Can notched P waves on an electrocardiogram (ECG) indicate Hypertrophic Cardiomyopathy (HCM)?

Can Notched P Waves Indicate Hypertrophic Cardiomyopathy?

Notched P waves can suggest HCM indirectly by indicating left atrial abnormality, which frequently accompanies left ventricular hypertrophy in HCM, but they are neither specific nor diagnostic for HCM itself. 1

Understanding the Relationship Between P-Wave Abnormalities and HCM

Notched P waves reflect left atrial abnormality rather than HCM directly. The mechanism involves:

• Delayed left atrial activation causing separation of right and left atrial peaks that are normally fused, creating the characteristic double-peaked or notched appearance 1
• Prolonged total atrial activation time (P-wave duration ≥120 ms) present in the majority of patients with left atrial abnormality 1, 2
• Wide notching with ≥40 ms separation between peaks has equal diagnostic value to P-wave duration criteria 1, 2

The connection to HCM occurs because left atrial abnormalities frequently accompany left ventricular hypertrophy and may represent the earliest ECG sign of hypertensive heart disease or cardiomyopathy. 1

Critical Limitations as an HCM Indicator

P-wave abnormalities should only be used as a supporting criterion, not a diagnostic criterion for HCM or LVH. 1 Here's why:

• Low specificity: Similar P-wave abnormalities occur frequently in the absence of LVH or HCM 1
• Multiple etiologies: Atrial dilatation, muscular hypertrophy, elevated atrial pressure, impaired ventricular distensibility, and delayed intraatrial conduction all produce similar P-wave changes 1, 2
• Inadequate clinical validation: Studies assessing the accuracy of P-wave criteria alone or combined with other criteria for diagnosing LVH have not been adequately reported 1

The ECG Profile in Confirmed HCM

When HCM is present, the ECG typically shows:

• Variable combination of LVH, ST- and T-wave abnormalities, and pathological Q-waves in 94% of referral cohort patients 1
• Normal ECG at presentation in approximately 6% of HCM patients 1, 3
• Less than 25% of HCM patients detected by screening echocardiography have abnormal ECG findings (LVH or T-wave inversion) 3
• Better prognosis in HCM patients with normal ECGs—none experienced cardiac death at follow-up in one study 4

Importantly, even with demonstrable echocardiographic evidence of HCM, the ECG may remain completely normal, indicating that ECG alone lacks sensitivity for HCM detection. 3, 4

Specific P-Wave Findings in HCM Populations

Research demonstrates that HCM patients have:

• Longer P-wave duration compared to healthy controls (149 ± 22 ms vs 130 ± 16 ms) 5
• Higher prevalence of interatrial conduction block of varying severity 5
• Conduction pattern changes most prominent in orthogonal Leads Y and Z 5

These findings suggest that prolonged P-wave duration in HCM reflects a higher prevalence of block in interatrial conduction routes rather than being pathognomonic for the disease. 5

Clinical Approach When Notched P Waves Are Identified

When you encounter notched P waves, follow this algorithm:

1. Measure P-wave duration: ≥120 ms suggests left atrial abnormality 1, 2
2. Assess notch width: ≥40 ms between peaks is significant 1, 2
3. Evaluate P terminal force in lead V1: Increased amplitude × duration of terminal negative component supports left atrial abnormality 1, 2
4. Search for underlying cardiac conditions: Mitral valve disease, hypertension, heart failure, or cardiomyopathies 2
5. Perform echocardiography: This is the primary imaging modality to assess left atrial size, left ventricular wall thickness, and exclude or confirm HCM 1, 2

Common Pitfalls to Avoid

• Do not rely solely on P-wave morphology for diagnosing HCM—correlation with clinical findings and imaging is essential 2
• Avoid outdated terminology like "P-mitrale" or "atrial hypertrophy"; use "left atrial abnormality" instead 1, 2
• Do not overlook normal variants and technical factors that can affect P-wave appearance 2
• Remember that interatrial conduction delay can cause bifid P waves even without atrial enlargement 2
• Do not assume ECG sensitivity: Up to 23% of HCM patients may have normal 12-lead ECGs despite having abnormal electrophysiological properties detectable by advanced techniques 6

Risk Stratification Context

In established HCM, ambulatory ECG monitoring is recommended at initial assessment to evaluate sudden cardiac death risk and stroke risk, as asymptomatic non-sustained ventricular tachycardia occurs in 25% of adults with HCM and paroxysmal supraventricular arrhythmias in up to 38%. 1 The presence of P-wave abnormalities indicating left atrial abnormality may correlate with increased atrial fibrillation risk. 2