901-30 Relationship Between Function, Perfusion and Contractile Reserve Early After Myocardial Infarction: A Dynamic Magnetic Resonance and Stress Echocardiographic Study in Man

Abstract

To assess the relationship between regional myocardial function, myocardial perfusion pattern and contractile reserve, 12 patients (age 53.5 ± 9.3 years; mean ± SD) were studied 4.5 ± 0.9 days after the occurrence of their first Q-wave acute myocardial infarction. Myocardial perfusion was evaluated by an ultrafast gradient echo sequence, implemented on a 0.5 T system for magnetic resonance imaging (MRI). During the acquisition of 64 consecutive, single slice, ECG triggered, diastolic, short axis images of the left ventricle a bolus of gadopentetate (0.05 mmol/kg) was injected intravenously. Six regions of interest (ROIs) were drawn on the left ventricle profile of the images and time-intensity curves were obtained. In each patient the time-intensity curve from a region with normal function was used as reference to cross-correlate curves from the other ROIs. A cross-correlation coefficient (CCC), which described the state of myocardial perfusion was obtained for each ROI ranging from 1 (normal perfusion pattern) to 0 (no perfusion). Regional contractile reserve was assessed by 2-D echocardiography at rest and following low dose (up to 10 mcg/kg/min) dobutamine infusion. Out of the 72 regions analysed, 44 segments had normal function and normal perfusion (CCC = 0.91 ± 0.13). The remaining 28 regions with resting dyssynergy showed a reduced perfusion (CCC = 0.61 ± 0.28; p < 0.05 vs normal regions). Perfusion deficit was more marked in the 11 aki-dyskinetic regions than in the 17 hypokinetic regions (CCC = 0.35 ± 0.20 vs 0.77 ± 0.20; p <0.05). Out of the 11 regions with severe dyssynergy (resting aki-dyskinesia) the 4 segments showing a functional improvement following dobutamine had a higher perfusion when compared to the 7 segments unresponsive to dobutamine (CCC = 0.54 ± 0.1 vs 0.24 ± 0.17; p < 0.05). In conclusion, early after an acute myocardial infarction, the severity of the perfusion deficit in the infarcted regions tends to mirror the severity of the mechanical dysfunction. In regions with severe baseline dyssynergy, perfusion is lower when no contractile reserve can be elicited by dobutamine. The integration of dynamic MRI and low dose pharmacological stress-echo allows to explore non-invasively the relationship between function, myocardial perfusion pattern and contractile reserve in man.