Double-Chambered Right Ventricle and Intraventricular Thrombosis Mimicking Double-Chambered Right Ventricle in Cynomolgus Monkeys (Macaca fascicularis)
Reports of congenital heart disease in nonhuman primates are rare, and double-chambered right ventricle (DCRV), which is a rare congenital heart disease, in which an abnormal muscle bundle divides the right ventricle into 2 chambers (a proximal high-pressure chamber and a distal low-pressure chamber), has not been previously reported. We diagnosed DCRV antemortem in 2 monkeys bred at The Tsukuba Primate Research Center that presented with cardiac murmurs. Subsequent diagnostic evaluation confirmed DCRV in one case, with the other diagnosed with midventricular obstruction having a pathophysiology similar to DCRV. The monkey that had DCRV exhibited a pathophysiology similar to that in humans with DCRV, while the other monkey had a condition mimicking DCRV which was due to a thrombus. We believe this to be the first report of DCRV and a rare DCRV-like pathophysiology due to a thrombus in the ventricle in nonhuman primates.
Radiograph images of the 2 cases. The radiographs in both cases demonstrate right atrioventricular enlargement. On the lateral projections, there is increased sternal contact (white arrowheads) while on the ventrodorsal (VD) projections, there is rounding of the right atrioventricular region of the cardiac silhouette (black dashed line). These radiographic findings suggested right atrial overload; however, there was no evidence of right-sided heart failure (for example, hepatomegaly, ascites, and pleural effusion) or lower airway disease that would result in cor pulmonale in either case.
Echocardiography of the 2 cases. In case 1, B-mode echocardiography showed RVOT obstruction with trabecular muscle hypertrophy (white arrow) and color Doppler showed high-velocity turbulent flow (4.5 m/s) in the RVOT. Additionally, case 1 showed hypertrophy of the right ventricular wall proximal to the stenosis, while the distal right ventricular wall was not hypertrophied. Case 2 had a heterogeneously hyperechoic ridge of tissue within the RVOT located 10 mm proximal to the pulmonary valve causing narrowing (white arrowheads) and color Doppler showed high-velocity turbulent flow (2.5 m/s) in the RVOT. Additionally, significant enlargement of the right atrium was observed. AM, abnormal muscle; LA, left atrium; LV, left ventricle; PA, pulmonary artery; PV, pulmonary valve; RA, right atrium; RV, right ventricle.
Electrocardiogram of the 2 cases. Case 1 had an abnormal wide R wave in all leads. Case 2 showed right axis deviation and a low-amplitude R wave in lead II, abnormal Q wave in lead III, and aVF. Additionally, both cases had corrected QT interval prolongation (amplitude: 20 mm/mV; paper speed: 50 mm/s).
Histopathological evaluation of the 2 cases. In case 1, necropsy showed abnormal muscle bundles in the right ventricle and RVOT stenosis (white arrowhead), as viewed from the apex (A). Cross section of a Masson trichrome (MT)-stained specimen of the heart in case 1 showed extensive fibrosis at the intraventricular septum and an abnormal muscle bundle causing stenosis (black dashed line) (B; bar = 10 mm). A high-magnification MT-stained image showed intricate arrangement of the myocardium (C; bar = 200 µm), abnormal myocardial bundles, and extensive fibrosis and loss of cardiomyocytes in the right ventricle (D; bar = 50 µm). Necropsy in case 2 showed a cardiac thrombus (white arrow) and dilation of the right atrium (E). HE staining showed that the cardiac mass in the RVOT consisted of a thrombus and its calcification (F; bar = 500 µm). There were no other concomitant diseases in either case. LV, left ventricle; RV, right ventricle; RA, right atrium.
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