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Nonparallel changes in global left ventricular chamber volume and muscle mass during the first year after transmural
J A Rumberger1, T Behrenbeck, J R Breen
1Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota 55905.
Insights
Left ventricular chamber volume increases progressively after anterior myocardial infarction, while muscle mass initially decreases then recovers. Ventricular wall tension is elevated post-infarction, suggesting therapeutic targets.
Area of Science:
- Cardiology
- Cardiovascular Research
- Medical Imaging
Background:
- Left ventricular (LV) chamber dilation is a known complication following transmural myocardial infarction (MI).
- Understanding time-dependent changes in LV volume and myocardial mass post-MI is crucial for patient management.
Purpose of the Study:
- To serially assess time-dependent changes in left ventricular chamber volume and myocardial muscle mass after myocardial infarction in humans.
- To investigate the relationship between LV dilation, muscle mass changes, and ventricular wall tension post-MI.
Main Methods:
- Cine computed tomographic scanning was used to quantify global LV chamber volumes and muscle mass.
- 18 patients with transmural MI (12 anterior, 6 inferior) were assessed at hospital discharge, 6 weeks, 6 months, and 1 year post-MI.
- Patients with no heart failure at baseline or follow-up were included.
Main Results:
- Patients with anterior MI showed progressive LV end-diastolic volume increase (discharge: 148 ml to 1 year: 180 ml; p < 0.001).
- LV muscle mass decreased significantly in the first 6 weeks post-MI but returned to baseline by 1 year.
- The LV end-diastolic volume to muscle mass ratio, an index of wall tension, increased steadily post-discharge.
Conclusions:
- LV volumes progressively increase post-MI in anterior wall infarction, but remain stable in inferior wall infarction.
- LV muscle mass decreases early post-MI, then recovers, with limited late hypertrophy.
- Elevated ventricular wall tension in the first year post-MI suggests potential benefit from afterload-reducing agents.
Objectives:
This study was designed to serially assess time-dependent changes in both chamber volume and myocardial muscle mass after infarction in humans.
Background:
Dilation of the left ventricular chamber has been previously described after transmural myocardial infarction.
Methods:
Global left ventricular chamber volumes and muscle mass were quantified by using cine computed tomographic scanning in 18 patients at hospital discharge and 6 weeks, 6 months and 1 year after an initial transmural myocardial infarction (12 anterior and 6 inferior). No patient had heart failure during the initial hospital stay or on any subsequent follow-up visit.
Results:
The patients with anterior myocardial infarction (estimated infarct extent 27 +/- 2% of left ventricle) demonstrated a progressive increase in left ventricular end-diastolic volume from 148 +/- 9 ml (mean +/- SEM) at hospital discharge to 180 +/- 9 ml at 1 year after infarction (p < 0.001). However, global left ventricular muscle mass decreased significantly during the 1st 6 weeks after infarction but returned by 1 year to nearly the value determined at hospital discharge (177 +/- 13 vs. 165 +/- 10 g, p = NS). The changes in global muscle mass did not parallel the steady and progressive increases in chamber end-diastolic volume. The end-diastolic chamber volume to muscle mass ratio, an index of global left ventricular wall tension, increased steadily after hospital discharge but remained level by 1 year after infarction. The time course of changes in global end-systolic chamber volume was roughly proportional to the concomitant changes in end-diastolic volume. During this same time period, left ventricular stroke volume remained constant or improved from that determined at baseline. Global left ventricular end-diastolic and end-systolic volumes remained relatively static during the 1st year in the patient subgroup with inferior wall myocardial infarction (estimated infarct extent 10 +/- 1% of left ventricle), but global muscle (myocardial) mass initially decreased and then increased in a pattern similar, although of smaller magnitude, to that observed in patients with anterior wall myocardial infarction.
Conclusions:
Overall, left ventricular end-diastolic and end-systolic chamber volumes increase progressively from hospital discharge to 1 year after an initial transmural myocardial infarction in patients with a moderately large anterior wall infarction but remain stable in patients with a small inferior wall infarction. Concurrently, total left ventricular muscle mass decreases significantly during the initial 6 weeks after infarction (presumed largely secondary to changes in the necrotic segments) but then returns to the hospital discharge baseline values by 1 year. These data are consistent with the late development of, at most, limited ventricular hypertrophy in the noninfarcted myocardium that occurs well after the early and progressive left ventricular chamber dilation observed in patients with a moderate to large myocardial infarction. These data, in particular as applied to patients with anterior infarction, suggest that ventricular wall tension is significantly elevated at least during the 1st year after an initial transmural myocardial infarction. These observations may explain the potential utility of agents aimed at reducing afterload or ventricular wall tension during the early convalescent phase after myocardial infarction.