Some recipients have reported ICD shocks to restart their hearts being similar to that from an electric fence, while others have compared it to being kicked in the chest by a horse.
But the feel of low-energy antifibrillation pacing would be mild and barely noticeable, except for a sensation of a return to normal heart rhythm.
This could soon be a reality, thanks to findings from Kiwi researcher Dr Bryan Caldwell, now based at the University of Texas Medical Branch, and University of Auckland senior research fellow Dr Mark Trew.
While scientists have long assumed low-energy defibrillation would not be as effective because it could not penetrate the heart wall like a high-powered shock, Dr Caldwell and Dr Trew believe they have found such a solution.
Using 3D imaging techniques, they have identified "hot spots" throughout the heart which can be stimulated even by weaker shocks.
Next, they used computer models to tinker with how cells communicated electrically, and proposed new ways that the low-energy shocks could be felt more strongly by cells deep inside the heart.
Dr Caldwell told the Herald patients with ICDs felt apprehension about getting a painful shock, which affected their quality of life.
"That would be improved if the shock severity was considerably lowered, which is what our results offer the potential for."
Their findings will be laid out in a soon-to-be published study and could guide the development of a new generation of ICDs.
"The research may indeed lead to lower-energy defibrillators which is likely to increase longevity of the devices," Heart Foundation medical director Dr Gerry Devlin said.
"Some patients struggle to cope with devices firing a lot - these lower-energy devices may not be noticed as much when they fire."
The findings do not apply to emergency defibrillation.
Findings
• Scientists have long believed energy from implantable cardioverter-defibrillators (ICDs) had to be high to correct an irregular heartbeat, with a large shock required to pulse through the whole heart.
• But Kiwi researchers have revealed that excitable "hot spots" found throughout the heart, along with a fresh understanding of how heart tissue connects, can mean the entire heart can be stimulated by less intensive shocks.
• The research could pave the way for low-powered, energy-efficient ICDs, putting an end to high-voltage shocks some patients have likened to being kicked in the chest by a horse.
