This study demonstrated that the value of GLS for predicting MACEs after PCI in STEMI patients is superior to that of LVEF and other clinical risk factors. Compared with the TIMI risk score alone, the TIMI risk score combined with GLS provides a more efficient risk assessment basis for predicting the prognosis of STEMI patients [14].
The TIMI risk score is a simple risk stratification tool. Many studies have confirmed that the TIMI score can be used to assess the short- and medium-term prognosis of STEMI patients [15–18]. STEMI patients with high TIMI scores at admission have a much higher probability of developing MACEs after discharge than those with low scores; thus, the TIMI score is an independent predictor of the occurrence of MACEs. The prognostic value of the TIMI risk score for predicting the risk of in-hospital mortality in STEMI patients (AUC = 0.803) [19], the 30-day mortality rate (in elderly people) (AUC = 0.67) [20] and the 1-year mortality rate (AUC = 0.73) [5] is not high, and it cannot be used to identify all high-risk patients. In our study, the prognostic value of the TIMI risk score for the occurrence of MACEs after 1 year was 0.703, which is similar to the results of previous studies. Therefore, it is necessary to identify objective indicators to improve the discriminant ability of the TIMI risk score.
GLS can detect subtle changes in the myocardium after infarction, thereby more accurately assessing systolic function and providing additional prognostic information [21–23]. A considerable number of STEMI patients have undergone PCI, and their LVEF is close to normal or may even remain unchanged; consequently, they are considered low-risk patients [24]. The absolute number of MACEs in STEMI patients with LVEF preservation is considerable .Previous studies [25] showed that patients with an LVEF < 40% had increased mortality and an increased incidence of MACE, massive hemorrhage and net adverse clinical event (NACE); furthermore, they reported that moderate left ventricular dysfunction was not a predictor of adverse clinical outcomes. In contrast, GLS improved the individualized risk stratification after STEMI, and in the population with known or suspected left ventricular dysfunction, GLS was superior to LVEF for predicting mortality. Therefore, compared to LVEF, GLS is a stronger predictor of MACEs [26–28].
This study further confirmed that GLS (HR = 1.312) was superior to LVEF and other clinical factors for predicting MACEs at 1 year. As the GLS level decreased, the risk of MACEs in STEMI patients increased significantly. The main pathophysiological explanations for this phenomenon are as follows: 1. The left ventricular myocardium is a heterogeneous structure containing myocardial spirals and multilayered fibers; thinning of the myocardium occurs at the infarcted segments, and compensatory hypertrophy develops in the noninfarcted myocardium. Therefore, all segments are not uniform, and there are certain limitations in replacing the global cardiac systolic function as a volumetric measurement of LVEF with local myocardial function in the absence of changes in cardiac morphology. 2. Longitudinal fibers are the main component of the subendocardial myocardium, and the subendocardial myocardium is more susceptible to changes in ventricular pressure and coronary blood supply and more sensitive to ischemia than the midmyocardium and subepicardial myocardium [29].Therefore, longitudinal stress is more sensitive to myocardial ischemia than other parameters (hoop, circumferential, and torsion stress) [29] and GLS has been shown to be a sensitive indicator of subclinical myocardial injury [30]. Although GLS can be used as a stable and sensitive indicator of cardiac function assessment, the clinical risk and prognosis of STEMI patients also differ due to differences in clinical characteristics [14]. Unless GLS is combined with the patient’s clinical data, it cannot provide a sufficient prediction of the prognosis.
This study showed that compared with the TIMI risk score alone, the GLS combined with the TIMI risk score (AUC: 0.810 vs 0.703) and the GLS and TnT combined with the TIMI risk score (AUC: 0.815 vs 0.703) had better predictive power. (Fig. 3). However, there was no significant difference between the TIMI risk score combined with GLS and the TIMI risk score combined with GLS and clinical risk factors. Comparatively speaking, the TIMI risk score combined with GLS was more efficient and effective in clinical application, which can accurately predict the occurrence of MACE.
In contrast, TIMI combined with GLS is more efficient and convenient in clinical application. The main reasons for this are as follows: 1) The TIMI risk score provides a comprehensive reference for patients’ clinical risk factors. It is highly subjective and lacks objective variables; especially for patients with atypical clinical symptoms and no characteristic ECG manifestations, it often underestimates the risk of disease [20]. 2) As an objective indicator of high-quality cardiac function evaluation, GLS is far superior to LVEF for predicting MACE. The inclusion of GLS in the TIMI risk score provides complementary advantages.
This study has the following limitations: (1) The sample size is small, and the influencing factors of the included studies are few. To confirm the effectiveness of the optimized combination indicators in this study for predicting the prognosis of STEMI patients, it is necessary to increase the sample size and conduct longer-term studies. (2) In this study, only a single GLS indicator was used. We should further study the guiding significance of different myocardial strain parameters in different periods on long-term prognosis while extending the follow-up time.