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Rapid Interpretation

  • Measurements: small box = 1 mm = 0.04 sec, large box = 5 mm = 0.2 sec, every 10 mm vertically = 0.1 mV of electrical potential
  1. Rate: Calculate the rate by dividing 300 by the number of large boxes between adjacent QRS complexes (300 = 1 box, 150 = 2 boxes, 100 = 3 boxes, 75 = 4 boxes, 60 = 5 boxes, 50 = 6 boxes.). If the rate is <50, multiply the number of QRS complexes on the rhythm strip by 6.
  2. Rhythm(normal sinus, idioventricular, junctional, wandering atrial pacemaker, multifocal atrial tachycardia, sinus brady-or tachycardia, paroxysmal SVT, atrial flutter, A-fib, V-tach, V-fib).
  3. Axis: If QRS negative in I = right axis deviation. If QRS negative in lead II = left axis deviation.
  4. Intervals
    1. PR interval (normal = 0.12-0.20 sec):-Firstdegree heart block = PR>0.2 sec with a QRS after every P-Mobitz type I: progressively longer PR until QRS drops-Mobitz type II: prolonged constant PR with sporadic dropped QRS-Thirddegree heart block: complete AV dissociation
    2. QRS interval (normal 0.08-0.10 seconds)-LBBB: QRS>0.12 sec, no S wave in lead I, RSR‘ in V5 and V6-RBBB: QRS>0.12 sec, broad S in lead I, RSR‘ in V1
    3. QTCinterval (QT interval divided by the square root of the RR interval): >0.44 sec is generally considered prolonged
  5. Hypertrophy and EnlargementLVH: R wave in aVL > 11 mm and V4-V6 > 25 mm or S wave in leads V1 + amplitude of R wave in lead V5 or V6 >35 mmRVH: R wave in V1 >7 mm or R wave in V1 + S wave in V6 >10 mmLeft atrial enlargement: wide (>1 mm) and deep (>1 mm) P wave in V1Right atrial enlargement: tall P wave >2.5 mm in leads II, III, or aVF
  6. Infarction-Check for ST elevation or depression, T wave inversion, and Q waves. Correlate with arterial distribution:Anterior (LAD) –V1-V2, Inferior (RCA) –II, III, aVF, Lateral (circumflex) –I, aVL, Right ventricular –V4R on right-sided EKG
  7. Special signs: U Wave in hypokalemia, peaked T waves in hyperkalemia, S1Q3invertedT3 in pulmonary embolism, diffuse ST elevation and PR depression in pericarditis