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regarding overall arrhythmia risk is unknown, but there may be some correlation with worsening ventricular function as well as the specific genetic trigger, such as scn5a or lmna mutations.425 The true prevalence is likely underestimated in LVNC, given the limited approach to arrhythmia surveillance in clinical practice Thromboembolic Disease Thromboembolism may be seen in LVNC and has been reported to occur in 10% to 25% of adults; it may present as a cerebrovascular accident, transient ischemic attack, mesenteric infarction, myocardial infarction, or peripheral embolism.425,426 Thromboembolic events have been reported in children but likely occur less commonly in them than in adults.410 Thrombi may originate from the ventricular cavity in the setting of dysfunction and dilation, the intertrabecular recesses, or the atria, especially in those patients with the restrictive form of LVNC and/or atrial fibrillation Clinical Features Physical Examination The diagnosis of LVNC can be delayed, given limited awareness of the disease and the lack of consensus regarding diagnostic criteria Index cases should undergo a thorough history and physical examination with careful attention to cardiac symptoms, including history of unexplained syncope In addition, a three-generation pedigree should be obtained The majority of pediatric patients with LVNC will have no obvious abnormalities on physical examination However, both children and adults with LVNC may have physical exam findings consistent with the phenotypic expression of disease (exam features with DCM, RCM, etc.) A notable exception to the general physical exam findings is patients with Barth syndrome Barth syndrome is characterized by cardiomyopathy, skeletal myopathy, neutropenia, growth failure, distinctive facial features, developmental delay, and aciduria Unfortunately the variable severity of phenotypic expression may lead to delayed diagnosis.289,427–429 Electrical Abnormalities and Arrhythmias ECG abnormalities are seen in the majority of patients with LVNC.411,412 Common abnormalities include left ventricular hypertrophy, diffuse or isolated T-wave inversion, ST-segment abnormalities or strain pattern, left axis deviation, prolonged QTc interval, and preexcitation Supraventricular arrhythmias have been reported and include atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia Complete atrioventricular block has also been reported Ventricular tachycardia has been reported and may point to patients at higher risk of sudden cardiac death Bradyarrhythmias have also been seen in patients with LVNC Echocardiography Echocardiography has been the mainstay in most centers for the diagnosis and follow-up of LVNC There are several proposed echocardiographic criteria for the diagnosis of isolated LVNC,420,430 the most commonly used being those proposed by Jenni et al.431 These include (1) absence of coexisting cardiac abnormalities, (2) segmental thickening of the left ventricular myocardial wall, consisting of a thin compacted epicardial layer and a thickened endocardial layer with evidence of deep recesses and prominent trabeculations, (3) noncompaction to compaction ratio of greater than 2 at end-systole, (4) localization of cardiac pathology in the apical, midlateral, and midinferior regions of the LV, and (5) color Doppler evidence of deep intertrabecular recesses Cardiac Magnetic Resonance Imaging CMRI is increasingly used in clinical practice to either establish or confirm the diagnosis of LVNC CMRI is also helpful in delineating cardiac morphology in those subjects with poor acoustic windows Petersen and colleagues developed criteria for the CMRI diagnosis of LVNC.432 That diagnosis is made when the ratio of noncompaction to compaction is 2.3 : 1 in diastole Quantitative diagnostic criteria have also been developed using noncompacted mass and higher ratios of noncompaction.433,434 Overall, the degree of trabeculation does not appear to have a significant prognostic impact after accounting for other phenotypic characteristics.409 Management Heart Failure Specific therapies have yet to be developed for the treatment of LVNC However, treatment is typically directed at the concomitant phenotype, as described in other sections of this chapter For those patients with the dilated LVNC phenotype, conventional heart failure therapies are typically employed based on existing guidelines We recently evaluated the efficacy of conventional remodeling therapies in children with LVNC and found improvement in ejection fraction and end-diastolic dimensions.435 For those patients with the HCM LVNC phenotype, consideration of medical therapy may be given to those with symptomatic obstruction Mechanical circulatory support may be needed in some patients, based on guidelines and local practice, and cardiac transplantation may be a consideration, especially for those with the restrictive LVNC phenotype Arrhythmias Significant and potentially life-threatening arrhythmias occur commonly in LVNC The LVNC subtype associated with early-onset arrhythmias has a risk of sudden death Thromboembolism The prevention of thromboembolic disease is an important part of the management strategy in patients with LVNC This is of particular importance in patients with systolic dysfunction (LVEF