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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., Competing Interests: The authors have declared that no competing interests exist.

We present a case of sinus arrest and junctional escape rhythm from sinus node artery (SNA) thrombus in a 55-year-old man after revascularisation of right coronary and proximal circumflex arteries for infero-posterior wall ST-segement elevation myocardial infarction (STEMI). Sinus arrest from occlusion of the SNA is uncommon. The ensuing bradycardia may have haemodynamic consequences requiring temporary pacing but is almost always self-limited., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: Concomitant surgical atrial fibrillation (AF) ablation is a safe and feasible procedure, recommended in guidelines. Pacemaker dependency is a known complication of AF ablation. We sought to determine independent predictors for pacemaker implantation after surgical AF ablation., Methods: Between January 2003 and November 2012, 594 patients underwent concomitant surgical AF ablation. Various energy sources, including cryoablation (n = 139), unipolar radiofrequency (n = 278), and bipolar radiofrequency (n = 177), were used. Left atrial (n = 463, 77.9%) and biatrial (n = 131, 22.1%) ablation was performed. Univariate and multivariate logistic regression analysis was used to identify independent predictors for pacemaker implantation within 30 days after surgical AF ablation., Results: The mean patient's age was 68.6 ± 9.4 years, and 66.8% were male. No major ablation-related complications occurred. A total of 41 (6.9%) of patients received pacemaker implantation during the 30-day follow-up period. Indications for pacemaker implantation were atrioventricular block in 25 (60.9%) of patients, sinus bradycardia or sinus arrest in 9 (22.0%) of patients, and bradyarrhythmia in 7 (17.1%) of patients. Demographic data, type of surgical procedure, and type of energy source did not have a significant impact on pacemaker implantation rate. However, biatrial ablation led to a significant pacemaker implantation rate compared with isolated left-sided ablation (6.3% vs 13.6%; P = .028)., Conclusions: Concomitant surgical AF ablation showed a pacemaker implantation rate of 6.9% after 30-day follow-up. Univariate and multivariate analysis showed biatrial lesion set as the only statistically significant predictor for pacemaker implantation after surgical AF ablation., (Copyright © 2014 The American Association for Thoracic Surgery. Published by Mosby, Inc. All rights reserved.)

Aims: Although patients with paroxysmal atrial fibrillation (AF) and prolonged sinus pauses [tachycardia-bradycardia syndrome (TBS)] are generally treated by permanent pacemaker, catheter ablation has been reported to be a curative therapy for TBS without pacemaker implantation. The purpose of this study was to define the potential role of successful ablation in patients with TBS., Methods and Results: Of 280 paroxysmal AF patients undergoing ablation, 37 TBS patients with both AF and symptomatic sinus pauses (age: 62 ± 8 years; mean maximum pauses: 6 ± 2 s) were analysed. During the 5.8 ± 1.2 years (range: 5-8.7 years) follow-up, both tachyarrhythmia and bradycardia were eliminated by a single procedure in 19 of 37 (51%) patients. Repeat procedures were performed in 14 of 18 patients with tachyarrhythmia recurrence (second: 12 and third: 2 patients). During the repeat procedure, 79% (45 of 57) of previously isolated pulmonary veins (PVs) were reconnected to the left atrium. Pulmonary vein tachycardia initiating the AF was found in 46% (17 of 37) and 43% (6 of 14) of patients during the initial and second procedure, respectively. Finally, 32 (86%) patients remained free from AF after the last procedure. Three patients (8%) required pacemaker implantation, one for the gradual progression of sinus dysfunction during a period of 6.5 years and the others for recurrence of TBS 3.5 and 5.5 years after ablation, respectively., Conclusion: Catheter ablation can eliminate both AF and prolonged sinus pauses in the majority of TBS patients. Nevertheless, such patients should be continuously followed-up, because gradual progression of sinus node dysfunction can occur after a long period of time.

A 52-year-old man presented with vomiting, dysphagia, left-sided ataxia and dissociated sensory loss. Diffusion-weighted MRI showed evidence of acute infarct in the left lateral medulla and left medial cerebellar hemisphere, probably secondary to thromboembolism from left vertebral artery dissection. While making an uneventful recovery as an inpatient, a routine 24 h ECG was performed 2 weeks after the stroke to investigate possible paroxysmal atrial fibrillation. The recording instead revealed 56 asymptomatic episodes of sinus arrest, necessitating implantation of a permanent pacemaker to prevent sudden cardiac death. The medulla contains key structures involved in autonomic regulation, including the dorsal vagal nucleus and the nucleus tractus solitarius. Acute infarction may disrupt cardiac autonomic regulation pathways, resulting in altered parasympathetic and sympathetic outflow to the sinoatrial and atrioventricular nodes, with potentially life-threatening effects.

Pyrethroids are common household insecticides. Even though they are less toxic to humans, reports of accidental and suicidal poisoning are not uncommon. Cardiotoxicity due to pyrethroid poisoning is rare. We report a case of cardiac conduction disturbance due to a pyrethroid, prallethrin. A 28-year-old female presented after a suicidal consumption of prallethrin. Her clinical and laboratory parameters were normal during the first 24 h of hospital stay. On the second hospital day, she developed metabolic acidosis and sinus arrest with escape junctional rhythm. Despite correction of metabolic acidosis, the sinus arrest persisted for 3 days. She reverted back to sinus rhythm with bradycardia after this period and was discharged on the seventh hospital day. Her follow-up was uneventful. Pyrethroid poisoning can affect the gastrointestinal, respiratory, and nervous system. Most serious effects of the toxin in humans are seizures and coma. Mechanism of pyrethroid neurotoxicity is believed to be due to its ability to modify sodium, chloride, and calcium channels of the neurons. Our case raises the possibility that cardiac arrhythmia due to pyrethroid poisoning can occur due to its effect on sodium channels in the heart.

Aims: The efficacy of catheter-based pulmonary vein isolation (PVI) for paroxysmal atrial fibrillation (AF) and prolonged sinus pauses [bradycardia-tachycardia syndrome (BTS)] has been already described. However, the effects of PVI on autonomic modulation in BTS patients remain to be determined. We, therefore, examined the alteration in the autonomic modulation through the PVI procedure by using a heart rate variability (HRV) analysis of 24 h ambulatory monitoring., Methods and Results: This study consisted of 26 symptomatic paroxysmal AF patients either with prolonged sinus pauses on termination of AF (>3.0 s, BTS group, n = 11) or without any evidence of sinus node dysfunction (control group, matched for sex and age, n = 15) who underwent PVI. All 11 BTS patients became free from both AF and prolonged sinus pauses without pacemaker implantation (23 +/- 14 months of observation). The mean heart rate significantly increased in the control group (P < 0.05), but not in the BTS group after the PVI procedure, although the HRV parameters of root-mean-square successive differences in the adjacent NN intervals, standard deviation of the NN intervals, and high frequency did significantly decrease in both groups (P < 0.05)., Conclusion: Although the parasympathetic modulation was significantly attenuated after the PVI procedure, the mean heart rate did not increase in the BTS patients, probably due to the pre-existing sinus node dysfunction.

Radiofrequency ablation has been associated with changes in autonomic function. In this case, a 52-year-old woman was referred for electrophysiologic study of recurrent supraventricular tachycardia. Typical slow/fast atrioventricular node re-entry tachycardia was induced and confirmed during the study. Radiofrequency ablation of the slow pathway of the atrioventricular node led to sinus arrest, which resolved once ablation was stopped. Given the distance of the ablation site from the sinus node, we inferred that mechanisms other than direct injury to the sinus node were involved. To our knowledge, this is only the 2nd reported finding of sinus arrest during slow-pathway ablation of the atrioventricular node. This case highlights the complex interaction between the autonomic nervous system and the cardiac conduction system. Possible mechanisms include a Bezold-Jarisch reflex and modification of the intrinsic autonomic nervous system.