Our study is the first study to investigate the clinical features and morphological characteristics of patients with MB of the LCX artery. We found that MB of the LCX artery was mostly located on the distal segment, and mostly MB of the LCX artery is superficial, long bridging, and non-left coronary dominant. Patients with bridging in the LCX artery are usually associated with chest discomfort and abnormal ECG, but with a normal CT-FFR value, which is different from the study results [15]. Coronary atherosclerosis did not occur in patients with MB of the LCX artery.
MB was discovered by Reyman through an autopsy in 1737 and was first described by Geringer in 1951 through coronary angiography [16, 17]. It has been proved to have a systole “Milk-effect” phenomenon and can result in a change in the hemodynamics of the bridging segment artery [18]. In 1960, Portsman and Iwig described it angiographically as a transient narrowing of the coronary artery during systole [19]. Furthermore, MB can lead to severe cardiac events such as myocardial ischemia, angina, myocardial infarction, and sudden death.
The LCX artery is one of the three major branches of the coronary artery, and it mainly supplies the left ventricular lateral wall and posterior wall of the heart. However, very few original papers mentioned MB of the LCX artery, but did not describe it in detail [20–26]. Furthermore, several researchers have reported case reports stating the characteristics of MB of the LCX artery[7–14]. Even though most MBs are considered congenital and asymptomatic, most cases have reported that patients with MB of the LCX artery experienced severe and chronic chest pain [7–9,11–14]. In 2005, Gunduz et al. first described a case of myocardial infarction in the first OM of the LCX artery [9]. Aksoy et al. reported that asymptomatic MB cases showed 100% systolic narrowing and incidentally presented with acute coronary syndrome [11]. A few reports on MB involving the LCX artery are shown in Table 3. MB involving the LCX artery may also be associated with changes in the ECG (7,8,10,12,13, angina [8], acute coronary syndrome, and severe cardiac events [12]. Published case reports suggest that ST-segment changes are the main changes in patients with MB of the LCX artery [8, 10, 13].
Table 3
Summarizing publishes of MB of LCX
| Study year | Study type | Imaging examination methods | age | sex | hypertensive | Smoking | Clinical findings | ECG | Other characteristics |
1 | Grag et al 2000[5] | Case report | Coronary angiography | 35 | male | no | yes | Atypical chest pain for 17 years | R wave poor progression and T waves inversion | unknown |
2 | Okmen et al 2002[6] | case report | Coronary angiography | 45 | male | yes | yes | Chest pain to the left shoulder on exertion for the last 4 months | ST-segment depression | exercise-induced angina pectoris; |
3 | Gunduz et al 2005[7] | letter to the editor | Coronary angiography & echocardiographic | 54 | male | no | unknown | chest pain and progressive dyspnea | unknown | Myocardial bridging in the obtuse marginal branch of LCX |
4 | Tuncer et al 2008[8] | case report | Coronary angiography | 63 | male | no | no | Chest pain radiating to the left shoulder | ST-segment changes | A significant systolic narrowing on the mid-LCX |
5 | Peters S 2019[9] | letter to the editor | Coronary angiography | 38 | female | unknown | unknown | Chest pain | unknown | unknown |
6 | Aksoy et al 2017[10] | case report | Coronary angiography | 62 | male | no | yes | Severe, squeezing chest pain | T wave inversion and R wave progression | unknown |
7 | Ibarrola et al 2019[11] | case report | Coronary CTA | 54 | female | unknown | unknown | unknown | ST depression | LCX arising from right sinus ostium |
8 | Kiris et al 2016[12 | Case report | Coronary CTA | 46 | male | unknown | unknown | With recurrent retrosternal chest pain of 3 months duration | unknown | MB in the LAD, ramus intermediate, and first OM |
Note: MB: myocardial bridging; LAD: left anterior descending artery; LCX: left circumflex artery; OM: obtuse marginal branch; ECG: electrocardiogram; CCTA: coronary computed tomography angiography. |
Few studies have pointed out that MB located on the proximal segment may easily prolong the development of coronary atherosclerosis and hemodynamic changes [15, 27].Therefore, knowing the position of bridging in the coronary artery is vital, as it provides diagnostic information that can guide management of the condition. In this study, the MB of the LCX artery was mostly located at the distal segment and was not associated with atherosclerosis. A study [5] has pointed out that the overall average MB length was 2.02 cm. However, in this study, the 95% CI of the length of bridging segment in LCX, LAD and RCA groups were, LCX: 2.88 (2.32, 3.42), 2.19 (1.68, 2.69), 2.57 (1.55, 3.60). In this study, we observed that bridging segments in the LCX artery were longer than that in the other arterial branches.
In this study, almost 70% patients with MB were associated with chest pain or discomfort for a long time, but all CT-FFRs were normal even in patients with chest discomfort or chest pain. The 95% CI of CT-FFR in the proximal segment of bridging of the three groups were, LCX: 0.96 (0.96, 0.97), LAD: 0.93 (0.91, 0.95), and RCA 0.95 (0.92, 0.97), respectively. Further, the 95% CI of CT-FFR in the distal segment of bridging of the three groups were LCX: 0.93 (0.92, 0.94), LAD: 0.89 (0.86, 0.92), RCA 0.89 (0.87, 0.93), respectively; with no significant difference between the three groups. This result may be related to the data inclusion criterion which only enrolled patients with isolated MB. Moreover, in most patients, MB of the superficial type was present.
However, most patients presented with chest pain and abnormal ECG was observed even in patients with superficial and normal hemodynamics, which is independent of the location of the MB. In this study, abnormal ECG findings were present in more than half of the patients with MB (LAD artery MB, 60.87% [14/23] vs. LCX artery MB, 52.17% [12/23] vs. RCA MB, 50% [5/10]).
Coronary artery dominance depends on the origin of the posterior descending artery, which supplies blood to the posterior portion of the interventricular septum [28–30]. There are three types of coronary artery dominance: right, co-dominant, and left. The right coronary dominant heart was defined as the posterolateral portion arising from the right coronary artery, and the left coronary dominant heart was defined as the posterior descending artery arising from the LCX artery [29]. It has been found that about 80–85% of the coronary arteries present a right-dominant pattern [31]. The coronary artery tree with different coronary artery dominance was reconstructed based on CCTA, as shown in Fig. 6. All the enrolled patients were found to have right dominant or co-dominant hearts, and no left dominant hearts were found. There are two reasons for this phenomenon. First, the right dominant and co-dominant heart commonly exist in the human heart, and MB involving the LCX artery is a rare cardiovascular disease. Second, in the left dominant heart, the LCX artery is the main coronary artery supplying the interventricular septum. Therefore, this phenomenon may be explained as an evolutionary occurrence as the heart and MB are congenital diseases. However, there was no left dominant heart in patients with MB of the RCA; but, its pathophysiology remains unknown.