Since its first report, TS has been increasingly diagnosed, with a current prevalence which is estimated at approximately 2% in all patients presenting with clinical manifestation of ACS and up to 10% if only women are considered. Other Authors think that TS prevalence is underestimated 19,20. In fact, according to Minhas et al., TS incidence has been increasing over the years 21. The diagnosis of TS remains a challenge due to its clinical manifestations, which may closely resemble ACS 1. Coronary angiography with left ventriculography is considered the gold standard diagnostic tool for a definitive diagnosis of TS 22, but this procedure is invasive and at risk of the onset of life-threatening events. For these reasons, several non-invasive imaging modalities have been proposed in assessing TS 1.CMR is an excellent tool aimed at assessing the typical regional wall motion abnormalities, with precise quantification of RV and LV systolic function. CMR allows also to detect the presence of reversible and irreversible myocardial injuries 6. Eitel et al. reported specific CMR criteria for TS diagnosis which include the combination of typical contraction pattern, oedema, and absence of LGE 5. Besides, CMR is better than other non-invasive imaging for the detection of RV involvement. 5,14 Right ventricular disfunction in TS has being recognized with an incidence from 13–50%, and it is associated with worse outcomes 14,23.
This study shows that tissue mapping techniques and CMR-TT can improve the diagnosis of TS. Its main findings are as follows: (1) parametric mapping and CMR-TT allow to detect LV impairment in TS patients; (2) particularly, T1 and T2 mapping enable the objective assessment of regional LV myocardial tissue alteration with excellent performance; (3) GLS in TS is significantly lower than in healthy subjects; (4) all apical strain parameters in TS are significantly impaired with respect to controls; (5) basal radial strain (RS) in TS is significantly higher in comparison with healthy subjects. These findings highlight the potential of parametric mapping and CMR-TT in refining the diagnosis of TS.
Diagnostic value of parametric mapping in TS patients
T1 and T2 mapping are quantitative imaging methods that enable an objective assessment of myocardial tissue properties, thus increasing CMR diagnostic accuracy16,17
We found significantly higher T1 and T2 mapping values in patients with TS, according to the current literature in the field 24,25, mainly at the apex but even in remote and apparently normal myocardium in TS patients with involvement of the whole LV. T2 mapping decreased gradually from apical to basal regions. Our results showed a higher parametric mapping values in patients segments without wall motion abnormalities. The substrate for this widespread myocardial involvement is so far unexplained. Histological studies suggest several mechanisms in the onset of TS, including multi-vessel coronary spasm, increased catecholamine levels inducing myocardial toxicity and an excessive transient ventricular afterload induced by a peak of catecholamines.26
Wilson et al. in post-mortem examination demonstrated that macrophages, predominantly M1, are the leading cellular protagonist in the onset of myocardial inflammation in TS. In addition, the authors reported that similar inflammation changes were observed even in normal myocardium of post-mortem TS patients.27
Consistently with a previous study, T1 and T2 mapping provided excellent performances in TS patients compared to healthy controls 24,25. Our study suggests that parametric mappings are robust markers in patients with TS and add information regarding the extent of myocardial tissue alterations in this setting.
Diagnostic value of CMR-TT in TS patients
Another specific CMR hallmark in TS are the typical regional wall motion abnormalities. Generally speaking, CMR is the gold standard for the assessment of cardiac function and volume quantification28. Many studies have demonstrated that myocardial strain reflects subtle changes in myocardium contractility 29–31. At echocardiography, STE is a very useful tool for quantitative assessment of myocardial function, but it is limited in case of suboptimal acoustic views in the setting of poor acoustic windows, such as in overweight and obese patients or in those with chest deformity or with chronic lung diseases 32. Furthermore, echocardiography evaluation of RV is challenging and frequently limited to a subjective qualitative assessment.33
Myocardial strain analysis with CMR-TT, despite being time-consuming, could help in this setting.
In the commonest type of TS, i.e. that with apical ballooning, LS parameters decrease from the base to the apex12. Our results are in line with the current literature12. In particular, we found that basal longitudinal strain (LS) is preserved with respect to mid- and apical LS. These results require further evaluation and might be due to partial myocardial recovery, as reported by Kim et al., who showed an improvement of LS from LV base to apex with time34
In addition, the higher value of basal RS in TS could be explained by the transient LV hyperkinetic motion of the basal segments, as already reported by Kobayashi et al 35. So, the hyperkinesis of basal segments is determined by an increase in RS, but not in LS and CS.
Finally, our findings did not show and significant RV involvement in the enrolled TS cohort.
A major limitation of this research is the relatively small number of patients. However, the study reflects a series of selected consecutive patients with a not so common disease. The relatively small sample size can certainly be improved in the future by enrolling a larger cohort. Moreover, the impairment in myocardial strain in TS patients would probably have been different if CMR had been performed within a shorter period of time, ideally the same day of admission to hospital.