ISSN:
1572-8595
Keywords:
Ventricular fibrillation
;
defibrillation
;
cardiac preload
;
inferior vena cava occlusion
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract Little is known about the effects of cardiac preload and cardiacgeometry on defibrillation efficacy with endocardial electrodes. We studiednine pigs implanted with an endocardial lead system in the normal andreduced preload state. In the reduced preload state, a balloon catheter wasinflated in the inferior vena cava (IVC) for 20 seconds prior to theinduction of ventricular fibrillation (VF). Complete occlusion of the IVCand reductions in preload were confirmed by observing deformation of thecontrast-filled balloon, a reduction in cardiac size by fluoroscopy, andreductions in ventricular pressures. Biphasic shocks were delivered after 10seconds of VF using a recursive up–down protocol. VF was induced 20times for each preload state, and the 50% effective doses (ED50) forenergy, current, and voltage were estimated by averaging all shocks for thatstate. At reduced preloads, energy decreased from 12.1 ± 3.0 J(±SD) to 10.5 ± 2.9 J (p 〈 0.01), voltage decreased from415 ± 51 V to 390 ± 51 V (p 〈 0.05), and current decreasedfrom 8.6 ± 1.5 A to 7.6 ± 1.5 A (p 〈 0.01), while impedancerose from 49.2 ± 3.8 Ξ to 52.8 ± 4.4 Ξ (p 〈 0.001).We conclude that reducing cardiac preload and cardiac size significantlylowers ED50 defibrillation energy, current, and voltage. Thisoutcome may be caused directly by the decrease in blood volume as evidencedby increased impedance and/or may be due to changes in heart geometry andstretch.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1009794813423
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