A novel low-energy electrotherapy that terminates ventricular tachycardia with lower energy than a biphasic shock when antitachycardia pacing fails

Abstract

Objectives: The authors sought to develop a low-energy electrotherapy that terminates ventricular tachycardia (VT) when antitachycardia pacing (ATP) fails.

Background: High-energy implantable cardioverter-defibrillator (ICD) shocks are associated with device failure, significant morbidity, and increased mortality. A low-energy alternative to ICD shocks is desirable.

Methods: Myocardial infarction was created in 25 dogs. Sustained, monomorphic VT was induced by programmed stimulation. Defibrillation electrodes were placed in the right ventricular apex, and coronary sinus and left ventricular epicardium. If ATP failed to terminate sustained VT, the defibrillation thresholds (DFTs) of standard versus experimental electrotherapies were measured.

Results: Sustained VT ranged from 276 to 438 beats/min (mean 339 beats/min). The right ventricular-coronary sinus shock vector had lower impedance than the right ventricular-left ventricular patch (54.4 ± 18.1 Ω versus 109.8 ± 16.9 Ω; p < 0.001). A single shock required between 0.3 ± 0.2 J to 5.9 ± 2.5 J (mean 2.64 ± 3.22 J; p = 0.008) to terminate VT, and varied depending upon the phase of the VT cycle in which it was delivered. By contrast, multiple shocks delivered within 1 VT cycle length were not phase dependent and achieved lower DFT compared with a single shock (0.13 ± 0.09 J for 3 shocks, 0.08 ± 0.04 J for 5 shocks, and 0.09 ± 0.07 J for 7 shocks; p < 0.001). Finally, a multistage electrotherapy (MSE) achieved significantly lower DFT compared with a single biphasic shock (0.03 ± 0.05 J versus 2.37 ± 1.20 J; respectively, p < 0.001). At a peak shock amplitude of 20 V, MSE achieved 91.3% of terminations versus 10.5% for a biphasic shock (p < 0.001).

Conclusions: MSE achieved a major reduction in DFT compared with a single biphasic shock for ATP-refractory monomorphic VT, and represents a novel electrotherapy to reduce high-energy ICD shocks.

Figure 1. Anatomic Position of Defibrillation Electrodes

Schematic of a canine heart with the locations of electrodes used for application of electrotherapies. Anteroposterior (left panel) and posteroanterior (right panel) views showing locations of the defibrillations leads (red lettering) and shock vectors (red arrows). Shocks were delivered from the RV defibrillation coil (RV) to the CS defibrillation coil (CS), or from the RV coil to epicardial LV defibrillation Patch (LVP). RA, right atrium; LA, left atrium; CS; coronary sinus; PT, pulmonary trunk; RV, right ventricle; LV, left ventricle.

Figure 2. Defibrillation Waveforms and Low Energy Electrotherapies

Schematic diagrams of the electrotherapies applied. Pulse widths of individual shocks were 10 ms. A: One (1MP), three (3MP), five (5MP) or seven (7MP) monophasic shocks delivered within one VT cycle length. B: A single biphasic shock (1BP) with pulse widths of 6 ms for the first (positive) phase and 4 ms for the second (negative) phase. C: Multi-Stage Electrotherapy (MSE). Stage 1 consisted of three monophasic shocks delivered in one VT cycle length, followed by a 100 ms delay. Stage 2 consisted of six lower voltage monophasic shocks delivered at a rate of 88 % of the VT CL, followed by a 100 ms delay. Stage 3 consisted of eight pacing stimuli each of 2 ms duration delivered from the endocardial RV lead (tip to ring) at a rate of 88 % of the VT CL. All shocks in MSE (stages 1 and 2) and all biphasic shocks were delivered from the RV coil to CS coil. MP, monophasic; BP, biphasic; CL, cycle length.

Figure 3. DFTs of Single and Multiple Monophasic Shock Electrotherapies

A: Surface ECG tracings during applications of single- and multiple- monophasic shock electrotherapies. An 80V (1.1 J) single monophasic shock (1MP) failed to terminate VT (top panel). In the same animal, 3 monophasic shocks (3MP; second panel), 5 monophasic shocks (5MP; third panel) and 7 monophasic shocks (7MP; lower panel) delivered within one VT cycle terminated VT successfully with 22V (0.24 J), 14V (0.16 J), and 13V (0.2 J), respectively. B: Mean DFTs (logarithmic scale) of 1MP, 3MP, 5MP, and 7MP with respect to peak voltage (left panel) and total energy (right panel) over N=6 dogs tested is shown. NS, not significant.

Figure 4. Sample Terminations and Mean Defibrillation Thresholds of a Single Biphasic Shock versus Multi-Stage Electrotherapy

A: Surface ECG and ventricular electrogram (VEG) of a termination of monomorphic VT by a single biphasic shock with peak leading edge voltage of 200 V (4.56 J). Arrows indicate the time of electrotherapy application. B: Surface ECG and VEG of a terminations of monomorphic VT by Multi-Stage Electrotherapy (MSE) with peak voltage of 20 V (0.22 J). C: Mean DFTs of a single biphasic shock (Single Biphasic) and MSE (Multi-Stage) are shown with respect to peak voltage (left panel) and total energy (right panel). 1BP, single biphasic shock; MSE, multi-stage electrotherapy; SR: sinus rhythm.