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Nursing 259 12 Lead EKG Electrical Axis Determination 12 Lead EKG Graphic recording of the electrical potentials associated with the heartbeat Electrical currents flow in different directions so different views preferable Each lead looks at different area of heart – overall looks in frontal and vertical planes Must be interpreted with client history, physical assessment and lab data Clinical Value of EKG Myocardial ischemia and infarction Cardiac conduction disturbances Arrhythmias Cardiac chamber enlargement Pericarditis Pulmonary hypertension Effects of cardiac drugs Electrolyte disturbances Practical Points Effective contact between skin and electrodes is essential; use electrode jelly Proper grounding of machine and patient is necessary to prevent AC interference Other electrical equipment in contact with patient may produce artifact Patient should be in supine position with arms at side of body Pathway of Conduction SA node transmits impulse anteriorly and inferiorly to AV node Simultaneously conducted to L atrium AV node to bundle of His Septum activated from left to right Simultaneously to ventricles - travels more quickly over right ventricle as it is thinner; left is thicker Sequence of Activation Conduction Pathway Since LV has larger muscle mass, mean QRS vector is down and to left If impulse is traveling towards the positive electrode, a positive complex is recorded in that lead Conduction Pathway If impulse is traveling away from the positive electrode ; a negative complex is recorded in that lead If impulse is traveling perpendicularly to the positive electrode a very small or biphasic complex will be recorded in that lead Mean QRS Vector Conduction Pathway Planes of Recording Bipolar Limb Leads Records electrical potentials in the frontal plane between 2 poles: 1 positive and 1 negative + electrode is recording electrode Lead I: RA (-); LA (+) Lead II: RA (-); LL (+) Lead III: LA (-); LL (+) Bipolar Limb Leads Unipolar Limb Leads Designated limb is + electrode in relation to center of heart which is neutral; also in frontal plane AVR - RA (+) AVL - LA (+) AVF - LL (+) Unipolar Limb Leads Unipolar Precordial Leads Horizontal view of electrical activity + electrode is electrode moved about on chest wall Leads V1-V6 Placement of precordial leads should be precise since QRS morphology and amplitude can change if inaccurate Precordial Leads V1 - 4th ICS - right sternal border V2 - 4th ICS - left sternal border V3 - midway between V2 and V4 V4 - 5th ICS - L midclavicular line V5 - 5th ICS - L anterior axillary line V6 - 5th ICS - L midaxillary line Precordial Leads Precordial Lead Views V1 and V2 are septal leads V2, V3 and V4 are anterior leads V4, V5 and V6 are lateral precordial leads Precordial Lead Views R wave progression V1 over right ventricle - impulse will travel towards electrode and then away - normal small R wave V6 over left ventricle - impulse first travels away from electrode and then towards it - normally small Q wave and large R wave R wave progression Between V1 and V6 is transitional zone - R wave should progressively increase across V leads - called R wave progression Poor R wave progression is suggestive of anterior wall MI since precordial impulse flow is interrupted R wave progression Right Precordial EKG Used in dextrocardia and right ventricular infarctions V1 and V2 - same site V3R - halfway between V1 and V4R V4R - 5th ICS - right midclavicular line V5R - 5th ICS - right anterior axillary line V6R - 5th ICS - right mid- axillary line Right Precordial EKG Electrical axis Orientation of heart’s electrical activity in frontal plane Review: depolarization of ventricle : first septum from left to right, then right ventricle, then left ventricle Mean QRS vector is down and to left Positive complex, negative complex and biphasic complex Electrical axis Hexaxial reference system: 6 limb leads intersecting at common center point Numerical designations are given to positive and negative poles of each lead Each lead divides the circle by 30 degrees The upper half of the circle is negative and the bottom half is positive Divide the circle into quadrants Normal electrical axis Down and to left From 0 to +90 (can vary from -30 to +110) QRS should be predominantly positive in Leads I and AVF - quadrant method For normal axis: impulse must travel in normal manner, normal muscle mass must be maintained and all myocardium must be able to conduct impulse Normal Axis Left Axis deviation From -30 to -90 QRS: positive in Lead I & negative in AVF Causes: Left atrial or ventricular hypertrophy Left bundle branch block Inferior wall MI Pregnancy Obesity Left axis deviation Right axis deviation From +110 to +180 QRS: positive in AVF - negative in Lead I Causes: Right ventricular hypertrophy Anterior MI Pulmonary disease Thin person Congenital heart disease Right axis deviation Indeterminate axis - 90 to 180 Extreme right or left Indeterminate axis Perpendicular method More accurate than quadrant method First do quadrant method Then look for smallest or most biphasic complex - the axis is perpendicular to this lead Look at right angle to that lead to obtain numerical value Normal axis QRS positive in I and AVF Answer is between 0 - +90 AVL smallest QRS Lead II is perpendicular to AVL Axis is +60 Left axis deviation QRS + in I, - in AVF Answer is between 0 and -90 Most biphasic is AVR Lead III is perpendicular to AVR Axis is -60 Right axis deviation QRS – in I, + in AVF Answer is between +90 to 180 AVF and II are most biphasic Leads I, AVL are perpendicular Axis is between +150 - +180 Axis is +165 That’s a hard one! Indeterminate axis All leads are biphasic Cannot determine!