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Update in Electrocardiography & Arrhythmias, 2011 ECG Case Review Basic 10:45 - 12:00 pm Prof. Barbara J. Drew University of California, San Francisco Standard 12-Lead ECG Frontal Plane _ _ Horizontal Plane _ + aVR + aVL LV V6 _ +I V5 _ _ + III + aVF + II Limb Leads V1 V2 V3 V4 Precordial Leads 1 Three things you have to know to figure out what the waveforms should look like in a given ECG lead: 1. How the heart is positioned in the chest 2. Where the positive and negative poles of the lead are 3. How the cardiac impulse is moving through the heart (i.e., sinus vs. ectopic rhythm) - V + 2 - + V - V V + 3 Right-Left & Superior-Inferior Limb Leads in the Frontal Plane S R L I What direction would limb leads be blind to? Answer: Anterior-Posterior What would the limb leads record if a current of myocardial injury flowed anteriorly? Frontal Plane _ _ _ + aVR + aVL _ +I _ _ + III + aVF + II Limb Leads Limb leads are blind to this acute anterior myocardial infarction 4 Precordial Leads in the Horizontal Plane Right - Left & Anterior - Posterior P L R V6 A V5 V1 V2 V3 V4 What direction would precordial leads be blind to? Answer: Superior-Inferior What would the precordial leads record if a current flowed inferior, then superior? Horizontal Plane V6 V5 LV V1 V2 V3 V4 Precordial leads are blind to superior-inferior atrial motion in atrial flutter 5 Limb Leads Lead I ─ RA Lead II LA RL + ─ RA Lead aVR + RA LA RL LL LA LL RA + LL RA LA LA RL Lead aVL LL ─ + Lead aVF + RA ─ LA ─ ─ RL Lead III RL LL RL LL + For resting “diagnostic” 12-lead ECGs, limb electrodes go on the extremity (not the torso) 6 7 8 Hexaxial System in the Frontal Plane _ _ _ + aVR + aVL _ +I _ _ + III + aVF + II 9 - Lead II + Determination of QRS Axis If patient is in sinus rhythm, assume lead wire reversal; repeat ECG Left Left Extreme Left Left Extreme Normal Right Right Normal Right 10 Determination of QRS Axis Step One: Determine whether normal, left, right, or extreme by checking QRS polarity in leads I and II - - - -Normal Axis 11 Left Axis Right Axis 12 Extreme Axis Summary of “Quick-Look” Method Lead I Lead II Normal Axis LAD RAD Right Superior Axis Indeterminate Axis 13 Practice ECGs for axis calculation Determination of QRS Axis Step Two: Determine degrees by checking polarity of the lead 90° from the lead with an isoelectric (or smallest) QRS 14 WNL +60° 15 +40° LAD 16 -70° RAD 17 +100° Right superior axis 18 ±180° RA-LA Lead-Wire Reversal + LA RA ─ Lead I Would RA-LA reversal alter precordial leads? 19 V6 ─ + V5 V1 + V2 + V3 + V4 + + PRECORDIAL LEADS The negative pole for precordial leads is the Wilson Central Terminal (combination of 3 limb leads into the negative pole) Negative pole located within the heart 20 RA-LA Lead-Wire Reversal + LA RA ─ Lead I NO Would RA-LA reversal alter precordial leads? Lead I - _ +I Dextrocardia 21 V6 V5 V1 V2 V3 V4 Dextrocardia alters the precordial leads as well as the limb leads Learn this “drill” Whenever you see a negative QRS in lead I, examine the P wave to see if it is also negative. If it is normal (positive), the patient just has an abnormal QRS axis. However, if the P wave is also negative, one of 2 things is possible: 1) RA-LA leadwire reversal, or 2) dextrocardia (heart is in a mirror-image position in the chest) 22 Determining Lead-Wire Reversal versus Dextrocardia RA-LA Lead Wire Reversal Dextrocardia Lead V6 Full 12-lead ECG in the same patient What is the diagnosis? Answer: Dextrocardia 23 Confirming Dextrocardia with Right Precordial Leads Standard Precordial Leads Right Precordial Leads Same patient with right ventricular leads recorded 24 Happy Halloween! 25