How fast — or slow — childrens' heart rates return to normal predicts heart health

New Orleans,LA – Middle school children whose heart rates remain elevated one minute after peak exercise are more likely to be obese, have higher cholesterol levels and other cardiovascular risk factors compared to those who get back to their resting heart rate more quickly.

The University of Michigan Cardiovascular Center study – the first to look at heart rate recovery in this population – suggests this simple test may offer a practical tool to assess cardiovascular fitness in children and identify those with risk factors for future heart disease those, according to research presented today at the American College of Cardiology’s 60th annual scientific session.

ACC.11 is the premier cardiovascular medical meeting, bringing together cardiologists and cardiovascular specialists to further advances in cardiovascular medicine.

HRR is traditionally used during exercise stress tests to evaluate heart function in adults. Previous studies have shown HRR to be a strong predictor of heart disease and death from all causes in adults with and without a history of heart disease. Authors of the present study investigated whether HRR is, in fact, associated with risk factors of heart disease and unhealthy lifestyle behaviors in kids.

“In general, the higher the heart rate is pushed during exercise and the longer it takes for the heart to return to a normal resting heart rate after exercise, the less fit the person is,” says senior author Elizabeth Jackson, M.D., M.P.H., assistant professor of internal medicine at the University of Michigan Health System. “We found this to be true among sixth graders, and our data also showed that heart rate recovery is strongly associated with cardiovascular risk factors you’d be concerned about in children.

“This would indicate that as parents, teachers and health care providers, we need to start thinking about heart disease prevention in children at an earlier age than we might think,” she says.

On average and compared to the most fit children (those in the lowest quartile of HRR), the less fit group (those in the upper quartile of HRR) had higher LDL or “bad” cholesterol levels (93.0 mg/dL vs. 86.7 mg/dL; P=0.02), higher triglycerides (132.4 mg/dL vs. 111.74 mg/dL; P=0.004) and lower HDL or “good” cholesterol (50.9 mg/dL vs. 55.9 mg/dL; P<0.001).

The higher children’s BMI, the more likely they were to be less fit as measured by longer HRR. Children were less fit also reported fewer days of strenuous to moderate exercise per week compared to children in the lowest quartile of HRR (4.8 vs. 4.1; P<0.001 for moderate exercise, and 3.6 vs. 3.0; P=0.001, for strenuous exercise).

Health ambassadors at Project Healthy Schools were trained to ensure data collection was standardized. Consent was secured from both parents and participating children.

HRR was determined by measuring children’s heart rates before and one minute after a 3-minute step test. The study included 1,276 sixth graders in Project Healthy Schools, a school-based intervention program in southeast Michigan.

In addition to heart rate, University of Michigan researchers collected and analyzed demographic information, physiologic factors such as cholesterol and blood sugar levels, body mass index (BMI) and blood pressure, as well as standardized health behavior questionnaires to assess diet, physical activity and sedentary behaviors.

Using quartiles of HRR as a marker of fitness, associations with demographic, physiologic and behavioral factors were investigated using Chi-squared and t-tests.

“Based on these findings, if communities or school administrators are looking for an easy, low cost marker for fitness, heart rate recovery could be considered,” Jackson says. “It can be done anywhere and this study shows that using HRR in addition to other screening tools that are already available like BMI can help us focus on overall cardiovascular fitness instead of just weight.”

The next step for Jackson and her team is to see whether there are improvements in cardiovascular health if students lose weight and exercise more often. As Project Health Schools expands to other geographic regions in Michigan, researchers will be able to consider racial, ethnic and economic diversity, which can play a role in risk factors for heart disease, including weight, cholesterol and high blood pressure.

This study was funded, in part, by the Mardigian Foundation, Hewlett Foundation, Adkins Foundation, AstraZeneca Foundation, Robert & Ellen Thompson Foundation, James Nicholson and NuStep.

Press release courtesy American College of Cardiology.

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