ECG and Bioelectric Potentials Quiz

Learning Objectives

• ECG
• EMG
• EEG
• Sleep Study

Bioelectric Potentials

• Purpose of 3, 5, and 12 lead ECGs
• Number of electrodes needed for a 12 lead ECG
• Groups of leads in a 12 lead ECG
• Einthoven Triangle
• Equations for each lead
• Establishing common points in augmented limb leads
• Effect of the right leg in all leads

Electro-Conduction System of the Heart

• Cardiac Axis and 12 Leads ECG
  • 6 unipolar chest leads
  • Location of leads: V1-V6
  • Description of the location of V1-V6 (intercostal space, sternal border, mid-way between V2 and V4, etc.)
  • Wilson terminal equation: VW = (VLA + VRA + VLL)/3
  • Leads V1 to V6 calculations using Wilson terminal (VCn – VW)
  • Diagram of Electro-Conduction System of the Heart, showing the placement of the leads

Rhythm Strip

• ECG is printed on standard thermal strips
• Small square = 1 mm x 1 mm, big square = 5 mm x 5 mm
• Horizontal axis = time, vertical axis = voltage
• Standard setting = 25 mm/s recording speed and x1 sensitivity
• Equals 0.04s/small square and 0.1mV/small square
• Calculating heart rate (HR) from rhythm strip (regular rhythm method)
  • Number of squares per minute = 1500 (or 25mm/s X 60s)
  • Number of squares per R-R interval
  • HR = 1500/x = (where x is the number of squares per R-R interval)
• Calculating HR from rhythm strip (irregular rhythm method)
  • Number of R-R intervals in a 6-second period (y)
  • HR = y * 10

Cardiac Arrhythmias

• Slow or fast rhythm (Bradycardia & Tachycardia)
• Propagation delays (e.g., PR timing)
• Conduction blockage (e.g., AV block)
• Cardiac arrest
• Fibrillation (atrial or ventricular)
• Asystole

Electrocardiograph (ECG Machine)

• Components
  • Sensing electrodes
  • Protection circuit
  • Lead selector
  • Lead-fail detector
  • Auto calibration
  • Bio-amplifier
  • Driver, right-leg circuit
  • Isolation circuit
  • Preamplifier
  • Baseline restoration
  • Memory
  • ADC
  • Recorder Printer
  • Micro-controller
  • Control program
  • Operator display
  • Keyboard
  • Power Supply
• Functions –detailed explanation to each component
  • Pick up ECG signals from the body
  • Prevent high voltage damage
  • Select appropriate leads (auto/manual)
  • Detect unconnected/ dry electrodes
  • Calibrate preamplifier and recorder
  • Digitize analogue signals (ECG signal)
  • Amplify ECG signals
  • Restore baseline stability in recordings
  • Ensure isolation between patient and equipment

Summary

• Cardiac Axis and 12 Leads ECG : Wilson terminal equation, Lead calculations
• Rhythm Strip –HR calculation : Regular rhythm, Irregular Rhythm Method
• Electrocardiograph (ECG Machine): Block Diagram