Different Waveforms, Different Results

1
Different Waveforms, Different Results

• Understanding the Differences Between Biphasic
  Technologies

2
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)

3
Damped Sine Wave

• Unchanged for 30 Years
• Requires high energy and current.
• Not highly effective for patients with high
  transthoracic impedance.

4
Biphasic Truncated Exponential

• The First Generation
• Adapted from low impedance ICD applications.
• Impedance causes waveform to change shape.

5
Rectilinear Biphasic Waveform

• Designed Specifically for External Use
• Constant Current eliminates high peaks
• Fixed Duration stabilizes waveform in face of
  varying impedance levels.

6
The Road Map for Today

• Scientific Data
• Experimental Studies
• Human Trials
• A Functional Comparison
• Current Delivery
• Impedance Handling
• The AHA Position

7
The Biphasic Advantage

• Experimental Studies Have Shown
• Performance varies with shape
• Lower defibrillation thresholds
• Less post-shock dysfunction

8
Performance Varies with Shape
9
Lower Defibrillation Threshold

• Key Findings
• Monophasic DFT increased by 40 (p lt0.05)
• Biphasic DFT remained constant

120
8030
100
80
5419
60
DFT (J)
3810
415
40
20
B
M
B
M
0
5 min
10 sec
Fibrillation time
Canine heart 3 minutes untreated followed by 2
minutes femoral compression
Walcott et al. Circulation 1998 982210-2215.
10
Reduced Dysfunction - 7 min VF
Biphasic defibrillation produces less dysfunction
Mean arterial pressure higher (plt0.05)
Ejection fraction higher (plt0.01)
Studied in pigs
Tang et al. Journal of American College of
Cardiology, 199934815-822.
11
Humans Data Is Plentiful

• Clinical Trials Show
• Efficacious for both VF AF
• Biphasic advantage grows with extended-duration
  VF
• Less energy required

12
Published Data is on Low Energy
Randomized Patients in Peer-Reviewed Journals
? 200J
gt 200J
1 Brady et al. Circulation 1996942507-2514. 2
Mittal et al. Journal of American College of
Cardiology, 1999 341595-1601. 3 Mittal et al.
Circulation 20001011282-1287. 4 Schneider et
al. Circulation 20001021780-1787. 5 Higgens et
al. Prehospital Emergency Care 20004305-313.
13
Agilent VF Trial - BTE Waveform
n 316 p ns
First-Shock Efficacy
Bardy et al. Circulation 1996942507.
14
Medtronic VF Trial - BTE Waveform
n 115 p ns
First-Shock Efficacy
Higgins, et al. Prehospital Emergency Care.
20004305-313.
15
ZOLL VF Trial - RBW
n 184 p 0.05
99
93
First-Shock Efficacy
Mittal et al. Journal of American College of
Cardiology, 1999 341595-1601.
16
RBW Superior for Difficult Patients
100
99
100
p 0.02
95
Defibrillation Efficacy
80
63
60
lt90 ohms
gt90 ohms
120J RBW
200J MDS
Mittal et al. Journal of American College of
Cardiology, 1999 341595-1601.
17
Out-of-Hospital Experience
Last Rhythm Recorded

• Key Findings
• All biphasic patients defibrillated
• Significantly more converted to an organized
  rhythm with biphasic waveform (Plt0.0003).

6.5 (1-17) minutes fibrillation
55
N210
93
N129
26
19
0
7
MONO 200-360J
BI 3 x 150J
Gliner White Resuscitation 1999.
18
Out-of-Hospital Experience

• ORCA Trial (n115)
• Comparison of 200-360J monophasic shocks with
  150J biphasic shocks for out-of-hospital cardiac
  arrest
• Collapse to first shock 8.9 minutes

Schneider et al. Circulation. 2000 1021780-1787.
19
Agilent AF Trial - BTE Waveform
n 209 p ns
Page, et al. Circulation 2000 Supplement 102
II-574 (abstract).
20
ZOLL AF Trial - RBW
Randomized MultiCenter n165
Mittal et al. Circulation 2000 1011282-1287.
21
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

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 102II-574 (abstract).
22
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.

23
A Functional Comparison

• Response to Impedance
• Current Delivery Characteristics
• Clinical Performance
• AHA View

24
1 WA Tacker. Electrical Defibrillation. Boca
Raton, Florida, CRC Press, Inc. 1980 p14.
25
The Important Relationship

• Ohms Law Tells Us . . .
• As the impedance increases, voltage must increase
  to deliver the same amount of current.

26
Effect of Patient Impedance on Biphasic Waveforms
High Impedance
Low Impedance
First Generation Biphasic
Rectilinear Biphasic
27
The Current Paradox
American Heart Association. Circulation.
20001029(suppl I)I-90-I-94.
28
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

29
Peak Current by Waveform
Monophasic at 200 Joules
Biphasic Truncated Exponential at 150 Joules
Rectilinear Biphasic at 120 Joules
Current
Time
30
Average Current at 150 Joules
Source ZOLL Medical Corporation
31
Average Current at Max Energy
Source ZOLL Medical Corporation
32
Next to a Common Standard
Studies Used 200J MDS as the Control
100
E
95
f
f
90
i
c
85
a
c
80
y
75
120J RBW
200J MDS
130J BTE
200J MDS
130J BTE
200J MDS
ZOLL3
Agilent2
Medtronic1
1 Higgens et al. Prehospital Emergency Care
20004305-313. 2 Bardy GH, et al. Circulation.
1996 94 2507-2514. 3 Mittal S., et al. Journal
of the American College of Cardiology. 1999 34
5.
33
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.
34
Guidelines 2000 . . .

• Define biphasic energy levels as ?200 joules
• Fail to address biphasic shocks in excess of gt200
  joules
• Protocols are waveform specific
• Given Class IIa recommendation to biphasic shocks
  ?200 joules

35
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