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Introduction to ecg

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Lecture By Dr.Haifa Khedier …

Lecture By Dr.Haifa Khedier
ER Doctor. MGH Madinah, KSA


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  • 1. What Makes ECG MYOCYTES PRODUCE Electrical impulse Human body conducting impulse Electrodes pick up potential difference ECG Machine read potential difference , and draw a graph
  • 2. What is electrode ?  Special Sensor devices  Connected to certain areas in the body  Pick up potential difference  They known as leads
  • 3. Types of leads ( Electrodes ) Bipolar Limb Leads Unipolar Leads Chest leads V1 to V6
  • 4. What is Bipolar leads Lead 1 Lead 11 Lead 111 • +ve LA • -ve RA • +ve LL • -ve RA • +ve LL • -ve LA
  • 5. Bipolar Limb Leads Can be located at any part of the limb 10 cm from the heart They form equilateral triangle Einthoven triangle
  • 6. Augmented Unipolar leads aVR • +ve • RA aVF • +ve • Lf aVL • +ve • LA
  • 7. Augmented Unipolar leads • No Negative pole • Instate the reference is the other two leads • The machine change the leads without addition of attached devices
  • 8. Chest leads Location V1 Rt 4th IC V2 Lt 4th IC V3 HALF WAY V2&V4 V4 LT 5th IC V5 5th IC , AAL V5 5th IC ,MAL
  • 9. Hexaxial system • Two victors(leads) are equal in intensity ,and polarity as long as they are parallel • Accordingly we can shit the leads to a point passing through the heart center, and they will be the same • The location of the lead is determined by its positive pole • Direction of the Lead is from Positive to Negative electrode
  • 10. • The direction of the unipolar lead is towards the center of the corresponding limb of the triangle, otherwise same is applied as in bipolar leads
  • 11. Hexaxial system
  • 12. Anatomical representations of the leads
  • 13. Anatomical representations of the leads
  • 14. ECG paper
  • 15. ECG paper
  • 16. ECG paper Calibration Box  Found at edge of ECG paper  Standard 10 mm height (1MV )  .2 second width  To confirm standard ECG format 
  • 17. ECG Components Waves Segment Interval • A deflections from the base line represent cardiac event • P- QRS- T waves • A specific portion of the complex • PR – ST • Distance measured as time between two cardiac events • QT- PR- TP
  • 18. Waves Waves represent :  Atrial , or ventricular depolarization , repolarization and conduction  Can be positive ,negative or biphasic deflection from the baseline  Baseline from one TP segment to the next
  • 19. ECG Representation of cardiac events • • • • • • Atrial depolarizatio Atrial Repolarization Conduction Ventricular depolarization Ventricular Repolarization Conduction
  • 20. ECG Segments & Intervals Segments Intervals Additional intervals PR PR RR ST QT PP
  • 21. P- Wave • First wave after TP • Represent atrial depolarization and conduction • Duration 0.08 – 0.11 second • Direction of the impulse is downwards & to the left • It is upright in leads 11,111,& aVf • Downwards in aVR • It must be upright in Leads 11 & aVF to say sinus rhythm
  • 22. TP wave • Represent repolarization of Atria • Usually not seen • It occurs when there is no QRS after P as in Av dissociation • It can also be seen in PR or ST depression
  • 23. PR Segment • From end of P to beginning of QRS • Usually at the base line • Depression of up to 0.8 mm is accepted as normal • Pathological depression in pericarditis and atrial ischemia
  • 24. PR Interval • Include P wave ,and PR segment • Cover the event from initiation of impulse at SA node to start of ventricular depolariz. • Duration o.12 sec. to 0.20 sec. • < 0.11 shortening • > 0.20 1st degree heart block
  • 25. QRS Complex • Composed of two or more waces • Represent ventricular depolarization • Duration is up to 0.12 second
  • 26. How to identify different waves Q wave R wave S wave • The first negative wave after P wave • The first Positive wave after P wave • The first negative deflection after R wave
  • 27. An X Prime wave • • • • • Extra wave in QRS It isn't an actual wave Change in QRS QRS become bizarre S wave : only when cross the baseline
  • 28. Q Wave Can be significant if :  0.03 second or wider  Equal to or greater than 1/3rd of height of R wave Non significant Q wave  Commonly found in Leads : 1 , aVL & V6
  • 29. The Intrinsicoid Deflection • Beginning of QRS to the beginning of negative down slope of the R wave when no Q wave • Represent the time of electrical impulse from purkinje fibers to surface of epicardium • It is longer in left preicordial leads V5, V6 • Prolongation in LVH , BBB
  • 30. The ST Segment • End of QRS to Beginning of T • Usually along the base line with normal variation of 1 mm in limbs leads & 3 mm in Right chest leads • The point of junction with QRS is called J point • Represent the period from depol. to repol. of ventricles
  • 31. The T Wave • Represent ventricular repolarization • negative or positive deflection after ST Segment • Should be The same direction of QRS • It is asymmetric , begin sloping and end is faster
  • 32. How to measure asymmetry • Draw a line from the peak of T wave to the base line , and measure each side • Asymmetry is usually a sign of pathology , but may be normal
  • 33. QT Interval  QRS + ST + T  Represent all the event of ventricular systole Varies with Rate ,age sex , and electrolyte abnormality prolongation predispose to arrhythmias
  • 34. Best way to measure QT Interval • Normal QT Is less than the half of R-R Interval • Accordingly lengthen when the heart rate slow, and shorten when fast • This makes it hard to calculate the interval at which QT is normal
  • 35. QTc Interval • • • • • Stand for QT corrected Interval Corrected for the heart rate QTc interval calculation is the best way. Normal QTc : 0.410 second prolonged QTc : > 0.419 second
  • 36. QTc Interval Equation QT 1.75(VR-60) QTc
  • 37. U - Wave • A small flat wave sometimes seen after the T wave • Representation unknown • Clinical significance : Hypokalemia Hyperkalemia Inaccuracy in measuring QT segment
  • 38. Additional Intervals • R-R Interval • The distance between peaks of R waves in two consecutive QRS • P-P interval • Distance between two identical points of one P to the next • These intervals are useful in evaluation of Rhythm