Getting older means getting slower, and the heart is no exception. A decreased maximum heart rate later in life reduces our capacity for strenuous work and can make it difficult to live alone. But why, exactly, does the heart slow down?

New research suggests that the fault lies with the sinoatrial node, a group of cells in the right atrium that acts as an internal pacemaker by generating the electrical impulses that keep the heart beating. Researchers from the University of Colorado School of Medicine recorded spontaneous electrical signals from those cells in old mice, and found that they simply could not keep up with those from younger mice.

Credit Chris Gash

There are probably other factors at play, said Catherine Proenza, a physiologist and an author of the study. And it is difficult to measure the overall significance of the slower cells. But “it is certainly a contributing factor,” she said. “Because these cells set the heart rate, if they go slower, the heart will go slower.”

The findings, which were published last week in Proceedings of the National Academy of Sciences, suggest a possible treatment for heart fatigue in older people, she added.

“We know that you can stimulate these cells, so if you could provoke them just a little bit more, you could boost the maximum heart rate just a little,” she said. “Suddenly a person is able to carry that laundry basket or go down those steps to the basement, so they can still live alone.”


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