Termination of sustained atrial flutter and fibrillation using low-voltage multiple-shock therapy.
BACKGROUND
Defibrillation therapy for atrial fibrillation (AF) and flutter (AFl) is limited by pain induced by high-energy shocks. Thus, lowering the defibrillation energy for AFl/AF is desirable.


OBJECTIVE
In this study we applied low-voltage multiple-shock defibrillation therapy in a rabbit model of atrial tachyarrhythmias comparing its efficacy to single shocks and antitachycardia pacing (ATP).


METHODS
Optical mapping was performed in Langendorff-perfused rabbit hearts (n = 18). Acetylcholine (7 ± 5 to 17 ± 16 μM) was administered to promote sustained AFl and AF, respectively. Single and multiple monophasic shocks were applied within 1 or 2 cycle lengths (CLs) of the arrhythmia.


RESULTS
We observed AFl (CL = 83 ± 15 ms, n = 17) and AF (CL = 50 ± 8 ms, n = 11). ATP had a success rate of 66.7% in the case of AFl, but no success with AF (n = 9). Low-voltage multiple shocks had 100% success for both arrhythmias. Multiple low-voltage shocks terminated AFl at 0.86 ± 0.73 V/cm (within 1 CL) and 0.28 ± 0.13 V/cm (within 2 CLs), as compared with single shocks at 2.12 ± 1.31 V/cm (P < .001) and AF at 3.46 ± 3 V/cm (within 1 CL), as compared with single shocks at 6.83 ± 3.12 V/cm (P =.06). No ventricular arrhythmias were induced. Optical mapping revealed that termination of AFl was achieved by a properly timed, local shock-induced wave that collides with the arrhythmia wavefront, whereas AF required the majority of atrial tissue to be excited and reset for termination.


CONCLUSIONS
Low-voltage multiple-shock therapy terminates AFl and AF with different mechanisms and thresholds based on spatiotemporal characteristics of the arrhythmias.
Ambrosi
Christina M
CM
Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.
Ripplinger
Crystal M
CM
Efimov
Igor R
IR
Fedorov
Vadim V
VV
D000818:Animals; D001281:Atrial Fibrillation / Q000628:therapy*; D001282:Atrial Flutter / Q000628:therapy*; D004554:Electric Countershock / Q000379:methods*; D004567:Electrodes, Implanted; D010147:Pain Measurement; D011817:Rabbits; D056969:Voltage-Sensitive Dye Imaging