Patients with Duchenne muscular dystrophy (DMD) are known to have progressive epicardial fibrosis of the free wall of the left ventricle, but standard noninvasive M-mode echocardiographic tests of left ventricular function are relatively insensitive detectors of this cardiomyopathy. We therefore used two-dimensional echocardiography to record three short axis levels of the left ventricle in 13 Duchenne patients. Serial studies were separated by 2 years for most patients. The two-dimensional echocardiographic technique allows qualitative evaluation of segmental contraction of the left ventricle. Four general principles were found during this study: (1) Obvious contraction abnormalities of the left ventricle were present in most patients with DMD. (2) In most patients, the contraction deficit was first noted in the left ventricular posterior free wall behind the mitral valve. (3) Once a contraction deficit was observed, the area of abnormal contraction progressed inferiorly to include additional areas of the left ventricular posterior free wall. (4) Standard M-mode left ventricular function techniques were unreliable for detecting individuals with segmental contraction abnormalities.
Boys with Duchenne's muscular dystrophy (DMD) usually have a cardiomyopathy characterized by fibrosis of the epicardial half of the left ventricle. This cardiomyopathy is difficult to detect by noninvasive techniques. We report a technique that evaluates incremental left ventricular posterior wall thickening and thinning. High-quality left ventricular posterior wall echoes in 24 boys with DMD and 32 controls were recorded at chordal level two times 1 year apart. Endocardial and epicardial echoes and a timing ECG were digitized and analyzed by minicomputer. Left ventricular wall amplitudes were determined at standardized temporal increments during contraction and relaxation. To compare with this left ventricular assessment technique, systolic ejection times, shortening fraction and mean velocity of circumferenial fiber shortening (Vcf) were also computed in the standard way. Mean year-to-year changes were minor. Mean Vcf, the ratio of preejection period to left ventricular ejection time and shortening fraction during the first year were statistically similar to those of the controls. Shortening fraction decreased slightly during the second year and became significantly different from the control, but remained within the normal range. Left ventricular wall thickness and cavity size were significantly less in boys with DMD than in controls. Therefore, we had to normalize incremental wall thickness to determine if any significant difference occurred. To do this, we evaluated the percentage of maximal wall thickness which occurred at a given percent of systole and diastole. Using this technique, it was shown that thickening during systole was a nearly linear process with respect to time in both groups. However, relaxation was significantly different between the groups. Relaxation was found to be an alinear process, and most thinning occurred in the first 40% of diastole. The major findings of this investigation was that the left ventricular wall of boys with DMD thinned at a slower rate than that of normal subjects. This new technique appears to be sensitive and demonstrates subtle changes in the left ventricular posterior wall.
In 19 patients with Duchenne's muscular dystrophy, left ventricular wall thickness in end-systole and end-diastole was determined serially every 12 months by echocardiography and compared with ventricular wall growth in normal subjects. In the normal subjects, left ventricular wall thickness increased linearly with increasing body surface area. A control group of wheelchair-bound patients with a variety of neurologic disorders, although not followed serially, had a distribution of end-diastolic wall thickness values similar to that of the normal subjects. In patients with muscular dystrophy, wall thickness increased linearly with respect to body surface area for some time and then began to thin. The time at which thinning began was not directly related to age, although it was more common in older than in younger patients. Those patients who died demonstrated marked deviation from normal wall growth. Free wall thinning is probably a result of fibrosis and loss of myofibrils.
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