Open arterial duct in dogs with tricuspid valve dysplasia: pathogenetic features and compensatory role of the shunt

Tricuspid valve dysplasia (TC) is a congenital malformation that leads to regurgitation and dilation of the right heart. Open ductus arteriosus (OAP) is a common congenital malformation in dogs that causes a left-right shunt and volume overload of the left heart. The combination of these defects is rare, and the hemodynamic interaction between them has not been sufficiently studied. The lack of standardized protocols for diagnosis and treatment of combined heart defects in dogs creates difficulties for veterinary specialists in choosing management tactics. The aim of this work was to analyze the pathogenetic features and evaluate the compensatory role of the shunt in tricuspid valve dysplasia in dogs with an open ductus arteriosus. The study was performed on the basis of the veterinary cardiology clinic "Kotonai", the object of observation is a Pomeranian dog, male, 4 years old, body weight 3.6 kg. The diagnostic examination included a clinical examination, echocardiography (EchoCG) in M-mode, 2D mode and with Dopplerography, an assessment of the size of the heart chambers, the degree of regurgitation on the heart, parameters of pulmonary hypertension, signs of stagnation in a large circle of blood circulation. Conservative drug therapy was performed: torasemide, pimobendan, sildenafil. Surgical correction of OAP was not performed. Dynamic observation - 11 months. The initial examination revealed dilatation of the right atrium (PP) and right ventricle (RV), grade 3 TC regurgitation, and continuous left-right ventricular failure; left atrium dilatation and pulmonary hypertension (PH) were absent (LA/Ao within the normal range). After 11 months, there was a progression of TC insufficiency (grade 4), an increase in the size of PP (4.14 cm) and RV (RViDd 3.01 cm), the appearance of mild/ moderate PH (sPAP 39 mmHg), and OAP became difficult to distinguish. The left atrium remained undeveloped (LA/Ao 1.26). Direct quantitative assessment of the shunt (Qp/Qs) is considered methodologically incorrect due to pronounced regurgitation on the TC. The results of the study allow us to conclude that the open ductus arteriosus in this case performs a compensatory function, maintaining preload of the left ventricle against the background of reduced pulmonary blood flow in case of pulmonary dysplasia. The closure of the OAP could lead to acute decompensation and, as a result, death of the animal. Thus, the study showed that surgical correction of OAP in patients with combined congenital malformation in dogs and the absence of signs of left-sided overload in the presence of drug control of right ventricular failure is not the determining tactic for the treatment of animals with these pathologies. The data obtained can serve as a basis for the development of regulatory protocols for diagnosis and treatment of combined congenital heart defects in dogs.