ECG basics
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The document provides a detailed overview of electrocardiogram (ECG) fundamentals, including waveforms, leads, and heart rhythm determination. It discusses the significance of different ECG components like the P wave, QRS complex, and T wave while also addressing potential pathologies and their implications. Key methods for interpreting heart rate and QRS axis deviations are outlined, along with conditions associated with abnormal wave patterns.
ECG basics
- 2. • Review of the conduction system • ECG waveforms and intervals • ECG leads • Determining heart rhythm / rate • Determining QRS axis • Normal waves / intervals
- 4. The electrocardiogram (ECG) is a representation of the electrical events of the cardiac cycle. Each event has a distinctive waveform, the study of which can lead to greater insight into a patient’s cardiac pathophysiology.
- 5. Runs at a paper speed of 25 mm/sec • Each small block of ECG paper is 1 mm2 • At a paper speed of 25 mm/s, one small block equals 0.04 s • Five small blocks make up 1 large block which translates into 0.20 s (200 msec) • Hence, there are 5 large blocks per second • Voltage: 1 mm = 0.1 mV between each individual block vertically
- 7. • Arrhythmias • Myocardial ischemia and infarction • Pericarditis • Chamber hypertrophy • Electrolyte disturbances (i.e. hyperkalemia, hypokalemia) • Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)
- 10. • 3 distinct waves are produced during cardiac cycle • P wave caused by atrial depolarization 13-63
- 11. • QRS complex caused by ventricular depolarization
- 12. • T wave results from ventricular repolarization 13-63
- 13. Leads are electrodes which measure the difference in electrical potential between either: 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)
- 14. The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads The axis of a particular lead represents the viewpoint from which it looks at the heart.
- 22. Limb Leads Precordial Leads Bipolar I, II, III - (standard limb leads) Unipolar aVR, aVL, aVF V1-V6 (augmented limb leads)
- 24. (Septum)
- 25. (Anterior Wall)
- 26. (Lateral Wall)
- 27. (Inferior Wall)
- 29. Normal Sinus Rhythm Each P wave is followed by a QRS o P wave rate 60 - 100 bpm with <10% variation o rate <60 = sinus bradycardia o rate >100 = sinus tachycardia o variation >10% = sinus arrhythmia
- 30. • Rule of 300 • 10 Second Rule
- 31. Take the number of “big boxes” between neighboring QRS complexes, and divide 300 into this number. The result will be approximately equal to the rate Although fast, this method only works for regular rhythms.
- 32. (300 / 6) = 50 bpm
- 33. (300 / ~ 4) = ~ 75 bpm
- 34. (300 / 1.5) = 200 bpm
- 35. It may be easiest to memorize the following table: # of big Rate boxes 1 300 2 150 3 100 4 75 5 60 6 50
- 36. As most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms.
- 37. The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ 33 x 6 = 198 bpm
- 38. 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)
- 39. 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)
- 40. • The Quadrant Approach • The Equiphasic Approach
- 41. Predominantly Predominantly Equiphasic Positive Negative
- 42. 2. In the event that LAD is present, examine lead II to determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it is pathologic.
- 43. The Alan E. Lindsay ECG Learning Center http://medstat.med.utah. edu/kw/ecg/ Negative in I, positive in aVF RAD
- 44. The Alan E. Lindsay ECG Learning Center http://medstat.med.utah. edu/kw/ecg/ Positive in I, negative in aVF Predominantly positive in II Normal Axis (non-pathologic LAD)
- 45. 1. Determine which lead contains the most equiphasic QRS complex. The fact that the QRS complex in this lead is equally positive and negative indicates that the net electrical vector (i.e. overall QRS axis) is perpendicular to the axis of this particular lead. 2. Examine the QRS complex in whichever lead lies 90° away from the lead identified in step 1. If the QRS complex in this second lead is predominantly positive, than the axis of this lead is approximately the same as the net QRS axis. If the QRS complex is predominantly negative, than the net QRS axis lies 180° from the axis of this lead.
- 47. The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ Equiphasic in aVF Predominantly positive in I QRS axis ≈ 0
- 48. The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ Equiphasic in II Predominantly negative in aVL QRS axis ≈ +150°
- 49. Normal P Waves height < 2.5 mm in lead II (higher = ? P-pulmonale) width < 0.11 s in lead II (wider = ? P-mitrale) Normal PR interval 0.12 to 0.20 s (3 - 5 small squares) Short PR interval (Wolff-Parkinson-White syndrome / Lown-Ganong-Levine syndrome) Long PR interval (first degree heart block / 'trifasicular' block)
- 51. P - mitrale Long P-R
- 52. Normal QRS complex < 0.12 s duration (3 small squares) No pathological Q waves Pathologic “Q”: - > 0.04 sec (small box) - > 25% of “R” amplitude Wide QRS (right or left bundle branch block, ventricular rhythm, hyperkalemia) o No evidence of left or right ventricular hypertrophy
- 53. Normal LVH
- 54. Wide Complex Pathologic “Q” wave
- 55. Normal QT interval: – Males: < 450 ms. – Females: < 470 ms. o Calculate the corrected QT interval (QTc) by dividing the QT interval by the square root of the preceeding R - R interval. o Long QT interval is a risk factor for VT / Torsades de Pointes. o Long QT interval (MI, myocarditis, diffuse myocardial disease / hypocalcaemia / hypothyrodism / intracerebral haemorrhage / drugs (sotalol, amiodarone) / hereditary (Romano Ward syndrome (autosomal dominant) / Jervill Lange Nielson syndrome (autosomal recessive)
- 57. Normal ST segment no elevation or depression ST elevation: acute MI / left bundle branch block, normal variants (e.g. athletic heart) acute pericarditis ST depression: myocardial ischaemia, digoxin effect / ventricular hypertrophy / acute posterior MI / right bundle branch block
- 58. Normal ST ST depression ST elevation
- 59. Normal T wave: variable morphology & amplitude / usually same direction as the QRS except in V1-2 leads. In the normal ECG the T wave is always upright in leads I, II, V3-6, and always inverted in lead aVR. Tall T: hyperkalemia / hyperacute myocardial infarction. Small, flattened or inverted T waves: ischaemia / LVH / drugs (e.g. digoxin) / pericarditis / PE / RBBB / electrolyte disturbance. Normal U wave: usually < 1/3 T wave amplitude & same direction in the same lead / prominent at slow heart rates. o Origin of the U wave is thought to be related to after depolarizations which interrupt or follow repolarization
- 60. The U Wave