More Than Innocent: A Continuous Murmur in an Infant

This patient is a 3-month-old, full-term infant with no personal or family cardiac history who presented to the pediatrician with a chief complaint of increased fussiness and spit ups and was found to have a new murmur.He was born via C-section for breech presentation following an uncomplicated pregnancy. He had an unremarkable neonatal course in the newborn nursery and was discharged 2 days later. At 2-months-old, he was diagnosed with cow’s milk protein allergy after an episode of bloody stool and was transitioned to hypoallergenic formula. Over the course of the first 3 months of life, he had multiple pediatrician visits for fussiness, gassiness, and spit ups. He drinks about 27 to 30 ounces of formula per 24 hours, generally consuming between 3 and 6 ounces at a time without issue. There is never any respiratory distress or diaphoresis during or surrounding feeds. The family has been educated on reflux precautions, and he has been trialed on famotidine for gastroesophageal reflux disease. He is generally growing well along his growth curve at the 42nd percentile weight-for-age.At 3-months-old, he presented with a complaint of increased fussiness with stooling and worsening spit ups. At this visit, he was newly noted to have a heart murmur. The murmur was described as a loud, III/VI continuous, machine-like murmur heard loudest at the left lower sternal border and apex, with no change with the respiratory cycle or with position. There was a normodynamic precordium and no palpable thrill. He was warm and well perfused with strong peripheral pulses. The physical examination was otherwise unremarkable. Of note, there is no significant family history of congenital heart disease, cardiomyopathy, arrhythmia, or sudden cardiac death. Given this finding, the patient was urgently referred to pediatric cardiology for further evaluation.It is not uncommon to discover a new murmur in pediatric patients, and this should prompt a detailed history and physical examination. Pediatricians are frequently faced with the task of determining which murmurs are benign, or “innocent,” and which are potentially pathologic, thereby warranting further evaluation and cardiology consultation. This patient presented with a loud, continuous, machine-like murmur at 3 months of age. A true continuous murmur continues through systole and into diastole. Although systolic murmurs in children are often innocent, diastolic murmurs (or murmurs with diastolic components, such as continuous murmurs) usually indicate underlying heart disease and should be given careful consideration.A possible benign cause of a continuous murmur is a venous hum, which is caused by turbulent jugular venous blood flow into the superior vena cava. This soft, low-pitched murmur is generally heard above the clavicle. Like many benign murmurs, the murmur of a venous hum can disappear with position changes, such as with rotation of the head, causing jugular vein compression, or from transitioning from sitting to supine, decreasing jugular venous flow.The most common congenital heart defect overall, and therefore a common cause of pathologic murmurs in pediatrics, is a ventricular septal defect (VSD). Although a VSD most often presents with a holosystolic murmur, in some cases, a diastolic rumble can be heard across the mitral valve from increased left-sided blood flow. Although not truly continuous, VSDs should be considered in the differential for a loud systolic murmur with a diastolic component in a child, particularly if symptomatic.Continuous murmurs can be heard with “runoff” lesions, which involve communication between a higher-pressure arterial system and a lower-pressure system. Clinically, these lesions may cause a widened pulse pressure, as well as bounding pulses. The most common pathologic cause of a continuous, machine-like murmur is a patent ductus arteriosus (PDA). A PDA murmur is best heard at the left upper sternal border or left infraclavicular area, with radiation to the back. The PDA involves a connection between the high-pressure (and high-resistance) systemic circulation and the lower-pressure (and lower-resistance) pulmonary circulation, resulting in left-to-right shunting in both phases of the cardiac cycle, thereby causing the continuous murmur. Aortopulmonary window, or other systemic to pulmonary shunts, can present similarly.There are a number of other lesions that can result in diastolic runoff and continuous murmurs, including arteriovenous malformations or arteriovenous fistulas. These are abnormal blood vessels or connections between arteries and veins, bypassing the normal capillary bed. These abnormalities can be congenital or acquired and can be associated with other congenital heart lesions. Coronary artery fistulas, which are abnormal communications between a coronary artery and either a cardiac chamber or other vascular structure, can also cause significant runoff. Although the coronary arteries are typically perfused in diastole, coronary artery fistulas can cause continuous murmurs due to a pressure difference between the 2 communicating chambers in both phases of the cardiac cycle. Lastly, aortic regurgitation can also cause a high-pitched, diastolic decrescendo murmur due to regurgitant blood from the aorta to the left ventricle. Although not truly continuous, aortic regurgitation may also be associated with a systolic murmur due to increased stroke volume across the aortic valve in systole, thus making it difficult to distinguish from continuous murmurs.At the pediatric cardiologist visit, the physical exam was consistent with the exam at the pediatrician’s office. The electrocardiogram (EKG) was normal with no suggestion of structural abnormality or ischemia (Figure 1). An echocardiogram was performed, which demonstrated a large coronary artery fistula from the left anterior descending artery (LAD) to the apex of the right ventricle, with a severely dilated left coronary system (Figure 2). The size and st