Letter by Jaeggi et al Regarding Article, “Perinatal Outcome of Fetal Atrioventricular Block: One-Hundred Sixteen Cases From a Single Institution”
To the Editor:
We have read with great interest the article by Lopes et al,1 which reveals that “the survival rate of >90% of untreated patients with isolated forms of atrioventricular (AV) block raises concerns about any decision to intervene with immunosuppressive agents.” The advice for a cautionary use of prenatal treatment is based on the observation that “unlike the study by Jaeggi et al,2 our untreated patients did not have such an unfavorable outcome.” We respectfully disagree in accepting the authors’ interpretations of study findings that are based on the impression that all forms of isolated AV block have the same risks, treatment and outcome. This has not been our experience:
Firstly, our study2 did not include transient 2:1 AV block, which likely results from arrhythmia-induced intermittent functional blockage of the antegrade AV conduction, similar to atrial bigeminy.3 Unlike in true 2:1 AV block, every alternating nonconducted atrial beat occurs more prematurely than physiologically expected. In Figure 3 of their article, Lopes et al show an example of transient AV block. On the atrial M-mode recording, neighboring systolic wall movements clearly differ in timing, and complete resolution of 2:1 AV block is expected. Inclusion of functional AV block improved the survival estimates of isolated heart block by 7% in this article.
Secondly, whether dexamethasone has beneficial effects on seronegative AV block is unknown: In the few cases we have seen with complete AV block (CAVB), dexamethasone was always weaned off but β-sympathomimetic support continued. To the credit of Lopes et al, our published guidelines do not address differences in management among seronegative and seropositive CAVB, and this was an oversight.2
Thirdly, the rationale for using routine transplacental immunosuppressive treatment is to improve outcome of seropositive CAVB, preferably by preventing rather than treating major disease-related complications such as myocardial inflammation and fibrosis. To be most effective, treatment is ideally initiated closest to the onset of CAVB, which typically appears before 24 weeks. Asymptomatic cases have a low risk of demise once they reach late gestation or birth1,4; thus, we treat only those with findings associated with poor outcome. A comparison of our study2 and that of Lopes et al suggests major differences in the 2 patient cohorts. Specifically, in our study isolated AV block was detected earlier (24.7 versus 29.5 weeks), was more likely complete (100% versus 72%; P=0.002), and was related to maternal anti-Ro antibodies (93% versus 63%; P<0.05). We found that with the introduction of transplacental treatment, live birth and 1-year survival improved to 95% and 90%, respectively for autoantibody-mediated fetal CAVB.2 No prenatally treated child developed late-onset cardiomyopathy. This result compares quite favorably to the outcome of isolated AV block in this study, with most fetuses having received no treatment. Given that every fourth fetus did not survive to infancy it may be misleading to simply point out the good outcome of untreated survivors. Many untreated cases had no need for steroids in the first place, whereas severely compromised fetuses were likely to obtain treatment preceding death. To eliminate any ambiguity on the utility of the use of steroids for antibody-associated fetal AV block, Lopes et al should present survival estimates of the 36 cases with proven exposure to maternal anti-Ro antibodies at the time of AV block diagnosis. While we agree with Lopes et al that survival with immune-mediated AV block is often possible without treatment, we would argue that the high attrition rate of this and similarly managed patient series2,4,5 supports rather than precludes the preventive use of steroids before the development of most severe complications.
Lopes LM, Tavares GM, Damiano AP, Lopes MA, Aiello VD, Schultz R, Zugaib M. Perinatal outcome of fetal atrioventricular block: one-hundred-sixteen cases from a single institution. Circulation. 2008; 118: 1268–1275.
Jaeggi ET, Fouron JC, Silverman ED, Ryan G, Smallhorn J, Hornberger LK. Transplacental fetal treatment improves the outcome of prenatally diagnosed complete atrioventricular block without structural heart disease. Circulation. 2004; 110: 1542–1548.
Carvalho J, Jaeggi E. Sustained fetal bradycardia: mechanisms and pitfalls. Ultrasound Obstet Gynecol. 2006; 28: 407. Abstract.