Basics of ecg
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This document provides an overview of electrocardiography (ECG) basics for technicians. It discusses the heart's conduction system and how ECGs work to record electrical activity. The 12 standard ECG leads and their placements are described. Key aspects of normal ECG waveforms and intervals like P waves, QRS complex, T waves, and QT interval are explained. Common abnormalities that can cause changes in axis or abnormal complexes are also summarized. The document concludes with tips on interpreting ECGs and the important aspects to include in an ECG report.
Basics of ecg
- 1. DR. PALLAB KANTI NATH MBBS, MD (ANESTHESIOLOGY) CONSULTANT PAIN MEDICINE, ANESTHESIOLOGIST, INTENSIVIST Basics of Electrocardiography for Technicians
- 2. What will we learn? 1. Basics of the conduction system of heart 2. ECG leads and recording methodology 3. ECG waveforms and intervals 4. Normal ECG and its variants 5. Interpretation and reporting of an ECG
- 4. What is an ECG? Recording of the electrical activity heart. Graph of voltage versus time
- 6. BasicsBasics ECG graph: 1 mm Small squares 5 mm Large squares Paper Speed: 25 mm/sec standard Voltage Calibration: 10 mm/mV standard
- 7. ECG Paper: DimensionsECG Paper: Dimensions 5 mm 1 mm 0.1 mV 0.04 sec 0.2 sec Speed = rate Voltage ~Mass
- 8. ECG Leads Leads are electrodes which measure the potential difference between: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
- 9. ECG Leads The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads
- 11. Precordial Leads
- 12. Electrode name Electrode placement RA On the right arm, avoiding thick muscle. LA On the left arm, avoiding thick muscle. RL On the right leg, lateral calf muscle. LL On the left leg, lateral calf muscle. V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum (breastbone). V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum. V3 Between leads V2 and V4. V4 5th Intercostal space at the midclavicular line V5 Anterior axillary line at the same level as V4 V6 Midaxillary line at the same level as V4 and V5
- 13. Arrangement of Leads on the ECG
- 14. Arrangement on an ECG strip
- 15. Normal standardization 1 mV=10 mm Will result in perfect right angles at each corner
- 16. Overdamping and Underdamping Overdamping: When the pressure of the stylus is too firm on the paper so that it’s movements are retarded – deflection fractionally wider and diminished amplitude Unerdamping: When the writing stylus is not pressed firmly enough against the paper - sharp spikes at the corners
- 17. Standard sites unavailableAmputation/ burns/ bandages leads should be placed as closely as possible to the standard sites
- 18. Specific cardiac abnormalities dextrocardia right & left arm electrodes should be reversed pre-cordial leads should be recorded from V1R(V2) to V6
- 22. Artefacts on ECG Distorted signals caused by secondary internal or external sources, such as muscle movement or interference from an electrical device.
- 23. ECG Artefacts ECG tracing is affected by patient’s motion. rhythmic motions (shivering or tremors) can create the illusion of arrhythmia. May lead to: Altered diagnosis, treatment, outcome of therapy and legal liabilities
- 24. Reducing Artefacts during an ECG Patient Positioning Supine or semi-Fowler’s position. If patient can’t tolerate lying flat, do the ECG in a more upright position. Instruct patient to place arms down by his side and to relax the shoulders. Patient’s legs should be uncrossed. Place electrical devices, such as cell phones, away from the patient as they may interfere with the machine.
- 25. Reducing Artefacts during an ECG Skin Preparation Dry the skin if it’s moist or diaphoretic. Shave any hair that interferes with electrode placement. ensures a better electrode contact with the skin. Rub an alcohol prep pad or benzoin tincture on the skin to remove any oils and help with electrode adhesion.
- 26. Reducing Artefacts during an ECG Electrode Application Check the electrodes to make sure the gel is still moist. Do not place the electrodes over bones. Do not place the electrodes over areas where there is a lot of muscle movement.
- 27. Interpretation of an ECG Heart Rate Rhythm Axis Wave morphology Intervals and segments analysis Specific changes (If any)
- 29. Determining the Heart Rate Rule of 300 10 Second Rule
- 30. Rule of 300 Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate Although fast, this method only works for regular rhythms.
- 31. The Rule of 300 It may be easiest to memorize the following table: # of big# of big boxesboxes Rate (appx)Rate (appx) 11 300300 22 150150 33 100100 44 7575 55 6060 66 5050
- 32. Rule of 300
- 33. 10 Second Rule As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms.
- 34. QRS axis The QRS axis represents the net overall direction of the heart’s electrical activity. Abnormalities of axis can hint at: Ventricular enlargement Conduction blocks (i.e. hemiblocks)
- 35. The QRS Axis By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. -30° to -90° is referred to as a left axis deviation (LAD) +90° to +180° is referred to as a right axis deviation (RAD)
- 36. Determining the Axis The Quadrant Approach The Equiphasic Approach
- 38. The Quadrant Approach Examine the QRS complex in leads I and aVF to determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.
- 39. Using leads I, II, III LEAD 1LEAD 1 LEAD 2LEAD 2 LEAD 3LEAD 3 NormalNormal UPRIGHTUPRIGHT UPRIGHTUPRIGHT UPRIGHTUPRIGHT PhysiologicaPhysiologica l Left Axisl Left Axis UPRIGHTUPRIGHT UPRIGHT /UPRIGHT / BIPHASICBIPHASIC NEGATIVENEGATIVE PathologicalPathological Left AxisLeft Axis UPRIGHTUPRIGHT NEGATIVENEGATIVE NEGATIVENEGATIVE Right AxisRight Axis NEGATIVENEGATIVE UPRIGHTUPRIGHT BIPHASICBIPHASIC NEGATIVENEGATIVE UPRIGHTUPRIGHT ExtremeExtreme Right AxisRight Axis NEGATIVENEGATIVE NEGATIVENEGATIVE NEGATIVENEGATIVE
- 40. Common causes of LAD May be normal in the elderly and very obese High diaphragm during pregnancy, ascites, or Abdominal tumors Inferior wall MI Left Anterior Hemiblock Left Bundle Branch Block WPW Syndrome Emphysema
- 41. Common causes of RAD Normal variant Right Ventricular Hypertrophy Anterior MI Right Bundle Branch Block Left Posterior Hemiblock WPW Syndrome
- 42. Normal Sinus Rhythm Originates in the SA node Rate between 60 and 100 beats per min Tallest p waves in Lead II Monomorphic P waves Normal PR interval of 120 to 200 msec Normal relationship between P and QRS Some sinus arrhythmia is normal
- 43. Normal QRS complex Completely negative in lead aVR , maximum positivity in lead II rS in right oriented leads and qR in left oriented leads (septal vector) Transition zone commonly in V3-V4 RV5 > RV6 normally Normal duration 50-110 msec, not more than 120 msec Physiological q wave not > 0.03 sec
- 44. QRS Complex
- 45. Amplitude of QRS Formed by electrical force generated by the ventricular myocardium Depends on: distance of the sensing electrode from the ventricles Body build - a thin individual has larger complexes when compared to obese individuals
- 46. Normal T wave Same direction as the preceding QRS complex Blunt apex with asymmetric limbs Height < 5mm in limb leads and <10 mm in precordial leads Smooth contours May be tall in athletes
- 47. QT interval The beginning of the QRS complex is best determined in a lead with an initial q wave leads I,II, avL ,V5 or V6 QT interval shortens with tachycardia and lengthens with bradycardia Normal 350 to 430 msec With a normal heart rate (60 to 100), the QT interval should not exceed half of the R-R interval roughly
- 48. QT Interval
- 49. Reporting an ECG
- 50. “ WHOSE ECG IS IT ?!” 1. Patient Details
- 51. “IS IT PROPERLY TAKEN ?” 2. Standardisation and lead placement
- 53. NORMAL OR ABNORMAL? 4. Segment and wave form analysis
- 54. “ DOES THE ECG CORRELATE WITH THE CLINICAL SCENARIO ?” Final Impression
- 55. Thank you !
Editor's Notes
- #10: Limb leads: Leads I, II and III are called the limb leads. The electrodes that form these signals are located on the limbs—one on each arm and one on the left leg. The limb leads form the points of what is known as Einthoven&apos;s triangle. Augmented limb leads: Leads aVR, aVL, and aVF are the augmented limb leads. They are derived from the same three electrodes as leads I, II, and III, but they use Goldberger&apos;s central terminal as their negative pole which is a combination of inputs from other two limb electrodes. Precordial leads: The precordial leads lie in the transverse (horizontal) plane, perpendicular to the other six leads. The six precordial electrodes act as the positive poles for the six corresponding precordial leads: (V1, V2, V3, V4, V5 and V6). Wilson&apos;s central terminal is used as the negative pole.
- #11: Einthoven&apos;s triangle is an imaginary formation of three limb leads in a triangle It is formed by the two shoulders and the pubis. The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed It is named after Willem Einthoven who theorized its existence
- #35: -0