Increased blood flow to the pulmonary artery reduces the pressure in the right atrium and increases the pressure in the left atrium, causing the second change, the closure of the foramen ovale. The third change is the closure of the ductus ateriosus. Constriction of the ductus ateriosus is triggered by the release of chatecholamines, bradykinin and prostaglandins. Over time the constricted ductus ateriosus becomes permanently closed through_________________. The fourth change is the closure of the ductus venosus. The mechanisms involved in bringing about this change are unknown.
Atrial Septal Defect
An atrial septal defect is a congenital hole in the intra-atrial septum, or a patent foramen ovale.
This hole allows the flow of oxygenated blood from the left atrium into the right atrium, causing dilation of the right atrium, __________ edema and a reduction in the left ventricular stroke volume. After a time, the pressure on the right side of the heart exceeds the pressure on the left side forcing deoxygenated blood form the right atrium into the left atrium, where it flows into the left ventricle and is pumped to the body. Once pressure is less on the right side of the heart than on the left the flow of blood through the defect will reverse, causing blood to flow from right to left again. Atrial septal defects are seen clinically as exercise intolerance, fatigue, heart murmur, peripheral edema, atrial fibrillation, right side heart failure and cyanosis.
Diagnosis is made through clinical signs and symptoms, ECG and EKG.
There is __________ treatment for atrial septal defect in the horse.
Ventricular Septal Defect
A ventricular septal defect is, in essence, a congenital hole through the intraventricular septum.
This defect allows blood to leak from the _____________ ventricle into the _____________ ventricle during ventricular contraction, reducing the amount of blood being pushed into the aorta and increasing the amount of blood in the right ventricle and the pulmonary artery. This causes ___________________ congestion and edema. Ventricular septal defects are most commonly located in the intraventricular septum near the atrioventricular node. It is seen in _____________ week old foals as exercise intolerance, difficulty suckling, dyspnea and heart murmur.
Diagnosis is made through the clinical signs and symptoms as well as EKG showing the defect.
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