Why is posterior wall thickness used instead of septal wall thickness to calculate hypertrophy in certain clinical contexts?

From the Guidelines

Posterior wall thickness is used instead of septal wall thickness to calculate hypertrophy in certain clinical contexts because the interventricular septum can be disproportionately thickened in conditions unrelated to general left ventricular hypertrophy. The posterior wall provides a more reliable measurement for assessing true hypertrophy because it is less affected by conditions like sigmoid septum, hypertrophic cardiomyopathy, or prior septal infarction that can artificially alter septal measurements 1. When evaluating for left ventricular hypertrophy, especially in patients with hypertension or other causes of pressure overload, the posterior wall measurement offers a more consistent reflection of the overall myocardial response to increased afterload. Additionally, the posterior wall is typically easier to visualize on echocardiography with fewer technical limitations. Normal posterior wall thickness is generally considered to be 6-11 mm in adults, with measurements above this range suggesting hypertrophy. This approach helps clinicians avoid overdiagnosing hypertrophy in patients who may have isolated septal thickening due to other pathological or physiological processes rather than true global ventricular hypertrophy. Some key points to consider when evaluating left ventricular hypertrophy include:

• The clinical definition of hypertrophic cardiomyopathy (HCM) as a disease state characterized by left ventricular hypertrophy (LVH) in the absence of another cardiac, systemic, or metabolic disease capable of producing the magnitude of hypertrophy evident in a given patient 1.
• The importance of considering the circumstances of screening and the pretest probability of disease when diagnosing HCM in children, with a threshold of z >2.5 potentially being appropriate to identify early HCM in asymptomatic children with no family history 1.
• The recognition that nearly any pattern and distribution of LV wall thickening can be observed in HCM, with the basal anterior septum in continuity with the anterior free wall being the most common location for LVH 1. However, the most recent and highest quality study 1 supports the use of posterior wall thickness for calculating hypertrophy.

From the Research

Posterior Wall Thickness in Hypertrophy Calculation

• Posterior wall thickness is used instead of septal wall thickness to calculate hypertrophy in certain clinical contexts because it provides a more accurate assessment of left ventricular hypertrophy 2.
• The septal wall thickness can be influenced by various factors such as body surface area, age, and disease conditions, which may lead to inaccurate measurements 3.
• In contrast, posterior wall thickness is a more reliable indicator of left ventricular hypertrophy, as it is less affected by these factors 4.

Clinical Significance of Posterior Wall Thickness

• Posterior wall thickness has been identified as a predictor of sudden cardiac death in pediatric patients with hypertrophic cardiomyopathy, and its prognostic importance has also been examined in adults 5.
• A study found that greater posterior wall thickness was an independent risk factor for late mortality after septal myectomy for obstructive hypertrophic cardiomyopathy 5.
• Additionally, left ventricular posterior wall thickness has been identified as an independent risk factor for paroxysmal atrial fibrillation 6.

Measurement Considerations

• Measurements of interventricular septum and posterior left ventricular wall thickness should be related to body surface area and age to assess their significance 3.
• The ratio of septal to posterior wall thickness can also provide valuable information about left ventricular hypertrophy, with a ratio greater than or equal to 1.3 being common in patients with concentric left ventricular hypertrophy 2.