SYSTEMATIC INTERPRETATION GUIDELINES for Electrocardiograms
RATE
Rate calculation
Common method: 300-150-100-75-60-50
Mathematical method: 300/# large boxes between R waves
Six-second method: # R-R intervals x10

RHYTHM
Rhythm Guidelines:
1. Check the bottom rhythm strip for regularity, i.e. - regular, regularly irregular, and irregularly irregular.
2. Check for a P wave before each QRS, QRS after each P.
3. Check PR interval (for AV blocks) and QRS (for bundle branch blocks). Check for prolonged QT.
4. Recognize "patterns" such as atrial fibrillation, PVC's, PAC's, escape beats, ventricular tachycardia, paroxysmal atrial tachycardia, AV blocks and bundle branch blocks.
AXIS
Lead I Lead aVF
1. Normal axis (0 to +90 degrees) Positive Positive
2. Left axis deviation (-30 to -90) Also check lead II. To be true left axis deviation, it should also be down in lead II. Positive Negative
3. Right axis deviation (+90 to +180) Negative Positive
4. Indeterminate axis (-90 to -180) Negative Negative
Left axis deviation differential: LVH, left anterior fascicular block, inferior wall MI.
Right axis deviation differential: RVH, left posterior fascicular block, lateral wall MI.

HYPERTROPHY
1. LVH -- left ventricular hypertrophy = S wave in V1 or V2 + R wave in V5 or V6 > 35mm or aVL R wave > 12mm.
2. RVH -- right ventricular hypertrophy = R wave > S wave in V1 and gets progressively smaller to left V1-V6 (normally, R wave increases from V1-V6).
3. Atrial hypertrophy (leads II and V1)
Right atrial hypertrophy -- Peaked P wave in lead II > 2.5 mm in amplitude. V1 has increase in the initial positive direction.
Left atrial hypertrophy -- Notched wide (> 3mm) P wave in II. V1 has increase in the terminal negative direction.
INFARCT
Ischemia Represented by symmetrical T wave inversion (upside down). Look in leads I, II, V2-V6.
Injury Acute damage -- look for elevated ST segments.
Infarct "Pathologic" Q waves. To be significant, a Q wave must be at least one small square wide or one-third the entire QRS height.
Certain leads represent certain areas of the left ventricle:
V1-V2 anteroseptal wall II, III, aVF inferior wall
V3-V4 anterior wall I, aVL lateral wall
V5-V6 anterolateral wall V1-V2 posterior wall (reciprocal)
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