A novel electrotherapy
The scientists knew from earlier experiments that the voltage needed to shut down ventricular tachycardia depended on the timing of the shock. This led them to ask whether a sequence of multiple, closely timed low-voltage shocks might be more effective than a single high-voltage shock, and be less sensitive to timing.
Indeed it turned out that if they shocked the heart multiple times they could reduce the peak shock amplitude from well over 200 volts to 20 volts, timing no longer mattered, and the therapy worked even if the ventricular tachycardia was very rapid.
Although this electrotherapy involves multiple shocks, the total energy it delivers is still lower than that of a single large shock, roughly 80 times lower.
Why do multiple shocks work better? Arrhythmias generate electrical wave vortices little electrical tornadoes in the heart and it is these vortices, or re-entrant circuits, that make the heart beat too fast and prevent it from pumping properly.
But immediately after it contracts, heart muscle goes through a refractory, or unresponsive, period during which it does not respond to electrical stimulation. The multiple shocks may do a better job of extinguishing the re-entrant circuits by creating an area of unresponsive muscle into which the re-entrant wavefront the electrical tornado crashes, the scientists suggest.
Relocating the Electrodes
Defibrillators now on the market apply shocks between the right ventricle (RV) and an "active can" located above the chest wall, below the collarbone. The shocks are painful i
|Contact: Diana Lutz|
Washington University in St. Louis