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Electrocardiographs ECG part2. Elements of the ECG: P wave: Depolarization of both atria; Relationship between P and QRS helps distinguish various cardiac arrhythmias Shape and duration of P may indicate atrial enlargement PR interval: from onset of P wave to onset of QRS

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Presentation Transcript
slide2

Elements of the ECG:

  • P wave: Depolarization of both atria;
    • Relationship between P and QRS helps distinguish various cardiac arrhythmias
    • Shape and duration of P may indicate atrial enlargement
  • PR interval: from onset of P wave to onset of QRS
    • Normal duration = 0.12-2.0 sec (120-200 ms) (3-4 horizontal boxes)
    • Represents atria to ventricular conduction time (through His bundle)
    • Prolonged PR interval may indicate a 1st degree heart block
  • QRS complex: Ventricular depolarization
    • Larger than P wave because of greater muscle mass of ventricles
    • Normal duration = 0.08-0.12 seconds
    • Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.
    • Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI
slide3

ST segment:

    • Connects the QRS complex and T wave
    • Duration of 0.08-0.12 sec (80-120 msec)
  • T wave:
    • Represents repolarization or recovery of ventricles
    • Interval from beginning of QRS to apex of T is referred to as the absolute refractory period
  • QT Interval
    • Measured from beginning of QRS to the end of the T wave
    • Normal QT is usually about 0.40 sec
    • QT interval varies based on heart rate
standard lead system

Lead I

Lead II

Lead III

Lead aVR

Lead aVL

Lead aVF

V1-V6

Standard Lead System

Lead I: LA- RA

Lead : LL - RA

Lead III: LL - LA

V1-V6: Locations of chest electrode:

ecg machines
It Consists of

* electronic part

1-Preamplifier

2-Power amplifier to move the galvanometer pen

3- 1 mv calibration source

4- Protecting circuits

* Stylus

ECG Machines
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1 mV

Lead

selector

Amplifier

Stylus

Galvanometer

Gear Train

Motor

patient cables
Patient cables
  • Most important part
  • Most frequently at fault.
  • There are several different cables:

Some constructed of two pieces: more expensive but more economical in the long run

  • One piece construction
  • Most ECG cables are made of shielded wire