ECG Interpretation Chapter 22

ECG Interpretation Rate Atrial rate: PP interval Ventricular rate: RR interval Rhythm P wave PR interval QRS voltage (height) width Axis Hypertrophy Blocks Infarct Ischemia

Standardization Standardization mark 10 mm vertical deflection = 1 mVolt

Rate Ventricular rate (heart rate) Atrial rate 3rd degree AV block RR interval Atrial rate PP interval 3rd degree AV block

Heart Rate Calculation 1500 divided by the number of small boxes between two R waves most accurate take time to calculate only use with regular rhythms 1 lg sq = 300 bpm 2 lg sq = 150 bpm 3 lg sq = 100 bpm 4 lg sq = 75bpm 5 lg sq = 60 bpm 6 lg sq = 50 bpm 300 divided by the number of large boxes between two R waves quick not too accurate only use with regular rhythm 10 multiplied by the number of R waves in 6 seconds less precise use with irregular rhythms very quick

Rhythm Sinus rhythm - consistent P waves Atrial rhythm - irregular P waves Junctional/Nodal rhythm - no P waves, late P waves, or inverted P waves Ventricular rhythm - no P waves, wide QRS

AV Junctional Rhythms Retrograde P waves immediately preceding the QRS complexes in aVR and II. Retrograde P waves immediately following the QRS complexes Absent P waves

ECG Waves P wave atrial depolarization ≤ 2.5 mm in amplitude < 0.12 sec in width PR interval (0.12 - 0.20 sec.) time of stimulus through atria and AV node prolonged interval = first-degree heart block

P wave Tall = RAE Wide = LAE

PR Interval Long PR interval = first degree AV block Short PR interval = WPW Short PR interval with inverted P waves = ectopic atrial or junctional pacemaker

Classification of AV Heart Blocks Degree AV Conduction Pattern 1St Degree Block Uniformly prolonged PR interval 2nd Degree, Mobitz Type I Progressive PR interval prolongation 2nd Degree, Mobitz Type II Sudden conduction failure 3rd Degree Block No AV conduction

Wolff-White-Parkinson Wide QRS due to early depolarization not due to a delay in depolarization Shortened PR interval Upstroke QRS complex is slurred; delta wave

ECG Waves QRS width 0.12 second or less

Normal QRS V6? V6? V1? V1? Fig. 4-6

Normal Q waves Septal r wave Septal q wave

Q Waves Abnormal if wider than 0.04 sec Greater than 25% of the R wave Leads I, II, III, aVf or leads V3 - V6. Greater than 25% of the R wave Note: Not all Q waves are abnormal, Not all Q waves are the result of MI.

QRS Width Wide RBBB or LBBB Premature ventricular beats WPW

QRS Voltage RVH LVH

Mean QRS Axis

Axis Deviation (or Lead II or III) LEAD I LEAD aVF LEAD aVR Normal Positive LAD Negative RAD (or Negative) Intermediate axis

R Wave Progression

Transmural MI Pathalogical Q waves ST segment elevation. Ischemia Tall T waves (and/or reciprocal T wave inversion) Injury ST segment elevation. T wave inversion of the previously tall T waves Infarct Pathalogical Q waves (at least one small box wide or 11/3 the entire QRS height)

Posterior (reciprocal) Overview LEAD AREA OF THE HEART V1-V2 Anterior/Septum V3-V4 Anterior Wall V5-V6 Anterior/Lateral II, III, aVF Inferior I and aVL Lateral Posterior (reciprocal)

ST Segments J point: end of QRS wave beginning of ST segment beginning of ventricular repolarization normally isoelectric (flat) changes, elevation or depression, may indicate pathological condition

Subendocardial Ischemia ST segment depression criteria 1 mm or more horizontal or downward lasts 0.08 seconds depression of only the J point with rapid upward sloping are considered normal.