What are the EKG criteria for P mitrale (P wave abnormality indicating left atrial enlargement)?

EKG Criteria for P Mitrale (Left Atrial Abnormality)

The definitive EKG criteria for P mitrale (left atrial abnormality) include P-wave duration ≥120 ms, widely notched P wave with ≥40 ms between peaks, and increased P terminal force in lead V1, all of which have equal diagnostic value. 1

Primary Diagnostic Criteria

Left atrial abnormality (P mitrale) is characterized by several specific EKG findings:

1. P-wave duration:

   • ≥120 ms (0.12 seconds) 1
   • Represents prolonged total atrial activation time

2. P-wave morphology:

   • Widely notched or double-peaked P wave with ≥40 ms between peaks 1
   • Notching occurs because right and left atrial peaks become more widely separated

3. P terminal force in lead V1:

   • Increased product of amplitude and duration of the terminal negative component 1
   • Often measured as area >40 ms·mm 2
   • Optimal threshold value of ≥0.06 mm·s has superior diagnostic accuracy 2

4. Additional criteria:

   • Left axis of the terminal P wave (30° to 90°) 1
   • Increased P-wave area in lead II (≥4 ms·mV has 85.8% sensitivity, 93.7% specificity) 3
   • Purely negative P wave in V1 (suggestive but not definitive) 1

Pathophysiological Basis

The EKG changes in left atrial abnormality occur because:

• Left atrial activation begins and ends later than right atrial activation 1
• Activation of the left atrium has a more leftward and posterior vector 1
• Delay often represents conduction delay in Bachmann's bundle and within left atrial myocardium 1
• Changes may reflect various pathophysiological processes including atrial dilatation, muscular hypertrophy, elevated pressure, impaired ventricular distensibility, and delayed conduction 4

Diagnostic Performance and Limitations

• Individual ECG criteria are more specific than sensitive for left atrial enlargement 5
• Sensitivity decreases and specificity increases with stricter criteria thresholds 2
• Obesity can significantly reduce the specificity of ECG criteria for LAE 5
• P-wave area correlates better with left atrial size (r=0.739) than P-wave duration (r=0.635) or amplitude (r=0.683) in mitral stenosis 3
• Histological factors affect P-wave morphology: cell diameter correlates with P-wave amplitude (r=0.69), while fibrosis correlates with PR segment and P-wave to PR segment ratio 6

Clinical Application

When evaluating for left atrial abnormality:

1. Use multiple ECG criteria rather than relying on a single parameter 1
2. Prefer the term "left atrial abnormality" over "enlargement," "overload," "strain," or "hypertrophy" 1
3. Consider the presence of intraatrial conduction delay when P-wave widening occurs without increased amplitude 1
4. Be aware that obesity may reduce the specificity of ECG criteria 5
5. Recognize that patients with left atrial abnormality should undergo comprehensive cardiovascular evaluation to identify underlying causes 4

Common Pitfalls

• Relying on a single criterion rather than multiple parameters
• Using outdated terminology (e.g., "enlargement" instead of "abnormality")
• Failing to consider obesity as a confounder
• Not recognizing that ECG criteria are more specific than sensitive (don't use ECG to exclude LAE)
• Using suboptimal threshold values for P terminal force in V1 (≥0.06 mm·s is superior to the traditional ≥0.04 mm·s) 2