*2.4. Echocardiographic Data Collection*

Echocardiography (two-dimensional, color Doppler, and M-mode) was performed to assess cardiac structure, ventricular size and function (fractional shortening and ejection fraction (EF)), and valvular regurgitation. The diagnosis of congestive heart failure (CHF) was defined by clinical findings of tachypnea, feeding difficulty, and cyanosis; cardiomegaly on chest radiography; and decreased LVEF on echocardiography. Cardiomegaly was defined as a cardiothoracic ratio of ≥ 0.55 (≥0.60 for patients aged less than 1 year) on chest radiography or LV end-diastolic diameter (LVDD) of ≥120% of the normal value on echocardiography.

Patients were diagnosed with LVNC based on the following criteria defined by Ichida et al.: (1) two-layered myocardium with a noncompacted-to-compacted (N/C) ratio of more than 2.0 at end diastole, (2) prominent endomyocardial trabeculations that are distributed in more than one LV wall segment, and (3) deep fossas filled with blood from the ventricular cavity on color Doppler imaging [8]. All echocardiographic records were analyzed by two reviewers (K.H. and S.O.).

The thickness of the LV wall and N/C ratio (N; the depth of trabecular recesses. C; compacted wall thickness) were measured according to previously reported methods to quantify the extent of the trabecular meshwork [9,10]. The thickness of the compacted layer in the LV posterior wall (LVPWC) and LVDD are represented as z-scores based on the body surface area [11].

N/C ratios of 5 LV wall segments at end diastole; the anterior, lateral, and posterior walls; and interventricular septum at the level of the papillary muscles in the short-axis view and the apex in the long-axis view were measured [12–14].
