1) rate and rhythm

• big box (0.20 sec) rule (for 1, 2, 3, 4, 5, and 6 boxes) 300, 150, 100, 75, 60, 50

unsure of rhythm? YES -> arrhythmia identification

2) PR interval

• PR < 0.12sec? YES -> delta wave with prolonged QRS? -> Wolff-Parkinson-White
• PR > .20sec? (including dropped beats) YES -> differential for prolonged PR interval

3) QRS interval

• QRS > .10 sec? YES -> differential for wide QRS (stop here unless RBBB)

4) signs of transmural infarction?

• Q waves > .03 sec in limb leads YES -> criteria for infarct age
• Q waves > 1/4 height of R wave in same limb lead YES -> criteria for infarct age
• Q waves in more than one limb lead YES -> criteria for infarct age
• abnormal R wave progression in chest leads YES -> criteria for infarct age

5) signs of hypertrophy?

6) QT/T wave abnormalities

• ST depression? YES -> myocardial ischemia
• ST elevation? YES -> myocardial injury
• ST scooping? YES -> digitalis effect
• prolonged QT with flat T waves? YES -> hypokalemia
• early, peaked T waves? YES -> hyperkalemia
• inverted T waves without Q waves (history, cardiac enzymes positive)? YES -> subendocardial infarction

[Bing 1981]