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Download Electrocardiographs ECG part2
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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• 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 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 I: LA- RA Lead : LL - RA Lead III: LL - LA V1-V6: Locations of chest electrode: Lead aVR Lead aVL Lead aVF V1-V6 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 1 mV Lead selector Amplifier Stylus Gear Train Motor Galvanometer 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 Standard cable color code AN/MS Plug Pins A Goes to RA Electrode Color Code White B LA Black C LL Red D C Brown E RL Green
