Stem Cell Treatment can help in treating Cardiac Arrhythmias
Transplantation of both skeletal myoblasts and stem cells into the region of infarcted myocardium results in improved myocardial function in both the murine and porcine infarct models. Intravenous injection of stem cells and bone marrow stimulating cytokines also improves cardiac function. The optimal cell type and dose, delivery route, delivery catheter, and the timing of cell injection are still being defined. In order for cell therapy to be widely clinically applicable, the optimal cell has to be compatible both mechanically and electrically with the host myocardium. In this issue of the Journal, Smits et al. extend the observations to humans, confirming the previous observations of Menasche et al. that myoblast transplantation improves global and regional left ventricular function late after myocardial infarction. This procedure has clinical application because cells could be delivered by trans-endocardial injection in the catheterization laboratory. Nevertheless, the study also exposes a potential serious limitation of both myoblast and stem cell therapy. In the current study , one of the five patients had sustained episodes of ventricular tachycardia and required implantable cardioverter-defibrillator (ICD) placement. The investigators also describe a subsequent unpublished experience of two sudden deaths and three serious ventricular arrhythmias in eight additional patients. These data seem to correspond to the Menasche et al. experience in which 4 of 10 patients required ICD implantation for ventricular arrhythmias after open chest autologous myoblast transplantation. Although, it remains possible that these arrhythmias reflect the natural history of myocardial infarction rather than the introduction of the new cells, it seems clear that we must consider the potential mechanisms of arrhythmia and strategies to control or eliminate them. Pro-arrhythmia after stem cell therapy might be attributed to one or more of the following reasons: 1) heterogeneity of action potentials between the native and the transplanted stem cells; 2) intrinsic arrhythmic potential of injected cells; 3) increased nerve sprouting induced by stem cell injection; and 4) local injury or edema induced by intramyocardial injection.
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