Background- A high degree of noncompacted (trabeculated) myocardium in relationship to compact myocardium (trabeculated to compact myocardium [T/M] ratio >2.3) has been associated with a diagnosis of left ventricular noncompaction (LVNC). The purpose of this study was to determine the normal range of the T/M ratio in a large population-based study and to examine the relationship to demographic and clinical parameters. Methods and Results- The thickness of trabeculation and the compact myocardium were measured in 8 left ventricular regions on long axis cardiac MR steady-state free precession cine images in 1000 participants (551 women; 68.1±8.9 years) of the Multi-Ethnic Study of Atherosclerosis cohort. Of 323 participants without cardiac disease or hypertension and with all regions evaluable, 140 (43%) had a T/M ratio >2.3 in at least 1 region; in 20 of 323 (6%), T/M >2.3 was present in >2 regions. A multivariable linear regression model revealed no association of age, sex, ethnicity, height, and weight with maximum T/M ratio in participants without cardiac disease or hypertension (P>0.05). In the entire cohort (n=1000), left ventricular ejection fraction (β=-0.02/%; P=0.015), left ventricular end-diastolic volume (β=0.01/mL; P<0.0001), and left ventricular end-systolic volume (β=0.01/mL; P<0.001) were associated with maximum T/M ratio in adjusted models, whereas there was no association with hypertension or myocardial infarction (P>0.05). At the apical level, T/M ratios were significantly lower when obtained on short- compared with long-axis images (P=0.017). Conclusions- A ratio of T/M of >2.3 is common in a large population-based cohort. These results suggest re-evaluation of the current cardiac MR criteria for left ventricular noncompaction may be necessary.
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