The Quest for Painless, Device-Based Antiarrhythmic Therapy

A high-voltage electrical shock to the heart is highly effective in restoring a normal rhythm in a patient with either an atrial or ventricular tachyarrhythmia. The main limitation, however, is intense pain. The source of the pain is controversial, but is likely at least in part due to direct stimulation of nerves and skeletal muscle. There have been many efforts over the past several years to develop a nonpharmacological therapy for atrial and ventricular arrhythmias that does not cause pain. 

One of the most successful developments that falls in the category of painless device therapy is antitachycardia pacing (ATP). So much value has been placed on ATP for ventricular tachycardia (VT) that some physicians have not accepted cardiac implantable electrical devices (CIEDs), such as the totally subcutaneous defibrillator, which cannot offer ATP. In fact, one of the drivers behind efforts to develop an extravascular defibrillator using a lead placed under the sternum is so that it can deliver ATP. 

Another strategy to treat ventricular tachyarrhythmias without pain is a defibrillation system that uses a Faraday cage.¹ An example of a device based on the Faraday cage concept is one with a shocking coil on the inside of the heart and a sock-like multielectrode basket on the outside of the heart. Using this configuration, the energy of a shock is confined to the local ventricular myocardium in a way that achieves defibrillation without causing significant extracardiac stimulation or pain.

An infamous example of failure in the quest of a pain-free device is the standalone atrial defibrillator. The idea was to develop a permanently implantable device with an intravascular lead configuration that could be used to cardiovert a persistent episode of atrial fibrillation (AF) with a low-energy shock and be associated with minimal discomfort. Unfortunately, even though electrical cardioversion could be achieved with shock energies below 5 Joules, the pain associated with the shock was still too high to be accepted by most patients. 

In the continued quest for a painless defibrillation technique, a group from the Mayo Clinic recently described the development of a novel prototype device that has the potential to painlessly defibrillate AF using cryotherapy.² They developed a proof-of-concept system that used something referred to as the “Peltier effect” to cool cardiac tissue. Peltier thermoelectric elements use electrical energy delivered between the junctions of two materials to create a heat flux, so that one side gets cold and the other side gets hot. This results in a cold surface that can be placed on the epicardium, and a hot opposite surface away from the heart where the heat can dissipate. When the atrium was cooled in their experiments using this technique, the atrial capture thresholds rose, atrial conduction became delayed, and when epicardial temperature reached -0.5° C, AF stimulated with rapid pacing terminated to sinus rhythm. 

Cardiac defibrillation was first described in Switzerland in 1899 by two physiologists, who discovered that small shocks could induce ventricular fibrillation in dogs, and that larger shocks could defibrillate.³ Although an electrical countershock is a highly effective method to defibrillate the heart, it is quite painful and poorly tolerated by patients who are awake. Given that we strive to improve the quality of life in our patents with heart rhythm disorders, and given that living life without pain has almost become a human right, it is important to continue to develop novel, pain-free methods to defibrillate the atrium and ventricle. The work by Naksuk and colleagues to develop an electrical device that terminates AF by cooling the atrium represents progress.

References

1. Jayam V, Zviman M, Jayanti V, Roguin A, Halperin H, Berger RD. Internal defibrillation with minimal skeletal muscle activation: A new paradigm toward painless defibrillation. Heart Rhythm. 2005;2:1108-1113.
2. Naksuk N, Killu AM, Gaba P, et al. Effect of epicardial cooling Peltier elements on atrial conduction: a proof-of-concept study for a potentially painless method of atrial defibrillation. Heart Rhythm. 2016;13(11):2253-2258.
3. Prevost JL, Batelli F. Some Effects of Electric Discharge on the Hearts of Mammals. Comptes Rendus Academie des Sciences. 1899;129:1267-1268.