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The Informed Parent

Innocent Heart Murmurs in Children…No Cause For Concern

by Louis P. Theriot, M.D., F.A.A.P.
Published on Jul. 02, 2012

As I looked at the schedule for the day I noticed that I was seeing a new patient who had been allotted extra time because of a problem. Nine-month-old Max had recently moved to Long Beach from out of state with his family. 

Max’s mom was anxious. Since the baby had been healthy, mom had made the appointment a few weeks previous to establish him as a new patient. But a few days ago he had a high fever and some diarrhea. Mom took him to an urgent care center to be evaluated.

As the doctor was examining Max he said in a startled voice, “Has anything ever been done about his heart murmur?” She told me, “I was dumbfounded when he said that…literally in a state of shock. At every well-check I was told by the pediatrician in Georgia how healthy he was. This floored me, and to make matters worse, he said this could be very serious and dangerous!” He then ordered a chest x-ray and an EKG and made me promise that I would take Max to a cardiologist as soon as possible. “I had this appointment with you today and thought I would wait to see what you said. I just hope I didn’t wait too long,” she said apologetically. 

I looked at Max sitting in mom’s lap. He seemed to be a happy, thriving infant. His weight and height put him at the 75thpercentile, which meant he was growing well. Developmentally he was ahead of the curve, and his exam was completely normal with the exception of a faint murmur that would have been easy to miss if I wasn’t looking for it. His pulses were equal and symmetrical in all four extremities and heard the murmur when he was lying on his back. I had him sit in mom’s lap and sure enough, the murmur was no longer heard. 

I then told Max’s mom that he had an innocent or functional murmur which was a normal finding in perfectly healthy children and that she should not give it another thought. She was noticeably relieved. We then went on to discuss innocent murmurs. The word murmur conjured up thoughts of serious heart issues and heart surgery. So what is a heart murmur anyway? Picture in your mind the heart sounds that one is so familiar with-the lub dup, lub dup. Basically a heart murmur is any extra noise that coincides with the normal sounds. Murmurs are caused by any disruption of the normal flow of blood through the four chambers of the heart or major blood vessels (the aorta and pulmonary artery). Abnormal or pathological murmurs are caused by anatomical or structural variances such as a hole in the wall of the heart, a narrowing of the major vessels, or a damaged valve. When this occurs, the blood flow is greatly disrupted causing turbulence of the blood, hence the murmur.

An innocent murmur is a benign condition that has been reported in as many as 40-50% of all children at some point in their early lives. The term “innocent” or “functional” was first described by William Evans in 1943. In an innocent murmur, the anatomy of the heart and great vessels is entirely normal. What happens is that the large column of blood that is ejected from the ventricles into the aorta and pulmonary artery with each beat passes with much force causing the walls of the vessels to vibrate resulting in the vibratory or innocent murmur. It is common for  innocent murmurs to be heard one day, and then not the next. Any condition that increases the dynamics of blood flow, such as fever or dehydration, can magnify the sound of the innocent murmur. I think this is what happened with Max. He had a high fever and was probably a bit dehydrated from the diarrhea when he was seen in the urgent care center. The murmur was most likely quite prominent and noticeable. But when I examined him it was barely perceptible. This is common with innocent murmurs. They vary in intensity and vary even with position. Innocent murmurs are soft and described as being musical and vibratory. Most pathological murmurs do not change with position and are described as being harsh in quality.

The reason innocent murmurs are so common in children and not adults has to do with the fact that children have relatively thinner chest walls, the blood flow in children is much more dynamic than in adults, and there is more angulation of the great blood vessels as they take off from the heart in children than in adults. 

Max’s mom was greatly relieved and asked, “Can I cancel my appointment with the cardiologist next week?” I made sure that the chest x-ray and EKG that were done in the urgent care center were normal and told her an unequivocal yes. I also stressed that Max had a perfectly normal heart and he was a healthy and normal little boy. He should not in any way be questioned by insurance companies about a “pre-existing condition” as Max’s heart is normal. I told mom that should a medical person ask about his heart, she should tell them that “I was told that Max has an innocent or functional murmur and that I was told not to worry about it!”

While Max’s case was very straightforward and obvious, many times this is not always so, especially in young infants. If there is ANY question about a murmur being innocent or not, that patient deserves a work-up including a chest x-ray, EKG and an echocardiogram, or an evaluation by a pediatric cardiologist.

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