Stem cell therapy for heart failure: are arrhythmias a real safety concern?

So far, the major safety issue raised by the use of stem cells for cardiac repair has been the occurrence of ventricular arrhythmias, particularly after skeletal myoblast transplantation. Although one cannot refute a potential intrinsic arrhythmogenicity of stem cells, primarily related to their common lack of electromechanical integration into the recipient myocardium, it is also important to recognize that patients eligible for cell replacement therapy are prone to develop arrhythmias because of their underlying ischemic heart disease. Another confounding factor is the method used for the intramyocardial delivery of the cells, which can cause enough inflammatory tissue damage to further increase ventricular irritability on top of an already high baseline level. Thus any strategy designed to minimize the risk of stem cell-associated ventricular arrhythmias should take into account, besides the cell-specific ability to appropriately couple with host cardiomyocytes, the method of cell transfer and the nature of the myocardial environment targeted for cell engraftment. A more accurate characterization of the baseline risk of arrhythmias in these patients would thus be helpful for better assessing the respective contribution of the donor cells and the host myocardium to these complications. The risk-to-benefit ratio of stem cell therapy will finally have to be revisited in light of the fact that because this baseline risk is usually high, most of these patients will in any way be fitted with an implantable defibrillator.