The Electrocardiogram

1. 5 The Electrocardiogram

2. The Electrocardiogram • Objectives • Define the term electrocardiogram • Describe the basics of EKG monitoring • List the types of EKG leads • Discuss the relevance of Einthoven’s triangle • Identify and explain the grids and markings on a representative strip of EKG graph paper

3. The Electrocardiogram • Objectives (continued) • Describe the relationship of the following EKG waveforms to the electrical events in the heart • P wave • PR interval • QRS complex • ST segment • T wave

4. The Electrocardiogram • Electrocardiogram • Graphic representation of the electrical activity of the heart • Electrocardiograph • Machine used to record the electrocardiogram, or EKG machine • EKG • Graphic tracing of electricalactivity of the heart, not mechanical activity

5. The Electrical Basis of the EKG • Electrical activity is sensed byelectrodes placed on the skin surface • Recorded in the form of anelectrocardiogram • Cardiac monitor depicts electrical impulses on monitor screen oroscilloscope

6. The Electrical Basis of the EKG • Electrical impulses present on the skin surface are very low voltage; impulsesare amplified by an EKG machine • The printed record of the electrical activity of the heart is called arhythm stripor anEKG strip

7. EKG Leads • Electrode • An adhesive pad that contains conductive gel and attaches to patient’s skin • Leads • How electrodes are connected to the cardiac monitor • 3 leads must have a positive, a negative, and a ground

10. EKG Leads

11. EKG Leads

12. EKG Leads

13. EKG Leads • Einthoven’s triangle • Imaginary inverted triangle formed around heart by proper placement of bipolar leads • Top formed by lead I, right side formed by lead III, and left side formed by lead II • Each lead represents adifferentlook at,or view, of the heart

14. EKG Graph Paper • Leaves the machine at constant speed of 25 mm/s • Time • Measured on horizontal line • Amplitudeorvoltage • Measured on vertical line on graph paper

15. EKG Graph Paper • Electrocardiographic • Paper divided into small squares • 1 mm in width • Time interval of 0.04 seconds

16. EKG Graph Paper • Electrocardiographic paper • Darker lines divide paper every fifth square • Vertically and horizontally • Large squares measure 5 mm in height and width • Represents time interval of 0.20 seconds • Five small squares in each large square

17. EKG Waveforms • Wave or waveform refers to movementaway from thebaselineorisoelectricline (beginning and ending of all waves) • Positive deflection • Above isoelectric line • Negative deflection • Below isoelectric line

18. EKG Waveforms • Electrical impulse leaves SA node, produces waveform on graph paper • One complete cardiac cycle =P, Q, R, S,(QRS complex) and T wave

19. P Wave • First wave produced by electrical impulsefromSA node • Smooth, rounded upward deflection • Depolarization of left and right atria • 0.10 secondsin length

20. PR Interval • Time impulse travels from SA node through internodal pathways in atria toward ventricles • Time interval from start of P wave to start of QRS • 0.12-0.20 seconds in length

21. QRS Complex • Consists ofQ, R, and Swaves • Represents conduction of impulse frombundle of Histhrough ventricular muscle • Ventricular depolarization

22. QRS Complex • Q wave • First downward deflection • R wave • First upward deflection • Largest deflection seen in lead I and II • S wave • Downward deflection after R wave • Measures less than0.12 seconds(3 small boxes)

23. ST Segment • Time interval during which ventricles depolarized and repolarization of ventricles begin • Isoelectric or consistent with baseline

24. T Wave • Follows ST segment • Representsventricular repolarization • Slightly rounded, positive deflection • Resting phaseof cardiac cycle

25. Summary of EKG Waveforms • P wave • Atrial depolarization • QRS complex • Ventricular depolarization, atrial repolarization • T wave • Ventricular repolarization