Left Ventricular Systolic Function
The importance of a baseline echocardiogram during the acute-phase of myocarditis is important as it allows for appropriate classification between severe and non-severe myocarditis, based on preservation of LVEF. This is important as these populations exhibit different pathologic changes, disease states and clinical outcomes(23). Impairment in LV systolic function in patients with myocarditis is attributed to a greater percentage of myocardial involvement secondary to an inflammatory myopathic process, which is consistent with the immune checkpoint inhibitor (ICI) myocarditis(24). As a result, there is development of regional and/or global systolic dysfunction, which is typically seen in more severe forms of myocarditis, such as immune-mediated myocarditis. Two of the included studies in this meta-analysis demonstrated no significant differences in LVEF between myocarditis and control populations, both in the initial phase(17), and on a follow-up at a mean period of 22 months, highlighting the heterogeneous nature of this disease process (15).Interestingly, the majority of patients with myocarditis in this systematic review had a normal LVEF. Only one study demonstrated an impaired mean LVEF in the myocarditis population. This study focused on patients with ICI myocarditis secondary to checkpoint inhibition chemotherapy (13).
This study also reinforces the value of LV-GLS in differentiating cases of both severe and non-severe myocarditis in both the acute- and sub-acute disease states. All included studies clearly demonstrated significantly lower LV-GLS values in myocarditis populations, compared to controls suggesting that LV-GLS may be a more sensitive marker of LV systolic function compared to LVEF. LV-GLS was shown to be directly associated with degree of myocardial inflammation, and diagnostic of regional myocardial fibrosis, when correlated with CMR(16). In some longitudinal studies, LV-GLS was shown also shown to remain impaired on follow-up(17) , which highlights the value of LV-GLS as a potential marker for monitoring and diagnosing chronic myocarditis or response to treatment.
The main advantages of LV-GLS compared to standard echocardiographic parameters in assessment of myocarditis, are the signal-to-noise ratio, angle independence and ability to differentiate between active and passive myocardial segmental motion(25). LV-GLS has recently emerged as a measure of cardiac function which is sensitive in detecting subclinical cardiac injury relative to LVEF and has been shown to have prognostic value in multiple pathologies