12 Lead ECGs: Axis Determination & DeviationTerry White, RN

Axis Determination & DeviationWhy Axis Determination?DefinitionsAxis QuadrantsAxis DeterminationAxis DeviationPhysiologic vs Pathologic

Axis Determination & DeviationWhy Axis Determination?Paramedics dont need to know thisThe ability to identify hemiblocks (fascicular blocks) is the main reason you need to be able to determine axisBut paramedics dont need to know this eitherShould they know this?

Axis Determination & DeviationIt is my opinion that the inability to determine the presence of a hemiblock has often been the cause of complete heart block when well-intentioned caregivers have improperly administered lidocaineMike Taigman, Taigmans Advanced Cardiology, Brady, 1995, p. 71

Axis Determination & DeviationWhat is Axis?the general (mean vector) direction of electrical impulses as they travel through the heartthe sum total of all electrical currents generated by the ventricular myocardium during depolarizationnormally from upper right to lower left

Axis Determination & DeviationWhat do you need to determine the axis of an ECG?The 12 Lead ECGLeads CORRECTLY placed on the patientRA on the right armLA on the left armLL on the left legNot on the chest or abdomenKnowledge of axis deviation

Axis ReferenceHexaxial Reference SystemThe six frontal leads create six poles that intersect at the center of the heartEach pole has a positive & negative axisEach + and - end is assigned a value expressed in degreesHexaxial then divided into quadrants (easier to use)

Axis QuadrantsQuadrantsLeft axis -30 to -90 Normal axis -30 to 90Right axis 90 to 180Extreme Right axis or No Mans Land -90 to 1800 I+90aVF+30+60II+120III+150+180aVR-150+120-90-60aVL-30NormalLADRADNo Mans Land

Axis DeterminationQuick Axis DeterminationDetermine the net QRS deflection in Leads I and aVF (positive or negative)Lead IaVFNormal axisLADRADERAD

Axis DeterminationEstimating Axis QuicklyDetermine the net QRS deflection in leads I and aVF (positive or negative)If the net QRS in Lead I is nearly the same as aVF, then axis midway between or 45We estimate by calling it, between +40 and +50If the net QRS in Lead I is positive and is obviously greater than aVF, then axis closer to lead IEstimate as Between 0 and 40If the net QRS in aVF is positive and greater than Lead I, then axis is +50 and +90

Axis DeviationPathologic vs Physiologic LADFirst stepDo I have LAD?If yes, then proceed onLook at Lead IIIf the net QRS deflection is more negative than positive, then the axis must be MORE NEGATIVE than -30

Axis Determination & DeviationExamples for Practice