UTRECHT, THE NETHERLANDS. It is generally accepted that lone atrial fibrillation (LAF) may develop when an overly sensitive heart tissue is combined with a dysfunctional autonomic nervous system and a trigger such as stress (involving excessive secretion of cortisol and aldosterone), caffeine (involving excessive adrenergic response), etc. Trigger avoidance is often effective in reducing AF frequency and catheter ablation and maze procedures isolate or destroy heart tissue which serves as starting points and as the substrate for AF. There is growing evidence that paroxysmal (intermittent) AF is involved in the formation of fibrotic heart tissue which, in turn, hastens the progression of paroxysmal AF to the persistent and permanent forms. At present, the only way of dealing with abnormal heart tissue enabling LAF is to destroy part of it. This may now change with the advent of stem cell therapy.

A group of Dutch researchers recently presented a review of the current state of the art concerning stem cell therapy and cardiac arrhythmias. They outline three areas of current interest:

• Biological pacemakers
• AV node repair
• Biological ablation

The goal of developing biological pacemakers is to replace current electronic pacemakers which need to be implanted, have their batteries replaced periodically, and are prone to lead failures. Animal experiments have shown that injections of stem cells into specific structures of the heart, notably the sino-atrial (SA) and atrioventricular (AV) nodes with their associated bundles of His and Purkinje fibres (see Heart Rhythm 101 for further explanation) can restore normal sinus rhythm and eliminate the need for pacemaker implantation. The AV node is the only connection between the atrial and ventricular part of the cardiac conduction system and plays a vital role in ensuring normal sinus rhythm. Although the art of repairing dysfunctional AV nodes through stem cell injections is still very much in its infancy, preliminary experiments have shown that it is possible to precisely inject stem cells into selected parts of the node using techniques similar to those used in catheter ablation.

The aim of biological ablation is to replace current catheter ablation and surgical procedures with stem cell-based techniques aimed at suppressing the excitability of the arrythmogenic substrate by transplanting cells that have been engineered to contain specific ion channels, in this case, channels for the inward rectifier potassium current. Animal experiments have proven the feasibility of this approach and resulted in increasing the local effective refractory period (a measure of reduced excitability and a commensurate reduction in the risk of AF). Whilst biological ablation certainly is an exciting prospect, there is still a very long way to go before it becomes a practical approach to curing AF. See Stem Cells 101 for more on stem cells.

Blank, AC, et al. Rewiring the heart: stem cell therapy to restore normal cardiac excitability and conduction. Current Stem Cell Research & Therapy, Vol. 4, No. 1, 2009, pp. 23-33

Editor's comment: The field of stem cell therapy is certainly an exciting and rapidly progressing one! However, there are obviously still lots of questions to be answered and problems to be solved. As an example, the work on stem cell therapy to regenerate failing heart muscles revealed that the stem cells used also removed fibrosis and dissolved scar tissue. Thus it is conceivable that this type of stem cell therapy might interfere with the lesions created in previous catheter ablations and maze procedures.