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Atrial dilated cardiomyopathy with progression to atrial standstill is an ultrarare arrhythmogenic disorder characterized by complete loss of atrial electrical and mechanical activity. This condition, which may occur sporadically or in familial clusters, is associated with a markedly increased thromboembolic risk. The electrocardiographic hallmark is the absence of P waves combined with a bradycardic junctional escape rhythm. Biatrial enlargement gradually evolves into giant atria with preserved biventricular systolic function, while supraventricular arrhythmias and progressive atrial inexcitability dominate the clinical course. Valvular regurgitation frequently worsens in parallel with atrial remodelling, and patients often require permanent pacemaker implantation as well as lifelong anticoagulation. Among the few genetic determinants identified, the homozygous c.449G>A (p.Arg150Gln) mutation in the Natriuretic Peptide A gene represents one of the best characterized mechanisms. Disertori et al. first reported this pathogenic variant in 13 affected individuals from Italian families, establishing a recessive inheritance pattern. More recently, Silva et al. and Forleo et al. described additional cases, expanding the phenotypic spectrum of NPPA-related atrial cardiomyopathy. These findings confirm that homozygous carriers develop a severe atrial phenotype, whereas heterozygous relatives typically remain asymptomatic, underlining the importance of genetic testing in young patients with unexplained atrial fibrillation or standstill. Recognition of atrial cardiomyopathy as a distinct clinical entity is crucial, since early diagnosis may guide timely anticoagulation, arrhythmia management, and tailored follow-up. Broader adoption of genetic screening in patients with isolated atrial dysfunction could support precision medicine approaches, improve risk stratification, and ultimately prevent adverse outcomes in this ultrarare but highly morbid condition.

Hyperkalaemia is an uncommon complication of general anaesthesia in healthy horses. This case report describes the occurrence of life-threatening acute hyperkalaemia in a 13-year-old, female French Trotter anaesthetised for experimental right and left atrial 3D electro-anatomical mapping. Intra-operative development of hyperkalaemia (7.55 mmol/L) (Ref. 3.00–4.00 mmol/L) with atrial standstill on ECG necessitated transvenous ventricular pacing while initial treatment with insulin and glucose was initiated. Plasma potassium levels continued to increase (8.00 mmol/L) prompting adjunctive treatment with 5 μg/kg of inhaled salbutamol and intravenous furosemide 0.93 mg/kg. Eight minutes after salbutamol administration, return of spontaneous atrial contraction was observed on echocardiography and plasma potassium concentration rapidly decreased on serial blood samples. To the authors’ knowledge, this is the first case report documenting the use of inhaled salbutamol in the treatment of life-threatening acute hyperkalaemia in an anaesthetised horse.

Abstract Background Juvenile onset of extensive atrial electromechanical failure, including atrial standstill, is a rare disease entity that may precede ventricular cardiomyopathy. Genetic variants associated with early-onset atrioventricular (AV) cardiomyopathy are increasingly recognized. Case summary A 16-year-old patient presented with atrial brady- and tachyarrhythmias and concomitant impaired atrial electromechanical function (atrial standstill). The atrial phenotype preceded the development of a predominantly right-sided AV dilated cardiomyopathy with pronounced myocardial fibrosis. A His-bundle pacemaker was installed for high-degree AV conduction block and sinus arrest. Using familial-based whole-exome sequencing, a missense mutation and a copy number variant deletion (compound heterozygosity) of the TAF1A gene (involved in ribosomal RNA synthesis) were identified. Discussion Juvenile onset of severe atrial electromechanical failure with atrial arrhythmias should prompt deep pheno- and genotyping and calls for vigilance for downstream cardiomyopathic deterioration. Video Abstract 10.1093/ehjcr/ytad255_video1 Video Abstract ytad255media1 6328944601112

The cardiac causes predominantly include rheumatic heart disease, mitral valve prolapse and congenital heart disease. Since the patient presented in junctional rhythm, our main differential included either transient causes (new onset atrial fibrillation, transient electrolyte abnormalities (hyperkalaemia), digoxin toxicity, acute myocarditis with atrial involvement, dilated cardiomyopathy) or permanent causes (associated with muscular dystrophies and genetic cardiomyopathies). Atrial standstill is a rare condition with absence of atrial mechanical/electrical activity characterized by “(1) the absence of P waves in the ECG and of A waves in the intracardiac recordings, (2) narrow QRS complexes, (3) evidence of atrial paralysis (absence of A waves in the jugular venous pulse, in the atrial pressure recording and in the mitral Doppler recording), and (4) inability to stimulate the atria.” Germline pathogenic variations in the HCN4 gene have been shown to be associated with familial sick sinus syndrome, specifically the autosomal dominant type 2 variety.5 The mechanism by which sick sinus syndrome due to gene mutations result in atrial standstill have been best described for SCN5A mutation which is the most common genetic cause in paediatric patients with atrial standstill.1 In patients with SCN5A mutations, slowing down of both pacemaker function and conduction of action potential across the SA node-atrium occurs.6 Histological examination of the atrial wall have been described to show presence of dense collagenous tissue, different stages of fibrosis with scattered myocardium.7 A combination of reducing pacemaking activity and atrial fibrosis contributes to the atrial standstill.

The case report shares evidence for a better understanding of atrial standstill. This being a rare arrhythmogenic condition. This is a 46-year-old woman presented with multiple sites of arterial embolism, including lower extremity arteries, coronary artery, and cerebral artery. Unexpectedly, multiple arterial embolization in the patient was due to atrial standstill by transthoracic echocardiography and cardiac electrophysiological study. An additional family investigation revealed that the patient’s brother and sister also suffered from this disease. In search of further understanding the case, we carried out the genetic testing of the family and a frame shift double-G insertion mutation at c.1567 in the LMNA gene was found in all the three individuals. The patient recovered well after anticoagulation therapy and left bundle branch area pacing. This report remarks on the importance of multiple sites of arterial embolism which should be wary of family atrial standstill.

Atrial standstill is a rare arrhythmogenic condition characterized by the absence of electrical and mechanical activity in the atria. The therapeutic options for these patients described in the current literature, in which no reversible cause is detected, are permanent cardiac pacing, anticoagulant, and heart failure treatment when the latter exists. We present a case of a young male with no personal or family history of cardiovascular disease, diagnosed with atrial standstill after multiple syncopal episodes, in whom, because of the high expected ventricular pacing percentage, we opted for conduction system pacing with left bundle branch area pacing.

Giant cell myocarditis (GCM) is a rare condition. Its association with SARS‐CoV‐2 has not been described before. The 46‐year‐old female patient was admitted to the clinic on September 2020. She had 7 year adrenal insufficiency history and infarct‐like debut of myocardial disease in November 2019. After COVID‐19 in April 2020, cardiac disease progressed. The examination showed low QRS voltage, QS complexes in V1–V5 leads, atrial standstill, left ventricular systolic and restrictive dysfunction, elevated anti‐heart antibodies, and subepicardial late gadolinium enhancement by magnetic resonance imaging. Endomyocardial biopsy and pacemaker implantation were performed, but the patient died suddenly due to ventricular tachycardia or ventricular fibrillation (the resuscitation was ineffective). The autopsy revealed GCM, SARS‐CoV‐2, and Parvovirus B19 were detected in the myocardium. The role of SARS‐CoV‐2 in the pathogenesis of autoimmune myocarditis is discussed.

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.

Bradyarrhythmias are caused by alterations of extracardiac factors (e.g. systemic disease), drugs, or primary abnormalities of the cardiac conduction system and can be classified as a physiological, iatrogenic, or pathological bradyarrhythmia, respectively. Commonly encountered bradyarrhythmias include sinus bradycardia, a pronounced sinus arrhythmia, forms of atrioventricular block, sinus node dysfunction (sick sinus syndrome), and persistent atrial standstill. This chapter offers the emergency clinician guidance for diagnosis, initial stabilization (medical management options or temporary pacing), and clinical management, including indications for permanent pacing, of dogs and cats affected with a bradyarrhythmia.