Does Myocardial Bridge Appear More Frequently and Diffusely on Radial Access Coronary Angiography?

Background: Although the incidence of myocardial bridge (MB) has been dened in different conventional coronary angiography (CCA) studies,the frequency of MB in radial access coronary angiography (RACA) is unknown.The aim of this study was to determine the incidence of MB in patients undergoing RACA. Method: A total of 2600 consecutive patients who underwent RACA were retrospectively investigated to detect the presence of MB.The clinical,laboratory, and angiographic features of the patients with MB were analyzed. Results: MB was detected at an incidence of 10.2%, in 255/2600 patients who underwent RACA.The most involved coronary artery was the left anterior descending artery (LAD) (86.9%) and the mid segment (84.9%) was the most affected section.Co-involvement of multiple coronary arteries by MB was 7.8%. Coronary artery disease (CAD) was determined in 102 (36.2%) of the coronary arteries with MB, 82.4% which were proximal to the MB. Conclusion: These data demonstrated that the incidence of MB able to be detected on RACA was much higher than reported in previous CCA studies. pectoris pectoris single photon emission computed treadmill 60 of these clinical,laboratory analyzed. The right radial artery was cannulated with a 6-f radial sheath after local inltration with 2% lidocaine.All patients received 5000 units of unfractionated heparin, 100–200 µg (depending on blood pressure) of nitroglycerin and 5 mg of diltiazem unless there was an absolute contraindication to diltiazem and anticoagulants.Coronary angiography was performed using the standard Judkins` technique via right radial access with a 5-f diagnostic catheter.Standard angiography images were obtained with a biplane cine-angiography system.Each angiogram was reviewed by the same two qualied cardiologists.The presence of MB was dened as the narrowing of the coronary artery lumen in systole and dilatation in diastole with no evidence of coronary vasospasm.The extent and severity of MB and its relationship with coronary artery disease (CAD) were examined on cine-angiograms.The quantication of systolic lumen compression and atherosclerotic stenosis in the coronary artery was performed using a digital caliper program to measure the lumen diameter reduction.The patients were separated into 3 groups according to the degree of systolic lumen compression caused by MB.


Introduction
Myocardial bridge (MB) is an anatomic variation in which some of the epicardial coronary arterial segments run into the myocardium.MB is characterized by narrowing during systole of the coronary artery by overlying muscle bers [1,2].It usually occurs in the mid-segment of the left anterior descending coronary artery (LAD) [3,4].MB may affect other coronary arteries less frequently and occasionally, all of them [5].Although MB is known to be usually benign, it may sometimes cause myocardial ischemia,arrhythmia,syncope and sudden cardiac death [6,7].Coronary heart disease can be caused by MB both by direct compression in cardiac systole and by exacerbation of atherosclerosis progression in the vessel proximal to the MB [8,9]. There is a great difference in the incidence of MB reported in angiographic series (0.5-2.5%) and in autopsy series (15-85%) [10].It has been shown that the frequency and extent of MB may differ according to imaging techniques.In comparative studies of the same patient population,the frequency of MB was 6% with conventional coronary angiography (CCA), and 30% with computed tomography coronary angiography (CTCA) [11].Those results con rmed that CCA is not sensitive enough to detect MB, especially of a mild type [12].Radial access for coronary angiography has been shown to reduce major bleeding and ischemic events compared to femoral access [13].Therefore,radial access has been the principal approach for coronary angiography in recent years.The aim of this study was to determine the incidence of MB in patients undergoing RACA with the administration of nitroglycerin and diltiazem.

Method
A retrospective evaluation was made of the coronary angiographies of 2600 consecutive patients who underwent RACA between January 2018 and February 2021.Patients with a history of coronary artery bypass grafting (CABG) were excluded from the study.Patients who underwent RACA for the diagnosis of coronary artery disease were grouped according to clinical conditions as non-anginal symptoms,stable angina pectoris (SAP),unstable angina pectoris (USAP), non-ST segment elevation myocardial infarction (NSTEMI), and ST segment elevation myocardial infarction (STEMI).Cardiac single photon emission computed tomography (SPECT) was positive in 24 and the treadmill exercise test was positive in 60 of these patients.The clinical,laboratory and angiographic features of patients with MB were analyzed.
The right radial artery was cannulated with a 6-f radial sheath after local in ltration with 2% lidocaine.All patients received 5000 units of unfractionated heparin, 100-200 µg (depending on blood pressure) of nitroglycerin and 5 mg of diltiazem unless there was an absolute contraindication to diltiazem and anticoagulants.Coronary angiography was performed using the standard Judkins` technique via right radial access with a 5-f diagnostic catheter.Standard angiography images were obtained with a biplane cine-angiography system.Each angiogram was reviewed by the same two quali ed cardiologists.The presence of MB was de ned as the narrowing of the coronary artery lumen in systole and dilatation in diastole with no evidence of coronary vasospasm.The extent and severity of MB and its relationship with coronary artery disease (CAD) were examined on cine-angiograms.The quanti cation of systolic lumen compression and atherosclerotic stenosis in the coronary artery was performed using a digital caliper program to measure the lumen diameter reduction.The patients were separated into 3 groups according to the degree of systolic lumen compression caused by MB.

Statistical analysis
Data obtained in the study were analyzed statistically using SPSS for Windows, vn.15.0 (SPSS Inc., Chicago, IL, USA).Conformity of the data to normal distribution was assessed using the Kolmogorov-Smirnov test.Continuous variables were reported as mean ± standard deviation (SD),median,minimum and maximum values, and categorical variables as number (n) and percentage (%).

Results
MB was detected in 255 of 2600 patients who underwent RACA,giving a total incidence of 10.2%.The 255 patients comprised 196 (76.9%) males and 59 (23.1%) females with a mean age of 57.5 ± 11.3 years (range, 25-83 years; median, 59 years).Hypertension was determined in 137 (53.7%) patients.The echocardiographic ndings showed left ventricular concentric hypertrophy (LVCH) in 86 patients,hypertrophic obstructive cardiomyopathy (HOCM) in 4, and aortic stenosis (AS) in 4.The demographic data and clinical features of the patients are presented in Table 1, and the laboratory features in Table 2.More than 90% (235/255) of patients had single vessel MB (Fig. 1), and 20 cases had more than one vessel MB (2 vessels in 13 patients, 3 vessels in 7) (Table 3).These patients had a total of 282 coronary arteries with MB.The most involved coronary artery was LAD (86.9%, 245/282) and the most affected section of LAD was the mid segment (84.9%, 208/245) followed by distal (13.9%, 34/245) and proximal (1.2%, 3/245) segments.The mean length of MBs on angiography was 18.2 ± 4.9 mm.Three groups were constituted according to the degree of systolic compression of the epicardial coronary artery among single vessel MBs; Group 1 comprised 45.9% of the patients, Group 2 25.1%, and Group 3 28.9%.The angiographic characteristics of the patients according to the MB grades are presented in Table 4.Of the coronary arteries with MB, 102 (36.2%) had CAD, of which 82.4% (84/102) were proximal to the MB. Of these cases with proximal CAD, 62 were mild, 2 were moderate, and 20 were severe.

Discussion
The results of this study showed the incidence of MB to be 10.2% in patients who underwent RACA.
MB is a congenital coronary artery anomaly,which is usually detected incidentally in coronary angiography performed for the diagnosis of coronary atherosclerosis.The incidence of MB differs between autopsy studies (15-85%) and angiographic studies (0.5-2.5%) [10]. Furthermore, the incidence of MB varies according to the coronary angiography method.For example, 0.6% incidence of MB in CCA was reported by Harikishen et al, whereas Kantarci et al. determined MB incidence of 3.5% in CTCA [14,15].In another study, Lu et al. found the incidence of MB to be 6% with CCA, and 30% with CTCA in the same population [11].The main reason for this difference is the variability in the sensitivity of coronary angiography methods in the detection of MB.Other factors that may affect the incidence of MB are the size and ethnicity of the study samples.Luminal narrowing is dynamic in CCA and mild systolic compressions may be overlooked.Structural evaluation can be performed with CTCA and the coronary artery course can be clearly observed, but super cial MBs may not be seen.In the current study,the main reason for the higher MB incidence compared to CCA studies was thought to be the routine use of nitroglycerin and diltiazem during the procedure.Nitroglycerin and diltiazem reduce coronary artery resistance [16,17].As a result of the synergistic effect of nitroglycerin and diltiazem, even low doses can dramatically modify coronary artery resistance. Nitroglycerin augments vessel wall constriction in patients with MB and previously unseen MBs can appear after the administration of nitroglycerin in coronary angiography.In addition, nitroglycerin increases vascular compliance, and facilitates diastolic expansion as well as systolic compression, so MB can be easily detected [18].
The most common coronary artery affected by MB is the LAD mid segment, as indicated both in the current study and many other studies [19][20][21][22].Although a previous study from Turkey reported almost equal distribution of MBs in the LAD middle and distal segments and no MB present in the proximal segment, the current study results showed much higher involvement of the LAD mid segment than proximal and distal segments [23].Compared to previous CCA studies, not only the MB incidence but also the number of simultaneously affected coronary arteries was higher in the current study.Although some studies [2,5,14,23] have shown that more than one coronary artery was almost never involved simultaneously, the involvement of two or three coronary arteries together was 5.1% and 2.7%, respectively in the current study. The reason for this,just like the incidence difference,can be attributed to the use of nitroglycerin and diltiazem enabling the detection of previously unseen MBs.In a cadaver study, it was shown that almost all major branches of both coronary arteries were affected and 36% of the samples had more than one MB [5].
There has been considerable controversy regarding the functional signi cance of MB.Some studies have stated that MB may be associated with ischemia,arrhythmia, and sudden cardiac death,while others have claimed that it is benign and may even protect against atherosclerosis [24][25][26][27][28].In the current study,ventricular tachycardia was observed in 2 patients before coronary angiography, but in both cases was due to acute myocardial infarction.It is generally accepted that MB causes coronary atherosclerosis in the LAD segment proximal to the MB and enhances its natural progression through several different mechanisms [3,9,10,29].Similar to those studies, 36.2% of the current study patients with MB had CAD, of which more than 80% were proximal to the MB, and the majority were mild degree (luminal narrowing between 30% and 50%).
There are 3 different therapeutic approaches for patients with symptomatic MB: Medication, stent placement in the bridged segment, and surgical treatment [8].Due to reducing coronary compression,betablocker therapy is the rst choice of treatment for symptomatic patients [30].Stent implantation therapy in the bridge segment remains controversial.Some studies [31,32] have stated that this therapy reduces direct coronary compression and improves coronary reserve ow,while others [32][33][34] have highlighted adverse effects of this therapy, such as coronary perforation,stent fracture, and early in-stent restenosis.Myotomy as a surgical treatment is a good option for patients refractory to medical therapy with good long-term results [8,35].All the patients in the current study were treated medically and none required surgical treatment.
This study had some important limitations,primarily that it was a retrospective,observational, singlecentre study.Therefore,the population investigated might have been heterogeneous. Further investigation was not performed for the incidence of MB in patients who underwent femoral access coronary angiography and the incidence of MB in those who underwent RACA was compared with previous CCA studies.The clinical signi cance of MB and its relationship with symptoms was not investigated.Dedicated clinical studies would be required to determine the relationship of MB with clinical symptoms by proving the presence of ischemia,especially in the absence of atherosclerotic coronary artery stenosis.

Conclusion
The results of this study demonstrated that the MB incidence in RACA patients was much higher than the rates reported in previous CCA studies.The LAD mid segment was the most affected coronary artery.Multiple coronary artery involvement was not uncommon and approximately one-third of the patients with MB had CAD proximal to MB.

Declarations
Ethics approval and consent to participate The study was designed in accordance with the principles of the declaration of Helsinki and got approval from the local ethics committee of our hospital (Bakırcay University Medicine Faculty (Decision number: 223).
Written informed consent was obtained from all patients included in the study.Patients younger than 18 years old were not included in the study.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Competing interests
The authors have no nancial con icts of interest.