August 23, 2010

Pulsed Light Paces the Heart

Illustration of a red laser beam targeting the heart of an avian embryo A pulsed beam of infrared light can be used to pace the heartbeat of a 2-day-old quail embryo.Salma Shaikhouni, Case Western Reserve University.

Researchers found that pulses of laser light can control the heartbeat of an avian embryo and essentially serve as a noninvasive pacemaker. The new technique may aid the study of the developing heart and might also be explored as a tool for pacing the adult heart.

The heart is one of the first organs to appear in the developing embryo of most animals. The hearts of birds start beating just 40 hours after conception. But certain functions of the embryonic heart have been difficult to study. The electrical methods used to stimulate and study the rhythm of adults hearts are often too invasive and destructive to apply to the study of delicate embryonic hearts.

A research team led by Dr. Andrew Rollins at Case Western Reserve University decided to explore the potential of using noninvasive light-based (optical) techniques to study cardiac development in animal embryos. Previous studies by other groups had hinted at light's effects on heart rhythm. For instance, visible light quickens the heartbeat of a chick embryo, and pulses of laser light can trigger rhythmic contractions in small groups of heart muscle cells. But the new study, reported in the advanced online edition of Nature Photonics on August 15, 2010, is the first to show that laser light can modify the pace of an entire heart within the body.

In research supported in part by NIH's National Heart, Lung and Blood Institute (NHLBI) and National Institute of Neurological Disorders and Stroke (NINDS), the scientists used a micromanipulator to position a laser fiber close to—but not touching—the surface of an embryonic quail near its heart. In a series of experiments, the researchers delivered 1- to 2-millisecond-long pulses of infrared light to the hearts of 2- to 3-day old quail embryos. The heart rate, they found, became synchronized with the laser pulses, with each pulse triggering a heartbeat. As the researchers changed the rhythm of the pulses, the heart rate shifted to stay in sync.

The scientists also determined the lowest possible level of light energy that could successfully pace the heart. At this relatively low energy level, the cells showed no signs of damage from the pulsed laser light.

With this optical approach, scientists can noninvasively explore cardiac development and the factors that contribute to different types of birth defects, including congenital heart defects, the most common type of birth defect in humans.

"The mechanisms behind many congenital defects are not well known," says Dr. Michael Jenkins, first author of the study. "There is a suspicion that when the early embryonic heart beats slower or faster than normal, that changes gene regulation and changes development."

The team is also investigating how optical methods might affect the pacing of adult heart tissue. Although there are many obstacles to overcome, with further research optical pacing may have potential clinical applications as well.

—by Vicki Contie

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