Heart disease is one of the most commonly-observed serious diseases in the United States, affecting over ten percent of the adult population to some degree. Heart disease essentially results from either an extreme deterioration or overgrowth of the muscular tissue of the heart that pumps blood throughout the body, and typically has grave implications for patients: over fifty percent die within five years of diagnosis.
Heart failure can be an extremely serious and debilitating ailment. Depending on the degree of failure, patients may experience conditions that at a physiological level cannot be effectively cured with drug therapy. Because it is also one of the most commonly-experienced health issues in middle-aged and elderly Americans, the demand for donor hearts considerably exceeds supply. Even in the event that a donor heart is available, after surgery, patients require immunosuppressive therapy for the rest of their lives to prevent the body from rejecting the donated organ. This, in turn, has driven the investigation of new therapies using stem cells to regenerate the heart.
Of these, one particularly promising apporach has recently been discovered at the Center for Cardiovascular Medicine at the University of Washington. Many earlier approaches to regenerating heart tissue involved regenerating heart muscle tissue either around a demuscularized skeleton of connective tissue from cadaver hearts, or regenerating small 'patches' of heart tissue outside the body to be surgically implanted in place of diseased tissue. But the latest and most successful attempt at regenating heart tissue at larger scale involves injecting large samples of undifferentiated stem cells directly into diseased areas of the heart.
This approach, which had been attempted previously with considerable success in mice and rats, was recently attempted in pigtail macaques, which are similar in size and build to rhesus monkeys, at the University of Washington. The monkeys had heart attacks induced, and then underwent injections of stem cells in areas of the heart where scar tissue had formed afterwards. In the treated monkeys, new heart muscle as wide as 3/5 of an inch formed successfully and was visually distinguishable with the naked eye - over ten times the size accomplished successfully by previous researchers. The grafts also successfully vascularized, growing not just muscle tissue but new blood vessels as well, drawing blood and therefore oxygen and nutrients to the new tissue, meaning that the tissue would likely continue to function successfully.
Previous attempts at the same technique in mice and rats, whose hearts can beat as fast as 400 beats per minute or more, had been considered completely successful as the heart's rhythm was not affected by the regenerated tissue. But in the macaques, whose heartbeat is considerably slower and, at an average of 115 beats per minute, much closer to that of humans' resting heart rate, the heartbeat became slightly irregular in the monkeys who received stem cell injections - which the researchers attributed to incomplete regrowth of the nerve tissue that would ordinarily regulate the heartbeat.
Future research, therefore, will likely focus on improving the regularity of the heartbeat in recipients of regenerated tissue. This may involve greater complexity of tissue regeneration in order to more completely regenerate the nerve tissue lost in the process of the patients' heart attacks; or it may involve combining stem cell injections with the use of a pacemaker and/or drugs that regulate the heartbeat so that patients experience fewer side effects of the resulting arrythmia. But in all cases, patients will, in the very near future, have access to a treatment for heart disease far superior to the options currently available.