Implantable defibrillators currently on the market apply between 600 and 900 volts to the heart, almost 10 times the voltage from an electric outlet, says Ajit H. Janardhan, MD, PhD, a cardiac electrophysiology fellow at the Washington University’s School of Medicine.
After being shocked, he says, some patients get post-traumatic stress disorder. Patients may even go so far as to ask their physicians to remove the defibrillator, even though they understand that the device has saved their lives.
The huge shocks are not only unbearably painful, they damage the heart muscle and have been shown in many studies to be associated with increased mortality.
In an advance online edition of the Journal of American College of Cardiology, Janardhan and Igor Efimov, PhD, professor of biomedical engineering in the School of Engineering & Applied Science, report on a low-energy defibrillation scheme that significantly reduces the energy needed to re-establish a normal rhythm in the heart’s main chambers.
They hope this electrotherapy will be much less painful than shocks from existing implantable defibrillators, and may even fall beneath the threshold at which patients begin to perceive pain.
The team has just received a National Institutes of Health grant to develop a prototype low-energy defibrillator for humans and plan to begin clinical trials of the device shortly.
A cardiac rhythm monitor, a Band-Aid like patch worn on the chest for a day or two to help diagnose cardiac problems, has picked up five rapid contractions of the heart’s ventricles (light blue area at bottom). In this instance the heart spontaneously re-established a normal rhythm but ventricular tachycardia, as this condition is called, can lead to sudden cardiac death.
The lub-dub of the heartbeat begins with an electrical impulse generated by the sinoatrial node, a group of cells on the wall of the right atrium that is the heart’s natural pacemaker.
Spreading through conductive pathways in the heart, the electrical signal first causes the two upper chambers of the heart (the atria) to contract, and then, a split second later, the two lower chambers (the ventricles), coordinated motions that efficiently pump blood to the rest of the body.
The synchronized squeezing of a normal heartbeat is called sinus rhythm, after the node that triggers it.
The rhythm can go wrong in many different ways, but the real killer is ventricular tachycardia. Ventricular tachycardia is an abnormal heart rhythm that starts in the ventricles rather than from the sinoatrial node, and that causes the heart to beat at a rate too fast (tachy is Greek for rapid or fast) to efficiently pump blood to the rest of the body.
Moreover, the rapid heartbeat can degenerate precipitously into ventricular fibrillation, or the loss of all rhythm, says Efimov. During ventricular fibrillation the uncoordinated contraction of heart muscle prevents the heart from pumping blood at all, and without immediate intervention, death quickly follows.
Most people who develop ventricular tachycardia and ventricular fibrillation outside the hospital die, says Janardhan, but studies show that if we implant a defibrillator in patients with a weak heart that does not pump as strongly as it should, we can significantly reduce mortality.Restarting the rhythm
The second is ablation, or the deliberate creation of nonconductive scar tissue within the heart that blocks abnormal conductive patterns and redirects electrical activity to more normal pathways.
The major problem with ablation, says Efimov, is recurrence. It’s a temporary measure, not a cure. Patients typically need additional treatment within five years.
The third therapy is an implantable cardioverter defibrillator, or ICD. These devices are placed beneath the skin in the chest and monitor the rate and rhythm of the heart. If they detect ventricular tachycardia, they try to break the rhythm by pacing the heart at a rate faster than its intrinsic rate, a strategy anti-tachycardia pacing.
Anti-tachycardia pacing is very low energy, so low that patients may not even sense it. But it is relatively ineffective when the heart is beating 200 time per minute or faster. At these higher rates, the ICS zaps the heart with a strong electrical shock that resets it and, with luck, allows the pacemaker node to restart it with a normal rhythm.
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 in part because they pass through the chest wall muscle and sensory nerves.
The investigators found they could reduce peak shock voltages by an additional 50 percent if they applied shocks between the RV and coronary sinus (CS), a vessel that collects deoxygenated blood from the heart muscle, rather than through the chest wall. Less energy was required because the shocks were confined to the heart itself, and for the same reason they were also less painful.
In an earlier paper, Efimov’s student Wenwen Li, PhD, now at St. Jude Medical, had reported on a similar strategy for restoring the rhythm of the atria, the two upper chambers of the heart, for a less serious but more common rhythm abnormality.
The team has already developed the first low-energy atrial defibrillator, which will soon be entering clinical trials. They hope for similarly rapid progress with the ventricular defibrillator.
“We think this technology can and will be implemented soon,” says Janardhan. “There’s a lot of cardiac research that may pan out 20 or 30 years from now,” he says, “but as a physician I want something that can help my patients now.“
Hot cars can hit deadly temperatures in as little as one hour
24.05.2018 | Arizona State University
3D images of cancer cells in the body: Medical physicists from Halle present new method
16.05.2018 | Martin-Luther-Universität Halle-Wittenberg
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
24.05.2018 | Ecology, The Environment and Conservation
24.05.2018 | Medical Engineering
24.05.2018 | Physics and Astronomy