy/x (standard error of the estimate) = 3.7 ms, r = 0.91, P < 0.001) when each fetus was represented by only one observation (Figure 3a). This relationship was even stronger than the linear regression between MV and MV-Ao time intervals (y = 56 + 0.27x, Sy/x = 3.7 ms, r = 0.62, P < 0.001) that is illustrated in the same figure.
By plotting the ICT, i.e. the difference between individual MV and MV-Ao time interval observations, against their average, as suggested by Bland and Altman18, it became even more evident that an increase in ICT was an important contributor to the prolongation of AV time intervals seen in some of our anti-Ro52 antibody-exposed fetuses (Figure 3b). The same observation was made when ICT was correlated with SVC-Ao time intervals (y = − 38 + 0.61x, Sy/x = 4.6 ms, r = 0.85, P < 0.001) recorded at the same examination (Figure 4a). There was no linear correlation, however, between ICT and heart rate, as demonstrated in Figure 4b.
Fifty-six fetuses had an MV-Ao time interval within our 95% reference range for normal pregnancies, seven fetuses had a time interval in the > 95 to 99% range, and 15 exceeded the 99% reference range (Table 1). Compared with fetuses within the 95% range, the ICT was longer in fetuses in the > 95 to 99% as well as those in the > 99% range. The ICT values measured on recordings from fetuses in the ≤ 95% range (33 ± 5.1 ms) were not different from the reference values obtained from our 106 normal pregnancies (31 ± 4.5 ms), but in both other groups they were significantly higher (P < 0.001). MV time intervals observed in fetuses exceeding the 99% range, but not those recorded from fetuses in the > 95 to 99% range, were higher than in those within the 95% range (Table 1). There were no differences in FHR or gestational age between the groups.
|MV-Ao group*||MV-Ao (ms)||n||GA (weeks)||ICT (ms)||MV (ms)||SVC-Ao (ms)||FHR (bpm)|
|≤ 95%||122 ± 6.4||56||21.6 ± 1.6||33 ± 5.1||90 ± 4.2||116 ± 7.1||144 ± 6.2|
|> 95 to 99%||135 ± 3.5||7||22.1 ± 1.5||43 ± 5.5†||92 ± 3.4||129 ± 5.4†||141 ± 2.1|
|> 99%||144 ± 6.1||15||22.6 ± 2.8||49 ± 6.2‡||95 ± 4.5†||140 ± 7.2†§||141 ± 7.1|
The eight fetuses of anti-Ro positive but anti-Ro52 negative mothers had MV-Ao time interval measurements within our normal reference range, and an ICT (30 ± 3.9 ms) that did not deviate from the values found in the 106 normal pregnancies. The 70 anti-Ro52 antibody-exposed fetuses had an ICT (37 ± 8.7 ms) that was significantly longer than that found in anti-Ro52 negative (P < 0.01) and normal (P < 0.005) pregnancies. When extending this analysis by plotting data from all 184 of these fetuses on the same graph, we observed that our measurements made on normal pregnancy fetuses closely followed the relationship between ICT and MV-Ao time intervals found in anti-Ro antibody-exposed fetuses (Figure 5). Not surprisingly, a positive linear relationship between ICT and MV-Ao time intervals (y = − 37 + 0.59x, Sy/x = 2.5 ms, r = 0.83, P < 0.001) was also demonstrated in our normal control fetuses.
We found that prolongation of the ICT was an important contributor to the prolongation of AV time intervals observed during mid-gestation in our anti-Ro52 antibody-exposed fetuses. Notably, prolongation of the ICT was only seen in anti-Ro52 positive pregnancies, but as the number of fetuses exposed to anti-Ro antibodies not targeted at the 52-kd component was small, it is not possible to draw any definitive conclusions regarding the specificity of the antibodies in relation to the occurrence of prolongation of ICT and AV time intervals.
As prolongation of MV and MV-Ao time intervals results in an increasing overlap of mitral E- and A-waves, and thus an artificial shortening of these intervals12, the relative contribution of the ICT to the prolongation of the total MV-Ao time interval might be exaggerated. However, as SVC-Ao time intervals do not suffer from this source of error, the slope of the relationship between ICT and SVC-Ao time intervals (0.61 ± 0.05 ms/ms), indicating that approximately 60% of the total AV time prolongation was confined to the ICT, might be expected to be a better estimate.
Our reference data for the AV time intervals do not rest only on 284 normal pregnancies7, 11 as they were recently confirmed in an independent study of 110 pregnant women19. Our ICT values observed in 106 normal pregnancies are approximately 3 ms longer than are recently published reference values obtained from 557 normal fetuses20, which is well explained by the fact that these investigators used an event that occurs slightly earlier on the Doppler tracing to denote the end of the ICT. The reference ICT values obtained in our present study (31 ± 4.5 ms) were also similar to our own previous data from newborn infants (35 ± 6.0 ms)12, supporting the previous observation that the ICT remains constant during gestation20–22. Hence, we have reason to believe that our anti-Ro52 exposed fetuses with abnormal AV time intervals also had abnormally long ICT intervals.
ICT has been demonstrated to show a strong negative correlation with the maximum rate of early systolic rise in left ventricular pressure23–26, which in turn is considered a sensitive measure of myocardial contractility27. Recent data also imply that ICT measurements from Doppler tracings can be used as a reliable index of cardiac contractility in the fetus25, 26. A prolongation of ICT was also seen with a reduction in diastolic ventricular filling or an increase in systolic arterial pressure27.
The most obvious explanation for the decreased cardiac performance, as indicated by the prolonged ICT, seen in a large proportion of our fetuses is a reduction in myocardial contractility. This idea is supported by current models of the pathogenesis of CHB, in which anti-Ro52 antibodies have been reported to cross-react with a cardiomyocyte cell surface protein and induce dysregulation of intracellular Ca2+ homeostasis16. Ca2+ is a main regulator of cardiomyocyte contraction, and disturbance in intracellular Ca2+ levels can be predicted to affect myocardial contractility independent of AV block progression. Reported clinical observations indicating a more global endomyocardial process, without concomitant second- or third-degree AV block5, 6, 8, 9, also support our concept of more discrete myocardial function disturbances without obvious structural changes in anti-Ro52 antibody-exposed fetuses.
Prolonged ICT values have been demonstrated to predict severe intrauterine growth restriction and adverse outcome in pregnancies with placental vascular disease21. In our present study all pregnancies, with the exception of one in which the fetus developed second-degree AV block, were considered normal, with an appropriately growing fetus, during the period of echocardiographic surveillance. Our visual validation of cardiac size and function as well as Doppler recordings from the SVC, MV, aorta and pulmonary artery also lead us to believe that abnormalities in ventricular filling and systolic arterial pressure are unlikely to have made any significant contribution to the observed disturbance in cardiac performance. As previously suggested, we did not find any effect of heart rate on ICT measurements21, 26.
Not only do our results suggest that maternal anti-Ro52 antibodies could have spontaneously reversible effects on fetal cardiac performance, they also have clinical implications. Of our 70 fetuses exposed to anti-Ro52 antibodies, 22 had MV-Ao time intervals exceeding our 95% reference range, but only two developed second- or third-degree AV block. One had a long ICT (49 ms) before the complete block was diagnosed and the other had an ICT of 70 ms when the second-degree heart block was diagnosed (Figure 1d). All other fetuses with abnormal mid-trimester AV time intervals spontaneously normalized their AV conduction before or shortly after birth. In the majority of these cases, AV time intervals did not exceed our reference values by more than 10 ms, with a significant contribution from the ICT (Figure 5), suggesting that the AV time prolongation seen in these cases might be due not only to an electrical conduction disturbance but also to a decrease in systolic cardiac performance. These observations are in accordance with a recent study demonstrating that two of six fetuses with abnormal AV time intervals had a normal PR interval on fetal electrocardiography28. Thus, when using AV time intervals including ICT it should be kept in mind that these intervals are the result of electrical and mechanical components, both of which can be prolonged. In accordance with these present observations we have so far only considered the isolated finding of abnormal AV time intervals as an indication for closer surveillance, withholding treatment with fluorinated steroids until the detection of signs of second-degree AV block or endomyocardial disease.
Financial support was provided through the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet, Karolinska Institutet, the Swedish Foundation for Research, and the Swedish Heart Lung Foundation. Dr Bergman was supported by Freemason's in Stockholm Foundation for Children's Welfare and the foundation Samariten, Stockholm.