Surprise! Heart Muscle Can Replenish Itself

It’s humbling to see medical dogma overturned, but that is exactly what happened when, contrary to deeply embedded thought, scientists led by Jonas Frisen from the Karolinska Institute in Stockholm reported in Science today that the heart can grow new muscle cells, and does so regularly, albeit slowly, in the course of a lifetime.

To cardiologists, this is a blockbuster discovery, since the heart has been pegged as a disadvantaged organ in terms of injury, healing, and repair. Susceptible to coronary blockages that can cut off blood and destroy major hunks of heart muscle at one time in a heart attack, the heart can only heal itself slowly, often leaving behind thinned and baggy scar tissue devoid of healthy, beating muscle. And the distortion and remodeling of the heart that comes with this muscle loss sets the patient up for cardiac failure, blood clots, and nasty heart rhythms. It was always assumed the heart could do no better. But that does not seem to be so.

The clever piece of work from Sweden used carbon dating to figure out the age of human heart cells. The spike in concentration of atmospheric radioactive carbon-14 triggered by above-ground Cold War nuclear tests between 1955 and 1963 allowed the researchers (with the help of physicists and sophisticated mass spectrometry from the Lawrence Livermore National Laboratory in California) to discover that, lo and behold, the heart has slow and silent regenerative abilities. The evidence: the many heart cells whose nuclei—which last the life of the cell—had radioactive carbon levels that coincided with the atmospheric spikes, occurring many years after the person was born. The study found that younger adults renew about 1 percent of their heart cells per year. The growth falls off to roughly half of that in the elderly.

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