Step 5: Inspect P waves for atrial enlargement

Analysis and Interpretation of the Electrocardiogram

How to use this module

The 12 lead ECG

Waves and complexes

Intervals and segments

Approach to the ECG

Step 1: Determine the heart rate

Step 2: Measure important intervals

Step 3a: Calculate the electrical axis

Step 3b: Calculate the electrical axis

Step 3c: Calculate the electrical axis

Step 4: Evaluate the cardiac rhythm

Step 5: Inspect P waves for atrial enlargement

Step 6: Inspect QRS complexes for ventricular hypertrophy or low voltage

Step 7a: Inspect QRS complexes for bundle branch block or fascicular block

Step 7b: Inspect QRS complexes for bundle branch block or fascicular block

Step 7c: Inspect QRS complexes for bundle branch block or fascicular block

Step 7d: Inspect QRS complexes for bundle branch block or fascicular block

Step 7e: Inspect QRS complexes for bundle branch block or fascicular block

Step 8: Assess Q waves and determine significance

Step 9: Assess ST segments and T waves

Step 10: Measure QT interval for specific diagnoses

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Step 5: Inspect P waves for atrial enlargement

The P waves in leads I, II, III and V1 should be inspected for evidence of right or left atrial enlargement. Usually, lead II will have the clearest P wave.

P wave amplitude should not exceed 3 small squares (3 mm or 0.3mV). If it does, this represents right atrial enlargement.
In lead V1, the terminal negative deflection of the P wave represents left atrial depolarization and should not exceed 1 mm (0.1mV). If it does, this is indicative of left atrial enlargement.

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