Preventive IVIG Therapy for Congenital Heart Block

Perhaps the strongest clinical association with autoantibodies against SSA/Ro-SSB/La is the development of congenital heart block (CHB) in an offspring, an alarming prospect facing 2% of primigravid mothers with these antibodies. Recurrence rates approach 20%. Disease can progress rapidly, with advanced block and life-threatening cardiomyopathy observed less than 2 weeks from normal sinus rhythm. Once 3rd degree (complete) block is identified, reversal has never been achieved, despite dexamethasone. This makes biologic sense since the signature lesion is fibrosis of the atrioventricular node. Thus, strategies aimed at preventing disease assume high priority. Although disease expression in the fetus requires additional factors to amplify the cascade to fibrosis, maternal anti-Ro/La antibodies are necessary. Accordingly, eliminating fetal exposure to these antibodies is a sound and important approach. Intravenous immune globulin (IVIG) is particularly exciting in its potential not only to lower maternal antibody levels (which is not accomplished with glucocorticoids or immunosuppression), but actually to influence effector mechanisms in the fetus itself. Aim 1 is a clinical trial to assess the efficacy of IVIG in preventing CHB. Proof of efficacy is challenging since CHB occurs in only 2% of first pregnancies of anti-Ro/La+ women. However, given the 10-fold higher risk of CHB in a pregnancy after the birth of child with neonatal lupus (NL), mothers with previous NL-affected children are the target population for study. Sample size calculations employ Simon's 2-stage optimal design. Based on a 2-sided significance level of 0.05, a power of 90% to show reduction of risk to 5% given the prediction that 18% of untreated subjects will get some degree of CHB, Stage 1 will enroll 19 women who have had a previous child with CHB or NL rash, to receive IVIG (400 mg/kg IVIG every 3 weeks for a total of 5 treatments) from weeks 12 through 24 of gestation. If fewer than 3 mothers have children with 2nd or 3rd degree block, then an additional 35 mothers will be enrolled in Stage 2 (total = 54 subjects). IVIG will be considered efficacious and worthy of further study if fewer than 6 of 54 subjects have a child with advanced CHB. Secondary outcomes include 1st degree block, myocardial injury absent conduction defects, and isolated endocardial fibroelastosis as assessed by serial fetal echocardiograms and EKG at birth.

Aim 2 will address: a) the effect of IVIG on antibody titer and subclass; b) genetic polymorphisms in Fc gamma receptor (FcgR) and platelet-activating factor acetylhydrolase and their potential association with response to IVIG; c) whether a decrease in anti-La antibodies positively correlates with the level of anti-La antiidiotypic antibodies; d) whether IVIG blocks expression of activation markers on human macrophages after challenge with opsonized apoptotic cardiocytes and whether this positively correlates with increased expression of the inhibitory Fc receptor, FcgRIIb.

In sum, IVIG is a promising agent that may have effects at several levels of the pathologic cascade to antibody-mediated CHB.