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The following case series presents three different pediatric patients with SCN5A- related disease. In addition, family members are presented to demonstrate the variable penetrance that is commonly seen. Identifying features of this disease is important, because even in the very young, SCN5A disorders can cause lethal arrhythmias and sudden death. [ABSTRACT FROM AUTHOR]

Abstract Pacemaker implantation is considered as a standard procedure for treatment of symptomatic bradycardia in both dogs and cats. Advanced second-degree and third-degree atrioventricular blocks, sick sinus syndrome, persistent atrial standstill, and vasovagal syncope are the most common rhythm disturbances that require pacing to either alleviate clinical signs or prolong survival. Most pacemakers are implanted transvenously, using endocardial leads, but rarely epicardial leads may be necessary. To decide whether a patient is a candidate for pacing, as well as which pacing modality should be used, the clinician must have a clear understanding of the etiology, the pathophysiology, and the natural history of the most common bradyarrhythmias, as well as what result can be achieved by pacing patients with different rhythm disturbances. The goal of this review was, therefore, to describe the indications for pacing by evaluating the available evidence in both human and veterinary medicine. We described the etiology of bradyarrhythmias, clinical signs and electrocardiographic abnormalities, and the choice of pacing modality, taking into account how different choices may have different physiological consequences to selected patients. It is expected that this review will assist veterinarians in recognizing arrhythmias that may require permanent pacing and the risk-benefit of each pacing modality and its impact on outcome. [ABSTRACT FROM AUTHOR]

Two young Labrador retriever dogs with bradycardia-induced syncope resulting from atrial myopathy underwent permanent transvenous pacemaker implantation. Both dogs developed heart failure 3–5 years after pacemaker implantation. Both were managed medically for approximately 7 years after pacemaker implantation and, ultimately, were humanely euthanized due to refractory heart failure signs and quality of life concerns. Long-term management of dogs with atrial myopathy and secondary atrial standstill with pacemaker implantation and medical therapy for heart failure is feasible and prognosis may be better than previously reported or speculated. [ABSTRACT FROM AUTHOR]

Atrial dilatation and atrial standstill are etiologically heterogeneous phenotypes with poorly defined nosology. In 1983, we described 8-years follow-up of atrial dilatation with standstill evolution in 8 patients from 3 families. We later identified 5 additional patients with identical phenotypes: 1 member of the largest original family and 4 unrelated to the 3 original families. All families are from the same geographic area in Northeast Italy.We followed up the 13 patients for up to 37 years, extended the clinical investigation and monitoring to living relatives, and investigated the genetic basis of the disease. The disease was characterized by: (1) clinical onset in adulthood; (2) biatrial dilatation up to giant size; (3) early supraventricular arrhythmias with progressive loss of atrial electric activity to atrial standstill; (4) thromboembolic complications; and (5) stable, normal left ventricular function and New York Heart Association functional class during the long-term course of the disease. By linkage analysis, we mapped a locus at 1p36.22 containing the Natriuretic Peptide Precursor A gene. By sequencing Natriuretic Peptide Precursor A, we identified a homozygous missense mutation (p.Arg150Gln) in all living affected individuals of the 6 families. All patients showed low serum levels of atrial natriuretic peptide. Heterozygous mutation carriers were healthy and demonstrated normal levels of atrial natriuretic peptide.Autosomal recessive atrial dilated cardiomyopathy is a rare disease associated with homozygous mutation of the Natriuretic Peptide Precursor A gene and characterized by extreme atrial dilatation with standstill evolution, thromboembolic risk, preserved left ventricular function, and severely decreased levels of atrial natriuretic peptide. [ABSTRACT FROM AUTHOR]

Most of the abnormal cardiac conduction system findings are atrial tachyarrhythmias in cardiac sarcoidosis. However, atrial standstill as a sick-sinus syndrome could be complicated in the case of diffuse atrial fibrosis. Herein, we present an interesting and valuable case of atrial standstill with suspected isolated cardiac sarcoidosis. < Learning objective: The chronic inflammation caused by isolated cardiac sarcoidosis could impair the conduction system. With atrial standstill, we recommend a comprehensive effort to investigate the potential etiology including cardiac sarcoidosis, particularly in the case of enlarged atrium and ventricular dysfunction.> [ABSTRACT FROM AUTHOR]

We report a 55-year-old female patient who presented with no P waves but with a wide QRS complex escape rhythm at 44 beats/min and prolonged QTc of 0.55 seconds on ECG. The patient had recurrence of ventricular fibrillations and loss of consciousness, and underwent defibrillation and cardiopulmonary resuscitation (CPR) several times because of cardiac arrest. The transthoracic echocardiography showed dilated cardiomyopathy and enlargement of both atria. The Doppler echocardiography documented the absence of A wave in the tricuspid and mitral valve flow. An electrophysiologic study demonstrated electrical inactivity in the right and left atria. Atrial pacing with maximum output did not capture the atria. These findings together with her electrocardiographic finding indicated atrial standstill. Sudden cardiac death was her first clinical manifestation of ventricular arrhythmia. The patient remained asymptomatic after receiving a single chamber implantable cardioverter-defibrillator (ICD) with VVI pacemaker function. [ABSTRACT FROM AUTHOR]

Background: Congenital atrial standstill has been linked to SCN5A. Incomplete penetrance observed in atrial standstill has been attributed in part to the digenic inheritance of polymorphisms in the atrial-specific gap junction connexin 40 (Cx40) in conjunction with an SCN5A mutation.Objectives: The purpose of this study was to determine the clinical and biophysical characteristics of a novel SCN5A mutation identified in a family with atrial standstill.Methods: Family members of an apparently sporadic case of atrial standstill underwent genetic screening of SCN5A and atrial-specific genes including Cx40. Biophysical properties of the wild-type (WT) and mutant SCN5A channels in a heterologous expression system were studied using the whole-cell patch clamp technique.Results: The novel SCN5A mutation L212P was identified in the proband (age 11 years) and his father. The father was in normal sinus rhythm. The proband had no P waves on surface ECG, and his right atrium could not be captured by pacing. The recombinant L212P Na channel showed a large hyperpolarizing shift in both the voltage dependence of activation (WT: -48.1 +/- 0.9 mV; L212P: -63.5 +/- 1.5 mV; P < .001) and inactivation (WT: -86.6 +/- 0.9 mV; L212P: -95.6 +/- 0.8 mV; P < .001) and delayed recovery from inactivation. Further screenings for genetic variations that might mitigate L212P dysfunction revealed that the proband, but not his father, carries Cx40 polymorphisms inherited from his asymptomatic mother.Conclusion: These results suggest that genetic defects in SCN5A most likely underlie atrial standstill. Coinheritance of Cx40 polymorphisms is a possible genetic factor that modifies the clinical manifestation of this inherited arrhythmia. [ABSTRACT FROM AUTHOR]

Abstract: Twelve-lead electrocardiograms revealed no atrial activity and a wide QRS escape rhythm at 38 beats/min in a 20-year-old man who presented with syncope. Doppler echocardiography documented the absence of A wave both in the tricuspid and mitral valve flow. The only mechanical activity was documented at the left atrial appendage. An electrophysiologic study demonstrated electrical inactivity in the right atrium and an atrial tachycardia in the left atrium. Atrial pacing with maximum output did not capture the atria. Our case represents an advanced stage of partial atrial standstill, with a mechanical and electrical atrial activity confined only to the left trial appendage. The patient remained asymptomatic after receiving a VVIR pacemaker and anticoagulation therapy. [Copyright &y& Elsevier]