Evolution of regional performance after an acute anterior myocardial infarction in humans using magnetic resonance tagging

Abstract

Regional remodelling after a left ventricular myocardial infarction is the first step in a cascade that may lead to heart failure and death. To understand better the mechanisms underlying this process, it is important to study not only the evolution in local deformation parameters but also the corresponding loading conditions. Using magnetic resonance (MR) myocardial tagging, we measured the regional contribution to ejection (regional ejection fraction) and loading (systolic blood pressure x radius of curvature (mean of short and long axes)/wall thickness) in 32 regions throughout the left ventricle (LV) in patients 1 week (1W) and 3 months (3M) after a first anterior infarction. Using positron emission tomography (PET), the LV was divided into infarct, adjacent and remote regions. In the remote regions the average deformation decreased between 1W and 3M (from 59.3 +/- 5.6 to 57.9 +/- 6.7 %, P < 0.05) due to an increase in loading conditions only (from 730 +/- 290 to 837 +/- 299 mmHg, P < 0.05). In the adjacent myocardium, no change in function was observed (49.0 +/- 10.8 to 49.0 +/- 6.5 %, P = n.s.), although loading increased (806 +/- 297 to 978 +/- 287 mmHg, P < 0.05). In the infarct region only, an increase in deformation was seen (30.7 +/- 14.2 to 37 +/- 6.9 %, P < 0.05), together with a higher loading level (1229 +/- 422 to 1466 +/- 284 mmHg, P < 0.05), which indicates a true improvement in function. The fact that MR tagging can identify both regional deformation and loading permits us to differentiate between changes due to alterations in regional loading conditions and true changes in function. After an acute myocardial infarction (MI), an improvement can be observed in the deformation-loading relation in the adjacent and infarct regions, but the improvement is mainly in the infarct region. Using this technique, types of intervention leading to even more functional gain could be evaluated.

Figure 1. Regional deformation analysis with MR tagging

By means of a combination of MR tagging along the cardiac short and long axes, the LV wall is divided in 32 small cuboids. Each cuboid is defined by 4 epicardial and 4 endocardial node points. The deformation is expressed in a local cardiac coordinate system for each epicardial and endocardial node point. The axes are radial (R), circumferential (C) and longitudinal (L). In each cuboid the best circular fit to the endocardial contour is calculated in 2 circumferential and 2 radial directions. As an example, the circle (and its radius) best fitting the inferior circumferential border of a cuboid is shown.

Figure 2. Regional ejection fraction

The delineation of a pie-shaped intracavitary volume by adjacent tag lines, crossing in the centre of the cavity, is shown at end-diastole and end-systole.

Figure 3. Average load values

The average load values and standard deviation are shown in the controls (Normal) and in the infarct patients (Infarct, Adjacent and Remote regions for the 1W and 3 M studies). *P < 0.01.

Figure 4. Relation between mean regional ejection fraction and load

The relation between average regional ejection fraction and average load is shown for the different regions and for the 1W and 3M studies. For reference the normal relation and regression line with 2 s.d. confidence lines are also depicted.

Figure 5. Regression between regional ejection fraction and load

The different regression lines between regional ejection fraction and load are shown in the different regions for the 1W and 3M studies in the infarct patients.

Figure 6. Distribution of regional EF (A) and load (B) around the circumference of the ventricle

Data shown for normals and infarct patients in the different regions (remote, adjacent, infarcted) at 1 week and 3 months. Eight locations around the circumference are shown: location 1–3 corresponds to interventricular septum, 4–5 to inferior wall, 6 to lateral wall, 7–8 to anterior wall.

Figure 7. Distribution of regional EF (A) and load (B) along the long axis of the ventricle

Data shown for normals and infarct patients in the different regions (remote, adjacent, infarcted) at 1 week and 3 months. Four levels from base to apex are shown: 1 base, 4 apex.