YOUR HEART MUSCLE NEEDS EXERCISE AT ANY AGE & STAGE OF LIFE…

STUDY SHOWS: Heart Cells Grow Throughout Life Span

Electron micrograph of cardiac muscle. Image by Dr. Giorgio Gabella. All rights reserved by Wellcome Images.

Researchers have discovered that the human heart continues to generate new cells throughout its life span. The finding may lead to the creation of new treatments to boost regeneration in people with heart problems, such as heart attack victims.

Scientists have long thought that organs such as the heart, brain and pancreas are unable to create new cells after development. This theory is largely based on the limited ability of these organs to recover after being damaged by illness or injury. In addition, primary cardiac tumors are very rare, suggesting restricted cell growth within the human heart. However, the rate of cell proliferation in the heart had not been directly measured.

Scientists at the Karolinska Institute in Sweden and Dr. Bruce Buchholz at Lawrence Livermore National Laboratory (LLNL) in California have developed an innovative way to solve this problem. Their method is based on the observation that cells in the body contain a carbon-14 “timestamp.”

The atmospheric concentration of carbon-14 was relatively stable until the Cold War, when above-ground testing of nuclear weapons in the late 1950s to early 1960s caused a spike worldwide. This increased the amount of carbon-14 that was incorporated into the DNA of everyone alive on Earth at the time. Since above-ground testing has been banned, the amount of carbon-14 in the atmosphere—and therefore the amount incorporated into new cells—has gradually fallen. Scientists can now pinpoint when a cell was created by measuring its concentration of carbon-14.

In the new study, the researchers performed carbon-14 analyses of DNA from heart muscle cells (cardiomyocytes) at LLNL’s National Resource for Biomedical Accelerator Mass Spectrometry, a research center supported by NIH’s National Center for Research Resources (NCRR). Tissue samples were obtained from people born up to 22 years before the onset of the nuclear bomb tests.

The researchers reported in Scienceon April 3, 2009, that the samples’ carbon-14 levels showed that cells in the human heart are created into adulthood. The scientists next determined the rate of heart cell growth over time by measuring the carbon-14 DNA profile of people born both before and after the 1950s testing. Mathematical modeling of the carbon-14 data revealed that a 50-year-old heart still contains more than half the cells it had at birth but that the turnover slows down with time. A 25-year-old heart replaces about 1% of all its cardiomyocytes over the course of a year, while a 75-year-old heart replaces about half a percent.

These findings raise the possibility that, if the heart produces more cardiomyocytes after a heart attack, techniques could be developed to enhance that process and potentially reverse heart damage.

“The advantage of cardiomyocyte regeneration over current clinical treatments is the possibility of repair,” Buchholz explains. “Heart attacks produce scar tissue that never functions properly. If the heart could be stimulated to repair the damage with new cells, recovery from heart attack may be much improved.”

—by Nancy Van Prooyen     

Exercise Is Safe, Improves Quality of Life in Patients With Chronic Heart Failure

Regular exercise is safe for heart failure patients and may slightly lower their risk of death or hospitalization, according to results from the largest and most comprehensive clinical trial to examine the effects of exercise in chronic heart failure patients. Supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health, the study also found that heart failure patients who add regular, moderate physical activity to standard medical therapy report a higher quality of life compared to similar patients who receive medical therapy only.

Researchers with HF-ACTION (Heart Failure – A Controlled Trial Investigating Outcomes of exercise TraiNing) have published two papers in the April 8, 2009, issue of the Journal of the American Medical Association. The study was conducted at 82 centers in the United States, Canada, and France.

“Many patients and health care providers have continued to be concerned about the safety of aerobic exercise for heart failure,” said NHLBI Director Elizabeth G. Nabel, M.D. “With the results of this robust clinical trial, we can now reassure heart failure patients that, with appropriate medical supervision, regular aerobic exercise is not only safe but it can also improve their lives in really meaningful ways.”

About 5 million people in the United States have heart failure, a potentially life-threatening condition in which the heart has a reduced ability to pump blood through the body. The number of people with heart failure is growing, and each year, another 550,000 people are diagnosed for the first time.

The leading cause of hospitalization among Americans age 65 and older, heart failure usually develops over several years and commonly results from coronary artery disease, high blood pressure, or diabetes. Treatment typically includes lifestyle changes, medicines, and regular outpatient follow-up with a health care provider. Some patients also need medical devices to help the heart pump better, or surgeries, such as a coronary artery bypass operation or heart transplant.

Earlier, smaller clinical trials have suggested that exercise is beneficial for heart failure patients, and clinical guidelines recommend moderate exercise for this condition. Nonetheless, safety concerns have persisted.

HF ACTION followed 2,331 patients with moderate-to-severe systolic heart failure (average age 59) for up to four years (average of 2.5 years). About one-half of the participants were randomly assigned to receive usual care alone, which included medical and device therapy as prescribed by their physicians and educational materials on disease management. They were also asked to engage in 30 minutes of moderate physical activity on most days of the week.

The other half of the participants were in the exercise training group, and they received usual care plus 36 sessions of group-based, supervised aerobic exercise training (walking or stationary cycling) of up to 35 minutes three times per week. These participants were asked to transition to home-based training at the same intensity five times per week for the remainder of the study and received a treadmill or stationary bike for home use and a heart rate monitor.

Compared to the usual care group, the exercise training group had slightly fewer (statistically non-significant) deaths or hospitalizations from any cause. When researchers adjusted the findings (as specified in the study design) for the strongest predictors of death or hospitalization — initial exercise capacity, history of atrial fibrillation, depression, cardiac pumping function, and cause of heart failure — exercise training was linked to an 11 percent lower risk of all-cause death or hospitalization and a 15 percent lower risk of cardiovascular-related death or heart failure hospitalization. In addition, there was no significant difference in serious adverse events between the two groups, such as an abnormal heart rhythm, hip fracture, or hospitalization related to exercise, suggesting that exercise training was well tolerated and safe.

The researchers note that the benefit of exercise may be underestimated by the observed study results because many of the usual care participants also exercised. In addition, adherence to prescribed exercise in the exercise training group was below goal in the majority of participants.

Overall, the exercise training was well tolerated. There was no significant difference between the two study arms in serious adverse events, including an abnormal heart rhythm, hip fracture, or hospitalization related to exercise.

Furthermore, after training, participants in the exercise group scored significantly higher than those in the usual care group on a standard, self-administered quality-of-life questionnaire. Participants reported fewer physical and social limitations and symptoms, and improved quality of life after three months. The improvements persisted throughout the follow-up period and were consistent regardless of sex, race, or age.

Lawton Cooper, M.D., M.P.H., NHLBI project officer for the study and a medical officer in the Division of Prevention and Population Sciences, is available to comment on these findings. Christopher M. O’Connor, M.D., lead author on the efficacy and safety study, and Kathryn E. Flynn, Ph.D., lead author on the health status study, are also available to comment.