A 26-year-old gentleman with a past medical history of hypertension, presented to our hospital with persistent fevers for 2 weeks. He was in his usual state of health when he began developing daily fevers associated with proximal shoulder and thigh weakness. His fevers were refractory to antipyretics. He denied any other associated symptoms including rashes, arthralgias, myalgias, headache, nuchal rigidity, cough, abdominal pain, nausea, diarrhea, or dysuria. He had not recently travelled outside of the United States and denied any sick contacts. His last sexual encounter was 1 year prior to presentation. He denied genital lesions or discharge. He reported no history of drug abuse. He was born in the Philippines and immigrated to the United States 9 years prior to presentation. At birth, the patient was told he had a hole in his heart that would spontaneously close by adolescence. He recalled “turning blue” while crying as a child, but had since denied cyanotic spells since childhood. As an adult, he could walk several blocks and climb flights of stairs without difficulty. However, he reported dyspnea with jogging and running, which he had attributed to deconditioning. He was unaware of any significant family history.\nUpon arrival to the emergency department, he was afebrile and hemodynamically stable. The physical exam was notable for left, anterior, nontender, mobile cervical adenopathy and a III/VI holosystolic murmur heard loudest at the 3rd left intercostal space. Initial labs were notable for a mild leukocytosis and elevated erythrocyte sedimentation rate and c-reactive protein. Electrocardiogram (EKG) showed increased voltage, prominent R waves in the precordial leads, and nonspecific ST segment and T wave changes (Figure ). Chest X-ray showed cardiomegaly and a chest computed tomography showed multiple pulmonary nodules in bilateral lung fields.\nA transthoracic echocardiogram (TTE) was obtained and showed moderate-to-severe right ventricular hypertrophy (RVH), RVOT, and a VSD consistent with Tetralogy of Fallot (TOF), although no evidence of an overriding aorta. He subsequently underwent a transesophageal echocardiogram (TEE) that again showed RVH and a VSD, but also noted a muscular band within the RV (Figures and ). Blood cultures grew aggregatibacter aphrophilus. He was diagnosed with endocarditis by Duke's criteria: one major (positive blood culture with HACEK organism), and three minor (fever, predisposing cardiac lesion, pulmonary emboli). He was discharged with a 4-week course of intravenous Ceftriaxone following the last negative blood cultures. After discharge, the patient was further evaluated to differentiate between TOF and DCRV. A cardiac catheterization showed an anomalous band dividing the RV into two chambers, with a peak-to-peak gradient of 115 mm Hg between proximal and distal RV consistent with DCRV (Figures and ). Additionally, the patient underwent a cardiac magnetic resonance imaging (MRI) showing a D-shaped left ventricle and RVOT with subpulmonic stenosis (Figure ). He was referred to cardiothoracic surgery for RV muscle band myomectomy and patch closure of VSD.
A 1.2 year-old, 28 kg, male intact Golden Retriever, was referred to our Cardiology Service for ascites evaluation. History included lethargy, anorexia and exercise intolerance over the previous five days. Prior to the onset of these signs, the dog was viable and readily able to exercise.\nPhysical examination showed a severely dyspneic, depressed, dehydrated dog, with moist but pale mucous membranes and a body condition score of 3/9. Rectal temperature was 38.9 °C. The femoral arterial pulse was irregularly irregular and weak, and a right cranial precordial thrill was palpable. Heart auscultation identified a grade V/VI systolic murmur with the point of maximal intensity located ventrad to the right heart-base region. Jugular venous distention was also noted and ascites was confirmed. Respiratory sounds were normal over all lung lobes, while the respiratory rate was elevated at 60 rpm.\nAn electrocardiographic (ECG) rhythm strip identified atrial fibrillation (AF) with widened (80 milliseconds) and splintered QRS complexes, and a right bundle branch block (RBBB) pattern, with an average ventricular response rate of 190 beats/min (Fig. ).\nRadiographs revealed well-ventilated lung fields and severe, right-sided cardiomegaly. Vertebral heart score was severely increased at 13.3v (Fig. ) (reference interval < 10 ± 0.5).\nTwo-dimensional echocardiography demonstrated a severely enlarged right atrium. There was evidence of congenital TVD: the tricuspid leaflets were malpositioned and displaced toward the right ventricular apex (Fig. ). A severe tricuspid insufficiency (TI) jet (Fig. ) with a 4.26 m/s peak flow velocity (compatible with a systolic pressure gradient of at least 72.6 mmHg across this valve) was recorded (Fig. ). The septal tricuspid leaflet was thickened and attached to very short chordae tendineae; the posterior tricuspid leaflet was also thickened. The right parasternal short axis view, at the level of the left ventricular papillary muscles, demonstrated systolic flattening of the interventricular septum (IVS), attributed to an elevated systolic right ventricular pressure (Fig. ). In that same view, an anomalous fibromuscular structure appeared to partially separate the right ventricular cavity into two compartments. A small, systolic, turbulent jet was identified between the two right-ventricular chambers (Fig. ).\nSpectral Doppler interrogation of the abnormal jet was attempted but accurate velocity measurements could not be performed due to less–than–ideal angulation. However, based on the turbulent appearance of the color flow jet its velocity seemed subjectively high.\nThe left cardiac chambers and valves demonstrated normal structure and function, and only mild left ventricular (LV) hypertrophy was seen. The left ventricular free wall thickness in end diastole (LVFWd) was 9.9 mm (reference ranges 8.04–8.94 mm), and the interventricular septum thickness in end diastole (IVSd) was 12.08 mm (reference ranges 9.99–11.05) [].\nPulmonary arterial flow had a normal profile and peak flow velocity. Aortic flow velocity was not accurately measured due to less-than-optimal beam-to-flow alignment.\nSerum biochemistry showed only mild liver enzyme elevation. Alanine transaminase (ALT) was 93 U/l (upper reference limit <40 U/l) and aspartate aminotransferase (AST) was 88 U/l (upper reference limit <40 U/l). Hematology was normal.\nFive liters of a sero–sanguinotic fluid were removed from the abdominal cavity via abdominocentesis. The fluid contained a low protein (< 2.5 g/dL) concentration, containing only a few scattered cells, including mostly red blood cells, neutrophils, and desquamated mesothelial cells.\nThe dog unfortunately responded poorly to pimobendan (0.25 mg/kg q 12 h) and furosemide (2 mg/kg q 12 h), and went on to die suddenly four days later.\nNecropsy revealed a severely enlarged right atrium (Fig. ). The septal and posterior leaflets of the tricuspid valve were both severely thickened. The septal leaflet was also adhered to the IVS (Fig. ). The tricuspid valve annulus was displaced ventrad and caudad, towards the right ventricular apex. The RV was partially divided into two separate compartments by a fibromuscular structure, which was more muscular near the RV apex and more fibrotic near the atrioventricular junction. The structure appeared to be part of the anterior tricuspid valve leaflet, without involving any of the papillary muscles. This impression was supported by the fact that the chordae tendineae of this specific leaflet were of normal length but their insertions were embedded inside the abnormal fibromuscular structure. This fibromuscular structure was attached to the RV apex, at an area rich with coarse septomarginal trabeculation. The two right ventricular compartments communicated only at the uppermost part of the abnormal fibromuscular structure (Fig. , ). The diameters of the oval communicating ostium were 0.8 X 1.2 cm. One right ventricular compartment contained inflow tract components, while the other contained outflow components. A resistive perimembranous VSD measuring 4 mm in diameter was also detected on necropsy, below the aortic valve cusps. The VSD opened into the RV distal chamber. Beneath the aortic valve cusps, there was a small, proliferative, stenotic nodule, partially obstructing the left ventricular outflow tract (LVOT). A fibrotic ring encircled the LVOT as well, at a distance of 1.5 cm from the aortic valve cusps (Figs. and ). These two combined findings were compatible with mild SAS, which presumably had triggered systolic left ventricular (LV) pressure elevation, based on the mildly pre-mortem, echocardiographically increased LV wall thickness.\nHistologically, the fibromuscular band that separates the right ventricle consists of longitudinal layers of dense fibrous connective tissue admixed with cardiomyocytes organized in a plexiform pattern (Fig. , ). The muscular component was present mainly in the ventral area of the band, being largely absent in the central zone. Superficially, the endocardium presented areas of nodular hyperplasia covering mainly the fibrous tissue-rich part of the band (Fig. ). The nodules were sharply demarcated and composed of loose connective tissue with myxoid appearance covered by hyperplastic endocardium (Fig. ).