Because of its powerful genetics, the adult zebrafish has been increasingly used for studying cardiovascular diseases. Considering its heart rate of~100 beats per minute at ambient temperature, which is very close to human, we assessed the use of this vertebrate animal for modeling heart rhythm disorders such as sinus arrest (SA) and sick sinus syndrome (SSS). We firstly optimized a protocol to measure electrocardiogram in adult zebrafish. We determined the location of the probes, implemented an open-chest microsurgery procedure, measured the effects of temperature, and determined appropriate anesthesia dose and time. We then proposed an PP interval of more than 1.5 seconds as an arbitrary criterion to define an SA episode in an adult fish at ambient temperature, based on comparison between the current definition of an SA episode in humans and our studies of candidate SA episodes in aged wild-type fish and Tg(SCN5A-D1275N) fish (a fish model for inherited SSS). With this criterion, a subpopulation of about 5% wild-type fish can be considered to have SA episodes, and this percentage significantly increases to about 25% in 3-year-old fish. In response to atropine, this subpopulation has both common SSS phenotypic traits that are shared with the Tg(SCN5A-D1275N) model, such as bradycardia; and unique SSS phenotypic traits, such as increased QRS/P ratio and chronotropic incompetence. In summary, this study defined baseline SA and SSS in adult zebrafish and underscored use of the zebrafish as an alternative model to study aging-associated SSS.

Previously we showed the generation of a protein trap library made with the gene-break transposon (GBT) in zebrafish (Danio rerio) that could be used to facilitate novel functional genome annotation towards understanding molecular underpinnings of human diseases (Ichino et al, 2020). Here, we report a significant application of this library for discovering essential genes for heart rhythm disorders such as sick sinus syndrome (SSS). SSS is a group of heart rhythm disorders caused by malfunction of the sinus node, the heart's primary pacemaker. Partially owing to its aging-associated phenotypic manifestation and low expressivity, molecular mechanisms of SSS remain difficult to decipher. From 609 GBT lines screened, we generated a collection of 35 zebrafish insertional cardiac (ZIC) mutants in which each mutant traps a gene with cardiac expression. We further employed electrocardiographic measurements to screen these 35 ZIC lines and identified three GBT mutants with SSS-like phenotypes. More detailed functional studies on one of the arrhythmogenic mutants, GBT411, in both zebrafish and mouse models unveiled Dnajb6 as a novel SSS causative gene with a unique expression pattern within the subpopulation of sinus node pacemaker cardiomyocytes that partially overlaps with the expression of hyperpolarization activated cyclic nucleotide gated channel 4 (Hcn4), supporting heterogeneity of the cardiac pacemaker cells.

Background: Traditional percutaneous device closure of perimembranous ventricular septal defects (PmVSDs) is a minimally invasive technique, but can result in high radiation exposure and can result in potential arterial complications. Here, we aimed to assess the safety and feasibility of device closure of PmVSDs via the femoral vein approach under transesophageal echocardiography (TEE) guidance in children. Methods: From January 2014 to December 2017, a total of 46 PmVSD patients (mean age, 6.5 ± 2.3 years [range, 4.2-12.0 years]; mean body weight 22.1 ± 6.6 kg [range, 16.0-38.5 kg]; VSD diameter, 4.1 ± 0.6 mm [range, 3.2-5.0 mm]) underwent attempted transcatheter closure via the femoral vein approach under the guidance of TEE without fluoroscopy. Results: The transcatheter occlusion procedure under TEE guidance was successful in 44 (95.7%) patients. Surgery was necessary in 2 (4.3%) patients. The procedure duration was 28.2 ± 8.7 min (range, 12.0-42.0 min). One patient had immediate post-operative trivial residual shunt and three patients had immediate incomplete right bundle branch block (IRBBB) after operation; the new IRBBB in 1 case was noted in the first postoperative month. No residual shunt was noted at 3 months after the procedure, and no intervention related complications were detected at 1-24 months follow-up. Conclusions: Percutaneous device closure of PmVSDs under TEE guidance solely by femoral vein approach is effective and safe, avoids radiation exposure, potential arterial complications and a surgical incision.