Introduction
Acute myocardial ischemia has a profound impact on myocardial structure and function [
1,
2]. Left ventricular ejection fraction (LVEF) serves as a well-established and robust predictor for worse clinical outcome in patients suffering from acute ST-elevation myocardial infarction (STEMI) [
3]. However, propulsion of the intraventricular blood pool is based on a complex interplay of longitudinal shortening, circumferential contraction, and torsion along the long axis of the left ventricle [
4]. The main factor for sufficient LV function is ventricular longitudinal shortening, accounting for about 60% of LV stroke volume both in healthy subjects and in disease, including STEMI [
5‐
7]. Therefore, atrioventricular plane motion has been suggested as an easy-to-measure surrogate for ventricular function and it has been shown that reduced amplitude of valvular plane movement in echocardiography is a predictor of adverse events in patients with various cardiovascular diseases [
8]. Impaired mitral annular plane systolic excursion (MAPSE) in cardiac magnetic resonance (CMR) imaging is an independent determinant of all-cause mortality in patients with reduced LVEF (< 50%), regardless of the underlying cause of impaired systolic function [
9]. Rangarajan et al highlighted a decreased MAPSE as determined by CMR to predict major adverse cardiac events (MACE) in a mixed population, including patients with known coronary artery disease or prior myocardial infarction [
10]. However, the prognostic implications of CMR-derived MAPSE in a large homogenously treated patient cohort with acute STEMI have not been assessed so far. The aim of this study was therefore to investigate whether CMR-determined MAPSE predicts MACE in patients with reperfused first-time STEMI and to evaluate its prognostic value in comparison with routine LVEF measurement.
Discussion
This study is the first to evaluate the prognostic value of CMR-derived MAPSE in a large STEMI cohort treated by pPCI. The main study findings can be summarized as follows:
1.
Septal MAPSE determined by CMR early after reperfused STEMI is a powerful, independent predictor of MACE at long-term follow-up (3 years).
2.
Patients with MAPSE ≥ 9 mm showed a significantly higher MACE-free survival than patients with MAPSE < 9 mm.
3.
The predictive value of MAPSE was significantly higher than that of conventional LVEF.
Therefore, these results argue for the routine assessment of MAPSE in patients early after acute STEMI.
The longitudinal function of the LV is the main contributor to left ventricular pump function [
6,
7]. Supposed longitudinal orientation of subendocardial myocardial fibers has long been discussed as a cause for impaired longitudinal function in patients with acute myocardial infarction [
5,
18‐
20]. However, recent studies on myocardial microstructure assessed by CMR diffusion tensor imaging reported a spiral configuration of myocytes gradually shifting from a right-hand helix subendocardially to a left-hand helix subepicardially, working as a syncytium [
21]. In myocardial infarction, myocardium adjacent to the scarred area shows a decrease in the right-hand helix of subendocardial fibers as well as a decreased range of helix angles across the whole myocardial wall in subacute myocardial infarction in a primate model [
22]. Additionally, myocardial microstructures termed “sheetlets,” consisting of several myocytes, work together as mechanical units to change tilting angle over the cardiac cycle and are thought to be accountable for systolic myocardial thickening [
21]. However, possible changes of sheetlet mechanics in myocardial infarction have not been studied yet. Therefore, underlying mechanisms of impaired longitudinal function in myocardial infarction are still to be discussed, as causality between myocardial fiber architecture and cardiac function has not been proven yet [
23].
However, global longitudinal function remains the main contributor to LVEF in ischemic heart disease [
5]. MAPSE as recorded by different echocardiographic methods, including M-mode, tissue Doppler, and strain imaging and speckle tracking assessed in both acute and chronic setting of myocardial infarction, was shown to predict adverse events [
18‐
20,
24]. However, although easily available and cost-efficient, these techniques suffer from several disadvantages such as angle dependency issues for M-mode method or problems that are related to signal noise [
25]. Strain imaging overcomes monodimensional focality by providing segmental and global information regarding longitudinal deformation but is highly dependent on imaging quality and operator experience [
26]. Advanced CMR tools provide incremental prognostic stratification in patients with STEMI [
27,
28] and easy-to-measure CMR-derived MAPSE has been linked to adverse outcome after STEMI. However, prognostic data of MAPSE in CMR either come from large all-comers cohorts without specific heart disease or from smaller groups of patients with myocardial infarction [
10,
29,
30]. Our homogeneously treated a large patient group with first acute STEMI septal MAPSE with an optimal cut-off value of 9 mm provided the highest value for MACE prediction. Furthermore, septal MAPSE was shown to provide significantly higher predictive value after STEMI compared with lateral or average MAPSE. Other CMR studies revealed threshold values for lateral MAPSE of 9 mm [
9] and 11 mm [
10] respectively as cut-off points for risk stratification in mixed CMR populations. Lateral mitral annulus movement in healthy subjects is usually greater than septal movement (16 ± 3 mm compared with 13 ± 3 mm) [
31]. Therefore, a larger cut-off value for lateral MAPSE is in accordance with anatomical properties. Romano et al used death as a primary endpoint, which might serve as an explanation why their reported cut-off for lateral MAPSE (9 mm) is equal as we found for septal MAPSE. However, Pahlm et al reported a decrease in global and regional MAPSE in infarcted as well as remote myocardium, supporting our thesis that septal MAPSE provides prognostic information regardless of infarct localization [
32]. Based on the significantly higher predictive value of septal MAPSE compared with lateral and average MAPSE in our population as well as on the independency of MAPSE decrease from infarct location, we consider the exclusive measurement of septal MAPSE to be reasonable.
Numerous studies have demonstrated LVEF as a marker of global systolic myocardial function and a powerful predictor of morbidity and mortality in patients with acute reperfused myocardial infarction [
33,
34]. Recently presented CMR indices and scores integrating several structural and/or morphological variables were suggested to provide incremental prognostic validity in STEMI patients [
27,
35]. However, septal MAPSE is a unique, simple measurable and effective marker in standard CMR and our study showed that it offers prognostic information that adds beyond traditional clinical and imaging cardiac risk factors. Moreover, the high reproducibility of MAPSE measurements shown by Romano et al was confirmed in our study by a very low intra- and inter-observer variability [
29]. The superior prognostic performance of MAPSE compared with that of LVEF in STEMI patients may be explained by the suspicion that longitudinally running myocardial fibers are located subendocardially and are most affected by ischemia. However, LVEF primarily tracks radial function of the myocardium. Anyhow, recent studies suggest more complex organization of cardiomyocyte microstructure and dynamics [
21]. In accordance with the findings previously reported by van Kranenburg et al, infarct size in our study was not significantly associated with MACE occurrence [
36]. To what extent large but only subendocardial infarcts are less favorable for long-axis function and prognosis than smaller but transmural infarcts remains to be investigated.
Despite rapid reperfusion of epicardial coronary circulation by pPCI in STEMI, severe microvascular dysfunction, related to initial ischemia and/or to reperfusion injury, may persist [
37]. MVO is a significant and independent short- and long-term prognosticator for morbidity and mortality after STEMI [
38,
39]. In our current study, patients with MVO showed a trend towards higher incidence of MACE but did not reach significance (
p = 0.07). One explanation could be that our definition of adverse outcome included stroke (23% of total MACE). Previous studies only included death and cardiac events (re-in
farction, hospitalization for heart failure) [
36,
38].
Specialized CMR techniques such as strain-encoded MR (SENC) [
39] and feature-tracking software promise risk stratification in patients with various cardiac diseases [
28,
40‐
45]. Several studies recently assessed the relationship of LV strain, infarct characteristics such as edema or hemorrhage, and their association with prognosis in patients with acute myocardial infarction; while Eitel et al [
45] highlighted CMR feature tracking to have incremental prognostic value above LVEF and infarct size, others [
41] showed tissue tracking to not substantially improve risk reclassification beyond LVEF, infarct size, and MVO. However, this technique requires the use of specialized software and consequently has not achieved widespread clinical use [
46]. Moreover, strain imaging is difficult to measure in the acute setting, and there is a lack of evidence for its benefit. Good image quality is an essential prerequisite for strain analysis as well as for LVEF measurement while in case of poor imaging quality, MAPSE could still be a suitable choice for assessing longitudinal function.
Septal MAPSE is simple to measure on 4-chamber routine cine images, available from any vendor without any specific software and with a good inter- and intra-observer variability.
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