1008Cardiac index after acute ST- segment elevation myocardial infarction measured with phase-contrast cardiac magnetic resonance imaging

Abstract

Objectives: Cine cardiac magnetic resonance (CMR) represents the gold-standard in the non-invasive determination of left-ventricular function, but might overestimate cardiac output in different pathophysiological conditions. Phase-contrast CMR might provide a fast and robust alternative. We therefore investigated the use of phase-contrast CMR to assess cardiac index in patients early after acute ST-segment elevation myocardial infarction (STEMI). Methods: We included n = 90 patients with first STEMI (mean age: 59 ± 11years) who underwent CMR within 7 days after primary angioplasty for the index event. Cine true-FISP sequences in the left-ventricular short-axis and a free breathing retrospectively gated velocity-encoded, phase-contrast CMR protocol on the level of the ascending aorta were applied. The phase-contrast protocol was validated against cine CMR in 15 healthy volunteers. Inter- and intraobserver agreement was determined in volunteers as well as in n = 16 STEMI patients. The correlations of clinical variables (age, gender, ejection fraction, NT-pro-brain natriuretic peptide [NT-proBNP]) with cardiac index in STEMI patients were calculated. Results: There was a strong agreement of cine CMR with phase-contrast CMR in healthy volunteers (r: 0.818, mean difference: -0.13 l/min/m2, error ±18%). Agreement was lower in STEMI patients (r: 0.611, mean difference: -0.17 l/min/m2, error ±32%). In STEMI patients cardiac index measured with phase-contrast CMR was 2.7 l/min/m2 and showed lower intraobserver (1.4 % vs. 8.8 %) and interobserver variability (8.5 % vs. 11.6 %) than cine CMR. Cardiac index decreased by 16ml/min/m2 per year (r = 0.356, p = 0.001) in STEMI patients. Furthermore, cardiac index was correlated with patients ejection fraction (r = 0.256, p < 0.02) and inversely correlated to NT-proBNP values (r = -0.220, p < 0.05). Conclusion: Phase-contrast CMR is a valid and robust method for the measurement of cardiac index. With the use of phase-contrast CMR we observed a decrease in cardiac index with age and ejection fraction in patients after acute STEMI. Observed differences in STEMI patients might be due to presence of subclinical mitral regurgitation, which occurs in up to 50% of STEMI patients and prompts further investigation. Because of the low agreement with cine CMR, measures should not be used interchangeably in patients after acute STEMI.