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INTRODUCTION

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Cardiac defects are the most common congenital malformation, occurring in up to 1% of all live births (even excluding bicuspid aortic valve and very small atrial and muscular ventricular septal defects), and present symptomatically in about 20% of such neonates. It is thus essential that the clinician diagnose symptomatic cardiac disease expeditiously. Because of the concern for serious cardiac disease, many clinicians consider the presence of a murmur as the most definitive evidence of heart disease. A murmur, however, is not an accurate sign of symptomatic neonatal heart disease. Many normal neonates have murmurs at some time during the first few days of life, whereas several common symptomatic cardiac defects, such as total anomalous pulmonary venous connection and simple transposition of the great arteries, are not associated with murmurs. In the neonatal period, the presence of a murmur is neither sensitive nor specific to the diagnosis of heart disease, yet it is commonly used both to consider and, most concerning, to exclude the presence of a significant cardiac defect.

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The change from a fetal circulatory system to a transitional circulation occurs immediately at birth, and the mature circulation develops within weeks. Because of these dramatic alterations in blood flow and oxygen uptake patterns, the fetus with a stable cardiovascular status can become a newborn with severe cardiovascular symptoms. On the other hand, advances over the last few decades have given the clinician the tools to rapidly stabilize these critically ill neonates, and subsequently correct or ameliorate even the most complex defects. Thus, it is essential that the pediatrician be able to recognize the infant with symptomatic heart disease quickly, so that the appropriate diagnostic and therapeutic interventions can be initiated as soon as possible.

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Although there are literally thousands of different congenital cardiac defects, in general, there are only three different, overlapping, modes of presentation of symptomatic heart disease in the newborn and infant, each very easy to recognize during a routine examination. These modes of presentation are cyanosis, decreased systemic perfusion (hypoperfusion), and respiratory distress/failure to thrive.

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Prior to considering the modes of presentation of symptomatic heart disease in the newborn, it is worthwhile to review fetal physiology to understand why symptomatic heart disease is rare in the fetus.

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FETAL PHYSIOLOGY

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The fetal circulation is unlike the postnatal circulation in that there are 3 major circulatory beds rather than 2 (the additional placental circulation) and that the 2 ventricles eject into the vascular beds that are not fully separated. There are 3 main connections, or shunts, between circulatory beds and/or cardiac chambers that allow for admixture of venous return to the ventricles and of their outputs to the arterial beds. These connections allow one ventricle to take over the work of the other when a congenital cardiac defect is present. Those shunts, along with the far lesser oxygen demand of the fetus compared to the ...

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