Optimized first phase tilt in "parallel-series" biphasic waveform

The effects of second and third phase duration on defibrillation efficacy of triphasic rectangle waveforms

BACKGROUND

Biphasic waveforms are superior to monophasic waveforms for the termination of ventricular fibrillation (VF). However, whether triphasic waveforms are more effective than biphasic ones is still controversial. In the present study, we investigated the effects of second and third phase duration of triphasic rectangle waveform on defibrillation efficacy in a rabbit model of VF.

METHODS

VF was electrically induced and untreated for 30s in 20 New Zealand rabbits. A defibrillatory shock was applied with one of the 7 waveforms: 6 triphasic rectangle waveforms and a biphasic rectangle waveform. The triphasic waveforms had identical first duration but with different second and third phase durations. A 5 step up-and-down protocol was utilized for determining the defibrillation threshold (DFT). After a 5min interval, the procedure was repeated. A total of 35 cardiac arrest events and defibrillations were investigated for each animal.

RESULTS

Two triphasic waveforms with identical first and second phase duration but shorter third phase duration had significantly lower DFT energy than biphasic waveform (0.57±0.18J vs. 0.80±0.28J, p=0.001; 0.60±0.18J vs. 0.80±0.28J, p=0.003). However, no statistical difference in DFT energy was observed between the two triaphsic waveforms that had identical phase duration but different voltages (0.57±0.18J vs. 0.60±0.18J, p=0.638).

CONCLUSIONS

Phase durations played a main role on defibrillation success for triphasic rectangle waveforms. The optimal triphasic rectangle waveforms that composed of identical second and first phase durations but with shorter third pulse were superior to biphasic rectangle waveform for ventricular defibrillation.

Comparison of rectilinear biphasic waveform with biphasic truncated exponential waveform in a pediatric defibrillation model

OBJECTIVE

To compare the rectilinear biphasic waveform with a biphasic truncated exponential waveform for pediatric defibrillation.

DESIGN

Prospective, randomized study.

SETTING

Experimental laboratory of a university-affiliated research institute.

SUBJECTS

Male domestic piglets (4-24 kg).

INTERVENTIONS

Eleven piglets (4-8 kg), which represented a patient <1 yr old, and ten piglets (16-24 kg), which represented a pediatric patient between the ages of 2 and 8 yrs, were anesthetized, intubated, and mechanically ventilated. Ventricular fibrillation was induced and maintained for 30 secs, and a predetermined shock was then delivered to defibrillate. Following defibrillation, the animal was permitted to stabilize hemodynamically for 4 mins. Fifty shocks were applied to each animal using a randomization schedule based on a predetermined permutation of 50. The 50 shocks were 25 shocks for each rectilinear biphasic and biphasic truncated exponential waveforms, comprising five shocks at five energy settings. Each group of five shocks was fixed at a predetermined energy value, depending on the body weight of the animal. Dose-response curves were constructed using logistic regression. Aortic pressure, electrocardiogram, left ventricular pressure, and left ventricular pressure value of 40 mm Hg were continually measured.

MEASUREMENTS AND MAIN RESULTS

Dose-response curves determined defibrillation thresholds at 50% (D50) and 90% (D90) probability of success. The rectilinear biphasic waveform defibrillated with <90% of the D50 and D90 energies required for a biphasic truncated exponential waveform. The rectilinear biphasic waveform also successfully defibrillated with significantly less energy per body weight and per heart weight compared with a biphasic truncated exponential waveform.

CONCLUSIONS

The rectilinear biphasic waveform has superior defibrillation performance compared with a biphasic truncated exponential waveform in a piglet defibrillation model for young children.

Stepped defibrillation waveform is substantially more efficient than the 50/50% tilt biphasic

BACKGROUND

Even with biphasic waveforms, patients with high defibrillation thresholds (DFTs) still are seen; thus, improved defibrillation waveforms may be of clinical utility. The stepped waveform has three parts: the first portion is positive with two capacitors in parallel, the second is positive with the capacitors in series, and the last portion is negative, also with the capacitors in series.

OBJECTIVES

The purpose of this study was to assess the clinical utility of improved defibrillation waveforms.

METHODS

We measured the delivered energy DFT in 20 patients in a dual-site study using the stepped waveform and a 50/50% tilt biphasic truncated exponential as the control. All shocks were delivered using an arbitrary waveform defibrillator, which was programmed to mimic two 220-microF capacitors (110 microF in series and 440 microF in parallel).

RESULTS

The peak voltage at DFT was reduced in 19 of the 20 patients. The median peak voltage was reduced by 32.0%, from 472 V to 321 V (P <.001). The median energy DFT was reduced by 33%, from 11.7 J to 7.8 J (P = .008). The mean voltage and energy were reduced by 25.3% and 20.2%, respectively. On average, the stepped waveform was able to defibrillate as well as the 50/50% tilt biphasic, with 33% more energy. The benefit was more pronounced in patients with either a lower ejection fraction or a superior vena cava coil. The benefit of the stepped waveform had an inverse quadratic correlation with the resistance (r(2) = 0.47), suggesting that the capacitance values chosen for the stepped waveform were close to optimal for a 35-Omega resistance.

CONCLUSION

The stepped waveform reduced the DFT compared to the 50/50% tilt waveform in this preliminary study.

Multicenter study of principles-based waveforms for external defibrillation

STUDY OBJECTIVE

The efficacy of a shock waveform for external defibrillation depends on the waveform characteristics. Recently, design principles based on cardiac electrophysiology have been developed to determine optimal waveform characteristics. The objective of this clinical trial was to evaluate the efficacy of principles-based monophasic and biphasic waveforms for external defibrillation.

METHODS

A prospective, randomized, blinded, multicenter study of 118 patients undergoing electrophysiologic testing or receiving an implantable defibrillator was conducted. Ventricular fibrillation was induced, and defibrillation was attempted in each patient with a biphasic and a monophasic waveform. Patients were randomly placed into 2 groups: group 1 received shocks of escalating energy, and group 2 received only high-energy shocks.

RESULTS

The biphasic waveform achieved a first-shock success rate of 100% in group 1 (95% confidence interval [CI] 95.1% to 100%) and group 2 (95% CI 94.6% to 100%), with average delivered energies of 201+/-17 J and 295+/-28 J, respectively. The monophasic waveform demonstrated a 96.7% (95% CI 89.1% to 100%) first-shock success rate and average delivered energy of 215+/-12 J for group 1 and a 98.2% (95% CI 91.7% to 100%) first-shock success rate and average delivered energy of 352+/-13 J for group 2.

CONCLUSION

Using principles of electrophysiology, it is possible to design both biphasic and monophasic waveforms for external defibrillation that achieve a high first-shock efficacy.

New approach to biphasic waveforms for internal defibrillation: fully discharging capacitors

INTRODUCTION

The use of two independent, fully discharging capacitors for each phase of a biphasic defibrillation waveform may lead to the design of a simpler, smaller, internal defibrillator. The goal of this study was to determine the optimal combination of capacitor sizes for such a waveform.

METHODS AND RESULTS

Eight full-discharge (95/95% tilt), biphasic waveforms produced by several combinations of phase-1 capacitors (30, 60, and 90 microF) and phase-2 capacitors (1/3, 2/3, and 1.0 times the phase-1 capacitor) were tested and compared to a single-capacitor waveform (120 microF, 65/65% tilt) in a pig ventricular fibrillation model (n = 12, 23+/-2 kg). In the full-discharge waveforms, phase-2 peak voltage was equal to phase-1 peak voltage. Shocks were delivered between a right ventricular lead and a left pectoral can electrode. E50s and V50s were determined using a ten-step Bayesian process. Full-discharge waveforms with phase-2 capacitors of < or =40 microF had the same E50 (6.7+/-1.7 J to 7.3+/-3.9 J) as the single-capacitor truncated waveform (7.3+/-3.7 J), whereas waveforms with phase-2 capacitors of > or =60 microF had an extremely high E50 (14.5+/-10.8 J or greater, P < 0.05). Moreover, of the former set of energy-efficient waveforms, those with phase-1 capacitors of > or =60 microF additionally exhibited V50s that were equivalent to the V50 of the single-capacitor waveform (344+/-65 V to 407+/-50 V vs 339+/-83 V).

CONCLUSION

Defibrillation efficacy can be maintained in a full-discharge, two-capacitor waveform with the proper choice of capacitors.

Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators

OBJECTIVES

We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation.

BACKGROUND

Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown.

METHODS

In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock.

RESULTS

First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 +/- 1 vs. 33 +/- 7 A, p < 0.0001). Although the efficacy of the biphasic and monophasic waveforms was comparable in patients with an impedance < 70 ohms (100% [biphasic] vs. 95% [monophasic], p = NS), the biphasic waveform was significantly more effective in patients with an impedance > or = 70 ohms (99% [biphasic] vs. 86% [monophasic], p = 0.02).

CONCLUSIONS

This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.

Fully discharging phases. A new approach to biphasic waveforms for external defibrillation

BACKGROUND

Phase-2 voltage and maximum pulse width are dependent on phase-1 pulse characteristics in a single-capacitor biphasic waveform. The use of 2 separate output capacitors avoids these limitations and may allow waveforms with lower defibrillation thresholds. A previous report also suggested that the optimal tilt may be >70%. This study was designed to determine an optimal biphasic waveform by use of a combination of 2 separate and fully (95% tilt) discharging capacitors.

METHODS AND RESULTS

We performed 2 external defibrillation studies in a pig ventricular fibrillation model. In group 1, 9 waveforms from a combination of 3 phase-1 capacitor values (30, 60, and 120 microF) and 3 phase-2 capacitor values (0=monophasic, 1/3, and 1.0 times the phase-1 capacitor) were tested. Biphasic waveforms with phase-2 capacitors of 1/3 times that of phase 1 provided the highest defibrillation efficacy (stored energy and voltage) compared with corresponding monophasic and biphasic waveforms with the same capacitors in both phases except for waveforms with a 30-microF phase-1 capacitor. In group 2, 10 biphasic waveforms from a combination of 2 phase-1 capacitor values (30 and 60 microF) and 5 phase-2 capacitor values (10, 20, 30, 40, and 50 microF) were tested. In this range, phase-2 capacitor size was more critical for the 30-microF phase-1 than for the 60-microF phase-1 capacitor. The optimal combinations of fully discharging capacitors for defibrillation were 60/20 and 60/30 microF. Conclusions-Phase-2 capacitor size plays an important role in reducing defibrillation energy in biphasic waveforms when 2 separate and fully discharging capacitors are used.

Biventricular shocking leads improve defibrillation efficacy

INTRODUCTION

A single lead active can configuration has been widely used in patients with life-threatening ventricular arrhythmias. Occasionally, however, such a defibrillation lead configuration may not achieve adequate defibrillation threshold (DFT). The purpose of this study was to determine whether addition of a left ventricular (LV) lead can improve defibrillation efficacy.

METHODS AND RESULTS

Three transvenous defibrillation leads (8.3-French with a 5-cm long unipolar coil) were placed in the right ventricle (RV), LV, and superior vena cava (SVC), along with an active can (92 cm2) in the left subpectoral area. The DFT stored energy of seven combinations of these defibrillation leads were compared in a pig ventricular fibrillation model using a biphasic defibrillation waveform (125 microF, 6.5/3.5 msec). A biventricular leads active can configuration in which the RV and LV leads were of the same polarity reduced the DFT stored energy by approximately 35% when compared to a single RV lead active can configuration (9.6 +/- 3.0 J vs 15.0 +/- 7.2 J, respectively, P = 0.02). Moreover, adding a SVC lead further reduced the DFT energy (8.4 +/- 3.3 J).

CONCLUSION

A biventricular leads active can configuration can significantly improve defibrillation efficacy as compared to a single lead active can configuration. In such a defibrillation lead configuration, the polarity of RV and LV leads should be the same.

Optimal small-capacitor biphasic waveform for external defibrillation: influence of phase-1 tilt and phase-2 voltage

BACKGROUND

Biphasic waveforms have been reported to be more efficacious than monophasic waveforms for external defibrillation. This study examined the optimal phase-1 tilts and phase-2 leading-edge voltages with small capacitors (60 and 20 microF) for external defibrillation. We also assessed the ability of the "charge-burping" model to predict the optimal waveforms.

METHODS AND RESULTS

Two groups of studies were performed. In group 1, 9 biphasic waveforms from a combination of 3 phase-1 tilt values (30%, 50%, and 70%) and 3 phase-2 leading-edge voltage values (0.5, 1.0, and 1.5 times the phase-1 leading-edge voltage, V1) were tested. Phase-2 pulse width was held constant at 3 ms in all waveforms. Two separate 60- microF capacitors were used in each phase. The energy value that would produce a 50% likelihood of successful defibrillation (E50) decreased with increasing phase-1 tilt and increased with increasing phase-2 leading-edge voltage except for the 30% phase-1 tilt waveforms. In group 2, 9 waveforms were identical to the waveforms in group 1, except for a 20- microF capacitor for phase 2. E50 decreased with increasing phase-1 tilt. Phase-2 leading-edge voltage of 1.0 to 1.5 V1 appeared to minimize E50 for phase-1 tilt of 50% and 70% but worsened E50 for phase-1 tilt of 30%. There was a significant correlation between E50 and residual membrane voltage at the end of phase 2, as calculated by the charge-burping model in both groups (group 1, R2=0.47, P<0.001; group 2, R2=0.42, P<0.001).

CONCLUSIONS

The waveforms with 70% phase-1 tilt were more efficacious than those with 30% and 50%. The relationship of phase-2 leading-edge voltage to defibrillation efficacy depended on phase-2 capacitance. The charge-burping model predicted the optimal external biphasic waveform.