Size of coronary artery in a myocardial bridge compared with adjacent nontunneled left anterior descending coronary artery

Optical coherence tomography and intravascular ultrasound assessment of the anatomic size and wall thickness of a muscle bridge segment

OBJECTIVE

To use optical coherence tomography (OCT) and intravascular ultrasound (IVUS) in assessing myocardial bridging (MB) vessel size and wall thickness.

BACKGROUND

During stent implantation, MB is associated with complications, especially perforation.

METHODS

OCT and IVUS were performed in 56 patients with typical angiographic "milking" from November 2016 to May 2017. The vessel area and thickness in the MB segments and adjacent proximal and distal reference segments were measured and compared with eight normal left anterior descending (LAD) segment (no atherosclerosis in a segment that was at least 20 mm long and that began ~40 mm distal to the LAD ostium).

RESULTS

Compared with the reference vessel size distal to the MB segment (6.3 ± 1.8 mm² ), the IVUS-measured size of the tunneled vessel during diastole was significantly smaller (6.0 ± 1.9 mm² , p < 0.05) (remodeling index = 0.79 ± 0.18). The minimum intramyocardial arterial wall thickness was 0.16 ± 0.02 mm, significantly thinner than that of the mean reference (0.22 ± 0.03 mm, p < 0.001). The location of the thinnest arterial wall was in the distal and middle MB segments in 45 (80.4%) and 11 (19.6%) patients, respectively, and was not related to the degree of systolic compression or remodeling index. The walls of the middle and distal MB subsegments, but not of the proximal MB subsegment, were thinner than that of the comparison group of normal LADs.

CONCLUSION

The coronary vessel involved in an MB is both smaller and thinner than that of the adjacent non-MB segment. This may explain the increased frequency and severity of coronary perforation during stent implantation.

Increased risk of coronary perforation during percutaneous intervention of myocardial bridge: What histopathology says

Introduction: Myocardial bridge (MB) is a segment of a major epicardial coronary artery that goes intramurally under a bridge of overlying myocardium. Complications have been reported during or after stent implantation particularly coronary perforation. The aim of this study was to determine histological differences between proximal left anterior descending artery (LAD) and the tunneled segment that may have a possible role in increased risk of coronary artery perforation during percutaneous coronary intervention.

Methods: Twenty specimens of MB were obtained from dissection of 45 cadavers. Sections were stained using hematoxylin and eosin (H&E), and trichrome methods. The proximal section and the tunneled artery were compared with a normal sample in terms of the characteristics of a muscle artery.

Results: The findings of this study showed an MB prevalence of 51%, as 23 out of the 45 examined cadavers were discovered to be afflicted by the MB. The intima layer in the suffering artery had gone through significant hypertrophy, while it had remained thin in the tunneled artery section. The epithelial cells under the bridge were spindle-shaped, while they were polygonal in the proximal section. In the myocardium the nuclei of the muscle fibers in the MB section were smaller than the normal section. Adventitial layer was almost normal.

Conclusion: The histopathological differences between MB and proximal part of vessel combined with small vessel diameter in the tunneled segment can explain the high incidence of the LAD rupture and perforation in the section under the bridge.

Coronary artery perforation in a patient with STEMI and a myocardial bridge: an increased risk for coronary artery perforation?

We present the case of a patient with ST-elevation myocardial infarction (STEMI) due to subtotal occlusion of the left anterior descending coronary artery caused by an atherosclerotic lesion and a myocardial bridge (MB). Stenting of the MB caused coronary artery perforation resulting in a fistula to the right ventricle that was closed by implantation of a PTFE-covered stent. Follow-up coronary angiography showed persistent shunting, which was sealed by inflation of a high-pressure balloon over the site of extravasation guided by intravascular ultrasound. Additionally, we provide a short review of cases with coronary artery perforation after stenting of an MB.

Application of Intravascular Ultrasound in the Emergency Diagnosis and Treatment of Patients with ST-Segment Elevation Myocardial Infarction

PURPOSE

This study aimed to examine the application of intravascular ultrasound (IVUS) in ST-segment elevation myocardial infarction (STEMI) patients with high thrombus burden (thrombus grade ≥3) undergoing emergency diagnosis and primary percutaneous coronary intervention.

METHODS

Eighty STEMI patients were enrolled and randomly assigned to the IVUS-guided group (38 patients) or non-IVUS group (42 patients). Stent implantation was performed in non-IVUS group patients. IVUS group patients were further divided into low-risk and high-risk patients on the basis of IVUS evaluation for determining whether stenting should be performed. Major adverse cardiac event (MACE) rates, changes in the left ventricular end-diastolic diameter (LVEDD) and ejection fraction (EF) values, and stent numbers were examined during hospitalization, and follow-up was performed at 1, 3, 6, and 12 months postoperatively.

RESULTS

During hospitalization, there were no significant differences in the MACE rates, LVEDD, and EF values and in the follow-up outcomes at 1, 3, 6, and 12 months postoperatively among the patients in the 2 groups (P > 0.05). A significantly lower number of stents were implanted in the IVUS group than in the non-IVUS group patients (P < 0.05).

CONCLUSION

During the IVUS-guided emergency intervention, enhanced antithrombotic therapy and best medical care for low-risk STEMI patients may be feasible.

Coronary artery perforation following implantation of a drug-eluting stent rescued by deployment of a covered stent in symptomatic myocardial bridging

We successfully rescued a patient whose coronary artery perforated following implantation of a drug-eluting stent (DES), by deploying a stent-graft in symptomatic myocardial bridging. Our case demonstrated that coronary perforation could be handled without difficulty when perforated myocardial bridging is confined to the interventricular groove

(1) coronary events caused by myocardial bridge

Myocardial bridge (MB), which covers a part of the left anterior descending coronary artery (LAD), is a normal anatomical variant structure (45% in frequency by autopsy) in LAD. MB contraction plays the role of a "double-edged sword" on the coronary events, suppressing coronary atherosclerosis under the MB, yet generating abnormal blood flow associated with coronary heart diseases (CHDs). High shear stress driven by MB compression causes the suppression of vascular permeability and vasoactive protein expression such as e-NOS and endothelin-1, which leads to the suppression of atherosclerosis in the LAD segment under the MB. However, despite the prevalent view of MB as benignancy by conventional coronary angiography (5-6% in frequency), with advance of imaging technique such as multislice spiral computed tomography [(MSCT); 16% in frequency], cardiologists are now frequently aware of symptomatic MB occurring not only in hospitalized patients, but also in young athletes free from atherosclerosis. Moreover, the large mass volume of MB muscle induces atherosclerosis evolution at the settled site in LAD proximal to MB and contributes to the occurrence of myocardial infarction. These events upon the coronary events result from the different pathophysiological mechanisms induced by contractile force of MB, which is solely determined just by the integration of anatomical properties of MB, such as the location, length and thickness of MB in an individual LAD. A recent MSCT provides the objective quantification of the anatomical variables that correlate with the histopathological results in relation to the occurrence of CHD. In this review, we therefore discuss the necessity to explore MB as a inherent chance anatomical risk factor for CHD.