During the last two decades, two-dimensional (2D) speckle tracking echocardiography (STE), an angle-independent technique, has been employed for quantifying both regional and global myocardial function in various clinical settings.1, 2, 3 This imaging modality measures the deformation (strain) of myocardial fibers on longitudinal, circumferential and radial directions and the rate at which this deformation occurs (strain rate).

Left ventricular (LV) global longitudinal strain (GLS) is the most commonly used 2D-STE derived index of myocardial contractility.

Even if LV-GLS is more sensitive than left ventricular ejection fraction (LVEF), assessed by conventional transthoracic echocardiography (TTE), for detecting subclinical myocardial dysfunction, it has not yet been incorporated into everyday clinical practice due to a number of intrinsic technical limitations which can affect the calculation of strain parameters and their physiological meaning.

Baykiz et al.4 should be congratulated for their scientific interest and effort, trying to evaluate depression, anxiety, and stress symptoms and their relationship with subclinical myocardial dysfunction assessed by LV-GLS, in patients who had recovered from COVID-19 infection.4 The authors hypothesized that patients who suffered from COVID-19 may be more prone to develop anxiety after recovery. A statistically significant negative correlation between LV-GLS values and a number of measures of event-specific distress, such as the Depression Anxiety Stress Scales (DASS)-21 total score, the DASS-21 anxiety subscale score, the Impact of Event Scale-Revised (IES-R) total score, the IES-R intrusion subscale and finally the IES-R hyperarousal score, was demonstrated in COVID-19 patients, especially in those patients with comorbid diseases or severe pneumonia. Interestingly, there was no significant correlation between the above-mentioned scores and the other conventional echocardiographic parameters in the same study population. In the multivariate linear regression analysis, educational level and DASS-21 total score were found to be independent predictors of LV-GLS impairment in recovered COVID-19 patients.

In light of their findings, the authors speculated that COVID-19 patients with higher scores may have experienced more psychological distress symptoms, which may have had a more negative impact on subclinical myocardial systolic function, as assessed by 2D-STE analysis.

No reported previous study has demonstrated the potential association between myocardial deformation indices and the psychological status of patients recovered from COVID-19 infection. We believe that this is the main strength of the study.

However, it has to be taken into account that the correlations between LV-GLS and several depression, anxiety and stress scores were statistically significant in a small group of patients only and with such low absolute values that the real clinical significance of these correlations appears very limited, at least at the individual case level. Notably, the most significant correlations have been reported in the small subgroups of patients with comorbidities and severe pneumonia. LV-GLS was also significantly correlated with other socio-economic variables, such as body mass index (BMI).

These findings make very difficult to understand the clinical meaning and relevance of such complex physiological information and how eventually using it in the clinical decision-making process in the individual case.

It's noteworthy that 2D-STE analysis depends on the temporal stability of tracking patterns and needs high quality grey-scale images for reducing inter- and intra-observer variability of tracking data.5 Another major limitation of 2D-STE methodology is the lack of standardisation, due to a relevant intervendor variability.5

Beyond the above-mentioned limitations, which are related to the technique itself, it's important to consider the possible influence of the chest wall conformation on the cardiac kinetics and deformation indices.5

The anterior chest wall deformity, due to pectus excavatum (PE), pectus carinatum and/or flat chest with straight back, can modify cardiac mechanics, through an extrinsic compression on cardiac chambers, leading to intraventricular dyssynchrony and consequent impairment in myocardial strain parameters.5

The chest wall conformation may noninvasively be assessed by using the modified Haller index (MHI), obtained by dividing the latero-lateral (L-L) maximum external thoracic diameter by the antero-posterior (A-P) minor internal thoracic diameter, without using chest X-ray (CXR), both diameters measured at the end of inspiration6 (Fig. 1 ).

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Fig. 1

The modified Haller index, obtained by dividing the L-L thoracic diameter (Panel A) by the A-P thoracic diameter (Panel B). The L-L thoracic diameter is measured with the subject in the standing position and with open arms, by using a rigid ruler in centimeters coupled to a level (the measuring device), placed at the distal third of the sternum, in the point of maximum depression of the sternum. The A-P thoracic diameter is measured, during conventional transthoracic echocardiography, as the distance between the true apex of the sector (the point of entry of ultrasound into the chest) and the posterior wall of the descending thoracic aorta, visualized behind the left atrium. A-P, antero-posterior; Asc ao, ascending aorta; Desc Ao, descending aorta; LA, left atrium; L-L, latero-lateral; LV, left ventricle; RV, right ventricle.

Compared to subjects with normal chest wall conformation, healthy individuals with PE, as noninvasively defined by an MHI >2.5,7 are commonly found with anxiety disorders, nonspecific ST-segment and T-wave (NS-STT) abnormalities and isolated ventricular premature beats on resting ECG, smaller cardiac chamber dimensions and mitral valve prolapse on TTE and finally significantly impaired strain parameters due to basal sternal compression on cardiac chambers.8, 9, 10, 11

An increased MHI, due to a narrow A-P chest diameter, may be the main anthropometric determinant of a reduction in myocardial deformation indices, particularly at basal level, detected in subjects with a concave-shaped chest wall and/or PE, in absence of any intrinsic myocardial dysfunction. A number of considerations would support the importance of this “mechanical theory”. First, the physiological apex-to-base gradient (highest-to-lowest) in left ventricular deformation is usually maintained in PE subjects, both in longitudinal and circumferential directions, thus indicating normal underlying myocardial function. Secondly, the alteration of LV-GLS is generally accompanied by LV global circumferential strain (GCS) impairment in PE subjects, departing from the typical behaviour of LV-GLS which usually becomes altered at an earlier stage compared to LV-GCS.12 Third, the correlation between MHI and strain parameters is strictly correlated to the degree of the anterior chest wall deformity (MHI >2.5), whereas it cannot be observed in individuals with normal chest conformation (MHI ≤2.5).8 Examples of LV-GLS bull's eye plot patterns obtained in two healthy subjects with PE and normal chest shape conformation, respectively, are depicted in Fig. 2 , A and B.

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Fig. 2

Examples of LV-GLS bull's eye plot patterns obtained in two healthy subjects, with PE (Panel A) and with normal chest shape (Panel B), respectively. The PE subject (MHI>2.5) was found with a significant impairment in basal myocardial strain (light pink and pale pink segments), with a moderate impairment in mid myocardial strain (light red segments) and with a normal apical strain (bright red segments); the resultant LV-GLS (−17.4%) was moderately impaired. On the other hand, the subject with normal chest wall conformation (MHI ≤2.5) was found with uniformly red pattern of the bull's eye plot, indicating normal regional and global longitudinal deformation of myocardial segments (LV-GLS = −27.2%). GLS, global longitudinal strain; LV, left ventricular; MHI, modified Haller index; PE, pectus excavatum.

It is then possible that the statistically significant correlation between LV-GLS and psychological distress symptoms detected in patients recovered from COVID-19 infection by Baykiz et al., might also be influenced by chest conformation and obesity in such patients, aside from comorbidities and severe pneumonia.4

In conclusion, we suggest the possibility that the restricted deformation of LV basal segments or a global impairment of myocardial strain indices might not always and necessarily be direct and univocal expression of intrinsic myocardial dysfunction, but may be possibly, at least in part, conditioned by artifactual and/or external chest shape determinants, which could be dominant in individual cases and should always be taken into account.