What is the cutoff value for interventricular septum (IVS) and posterior wall (PW) thickness to diagnose left ventricular hypertrophy (LVH), 10mm or 11mm?

Diagnostic Cutoff for Left Ventricular Hypertrophy: IVS and Posterior Wall Thickness

The diagnostic cutoff for left ventricular hypertrophy (LVH) in the context of hypertrophic cardiomyopathy is ≥15 mm of maximal LV wall thickness anywhere in the left ventricle, with 13-14 mm considered diagnostic in family members of HCM patients or those with positive genetic testing. 1, 2

Standard Diagnostic Thresholds

Primary Cutoff for HCM Diagnosis

• A maximal end-diastolic LV wall thickness of ≥15 mm measured by 2D echocardiography or CMR establishes the diagnosis of HCM in adults, provided other causes of hypertrophy are excluded 1, 2
• This 15 mm threshold applies to any location in the left ventricle, including the interventricular septum (IVS) and posterior wall (PW) 1, 2

Borderline/Lower Threshold

• Wall thickness of 13-14 mm is considered diagnostic when the patient is a first-degree family member of someone with confirmed HCM or when a pathogenic sarcomere gene variant has been identified 1, 2
• These borderline measurements (13-14 mm) require additional supporting evidence and should not be used as standalone diagnostic criteria in unselected populations 1

Context-Specific Considerations

Athletic Populations

• In athletes, physiologic LVH can reach up to 15 mm in white males and 16 mm in Afro-American males, with lower values in females (11 mm in white females, 13 mm in Afro-American females) 1
• This creates a diagnostic "gray zone" between 13-16 mm where distinguishing pathologic HCM from athlete's heart requires additional clinical markers 1
• Athletes typically show LV cavity enlargement (end-diastolic diameter >54 mm) and homogeneous wall thickness distribution with <2 mm difference between segments 1

Pediatric Populations

• In children, the diagnostic threshold is a body surface area-adjusted z-score ≥2 standard deviations above the mean 1
• For asymptomatic children without family history, a z-score >2.5 may be more appropriate to avoid overdiagnosis 1
• For children with definitive family history or positive genetic testing, a z-score >2 may suffice for early diagnosis 1

Critical Exclusion Requirements

Before diagnosing HCM based on wall thickness, you must systematically exclude: 1, 2

• Long-standing systemic hypertension causing secondary LVH
• Aortic stenosis or discrete subaortic stenosis
• Infiltrative diseases (amyloidosis, sarcoidosis, Fabry disease)
• Storage diseases (glycogen storage disorders, Danon cardiomyopathy)
• RASopathies and mitochondrial myopathies
• Athletic remodeling in highly trained individuals

Common Diagnostic Pitfalls

The 10 mm vs 11 mm Question

• Neither 10 mm nor 11 mm is used as a diagnostic cutoff for HCM 1, 2
• These values fall well below the established diagnostic threshold and would represent normal or minimally increased wall thickness
• Wall thickness in this range may be seen in genotype-positive/phenotype-negative individuals who carry HCM mutations but have not yet developed overt hypertrophy 1

Measurement Considerations

• The measurement should reflect maximal wall thickness anywhere in the LV, not just the septum or posterior wall in isolation 1, 2
• Asymmetric septal hypertrophy with an IVS/PW ratio ≥1.3 suggests pathologic hypertrophy rather than physiologic adaptation 1, 3
• Focal or segmental hypertrophy limited to 1-2 LV segments can occur in HCM and may be missed if only standard parasternal views are examined 1, 2

When Standard Thresholds Don't Apply

• Any degree of wall thickness is compatible with the presence of HCM genetic substrate in genotype-positive individuals 1
• Genotype-positive/phenotype-negative family members should be considered "at risk" but do not yet have clinically evident HCM 1, 2
• Serial imaging every 12-18 months is reasonable for high-risk family members to detect emerging phenotype 1

Imaging Modality Considerations

• Transthoracic echocardiography is the first-line imaging modality for measuring wall thickness 2
• CMR should be used when echocardiography is inconclusive or when apical hypertrophy is suspected, as it provides superior visualization of all LV segments 1, 2
• CMR may detect hypertrophy in unusual locations that are poorly visualized by echocardiography 1