Systematic Approach to 12 Lead EKG Interpretation Maureen Knechtel MPAS, PA-C Wellmont CVA Heart Institute Disclosure Statement of Financial Interest I, Maureen Knechtel, do not have a financial interest/arrangement or affiliation with one or more organizations that could be perceived as a real or apparent conflict of interest in the context of the subject of this presentation. Objectives 1. Establish a concise approach to EKG interpretation 2. Gain confidence in the ability to correctly and thoroughly interpret an EKG 3. Use EKG findings to guide clinical management 4. Know when to refer based on EKG findings Follow a System Rate Rhythm Axis Infarction Block
Rate Rate Large box = 200 ms Find R wave on thick line Count to next thick line to estimate HR Rate Rhythm: Regular or Irregular If less than 40 bpm, divide rhythm strip in 2 and multiply number of QRS complexes by 10
Axis Lead I: QRS positive = axis points to Lead avf: positive: axis in lower left quadrant: axis normal Lead avf: negative: axis in upper left quadrant: left axis deviation Axis quadrants: defined by intersection of leads I and avf Normal: 0 to +90 Right Axis Deviation: +90 to +180 Left Axis Deviation: -1 to -90 Axis Lead I: QRS negative = axis points to Lead avf: positive: axis in the lower right quadrant: right axis deviation Lead avf: negative: axis indeterminate Axis
Axis Causes of Axis Deviation Left Axis Inferior MI LVH Obesity LBBB LAFB Right Axis Lateral MI RVH Tall, thin frame COPD RBBB LPFB Ischemia and Infarction Ischemia Diminished blood flow causes a delay in the depolarization and repolarization pattern T wave inversion, ST depression Injury ST segment elevation Define in millimeters from baseline 2 mm = clinically significant Infarct Q waves = no depolarization, scar tissue Ischemia and Infarction EKG Leads Myocardial Distribution Reciprocal Changes (Injury Pattern) RCA II, III, avf Inferior Wall Lateral Leads LAD V1-V4 Anterior Wall Inferior Leads Left Circumflex I, avl, V5-V6 Lateral Wall Inferior Leads
Reciprocal Changes Posterior Ischemia Coronary Blood Supply and the Conduction System Block Coronary Artery Right Coronary Left Anterior Descending Left Circumflex Conduction System SA Node, AV Node Right Bundle Branch Left Bundle Branch SA Node (less common) AV Node (less common) Inferior wall MI can be complicated by sinus arrest or complete heart block Anterior infarction can be complicated by new bundle branch block or complete heart block LAD supplies interventricular septum 1st Degree AVB 2nd Degree AVB (Type 1 and 2) 3rd Degree RBBB LBBB
First Degree AVB 2 nd Degree Type I 2 nd Degree Type II 3 rd Degree AV Block
RBBB RBBB QRS > 120 ms Findings due to slow, rightward spread of ventricular depolarization from LV Can occur in structurally normal heart or any condition that affects R heart R wave: LV activation V6: RS R wave: LV activation S wave: RV activation LBBB QRS > 120 ms Findings due to slow, leftward spread of ventricular depolarization from RV More likely associated with structural heart disease V1: QS Q: RV activation S: LV activation V6: Tall R wave, +/- R wave: RV activation LBBB
Ischemia and LBBB LBBB affects early and late phases of ventricular depolarization LBBB is reflected by Q waves, ST segment and T wave changes These are the same findings that can be present in ischemia and infarction ST Elevation Discordant with QRS Ischemia and BBB ST elevation > 1mm in leads with a positive QRS complex (QRS concordant with ST segment) ST elevation > 5 mm in leads with a negative QRS complex (QRS discordant with ST segment) ST depression > 1 mm in V1 to V3 Obtain serial EKGs if you are suspicious of an acute event
Obtain serial EKGs if you are suspicious of an acute event Left Hemiblock Diagnose by: Axis deviation QRS patterns QRS duration may be normal LAFB Left Anterior Fascicle Anterolateral LV Delay in electrical activation shifts general axis towards left Left axis deviation -30 or more negative QRS negative inferior: rs QRS positive lateral: qr LAFB
LPFB LPFB Left Posterior Fascicle Inferoseptal portion of LV Delay in electrical activation shifts axis towards right Right axis deviation +120 or more positive QRS negative lateral: rs QRS positive inferior: qr Prolonged QTc QTc prolongation QT > ½ the R-R Interval Examine drug list: Antipsychotics Antidepressants: SSRIs Antibiotics: fluoroquinolones and macrolides Antifungals Antiarrhythmics www.torsades.org
Summary Always follow a pattern in order to correctly and efficiently interpret a 12 lead EKG Examine the EKG leads as groups Use EKG clues to guide clinical management and refer when high risk findings are present