17. ECG Leads which measure the difference in electrical potential between two points 1. Bipolar Leads: Two different points on the body 2. Unipolar Leads : One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart
18. ECG Leads The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads
70. Goldberger AL. Goldberger: Clinical Electrocardiography: A Simplified Approach. 7th ed: Mosby Elsevier; 2006. Variable Shapes Of ST Segment Elevations in AMI
87. Normal QRS axis 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) The QRS Axis
Atrial depolarisation Electrically both atria act almost as one. They have relatively little muscle and generate a single, small P wave. P wave amplitude rarely exceeds two and a half small squares (0.25 mV). The duration of the P wave should not exceed three small squares (0.12 s). The wave of depolarisation is directed inferiorly and towards the left, and thus the P wave tends to be upright in leads I and II and inverted in lead aVR. Sinus P waves are usually most prominently seen in leads II and V1. A negative P wave in lead I may be due to incorrect recording of the electrocardiogram (that is, with transposition of the left and right arm electrodes), dextrocardia, or abnormal atrial rhythms. Normal P waves may have a slight notch, particularly in the precordial (chest) leads. Bifid P waves result from slight asynchrony between right and left atrial depolarisation. A pronounced notch with a peaktopeak interval of > 1 mm (0.04 s) is usually pathological, and is seen in association with a left atrial abnormality—for example, in mitral stenosis.
The R wave in lead V6 is smaller than the R wave in V5, since the V6 electrode is further from the left ventricle. The depth of the S wave, generally, should not exceed 30 mm in a normal individual (although > 30 mm are occasionally recorded in normal young male adults) In another website it is also shown that small q wave seen in leads III and aVF Normal q-waves reflect normal septal activation (beginning on the LV septum); they are narrow (<0.04s duration) and small (<25% the amplitude of the R wave). They are often seen in leads I and aVL when the QRS axis is to the left of +60o, and in leads II, III, aVF when the QRS axis is to the right of +60o. Septal q waves should not be confused with the pathologic Q waves of myocardial infarction (http://medstat.med.utah.edu/kw/ecg/ecg_outline/Lesson3/index.html)
Sokolow + Lyon (Am Heart J, 1949;37:161) S V1+ R V5 or V6 > 35 mm Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm S V1 or V2 + R V5 or V6 > 35 mm R I + S III > 25 mm Romhilt + Estes (Am Heart J, 1986:75:752-58) Point score system
Sokolow + Lyon (Am Heart J, 1949;37:161) S V1+ R V5 or V6 > 35 mm Cornell criteria (Circulation, 1987;3: 565-72) SV3 + R avl > 28 mm in men SV3 + R avl > 20 mm in women Framingham criteria (Circulation,1990; 81:815-820) R avl > 11mm, R V4-6 > 25mm S V1-3 > 25 mm S V1 or V2 + R V5 or V6 > 35 mm R I + S III > 25 mm Romhilt + Estes (Am Heart J, 1986:75:752-58) Point score system
ST segment depression is always an abnormal finding, although often nonspecific (http://medstat.med.utah.edu/kw/ecg/ecg_outline/Lesson3/index.html)
As a general rule, T wave amplitude corresponds with the amplitude of the preceding R wave, though the tallest T waves are seen in leads V3 and V4. Tall T waves may be seen in acute myocardial ischaemia and are a feature of hyperkalaemia.
Poor Man's Guide to upper limits of QT: For HR = 70 bpm, QT<0.40 sec; for every 10 bpm increase above 70 subtract 0.02 sec, and for every 10 bpm decrease below 70 add 0.02 sec. For example: QT < 0.38 @ 80 bpm QT < 0.42 @ 60 bpm
