Echocardiography in myocardial infarction : aspects on diastolic function and evaluation by cardiovascular magnetic resonance imaging

Abstract

Background: Echocardiography is routinely used to evaluate patients with known or suspected myocardial infarction (MI). Cardiovascular magnetic resonance imaging (CMR) provides the ability to quantify myocardial infarction size (IS), and to establish an underlying diagnosis in MI cases with nonobstructive coronary arteries (MINOCA). While echocardiography provides valuable information regarding cardiac function, the relationships between how pathology is manifested on CMR, and the information gleaned from echocardiography are not fully explored. The focus of this thesis was 1) to assess diastolic function and mechanics in MI, and 2) to assess the ability of echocardiography to identify patients needing further evaluation by CMR in MINOCA.

Methods and results: In Study I, a software application was developed for the purpose of facilitating the analysis of diastolic function using the parameterized diastolic filling (PDF) method. Inter- and intraobserver variability was studied using patients from Study III and Study IV. The software was successfully developed and made publicly available at www.echoewaves.org, and inter- and intraobserver reliability was good or excellent for most PDF measures (intraclass correlation coefficient 0.80-0.99).

In Study II, an available clinical database of patients undergoing resting and stress echocardiography was used to identify a cohort of patients with normal echocardiographic findings. PDF analysis was performed in 138 patients for the establishment of normal reference values for the method, and presented as sex-specific 95% reference intervals.

In Study III, a pre-planned substudy of the RECOND trial, the association between myocardial infarction size (IS) and parameters of diastolic function, and whether the peri-infarction edema of the myocardium at risk (MaR) influenced these relationships was investigated. Weak associations were found between IS and deceleration time (R² = 0.24, p < 0.001), left atrial volume index (R² = 0.13, p = 0.01), and the PDF stiffness parameter k (R² = 0.21, p < 0.001). The only parameter influenced by the addition of MaR was e′ (increase in adjusted R² = 0.08, p = 0.02). The PDF damping parameter c was the only parameter associated with final IS at 6 months follow-up (R² = 0.22, p = 0.001).

In Study IV, a pre-planned substudy of the SMINC2 study, the value of normal vs pathological echocardiography, as well as the blood biomarkers hs-TnT and NT-pro-BNP, for selecting patients presenting with MINOCA for further evaluation with CMR was investigated. Pathological echocardiography identified patients with a CMR diagnosis with sensitivity 77%, specificity 38%, positive predictive value 82%, and negative predictive value 30%. At low levels of hs-TnT and NT-pro-BNP, the probability of obtaining a diagnosis by CMR was still substantial (> 25%).

Conclusions and summary: In summary, a freely available and reliable software application for the application of the PDF method was developed (Study I), and normal reference limits were provided, for use in further clinical research (Study II). IS as measured by CMR does not seem to be a major determinant of diastolic dysfunction after MI, and other factors are likely to be more important (Study III). CMR is a valuable diagnostic tool for the evaluation of patients with MINOCA, even when echocardiographic examinations are normal, and levels of hs-TnT and NT-pro-BNP are low (Study IV).