Thursday, July 28, 2011

A New Technique For Restoring Heart Rhythm

A high-amplitude, and often painful, electrical shock is the only currently available method for treating certain cases of chronic cardiac arrhythmia. But now a new technique using much weaker impulses has been developed by an international team of physicists and cardiologists (1), including Alain Pumir, CNRS researcher at the ENS Lyon physics laboratory (CNRS/ENS Lyon/Université Lyon 1). 

The evolution of chaotic excitation waves on the surface of a heart during fibrillation in response to an arrhythmia. Color code: tissue at rest appears in black and excited tissue in yellow. 
Credit: © S. Luther and F. Fenton

Tested in vivo, it has proved effective in restoring heart rhythm in animals suffering from atrial fibrillation, the most common type of arrhythmia worldwide. Even though the technique has yet to be tried on human patients, these encouraging initial results could lead to the development of painless defibrillation methods. These results were published in Nature.

Affecting more than 10 million persons in Europe and the US, atrial (or auricular) fibrillation is the most common heart rhythm disorder. This type of arrhythmia (2) is characterized by the uncoordinated action of certain cells in the cardiac muscle tissue. As a result, chaotic electrical impulses propagate in the heart, preventing regular contractions and hampering the organ's capacity to circulate blood throughout the organism. It is simply not possible to reduce atrial fibrillation and restore normal heart rhythm by medication alone. 

The most effective treatment is still the application of an external electrical shock using a defibrillator. Defibrillation consists of intentionally applying an electrical current to the heart in order to restore a normal heartbeat. Although brief, this high-intensity impulse (with a high electric field) can damage the tissues and is often perceived as being very painful. Until now it was impossible to reduce its intensity without running the risk of an unsuccessful defibrillation.

The researchers began by studying the interactions between the electrical field and the cardiac tissues. The use of a high electric field (as with conventional defibrillators) generates waves in the cardiac tissue, primarily through the blood vessels. This set of waves is then cut off, restoring the heart rhythm. The researchers presumed that the use of a lower electric field would result in fewer sources being excited. Their working hypothesis was that the weaker electrical shock would need to be repeated several times. This was then verified in vivo. 

Using a conventional cardiac catheter, the team applied a series of five low-intensity impulses to the heart of an animal suffering from arrhythmia. After a few seconds, the heart started to beat regularly again.Called "LEAP" (Low-Energy Anti-fibrillation Pacing), their new technique is based on the same principle as existing defibrillators but elicits a very different response in the heart. Shortly after the shock, the cardiac tissue can no longer transmit electrical signals; the chaotic activity stops and the heart resumes its normal functioning.

Since it uses low electric fields, the new LEAP technique should be less painful and less damaging to cardiac tissue than existing defibrillators (reducing the energy needed by 80%). It also offers the advantage of restoring heart rhythm more gradually than the current techniques. Each impulse activates more tissue, gradually eliminating any turbulent cardiac activity. The blood vessels and other cardiac "heterogeneities," such as the misalignment of heart fibers, act as control centers: once activated, they make it possible to "reprogram" the heart.

In order to achieve these results, the researchers needed a thorough understanding of the effect of the electric field on the cardiac muscle. To this end, Alain Pumir contributed his expertise as a physicist. The experiments conducted by the teams headed by Stefan Luther and Eberhard Bodenschatz at the Max Planck Institute in Germany, and by Flavio Fenton and Robert Gilmour at Cornell University in the US, focused on high temporal or spatial resolution visualization techniques. Supplemented by digital simulations, they yielded a very precise picture of the phenomena involved.

Demonstrated on animals for atrial fibrillation, these results could also apply to the treatment of ventricular fibrillation, a fatal form of arrhythmia. LEAP could make it possible to eliminate pain while improving the treatment's success rate, in addition to prolonging the life of the batteries used to power implanted or external defibrillators. The next step is to test the technique on human patients, before new therapies for treating cardiac arrhythmias can be developed.

(1) The project united the Max Planck Institute and Göttingen University of Medicine in Germany, Cornell University and the Rochester Institute of Technology in the US, and the ENS Lyon physics laboratory (CNRS/ENS Lyon/Université Claude Bernard Lyon 1) and the Nonlinear Institute of Nice (CNRS/Université de Nice) in France.
(2) In a so-called "normal" heart, electrical impulses are propagated in the cardiac muscle in an orderly way, enabling regular contractions.

Contacts and sources:
CNRS (Délégation Paris Michel-Ange)

Citation:  Low-energy Control of Electrical Turbulences in the Heart. Stefan Luther, Flavio H. Fenton, Bruce G. Kornreich, Amgad Squires, Philip Bittihn, Daniel Hornung, Markus Zabel, James Flanders, Andrea Gladuli, Luis Campoy, Elizabeth M. Cherry, Gisa Luther, Gerd Hasenfuss, Valentin I. Krinsky, Alain Pumir, Robert F. Gilmour Jr., Eberhard Bodenschatz. Nature, 14 July 2011.

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