Abstract 393: Is High Grade Atrioventricular Block Reversible in Hypothyroidism

Abstract

Background: Hypothyroidism is considered a reversible cause of atrioventricular block (AVB) but rigorous studies to support this are limited. An important consideration in clinical practice is whether pacemaker placement should be deferred in patients with hypothyroidism who present with high degree AV block while awaiting reversal of block. This period of waiting places patients at risk of morbidity and mortality, while extending length of stay and cost of care. Objective: To evaluated if high degree AVB in hypothyroidism is in fact reversible, and therefore justify delaying pacemaker(PM) placement. Method: Retrospective review of all adult admission with high degree (Mobitz type II or type III) AVB admitted to a Regional hospital over a 10 year period. Out of 271 cases identified, 41 had hypothyroidism (either prior history or newly diagnosed), and were matched by age and sex with 41 patients with AVB but without hypothyroidism. Each group of 41 patients had 25 females (61%) and 16 men (39%). Placement of PM is assumed to indicate lack of reversibility of AVB. Statistic analysis for matched pairs was by McNemar’s test with Yates continuity correction. Results: In the hypothyroidism group, 31 of 41 patients(76%) received PM, while 34 of 41 patients (83%) in the group without hypothyroidism received PM. The calculated test statistic was 12.02, and when referred to the Chi-squared distribution table with 1 degree of freedom, gives a probability of < 0.01, which is highly significant. 14 of the 41 patients(34%) with hypothyroidism had thyroid dysfunction based on thyroid hormone levels, with 10(24%) having sub-clinical hypothyroidism, and 4 (10%) having overt disease. The mean duration in days from time of admission to time of PM placement in the hypothyroidism group was 4.35, while that in the group without hypothyroidism was 2.26. Conclusion: The finding rejects the null hypothesis that there is no difference in need for PM (and thus reversibility of AVB) in both groups, suggesting AVB may in fact be reversible in hypothyroidism. Larger and more rigorous studies are therefore warranted to definitively determine if AVB in hypothyroidism is reversible, and adopt delaying PM placement while awaiting reversal, as standard of care.