Distribution and composition of glycosaminoglycans in the left human coronary arterial branches under myocardial bridge

Relationship between myocardial bridges and reduced coronary atherosclerosis in patients with angina pectoris

BACKGROUND

A myocardial bridge (MB) is a band of myocardium covering a coronary artery segment, typically located in the left anterior descending coronary artery (LAD). Bridged segments of the coronary artery are isolated from the influence of perivascular adipose tissue. The aims of this study were to investigate the relationship between MBs and atherosclerosis in bridged LAD segments and to evaluate whether perivascular adipose tissue is involved in this relationship.

METHODS

MBs were identified in the coronary arteries of patients referred for diagnostic cardiac CT. The calcium score of MBs of the LAD or, in patients without LAD-MBs, of a corresponding LAD segment at the same distance from its origin and over the same length was measured.

RESULTS

Of 128 patients, 56 (44%) had in total 73 MBs. The mean MB length was 22 ± 14 mm and the median MB thickness was 0.8mm (interquartile range 0.3-2.1mm). MBs in the LAD were present in 40 patients (31%). The calcium score was 0 in 95% of the LAD segments with MBs compared with 52% of the corresponding LAD segments without MBs. The association between LAD-MBs and calcium score (OR 0.06, 95% CI 0.01-0.25) was not influenced by age and gender, but was attenuated by local perivascular adipose tissue thickness (OR 0.35, 95% CI 0.04-2.70).

CONCLUSIONS

Coronary artery segments covered with an MB have a lower calcium score than segments without an MB. The association between MBs and calcium scores was influenced by local perivascular adipose tissue thickness.

The investigation of perivasculary space under the myocardial bridge in different species

Our purpose in this study was to investigate the perivasculary space under the myocardial bridges (MB) in dog, sheep, goat and human hearts. A total of 160 hearts were studied, and perivasculary space under the myocardial bridges was examined under microscope. The specimens belonged to 25 dogs, 100 sheep, 25 goats and 10 humans. Special attention was paid to evaluate the distance between the MB and coronary arteries (CA), CA and underlying myocardium (UM) and to find the relation of concomitant vein number accompanying the CA and MB. 219 myocardial bridges were found in total of hearts, and specimens from these bridges were examined under microscope. There were large variations in distance between the MB and CA (0-714 microm) and distance between CA and UM (0-309 microm). The myocardial bridges were classified into three groups in terms of the number of veins accompanying CA, the bridges with no concomitant veins with one concomitant vein and with two concomitant veins. This suggests that the distance between the MB and CA is crucial to determine how much force is on the CA. The environment surrounding the CA may be a crucial factor in determining whether the MB influences the induction of heart disorders or not.

Angiographic restenosis after myocardial bridge stenting

Data on restenosis after stent implantation in myocardial bridges (MB) are very limited. Six-month angiographic results for 12 symptomatic patients who underwent stent implantation for myocardial bridges were compared retrospectively with those of 39 patients who underwent direct stent implantation for de novo atherosclerotic lesions in the left anterior descending artery. Diameter stenosis decreased from 69 +/- 8% to 4 +/- 5% in the MB group and from 79 +/- 8% to 7 +/- 6% in the control group after stent deployment. Systolic narrowing was abolished in all patients with MB. In follow-up, quantitative angiography revealed late loss of 1.8 +/- 1.3 mm in the MB group and 0.9 +/- 0.9 mm in the control group (P = 0.025). The in-stent restenosis rate was also higher in the MB group compared to the control group (67% versus 28%; P = 0.037). Despite favorable immediate results, stent implantation in MBs may not be promising because of the higher in-stent restenosis rate compared to stenting in de novo atherosclerotic lesions.

A general model for genetic regulation of turnover of glycosaminoglycans suggests a possible procedure for prediction of severity and clinical progress of mucopolysaccharidoses

Mucopolysaccharidoses are rare genetic diseases from the group of lysosomal storage disorders caused by deficiency of enzymes involved in degradation of mucopolysaccharides (glycosaminoglycans, GAGs). Within each mucopolysaccharidosis, there is a continuous spectrum of clinical features from the very severe to the more mildly affected individuals. Surprisingly, in most cases, it is not possible to predict severity and clinical progress (i.e., the natural history) of the disease on the basis of detection of particular mutations or residual activity of the deficient enzyme. In this article, the reasons for such an unexpected difficulty are discussed. A model for the correlation between residual activity of a lysosomal enzyme and the turnover rate of its substrate(s) has been proposed previously by others, however, in that model it was assumed that substrate concentration in the lysosome is not regulated, thus the residual activity of a hydrolase would be the only determinant of the rate of substrate accumulation. On the other hand, both a general model for genetic regulation of turnover of GAGs and results of very recent studies strongly suggest that expression of genes coding for enzymes involved in GAG synthesis is precisely regulated and may vary between individuals. Therefore, we propose that apart from measurement of residual activity of the enzyme involved in degradation of GAGs, the efficiency of synthesis of these compounds should also be estimated. If the hypothesis presented in this article is true, the ratio of the synthesis of glycosaminoglycans to the residual activity of the deficient enzyme should be of considerable prognostic value.