Heart-Wave Findings Might Lead to Better Defibrillation

Originally Published MDDI February 2004

R&D DIGEST

Erik Swain

Scientists at Vanderbilt University (Nashville, TN) have made some discoveries about electrochemical waves in the heart that could lead to improved defibrillator designs or better ways to use such devices.

Fibrillation happens when contractions in the heart are caused by uncoordinated electrochemical waves. These waves stop the heart from pumping blood, which in turn causes death. The condition is stopped with a defibrillator, either an implanted one or a model with paddles. Defibrillation shocks stop the heart's waves and prevent new ones from occurring. 

Caregivers prefer to use as low voltage a shock as possible in order to minimize tissue damage and preserve the batteries of implantable devices. “However, if the voltage is too low, fibrillation returns immediately and you have to try again,” explains John Wikswo, one of the Vanderbilt researchers involved in the project. “The puzzle is why.”

The team is investigating the role of a little-studied slow electrochemical wave known as a damped wave (DW). “Damped propagating waves are generally not well understood, largely because they are difficult to view and study,” says Wikswo, who is director of the Vanderbilt Institute for Integrative Biosystems Research and Education. “It turns out that cardiac tissue provides a beautiful example of these waves.” 

The study, which for now is being done on rabbit hearts, is examining whether the damped waves are not fully extinguished by a low-voltage shock, or if new waves are created by the shock. Because damped waves are difficult to detect, they might be propagating slowly in the heart wall rather than dying out, unbeknownst to caregivers. In turn, that might cause a return to fibrillation or an onset of cardiac arrhythmia. 

The team has created a damped wave with a weak stimulus and sent it in the wake of a smooth-moving wave with a strong stimulus. Figure 1 provides a detailed analysis of damped wave propagation. “If you timed it just right, you could find that the second [damped] wave would hesitate and then split in two,” says Wikswo. “One half would get smaller and slowly die, while the other half would sharply increase and eventually become a self-containing wave on its own [and cause a defibrillation failure]. What surprised us is the ease with which we could create damped waves that hung around for 50 milliseconds, which is a long time when you are defibrillating the heart.” Findings were published in the November 14, 2003, issue of Physical Review Letters.

Future research will aim at determining whether the waves created in this experiment can also occur spontaneously after defibrillation. If so, that might lead to studies that show how to better manage these waves and how to improve the efficiency of cardiac defibrillators.

Wikswo's collaborators at Vanderbilt include Veniamin Sidorov, Rubin Aliev, Marcella Woods, Franz Baudenbacher, and Petra Baudenbacher.

Copyright ©2004 Medical Device & Diagnostic Industry