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Slow Heart Registry of Fetal Immune-mediated High Degree Heart Block

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

Who can join

Ages 16 to 50 · Women

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)

About the study

Few studies are specifically designed to address health concerns that are already relevant during pregnancy. The consequence is a lack of evidence on best clinical practice. This includes mothers and their babies when pregnancy is complicated by an abnormally slow heart rate due to maternal antibody-mediated heart disease in the unborn baby (fetus). Since the late seventies, it has been possible to detect and monitor fetal disease by ultrasound images and to treat selected conditions with pharmaceuticals administered via the mother. To this day, physicians need to make decisions about the management of such pregnancies without evidence from prospective clinical trials on drug efficacy and safety. The SLOW HEART REGISTRY is a multi-centered prospective observational study that will address the knowledge gap to guide future management of high-degree immune-mediated heart block to the best of care. The study seeks to establish an international database of the management and outcome of affected fetuses, to be used to publish information on the results of currently available prenatal care and to evaluate the need for additional research.

What is being tested

• Dexamethasone (drug)
• No Dexamethasone (other)

Sponsor: The Hospital for Sick Children · Participants: 350 · Started: Jan 1, 2020

Contact the study team

• Diana Balmer-Minnes, BSc, CCRP · Phone: 416-813-7654
• Edgar Jaeggi, MD · Phone: 418-813-7466

Official record on ClinicalTrials.gov — NCT04559425

Locations in the U.S.

From ClinicalTrials.gov, data retrieved Sep 30, 2026. Each study sets its own eligibility; the study team decides who can join.