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The Electrocardiogram

5. The Electrocardiogram. 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

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The Electrocardiogram

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  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

  8. EKG Leads

  9. EKG Leads

  10. EKG Leads

  11. 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

  12. 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

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

  14. 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

  15. 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

  16. 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

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

  18. 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

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

  20. 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)

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

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

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

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