Practical Electrocardiography - QRS Axis Determination Scott Ewing, D.O. Cardiology Fellow August 9, 2006

From Last Time Why is the rhythm strip usually Lead II? Questions?

Syllabus Introduction QRS Axis Determination Atrial Arrhythmias, Bradycardias, and AV Conduction Block Junctional and Broad Complex Tachycardias Myocardial Ischemia and Acute Myocardial Infarction Conditions Affecting the Left Side of the Heart Conditions Affecting the Right Side of the Heart Conditions Not Primarily Affecting the Heart Exercise Tolerance Testing

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

Left Axis Deviation Artificial cardiac pacing Ascites COPD Expiration High diaphragm Hyperkalemia Inferior myocardial infarction Left anterior hemiblock Left atrial hypertrophy 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 Anterolateral myocardial infarction Atrial Septal Defect COPD Dextrocardia Inspiration Left posterior hemiblock Left ventricular ectopic rhythms Left ventricular failure with right ventricular strain 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 Artificial cardiac pacing COPD Hyperkalemia Lead transposition Ventricular tachycardia

Depolarization

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

ECG Frontal Plane

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

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

ECG Axis Frontal plane leads are represented on a hexaxial diagram 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

QRS Axis Determination Lead orientation Normal axis -30° to 100° I II aVF III aVR aVL

QRS Axis Determination - Approach 1st Method (Quick) Is it normal? 2nd Method Use algebraic sum of the deflections in 2 leads, usually I and aVF Plot out axis 3rd Method 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 Lead I lies at 0° If the QRS in Lead I is mainly positive (even if only slightly) it means the axis will be anywhere between -90° to 90° Now, look at Lead II I II aVF III aVR aVL

QRS Axis Determination - Quick Method Lead II lies at 60° If the QRS in Lead II is mainly positive (even if only slightly) then the axis can be anywhere between -30° to 150° I II aVF III aVR aVL

QRS Axis Determination - Quick Method If Lead I is positive the axis is between -90° and 90° If Lead II is positive the axis is between -30° and 150° Combined, the axis must lie between -30° and 90° I II aVF III aVR aVL

Normal or Abnormal???

QRS Axis Determination - Approach 1st Method (Quick) Is it normal? 2nd Method Use algebraic sum of the deflections in 2 leads, usually I and aVF Plot out axis 3rd Method 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 aVF 0° - Lead I 90° - Lead aVF -30° 100°

Case #1

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

QRS Axis Determination – Case #1 Plot Results 0° - Lead I 90° - Lead aVF -30° 100°

Case #2

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

QRS Axis Determination – Case #2 Plot Results 0° - Lead I 90° - Lead aVF -30° 100°

Case #3

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

QRS Axis Determination – Case #3 Plot Results 0° - Lead I 90° - Lead aVF -30° 100°

Case #3

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

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

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

Same Results?

QRS Axis Determination

QRS Axis Determination - Approach 1st Method (Quick) Is it normal? 2nd Method Use algebraic sum of the deflections in 2 leads, usually I and aVF Plot out axis 3rd Method 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 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 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 Find the perpendiculars for each lead and choose an approximate QRS axis within the 30° range

QRS Axis Determination - Using Isoelectric Lead II aVF III aVR aVL

Case #1

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

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

QRS Axis Determination - Case #1 aVL - isoelectric II – axis near here

QRS Axis Determination - With Original Findings aVL - isoelectric II – axis near here

Case #3

QRS Axis Determination - Using Isoelectric Lead aVR aVL I III II aVF

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

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

QRS Axis Determination - Case #3 aVL – axis near here II – isoeletric

QRS Axis Determination - With Original Findings aVL – axis near here II – isoeletric

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

Normal or Abnormal Axis?

Axis?

Axis?

Questions???