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One hundred and twenty dogs were enrolled to value the effect of loading condition changes on left ventricular volumes before and 24-hours after the patent ductus arteriosus (PDA) occlusion by Amplatzer Canine Duct Occluder (ACDO) using standard echocardiography. The animals were divided in pure breed (n. 94) and mixed breed (n. 26); subsequently, the pure breed dogs were divided on the basis of the size of the breed of belonging in 3 groups (small size n. 36; medium size n. 8; large size n. 50). Moreover, the animals were divided in three classes based on their age: until 6 months; 6-12 months; over 12 months. A significant reduction of all the examined parameters (left ventricle internal diameter at end-diastole-LVIDd; left ventricle internal diameter at end-systole-LVIDs; end-diastolic volume-EDV; end-systolic volume-ESV; end-diastolic volume index-EDVI; end-systolic volume index-ESVI; fractional shortening-FS) was observed after ductal closure. Twenty-four hours after the closure, the evaluation of the relative percentage difference (RPD) of the echocardiographic parameters showed a significant reduction, higher in small size breed than in large size breed dogs. No significant difference related to breed size was observed only for RPD_FS variable. A significant interaction effect, between breed size and age classes, was observed only for RPD_EDVI (F = 3.39; p = 0.039). Until six months of age there was no significant difference in RPD_EDVI reduction, but over 6 months a significant reduction between small size and large size breed dogs at 24-hours from the occlusion was observed. In conclusion, our data seem to indicate that small breed dogs show a greater tolerance to congenital volume overload than large breed dogs, and this finding could be justify a delay of PDA closure in order to simplify the interventional procedure.

Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart disease. If left untreated, it carries a 33% mortality in the first year of life and a 50% mortality in the first 3 years of life. Since the introduction of the first open-heart repair by Lillehei and Varco in 1954, surgical management of TOF has evolved to be the primary repair during infancy in the majority of patients. Surgical management of TOF results in anatomic and functional abnormalities in the majority of patients, such as chronic pulmonary valve regurgitation and right ventricular (RV) dysfunction. Long-standing chronic pulmonary valve regurgitation can result in RV dilatation and failure, increasing tricuspid regurgitation, impaired exercise performance and supraventricular or ventricular arrhythmias. A timely reoperation may prevent these consequences, with a complete RV-function recovery. This article provides insight into the questions of when to perform a pulmonary valve implantation and in whom.