Bifid P Wave in Chest Leads
A bifid (notched or double-peaked) P wave in chest leads indicates left atrial abnormality, reflecting delayed left atrial activation and intraatrial conduction delay, most commonly caused by conditions such as mitral valve disease, hypertension, or heart failure. 1, 2
Pathophysiological Mechanism
The bifid appearance occurs because left atrial activation begins and ends later than right atrial activation. 1 When intraatrial conduction is delayed—often through Bachmann's bundle (the specialized interatrial pathway)—the normally simultaneous right and left atrial peaks become separated, creating the characteristic M-like or notched morphology. 1, 2
The separation between the two peaks must be ≥40 ms to be clinically significant for left atrial abnormality. 1, 2
Diagnostic Criteria to Assess
When you identify a bifid P wave in chest leads, measure the following parameters:
- P wave duration: ≥120 ms indicates left atrial abnormality and is present in the majority of affected patients 1, 2
- Notch width: The separation between peaks should be ≥40 ms to confirm left atrial abnormality 1, 2
- P terminal force in lead V1: Calculate the product of amplitude and duration of the terminal negative component; this is the most frequently used criterion with 76% sensitivity and 92% specificity 2
- P wave morphology in V1: Look for a prominent terminal negative deflection or purely negative P wave 1
Clinical Significance and Next Steps
Evaluate for underlying cardiac conditions immediately: 2
- Mitral valve disease (most classic association with "P-mitrale" pattern)
- Hypertension (chronic pressure overload)
- Heart failure (impaired ventricular distensibility)
- Assess arrhythmia risk: Left atrial abnormality increases risk for atrial fibrillation 2
Order echocardiography to assess left atrial size and function, as this remains the gold standard for measuring left atrial dimensions despite ECG findings. 2 The ECG changes reflect a combination of atrial dilatation, muscular hypertrophy, elevated atrial pressure, and conduction delay—factors that cannot be distinguished by surface ECG alone. 1, 2
Important Caveats
Use correct terminology: Refer to this finding as "left atrial abnormality" rather than outdated terms like "P-mitrale," "left atrial enlargement," "atrial hypertrophy," or "atrial strain." 1, 2 The P wave changes represent multiple pathophysiological processes, not just anatomic enlargement. 1
Do not rely on P wave morphology alone: Multiple ECG criteria should be used simultaneously (P wave duration, notch width, P terminal force in V1) to enhance diagnostic accuracy. 1, 2 However, even with multiple criteria, ECG has limited sensitivity and specificity compared to imaging. 2
Consider interatrial conduction delay: Bifid P waves can occur from pure conduction delay through Bachmann's bundle even without actual atrial enlargement. 1, 2 This is why "left atrial abnormality" is the preferred term—it encompasses both structural and electrical abnormalities.
Check multiple leads: While bifid P waves are most commonly identified in chest leads (particularly V1-V6), also examine leads II and the limb leads, as these patterns can appear in any lead. 3 The "dome-and-spike" morphology (right atrial component forming a dome, left atrial component forming a spike) is particularly specific when visible. 3
Exclude technical factors: Normal variants and poor electrode placement can mimic bifid P waves, so ensure proper lead placement and adequate ECG quality before making clinical decisions. 2