Left ventricular noncompaction (LVNC) cardiomyopathy is characterized by prominent myocardial trabeculations and deep recesses.^1-3 The clinical spectrum of the disorder ranges from being completely asymptomatic to progressive left ventricular (LV) systolic impairment, a tendency to fatal arrhythmias and systemic thromboembolic events.³ The clinical diagnosis is predominantly reliant on three proposed echocardiographic criteria and based on an increased ratio of the noncompacted inner layer to the compacted outer layer of the LV myocardium (Figure 1).³

Figure 1: Echocardiographic Criteria for LV Noncompaction

The past two decades have witnessed significant advances in tissue harmonics and image resolution in echocardiography, which has enabled detailed assessment of the ventricular myocardium. Coinciding with these developments has been an increasing number of reports of athletes with LVNC.^4-7

In a large study⁴ of over 1,000 asymptomatic athletes, 18% showed increased LV trabeculation and 76 (8%) fulfilled echocardiographic criteria for LVNC. These findings suggest that in most athletes, increased LV trabeculation, which may fulfill criteria for LVNC represents a non-specific epiphenomenon in response to a chronic increase in preload and afterload associated with exercise. However, 10 (0.9%) athletes had T-wave inversion and reduced resting indices of systolic function that may be considered diagnostic of LVNC. This gray zone is smaller than that observed in hypertrophic cardiomyopathy (2%)⁸ but conversely greater than that for ARVC (0.3%).⁹ The distinction between cardiac remodeling from athletic training and LVNC is important given that the primary cardiomyopathies are the most common cause of exercise related sudden cardiac death in young athletes.¹⁰

The dilemma in differentiating benign myocardial trabeculations from LVNC arises because the current LVNC criteria^1,2,11,12,13 are derived from small cohorts and lack specificity particularly in asymptomatic, low-risk populations. Although the criteria rely on the presence of increased LV trabeculations and the presence of a double myocardial layer, an outer compacted area and an inner noncompacted layer, they differ from each other with respect to the precise area and timing in the cardiac cycle for the measurement of the compacted and noncompacted layers.

The authors of this Expert Analysis article propose the following guidance, which requires utilizing several diagnostic modalities, for the assessment of athletes with a triad of echocardiographic features fulfilling criteria for LVNC, impaired resting LV function and T-wave inversion on the electrocardiogram (Figure 2). The proposal is based on experience of comparing athletes with features of LVNC and actual patients diagnosed with the condition.⁴

Figure 2: Differentiating Physiological Increased LV Trabeculations From Pathological Left Ventricular Noncompaction AF = atrial fibrillation; CMR = cardiac magnetic resonance imaging; LBBB = left bundle branch block; LV = left ventricular; VT = ventricular tachycardia.

Patients with LVNC frequently (75%) express symptoms of LV dysfunction whereas athletes are asymptomatic. These individuals also frequently (66%) demonstrate a LV cavity >64 mm, an ejection fraction <45%, suppressed longitudinal LV function (Sa <9 cm/sec), and impaired LV filling (E' <9 cm/sec). In contrast, athletes with increased LV trabeculation and reduced EF usually show an EF range of 45-50% and normal indices of longitudinal LV function and normal diastolic function. Other echocardiographic parameters, including speckle tracking and strain, may be helpful in borderline cases.

The pattern of T-wave inversion is different between the two groups; patients with noncompaction show T-wave inversion in the inferolateral leads, whereas the majority of athletes showed T-wave inversion in V1-V3. Left bundle branch block (LBBB) is most unusual in athletes but is common in patients with LVNC. In the authors' experience, a cardiopulmonary exercise stress test followed by a peak exercise echocardiography is useful in the differentiation between the two groups. Athletes reveal a high peak VO₂ (>120% predicted for age and size) and dynamic LV contraction, whereas patients with LVNC show low peak VO₂ and exercise echocardiogram reveals poor LV contractile reserve on exercise. The identification of non-sustained ventricular tachycardia during exercise in athletes with criteria for LVNC would support pathology. In situations in which image quality is poor on transthoracic echocardiography, cardiac MRI may support a myopathic process by revealing fibrosis following gadolinium.

Long-term follow-up is crucial for athletes with a family history of premature sudden cardiac death and heart failure. We would also recommend screening of first-degree relatives for features of LVNC; the detection of another member with a similar phenotype would favor a diagnosis of LVNC.

Conclusion

Current imaging criteria for LVNC are non-specific in athletes and prone to an erroneous diagnosis. Increased cardiac preload is the most probable mechanism for increased trabeculation in the majority of athletes. A minority of athletes reveal the triad of increased LV trabeculations fulfilling LVNC criteria, T-wave inversion and LV systolic dysfunction. This group requires more detailed investigation and long-term follow-up.

References

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Keywords: Athletes, Bundle-Branch Block, Cardiomyopathies, Cardiomyopathy, Hypertrophic, Death, Sudden, Cardiac, Diastole, Echocardiography, Electrocardiography, Exercise Test, Follow-Up Studies, Gadolinium, Heart Failure, Humans, Myocardium, Phenotype, Sports, Tachycardia, Ventricular

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