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 = sec ( 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 = 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 sec ( 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

Lead ILead IILead III Lead aVRLead aVLLead aVF V 1 -V 6 Lead I: LA- RA Lead : LL - RA Lead III: LL - LA V1-V6: Locations of chest electrode: Standard Lead System

It Consists of * electronic part 1-Preamplifier 2-Power amplifier to move the galvanometer pen 3- 1 mv calibration source 4- Protecting circuits Stylus * Stylus ECG Machines

Amplifier Galvanometer Stylus Lead selector 1 mV Gear Train Motor

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 Electrode Color Code Goes toAN/MS Plug Pins WhiteRAA BlackLAB RedLLC BrownCD GreenRLE