What are the diagnostic guidelines for P mitral (P wave indicative of mitral valve disease) on a 12-lead electrocardiogram (ECG)?

Diagnostic Criteria for P Mitrale on 12-Lead ECG

P mitrale is diagnosed on 12-lead ECG by a P wave duration ≥120 ms with characteristic double-peaked or notched morphology (≥40 ms between peaks), representing left atrial abnormality most commonly associated with mitral valve disease. 1

Specific ECG Criteria

The following findings define P mitrale and left atrial abnormality:

• P wave duration ≥120 ms (prolonged total atrial activation time), which is the primary diagnostic criterion 1
• Double-peaked or notched P wave with ≥40 ms separation between the two peaks, creating the characteristic "M-shaped" morphology that gives P mitrale its name 1
• Negative terminal component of P wave in lead V1 (P terminal force), representing delayed left atrial activation 1
• Left axis deviation of the terminal P wave (30° to 90°) 1
• Purely negative P wave in V1 may be present in some cases 1

Lead-Specific Findings

• Lead II is the optimal lead for identifying the notched, bifid P wave morphology characteristic of P mitrale 1
• Lead V1 demonstrates the negative terminal deflection, which reflects left atrial depolarization occurring after right atrial activation 1

Clinical Context and Interpretation

P mitrale specifically indicates left atrial abnormality, not right atrial pathology. This distinction is critical because right atrial abnormality (P pulmonale) presents differently with tall, peaked P waves >2.5 mm in lead II, prominent initial positivity in V1 or V2 (≥1.5 mm), but normal P wave duration 1. The term "atrial abnormality" is preferred over "atrial enlargement" because ECG changes reflect electrical abnormalities that may not always correlate with anatomic chamber size 1.

Diagnostic Accuracy Considerations

Individual ECG criteria for left atrial abnormality, including P mitrale, are 88-99% specific but not sensitive for anatomic left atrial enlargement. 2 This means that when P mitrale is present, it reliably indicates left atrial pathology, but its absence does not exclude left atrial disease. The presence of at least one ECG criterion for left atrial abnormality is 90% sensitive but nonspecific 2.

Verification and Confirmation

• Use multiple electrocardiographic criteria together rather than relying on a single finding to confirm left atrial abnormality 1
• Examine all 12 leads carefully to avoid missing subtle P wave changes that may be more apparent in certain leads 3
• Echocardiography is essential for evaluating the underlying cause of P mitrale, particularly to assess for mitral valve stenosis, mitral regurgitation, or other structural heart disease 4, 5

Common Clinical Associations

P mitrale is classically associated with:

• Mitral valve stenosis, where left atrial pressure overload causes electrical remodeling 4
• Mitral regurgitation, particularly chronic severe regurgitation causing left atrial volume overload 6, 7
• Any condition causing left atrial pressure or volume overload that results in atrial electrical remodeling 1

Important Pitfalls to Avoid

• Do not confuse P mitrale with P pulmonale: P pulmonale shows increased amplitude with normal duration, while P mitrale shows increased duration with characteristic notching 1, 4
• Intraatrial conduction delay can cause P wave widening without increased amplitude and should be recognized as a distinct category of atrial abnormality 1
• Combined atrial abnormality may be present when features of both right and left atrial abnormality coexist, warranting more comprehensive cardiac evaluation 1