06-12-2012, 12:00 PM
Electrocardiography
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•A recording of the electrical activity of the heart over time
•Helps detect electrolyte disturbances (hyper-& hypokalemia)
•Allows for detection of conduction abnormalities
•Screening tool for ischemic heart disease during stress tests
•Helpful with non-cardiac diseases (e.g. pulmonary embolism or hypothermia
ECG Graph Paper
•Runs at a paper speed of 25 mm/sec
•Each small block of ECG paper is 1 mm2
•One small block equals 0.04 s
•Fivesmallblocksmakeup1largeblockwhichtranslatesinto0.20s(200msec)
•Hence, there are 5 large blocks per second
•Voltage: 1 mm = 0.1 mV between each individual block vertically
•QRS complex:
•Represents 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
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
Arrhythmias Detected on ECG continued
•In fluttercontraction rates can be 200-300/min
•In fibrillationcontraction of myocardial cells is uncoordinated & pumping ineffective
–Ventricular fibrillationis life-threatening
•Electrical defibrillationresynchronizes heart by depolarizing all cells at same time