[The effect of ventricular fibrillation time and NYHA classification on defibrillation in intensive care unit patients].

OBJECTIVE: To investigate whether the sequence of defibrillation (DF) and cardiopulmonary resuscitation (CPR), duration of ventricular fibrillation (VF), and New York Heart Association (NYHA) classification would affect DF result in intensive care unit. METHODS: Ninety-three cases needing instantaneous DF were divided into three groups according to VF lasting time: <4 minute group (n=53), 4 - 8 minute group (n=24), >8 minute group (n=16), and each group was randomly divided into two sub-groups according to time sequence: the prior DF group or the prior CPR for five cycles followed by DF group (prior CPR group). The effect of VF time, the sequence of DF and CPR, and NYHA classification on success rate of DF were observed. RESULTS: With prolonging VF time, success rate of DF obviously lowered [success rate of DF for VF<4 minute, 4 - 8 minute, and >8 minute groups were 83.0% (44/53), 62.5% (15/24), and 25.0% (4/16), respectively, all P<0.01]. When VF time lasted less than 4 minutes, success rate of DF in the prior DF group was obviously higher than that in the prior CPR group [88.9% (24/27) vs. 76.9% (20/26), P<0.05]. When VF time lasted for 4 - 8 minutes, the prior DF group had slightly higher success rate of DF compared with the prior CPR group [66.7% (8/12) vs. 58.3% (7/12), P=0.09]. When VF time lasted longer than 8 minutes, the success rate of DF in the prior CPR group was obviously higher than that in the prior DF group [37.5% (3/8) vs. 12.5% (1/8), P<0.01]. The success rate of DF was lowered in higher NYHA classification [success rate of DF for NYHA classification I-IV was 96.4% (27/28), 80.0% (20/25), 47.8% (11/23), 29.4% (5/17), respectively, P<0.05 or P<0.01]. CONCLUSIONS: VF lasting time and NYHA classification are key factors to success rate of DF, and the choice of sequence of DF and CPR depends on the lasting time of VF. For cases with the high NYHA classification, we should make some judgement beforehand and prepare some preventive measures.

La desfibrilación temprana fuera del ámbito sanitario: marco legal / No disponible

En el tratamiento de la parada cardiaca, la desfibrilación temprana integrada en una cadena de socorro efectiva es la llave para la supervivencia. Por ello las organizaciones científicas internacionales han elaborado un conjunto de recomendaciones dirigidas a potenciar, con suficientes garantías de seguridad, la difusión de la desfibrilación semiautomática en la comunidad. Este artículo tiene como objetivo plasmar el resultado de una minuciosa revisión de la literatura científica sobre el desarrollo de la desfibrilación temprana, dando a conocer la señalización internacional de la presencia de un desfibrilador externo semiautomático, así como la evolución legal que regula la utilización de los desfibriladores semiautomáticos fuera del ámbito sanitario mediante el establecimiento de los requisitos mínimos de seguridad y calidad en su uso en todo el territorio, dando eficaz y amplia cobertura a las exigencias de utilización de estos aparatos en las situaciones de emergencia que requiere la desfibrilación temprana, favoreciendo su disponibilidad en el mayor número de lugares donde se concentre una gran afluencia de personas y fijando los contenidos esenciales de la formación de quienes estén habilitados para usarlos(AU)

In the treatment of the cardiac stop, the early desfibrilación integrated to an effective chain of help, is the key for the survival. for it the scientific international organizations have elaborated a set of recommendations directed to promoting, with sufficient guarantees of safety, the diffusion of the semiautomatic desfibrilación in the community. This article has as aim form the result of a meticulous review of the scientific literature on the development of the early defibrillation, announcing the international signposting of the presence of an external semiautomatic defibrillator, as well as the royal decree that regulates the utilization of the semiautomatic desfibriladores out of the sanitary area by means of the establishment of the minimal requirements of safety and quality in his use in the whole territory, giving effective and wide coverage to requirements of utilization of these devices in the emergency situations that the early defibrillation needs, favouring his availability in the major number of places where people great abundance centers and fixing the essential contents of the formation of those who are enabled to use them(AU)

Automated external defibrillators (AEDs).

Automated external defibrillators, or AEDs, will automatically analyze a patient's ECG and, if needed, deliver a defibrillating shock to the heart. The basic function of an AED is similar to that of a traditional defibrillator/monitor, but AEDs are much easier to use. As such, these devices can be used by a variety of medical and nonmedical personnel after only minimal training. The use of AEDs by nonmedical personnel (e.g., security guards, flight attendants) is often referred to as public access defibrillation, or PAD. In this Evaluation, we present our findings for eight newly evaluated models from five suppliers. We also summarize our findings for three previously evaluated models that are still on the market. We rate the models for first-responder use and for PAD use. Our ratings apply to the use of these devices both within the hospital and in the prehospital environment.

Willem Einthoven. Padre de la electrocardiografía / Willem Einthoven. Father of the electrocardiography

En 1908, Einthoven publica el más extenso y detallado artículo sobre el tema, "Concideraciones generales sobre el electrocardiograma", con 5 capítulos destinados a la electrocardiografía en la rana, el perro y el hombre, con una experiencia de más o menos 5000 ECG. Como todo hombre sábio, humilde y honesto, reconoció, en una de sus visitas a Londres, que el primer registro electrocardiográfico fue realizado por Augustus Desiré Waller, él mismo introdujo a la ciencia médica el término "ELECTROCARDIOGRAMA" y que el Dr. Thomas Lewis fue el primer médico que relacionó electrocadiograma con la clínica.

Effect of shock timing on defibrillation success.

The goal of this study was to determine whether delivering transvenous defibrillation shocks, coordinated with the up/down-slope VF waveform patterns in the shocking lead, would improve the probability of successful defibrillation. Anesthetized swine (32-38 kg, n = 8) were implanted with an RV-->SVC + SQArray transvenous system to measure VF waveform patterns and to deliver shocks. The shocks were generated by a Cardiac Pacemakers Inc. biphasic waveform generator. Energy required for 50% success probability (E50) was determined using the multishock up-down protocol. VF was repeatedly induced and defibrillation shocks at E50 were given after 10 seconds. The defibrillation outcome, delivered energy (Ed), peak voltage (V), peak current (I), system impedance (Z) and VF waveform pattern at the time of shock were recorded and measured. Out of a total of 685 shocks, 324 (47%) succeeded and 361 (53%) failed. The Ed, V, I, and Z were similar for the two defibrillation outcome groups (success or failure). VF patterns were classified as high or low amplitude at the time of the shock based on the peak-to-peak amplitude of signals recorded between the shocking electrodes. Shocks that coincided with high amplitude VF patterns were further divided into shocks that occurred on the up-slope or on the down-slope. The probability of success when the E50 shocks were coincident with high or low amplitude fibrillation did not differ significantly (Student's t-test: 46% vs 48%. P = NS). However, during high amplitude fibrillation, shocks delivered on the up-slope were significantly more successful than those delivered on the down-slope (Chi-square: 67% vs 39%; P < 0.001). These results suggest that delivering defibrillation shocks during the up-slope of the high amplitude signal in the shocking lead may improve the probability of successful defibrillation of ICDs.

Comparison of defibrillation efficacy using biphasic waveforms delivered from various capacitances/pulse widths.

The efficacy of the biphasic waveform shock for the defibrillation of the ventricular myocardium has been reported by researchers and physicians. Although many authors have suggested that biphasic waveforms delivered from lower capacitances and shorter pulse widths could result in the reduction of the energy required for successful defibrillation, no report has described the smallest capacitance and pulse width yielding the lowest DFT. In this study, we compared efficacies of the biphasic waveform shocks and DFT safety margins among five different capacitances (175 mu f, 125 mu f. 100 mu f. 75 mu f, and 50 mu f) combined with 1-3 pulse widths. These experiments performed in six dogs used an endocardial lead/subcutaneous patch defibrillation electrode system. The average DFTs at E50 for 175 mu f (6.5/3.5 ms), 125 mu f (6.5/3.5 ms), 100 mu f (6.0/3.0 ms), 75 mu f (4.0/2.0) ms, and 50 mu f (3.0/2.0 ms) were 8.5, 10.0, 11.0, 14.0, and 16.5), respectively. These results indicate that a biphasic waveform delivered from a larger capacitance with a proper pulse width could achieve a higher defibrillation efficacy. All DFTs at E50 for all waveforms were compared to their deliverable energies and maximum stored energies. This comparison indicated a narrow DFT safety margin with capacitances below 100 mu f. Therefore, it is concluded that higher energy and higher leading edge voltage are required for a biphasic waveform delivered from a smaller capacitance with a shorter pulse width. Since the current capacitor technology provides a maximum voltage of 750 V using two capacitors in series, with the electrode impedance system used in this study, smaller capacitors appear to have a decreased probability of defibrillation success at a given energy.

Temporary transvenous cardioversion and defibrillation: a new method for practical tachyarrhythmia management.

The use of transvenous ICD systems and the recent advances in atrial defibrillation techniques have heightened interest in internal defibrillation. However, most shocks for induced or spontaneous arrhythmias in patients without devices are still delivered transthoracically using high energy. We describe the history of temporary internal defibrillation techniques and report the initial clinical results with a custom built disposable catheter for internal cardioversion and defibrillation. This prototype successfully converted more than 95% of 109 episodes of VT or VF in 28 patients, with biphasic energies < or = 20 J. A newer disposable catheter, using 40-wire Matrix technology as the defibrillating electrode, has design features that provide high surface area, low impedance, and low current density when compared to other leads used for similar purposes. Temporary internal cardioversion-defibrillation of induced and spontaneous arrhythmias using such catheter designs is likely to be widely applicable to patients undergoing electrophysiology procedures and to those in critical care units prone to tachyarrhythmias.

Circadian modulation of ventricular tachycardia cycle length variability in ICD patients with dilated cardiomyopathy.

VT is usually characterized by stability of the RR intervals after a few cycles from the onset. The aim of this study was to evaluate the VT cycle length (VTCL) variability in patients with dilated cardiomyopathy (DCM), in whom a third-generation ICD was previously implanted. Eighty-three episodes of VT were analyzed in 10 patients (8 male, 2 female, 65 +/- 6 years) with DCM, and NYHA Class II (7 patients) or III (3 patients). As an index of VTCL variability, the coefficient of variance of the last 15 consecutive RR intervals (CVRR) of the detected and stored VT by the device was considered. The mean value of the RR intervals and the mean value of CVRR of the VT episodes recorded during day versus night time were compared. Fifty-five VT episodes were recorded during the day and 28 episodes during the night time. The mean RR intervals of VT episodes during day time was 335 +/- 29 ms and during the night time was 350 +/- 22 ms (P = NS). The mean CVRR of VT episodes during day time and night time were 2.83 +/- 0.52 and 3.36 +/- 0.48, respectively (P = 0.017). In conclusion, a circadian modulation of VTCL variability exists in patients with DCM. The VTCL variability is less during day time compared to night time. A possible explanation is a circadian alteration of sympathovagal balance modifying the electrophysiological properties of the arrhythmogenic substrate.

Threshold reduction with biphasic defibrillator waveforms. Role of charge balance.

Mechanism underlying improved defibrillation efficacy of biphasic waveforms at low shock intensities remain poorly understood. Recent studies suggest that biphasic waveforms produce a longer mean postshock response throughout the ventricle. This prolongs the cellular refractory period, blocks fibrillation wave fronts, and causes fibrillation to cease. Previous studies showed that hyperpolarizing monophasic waveforms, delivered during the refractory period, can shorten action potential duration (APD90), which would be deleterious for defibrillation. This study tested the hypothesis that a balanced-charge biphasic waveform produces a longer mean total mean APD than a comparable monophasic waveform by preventing this shortening in hyperpolarized regions as well as by prolonging APD in depolarized regions. To test this hypothesis, the authors examined transmembrane potential changes produced by hyperpolarizing and depolarizing monophasic and balanced-charge symmetrical biphasic waveforms using a computer model of the ventricular action potential. Shock intensities within the low-intensity "window," where biphasic waveforms defibrillate with higher efficacy than monophasic waveforms (1.5-3 times diastolic threshold), were used. Results show that biphasic S2 produced a significantly longer response both under hyperpolarizing and depolarizing conditions. The hyperpolarizing/depolarizing biphasic S2 produced a prolonged response with a well-defined plateau. Following the depolarizing/hyperpolarizing S2, APD90 did not shorten as with the hyperpolarizing monophasic S2. Rather, repolarization continued near the original S1 times course, but with slight prolongation of S1 APD90. These results suggest that biphasic waveforms enhance the prolonged refractory periods required for defibrillation throughout the heart, including regions exposed to both anodal and cathodal stimulation.

Effective defibrillation in pigs using interleaved and common phase sequential biphasic shocks.

Previous studies have shown that low internal defibrillation thresholds (DFTs) can be attained by using two pairs of electrodes and combining biphasic shocks with sequential timing. The purpose of this two-part study was to test the defibrillation efficacy of two new shock sequences, an interleaved biphasic, and a common phase sequential biphasic, that utilized two pairs of electrodes and were developed from the concept of sequential biphasic shocks. In the first part, defibrillation catheters were placed in the right ventricle and the superior vena cava of six anesthetized pigs. A small patch electrode was placed on the LV apex through a subxiphoid incision and a cutaneous patch was placed on the left thorax. The mean DFT energies for the interleaved biphasic (5.2 +/- 0.4 J) and the common phase sequential biphasic waveforms (5.4 +/- 0.4 J) were substantially less (P < 0.0001) than those for either the sequential monophasic (10.6 +/- 1.0 J) or single biphasic waveforms (9.0 +/- 1.0 J). In the second study, which used nine anesthetized pigs, the importance of phase reversal was demonstrated by the finding that the DFT energy of a common phase sequential biphasic shock (6.2 +/- 0.4 J) was much less than a common phase sequential monophasic shock (17.9 +/- 1.3 J, P < 0.0001); furthermore, the average DFT for four common phase sequential biphasic configurations (5.7 +/- 0.2 J) was much less than for a configuration that was similar except that current flow was not reversed in one phase so that no biphasic effect was present (19.7 +/- 1.2 J). The efficacy of common phase sequential biphasics was comparable to that of sequential biphasics. The effectiveness of sequential biphasics, interleaved biphasics, and common phase sequential biphasics is possibly due to two mechanisms: (A) an increase in the potential gradient during a later phase in regions that were low during the first phase, and (B) the exposure of most of the myocardium to a biphasic shock that reduces the minimum extracellular potential gradient needed to defibrillate.

Defibrillator/monitor/pacemakers.

Combined defibrillator/monitors enable the operator to assess and monitor the ECG and rapidly deliver a defibrillating countershock to patients suffering from ventricular fibrillation during a cardiac arrest. In addition, these units provide synchronized cardioversion for treating other arrhythmias, such as ventricular tachycardia, and most now offer external noninvasive pacemaker capability for treating patients with ventricular bradycardia or asystole. Defibrillator/monitors are critical resuscitation instruments and must perform effectively to avoid the otherwise preventable death of a cardiac arrest patient. However, both ECRI and the Food and Drug Administration (FDA) continue to receive a large number of problem reports on these devices each year. Device failures can occur for such reasons as operator error, depleted or defective batteries, or component failures. We evaluated eight units--three intended for crash-cart use and four intended for portable use, all with noninvasive pacemaker capability either standard or as an option, as well as one portable physiologic patient monitor to which a defibrillator (with or without a pacing option) can be attached--from six manufacturers.* We also evaluated one stand-alone noninvasive pacemaker. Although we did not include automated external defibrillators (AEDs) in our study, two of the evaluated units have options that allow them to function as AEDs. We rated the seven crash-cart and portable defibrillator/monitor/pacemakers according to three primary applications: (1) general crash-cart use, (2) prehospital (emergency medical service [EMS]) use, and (3) in-hospital transport. They are rated either Acceptable or Acceptable--Not Recommended for these applications, based primarily on technical performance (including battery operation, which is especially important in portable units), characteristics (such as line-powered operation and portability), features (such as automatic documentation), and human factors design (especially ease of use); some are inappropriate for specific uses because of their respective limitations in these applications. The portable physiologic patient monitor is not rated, but is discussed.** All of the pacemakers available as components of the evaluated units are acceptable for use; however, in most cases, purchasing decisions should be made according to defibrillator/monitor needs. The stand-alone pacemaker is rated Unacceptable because of its numerous performance, safety, and human factors disadvantages and because, other than its being a stand-alone unit, it offers no advantages over the other evaluated pacemakers; see "The Zoll NTP-1000 Stand-alone Noninvasive Pacemaker." Readers are cautioned not to base purchasing decisions on our ratings and rankings alone, but on a thorough understanding of the issues surrounding defibrillator/monitors and noninvasive pacemakers, which can be gained only by reading this study in its entirety.(ABSTRACT TRUNCATED AT 400 WORDS)