Transcript Document

Different Waveforms,
Different Results
Understanding the Differences
Between Biphasic Technologies
Defibrillation Waveforms
• Waveforms describe the electrical pulse
 Current Delivery
 Time
 Direction of Current Flow
• Three in use today
 Monophasic Damped Sine Wave (MDS)
 Biphasic Truncated Exponential (BTE)
 Rectilinear Biphasic (RBW)
Damped Sine Wave
Unchanged for 30 Years
• Requires high energy
and current.
• Not highly effective
for patients with high
transthoracic
impedance.
Biphasic Truncated Exponential
The First Generation:
• Adapted from low
impedance ICD
applications.
• Impedance causes
waveform to
change shape.
Rectilinear Biphasic Waveform
Designed Specifically
for External Use:
• Constant Current
eliminates high
peaks
• Fixed Duration
stabilizes waveform
in face of varying
impedance levels.
The Road Map for Today
• Scientific Data
Experimental Studies
Human Trials
• A Functional Comparison
Current Delivery
Impedance Handling
• The AHA Position
The Biphasic Advantage
Experimental Studies Have Shown:
• Performance varies with shape
• Lower defibrillation thresholds
• Less post-shock dysfunction
Defibrillation Threshold
(Volts)
Performance Varies with Shape
300
250
200
150
100
)
50
0
10M 2.5-7.53.5-6.5 5-5 6.5-3.57.5-2.5
Waveform Shape (msec)
(Canine) epicardial electrodes
Dixon et al. Circulation 1987;117:358-364.
Lower Defibrillation Threshold
Key Findings
120
80±30
100
DFT (J)
1 Monophasic DFT
increased by 40%
(p <0.05)
2 Biphasic DFT
remained constant
80
54±19
60
38±10
41±5
40
20
M
B
M
B
0
5 min
10 sec
Fibrillation time
Canine heart
3 minutes untreated followed by 2 minutes
femoral compression
Walcott et al. Circulation 1998; 98:2210-2215.
Reduced Dysfunction - 7 min VF
Biphasic defibrillation
produces less
dysfunction
Mean arterial pressure higher (p<0.05)
Ejection fraction higher (p<0.01)
Studied in pigs
Tang et al. Journal of American College of Cardiology, 1999;34:815-822.
Humans Data Is Plentiful
Clinical Trials Show:
• Efficacious for both VF & AF
• Biphasic advantage “grows” with
extended-duration VF
• Less energy required
Published Data is on Low Energy
Randomized Patients in Peer-Reviewed Journals
Low-Energy
Biphasic
912 Patients 1,2,3,4,5
 200J
High-Energy
Biphasic
0 Patients
> 200J
0
1
200
400
600
Brady et al. Circulation 1996;94:2507-2514.
Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601.
3 Mittal et al. Circulation 2000;101:1282-1287.
4 Schneider et al. Circulation 2000;102:1780-1787.
5 Higgens et al. Prehospital Emergency Care 2000;4:305-313.
2
800
1000
Agilent VF Trial - BTE Waveform
100%
n = 316
p = ns
86%
86%
80%
60%
130J BTE
Bardy et al. Circulation 1996;94:2507.
200J MDS
Medtronic VF Trial - BTE Waveform
100%
90%
83%
80%
60%
130J BTE
Higgins, et al. Prehospital Emergency Care. 2000;4:305-313.
200J MDS
n = 115
p = ns
ZOLL VF Trial - RBW
100%
n = 184
p = 0.05
99%
93%
95%
90%
85%
80%
75%
120J RBW
200J MDS
Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601.
RBW Superior for Difficult Patients
100%
100%
99%
p = 0.02
95%
80%
63%
60%
<90 ohms
120J RBW
>90 ohms
200J MDS
Mittal et al. Journal of American College of Cardiology, 1999; 34:1595-1601.
Out-of-Hospital Experience
Last Rhythm Recorded
Key Findings
~6.5 (1-17) minutes fibrillation
100%
Organized
Asystole
VF
1 All biphasic patients
defibrillated
90%
70%
55%
2 Significantly more
converted to an
organized rhythm
with biphasic
waveform (P<0.0003).
60%
N=210
80%
93%
50%
N=129
40%
30%
26%
20%
10%
19%
7%
0%
MONO
200-360J
Gliner & White: Resuscitation 1999.
0%
BI
3 x 150J
Out-of-Hospital Experience
ORCA Trial (n=115)
• Comparison of 200-360J monophasic shocks
•
with 150J biphasic shocks for out-of-hospital
cardiac arrest
Collapse to first shock = 8.9 minutes
Outcome
Monophasic
Biphasic
1st shock success
36/61 (59%)
52/54 (96%)
p<0.0001
3rd shock success
42/61 (69%)
53/54 (98%)
p<0.0001
Overall Success
49/58 (84%)
54/54 (100%)
p=0.003
Schneider et al. Circulation. 2000; 102:1780-1787.
Agilent AF Trial - BTE Waveform
100%
91%
86%
80%
60%
40%
20%
0%
200J BTE
360J MDS
Page, et al. Circulation 2000; Supplement 102: II-574 (abstract).
n = 209
p = ns
ZOLL AF Trial - RBW
Randomized MultiCenter
n=165
p=0.005
p<0.0001
Cardioversion Efficacy
100%
91%
85%
79%
80%
68%
94%
68%
60%
44%
40%
21%
20%
0%
100 J 200 J 300 J 360 J
Monophasic
Mittal et al. Circulation 2000; 101:1282-1287.
70 J 120 J 150 J 170J
Rectilinear Biphasic
RBW in Clinical Practice
Initial Report:
• 100% efficacy for 125
AF patients
• 85% converted at 50
joules
• 100% efficacy in
subset of patients
previously converted
with 720J
monophasic
Energy (J)
Current (Amp)
AF – Mono
185
32
AF – Bi
67
10
-64%
-69%
p < 0.01
p < 0.01
Diff
p value
In a continuation of the
series they reported
success in 713 of 714
patients (99.8%).
Niebauer MJ, et al. PACE 2000; 23: 605 (abstract).
Niebauer, MJ, et al. Circulation. 2000 Supplement 102:II-574 (abstract).
Overall Findings
• Biphasic waveforms are effective for
both VF and AF.
• Low-energy BTE waveforms produce
clinical results equivalent to
monophasic technology.
• Low-energy RBW waveforms
produce clinical results superior to
monophasic technology.
A Functional Comparison
•
•
•
•
Response to Impedance
Current Delivery Characteristics
Clinical Performance
AHA View
“. . . the essential
requirement for electrical
ventricular defibrillation is
the attainment of a sufficient
current density. . .” 1
1
WA Tacker. Electrical Defibrillation. Boca Raton, Florida,
CRC Press, Inc.; 1980 p14.
The Important Relationship
Voltage
= Current
Impedance
Ohm’s Law Tells Us . . .
• As the impedance increases, voltage must
increase to deliver the same amount of current.
Effect of Patient Impedance
on Biphasic Waveforms
Low Impedance
First Generation
Biphasic
50
50
40
40
30
30
20
20
10
10
0
0
-10
-10
-20
-20
0
Rectilinear
Biphasic
High Impedance
4
8
12
50
50
40
40
30
30
20
20
10
10
0
0
-10
-10
-20
-20
0
4
8
12
0
4
8
12
0
4
8
12
The Current Paradox
“Defibrillation depends on the
successful selection of energy to
generate sufficient current flow
through the heart (transmyocardial
current) to achieve defibrillation
while at the same time causing
minimal injury to the heart.”
American Heart Association. Circulation. 2000:1029(suppl I):I-90-I-94.
Two Components of Current
Peak Current
• Highest current delivered over the
course of shock delivery
• Associated with myocardial dysfunction
Average Current
• Average delivered over the course of
the shock
• Determinant of successful defibrillation
Peak Current by Waveform
Monophasic at 200 Joules
RBW
@ 120J
15
Biphasic Truncated Exponential
at 150 Joules
Current
Rectilinear Biphasic
at 120 Joules
BTE
@ 130J
35
Mono
@ 200J
43
0
Time
10
20
Amps
30
40
50
Average Current at 150 Joules
Current (amps)
20
150J BTE
150J RBW
17
14
11
8
5
75
100
125
Resistance (ohms)
Source: ZOLL Medical Corporation
150
Average Current at Max Energy
Current (amps)
25
360J BTE
200J RBW
20
15
10
75
100
125
Resistance (ohms)
Source: ZOLL Medical Corporation
150
Next to a Common Standard
Studies Used 200J MDS as the Control
100%
E
f
f
i
c
a
c
y
95%
90%
85%
80%
75%
1
200J 130J
MDS BTE
200J 130J
MDS BTE
200J 120J
MDS RBW
Medtronic1
Agilent2
ZOLL3
Higgens et al. Prehospital Emergency Care 2000;4:305-313.
Bardy GH, et al. Circulation. 1996; 94: 2507-2514.
3 Mittal S., et al. Journal of the American College of Cardiology. 1999; 34: 5.
2
Versus the AHA Thresholds
The 1997 AHA Statement on Biphasic
Waveforms defined thresholds for waveform
equivalency and superiority.
Only the clinical performance of the
Rectilinear Biphasic waveform
exceeds the threshold for superiority.
American Heart Association. Automatic external defibrillators for public access
defibrillation: recommendations for specifying and reporting arrhythmia analysis
algorithm performance, incorporating new waveforms, and enhancing safety.
Circulation. 1997; 95: 1677-1682.
Guidelines 2000 . . .
• Define biphasic energy levels as 200 joules
• Fail to address biphasic shocks in excess of
>200 joules
• Protocols are waveform specific
• Given Class IIa recommendation to biphasic
shocks 200 joules
Summary
• Biphasic waveforms differ
 Shape
 Response to Impedance
 Current Delivery
 Documented Clinical Performance
• Biphasic waveforms are effective for external
defibrillation
 Equivalent performance with less energy
 Rectilinear biphasics promise superior performance