A kinder, gentler defibrillator : Nature News

A kinder, gentler defibrillator : Nature News: "A kinder, gentler defibrillator

A new technique could lower the intensity of the shock needed to reset electrical instabilities in the heart.

Alla Katsnelson

Could dramatic scenes like this be a thing of the past?Corbis Premium RF/Alamy


When electrical rhythms in the heart go haywire, applying a strong electric shock to the chest can set them straight. But the procedure can also damage heart tissue and cause intense pain, prompting a search for a gentler approach. A technique tested in dogs now claims to be just that: it resets heart arrhythmias by applying a series of five small shocks, instead of one large one, slashing the amount of energy needed by about 84%.

Standard defibrillation, used since the 1950s, works by applying about 1,000 volts of electricity to the outside of the chest in medical emergencies such as cardiac arrest. Like a reset button, it depolarizes each cell and returns the whole system to a resting state. Some patients with previous heart problems have surgically implanted defibrillators, which apply about 350 volts, 'but even that is very painful,' says Flavio Fenton, a physicist at Cornell University in Ithaca, New York, and one of the researchers involved in the work.

Fenton, Stefan Luther, a physicist at the Max Planck Institute of Dynamics and Self-Organization in Göttingen, Germany, and their colleagues, found that the shape of the heart's vasculature determined spatial patterns of electric currents and that it could be used to create 'virtual electrodes' that essentially amplify the voltage applied to the tissue. The results are published today in Nature1.

'It's a really different approach to thinking about the problem,' says Richard Gray, a biomedical engineer at the US Food and Drug Administration's Center for Devices and Radiological Health in Silver Spring, Maryland.
Electrical insights

The heart pumps blood using propagating waves of muscle contractions generated by electrical impulses travelling from the atria to the ventricles. The researchers based their work on studies showing that the heterogenous nature of cardiac tissue — which consists of muscle, blood vessels and fatty tissue — can affect the strength and direction of the current when an electric field is applied in the heart2,3.

The researchers induced arrhythmias in isolated pieces of dog atria and ventricles and used optical dyes to trace the electrical waves they generated. They then imaged the tissue's blood vessels and quantified how their structure changed the flow of current. By adjusting the intensity of the electric field they applied, they could affect the number of waves emitted at distinct places in the vasculature.

With the right conformation of virtual electrodes, a series of five small pulses progressively restored order to the electrical chaos caused by the arrhythmias. The technique also worked when in the atria of living dogs, in which the low-power charge was delivered with coiled wire electrodes.

Fenton says that the voltage the technique requires is at or below what researchers believe is the pain threshold for electric shocks, but he thinks it may be possible to further optimize the virtual electrodes to reduce the voltage even more.

Theoretically, however, there is a limit to how small the voltage can be, says Gray. Also, he says, no one knows whether the approach will work better or worse in a diseased heart, which may have a different geometry.

"The concepts and ideas are very exciting, but this cannot be directly translated into the clinic now," Gray says, adding that the researchers showed the technique worked in vivo in the atria, but only in vitro in the ventricles, where the need is greatest.

Fenton and Luther say that preliminary in vivo experiments in the ventricles showed positive results, and that they are conducting more extensive studies. Although there are still many things to tweak, says Luther, "we don't see any reason why this technique could not be translated to the clinic".

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References
1. Luther, S. et al. Nature 475, 235-239 (2011). | Article |
2. Fenton, F. H. et al. Circulation 120, 467-476 (2009). | Article | PubMed | ISI |
3. Sambelashvili, A. T., Nikolski, V. P. & Efimov, I. R. Am. J. Physiol. Heart Circ. Physiol. 286, H2183-H2194 (2004). | Article | PubMed | ISI | ChemPort |

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Actualidad Ultimas noticias - JANOes - Descubren una tecnica de desfibrilacion indolora - JANO.es - ELSEVIER: "CARDIOLOGÍA
Descubren una técnica de desfibrilación indolora

JANO.es · 14 Julio 2011 09:15


Un estudio publicado en 'Nature' presenta una alternativa a la descarga eléctrica de alta energía basada en una secuencia de pulsos débiles.

La fibrilación es un trastorno del ritmo cardíaco que hace que los impulsos se vuelvan caóticos y las contracciones se vuelvan arrítmicas.

Hasta ahora, para controlar la turbulencia eléctrica en el corazón se utilizaban impulsos eléctricos de alta energía, que pueden provocar efectos secundarios graves que incluyen daño en los tejidos y dolor traumático. Ahora, un nuevo estudio plantea un enfoque totalmente diferente.

“Una secuencia de pulsos eléctricos débiles perturba el sistema cerca de los núcleos de vórtices y, progresivamente, se sincroniza el tejido”, explica Stefan Luther, investigador del Instituto Max Planck de Alemania, que ha dirigido el trabajo junto a Flavio Fenton, de la Universidad de Cornell (Estados Unidos). La nueva técnica, probada en perros, es conocida como ‘estimulación de baja energía contra la fibrilación’ (LEAP, por sus siglas en inglés). Los resultados, publicados esta semana en la revista Nature, muestran que reduce la energía en un 84% en comparación con la desfibrilación estándar.

“Este método abre el camino para la solución indolora y no perjudicial de las arritmias cardíacas”, subraya Fenton. Los autores estiman que su método funciona mediante la estimulación de las heterogeneidades naturales, como los vasos sanguíneos y el tejido graso, para redistribuir la corriente alrededor del corazón y restaurar el ritmo sinusal normal.
La fibrilación es un trastorno del ritmo cardíaco en la que una de las cámaras del corazón desarrolla múltiples circuitos de reentrada y hace que los impulsos se vuelvan caóticos y las contracciones se vuelvan arrítmicas. La fibrilación puede afectar a los atrios -fibrilación atrial- o a los ventrículos -fibrilación ventricular-.

Nature (2011); doi:10.1038/nature10216
A kinder, gentler defibrillator : Nature News: "- Enviado mediante la barra Google"

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