Defibrillation threshold and cardiac responses using an external biphasic defibrillator with pediatric and adult adhesive patches in pediatric-sized piglets

Abstract

Before recommendations for using an automatic external defibrillator on pediatric patients can be made, a protocol for the energy of a biphasic waveform energy dosing needs to be determined that will allow ventricular defibrillation of 8 year olds while causing only a minimal amount of cardiac damage to infants. Pediatric- and adult-sized electrode patches were alternately applied to 10 isoflurane-anesthetized piglets weighing 3.8–20.1 kg to approximate the body weights of newborns to children <8 years old. The defibrillation threshold (DFT) was determined for biphasic truncated exponential waveform shocks. Additional shocks, varying from the DFT to 360 Joules (J), were delivered during sinus rhythm or following 30 s of ventricular fibrillation (VF). The DFT was 2.4±0.81 and 2.1±0.65 J/kg for pediatric and adult patches, respectively (P=N.S.). The change in left ventricular (LV) dP/dt from baseline as a function of shock strength was significantly different at 1 and 10 s after shocks of increasing energy that were delivered in sinus rhythm, and 1, 10, 20, and 30 s after defibrillation shocks. There was no significant difference in LV dP/dt with increasing shock energy at 60 s with either patch size. The time to return of sinus rhythm, ST-segment deviation, and cardiac output were also not significantly different from baseline 60 s following shocks of up to 360 J delivered during sinus rhythm or VF with either patch. The same amount of energy delivered with a biphasic external defibrillator successfully defibrillated VF whether adult or pediatric patches were used. Cardiac rhythm and hemodynamic variables were unaltered at 60 s after shocks delivered at energies of up to 360 J. These data suggest that there is a substantial safety margin above a DFT strength shock for this biphasic waveform in piglets.

Sumàrio

Antes de emitir recomendações para o uso de desfibrilhador automático externo em doentes pediátricos é necessário estabelecer um protocolo para o cálculo da energia em onda bifásica, que permita desfibrilhar crianças com 8 anos de idade e que cause o mı́nimo de dano cardı́aco em crianças mais pequenas. Aplicaram-se a 10 leitões anestesiados com isoflurano, pesando 3.8–20.1 Kg, de forma a aproximar ao peso corporal de recém-nascidos até crianças com <8 anos de idade, alternadamente adesı́vos de eléctrodos com tamanhos de adulto e pediátricos. O valor da energia da desfibrilhação (DFT) foi determinado para choques com ondas exponenciais bifásicas truncadas. Choques adicionais, variando desde a DFT até 360 Joules (J) foram aplicados durante ritmo sinusal ou após 30 s de fibrilhação ventricular (FV). A DFT foi de 2.4±0.81 e 2.1±0.65 J/kg para os adesı́vos pediátricos e de adulto, respectivamente (P=N.S.). A alteração no dP/dt ventricular esquerdo (LV) em relação à linha de base, em função da intensidade do choque foi significativamente diferente 1 e 10 s após choques de energia crescente que foram aplicados em ritmo sinusal; e 1, 10, 20 e 30 s após os choques de desfibrilhação. Não houve diferenças significativas no dP/dt do LV aos 60 s com aumentos crescentes da energia, com os dois tamanhos de adesı́vos. O tempo para retorno a ritmo sinusal, desvio do segmento S-T e débito cardı́aco não foram significativamente diferentes em relação à linha de base 60 s após os choques até 360 J aplicados durante ritmo sinusal ou FV, com qualquer dos adesı́vos. A mesma quantidade de energia aplicada com um desfibrilhador externo bifásico desfibrilhou com sucesso a FV, quer fossem utilizados adesı́vos de adulto ou pediátricos. O ritmo cardı́aco e variáveis hemodinâmicas mantiveram-se sem alteração, 60 s após choques aplicados com energias até 360 J. Estes dados sugerem que existe uma margem de segurança substâncial acima da potência de choque da DFT para ondas bifásicas em leitões.

Resumen

Antes de poder hacer una recomendación para usar un desfibrilador automático externo en pacientes pediátricos, debe determinarse un protocolo para dosificación de energı́a de ondas bifásicas que permita la desfibrilación ventricular en menores de 8 años al igual que desfibrilar causando un mı́nimo de daño en los infantes. Se aplicaron alternadamente electrodos de parche tamaño adulto y pediátrico a 10 cerdos jovenes, anestesiados con isofluorano, de 3.8–20.1 kg para aproximar el peso corporal a los recien nacidos hasta niños de <8 años. Se determinó el umbral para desfibrilación (DFT)para descargas con onda bifásica exponencial truncada. Se entregaron descargas adicionales, variando desde el DFT hasta 360 Joules (J), durante ritmo sinusal o después de 30 segundos de fibrilación ventricular (VF). El DFT fue de 2.4±0.81 y 2.1±0.65 J/kg para los parches pediátricos y adultos respectivamente (P=N.S.). Los cambios en el dP/dt del ventrı́culo izquierdo (LV) desde el nivel basal son función de la fuerza de la descarga fue significativamente diferente a 1 y 10 segundos después de las descargas de energı́a creciente que fueron entregadas en ritmo sinusal, y 1, 10, 20, y 30 segundos después de las descargas desfibriladoras. No hubo diferencia significativa en dP/dt del ventrı́culo izquierdo al aumentar la energı́a a los 60 s con ninguno de los tamaños de parche. El tiempo de retorno a circulación espontánea, la desviación del segmento ST, y el gasto cardı́aco también presentaron diferencias no significativas de la lı́nea de base 60 s depués de las descargas hasta de 360 J entregadas durante ritmo sinusal o VF con cualquiera de los parches. La misma cantidad de energı́a entregada con un desfibrilador automático externo desfibriló exitosamente FV habiendo usado parches de adulto o pediátrico. El ritmo cardı́aco y las variables hemodinámicas no estaban alteradas 60 s después de la entrega de descargas con energı́as de hasta 360 J. Estos datos sugieren que existe un margen de seguridad substancial por encima del nivel de fuerza del DFT Para esta forma de onda en cerditos.

Introduction

Biphasic truncated exponential waveforms require less energy than monophasic waveforms for internal defibrillation [1], [2]. Recently, biphasic waveforms have been incorporated into automatic external defibrillators (AEDs) with the advantage that these waveforms provide increased defibrillation efficacy at significantly lower energy levels and may produce less impairment of cardiovascular function compared to monophasic waveforms [3], [4], [5].

The American Heart Association supports the concept of a strong chain of survival with early defibrillation as the most important link [6]. Nonetheless, the use of AEDs is not recommended for infants or children <8 years of age [7]. One reason that current international guidelines do not recommend AED use in children <8 years old is that the appropriate energy dose for treatment of ventricular fibrillation (VF) and pulseless ventricular tachycardia has not been determined. However, data indicate that children with out-of-hospital ventricular arrhythmias have improved survival when treated by rapid response emergency medical systems [8], [9]. Before a pediatric biphasic AED can be designed, a dose strategy needs to be determined that will allow defibrillation of 8 year olds (∼25 kg) down to newborns (∼3.5 kg) [10] without causing persistent cardiac injury to the smallest patients.

Data from monophasic waveforms in anesthetized dogs suggest that the external defibrillation threshold (DFT) dose is approximately 1.5 J/kg [11]. Babbs et al. reported that it took 20 times more energy to produce detectable gross or histologic damage and 320 times more energy to kill a dog than it did to defibrillate [11]. Van Vleet et al. [12] reported a threefold margin of safety above the DFT before slight microscopic damage was detected in 1 of 5 dogs. The apparent safety margin between defibrillation and cardiac damage in animals suggests that there may be a dose strategy that will allow for defibrillation of larger children while not causing cardiac damage to infants.

The purposes of this study were to examine the ability of external biphasic shocks to defibrillate a range of animal sizes, and to determine the incidence of arrhythmias and hemodynamic changes in those same piglets using adult and pediatric defibrillation patches. The DFT was determined in animals of different sizes chosen to approximate the weights of newborns up to ∼8 year old children. The time to return of normal sinus rhythm and first perfusing beat, changes in cardiac output, changes in left ventricular (LV) dP/dt, and ST-segment changes were also determined over a range of shock energies following 30 s of VF. To help differentiate damage due to the shock from damage due to circulatory arrest secondary to VF, the same variables were measured following shocks delivered during normal sinus rhythm.