Heart like a wheel: a relatively simple model of electrical activity in the heart may help explain sudden coronary deaths

Article Abstract:

A bewildering array of electrical events must coincide precisely to produce a single heartbeat; the complexity of the contraction becomes even greater if one considers the events within damaged hearts. Yet a new theoretical insight may provide a basis for testing ideas about treatment for ailing hearts - ideas which may help some of the 500,000 Americans who die each year from heart disease. The theoretical insights stem from the work of Arthur Winfree, who, along with many others, has been interested in the mathematics behind chemical waves, best illustrated by the Belousov-Zhabotinsky reaction. Chemical waves and the propagation of electrical impulses in the heart have a few things in common. Being waves that propagate through an "excitable medium," they behave far differently from more familiar waves. Two pebbles thrown into a pond produce two sets of circular ripples. As the expanding circular ripples meet, they simply pass through each other and continue to expand. Two travelling chemical waves, on the other hand, simply cancel when colliding, and nothing is left behind to continue propagating. Two colliding waves of electrical excitation in a nerve or a piece of muscle simply cancel each other, and the excitation stops. A new mathematical description is necessary for this new type of wave, and that is what the researchers have provided. This mathematical description seems to provide surprising insights into the physiology of the heart. Most notable is the discovery that, mathematically at least, normal heart muscle may produce rotating spiral waves of excitation. In an intact heart, this would lead to tachycardia, rapid beating of the heart. Previously it had been thought that tachycardia required at least some damaged heart muscle be present. Tachycardia caused in this way will lead to fibrillation, where the quivering heart can no longer manage appropriately coordinated beats. Although the events leading to tachycardia and fibrillation in heart attack victims are not fully understood, experiments with sheep heart muscle have demonstrated that rotating spiral waves do occur at least under laboratory conditions. The theory provides testable ideas regarding such very practical questions such as how big pacemaker leads should be, and what is the optimal method for applying shocks for defibrillation. Mathematical models of the physiology of the healthy heart may directly lead to new insights into the care and treatment of ailing hearts. (Consumer Summary produced by Reliance Medical Information, Inc.)

Models, Physiological aspects, Ventricular fibrillation, Tachycardia, Electromagnetic radiation, editorial, Electric waves

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Making 3-D movies of the heart

Article Abstract:

A modification of magnetic resonance imaging (MRI) has allowed cardiologists to make three-dimensional movies of the beating heart. The procedure is non-invasive and sensitive enough to pick out small abnormalities in various regions of the heart. These movies also allow the study of the normal heart and the evaluation of therapies, such as clot-dissolving drugs and balloon angioplasty (balloons inserted into blocked arteries of the heart and then inflated to improve blood flow), and to diagnose the extent and location of damage after a heart attack. The procedure was devised by researchers at Johns Hopkins University from different fields of science, including radiology, cardiology engineering, and physics. (Consumer Summary produced by Reliance Medical Information, Inc.)

Research, Methods, Magnetic resonance imaging, Cardiology

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Throwing a switch on a nanoscale sieve

Article Abstract:

Researchers have developed an artificial membrane that acts as a molecular sieve with pores only 1.6 nanometers across, whose selectivity for negative or positive ions can be switched by changing its potential. The sieves could allow one-step separation of molecules by both size and charge.

Innovations, Microtubules, Molecular sieves

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