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ECG- ELECTROCARDIOGRAM basics and interpretation
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- 8. • The standardECG has 12 leads. Six of the leads are considered “limb leads” because they are placed on the arms and/or legs of the individual. The other six leads are considered “precordial leads” because they are placed on the torso (precordium). • The six limb leads are called lead I, II, III, aVL, aVR and aVF. The letter “a” stands for “augmented,” as these leads are calculated as a combination of leads I, II and III. • The six precordial leads are called leads V1, V2, V3, V4, V5 and V6.
- 17. • A normalECG contains waves, intervals, segments and one complex, as defined below. • Wave: A positive or negative deflection from baseline that indicates a specific electrical event. The waves on an ECG include the P wave, Q wave, R wave, S wave, T wave and U wave. • Interval: The time between two specific ECG events. The intervals commonly measured on an ECG include the PR interval, QRS interval (also called QRS duration), QT interval and RR interval. • Segment: The length between two specific points on an ECG that are supposed to be at the baseline amplitude (not negative or positive). The segments on an ECG include the PR segment, ST segment and TP segment. • Complex: The combination of multiple waves grouped together. The only main complex on an ECG is the QRS complex. • Point: There is only one point on an ECG termed the J point, which is where the QRS complex ends and the ST segment begins. • The main part of an ECG contains a P wave, QRS complex and T wave. Each will be explained individually in this tutorial, as will each segment and interval. • The P wave indicates atrial depolarization. The QRS complex consists of a Q wave, R wave and S wave and represents ventricular depolarization. The T wave comes after the QRS complex and indicates ventricular repolarization.
- 23. • P wave- atrial depolarisation - amplitude- 0.05 to 0.25 mV - duration- 0.08 to 0.10 seconds - Always positive in lead 1 and 2 in NSR - Always negative in AVR - Biphasic in V1 - First portion-right atrial depolarisation and terminal portion left atrial depolarisation. - P mitrale / P pulmonale - Sinus rhythm – P followed by QRS - No P waves means….?
- 24. • QRS wave– ventricular depolarisation - duration-0.06 to 1.2 s - broad/ morphology FIRST NEGATIVE? FIRST POSITIVE? q or Q r or R what is QS?
- 25. • T wave- Ventricular repolarisation • QT interval
- 28. • Name • Gender •Age • Date • Clinical history/ Examination • Indication for ECG
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- 30. 2.Rate • Count thenumber of QRS cycles on a 6- second strip and multiply that number by 10 to roughly estimate the rate. • Rate=1500/number of small squares between two R waves.
- 31. 3.Rhythm • Determine whethereach QRS is preceded by a P wave, look for variation in the PR interval and RR interval (the duration between two QRS cycles), and look for ectopic beats. • So, by doing this you comment- if the rhythm is regular sinus rhythm or not.
- 32. 4.Axis • If theQRS is upright (more positive than negative) in leads I and aVF, the axis is normal. The normal axis range is –30 degrees to +90 degrees.
- 33. Determination of Axis •Quadrant method • Lead 1 and aVF • Lead 1, 2 and aVF • Isoelectric lead method • Looking at lead 1 and lead 3- see if they are reaching each other( right axis deviation) or leaving each other ( left axis deviation).
- 34. 5.Waves, Complexes andIntervals • Waves- P and T waves • QRS complex- QRS • Intervals-PR and QT intervals. Intervals are measured in the limb leads. The PR should be 0.12–0.20. The QT interval increases with decreasing heart rate, usually < 0.44 s. The QT interval usually does not exceed one half of the RR interval (the distance between two R waves).
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- 36. ATRIAL FIBRILLATION • Normallysinus impulse transmitted uniformly, evenly and contiguously to all parts of the atria. • In AF excitation and recovery of the atria are disorganized and chaotic. • Atria functionally fractionated into numerous tissue islets in various stages of excitation and recovery. • These excitatory wavelets course irregularly through the atria and reach AV node at frequent and irregular intervals.
- 37. • 400 –600 per minutes may reach the AV node. • But the AV node ca conduct only some because following conduction of one such stimulus, it is refractory for a short period and impulses reaching the AV node are blocked. • The refractory period varies with multiple factors- transmision irregular
- 38. How does theECG look? • Ragged , irregular baseline • No p waves • Varying RR interval • Irregularly irregular • AF with FVR • AF with CVR • Long standing – slow rate
- 45. Left Ventricular Hypertrophy •Systolic overload –resistance to outflow • Diastolic overload- overfilling
- 47. LVH-systolic overload-strain pattern • Increasedmagnitude of QRS deflexions • S in V1 + R in V6 more than 35 mm • R in lead 1 , aVL more than 15 mm • R in V6 more than R in V5 • R in aVL is or more than 11 mm • Total QRS voltage – all 12 leads more than 175 mm
- 48. …some more • Attenuationof initial q wave in left oriented leads • Increase in left ventricular activation time- beginning of QRS complex to the apex of R. More than 0.05 sec in LVH • Small equiphasic rs complex in Avf • Counter clockwise rotation- transition zone shifted to patients right- V3 or even V2
- 49. • General principle-T wave force directed away from diseased or compromised region • Hypertrophied ventricle is under strain • T wave directed away from left and towards the right. • T waves inverted in left oriented leads- V5, V6, lead 1, aVL and they will be upright in right oriented leads- V1, V2 and aVR • Left atrial enlargement- wide notched P in lead 1 and prominent delayed terminal deflexion in V1
- 50. Romhilt and Estespoint score system(systolic mainly) • Increased QRS magnitude- 3 points • ST-T abnormalities- 3 points • P wave of left atrial enlargement- 3 points • Left axis deviation- 2 points • Increased ventricular activation time- 1 point • Score of 5 or more - LVH
- 51. Diastolic overload • TallR waves in right sided leads- 40 / 50 mm • Deep S waves in left sided leads- except in mitral incompetence • Deep narrow waves in left oriented leads 2- 4 mm in depth but may reach 5- 10 mm • Tall symmetrical T waves in left precordial leads • Minimally elevated ST segments in left leads- concave upward -1 mm J point elevation • Inverted U waves V4 to V6
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- 62. • The sequenceof features characteristic of full thickness/ ST elevation/ transmural myocardial infarction - Normal ECG - Hyperacute Ischemia - tall t waves - ST segment elevation - Development of Q waves - ST segment returns to baseline - T become inverted The leads that show the typical changes depends on the part of the heart affected
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- 66. • Infarction orIschemia. Check for ST-segment elevation or depression, Q waves, inverted T waves, and poor R-wave progression in the precordial leads.
- 67. Right ventricular Hypertrophy •RVH is diagnosed on ECG in the presence of a R/S ratio of greater than 1 in lead V1 in the absence of other causes. • R wave in lead V1 is greater than 7 millimeters tall. • The strain pattern occurs when the right ventricular wall is quite thick, and the pressure is high, as well. • Strain causes ST segment depression and asymmetric T wave inversions in leads V1 to V3. • Persistent S wave in V6
- 68. Other causes ofan R/S ratio of greater than 1 in lead V1: • Posterior wall myocardial infarction (also causes ST segment depression in V1-V3, but T waves are symmetrically inverted, and the patient would be presenting with chest pains) • Right bundle branch block • Wolff-Parkinson-White Type A • Lead misplacement (if V1 is placed too high) • Isolated posterior wall hypertrophy (occurs in Duchenne’s muscular dystrophy)
- 71. Supraventricular Tachycardia • Supraventriculartachycardia (SVT) is an abnormally fast heart rhythm arising from improper electrical activity in the upper part of the heart. • There are four main types: - atrial fibrillation, - paroxysmal supraventricular tachycardia (PSVT), - atrial flutter, and - Wolff–Parkinson–White syndrome. Symptoms may include palpitations, feeling faint, sweating, shortness of breath, or chest pain.
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- 77. Don’t show • Regulartachycardia ~140-280 bpm. • QRS complexes usually narrow (< 120 ms) unless pre-existing bundle branch block, accessory pathway, or rate related aberrant conduction. • ST-segment depression may be seen with or without underlying coronary artery disease.
- 78. Don’t show • QRSalternans – phasic variation in QRS amplitude associated with AVNRT and AVRT, distinguished from electrical alternans by a normal QRS amplitude. • P waves if visible exhibit retrograde conduction with P-wave inversion in leads II, III, aVF. • P waves may be buried in the QRS complex, visible after the QRS complex, or very rarely visible before the QRS complex.
- 79. RBBB- Right BundleBranch Block
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- 84. • When facedwith an ECG with broad QRS complex- look at the QRS in V1- if positive- think of RBBB. If negative – think of LBBB. • If you find a S wave in lead 1- normal QRS duration – look at lead V1- look for criteria for RVH. • If you find a broad S in lead 1 , look at slurred S wave in V6. This along with rsR’ pattern in lead V1, confirms RBBB