Common Atrium in a Dog

Abstract

A 4-month-old 2.7-kg male Miniature Schnauzer was referred for evaluation of a heart murmur. On physical examination the dog was thin and was mildly dyspneic when handled. The respiratory rate was 45 breaths/min and the heart rate was 180 beats/min. The patient's mucous membranes were slightly pale with a normal capillary refill time. The jugular veins were distended but no abdominal enlargement was present. Thoracic auscultation revealed accentuated bronchovesicular sounds, and a grade V/VI pansystolic murmur with a point of maximal intensity at the left sternal border. A 6-lead electrocardiogram (ECG) demonstrated a left anterior fascicular block pattern. Thoracic radiographs (Fig 1) revealed severe generalized cardiomegaly.The interatrial septum was not evident on the standard long-and short-axis right parasternal views during echocardiographic examination, suggesting a single atrial chamber (Fig 2). The septal leaflets of the atrioventricular valves inserted at the same level on the crest of the ventricular septum, and the motion of the mitral valve leaflets was abnormal. An echolucent space between the left atrium and the pericardium was interpreted to be a dilated coronary sinus (Fig 2). M-mode measurements revealed that the right ventricular internal diameter in diastole was 11 mm (reference range, 2-9 mm), 1 left ventricular internal diameter in diastole was 36.0 mm (reference range, 24.6 Ϯ 6.2 mm), 2 the left ventricular internal diameter in systole was 21.5 mm (reference range, 13.6 Ϯ 5.5 mm), 2 the left ventricular diastolic wall thickness was 7.4 mm (reference range, 5.0 Ϯ 2.1 mm), 2 the left ventricular systolic wall thickness was 11.4 mm (reference range, 7.2 Ϯ 1.7 mm), 2 the interventricular septal diastolic thickness was 9.1 mm (reference range, 5.8 Ϯ 2.1 mm), 2 the interventricular septal systolic thickness was 14.7 mm (reference range 9.8 Ϯ 2.6 mm), 2 E-point septal separation was 1.1 mm (normal Ͻ5-6 mm), 2 aortic root at end-diastole was 10.6 mm (reference range, 13.8 Ϯ 3.6 mm), 2 and shortening fraction was 40.4% (normal 28-44%). 2 Color-flow mapping and spectral Doppler echocardiography revealed mitral, tricuspid, and pulmonic regurgitation. The pulmonic blood flow velocities (pulsedwave Doppler echocardiography) recorded from right parasternal short-axis view were maximum peak systolic velocity 0.87 m/s (normal Յ 1.3 m/s) 3 and pulmonic regurgitation 1.8 m/s. The mitral valve flow velocities (pulsed-wave The direction of the shunting into the common atrial chamber could not be accurately determined because of the turbulent jets of mitral and tricuspid regurgitation and the atrial chamber inflow. After a right cephalic vein injection of 5 mL of 0.9% NaCl, bubbles were seen within the atrial chamber. When 5 mL of saline was injected into the left cephalic vein, bubbles were seen in the coronary sinus and then in the atrial chamber, suggesting a persistent left cranial vena cava. Results of a CBC and serum chemistry were within reference range.A tentative diagnosis of a common atrial chamber ...