Fractal analysis of left ventricular trabeculae in post-STEMI: from acute to chronic phase

Abstract

Purpose: The temporal evolution of ventricular trabecular complexity and its correlation with major adverse cardiovascular events (MACE) remain indeterminate in patients presenting with acute ST elevation myocardial infarction (STEMI).

Methods: This retrospective analysis enrolled patients undergoing primary percutaneous coronary intervention (pPCI) for acute STEMI, possessing cardiac magnetic resonance (CMR) data in the acute (within 7 days), subacute (1 month after pPCI), and chronic phases (6 months after pPCI) from January 2015 to January 2020 at the three participating sites. Fractal dimensions (FD) were measured for the global, infarct, and remote regions of left ventricular trabeculae during each phase. The potential association of FD with MACE was analyzed using multivariate Cox regression.

Results: Among the 200 analyzed patients (182 men; median age, 61 years; age range, 50-66 years), 37 (18.5%) encountered MACE during a median follow-up of 31.2 months. FD exhibited a gradual decrement (global FD at acute, subacute, and chronic phases: 1.253 ± 0.049, 1.239 ± 0.046, 1.230 ± 0.045, p < 0.0001), with a more pronounced decrease observed in patients subsequently experiencing MACE (p < 0.001). The global FD at the subacute phase correlated with MACE (hazard ratio 0.89 (0.82, 0.97), p = 0.01), and a global FD value below 1.26 was associated with a heightened risk.

Conclusion: In patients post-STEMI, the global FD, serving as an indicator of left ventricular trabeculae complexity, independently demonstrated an association with subsequent major adverse cardiovascular events, beyond factors encompassing left ventricular ejection fraction, indexed left ventricular end-diastolic volume, infarct size, heart rate, NYHA class, and post-pPCI TIMI flow.

Critical relevance statement: In patients who have had an ST-segment elevation myocardial infarction, global fractal dimension, as a measure of left ventricular trabeculae complexity, provided independent association with subsequent major adverse cardiovascular event.

Key points: • Global and regional FD decreased after STEMI, and more so in patients with subsequent MACE. • Lower global FD at the subacute phase and Δglobal FD from acute to subacute phase were associated with subsequent MACE besides clinical and CMR factors. • Global FD at the subacute phase independently correlated with MACE and global FD value below 1.26 was associated with higher risk.

Keywords: Cine; Fractals; Magnetic resonance imaging; Myocardium; ST elevation myocardial infarction.

Fig. 1

Case example. Cardiac magnetic resonance (CMR) images of a 37-year-old man with acute right coronary artery (RCA) infarction. Primary percutaneous coronary intervention (pPCI) was conducted 24 h after the initial symptoms emerged. CMR was performed on day 3, 1 month, and 6 months. No subsequent MACE occurred within the 25-month follow-up

Fig. 2

Study inclusion flowchart. STEMI: ST elevation myocardial infarction, pPCI primary percutaneous coronary intervention, CMR cardiac magnetic resonance, MI myocardial infarction, MACE major adverse cardiovascular event

Fig. 3

Fractal dimension (FD) in subjects with versus without major adverse cardiovascular events (MACE). A Paired t-test of FD in patients with subsequent MACE. B Paired t-test of FD in patients without MACE. C FD distribution from base to apex in patients with subsequent MACE. D FD distribution from base to apex in patients without MACE. *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001; ns, not significant

Fig. 4

Case examples of patients with subsequent major adverse cardiovascular events (MACE) (A) and without MACE (B). Only mid-ventricular level images of late gadolinium enhancement, cine, and global FD figures at acute, subacute, and chronic phases are summarized in this figure. A A 50-year-old man with acute left anterior artery (LAD) infarction. Global FD decreased from the acute phase to the chronic phase. Heart failure occurred 19 months after primary percutaneous coronary intervention. B A 65-year-old man with acute LAD infarction. Global FD slightly elevated in the subacute phase and then decreased in the chronic phase. No subsequent MACE occurred within the 38-month follow-up

Fig. 5

A Receiver operating characteristic analysis of global and Δglobal fractal dimension (FD) of the subacute phase for the prediction of major adverse cardiac events (MACE). The area under the curve (AUC) in the ROC analysis of global FD and Δglobal FD in the subacute phase for predicting MACE was 0.639 and 0.747, respectively. The cut-off values for global FD (1.26) and Δglobal FD (-0.009) were determined by the Youden index. B Kaplan–Meier curves for MACE based on the optimal cut-off of global FD in the subacute phase (> 1.26 versus ≤ 1.26), p = 0.006. C Kaplan–Meier curves for MACE based on the optimal cut-off of Δglobal FD in the subacute phase (> -0.009 versus ≤  -0.009), p = 0.0001