Surgery in infancy or childhood can often correct even the most complex congenital heart defects (CHD). But there is no such thing as a complete repair of a defect. Even after surgery, the heart of a child with CHD will never be completely normal; there will always be residual issues.
As patients grow, pediatric cardiologists have to figure out how their uniquely abnormal hearts function differently than anatomically correct hearts. While an echocardiogram works fine while a patient is lying down, children are always active and moving. How do doctors know whether enough blood flow is getting to the heart while their patients are walking to school, doing chores or playing sports?
Invasive tests such as coronary angiography can provide this insight, as can nuclear imaging, which is non-invasive but involves a high dose of radiation (just one nuclear imaging scan has the same amount of radiation as about 500 chest x-rays). There is another alternative, however—one that requires no radiation, is non-invasive, and doesn’t even require the child to be stuck by a needle: exercise stress echocardiography (ESE).
ESE is an echocardiogram performed immediately before and after a patient exercises on a treadmill or bicycle. For years, this modality was used exclusively on adults, mostly to see if blockages in their coronary arteries were impairing physical endurance. While ESE does not replace or eliminate the need for nuclear medicine tests and coronary angiography altogether, it is another way for cardiologists to gather information that can help them decide on the best care plan for a patienten.
“Ten years ago, we had fewer choices and relied heavily on nuclear medicine tests, which involve exposure to ionizing radiation,” says Ming Hui Chen, MD, FACC, FASE, a non-invasive cardiologist in Boston Children’s Heart Center who coordinated with colleagues and technicians to bring ESE to Boston Children’s in 2007. “Since then, we have been ordering fewer and fewer nuclear medicine tests each year. Stress echoes have helped drastically decrease the amount of radiation our patients may receive.”
“A stress echo can help us understand if there is sufficient blood getting to the heart during exercise and/or physical activity,” she adds. “And it can also help us correlate patients’ symptoms with their daily activity.”
Understanding how the heart functions under different degrees of exertion is especially important for children with certain cardiac diagnoses. In hypertrophic cardiomyopathy, for instance, the muscular walls of the heart are thickened, creating a risk for blood flow obstructions. ESE can reveal obstructions that may not be captured on a resting echo taken when the patient is not exercising. ESE is also useful in various valve diseases and different types of congenital heart disease.
Today, Boston Children’s is one of just a handful of pediatric hospitals with a dedicated ESE program. The growth of the program—which services both children and adults—has caused the Heart Center to bring on another clinician, Keri Shafer, MD, to join Chen in supervising these tests.
“Exercise stress echocardiography is a low-cost, minimally invasive test that can reveal a lot of valuable information about children with heart disease,” says Chen. “Kids and their families have appreciated that the test requires no needle sticks. Since implementing stress echocardiography at the Heart Center almost a decade ago, we have aimed to improve patient care and patient comfort, while minimizing radiation exposure to children.”
How to run a stress echo
Chen describes the three general steps of conducting a stress echo:
- The patient starts off lying on the echo bed. A specially trained sonographer performs an echo capturing video of the heart pumping, allowing for measurements to be performed.
- The patient gets up and exercises on a bike or treadmill as per protocol, for as long as he or she can (up to fifteen minutes). For a treadmill test, the patient begins with a leisurely stroll. Slowly, the speed and incline are increased. A brisk walk becomes a jog, and then a full-out sprint. When the patient needs to stop exercising at the end, the reason for stopping (such as “I was getting too winded” or “my legs were very tired.”) is recorded.
- Then the patient quickly lies back down on the echo bed. While the patient’s heart is still racing, another echo is performed to capture its pumping function during periods of increased blood flow. The sonographer then repeats the measurements, allowing for comparison with conditions at rest. Time is of the essence: all the post-exercise information should be captured in the first 5 minutes after exercise, and cardiologists must be able to scan these short echos and quickly discern answers to their clinical questions.
To learn more about ESE or refer a patient for this test, contact the Division of Noninvasive Cardiac Imaging.