Biphasic Truncated Exponential Waveform Research Articles

Automated external defibrillator electrode size and termination of ventricular fibrillation in out-of-hospital cardiac arrest

Smaller electrodes allow more options for design of automated external defibrillator (AED) user interfaces. However, previous studies employing monophasic-waveform defibrillators found that smaller electrode sizes have lower defibrillation shock success rates. We hypothesize that, for impedance-compensated, biphasic truncated exponential (BTE) shocks, smaller electrodes increase transthoracic impedance (TTI) but do not adversely affect defibrillation success rates. Methods and ResultsIn this prospective before-and-after clinical study, Amsterdam police and firefighters used AEDs with BTE waveforms: an AED with larger electrodes in 2016–2017 (113 cm2), and an AED with smaller electrodes in 2017–2020 (65 cm2). We analyzed 157 and 178 patient cases with an initial shockable rhythm where the larger and smaller electrodes were used, respectively. A single 200-J shock terminated ventricular fibrillation (VF) in 86% of patients treated with large electrodes and 89% of patients treated with smaller electrodes. Small electrodes had a non-inferior first shock defibrillation success rate compared to large electrodes, with a difference of 3% (95% CI: –3% −9%) with the lower confidence limit remaining above the defined non-inferiority threshold. TTI was significantly higher for the smaller electrodes (median: 100 Ω) compared to the larger electrodes (median: 88 Ω) (p < 0.001). ConclusionsFor AEDs with impedance-compensating BTE waveforms, TTI was higher for smaller electrodes than the large electrode electrodes. Overall defibrillation shock success for AEDs with smaller electrodes was non-inferior to the AEDs with larger electrodes.

Cardioversion of Atrial Fibrillation and Flutter: Comparative Study of Pulsed vs. Low Energy Biphasic Truncated Exponential Waveforms.

Despite the widespread use of biphasic waveforms for cardioversion and defibrillation, the efficacy and safety of shocks has only been compared in a few studies. This retrospective study aims at comparing the efficacy and safety of biphasic truncated exponential (BTE) pulsed energy (PE) waveform with a BTE low energy (LE) waveform for cardioversion of atrial fibrillation (AF) and atrial flutter (AFL). The treatment energies were following an escalating protocol for PE waveform (120-200-200J in AF and 30-120-200J in AFL) and LE waveform (100-200-200J in AF and 30-100-200J in AFL). The protocol was stopped at successful cardioversion (sinus rhythm at 1 minute post-shock), otherwise after the 3rd shock. If the 3rd BTE shock failed, a monophasic shock of 360J was delivered. From May 2008 to November 2017, 193 patients (153 PE, 40 LE) were included in the study. Both groups significantly differed in a few characteristics, including chest circumference (p<0.05). After adjustment, the success rate was not significantly different for the two waveforms (94.5% PE vs 92.5% LE, Odds Ratio [95% Confidence Interval] = 0.25 [0.03-2.2]).There was no difference in safety: post-shock changes in Hsc-TnI levels were similar (p=0.25). The efficient cumulative energy was particularly related with BSA (β = 131.5, p=0.05), AF/AFL duration (β = 0.24, p=0.01) and gender (β = 61.8, p=0.05). The major clinical implications of this study concern the high success rate of cardioversion with both biphasic pulses and no superiority of LE over PE waveform with an excellent safety profile without post-shock myocardial injuries.

Ascending Defibrillation Waveform Significantly Reduces Myocardial Morphological Damage and InjuryCurrent.

This study tested the hypothesis that a biphasic defibrillation waveform with an ascending first phase (ASC) causes less myocardial damage by pathology and injury current than a standard biphasic truncated exponential (BTE) waveform in a swine model. Although lifesaving, defibrillation shocks have significant iatrogenic effects that reduce their benefit for patient survival. An ASC waveform with an 8-ms linear ramp followed by an additional positive 0.5-ms decaying portion withamplitudes of 20J (ASC 20J) and 25J (ASC 25J) was used. The control was a 25-J BTE conventional waveform (BTE25J) RESULTS: The ASC 20J and ASC 25J shocks were both successful in 6 of 6 pigs, but the BTE 25J was successful in only 6of 14 pigs (p<0.05). Post-shock ST-segment elevation (injury current) in the right ventricular electrode was significantly greater with BTE 25J than with ASC 20J and ASC 25J. With a blinded pathology reading, hemorrhage, inflammation, thrombi, and necrosis 24h post-shock were significantly greater with BTE 25J than with ASC 20J and ASC 25J. Troponin levels were also markedly lower at 3, 4, 5, and 6h post-shock. Defibrillation shocks cause electrophysiological, histological, and biochemical signs of myocardial damage and necrosis. These signs of damage are markedly less for an ASC waveform than for a conventional BTEwaveform.

Average current is better than peak current as therapeutic dosage for biphasic waveforms in a ventricular fibrillation pig model of cardiac arrest

ObjectiveDefibrillation current has been shown to be a clinically more relevant dosing unit than energy. However, the effects of average and peak current in determining shock outcome are still undetermined. The aim of this study was to investigate the relationship between average current, peak current and defibrillation success when different biphasic waveforms were employed. MethodsVentricular fibrillation (VF) was electrically induced in 22 domestic male pigs. Animals were then randomized to receive defibrillation using one of two different biphasic waveforms. A grouped up-and-down defibrillation threshold-testing protocol was used to maintain the average success rate of 50% in the neighborhood. In 14 animals (Study A), defibrillations were accomplished with either biphasic truncated exponential (BTE) or rectilinear biphasic waveforms. In eight animals (Study B), shocks were delivered using two BTE waveforms that had identical peak current but different waveform durations. ResultsBoth average and peak currents were associated with defibrillation success when BTE and rectilinear waveforms were investigated. However, when pathway impedance was less than 90Ω for the BTE waveform, bivariate correlation coefficient was 0.36 (p=0.001) for the average current, but only 0.21 (p=0.06) for the peak current in Study A. In Study B, a high defibrillation success (67.9% vs. 38.8%, p<0.001) was observed when the waveform delivered more average current (14.9±2.1A vs. 13.5±1.7A, p<0.001) while keeping the peak current unchanged. ConclusionIn this porcine model of VF, average current was better than peak current to be an adequate parameter to describe the therapeutic dosage when biphasic defibrillation waveforms were used.The institutional protocol number: P0805.

GENERATION OF RECTANGULAR BIPHASIC WAVEFORM TO DECREASE DEFIBRILLATION THRESHOLD FOR EXTERNAL DEFIBRILLATOR

Studies have shown that defibrillation threshold for current amplitude of biphasic truncated exponential (BTE) waveform has a hyperbolic strength–duration relationship. Theoretical and experimental results have shown that decreasing the tilt of BTE waveforms decreases the defibrillation threshold. On the other hand, low peak current waveform reduces probability of myocardium damage and burn. Therefore, achieving a waveform with low tilt and low peak current is desired. All DC defibrillators use a capacitor to store and deliver required energy. Because of capacitor discharging nature, the tilt of waveforms is high. In rectilinear biphasic waveform (RBW), which was generated by ZOLL M-series defibrillator, the tilt of the first phase was decreased using an adjustable resistor connected in series with current path. But the defibrillator cannot keep the current constant in the second phase and in the both phases for high transthoracic impedances (TTI) either. In this paper, for solving these problems, a circuit that generates rectangular biphasic waveform is designed. In this circuit, five resistors are used and connected in series. Then an IGBT switch is connected to each resistor in parallel. Also, control of minimum current ripple is applied in order to decide which resistors should be worked in each time. The circuit is simulated in MATLAB/Simulink and a prototype model is constructed. Results demonstrate that the tilt of the waveform is notably reduced to a value less than 10%.

A comparison of rectilinear and truncated exponential biphasic waveforms in elective cardioversion of atrial fibrillation: A prospective randomized controlled trial

BackgroundSeveral different biphasic waveforms are used clinically, but few studies have compared their efficacy. The two main waveforms are the biphasic rectilinear (BR) and biphasic truncated exponential (BTE) waveforms, both of which have important differences, particularly at the extremes of transthoracic impedance. ObjectiveTo compare the efficacy of two commonly used defibrillation waveforms in the elective cardioversion of atrial fibrillation. MethodsIn a prospective randomized controlled study, sequential adult patients undergoing elective cardioversion for AF were recruited. Patients were randomized to receive synchronized defibrillation using either a BR or BTE waveform, both using a 50J, 100J, 150J, 200J, 200J selected energy escalating protocol. Failure to cardiovert after the fifth shock was classed as failed defibrillation. The power of this study was 80% with 5% significance level to detect a difference of 20% or greater between groups. Survival analysis was used to compare the total energy delivered to achieve successful cardioversion between groups. ResultsA total of 202 patients were recruited, of which data are complete for 199 (100 BR; 99 BTE). Median number of shocks to achieve cardioversion was 2 for the BR waveform and 3 for the BTE waveform (P=0.059). In the BR waveform group, 95/100 (95.0%) achieved sinus rhythm. In the BTE waveform group, 90/99 (90.9%) achieved sinus rhythm and this group required on average 117.1J more energy to achieve the outcome compared to the BR waveform group (P=0.838). ConclusionsBR and BTE waveforms show similar high efficacy in the elective cardioversion of atrial fibrillation.

Abstract 244: A Prospective Randomized Study of the Efficacy of Rectilinear and Truncated Exponential Biphasic Waveforms in the Elective Cardioversion of Atrial Fibrillation

INTRODUCTION: Several different biphasic waveforms are now available for clinical use. Few studies have compared differences in the efficacy of these waveforms. We compared biphasic rectilinear (BR) and biphasic truncated exponential (BTE) waveforms in their efficacy to cardiovert patients undergoing elective cardioversion for atrial fibrillation. METHODS: In a prospective randomised study, sequential adult patients undergoing elective cardioversion for atrial fibrillation were recruited. Patients were randomised to receive synchronised defibrillation using either a BR or BTE waveform, both using a 50J, 100J, 150J, 200J, 200J selected energy escalating protocol. Successful cardioversion was defined as a return to sinus rhythm immediately after a given shock. Failure to cardiovert after a second 200J shock was classed as failed defibrillation. The power of this study was 80% with 5% significance level to detect a difference of 20% or greater between groups. Survival analysis was used to assess the total energy delivered (and number of shocks) to achieve successful cardioversion between groups. RESULTS: A total of 202 patients were recruited over a four-year period, of which data was complete for 199 (100 BR waveform; 99 BTE waveform). There was no major difference in demographic data (Median age; BR 65.5 yrs, BTE 68.0 yrs: Median weight; BR 90.2 kg, BTE 88.9 kg; Median duration of AF; BR 7.0 months, BTE 6.0 months: Amiodarone; BT 23.8%, BTE 18.2%). Cardioversion rates and associated energy delivered are shown below. Median number of shocks to achieve cardioversion was 2 for the BR waveform and 3 for the BTE waveform (Log rank test, P=0.059). CONCLUSIONS: BR and BTE waveforms show similar efficacy in the elective cardioversion of atrial fibrillation.

Comparison between biphasic quasisinusoidal and truncated waveforms in a swine model of VF

Purpose of the study: To compare the effectiveness of biphasic quasisinusoidal (BQ – Gurvich – Venin) waveform (5 ± 1/6 ± 2 ms) and biphasic truncated exponential (BTE) waveform (4.5 ± 0.45/4.5 ± 0.45 ms) in the termination of VF. Materials and methods: This is a controlled experimental study on piglets (n = 14) weighing 25.2 ± 0.73 kg. After induced anesthesia, animals were placed in a supin position, and the trachea was intubated. After intubation, piglets were ventilated with volume – controlled ventilator. VF was induced by drug administration (adrenalin 4 mg and potassium 7.5% – 5 ml intravenously). Induced VF was shocked at 40 s after onset. Two groups were compared (1. BQ waveform by defibrillator DKI – N – 02; 2. BTE waveform by defibrillator DKI – N – 15Ct Biphasic, Metekol, Ukraine). Results: Impedans was no difference between the two groups (59.25 ± 3.7 Ohms vs 58.5 ± 4.5 Ohms). BTE waveform were more safety than BQ – injury threshold 16.7 ± 0.8 amps vs 12.24 ± 1.2 amps and energy injury threshold 50.9 J ± 1.5 vs 23.2 ± 1.6 J. ROSC was achieved in 100% in both groups. Defibrillation threshold was below in BTE waveform group (12.75 ± 1.4 amps vs 21.87 ± 0.8 amps), as and energy defibrillation threshold (22.5 ± 1.7 J vs 57.5 ± 1.3 J). Gurvich electrotherapeutical index1 (correlation between thresholds injury and defibrillation) for BTE waveform 1.30 ± 0.36 vs 0.56 ± 0.29 for BQ waveform. Conclusion: In a swine model VF BTE waveform were more effective and safety than BQ waveform.

Improved defibrillation efficacy with an ascending ramp waveform in humans

The purpose of this study was to compare an ascending ramp waveform (RAMP) with a standard, clinically available biphasic truncated exponential waveform (BTE) for defibrillation in humans. In animal studies, RAMP had a lower defibrillation threshold (DFT) than BTE. We studied 63 patients at implantable cardioverter-defibrillator placement using a dual-coil lead and left pectoral active can. The subjects were divided into two groups, one with a 12-ms ascending first phase and one with a 7-ms ascending first phase. Phase 2 of RAMP for both groups was a truncated exponential decay with 65% tilt and reversed polarity. The BTE had a 50% tilt in each phase. DFT and upper limit of vulnerability (ULV) were measured for both waveforms using a binary search protocol. The patient population was 77% male, with a mean age of 63 +/- 10 years and ejection fraction of 33 +/- 13%. Delivered energy at DFT was lower with the 7-ms RAMP vs BTE (5.4 +/- 2.6 J vs 6.5 +/- 3.4 J; P < .01) but unchanged with the 12-ms RAMP (7.4 +/- 4.5 J vs 7.1 +/- 4.9 J). Maximal voltage at DFT was significantly lower with either RAMP compared to BTE (P < .01). There was a strong correlation between ULV and DFT for both RAMP and BTE (P < .01). The 7-ms ascending ramp waveform significantly reduced delivered energy (18%) and voltage (24%) at DFT, whereas the 12-ms RAMP reduced only DFT voltage. This is the first report of a waveform that is superior to a BTE for defibrillation in humans. ULV correlates with DFT for RAMP, supporting the use of ULV testing for implantation of devices.

Prospective, randomized comparison of two biphasic waveforms for the efficacy and safety of transthoracic biphasic cardioversion of atrial fibrillation

The purpose of this study was to determine if there is a difference in commercially available biphasic waveforms. Although the superiority of biphasic over monophasic waveforms for external cardioversion of atrial fibrillation (AF) is established, the relative efficacy of available biphasic waveforms is less clear. We compared the effectiveness of a biphasic truncated exponential (BTE) waveform and a biphasic rectilinear (BR) waveform for external cardioversion of AF. Patients (N = 188) with AF were randomized to receive transthoracic BR shocks (50, 75, 100, 120, 150, 200 J) or BTE shocks (50, 70, 100, 125, 150, 200, 300, 360 J). Shock strength was escalated until success or maximum energy dose was achieved. If maximum shock strength failed, patients received the maximum shock of the opposite waveform. Analysis included 141 patients (71 BR, 70 BTE; mean age 66.5 +/- 13.7. Forty-seven randomized patients were excluded because of flutter on precardioversion ECG upon blinded review (n = 25), presence of intracardiac thrombus (n = 7), or protocol deviation (n = 15). Groups were similar with regard to clinical and echocardiographic characteristics. The success rate was similar for the two waveforms (93% BR vs 97 BTE, P = .44), although cumulative selected and delivered energy was less in the BTE group. Only AF duration was significantly different between successful and unsuccessful patients. No significant complications occurred. Biphasic waveforms were very effective in transthoracic cardioversion of AF, and complication rates were low. No significant difference in efficacy was observed between BR and BTE waveforms. Impedance was not an important determinant of success for either biphasic waveform.

Efficacy of lower-energy biphasic shocks for transthoracic defibrillation:: A follow-up clinical study

ObjectiveThis clinical study prospectively evaluated the first-shock defibrillation efficacy of 150-joule impedance-compensated, 200-μF biphasic truncated exponential (BTE) shocks in patients with electrically-induced ventricular fibrillation (VF), and compared it with a historical control group treated with 200-J monophasic damped sine (MDS) shocks. MethodsVentricular tachyarrhythmias were induced in patients undergoing electrophysiologic (EP) testing for ventricular arrhythmias or testing of an implantable cardioverter-defibrillator (ICD). A 150-J shock was delivered as the primary therapy to terminate induced arrhythmias in the EP group, and as a “rescue” shock when a single ICD shock failed to terminate the arrhythmias in the ICD group. ResultsNinety-six patients received study shocks. The preshock rhythm was classified as VF in 77 patients and as ventricular tachycardia (VT) in 19 patients. First-shock success rates for VF and VT were 75 out of 77 (97.4%) and 19 out of 19 (100%) for the 150-J BTE compared with the historical control rates of 61 out of 68 (89.7%) and 29 out of 31 (94%) for 200-J MDS. The first-shock success rate for VF treated with 150-J BTE was technically equivalent to that of 200-J MDS (p=0.001). The transthoracic impedance did not vary between groups, yet the peak current delivered by the 150-J BTE shock was about 50% lower. ConclusionsThis study demonstrated that 150-J shocks of this impedance-compensated, 200-μF BTE waveform provided very high efficacy for defibrillation of short duration, electrically-induced VF. These lower-energy biphasic shocks had a success rate equivalent to that of 200-J MDS shocks, and they provided this efficacy while exposing patients to much less current than the monophasic shocks.

A randomized trial comparing monophasic and biphasic waveform shocks for external cardioversion of atrial fibrillation

Background We compared efficacy of and pain felt after biphasic truncated exponential (BTE) and monophasic damped sine (MDS) shocks in patients undergoing external cardioversion of atrial fibrillation (AF). Methods Patients with AF were randomized to BTE or MDS waveform cardioversion. Successive shocks were delivered at 70, 100, 200, and 360 J until successful cardioversion, with one 360 J attempt of the alternate waveform when all 4 shocks failed. Success was determined by blinded over-read of electrocardiograms. Peak current was calculated from energy and impedance. Patients rated their pain at 1 and 24 hours after cardioversion. Results Fourteen of 37 (38%) patients treated with MDS and 34 of 35 (97%) treated with BTE shocks were cardioverted at ≤200 J ( P < .0001). Success rates of MDS versus BTE shocks were 5.4% versus 60% for 70 J, 19% versus 80% for ≤100 J, and 86% versus 97% for ≤360 J. BTE shocks cardioverted with less peak current (14.0 ± 4.3 vs 39.5 ± 11.2 A, P < .0001), less energy (97 ± 47 vs 278 ± 120 J, P < .0001), and less cumulative energy (146 ± 116 vs 546 ± 265 J, P < .0001). Patients felt less pain after BTE than MDS shocks at 1 hour ( P < .0001) and 24 hours ( P < .0001) after cardioversion. Conclusion This BTE waveform is superior to the MDS waveform for cardioversion of AF, requiring much less energy and current, and causing less postprocedural pain.

EFFICACY OF LOWER-ENERGY BIPHASIC SHOCKS FOR TRANSTHORACIC DEFIBRILLATION: A FOLLOW-UP CLINICAL STUDY

Objective. This clinical study prospectively evaluated the first-shock defibrillation efficacy of 150-joule impedance-compensated, 200-µF biphasic truncated exponential (BTE) shocks in patients with electrically-induced ventricular fibrillation (VF), and compared it with a historical control group treated with 200-J monophasic damped sine (MDS) shocks. Methods. Ventricular tachyarrhythmias were induced in patients undergoing electrophysiologic (EP) testing for ventricular arrhythmias or testing of an implantable cardioverter-defibrillator (ICD). A 150-J shock was delivered as the primary therapy to terminate induced arrhythmias in the EP group, and as a “rescue” shock when a single ICD shock failed to terminate the arrhythmias in the ICD group. Results. Ninety-six patients received study shocks. The preshock rhythm was classified as VF in 77 patients and as ventricular tachycardia (VT) in 19 patients. First-shock success rates for VF and VT were 75 out of 77 (97.4%) and 19 out of 19 (100%) for the 150-J BTE compared with the historical control rates of 61 out of 68 (89.7%) and 29 out of 31 (94%) for 200-J MDS. The first-shock success rate for VF treated with 150-J BTE was technically equivalent to that of 200-J MDS (p = 0.001). The transthoracic impedance did not vary between groups, yet the peak current delivered by the 150-J BTE shock was about 50% lower. Conclusions. This study demonstrated that 150-J shocks of this impedance-compensated, 200-µF BTE waveform provided very high efficacy for defibrillation of short duration, electrically-induced VF. These lower-energy biphasic shocks had a success rate equivalent to that of 200-J MDS shocks, and they provided this efficacy while exposing patients to much less current than the monophasic shocks.

P-068 Comparison of the efficacy of two transthoracic biphasic waveform defibrillators

Biphasic truncated exponential (BTE) wavefoms are generated by all modem implantable cardioverter defibrillators (ICDs), and are now being implemented in tmnsthoracic defibrillators. Not all BTE waveforms are the same; therefore we compared the efficacy of 2 commercial transthoracic defibrillators. A Physio-Control (PC) Lifepak 12 and a Medical Research Labs (MRL) PIC were compared in a canine model of both normal and higher impedance patients. Methods: Animals were anesthetized and adhesive defibrillating electrode pads were placed on the shaved left and right chest walls. Ventricular fibrillation (VF) was induced with 60 Hz current, and allowed to persist for 10 seconds. The ED50 peak current and energy were estimated with an up-down protocol, and logistic regression analysis. In group 1, canines (n=6, 61.6&5.5 Ibs) were tested without any added series resistance. In group 2, canines (n=6, 53.7&6.1 Ibs) were tested with a 32 ohm resistor added in series to simulate higher impedance patients. Results: Mean ED50 peak current and energy estimates are shown in the table below. MRL BTE mean peak current was lower than PC BTE in both groups (p < 0.001). The mean ED50 delivered energy for the MRL BTE and PC BTE were not different (p = ns). Mean impedance for group 1 was 55.3 ohms, and for group 2 (including added series resistance) was 94 ohms.

Defibrillation waveform and post-shock rhythm in out-of-hospital ventricular fibrillation cardiac arrest

The importance of the defibrillation waveform on the evolving post-shock cardiac rhythm is uncertain. The primary objective of this study was to evaluate cardiac rhythms following the first defibrillation shock, comparing biphasic truncated exponential (BTE), monophasic damped sinusoidal (MDS), and monophasic truncated exponential (MTE) waveforms in patients experiencing out-of-hospital ventricular fibrillation cardiac arrest (OHCA). We reviewed the automated external defibrillator (AED) and emergency medical services (EMS) records of 366 patients who suffered OHCA and were treated with defibrillation shocks by first-tier emergency responders between 1 January 1999 and 31 August 2002 in King County, Washington. The post first shock rhythms were determined at 5, 10, 20, 30, and 60 s and compared according to defibrillation waveform. The MDS and BTE waveforms were associated with significantly higher frequency of defibrillation than the MTE waveform, though only the BTE association persisted to 30 and 60 s. No difference in defibrillation rates was detected between MDS and BTE waveforms. By 60 s, an organized rhythm was present in a greater proportion for BTE (40.0%) compared with MDS (25.4%, P=0.01) or MTE (26.5%, P=0.07). In this retrospective cohort investigation, MDS and BTE waveforms had higher first shock defibrillation rates than the MTE waveform, while patients treated with the BTE waveform were more likely to develop an organized rhythm within 60 s of the initial shock. The results of this investigation, however, do not provide evidence that these surrogate advantages are important for improving survival. Additional investigation is needed to improve the understanding of the role of waveform and its potential interaction with other clinical factors in order to optimize survival in OHCA.

Comparison of the efficacy and safety of two biphasic defibrillator waveforms for the conversion of atrial fibrillation to sinus rhythm

The overall efficacy of transthoracic biphasic shocks delivered for conversion of atrial fibrillation (AF) has been demonstrated. We compared 2 different energy waveforms, either the biphasic rectilinear (BRL) waveform or the biphasic truncated exponential (BTE) waveform, in the conversion of AF to sinus rhythm. The relation between energy required for the conversion of AF, the type of biphasic waveform, and patient characteristics were examined. Serum levels of cardiac troponin I were measured before and after cardioversion, as well as postprocedural skin erythema and discomfort. In this prospective trial, 101 patients (mean age 61 ± 15 years, 72 men [71%]) referred for elective electrical cardioversion of AF were randomized to either a BTE or a BRL device. Shocks were delivered in a step-up fashion beginning with 50 J (then 100 J, 200 J, repeat 200 J, and then crossover to 360 J). One hundred patients were successfully converted to sinus rhythm (99% success rate). There was no difference in efficacy at any energy level used, regardless of the duration of the arrhythmia. In addition, there was no difference in cumulative success. Troponin I did not significantly increase after cardioversion, regardless of the total energy used. A positive correlation between skin erythema and skin discomfort after shock (24 to 48 hours) was seen with increasing cumulative energies. There was also a positive trend toward increasing energy requirements as chest circumference and body mass index increased. Thus, biphasic waveforms are safe and effective at converting AF to sinus rhythm. In this study population, there was no clinical difference between the BRL and the BTE waveforms.

Early out-of-hospital experience with an impedance-compensating low-energy biphasic waveform automatic external defibrillator.

Impedance-compensating low-energy biphasic truncated exponential (BTE) waveforms are effective in transthoracic defibrillation of short-duration ventricular fibrillation (VF). However, the BTE waveform has not been examined in out-of-hospital cardiac arrest (OHCA) with patients in prolonged VF often associated with myocardial ischemia. The objective of this study was to evaluate the BTE waveform automatic external defibrillator (AED) in the out-of-hospital setting with long-duration VF. AEDs incorporating a 150-J BTE waveform were placed in 12 police squad cars and 4 paramedic-staffed advanced life support ambulances. AEDs were applied to arrested patients by first-arriving personnel, whether police or paramedics. Data were obtained from PC Data Cards within the AED. Defibrillation was defined as at least transient termination of VF. Ten patients, 64 +/- 14 years, were treated for VF with BTE shocks. Another 8 patients were in nonshockable rhythms and the AEDs, appropriately, did not advise a shock. Five of the 10 VF arrests were witnessed with a 911 call-to-shock time of 6.6 +/- 1.7 minutes. VF detection and defibrillation occurred in all 10 patients. Spontaneous circulation was restored in 3 of 5 witnessed arrest patients and 1 survived to discharge home. Fifty-one VF episodes were converted with 62 shocks. Presenting VF amplitude and rate were 0.43 +/- 0.22 (0.13-0.86) mV and 232 +/- 62 (122-353) beats/min, respectively, and defibrillation was achieved with the first shock in 7 of 10 patients. Including transient conversions, defibrillation occurred in 42 of 51 VF episodes (82%) with one BTE shock. Shock impedance was 85 +/- 10 (39-138) ohms. Delivered energy and peak voltage were 152 +/- 2 J and 1754 +/- 4 V, respectively. The average number of shocks per VF episode was 1.2 +/- 0.5 (1-3). More than one shock was needed in only 9 episodes; none required > 3 shocks to defibrillate. Impedance-compensating low-energy BTE waveforms terminated VF in OHCA patients with a conversion rate exceeding that of higher energy monophasic waveforms. VF was terminated in all patients, including those with high impedance.