Clinical Neonatal Cardiac Physiology

During circulatory development from the embryonic to fetal to neonatal stage, transformation occurs in blood flow, from a single circular system to a double parallel circuit. At the time of birth and during early neonatal period, circulatory changes result in the formation of two separate circuits in series. The first step in evaluating heart sounds in the foal involves knowledge of the anatomical position of the heart within thorax. Auscultation of normal heart sounds is best accomplished over mitral valve area in neonatal foal. Foals are often born with low-grade heart murmurs that should disappear within the first 3 days of life. The description of heart murmurs requires purposeful auscultation and typically involves six characteristics: grade, timing, point of maximal intensity, shape, character and duration. Blood pressure monitoring is particularly important in foals undergoing inhalational anesthesia, in hemodynamically unstable patients, and in those at risk of cardiovascular complications.