Left Ventricular Outflow Tract Obstruction Secondary to Hemangiosarcoma in a Dog

Abstract

A 3-year-old, 8-kg male standard Schnauzer was referred to the Murcia University Veterinary Teaching Hospital with a history of exertional syncope over the preceding 2 days. No history of previous cardiac or systemic disease was reported by the owner except for a murmur detected when the dog was a puppy. On physical examination, the dog appeared bright and alert, with slightly pale mucous membranes and a capillary refill time of more than 2 seconds. Respiratory rate and heart rate were within the reference range and femoral pulses were unremarkable. Thoracic auscultation revealed a regular cardiac rhythm and a grade V/VI systolic murmur with the point of maximal intensity at the left heart base with radiation to the right cranial hemithorax. Systolic blood pressure (Doppler method) and ECG measurements were within reference limits. Thoracic radiographs revealed an elongated cardiac silhouette (12.0 vertebral heart size [VHS]; reference VHS, 9.7 6 0.5) 1 with normal pulmonary parenchyma and pulmonary vasculature. Two-dimensional echocardiography showed an echodense mass located within the left ventricular outflow tract (LVOT), below the aortic valve. The mass was best seen using right parasternal long-and short-axis views and a sub-costal view (Fig 1) and depending on the echocardio-graphic views, the mass appeared round or oval. M-mode measurements were compatible with left ventric-ular concentric hypertrophy. Color-flow mapping revealed an aliased color-flow pattern in the LVOT and ascending aorta (Fig 2). The pulmonic, mitral, and tricuspid color blood flow patterns and velocities (V) (pulsed-wave Doppler echocardiography), recorded from standard positions, were within the reference range. The aortic blood flow velocity (continuous-wave Doppler echocardiography) recorded from subcostal position was 5.05 m/s (reference range, 1.48 6 0.03 m/s) 2 with a maximum instantaneous systolic Doppler pressure gradient (DPG) of 102.01 mm Hg (DPG 5 4[V] 2). No cardiac arrhythmias were noted during the continuous ECG throughout the echocardiographic examination. Hematologic and biochemical values were un-remarkable. A tentative diagnosis of a cardiac tumor was made. Continuous ambulatory electrocardiography (24-hour Holter monitoring) was recommended to investigate the cause of the syncope, but the owner declined this. The dog was discharged and we recommended exercise restriction and 6.25 mg of atenolol PO q12h. The dog died suddenly 3 weeks later. At postmortem examination, the gross appearance of the skin, head, abdominal organs, and lungs was unremarkable. The heart weight to body weight ratio was increased (15 g/kg; reference range, 5.5-10.5 g/kg). 3 The interventricular septum and left ventricular free wall appeared grossly hypertrophied. A solitary 1.5-cm, greenish brown firm round mass was present in the LVOT below the aortic valve, raised above the endocardium. One section of the mass showed this tissue extending into the myocardium of the interven-tricular septum. A whitish fibrous band also was present below the aortic valves, extending on both sides of the mass, compatible with a subvalvular aortic stenosis (SAS). Samples of the heart and other organs were obtained. All samples were fixed in 10% buffered formalin, processed routinely in Poliwax, a and stained with hematoxylin and eosin, toluidine blue for metachroma-sia, Gallego's trichrome for collagen and muscle fibers, and an immunohistochemical technique using von Willebrand factor b for endothelial cells. On histologic examination, the greenish brown, firm, round mass was characterized by variably sized vascular spaces filled with erythrocytes and lined by cells ranging from spindle shaped to ovoid. Solid groups of poorly differentiated and vacuolated cells appeared between the vascular spaces (Fig 3A). Neoplastic cells were positive for von Willebrand factor (Fig 3B). Solid groups were infiltrated by numerous mast cells (Fig 3C). The whitish fibrous band present below the aortic valves consisted of connective tissue with abundant accumulation of mu-cinous ground substance below the endothelial layer of the endocardium and small areas of cartilage formation in the inner part (Fig 4). No lesions were seen in the other organs examined. The most common form of left ventricular outflow tract obstruction (LVOTO) in dogs is SAS, which especially affects large breeds of dogs. 4-6 The lesion is due to a fibrous or fibromuscular ridge partially or totally encircling the LVOT at variable distances beneath the aortic valve. 4,5 The lesions have been classified as grades 1-3 depending on the severity of