Model Reseach of Effects of Defibrillation Waveform on Action Potential Duration / 航天医学与医学工程

Objective To explore the mechanism underlying the superiority of the biphasic waveform to monophasic waveform in defibrillation.Method The Luo-Rudy model was adjusted so that it could be used to study defibrillation.Based on the adjusted model the effects of different defibrillation waveforms on cell action potential duration(APD) were studied.Result Biphasic electrical field pulse extended the APD longer than that with monophasic one.Moreover,biphasic waveforms with different strengths could prolong the APD almost equally,while monophasic pulses with different strengths showed different ability to prolong the APD and the spatial distribution of the APD became dispersed.It was also found that the strength of electrical fields pulse contributed much to the change of APD while the duration showed little effect.Conclusion The clinical superiority of biphasic pulses to monophasic pulses in defibrillation is resulted from its ability to prolong the time course of the APD and more importantly,it causes even spatial distribution of the APD.

Doble choque eléctrico secuencial transtorácico para la fibrilación auricular refractaria / Double sequential electrical transthoracic shocks for refractory atrial fibrillation

Antecedentes: Estudios clínicos han mostrado que el éxito de la cardioversión transtorácica en fibrilación auricular depende de alcanzar un flujo de corriente adecuado al corazón y que es dependiente de la impedancia transtorácica. Cuando múltiples cardioversiones convencionales fallan para restaurar el ritmo sinusal en pacientes con fibrilación auricular el doble choque secuencial transtorácico puede ser una alternativa. Métodos y resultados: 21 pacientes consecutivos con fibrilación auricular paroxística o persistente refractaria al menos a dos choques monofásicos con energía inicial alta 360 J ó 200-300 y 360 J recibieron choques secuenciales con 720 J mediante dos desfibriladores. Edad media 64 ± 11 años y peso medio 97 ± 19 kg (intervalos, 49 a 112). La evolución de la fibrilación auricular fue < 3 meses en el 76%. La hipertensión presente en 38% y ausencia de cardiopatía en 33%. El tamaño medio de la aurícula izquierda fue 4.5 ± 0.7 cm (intervalos, 3.5 a 6.0). El ritmo sinusal se alcanzó en 19 (90.4%), incluyendo 2 casos refractarios a choques bifásicos con una mediana de 1,050 J (intervalos, 660 a 1,440 J) sin complicaciones mayores. El análisis multivariable identificó a la duración de la fibrilación auricular, > 90 días (RR 0.98, IC 0.95-0.98 p = 0.02) y al peso corporal, 101 ± 11 kg (RR 0.64, IC 0.46-0.90 p = 0.01) como variables independientes asociadas con el fracaso de la cardioversión. El peso corporal, p = 0.002 fue el predictor univariable de cardioversión no exitosa. La cardioversión de alta energía no causa daño miocárdico evidenciado por estimación con troponina T. Conclusión: Para la fibrilación auricular refractaria a la cardioversión eléctrica convencional el doble choque secuencial transtorásico representa una alternativa segura y altamente eficaz y puede tener una aplicabilidad general.

Background: Clinical studies have shown that transthoracic cardioversión of atrial fibrillation is dependent on achieving adequate current flow to the heart, which is dependent on transthoracic impedance. When multiple standard cardioversión fails to restore sinus rhythm in patients with atrial fibrillation the double sequential transthoracic shock may be an alternative. Methods and results: Twenty one consecutive patients with paroxysmal or persistent atrial fibrillation refractory to at least two initial high energy 360 J or 200-300 and 360 J monophasic shocks underwent double sequential shocks with 720 J by means two defibrillators. Mean age was 64 ± 11 years and mean weight 97 ± 19 kg (range, 49 to 112). Duration of atrial fibrillation was present < 3 months in 76%. Arterial hypertension was present in 38% and lone atrial fibrillation in 33%. Mean left atrial size was 4.5 ± 0.7 cm (range, 3.5 to 6.0). Sinus rhythm was achieved in 19 (90.4%). Two refractory to biphasic shocks with a median 1,050 J (range, 660 to 1,440 J) without major complications. Multivariate analysis identified duration of atrial fibrillation, > 90 days (RR 0.96, Cl 0.95-0.98 p = 0.02) and body weight, 101 ± 11 kg (RR 0.64, Cl 0.46-0.90 p = 0.01) variables independently associated with cardioversión unsuccessful. Patient weight, p = 0.002 was the univariate predictor of unsuccessful cardioversión. High energy cardioversión does not cause cardiac damage evidenced from cardiac troponin T estimation. Conclusion: For refractory atrial fibrillation to conventional cardioversión double sequential transthoracic shocks represents a safe and highly efficacious alternative and may have a general applicability.

Application of Defibrillation Techniques in Cardiopulmonary Resuscitation / 医疗卫生装备

Objective To investigate the techniques of electrical defibrillation and their application to cardiopulmonary re-suscitation(CPR).Methods On the basis of reviewing the definition of electrical defibrillation,the main defibrillation tech-niques and their developments were introduced,as well as the selection of shock energy.The role that defibrillation played during CPR was defined according to the consensus.Results As an unfashionable technique,monophasic waveforms was inclined to be replaced by present biphasic waveform including biphasic truncated exponential(BTE) waveform and recti-linear biphasic waveform(RBW).The selected shock energy varied with the waveform that a defibrillator made use of,i.e.a monophasic defibrillator required a higher energy level as usual,whereas a biphasic one did not.It was deemed that biphasic technique presented an excellence in less damage to heart in addition to higher rate of successful defibrillation.In the critical care for sudden cardiac arrest with a shockable rhythm,the protocol of "1 shock + 5 cycles of CPR" should be recommended.Conclusion Electrical defibrillation techniques consist mainly of monophasic waveform and biphasic wave-form,between which the latter gains an advantage over the former.On the grounds of modern emergency medicine,defib-rillation has to be performed in combination with CPR.