Category Archives: Science

Science

Wednesday Article Review: Unpinning of a Rotating Wave in Cardiac Muscle by an Electric Field

For the past few weeks, I’ve made Wednesday “Article Review” day. I’ll still post reviews that I deem pertinent on other days, but the goal is to post one each Wednesday at a minimum.

The Hubmed page for today’s article is here: Unpinning of a Rotating Wave in Cardiac Muscle by an Electric Field by Alain Pumir and Valentin Krinsky

Tachycardia (fast heart beat) is commonly caused by a rotating wave of activation in the heart. The study of rotating waves of this type has years of legacy in theoretical and chemical dynamics studies. Today’s article covers rotating waves pinned to anatomical obstacles such as valve openings in the heart. Rotating waves circle a core, which can be functional (a property of the wave shape and dynamics) or anatomical (an obstacle). In the case of an anatomical obstacle, the wave can be eliminated by ablation, which is commonly used in the atria, electrical defibrillation, or possibly unpinning / antitachycardia pacing (ATP). Ablation is typically invasive, requiring catheterization, and defibrillation requires an external shock, or surgery to implant an ICD. Defibrillation, either externally or internally, damages the heart, is painful, and often causes loss of consciousness. Antitachycardia pacing and electrical unpininning open the possibility of elimination of tachycardia with small shocks.

The principle of electrical unpinning, proposed by Huyet et al. (1998) and Krinsky et al. (1995), is that when a localized stimulus is applied in a certain part of the wave tail, it may move the core of the rotating wave. It’s difficult to place a stimulus in a particular place at a particular time in a patient’s heart, but it turns out that when an electrical field is applied over an obstacle, areas of depolarization (positive change) and hyperpolarization (negative change) manifest on the borders of the obstacle.

The paper by Pumir and Krinsky details how a small electrical field may be applied at a specific timing relative to wave rotation in order to create such a depolarization on an obstacle that will unpin a wave attached to that same obstacle. They used simplified models of cardiac action potentials, including the Beeler-Reuter and Fitzhugh models. Since the method deals with the dynamics of a spiral wave, and not with particulars of ionic currents, it’s a safe bet that the methods will apply in more complex models and cardiac tissue.

I won’t repeat the article’s simple and logical explanation of how it works — go read it. It’s only 9 pages, the figures are clear, and the math is mercifully simplified in a way that (ostensibly) doesn’t undermine the results.

Biolicious Blog and Ion Channel Media Group

I came across this blog via one of my Technorati keyword watchlists. The parent site/company, Ion Channel Media Group, was a bit hard to figure out from just their website. According to the CEO, who was kind enough to reply to my inquiring email, the company does, “citation analysis to create alerts for researchers in specific life sciences fields. We use this information to produce a number of portals and then sell advertising, email marketing and PR campaigns.”

It’s curious, to be sure. Nonetheless, the blog looks pretty interesting, and the latest article covers something I was going to do a complete post on — the recent scandals over fraudulent scientific research. There are also some interesting stories on electrophysiology — automatic patch clamping and the like. It’s probably worth checking out if you follow electrophysiology, but I find the whole site/company/webring a bit strange.

Biolicious Blog

fresh research in biomedical science – from Ion Channel Media Group

Using Retinal Imaging to Screen for Systemic Diseases

Found via Slashdot, an article on how images of the retina can be used to screen for common diseases, including heart disease and hypertension:

LiveScience.com – Window to the Heart: New Eye Exam Spots Disease Risk

Tien Wong of the Center for Eye Research Australia at the University of Melbourne has shown in several large-scale studies that abnormalities of the blood vessels in the retina can be used to predict patients’ risk for diabetes, hypertension (or high blood pressure), stroke and heart disease.

As the article notes but doesn’t focus on, this could become a major aspect of diagnosis and triaging, since retinal photographs are cheap, fast, and easy to acquire.

Wasp zombifies cockroaches, then lays eggs on/in them

I’ve been trying to keep the blog more cardiac electrophysiology oriented lately, but I saw this on Slashdot, and I just had to link to it:

(Warning – contains pictures of wasps and cockroaches)

The Wisdom of Parasites. The Loom: A blog about life, past and future

As an adult, Ampulex compressa seems like your normal wasp, buzzing about and mating. But things get weird when it’s time for a female to lay an egg. She finds a cockroach to make her egg’s host, and proceeds to deliver two precise stings. The first she delivers to the roach’s mid-section, causing its front legs buckle. The brief paralysis caused by the first sting gives the wasp the luxury of time to deliver a more precise sting to the head. The wasp slips her stinger through the roach’s exoskeleton and directly into its brain. She apparently use ssensors along the sides of the stinger to guide it through the brain, a bit like a surgeon snaking his way to an appendix with a laparoscope. She continues to probe the roach’s brain until she reaches one particular spot that appears to control the escape reflex. She injects a second venom that influences these neurons in such a way that the escape reflex disappears. From the outside, the effect is surreal. The wasp does not paralyze the cockroach. In fact, the roach is able to lift up its front legs again and walk. But now it cannot move of its own accord. The wasp takes hold of one of the roach’s antennae and leads it–in the words of Israeli scientists who study Ampulex–like a dog on a leash. The zombie roach crawls where its master leads, which turns out to be the wasp’s burrow. The roach creeps obediently into the burrow and sits there quietly, while the wasp plugs up the burrow with pebbles. Now the wasp turns to the roach once more and lays an egg on its underside. The roach does not resist. The egg hatches, and the larva chews a hole in the side of the roach. In it goes. The larva grows inside the roach, devouring the organs of its host, for about eight days. It is then ready to weave itself a cocoon–which it makes within the roach as well. After four more weeks, the wasp grows to an adult. It breaks out of its cocoon, and out of the roach as well. Seeing a full-grown wasp crawl out of a roach suddenly makes those Alien movies look pretty derivative.

That is so very cool.