Left-to-Left Acquired Cardiac Shunt: Aorto-Left Atrial Fistula Due to Aortic Infective Endocarditis in a Dog

Abstract

Infective endocarditis is a severe but rarely diagnosed disease, characterized by the presence of bacterial infection at the level of the cardiac valves. Although the incidence of the disease is very low, the consequences are severe and the prognosis is very poor, outlining a high mortality rate among cases. The present report highlights the case of a 7-year-old dog presented with abrupt changes in the respiratory pattern, obtunded and in lateral recumbency. The physical examination of the patient revealed fever and a IV/VI systolic heart murmur, with the point of maximal intensity on the left hemithorax. Echocardiography identified hyperechoic and cavitary changes beneath the aortic valves and a retrograde turbulent jet originating in the left ventricle outflow tract communicating with the left atrium through a rupture in the aortomitral intervalvular wall. Because of very unstable hemodynamic changes, the dog suddenly died despite the initiation of intensive care supportive treatment, and the postmortem evaluation of the heart confirms the suspicion of infective aortic endocarditis with the development of a paravalvular abscess and an aorto-left atrial fistula.

Keywords: aortocardiac fistula; cardiac shunt; infective endocarditis; paravalvular abscess.

Figure 1

A five-chamber long-axis view in a 7.7-year-old American Staffordshire mix male. (a) A double-cavitary structure with isoechoic walls is identified at the level of the left ventricle outflow tract (arrow). (b,c) Discontinuation of the aortomitral intervalvular wall (arrow) with an isoechoic structure protrusion through the discontinuation into the left atrium (LA). (d) A short-axis view at the base of the heart shows cavitary changes on the non-coronary aortic cusp. LVOT = left ventricle outflow tract, LA = left atrium, LV = left ventricle, AO = aorta.

Figure 2

A long-axis five-chamber view in a 7.7-year-old American Staffordshire mix male. Color Doppler interrogation at the level of the defect underlined a continuous turbulent flow both in end-diastole (a) and end-systole (b).

Figure 3

Gross and histopathological images of the aortic–atrial fistula. (a,c) Focally, the left atrial wall is disrupted by an anfractuous fistula (arrows) located within the aortic outflow tract and near the insertion of the anterior leaflet of the mitral valve. (b,d) The margins of the fistula are extensively ulcerated (black arrows) and covered with septic thrombi containing many basophilic colonies of cocci ((d) and inset) admixed with fibrin, blood, necrotic cell debris and neutrophils (black asterisk); the inflammatory process extensively infiltrate and replace the subjacent myocardium and subepicardial fat (blue asterisk). H&E stain, ob×10 (b) and ×40 (d). Scale bar = 1 cm for (a,c), 400 µm for (b), 100 µm for (d) and 20 µm for the inset. LV = left ventricle, LA = left atrium, MV = mitral valve, MV (a) = anterior leaflet of the mitral valve, MV (p) = posterior leaflet of the mitral valve, Ao = aorta.