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Fall 2007
News this month Recent research is providing early evidence that stem cells derived from bone marrow may be able to replace damaged heart muscles. Stem cells are immature cells that have the ability to develop into specialized functions such as heart muscle. They come from sources such as blood, bone marrow and skeletal muscle. Two German studies using injected stem cells to strengthen the heart muscles of patients after a heart attack have shown promising results, while a small Norwegian trial showed no benefit. In each study, reported in the Sept. 21, 2006 issue of the New England Journal of Medicine, stem cells were infused into the heart through a cardiac catheterization. A tiny balloon momentarily blocked regular blood flow into the heart and stem cells were injected in an attempt to give them a couple of minutes to try to take root. Success was measured by changes in the amount of blood pumped out with each heartbeat. Possibly the most successful results came from the German trial conducted by researchers at the University of Frankfurt, which enlisted 204 patients, half of whom had stem cells injected three to seven days after a heart attack. Four months later, the ejection fraction — a measure of the heart’s ability to pump blood — was significantly better in patients who got the stem cells. The ejection fraction of the stem cell recipients improved by 5.5 percent, compared to 3 percent for those who got conventional treatment. After a year, the stem cell recipients had a significantly lower incidence of second heart attacks. Their death rate was lower, and fewer of them needed treatment to reopen blocked blood vessels. A smaller trial of 75 patients, also conducted by German researchers, had patients receiving either bone marrow or circulating blood-derived stem cells at least three months after their heart attack. The treatment produced moderate but significant improvement in the ejection fraction after three months, the researchers reported. Conversely, the Norwegian study of 100 heart attack patients, half of whom got stem cells, showed no beneficial effect. There was no improvement in ejection fraction or the amount of heart muscle damage. Incidence of adverse effects was the same for patients who did or did not get stem cell therapy. It’s not clear why one study found no effect and two found modest benefits. The explanation may be differences in how many stem cells were used, or in how the cells were handled and prepared. It’s not clear why one study found no effect and two found modest benefits. The explanation may be differences in how many stem cells were used, or in how the cells were handled and prepared. "I think this therapy has no place in medical practice at this moment," said Ketil Lunde, MD, a research fellow at the Rikshospitalet University, and lead author of the Norwegian report. "It should be applied only for research applications." Andreas Zeiher, MD, professor of medicine at the University of Frankfurt and leader of the two German studies, agrees. "For the time being, there is no recommendation for routine use in clinical practice," said Dr. Zeiher. "We have to show in larger trials reduced endpoints such as second heart attacks, deaths and re-hospitalizations." The Frankfurt researchers plan an expanded study of 200 or more heart-attack patients to be completed in two years.
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Repeat, larger-scale studies are needed Damage to the heart muscle that occurs during a heart attack reduces the pumping function of the heart. This reduced "ejection fraction" is the most important independent predictor of survival, even in the era of aggressive reperfusion therapy with coronary angioplasty and stenting. Clinical heart failure that develops after a myocardial infarction remains a major cause of death and disability. Despite efforts at early opening of a closed artery to limit heart damage during a heart attack, further advancements in our treatment options are needed. "Clinical heart failure that
develops after a myocardial infarction remains a major cause of death and
disability."
Experimental studies have suggested that administration of stem cells from bone marrow may help regenerate and heal damaged heart muscle and improve growth of new blood vessels in heart muscle. The resulting improvement in heart strength, especially in people with large heart attacks and weak hearts, may be beneficial and improve outcomes. Two of these three studies showed benefit to the ejection fraction (heart strength) and also suggest improved one-year outcomes. All three studies showed safety in the technique of stem cell administration, and no increase in adverse events. The differences in the study outcomes may have several explanations. The timing of the stem cell injection varied by design of the studies ranging from three days to nine months following the heart attack. This has important implications as the best improvement may occur closest to the time of the damage (heart attack). Also, the technique of measuring the ejection fraction varied between the studies, and may have yielded slightly different results. The most accurate comparisons would use the same technique. Additionally, the size of the studies varied, and the statistical reliability may be altered if the study is too small. Lastly, the greatest benefit was seen in the patients with the most damage to the heart muscle. Perhaps the results would be more uniform if all the patients studied had similar poor ejection fraction. This is important as these are the very patients that have the highest risk and the most benefit to gain. Repeat, larger-scale studies are needed to explore the potential benefit of this promising new technique in salvaging and repairing damaged heart muscle, especially in sicker patients with larger heart attacks. Fortunately, there is much interest in bettering our cardiac treatments that we can offer to our patients. As time goes on, we continue to provide greater care and improved outcomes Dr. Swirsky is a cardiologist in private practice in New Haven and on the medical staff at Yale-New Haven Hospital |
