Registry for Fetal Immune-mediated Heart Block

Slow Heart Registry: A Prospective Observational Cohort Study of Fetal Immune-mediated High Degree Heart Block

Observational The Hospital for Sick Children · NCT04559425

This study is trying to see how different treatments for fetuses with a serious heart condition affect their health and survival as they grow up.

Quick facts

Study typeObservational
Enrollment350 (estimated)
Ages16 Years to 50 Years
SexFemale
SponsorThe Hospital for Sick Children Academic / other
Locations27 sites (Phoenix, Arizona and 26 other locations)
Trial IDNCT04559425 on ClinicalTrials.gov

What this trial studies

The SLOW HEART REGISTRY is a multi-centered observational study focused on fetuses diagnosed with high-degree immune-mediated atrio-ventricular heart block (AVB). It aims to create an international database to document management strategies and outcomes for affected fetuses, comparing those treated with glucocorticoids to those who are not. The study will evaluate various clinical outcomes, including survival rates and the need for additional treatments, from diagnosis through the first few years of life. This research addresses a significant gap in prenatal care by providing evidence-based insights into the management of this condition.

Who should consider this trial

Good fit: Ideal candidates for this study are pregnant women whose fetuses have been diagnosed with high-degree AVB and have positive or pending anti-Ro/La antibody test results.

Not a fit: Patients whose AVB is associated with major congenital heart defects or who have negative anti-Ro/La antibody test results may not benefit from this study.

Why it matters

Potential benefit: If successful, this study could improve prenatal management strategies for fetuses with immune-mediated heart block, potentially enhancing survival rates and health outcomes.

How similar studies have performed: While there is limited evidence from similar studies, this registry approach is novel and aims to fill a critical knowledge gap in the management of fetal heart block.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Written informed maternal consent to participate in the Slow Heart Registry
* High-degree (2nd; 2:1; 2nd-3rd or 3rd degree) AVB diagnosed ≤ 32+0 weeks with or without hydrops
* Enrollment within maximally 8 days of high-degree AVB diagnosis
* Positive or pending anti-Ro/La antibody test results at the time of enrollment

Exclusion Criteria:

* AVB associated with major CHD (e.g. left atrial isomerism, cc-TGA)
* AVB with known negative anti-Ro and/or La antibody test result at enrollment
* 1st degree AVB
* Sinus bradycardia with normal 1:1 AV conduction
* Blocked atrial bigeminy (irregular atrial rate with failure of AV conduction of the premature atrial beat)
* Primary delivery for postnatal treatment
* Maternal-fetal conditions (other than cardiac NL) associated with high odds of premature delivery or death (e.g. renal failure, significant infectious diseases, major extracardiac anomalies, PROM, etc.)
* Preexisting maternal mental disorder (e.g. bipolar, mania, severe depression, substance abuse)
* Poorly controlled insulin-dependent diabetes (HbA1c \>7%) at CAVB diagnosis
* Oligohydramnios (deepest/maximal vertical pocket \<2 cm)
* Severe IUGR (estimated fetal weight \<3rd percentile)

Where this trial is running

Phoenix, Arizona and 26 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Heart Block CompleteHeart Block Second Degreefetalheart blockanti-Ro antibodiessteroidsoutcome
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.