A Delogu

E Mattei

F Aguel

F Censi

G Calcagnini

J Stohlman

M Triventi

P Bartolini

V Krauthamer

CiteSeerX

In-Vitro Investigation of Very Long 
Defibrillation Shocks: Design and 
Testing of a Capacitor-Free 
Defibrillator 
 
M Triventi
1
, E Mattei
1,3
, A Delogu
1
, F Censi
1
, G Calcagnini
1
,  
P Bartolini
1
, F Aguel
2
, J Stohlman
2
, V Krauthamer
2
 
 
1
Italian Institute of Health, Rome, Italy 
2
Center for Device and Radiological Health, FDA, Silver Spring, MD, USA 
3
"La Sapienza" University of Rome, Rome, Italy 
Abstract 
The aim of this paper is to describe a defibrillator that 
allows the delivery of arbitrary waveform shocks, with 
energy up to 10J and duration up to 100ms. In addition, 
data from shocks delivered to isolated rabbit’s hearts are 
presented. The solutions adopted in the design and 
realization of the defibrillator were: rechargeable battery 
power; linear AB class power amplifier output in bridge 
configuration; optical isolation of analog and digital 
lines to and from the PC and earth ground; measure of 
the actual voltage, current and energy delivered to the 
load. Laboratory testing showed that the defibrillator is 
capable to deliver shocks with a rising time less than 150 
us, no tilting also for very long waveforms (100ms), peak 
current  up to 10 A. The system was then used on rabbit 
hearts to define a protocol to investigate the effect of 
waveform duration on defibrillation threshold. We 
demonstrate the feasibility of an experimental 
defibrillator for the generation and delivery of true 
arbitrary waveforms. 
 
1. Introduction 
Research to understand and improve defibrillation 
waveforms has, so far, suffered from the intrinsic  
limitation of the capacitor discharge approach. The use of 
biphasic waveforms has allowed for the reduction of the 
defibrillation threshold and thus has gained popularity 
[1][2]. For practical reasons, most of the defibrillation 
studies are conducted using relatively short falling 
exponential voltage waveforms. Both monophasic and 
biphasic waveforms, when delivered by capacitor 
discharge have a load-dependent exponential decay 
which allows for few changes in the basic morphologies. 
The major advantage in the capacitor-discharge approach 
is that it relies in the high voltage / high current which are 
easily obtainable with such a design. In addition, data on 
the current and voltage characteristics during the shock 
are scarce. In-vitro research, however requires relatively 
lower energies and thus a greater flexibility in the 
defibrillator design. A research defibrillator capable of 
delivering arbitrary waveforms is useful to compare the 
performance of standard vs experimental waveforms [3], 
as well as to understand the basic mechanisms involved 
in the defibrillation. Researches to improve cardioverter-
defibrillator waveforms and to investigate the 
mechanisms underlying electrical cardioversion / 
defibrillation are carried out in several laboratories 
[1][2][4-6], because reduction in the energy for 
successful defibrillation potentially leads to less damage 
to cardiac tissue, less discomfort for the patient and to 
smaller and cheaper devices. We present a new 
defibrillator design based on linear power amplifiers, 
which can generate arbitrary waveforms up to 10 J on 
loads up to 25 ohms.  
2. Methods 
In order to be used in in-vitro electrophysiological 
investigations we set the following design goals for the 
defibrillator: arbitrary waveforms floating output from 
DC to 100KHz, PC controlled, isolation from ground, 
output energy up to 10 J, and pulse duration from 6 to 
100 msec, through a load of 10 ohm impedance. Given 
these parameters we designed the various components of 
the defibrillator. Figure 1 shows the main blocks, which 
are discussed in details below.   
 
Power Supply 
In order to obtain an isolated power supply we used a 
series of rechargeable sealed lead-acid batteries. A 
limitation of lead-acid batteries is the maximum rated 
battery power. We overcame this problem with the use of 
lead-acid batteries that can deliver high surge current 
ISSN 0276−6574 493 Computers in Cardiology 2008;35:493−496.
 
 
over few seconds, and compensated for the voltage drop 
that occurs incorporating a robust voltage regulator. A 
drawback of relying on the surge current from the 
batteries is the significant voltage drop occurring. In 12V 
lead-acid batteries, this voltage drop can be as high as 2V 
for 10 A current. We thus designed a robust voltage 
regulator, connected to the output of a series of 8 12V 
batteries. Such an assembly produces a regulated output 
of 70V, with a peak current capacity of 10 A.  
On the basis of empirical measures of surge currents 
and voltage drops, we found that batteries with a nominal 
capacity of 1.2 Ah provided an acceptable tradeoff 
between surge current, voltage drop, weight and size of 
the final assembly.  
Analog Output
Analog Inputs
PC interface
 –
 decoupling 
board Voltage and 
Current 
measurement 
circuit
+
-
Power Stage
DaqCard NI 6062E
Grouded Power Supply 
±12V, +5V
Batteries + 
Charging circuit
Batteries + 
Charging circuit
Voltage 
regulator
Voltage 
regulator
V
I
High Voltage Power Supply
Waveform
+70V
-70V
PA03
PA03
 
 
Figure 1. Major components of the defibrillator and their 
connections. 
 
Battery charging was obtained using a series of DC/DC 
converters, so that the batteries can be charged in parallel, 
without disconnecting them from their serial connections 
to the output circuits. Because the amplifiers can safely 
operate only with a dual power supply, additional 
circuitry was added to guarantee that both supplies are 
available and fall into a proper range. This circuit is 
based on four comparators with hysteresis (LM 358, with 
positive feedback network): two comparators 
continuously check whether the positive supply is within 
the minimum (68V) and maximum (72V) allowed 
ratings; the same is done for the negative supply (allowed 
rating range -68V to -72V). The outputs of the 
comparators are used as inputs of a 4-AND logic ports 
which drives two relays, to disconnect the amplifiers 
from the supply, if the supply voltage is out of range. 
 
PC interface and decoupling board 
Arbitrary defibrillation waveforms are generated using 
a PCMCIA digital-to-analog converter board (DaqCard 
6062E, National Instruments, Austin, TX), with 10us 
temporal resolution, using LabVIEW. The analog 
waveform is optically isolated and then injected into the 
amplifiers of the defibrillator output stage. In addition, 
the actual voltage and current delivered are measured, 
optically isolated and acquired by the A/D channels of 
the same converter board (figure 2). 
The power for the floating section of the optical 
isolation board is supplied by DC-DC converters. Note 
that the measure of voltage and current requires its own 
floating power supply. For measuring the delivered 
current, the input of an optoisolated differential amplifier 
(HCPL-7800) is connected directly to a current sensing 
resistor (0.02 ohm). Voltage is measured from a voltage 
divider. 
 
Output stage 
As depicted in figure 3, we configured two power 
amplifiers (PA03, Apex Microtechnology Corporation, 
US) in a bridge circuit. In this configuration, the 
amplifiers supply an output-voltage swing twice that of a 
single op amp. In addition, this configuration doubles the 
slew rate and any nonlinearities become symmetrical, 
reducing second harmonic distortion compared to a single 
amplifier circuit. The PA03 is a high current, MOSFET 
operational amplifier designed for driving continuous 
output currents up to 14A and pulse currents up to 30A. 
 
  
 
Figure 2. Scheme of the coupling board. Note the two 
isolated power supplies (bold lines) in the defibrillator 
output side.  
Safe operating area protection circuit 
In order to protect the whole system from software 
faults that could lead the system to work out of the PA03 
safe operating area, a hardware-temporized enable circuit 
was designed. This circuit keeps the amplifier in the 
“sleep” mode unless the user requests a shock (by a user-
operated button): in this case a wake up signal lasting 100 
ms is sent to the amplifiers and triggers the waveform 
PC Defibrillator  
Measured  
Voltage
Measured  
Current
Waveform 
from PC
To power stage
To PC
To PC
Grounded power supply 
Isolated power supply
Isolated power supply
494
 
 
generation from the PC. This circuit also increases the 
safety of the system, since it prevents unexpected shocks 
originated by software crash/malfunctions. 
 
 
 
Figure 3. Bridge configuration of the PA03 power 
amplifiers. 
 
3. Results 
The defibrillator was tested on known loads to analyze 
the output features and then used at the Electrophysiology 
Laboratory of the Center for Devices and Radiological 
Health of the FDA. Figure 4 shows a biphasic rectangular 
voltage waveform (panel A) on 25 ohm load, delivering  
2J: the rising front is detailed in panel B (less than 150 
µs) for a voltage swing of 70V.  
To test the defibrillation in the electrophysiology lab it 
was designed for, shocks were delivered to a perfused 
rabbit heart, as depicted in figure 5. An example of the 
voltage and current waveforms delivered by the 
defibrillator are illustrated in figure 6. 
 
4. Discussion and conclusions 
We designed and realized a research defibrillator able 
to test a wide variety of waveforms, suitable for in-vitro 
electrophysiological investigations. The defibrillator is 
able to deliver up to 10J, obtained with arbitrary shaped 
waveforms, with duration up to 100ms. The output stage 
can be connected to loads from 10 to 25 ohms. The 
possibility of delivering very long shocks (up to 100ms) 
is a unique for device. The combined use of linear AB 
amplifier and software generation of input waveforms 
allows the user to design any waveform, with the only  
  
Figure 4. A biphasic rectangular waveform (panel A) on 
25 ohm load.  Panel B shows the rising front (zoomed 
from panel A) 
 
 
 
Figure 5. Set-up for the defibrillator testing on a perfused 
rabbit heart. 
 
68.1k 
PA03 
- 
+ 
3.8k 240 
- 
+ 
68.1k 
3.8k 
IN 
OUT 
PA03 
495
 
 
 constraints given by the internal power dissipation 
and bandwidth of the amplifiers. To test the defibrillator 
performance, a preliminary series of tests on known loads 
were conducted. The system was further successfully 
tested in electrophysiological experiments on isolated 
rabbit hearts.  
A similar approach has been previously used by 
Malkin et al [7], who developed a defibrillator able to 
deliver arbitrary waveforms up to a remarkable 700V 
peak amplitude, with a maximum duration of about 
20msec. Since we aimed at studying longer defibrillation 
waveforms  (up to 100 msec), with an experimental set-
up having low impedance and requiring high currents, we 
needed to trade-off peak-voltage to current and shock 
duration. This required a different choice of the power 
amplifiers and a different approach to the power supply.  
Rabbit heart
0
10
20
30
40
50
60
70
0 10 20 30
Time (ms)
V
o
lt
a
g
e
 (
V
)
 
Rabbit heart
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
0 10 20 30
Time (ms)
C
u
rr
e
n
t 
(A
)
 
Figure 6. Voltage (upper panel ) and Current (lower 
panel) waveforms delivered to a rabbit heart.  
 
In conclusion, we presented a new approach to 
experimental defibrillator design, based on linear output 
stages. It overcomes the major limitations of the capacitor 
discharge approach and allows the generation and 
delivery of true arbitrary waveforms. 
  
Disclaimer  
The mention of commercial products, their sources, or 
their use in connection with material reported herein is 
not to be construed as either an actual or implied 
endorsement of such products by the U.S. Department of 
Health and Human Services. 
 
References 
[1] Szili-Torok T, Theuns D, Verblaauw T, Scholten M, 
Kimman GJ, Res J, Jordaens L. Transthoracic 
defibrillation of short-lasting ventricular fibrillation: a 
randomised trial for comparison of the efficacy of low-
energy biphasic rectilinear and monophasic damped sine 
shocks. Acta Cardiol. 2002 Oct;57(5):329-34. 
[2] Clark CB, Zhang Y, Davies LR, Karlsson G, Kerber RE. 
Transthoracic biphasic waveform defibrillation at very 
high and very low energies: a comparison with 
monophasic waveforms in an animal model of ventricular 
fibrillation. Resuscitation. 2002 Aug;54(2):183-6.   
[3] Dosdall D, Rothe D, Sweeney J. Programmable arbitrary 
waveform generator for internal defibrillation research. 
Conf Proc IEEE Eng Med Biol Soc. 2004;6:3971-4. 
[4] Seidl K, Denman RA, Moulder JC, Mouchawar G, 
Stoeppler C, Becker T, Weise U, Anskey EJ, Burnett HE, 
Kroll MW. Stepped defibrillation waveform is 
substantially more efficient than the 50/50% tilt biphasic. 
Heart Rhythm. 2006 Dec;3(12):1406-11. Epub 2006 Aug 
25.  
[5] Shorofsky SR, Rashba E, Havel W, Belk P, Degroot P, 
Swerdlow C, Gold MR. Improved defibrillation efficacy 
with an ascending ramp waveform in humans. Heart 
Rhythm. 2005 Apr;2(4):388-94. 
[6] White RD. New concepts in transthoracic defibrillation. 
Emerg Med Clin North Am. 2002 Nov;20(4):785-807. 
[7] Malkin RA, Jackson SR, Nguyen J, Yang Z, Guan D. 
Experimental verification of theoretical predictions 
concerning the optimum defibrillation waveform. IEEE 
Trans Biomed Eng. 2006 Aug;53(8):1492-8.  
 
Address for correspondence 
 
Michele Triventi 
Dept. of Technologies and Health –  
Istituto Superiore di Sanità  
Viale Regina Elena 299, 00161 Roma – Italy  
Tel. +390649902099     Fax. +390649387079 
michele.triventi@iss.it 
496


In-Vitro Investigation of Very Long Defibrillation Shocks: Design and Testing of a Capacitor-Free Defibrillator

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=AB163818C560EC8017204016A2546A06?doi=10.1.1.1035.1664&rep=rep1&type=pdf

In-Vitro Investigation of Very Long Defibrillation Shocks: Design and Testing of a Capacitor-Free Defibrillator

Abstract

Similar works

Full text

Available Versions

CiteSeerX