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.
Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.
Christina M
CM
Ambrosi
Crystal M
CM
Ripplinger
Igor R
IR
Efimov
Vadim V
VV
Fedorov
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