Download Medical Applications Electrocardiogram (ECG)

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Medical Applications
Electrocardiogram (ECG)
Glossary of Terms

AED

EKG/ECG

Holter Monitor

Defibrillation

T-wave alterans

Right Leg Drive

RFI
ESD

2
Automated External Defibrillator – Auto diagnosis with
voice directed treatment.
ElectroCardioGram – skin surface, heart
monitor
Portable device for continuously monitoring
the electrical activity of the heart for at least 24
hours. Can be external or implantable.
Delivering a therapeutic dose of electrical
energy to the heart.
A change in the shape of the heartbeat signal on an every
other beat basis that is not apparent to the naked eye.
An operational amplifier deriving common mode voltage is
used to invert the common-mode signal and drive it back
into the patient through the right leg.
Radio Frequency Interference
Electro Static Discharge
ECG Markets
ECG
Professional Healthcare
Consumer
battery
line
line
battery
AED
Commercial
Fitness Equipment
Above Diagnostic
Defibrillators
Diagnostic
3
Holter Monitor
Home Products
ECG Waveform (Filtered)
4
ECG – Waveform Characteristics
 ECG
Signals have two components:
 ECG
Waveform
 0.05 Hz to 150 Hz bandwidth per Medical Standards
 Average R Wave Amplitude is 1.8mV
 Some waveforms can be as big as 10 mV p-p.
 T wave Alterans are only a few microvolts in amplitude
 Pacing ArtifactS
 Medical Standards require 2mV and 200µs detection
 Average pulse is 1 mV and 500µs but can be much smaller
5
ECG – Patient Skin Surface Characteristics
 Skin
Impedance
 Standards
require of common mode rejection at 51K ohms skin to
electrode impedance at 10Hz
 Good Silver-Silver Chloride electrodes yield about 10 K ohm
electrode to skin impedance
 Stainless Steel electrodes can yield skin impedances of several
meg-ohms
 Defibrillation
 5000
 DC
Voltage
volts, 360 Joules
Voltage
 Medical
Standards require being capable of acquiring ECG with
300 mV of DC. Mostly due to half cell potential of electrodes,
stainless steel can yield 500 mV of DC
 60
Hz Noise
 Average
6
is several mV
The World Leader in High Performance Signal Processing Solutions
Signal Chains
Diagnostic ECG (Clinical Use)
8
Diagnostic ECG
In-amp + Right Leg Drive
Instrumentation
Amplifier
G=14
A
B
15kΩ
+5V
2.2pF
10kΩ
10pF
10kΩ
2.2pF
+5V
4.7μF
24.9kΩ
-5V +5V24.9kΩ
AD8220
220p F
4.12kΩ
-5V
-5V
+5V
From Lead I
OP2177
C
-5V
op amps
68pF
866kΩ
499kΩ +5V
OP2177
-5V
9
12.7kΩ
switch
ADG601
REF/2
From Lead II
From Lead III
12.7kΩ
ADG620
866kΩ
Diagnostic ECG
Filters + Pace Detection
High PassFilter 0.033Hz
Low Pass 5th Order Filter at 157Hz
G=50
1.18kΩ
57.6kΩ
14kΩ
14kΩ
19.3kΩ
14.5kΩ
33nF
68nF
REF/2
47nF
+5V
+5V
4.7μF
19.3kΩ
+5V
AD8618
AD8618
14.5kΩ
+5V
AD8618
AD8618
10nF
220p F
switch
ADG601
1MΩ
1.15kΩ
33nF
REF/2
From Lead II
From Lead III
REF/2
12.7kΩ
ADG620
866kΩ
Lead Detection
50kHz
10
22nF
4.99kΩ
REF/2
Pacing Artifact
Detection Circuitry
33Ω
REF/2
Diagnostic ECG
ADC + Isolation + Processing
11
Low Power, Low Cost, Wireless ECG
(Holter Monitor)
108pF
AD623
RA
Electrode
RL
Electrode
G=10.6
499kΩ
12
AD8641
681kΩ
ESD
Defib
Protect
AD8603
5.23kΩ
10kΩ
Anti-aliasFilter
-3dB, 1592 Hz
G = 22.05
0.47μF
ESD
Defibrillation
Protection
5.23kΩ
5pF
RL
Electrode
475Ω
High-PassPole
0.5Hz
ADuC7022
Additional
Digital Filter
Level Shift
Anti-Alias
Total Gain ~ 220
ADF702x*
Dependent on Frequency Band Used (WMTS or ISM)
Low Cost, Low Power AED
Single pole
anti-alias
filter
Patient
Pads
Digital Filtering
LCD Display
ADR365
AD8220/4
AD8606
Filter
and
Protection
Network
AD7685
ADuC70xx
or
Blackfin®
Blanking
AD8605
High
Voltage
Discharge
13
Power
Control
ADP1712
Li Ion
Battery
Exercise Heart Rate Monitor
(Example: treadmill with heart rate monitor)
+5V
40 Hz Low PassFilter
Input
Protection
AD8553
AD8692
AD8692
REF
REF
REF
AD8691
REF
High PassFilter
14
ADuC70xx