Some heart murmurs reflect underlying heart disease. If you understand the physiologic causes for these heart murmurs, you will more readily be able to identify them and distinguish them from innocent heart murmurs. Obstructive lesions are caused by normal blood flow through valves that are too small for normal flow. Since this problem is not dependent on the drop in pulmonary vascular resistance that occurs following birth, these murmurs are audible at birth. Defects with left-to-right shunts, on the other hand, are dependent on the drop in pulmonary vascular resistance and are, therefore, not heard until a week or more after birth in the case of high-pressured shunts such as ventricular septal defect, patent ductus arteriosus, and persistent truncus arteriosus. Low-pressured left-to-right shunts, such as in atrial septal defects, may not be heard for a considerably longer time, usually first being noted at a year or more of age. It is important to note that many children with congenital cardiac defects have combinations of defects or variations of abnormalities, so that findings on cardiac examination will not follow these classic patterns. This table shows a limited selection of the more common defects.
Characteristics of the Murmur Associated Findings n -<
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