Shadechapter02.ppt [read only]
- 1. Q I A 2 Fast & Easy ECGs – A Self-Paced Learning Program The Electrocardiogram
- 2. Electrocardiogram • A tracing of the heart’s electrical activity
- 3. Electrocardiograph • Detects heart’s electrical activity through electrodes positioned on patient’s skin I
- 4. ECG Paper I
- 5. ECG Paper • Each small square = 0.04 sec in duration and 0.1 mV in amplitude • Five small squares = One large box and 0.20 seconds in duration • Horizontal measurements determine heart rate I
- 6. Isoelectric Line • Flat line that occurs: – When no electrical activity is occurring – When impulses are too weak to be detected • Used as a baseline to identify changing electrical movement
- 7. P Wave • Produced by: – initiation of impulse in SA node – depolarization of RA and LA – Impulse passing through AV junction • Waveform is upright and round
- 8. PR Segment • Flat (isoelectric) line seen as impulse travels through His- Purkinje system
- 9. QRS Complex • Follows PR segment and consists of: – Q wave • First negative deflection following PR segment – R wave • First positive deflection following Q wave or PR segment – S wave • First negative deflection that extends below the baseline following the R wave I
- 10. ST Segment and T Wave • ST segment is flat line that follows QRS complex • T wave is larger, slightly asymmetrical waveform that follows ST segment I
- 11. QT Interval • The distance from onset of QRS complex until end of T wave – Measures time of ventricular depolarization and repolarization • Has normal duration of 0.36 to 0.44 seconds I
- 12. Typical ECG • Upright, round P waves occurring at regular intervals at a rate of 60 to 100 beats per minute • PR interval of normal duration (0.12 to 0.20 seconds) followed by a QRS complex of normal upright contour, duration (0.06 to 0.12 seconds) and configuration • Flat ST segment followed by an upright, slightly asymmetrical T wave
- 13. Calibration or Registration Mark • Helps ensure ECG machine is properly calibrated • Serves as reference point on ECG tracing I
- 14. Artifact • Markings on ECG tracing that are not a product of heart’s electrical activity – Patient movement is among its many causes – Can mimic life- threatening dysrhythmias I
- 15. ECG Machines • A variety of machines are available – Some monitor from one to five different leads – Others are capable of monitoring up to twelve or more leads simultaneously I
- 16. ECG Leads • Each lead provides a different view of the heart: – Electrodes are placed on chest, arms and legs – Sites vary depending on which view of the heart's electrical activity is being assessed I
- 17. ECG Leads • Direction an ECG waveform takes depends on whether electrical currents are traveling toward or away from a positive electrode I
- 18. ECG Leads • Planes provide a cross-sectional view of heart – Frontal plane – Horizontal plane I
- 19. Limb Leads • View the frontal plane • Include leads I, II, III, aVR, aVL and aVF • Provide inferior, superior, and lateral views of heart
- 20. Precordial Leads • View horizontal plane and include leads V1, V2, V3, V4, V5, and V6 • Provide inferior, superior, and lateral views of heart
- 21. Unipolar Leads • Use one positive electrode and a reference point which is calculated by the ECG machine
- 22. Uses for Different Leads • A given lead may be used to highlight: – A specific part of ECG complex – Electrical events of a specific cardiac cycle – Conditions such as an enlargement of heart muscle or presence of ischemia, injury and infarction I
- 23. Bipolar Leads • Record difference in electrical potential between a positive and negative electrode • Uses a third electrode called a ground • Include leads I, II and III I
- 24. Limb Leads - Lead I • Positive electrode - left arm (or under left clavicle) • Negative electrode - right arm (or below right clavicle) • Ground electrode - left leg (or left side of chest in midclavicular line just beneath last rib) • Waveforms are positive
- 25. Limb Leads - Lead II • Positive electrode - left leg (or on left side of chest in midclavicular line just beneath last rib) • Negative electrode - right arm (or below right clavicle) • Ground electrode - left arm (or below left clavicle) • Waveforms are positive
- 26. Limb Leads - Lead III • Positive electrode - left leg (or left side of the chest in midclavicular line just beneath last rib) • Negative electrode - left arm (or below left clavicle) • Ground electrode - right arm (or below right clavicle) • Waveforms are positive or biphasic
- 27. Limb Leads - Augmented Leads • Includes aVR, aVL and aVF • Unipolar • Enhanced by ECG machine because waveforms produced by these leads are normally small I
- 28. Limb Leads - Lead aVR • Positive electrode placed on right arm • Waveforms have negative deflection
- 29. Limb Leads - Lead aVL • Positive electrode placed on left arm • Waveforms have positive deflection
- 30. Limb Leads - Lead aVF • Positive electrode located on left leg • Waveforms have a positive deflection
- 31. Precordial Leads • Includes leads V1, V2, V3, V4, V5 and V6 • Positioned in order across the chest • Unipolar – Opposing pole is center of heart as calculated by ECG I
- 32. Modified Chest Leads (MCL) • MCL1 and MCL6 provide continuous cardiac monitoring • Place positive electrode in same position as precordial leads V1 or V6 I
- 33. Summary • Electrodes placed on patient’s skin detect heart’s electrical activity. • Graphic record or tracing is called an electrocardiogram. • Abnormalities in cardiac rate and/or rhythm are called dysrhythmias.
- 34. Summary • ECG paper consists of horizontal and vertical lines that form a grid. • Horizontal measurements used to determine heart rate and duration of various waveforms, segments and intervals. • Vertically on ECG paper, distance between lines, or boxes, represents amplitude in millimeters (mm) or electrical voltage in millivolts (mV).
- 35. Summary • Conduction of electrical impulse through the heart can be seen on ECG as P wave, PR interval, QRS complex, ST segment and T wave. • Artifact is markings on ECG tracing that have no relationship to electrical activity of the heart.
- 36. Summary • Each lead provides a different view of heart. • Impulses traveling toward a positive electrode are recorded on ECG as upward deflections. • Impulses traveling away from a positive electrode or toward a negative electrode are recorded as downward deflections.
- 37. Summary • Limb leads are produced by placing electrodes on right arm (RA), left arm (LA) and left leg (LL). – Include leads I, II, III, augmented vector right (aVR), augmented vector left (aVL) and augmented vector foot (aVF). • Precordial leads include leads V1, V2, V3, V4, V5, and V6.