Medical Applications Electrocardiogram (ECG)

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Medical ApplicationsElectrocardiogram (ECG)
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Glossary of Terms

• AED Automated External Defibrillator Auto
  diagnosis with voice directed treatment.
• EKG/ECG ElectroCardioGram skin surface, heart
  monitor
• Holter Monitor Portable device for continuously
  monitoring the electrical activity of the
  heart for at least 24 hours. Can be external
  or implantable.
• Defibrillation Delivering a therapeutic dose of
  electrical energy to the heart.
• T-wave alterans A change in the shape of the
  heartbeat signal on an every other beat basis
  that is not apparent to the naked eye.
• Right Leg Drive 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.
• RFI Radio Frequency Interference
• ESD Electro Static Discharge

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ECG Markets
ECG
Professional Healthcare
Consumer
battery
line
battery
line
AED
Home Products
Commercial Fitness Equipment
Above Diagnostic
Defibrillators
Diagnostic
Holter Monitor
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ECG Waveform (Filtered)
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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 Artifact
• Medical Standards require 2mV and 200µs detection
• Average pulse is 1 mV and 500µs but can be much
  smaller

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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 Voltage
• 5000 volts, 360 Joules
• DC 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 is several mV

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Signal Chains
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Diagnostic ECG (Clinical Use)
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Diagnostic ECG In-amp Right Leg Drive
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Diagnostic ECG Filters Pace Detection
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Diagnostic ECG ADC Isolation Processing
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Low Power, Low Cost, Wireless ECG (Holter
Monitor)
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Low Cost, Low Power AED
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Exercise Heart Rate Monitor (Example treadmill
with heart rate monitor)