Detection of myocardial bridge and evaluation of its anatomical properties by coronary multislice spiral computed tomography

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Abstract

Background

Myocardial bridge (MB) is a common anatomical condition, under which a part of the coronary artery running in the epicardial adipose tissue, is covered with myocardial tissue. It regulates atherosclerosis development and sometimes evokes coronary heart disease through haemodynamic alterations. We attempted to efficiently detect MB and evaluate the anatomical properties of MB by coronary multislice spiral computed tomography (MSCT).

Methods

Sixteen-row MSCT was conducted on 148 patients with coronary heart disease. MSCT images were reconstructed and reformed with transverse scans, curved planar reformat and three-dimensional volume-rendered images. The MB, over 1.0 mm in thickness, was identified by the presence of the “step-down and step-up” appearance. After “trial and error” essays, we could consistently examine the frequency of MB and evaluate the anatomical properties of MB, especially its thickness, together with coronary wall lesions.

Results

Twenty-three patients (15.8%) had MB over 1.0 mm in thickness: 21 MBs (87.5%) were located in the left anterior descending artery with a mean thickness and length of 1.8 ± 0.7 and 20.0 ± 8.6 mm. Moreover, although the tunneled segment beneath MB was always free of coronary wall lesions, 79.2% (19/24) of the segments proximal to MB demonstrated coronary wall lesions. Of special significance were three symptomatic MB patients without any atherosclerotic lesion throughout all the coronary arteries.

Conclusion

Coronary MSCT is a new imaging technique that provides a non-invasive diagnostic tool for MB and yields much better results of MB detection than previous imaging methods.

Introduction

The myocardial bridge (MB) is a common anatomical condition, under which a part of the coronary artery running in the epicardial adipose tissue is covered with myocardial tissue (Fig. 1) [1]. The coronary artery covered by MB has been also called tunneled artery. MB appears almost exclusively in the left anterior descending coronary artery (LAD) [2], and its frequency at autopsy is sometimes over 50% [3]. It is known that MB in LAD consistently influences the distribution of atherosclerotic lesions along the entire course of this artery, where the segment beneath MB is free of atherosclerotic development despite frequent plaque formation in the segment proximal to MB [2], [4]. MB is generally benign, but symptomatic cases have been described: ischaemic heart disease, ventricular fibrillation, atrioventricular block and sudden death [1], [5]. These symptoms are considered to be caused by coronary ischaemia attributed to a reduction in blood flow subsequent to coronary compression by MB at systole or delayed arterial relaxation at diastole, or both [6], [7], which may be naturally influenced by blood flow changes characteristic of the inherent anatomical properties of MB.

In contrast, the frequency of MB detected by coronary angiography is less than 5%, which is significantly lower than that by autopsy studies [1]. The detection by coronary angiography depends on transient systolic constriction of the bridged segment and the “milking effect” [5], which are based on indirect images only suggesting the presence of MB. The imaging techniques of intravascular ultrasound (IVUS) and intracoronary doppler (ICD) are also known [6], [7] to directly detect the bridged muscle itself. In addition, recent developments of multislice spiral computed tomography (MSCT) in radiography have made possible the clear detection of the entire running course of coronary arteries and MB itself, as well as of coronary wall lesions [8], [9]. MSCT provides an accurate demonstration of the anatomical characteristics of MB in LAD, such as location, thickness and length, which modulate coronary atherosclerotic evolution [10].

In this study, we used 16-row MSCT to detect MB among patients with coronary heart diseases and evaluated the anatomical characteristics of MB with a view of providing raw data for the consideration of haemodynamic changes attributed to the presence of MB.

Section snippets

Preliminary comparison between MSCT and angiography

Before examining the coronary artery by our MSCT described in Sections 2.3 Coronary MSCT studies (, 2.4 Image reconstruction, 2.5 Image reformation and evaluation, 2.6 Determination of MB below, we first confirmed that the results of MB detection by MSCT accorded with that by conventional coronary angiography for an each identical patient in the three cases. The MSCT findings of soft tissue density covering the coronary artery, which disclosed the same contrast enhancement as myocardial tissue

Visualization of MB by coronary MSCT

Normal coronary arteries were demonstrated good contrast enhancement for the lumen in all but two patients showing motion artifacts of arrhythmia or breathing. On transverse scan and CPR images, MB was evaluated by coronary MSCT, and the tunneled artery was found with the covering myocardial tissue (Fig. 4, Fig. 5).

Frequency of MB and clinical backgrounds

Two patients were excluded from this study because of motion artifacts. Among the 146 patients, the clinical backgrounds of 23 (15.8%) with MB in the coronary arterial branch are

Evaluation of MB with coronary MSCT

The efficiency of MB detection was greatly improved by our newly devised modification of MSCT after simple “trial and error” essays. Consequently, the study clearly proved that coronary MSCT made possible the detection of MB much more objectively and non-invasively than the previous examination methods, such as conventional angiography, IVUS or ICD. MSCT revealed MB in 15.8% of the present 146 Japanese patients with various coronary heart diseases, which is evidently higher than the results of

Conclusion

Coronary MSCT has recently been established as a reliable and non-invasive technique for the diagnosis of intracoronary lesions and periarterial abnormalities. Furthermore, it provides several potential advantages over other invasive techniques and is a new evolving imaging technique allowing a non-invasive diagnostic option for MB. Because of its capability of accurately locating the site and measuring the thickness as well as the length of MB, coronary MSCT is a useful tool for defining the

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