Indexing left ventricular wall thickness to body surface area improves prognostic value

Background: Guidelines provide normal ranges of left ventricular (LV) wall thicknesses (WT) without indexing. We hypothesized that indexing WT to body surface area (BSA) improves prognostic value.

Methods: We examined the relationship between WT and BSA in 9737 patients undergoing echocardiography without risk factors for LV hypertrophy other than obesity. We compared WT to BSA and examined the relationship of WT and LV mass index (LVMI) to mortality.

Results: There is a linear relationship between BSA and septal and posterior WT (r = 0.38, P < 0.001 for each). Higher quartiles of BSA were associated with increased WT (P < 0.001). After adjusting for age and gender, greater mean WT (MWT) (Hazards Ratio [HR] 1.10 per mm, 95% Confidence Interval [CI] 1.04-1.16, P = 0.001, C-statistic 0.66), LVMI (HR 1.01, 95% CI 1.001-1.01, P = 0.01, C-statistic 0.66), and indexed MWT (HR 1.34 per mm/m² , 95% CI 1.23-1.47, P < 0.001, C-statistic 0.67) are each associated with increased mortality, with indexed MWT having the highest prognostic value. Each decile of indexed MWT ≥8th decile was associated with increased mortality compared to the 1st decile (P < 0.01 for each). Individuals with indexed MWT ≥8th decile (≥5.0 mm/m² ) had increased adjusted mortality (HR 1.67, 95% CI 1.43-1.94, P < 0.001, C-statistic 0.67); this had improved prognostic value over guideline definitions of increased MWT (C-statistic 0.66) or LVMI (P = NS).

Conclusions: We observe a linear relationship between BSA and WT. Indexing WT improves mortality prediction over LVMI and nonindexed WT. These findings support indexing WT to BSA.