Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is a frequent cause of acute medical presentations. However, misattribution of the cause of such episodes based on bias from pre-existing diagnostic history (i.e., diagnostic anchoring) can lead to poor appraisal of co-existing life-threatening pathology unrelated to COPD. We present a 67-year-old male with a known background of severe COPD who presented with sudden-onset breathlessness but also recurrent syncope, where a presumed AECOPD served as a diagnostic red herring. Driven by implicit framing biases, the admitting team prematurely closed the diagnostic process and empirically initiated intravenous corticosteroids and nebulised bronchodilators without fully exploring alternative diagnoses. Multidisciplinary team review noted the absence of hypoxia or hypercapnia on arterial blood gas analysis and identified syncope as an atypical diagnostic feature of AECOPD, prompting a pivot away from respiratory management. A pre-hospital ECG had captured an irregularly irregular tachycardia suggestive of a focal atrial tachycardia with variable block or a multifocal atrial tachycardia (MAT), and a subsequent electrocardiography (ECG) revealed a consistently short PR interval (110 ms), raising the possibility of an underlying arrhythmic cause of the event. Corticosteroids were safely discontinued, and an outpatient implantable loop recorder (ILR) was arranged for long-term tachyarrhythmia surveillance. This report highlights the risks of diagnostic anchoring and premature closure in patients in the context of a known background diagnosis, the necessity of holistic clinical assessment with maintenance of a broad differential, and the importance of reassessing atypical clinical features through multidisciplinary review.

A 34-year-old man presented with recurrent palpitations and dyspnea on exertion. Palpitations started at the age of 13 years; he received direct-current cardioversion for unstable tachycardia at 22 years and recently developed an acute ischemic stroke. The admission 12-lead electrocardiogram showed atrial fibrillation, and echocardiography demonstrated a hypertrophic cardiomyopathy (HCM) phenotype with moderate left ventricular systolic dysfunction. His father was diagnosed with HCM and high-grade conduction disease requiring a permanent pacemaker at the age of 46 years. After cardioversion, the sinus rhythm electrocardiogram revealed a short PR interval with ventricular pre-excitation (mid-septal pattern). Electrophysiological study showed a short, fixed HV interval of 24 ms that remained unchanged during atrial pacing and after adenosine, with persistence of the pre-excited QRS morphology during junctional beats and no inducible tachycardia. These findings were diagnostic of a fasciculoventricular pathway. Cardiac magnetic resonance imaging revealed asymmetric septal hypertrophy with multifocal late gadolinium enhancement, and targeted genetic testing confirmed a pathogenic PRKAG2 variant (c.905G>A, p.Arg302Gln). Because no ablatable arrhythmic substrate was present, management was directed at heart failure, anticoagulation, rhythm control of atrial fibrillation, and surveillance for progressive conduction disease with cascade family screening. In conclusion, this case illustrates the clinical manifestations of PRKAG2 mutation-associated glycogen-storage cardiomyopathy, a phenocopy of HCM characterized by ventricular pre-excitation and progressive conduction disease, highlighting the convergence of structural, electrophysiological, and genetic mechanisms.

Mitral valve prolapse (MVP) is associated with an increased risk of infective endocarditis (IE), particularly in patients with mitral regurgitation and leaflet thickening. Historically, a subset of patients with mitral valve prolapse were considered for antibiotic prophylaxis before dental procedures. Conversely, current recommendations limit prophylaxis to the highest-risk cardiac conditions, such as congenital heart defects, mechanical valves, heart transplant with valvular issues, and a history of IE. We present a case of a 59-year-old man with a history of MVP with mildly thickened posterior leaflet, hypertension, hyperlipidemia, and prior tobacco use who presented to the hospital with nausea and vomiting four weeks after a tooth extraction. Initial laboratory evaluation was notable for elevated inflammatory markers, elevated transaminases, hyperbilirubinemia, and elevated troponin levels. Blood cultures grew methicillin-sensitive Staphylococcus aureus (MSSA). Transthoracic echocardiography demonstrated MVP with new moderate mitral regurgitation. Brain MRI showed multifocal embolic infarcts and a small subarachnoid hemorrhage. Transesophageal echocardiography (TEE) revealed vegetations involving both mitral valve leaflets, extension into the mitral annulus and left atrial wall, and annular abscess formation. The patient's hospital course was complicated by septic shock, respiratory failure, intermittent ventricular tachycardia, transient complete heart block, acute tubular necrosis, postoperative atrial fibrillation, and new-onset cardiomyopathy. He ultimately required urgent mitral valve replacement with extensive debridement of the mitral annulus and left atrial wall, followed by prolonged intravenous antibiotic therapy. Follow-up imaging showed a well-seated prosthetic valve without recurrent vegetation. This case highlights the severe complications of IE in patients with MVP and mildly thickened leaflets following dental procedures. Current guidelines do not recommend routine prophylaxis in this population. This case raises important questions regarding whether selected moderate-risk MVP patients with leaflet thickening and mitral regurgitation may benefit from individualized prophylactic strategies.

A 12-year-old, 20-kg, Cocker spaniel was evaluated for the recent onset of marked weakness. Cardiologic assessment revealed myxomatous degeneration of the atrioventricular valves, moderate left atrial dilation, and a sustained narrow QRS complex tachycardia primarily consistent with focal atrial tachycardia. Moreover, two-dimensional imaging of the interatrial septum showed a hyperechoic, multifocal thickening (maximum thickness: 10 mm). Differential diagnoses included neoplastic infiltration, intracardiac thrombosis, and mural endocarditis. Despite prompt hospitalization in the intensive care unit and combination antiarrhythmic therapy, adequate control of the tachyarrhythmia was not achieved, and euthanasia was ultimately elected. Necropsy confirmed myxomatous mitral valve degeneration and excluded cardiac neoplasia, thrombosis, and mural endocarditis. Histologic examination of the interatrial septum revealed abnormal infiltration by mature adipose tissue, causing full-thickness separation and dissociation of septal myofibers. Based on antemortem and postmortem findings, the diagnosis was lipomatous hypertrophy of the interatrial septum, a condition not previously reported in dogs but well recognized in human cardiology.

While the majority of individuals with Costello syndrome share characteristic findings affecting multiple organ systems, the phenotypic spectrum is wide, ranging from a milder or attenuated phenotype to a severe phenotype with early lethal complications. Costello syndrome is typically characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including: cardiac hypertrophy (usually typical hypertrophic cardiomyopathy), congenital heart defect (usually valvar pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially chaotic atrial rhythm/multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults.

Arrhythmias affect approximately half of patients with Costello syndrome (CS, OMIM # 218040), with non-reentrant atrial tachycardia being the most common. This case describes an infant with Costello syndrome carrying the pathogenic HRAS c.34G>A (p.G12S) variant who developed early-onset, drug-refractory multifocal atrial tachycardia (MAT). Despite multiple antiarrhythmic therapies, rhythm control remained inadequate until trametinib was initiated, resulting in rapid resolution of MAT and allowing stepwise discontinuation of adjunct antiarrhythmics. Although MAT did not recur after the MEK inhibitor was stopped, the patient subsequently developed hypertrophic cardiomyopathy only after trametinib was discontinued, suggesting a potential disease-modifying cardioprotective effect during active treatment. This case supports MEK inhibition as a targeted antiarrhythmic strategy in Costello syndrome, with benefits that may extend beyond acute rhythm stabilization to include prevention of cardiac hypertrophy. While spontaneous resolution of MAT can occur in Costello syndrome, the rapid and sustained response in this patient strengthens the hypothesis that trametinib exerts a direct antiarrhythmic effect.

Emery-Dreifuss muscular dystrophy is an inherited myopathy which can cause forms of tachycardia and bradycardia. We present a complex case of a patient with multiple flutter and intra-atrial re-entrant circuits with complex ablation performed. To minimize deep anesthesia risk, pulse field ablation was used with good outcome and without complication in this teenager.

Monensin is an antibiotic ionophore used as feed additive in production animals, however, overdose with monensin is associated with poisoning in livestock. This study describes a mortality outbreak in sheep associated with ingestion of a feed supplement containing elevated concentrations of monensin. The objectives were characterize pathological lesions from monensin toxicosis, correlate these findings with serum creatine kinase myocardial band (CKMB) to estimate the extent of myocardial injury, as well as with electrocardiogram to evaluate the progression and severity of cardiac damage. A farm with 49 Texel sheep provided 275 Kg of supplement containing 1.102 mg/kg of monensin undiluted, freely available in the trough for seven days (40 Kg/day). From the 5th day onward animals presented sternal recumbency, submandibular edema, dyspnea and tachycardia followed by death in 15 animals. At necropsy, the main lesions were globular heart with eccentric dilatation of cardiac chambers, pale myocardium, lungs with edema and congestion, hydrothorax, hydropericardium, ascites, liver with enhanced lobular pattern and pale skeletal musculature. Histologically, in six sheep that died within the first days necrotic myocarditis multifocal to coalescing, mild to moderate with discrete degree of fibrosis, and in nine sheep that died later fibrosis became pronounced. Mapping of cardiac lesions revealed predominance of lesions in left and right ventricles, atria, and interventricular septum, with degree varying between 2 and 3. In apex, right and left papillary muscles lesions ranged from grades 0-2. There was evidence of discrete multifocal necrotic myositis, pulmonary edema and congestion, necrotic hepatitis and centrilobular congestion. In the animals which the CKMB enzyme was measured, the mean value was 1008.88 u/L (104-2480 u/L). Electrocardiogram in four animals showed sinus tachycardia, atrial fibrillation and decreased wave P amplitude. Monensin poisoning caused predominant damage to heart with right and left congestive heart failure, which continued to be present in the surviving animals.

Paroxysmal supraventricular tachycardias (PSVTs) affect approximately 36 out of 100,000 individuals annually in the United States, with women being twice as likely as men to develop the condition. The risk of PSVT increases significantly with age, with older individuals being 5 times more likely to experience the arrhythmia compared to younger people. PSVT accounts for 10% to 15% of cases in adults undergoing catheter ablation, while in children, it accounts for 10% to 20% of cases.  Focal atrial tachycardia (AT) is a supraventricular arrhythmia with rapid heart rates originating from ectopic atrial foci independent of the sinus or atrioventricular (AV) nodes, and it is a common mechanism of PSVT. Presenting as either unifocal or multifocal, AT has distinct pathophysiological mechanisms. Unifocal AT arises from enhanced automaticity, triggered activity, or micro-reentry mechanisms, resulting in a single, consistent P-wave morphology with an atrial rate of 150 to 250 bpm. Typically benign and paroxysmal, unifocal AT is often nonsustained. However, incessant tachycardia may cause tachycardia-induced cardiomyopathy. On the other hand, multifocal atrial tachycardia (MAT) involves three or more distinct P-wave morphologies and an irregular atrial rate exceeding 100 bpm. Enhanced automaticity is the primary mechanism, with triggered activity also playing a role. MAT is frequently associated with underlying conditions such as pulmonary disease, metabolic imbalances, or drug effects.  Electrophysiology (EP) studies and catheter ablation are crucial for diagnosing and managing AT. Successful elimination of unifocal AT is frequently achieved through catheter ablation with low complication rates, while the management of MAT focuses on treating underlying causes. Advances in mapping technologies and ablation techniques have greatly enhanced outcomes for patients undergoing these procedures, making ablation a cornerstone in focal AT treatment. This review explores the mechanisms, diagnostic strategies, and therapeutic approaches, emphasizing the essential role of EP studies and ablation in contemporary cardiac care.