ECG (1) PDF

Electrocardiogram (ECG)  Electrocardiogram Def: it is a modified biphasic record of the electrical activity of the heart during the cardiac cycle. Apparatus: 1. Sensitive galvanometer with a pen recorder which write on a moving paper...

Electrocardiogram (ECG)  Electrocardiogram Def: it is a modified biphasic record of the electrical activity of the heart during the cardiac cycle. Apparatus: 1. Sensitive galvanometer with a pen recorder which write on a moving paper. 2. Amplifier which magnifies potential changes recorded by electrodes of galvanometer. 3. Recording electrodes in which Positive electrode attached to +ve pole of galvanometer. Negative electrode attached to –ve pole of galvanometer.  Principle of record Electrical currents of depolarization & repolarization of heart are conducted through body tissues surrounding the heart (thorax acts as a conducting medium). Therefore can be measured by electrodes located on the body surface. The waves recorded in ECG represent waves of depolarization & repolarization of atria & ventricles  How heart electric activity is recorded by electrocardiograph: By electrical connections between person body & electrocardiograph. The term “lead” means a combination of 2 wires & their electrodes to make a complete circuit, measuring potential difference between 2 points. Are arranged in a way to look at the heart from 12 different view  ECG Leads Leads measure the difference in electrical potential between either: Two different points on the body (bipolar leads). One certain point (Unipolar leads)  ECG Leads; 12 standard Leads According to the placement of recording electrodes 3 Standard Limb Leads (Bipolar): lead I, Lead II, Lead III 3 Augmented Limb Leads (unipolar): aVR, aVL, aVF 6 Chest Leads (unipolar anterior leads): V1,2,3,4,5,6 William Einthoven who first recorded ECG, developed leads based on Einthoven triangle  Standard Limb Leads: one +ve & one –ve electrode measuring potential difference between 2 limbs  Augmented Limb Leads; recording potential difference between one limb (+ve electrode) & other 2 limbs (-ve electrode).  Unipolar leads The potential at one pole(-ve) of ECG is made Zero by connecting it to central terminal point that receive electrodes from (LA, RA, LF). (+ve)electrode connected to ECG is placed on limbs and chest called (exploring electrode).  Chest leads; recording potential difference at certain point on the chest (+ve electrode), while the other 3 limbs connected to –ve electrode).  MCL Unipolar chest leads V1 up to V6 V1 V2 V3 V6 V4 V5 MAL AAL Normal ECG;  ECG paper time Amplitude Waves of ECG  Components of ECG Trace Wave P wave: represent depolarization of s both atria. QRS complex: Represent depolarization of both ventricles Larger than P wave bec. Of greater bulk of ventricular ms. T wave: repolarization of ventricles  Components Intervals & of ECG Trace P-R interval: Segment From onset of P wave to onset of QRS. Time for Conduction of impulse from atria to ventricles + AVN delay. Normal duration:0.12-0.2 sec (3-4 small boxes). Q-T interval: From onset of QRS to end of T wave. All ventricular activity. Normally = 0.4 sec. S-T segment: Between end of QRS & onset of T wave Isoelectric. Duration: 0.08-0.12 sec.  Determination of Heart Rate from ECG trace: by counting large boxes between 2 R & divide 300/no of large boxes - Or, Divide 1500/no. of small boxes between 2R Calculating HR;  Detecting the Rhythm A sinus rhythm means: + ve P wave in lead I ,II. P wave is followed by a QRS complex.  Normal Sinus Rhythm Regular rhythm Normal rate +ve P followed by QRS Normal P, QRS