Biphasic WaveControl™ Technology
The Access CardioSystems
Biphasic WaveControl™ creates the best possible features
of defibrillation safety and effectiveness. The WaveControl™
provides a waveform based on clinically proven principles of
biphasic defibrillation and the established clinical
efficacy of these principles. It provides a limitation of
peak current in low impedance patients and offers escalating
energy with 200J on first shock and 360J for subsequent
Clinical Background on Biphasic
Waveform Safety and Effectiveness
studies using available biphasic waveforms have
demonstrated 99-100% first shock efficacy with an
average first phase current of about 15 amps in
patients with average impedances of 75 ohms [1, 3].
and animal studies have shown that higher biphasic
energy and higher corresponding average current (at
75 ohms, approximately 15 amps versus 12 amps)
results in greater first shock efficacy [1, 2].
waveforms in clinical use perform well in mid-range
impedances of 50-90 ohms. [1,3] In low impedance
patients, the goal is to control peak current and
avoid high peak currents . In high impedance
patients, the goal is to provide longer first phase
duration with lower tilt in order to hold average
current as high as possible. 
waveforms with a second phase to first phase charge
balance ratio in the range of 0.38 +/- 0.17 have
lower defibrillation threshold values. 
Animal Data Comparing Biphasic
Biphasic waveforms are used
extensively in human clinical applications. Access
CardioSystems has demonstrated the performance of its
Biphasic WaveControl™ in the animal laboratory. This trial
successfully compared the defibrillation thresholds of the
Access CardioSystems waveform to those of clinically used
biphasic waveforms. The Access CardioSystems waveform is not
compared in human clinical tests to damped sinewave
waveforms, but Access CardioSystems defibrillation
thresholds have been compared to damped sinewave
defibrillation thresholds in animal tests.
Rationale for Animal
have been extensively studied over many years. Monophasic
waveforms, initially studied in animals, have now been used
very successfully in humans for more than 25 years.
Approximately 20 years ago, biphasic waveforms were
developed. Animal studies compared biphasic waveforms to
monophasic waveforms and demonstrated that biphasic
waveforms are significantly better than monophasic
waveforms. Initial animal studies were replicated in humans
and demonstrated that animal data can be used to predict
The justification for using animal
data for waveform validations, rather than human clinical
studies allow more shocks per study subject and,
thus, enable the collection of larger samples of
data. This provides better comparison of waveforms.
studies avoid putting humans at the unnecessary risk
from additional episodes of ventricular fibrillation
and additional defibrillation shocks.
mechanism of defibrillation in animals is the same
as that in humans.
Conclusion from Animal Data:
Defibrillation threshold data
suggests that the Access CardioSystems waveform is at least
as effective as the tested and clinically used waveforms.
Access CardioSystems WaveControl™
first shock with higher average current for greater
defibrillation efficacy margin
escalating energy with controlled waveform shape
peak current for better safety margin in low
pulse duration with low tilt in high impedance
optimal phase 2 to phase 1 charge balance
Specific Waveform Characteristics
Optimal Average Current
Shock Comparison at 75 Ohms
The Access CardioSystems waveform delivers 200J
first shock energy and, for a patient with impedance
of 75 ohms, a first shock average current of about
17 amps. For the 75 ohm patient, the Access
CardioSystems waveform delivers additional average
current and additional defibrillation efficacy
margin compared to other biphasic waveforms in
clinical use [6, 7].
Shock Escalating Energy
Access CardioSystems has designed a 360J second
shock selection to deliver higher average current,
while maintaining nearly identical shape to its 200J
first shock waveform.
Access CardioSystems waveform also ensures patient
safety by limiting the delivered peak current to
less than 30 amps.
restriction on peak current limits the potential for
myocardial damage and post-shock dysfunction,
providing a better margin for safety. There is very
little clinical data published on patients with 25
of first phase duration from 7.5 msec to 8.5 msec in
higher impedances delivers greater charge and
Charge Balance of Second Phase
versus First Phase
CardioSystems WaveControl™ maintains a charge
ratio demonstrated to yield a lower defibrillation
CardioSystems maintains a similar waveform shape for
all patient impedances by controlling the waveform
tilt, limiting the peak current and extending first
phase duration with increased patient impedance.
patient with higher impedance of 100 ohms or
greater, the Access CardioSystems waveform shape has
an extended first phase, low tilt, and more first
shock current than other biphasic waveforms in
current clinical use. [6,7]
Access CardioSystems WaveControl™
Technology 360 Joule Selection:
Waveform Validation Study
The Access CardioSystems biphasic waveform was tested in the
animal laboratory. Defibrillation threshold currents (DFTs)
were measured for three biphasic waveforms, including two
waveforms in current clinical human use. A total of 292 DFTs,
nearly 100 for each waveform, were measured in random order.
A swine model was used in a
protocol approved by the Institutional Animal Care and Use
Committee. The pigs used weighed between 38.0 and 47.0
kilograms (mean weight 43.64 kg). Monitoring was provided
for ECG, temperature and pulse oximetry. A catheter was
inserted in the right ventricle via the jugular vein for
induction of ventricular fibrillation and for pacing if
Induction of fibrillation was
accomplished by delivering a 50 hertz, 2 msec wide pulse for
a period of 3 seconds. The ECG was monitored to confirm the
presence of fibrillation. Fibrillation was sustained for a
period of 10 seconds from the initiation of the induction
pulses to the first shock. The maximum duration of
fibrillation was limited to 30 seconds by providing a rescue
shock if required. Defibrillation was delivered by a series
of three increasing shock strengths and a rescue shock if
required. A resting period of 2 minutes was provided if the
first shock was successful, and a period of 3 minutes was
provided if 2 or more shocks were required.
The animal threshold was
determined by using a modified Bourland protocol. This
protocol determined the 50% probability for successful
defibrillation. A pair of defibrillation shocks were
obtained with current levels within 10% of each other, and
where one shock was successful and the other was
unsuccessful in converting defibrillation into a normal
The sequence used to determine a
threshold was to induce fibrillation and deliver a first
shock. If the shock fails to convert the fibrillation, a
second shock was delivered with a 10% increase in the
current level. If a third shock was required, the current
level was increased by 20%. If a fourth shock was needed, a
biphasic rescue shock using full energy was delivered. The
threshold was determined by using only the first two shocks
of a rescue sequence. The third shock was only used to
estimate the starting level of the next shock sequence.
The summary of rules for
calculating a threshold were:
conversion of fibrillation to a normal rhythm. Note
that pacing was permitted for post-shock
data included only the first or second shock in a
defibrillation thresholds were based on a current
level within 10% of a failed shock.
Defibrillation waveform data was
collected and stored using a digital storage oscilloscope.
The stored data includes the waveforms for delivered current
and voltage. This data allowed calculation of thoracic
impedance and delivered energy. Additional data was
collected and manually recorded after each resuscitation
sequence. This data included: shock sequence number, time,
peak voltage, peak current, calculated impedance,
defibrillation success or failure, annotation of a
defibrillation threshold, and comments. The comments
included changes in ventilation, anesthesia, ST segment
elevations, or defibrillation pad skin observations.
Animal Data Findings:
Current Threshold (amps)
Phase Duration (msec)
|W1 (100 µF)
|W2 (100 µF)
Access CardioSystems waveform has statistically
lower average current and similar energy delivered
at 50% probability threshold compared to waveform
W2, the first clinically used waveform that was
tested in this study.
Access CardioSystems waveform has the same average
current, energy, and duration at 50% probability
threshold as the second clinically used waveform.
threshold data suggests that the Access
CardioSystems waveform is at least as effective as
the tested and clinically used waveforms.
The Access WaveControl Biphasic
Waveform was validated in a prospective multi-center study
in the United States and Europe. In this study, sixty (60)
patients undergoing ICD implant or testing had ventricular
fibrillation induced. All 60 patients (100%) were
successfully defibrillated on the first administered shock
at the lowest energy setting (200J). The waveform maintained
efficacy at the highest impedances (> 90 ohms). Peak
current did not exceed 35 amps, including those patients
with the lowest impedances (< 50 ohms). By comparison,
monophasic waveforms, a standard benchmark, yield first
shock efficacy of 86%8. No ECG or skin changes were observed
at the time of patient discharge in the current study. This
study confirmed the safety and high first shock efficacy of
the Access WaveControl Biphasic Waveform in ventricular
S.L., et al., A comparison of biphasic and
monophasic shocks for external defibrillation.
Prehosp Emerg Care, 2000. 4(4): p. 305-13.
R.G., et al., Comparison of Clinically Used Biphasic
Waveforms for External Defibrillation. Acad Emerg
Med, 2001. 8(5): p. 432-433.
S., et al., Comparison of a novel rectilinear
biphasic waveform with a damped sine wave monophasic
waveform for transthoracic ventricular
defibrillation. J Am Coll Cardiol, 1999. 34(5): p.
WA. Defibrillation of the Heart. St. Louis, MO.
Mosby YearBook. 1994. pgs. 288-291.
L.A. and W. Havel, Evolution of the optimum
bidirectional (+/- biphasic) wave for
defibrillation. Biomed Instrum Technol, 2000. 34(1):
data. Access CardioSystems. 2001.
B.E., et al., Treatment of out-of-hospital cardiac
arrest with a low-energy impedance- compensating
biphasic waveform automatic external defibrillator.
The LIFE Investigators. Biomed Instrum Technol,
1998. 32(6): p. 631-44.
et al., Multicenter comparison of truncated biphasic
shocks and standard damped sine wave monophasic
shocks for transthoracic ventricular defibrillation.
Transthoracic Investigators. Circulation, 1996.
94(10): p. 2507-14.
||Biphasic WaveControl™ Technology
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