persistent ductus arteriosus (Left to Right Shunt)
the patient: a three year-old boy
reason for admission: a continuous systolic and diastolic murmur
history: The boy was a native of Columbia, living in a small town near Bogota at an elevation of 8600 feet above sea level. Three weeks after birth a murmur was noted by the local physician. From birth he was bothered by a cough and vomiting associated with feeding, nonetheless his growth and development were excellent. On examination at Southern Maine Medical Center at six months of age, one day after arriving by plane from Bogota, the child appeared well with the exception of a grade III systolic murmur. His chest film showed a normal-sized heart and his electrocardiogram indicated mild combined ventricular hypertrophy. On two-dimensional echocardiography, no specific abnormality was seen, although the left atrium appeared large. He was studied for gastric reflux.
Upon returning to SMMC three years later, this time having been in the Biddeford area for six weeks, he was re-examined and found to have a roaring continuous murmur, a wide pulse pressure, and prominent peripheral pulses. No cyanosis was noted. His electrocardiogram again showed combined left and right ventricular hypertrophy with a mean electrical axis of 95 degrees. A chest film showed a large aorta and pulmonary artery with left ventricular and left atrial enlargement and pulmonary vascular engorgement. Two-dimensional echocardiography showed a non-specific left ventricular overload with an increased left atrial-aortic ratio and identified the presence of a patent ductus arteriosus. He underwent cardiac catheterization because of the unusual combination of a right ventricular hypertrophy and a continuous murmur; this procedure revealed a left-to-right shunt with a pulmonary:systemic flow ratio of 1.5:1 and an increase in the oxygen saturation of the pulmonary artery above that of the right ventricle. A small left-to-right atrial shunt was also noted. The small persistent ductus arteriosus was closed during the procedure, using an umbrella occluding device. When examined six months later, he was well.
STUDY QUESTIONS
1. What probably caused the murmur heard in this child? The constant flowing of blood from the aorta to the pulmonary artery.
2. What factors contributed to the widening of the pulse pressure in this patient? The LV hypertrophy is from greater muscle so the heart is stronger to eject blood at greater pressures so peak pressures in the aorta are high. Because blood flows easily from the aorta to the pulmonary artery as well as to the periphery the arterial pressure will drop drastically before the next beat so the difference will be large thus equaling a large pulse pressure.
3. How does this patient's condition differ from that of the boy in case A? Why is this child's condition more serious? It is greatly effecting both the left and right side of the heart. This is evident by both L and R hypertrophy. It is bound to give out at some point.
4. What normally causes closure of the ductus arteriosus? Increased pulmonary vascular pressure when the baby takes its first breath.
5. What can you say about this patient's left ventricular preload? It is larger than normal due to the increased amount of blood flowing into the LV. The total LV filling flow is all the blood that is pumped from the RV + the blood that flows from the aorta to the pulmonary artery.