Electrophysiological Consequences of Congenital Heart Defects Shaped by Primary Cilia‐Dependent Cardiac Developmental Processes

Abstract

Congenital heart defects (CHD) affect approximately 8 out of every 1,000 newborns, resulting in the birth of 35,000 babies with CHD annually in the United States. Primary cilia are small, finger‐like structures that extend from almost all eukaryotic cells and have been found to play a pivotal role in both development and maturation of embryonic and perinatal heart. Our laboratory presents a novel cardiac phenotype resulting from the elimination of primary cilia from cardiac neural crest cells (cNCC) of the embryonic mouse heart. This phenotype combines a high incidence of outflow tract defects, including double‐outlet right ventricle, with severe damage to the membranous interventricular septum, non‐compaction of the developing ventricular myocardium, and perinatal lethality. The purpose of this ongoing project is to develop a reliable method for obtaining electrocardiograms (ECG) in perinatal mice, to perform a comprehensive and diagnostic analysis of the combined anatomical and physiological data and to better understand the perinatal lethality resulting from primary cilia elimination. A Cre recombinase‐expressing mouse (Wnt1:Cre) was crossed with the Ift88flox/flox mouse, resulting in elimination of primary cilia from cNCC during mid embryonic heart development. Extensive histological and imaging analyses were previously performed to characterize and reconstruct the anatomical abnormalities. Perinatal electrocardiography (ECG) was then performed on 34 pups within the first day of life (P1), where mice remained conscious in the prone position. Modified gel‐coated ECG electrodes were placed in the right axilla of the left lower quadrant of the abdomen, allowing for a two‐lead electrophysiological evaluation. ECGs were collected for a total of 5 minutes, after which, pups were euthanized for further histological evaluation. ECG analysis included heart rate (HR; minimum, maximum and mean), QRS duration, P wave presence, PR interval, and overall ECG interpretation. Mutant mice (n=26) demonstrated a significantly lower HR when compared to littermate wildtype (WT) (n=8) mice (233±24 beats per minute (bpm) vs 30±2 bpm, p<0.0001). QRS duration was significantly lengthened in the mutant mice compared with WT (0.020±0.001 milliseconds (ms) vs 0.014±0.001 ms, p=0.018). P wave activity was absent in 54% of mutant mice when compared to 100% appearance in WT mice. Combined incidence of bradycardia, HR irregularity and the absence of P wave activity seen in the mutant mice suggests that the QRS complexes demonstrated were not sinus in nature, rather of a junctional or ventricular origin. Whether this is due to a defect in SA node development, communication between the atria and ventricles, or hypoxia is currently under investigation. Increased QRS duration seen in mutant mice is suggestive of additional depolarization abnormalities. Collectively, these results characterize a relationship between the anatomical phenotype resulting from primary cilia elimination and abnormal embryological development of cardiac electrical conduction pathways.Support or Funding InformationGenerous support for this project was made possible by the Saving tiny Hearts Foundation and the Peter Morgane Fellowship Program at the University of New England.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.