ECG 101 QRS Axis Determination Scott E Ewing

ECG 101 - QRS Axis Determination Scott E. Ewing DO Lecture #3

Review ECG Frontal Plane n Rate n Rhythm n

ECG Frontal Plane

Rate

Normal Sinus Rhythm

Question n Why are the rhythm strips usually Leads II and V 1?

8 -Step Method ECG Interpretation 1. 2. 3. 4. 5. 6. 7. 8. Rate Rhythm QRS Axis P wave PR interval QRS complex QT interval ST segment and T wave

QRS Complex n QRS Axis Represents direction of the mean QRS vector in the frontal plane n Determined using hexaxial reference system derived from the Einthoven equilateral triangle n

QRS Complex n Normal QRS axis is 30° to 100° Axis is usually shifted leftward with age n In individuals < 30, axis is seldom superior to 0° (normal 0° to 100°) n In individuals > 40, axis is seldom to right of 90° (normal 30° to 90°) n

QRS Complex n There is an association between QRS axis and body weight Thinner persons tend to have more vertical axes (toward 90°, or rightward) n Obese persons tend to have more horizontal axes (toward 0°, or leftward) n n There is no significant gender difference in the axis

QRS Axis n n Positive pole of each lead axis (solid line) and negative pole (hatched line) are designated by their angular position relative to the positive pole of lead I (0°) Mean electrical axis of the QRS complex is measured with respect to this display

Why Determine the Axis? Conduction defects – left anterior and posterior fasicular block n Ventricular enlargement – left and right ventricular hypertrophy n Broad complex tachycardia – bizarre axis suggestive of ventricular origin n Congenital heart disease – atrial septal defects n Pre excited conduction – Wolff Parkinson White syndrome n Pulmonary embolus, lateral / inferior wall MI n

Left Axis Deviation n n n n Artificial cardiac pacing Ascites COPD Expiration High diaphragm Hyperkalemia Inferior myocardial infarction Left anterior hemiblock Left atrial hypertrophy n n n n Left Bundle Branch Block Left ventricular hypertrophy Normal variations Ostium primum atrial septal defect (ASD) Right ventricular ectopic rhythms Tricuspid atresia Wolff Parkinson White Syndrome

Right Axis Deviation n n n n Anterolateral myocardial infarction Atrial Septal Defect COPD Dextrocardia Inspiration Left posterior hemiblock Left ventricular ectopic rhythms Left ventricular failure with right ventricular strain n n n n Normal variation (children, tall thin adults) Pulmonary Embolus Pulmonary Hypertension Right Bundle Branch Block Right ventricular hypertrophy Switched electrodes Ventricular Septal Defect (VSD) Wolff Parkinson White Syndrome

Extreme Axis Deviation n n Artificial cardiac pacing COPD Hyperkalemia Lead transposition Ventricular tachycardia

QRS Axis Determination n n Lead orientation Normal axis 30° to 100° a. VR a. VL I III a. VF II

QRS Axis Determination - Approach n 1 st Method (Quick) n n 2 nd Method n n n Is it normal? Use algebraic sum of the deflections in 2 leads, usually I and a. VF Plot out axis 3 rd Method n n Find lead with isoelectric complex QRS is perpendicular to this lead, with positive terminus pointing toward lead with largest net positive deflection

QRS Axis Determination - Quick Method n n n Lead I lies at 0° If the QRS in Lead I is mainly positive (even if a. VR only slightly) it means the axis will be anywhere between 90° to 90° Now, look at Lead II a. VL I III a. VF II

QRS Axis Determination - Quick Method n n Lead II lies at 60° If the QRS in Lead II is mainly positive (even if a. VR only slightly) then the axis can be anywhere between 30° to 150° a. VL I III a. VF II

QRS Axis Determination - Quick Method n n n If Lead I is positive the axis is between 90° and a. VR 90° If Lead II is positive the axis is between 30° and 150° Combined, the axis must lie between 30° and 90° a. VL I III a. VF II

Normal or Abnormal Axis?

QRS Axis Determination - Approach n 1 st Method (Quick) n n 2 nd Method n n n Is it normal? Use vector sum of the deflections in 2 leads, usually I and a. VF Plot out axis 3 rd Method n n Find lead with isoelectric complex QRS is perpendicular to this lead, with positive terminus pointing toward lead with largest net positive deflection

QRS Axis Determination - Using Leads I and a. VF 30° 0° Lead I 100° 90° Lead a. VF

Case #1

QRS Axis Determination - Case #1 n n n Lead I corresponds to the x axis Sum the total positive and negative deflection 8 mm in this case Lead I

QRS Axis Determination - Case #1 n n n Lead a. VF corresponds to the y axis Sum the total positive and negative deflection 9 mm in this case Lead a. VF

QRS Axis Determination – Case #1 Plot Results 30° 0° Lead I 100° 90° Lead a. VF

Case #2

QRS Axis Determination - Case #2 n n n Lead I corresponds to the x axis Sum the total positive and negative deflection 9 – 5 = 4 mm in this case Lead I

QRS Axis Determination - Case #2 n n n Lead a. VF corresponds to the y axis Sum the total positive and negative deflection 4 2 = 2 mm in this case Lead a. VF

QRS Axis Determination – Case #2 Plot Results 30° 0° Lead I 100° 90° Lead a. VF

Case #3

QRS Axis Determination - Case #3 n n n Lead I corresponds to the x axis Sum the total positive and negative deflection 6 mm in this case Lead I

QRS Axis Determination - Case #3 n n n Lead a. VF corresponds to the y axis Sum the total positive and negative deflection 0 7 = 7 mm in this case Lead a. VF

QRS Axis Determination – Case #3 Plot Results 30° 0° Lead I 100° 90° Lead a. VF

Case #3

QRS Axis Determination - Using Leads I and III 30° 0° Lead I 120° Lead III 100°

QRS Axis Determination n Lead I corresponds to the x axis Sum the total positive and negative deflection 6 mm in this case Lead I

QRS Axis Determination n Lead III corresponds to the y axis Sum the total positive and negative deflection 0 11 = 11 mm in this case Lead III

QRS Axis Determination - Using Leads I and III 30° 0° Lead I 120° Lead III 100°

Same Results?

QRS Axis Determination

QRS Axis Determination - Approach n 1 st Method (Quick) n n 2 nd Method n n n Is it normal? Use algebraic sum of the deflections in 2 leads, usually I and a. VF Plot out axis 3 rd Method n n Find lead with isoelectric complex QRS is perpendicular to this lead, with positive terminus pointing toward lead with largest net positive deflection

QRS Axis Determination n n Find the isoelectric lead if there is one (i. e. the lead with equal forces in the positive and negative direction) Often this is the lead with the smallest QRS axis is perpendicular to that lead's orientation Since there are two perpendiculars to each isoelectric lead, choose the perpendicular that best fits the direction of the other ECG leads If there is no isoelectric lead, there are usually two leads that are nearly isoelectric and these are always 30° apart

QRS Axis Determination - Using Isoelectric Lead a. VR a. VL I III a. VF II

Case #1

QRS Axis Determination - Case #1 n n Lead a. VL = 30° is the most isoelectric lead Lead II is perpendicular at 60° (and 240°) Lead a. VL

QRS Axis Determination - Case #1 n n n Lead II positive Axis is close to 60° What if Lead II had total negative deflection? n Axis closer to 240° Lead II

QRS Axis Determination - Case #1 a. VL isoelectric II – axis near here

QRS Axis Determination - With Original Findings a. VL isoelectric II – axis near here

Case #3

QRS Axis Determination - Using Isoelectric Lead a. VR a. VL I III a. VF II

QRS Axis Determination - Case #3 n n Lead II = 60° is the most isoelectric lead Lead a. VL is perpendicular at 30° (and 150°) Lead II

QRS Axis Determination - Case #3 n n n Lead a. VL positive Axis is close to 30° What if Lead a. VL had net negative deflection? n Axis closer to 150° Lead a. VL

QRS Axis Determination - Case #3 a. VL – axis near here II – isoeletric

QRS Axis Determination - With Original Findings a. VL – axis near here II – isoeletric

QRS Axis Determination Isoelectric lead approach is tricky at first since often a true isoelectric lead is not present n Choose the best and look at the “next door” lead n If “next door” is opposite positive / negative, then you know the isoelectric direction is “inbetween” the two n The correct axis is adjusted accordingly n

Axis?

Axis?

Axis?

Questions? ? ?