2 Basics - ECG Leads The standard EKG has 12 leads: 3 Standard Limb Leads3 Augmented Limb Leads6 Precordial LeadsThe axis of a particular lead represents the viewpoint from which it looks at the heart.
7 What do they mean? P Wave. QRS Complex. Q Wave. T Wave. Caused by depolarization of the atria.With normal sinus rhythm, the P wave is upright in leads I, II, aVF, V4, V5, and V6 and inverted in aVR.QRS Complex.Represents ventricular depolarizationQ Wave.The first negative deflection of the QRS complex (not always present and, if present, may be pathologic).To be significant, the Q wave should be > 25% of the QRS complex.T Wave.Caused by repolarization of the ventricles and follows the QRS complexNormally upright in leads I, II, V3, V4, V5, and V6 and inverted in aVR
9 How to read an ECG systematically RateRhythmAxisInterval
10 1. Rate- Rule of 300Take the number of “big boxes” between neighboring QRS complexes, and divide this into The result will be approximately equal to the rateAlthough fast, this method only works for regular rhythms.
18 Lead II : sinus arrhythmia in a healthy 26 year-old woman Lead II : sinus arrhythmia in a healthy 26 year-old woman. Note the marked variation in the P-P intervals induced by respiration.Courtesy of Morton Arnsdorf, MD.Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.Courtesy of Morton Arnsdorf, MD.
21 3. The QRS AxisThe QRS axis represents the net overall direction of the heart’s electrical activity.Abnormalities of axis can hint at:Ventricular enlargementConduction blocks (i.e. hemiblocks)
22 The QRS AxisBy 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)
23 Determining the Axis Predominantly Positive Predominantly Negative Equiphasic
24 The Quadrant Approach1. 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.
25 The Quadrant Approach2. 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.
26 Quadrant Approach: Example 1 The Alan E. Lindsay ECG Learning CenterNegative in I, positive in aVF RAD
27 Quadrant Approach: Example 2 The Alan E. Lindsay ECG Learning CenterPositive in I, negative in aVF Predominantly positive in II Normal Axis (non-pathologic LAD)
28 4. Intervals PR <0.2 sec, QRS <0.12 sec, QT <0.4 sec P wave Always positive in leads I and IIAlways negative in lead aVR<3 small squares in duration<2.5 small squares in amplitudeQRSA normal QRS width should be less than 0.12 s.ST segmentNormally isoelectric
30 T waves Normal T wave is asymmetrical First half having more gradual slope than the second halfAmplitude rarely exceeds 10 mmAbnormal T waves are symmetrical, tall, peaked, biphasic or invertedAs a rule T waves follows direction of main QRS deflectionNormal T wave is always negative in lead aVR and positive in lead II
31 QT interval QT interval decreases when HR increases QT interval decreases when HR increasesShould not be more than half of the interval between adjacent R waves (R-R interval)
33 Acute anterior wall ST elevation MI (STEMI) Note the marked ST elevations and hyperacute T waves in the anterior/lateral leads, including V2-V5, I and aVL.
34 Acute transmural anterior wall myocardial infarction A chronic anterior wall infarction is diagnosed by the presence of initial deep and broad Q waves in any of the precordial leads; in this case they are present in leads V1 to V4.Chronic anterior wall myocardial infarction
35 ECG made easy page 138 (7th edn.) has list of all problems and what to expect on an ECG