MB constitutes a band of myocardial fibers enveloping a subepicardial segment of the coronary artery [8]. The inaugural anatomical delineation of myocardial bridges was provided by Reyman in 1737, followed by Black in 1805, with subsequent autopsy examination by Geiringer in 1951 and radiological identification by Portsmann and Iwig in 1960 [2].
The angiographic manifestation of MB is contingent upon a multitude of factors, including the myocardial bridge's thickness and length, the presence of loose connective or adipose tissue surrounding the bridged segment, myocardial contractility status, the tissue composition between the coronary artery and the myocardium, and the observer's proficiency. Consequently, numerous bridging instances, encompassing the involvement of the LCx and RCA, may remain undetected [6]. The reported prevalence of MB exhibits considerable variation depending on the employed diagnostic modality. Traditional imaging techniques, such as conventional angiography, demonstrate lower detection rates relative to advanced imaging modalities like CTA, which afford comprehensive anatomical visualization. The incidence of MB identified through CTA ranges from 3.5–100% [12].
Myocardial bridges predominantly occur in the middle segment of the LAD, yet they may also manifest in any epicardial coronary artery, such as the diagonal branches, the posterior descending branch of the RCA, or the marginal branches of the LCx [2]. The presence of myocardial bridges in the right coronary system is comparatively rare. Corban et al. reported the prevalence of MK in the LAD to be between 67% and 98%, while Möhlenkamp et al. documented incidences of 18% and 40% for diagonal and marginal branches, respectively [13, 14].
In the literature, reports concerning MB in the RCA and its branches are primarily documented as case reports. Nguyen et al. described a rare instance of MB in two posterolateral branches of the RCA. Tiryakioğlu et al. illustrated significant bridging in the middle segment of the posterior interventricular branch of the RCA [15]. Kulkarni et al. reported a case of isolated MB in the RCA [16]. Riezzo et al. presented a case of superficial bridging approximately 1 cm from the starting point in the descending branch of the RCA [6]. Studies encompassing case series are limited in number. While the reported prevalence of MB segments in the RCA is 2.9%, the rate in the branches of the RCA ranges between 3.7% and 5.9% [12]. In our study, we determined the prevalence of MB in the RCA to be 2.06%. However, this finding is inconsistent with the high incidence of 41.4% of MB in the RCA and its branches detected by Polacek in autopsies [5].
The existence of multiple myocardial bridges spanning various areas within both the left and right coronary arteries has been infrequently documented [17]. Richter et al. have detailed three instances in which MB was concurrently present in the RCA and the LAD [18]. In our study, isolated MB in the RCA was observed in 39.4% of cases. In addition to this, in the remaining 60.6% of the cases, we encounted superficial and/or deep MB in the LAD. Moreover, among patients with MB in the RCA, anomalies such as dual RCA, IARCA, and RCA origin anomalies were identified.
The relationship between coronary dominance and the prevalence of MB in the RCA has not been explored in the literature's case series; however, our research found right coronary dominance in all but one patient. Our findings also indicated a higher incidence of MB in the RCA among male participants.
MB is delineated as either superficial or deep, contingent upon its depth within the myocardium, and it is possible for a vessel to harbor several bridged segments [2, 19]. Gould et al. have categorized myocardial bridges as superficial if the depth ranges from 1 to 2 mm, and as deep if the bridge extends beyond 2 mm within the myocardium [20]. Superficial MB, reported at 75% in the literature, predominates over deep bridges, which account for 25% of reports [2]. In our analysis, the mean MB depth in the RCA was established at 1.7 mm, with superficial MB constituting 78.8% of instances.
The literature posits the average MB length at 20.2 mm and the depth at 3.1 mm. Studies utilizing angiography and autopsy reveal only marginal disparities in average MB length and thickness. The mean length is documented as 21.0 mm in investigations employing computed CTA and conventional angiography, and 19.3 mm in those utilizing autopsy/cadaver dissection. The average MB thickness or depth stands at 3 mm for both CTA and conventional angiography, and at 3.2 mm for autopsy/cadaver dissection, indicating minimal variance between examination methods. Employing imaging techniques such as CTA for MB dimension assessment yields findings congruent with autopsy outcomes. A correlation between artery compression and its depth has been established [12]. Our research found the MB segment length in the RCA to average 21.9 mm, with a prevalent location in the middle segment at 60.6%. Furthermore, our study contributes to the literature by detailing the localization of MB segments; 66.7% demonstrated an intramyocardial course within the right atrium, while the rest were within the right ventricle.
The impact of MB on coronary physiology has sparked considerable debate. Although MB is predominantly perceived as benign, it has been frequently linked to myocardial ischemia, infarction, ventricular arrhythmias, and sudden death, especially in the context of hypertrophic cardiomyopathy and coronary atherosclerosis [6]. The involvement of myocardial bridges in atherosclerosis represents an additional area of contention, as highlighted by Soran et al. [1]. Loukas et al. have posited the potential for "protective effects" of myocardial bridges [21]. Conversely, Ishii et al., Lee and Chen, and Zeina et al. have noted that while the proximal segment to the bridged area exhibits atherosclerotic changes, the segment under the bridge appears to be shielded from atherosclerosis [4, 22, 23]. Schar, however, contests the notion of the bridged segment being safeguarded against atherosclerotic alterations [24]. In our observations, none of the segments with bridging presented atherosclerotic involvement, yet about half (51.5%) demonstrated atherosclerotic presence in other segments of the RCA not affected by bridging. In alignment with this, no calcified atherosclerotic plaques were identified within the bridged segment of the RCA, yet 24.2% of the instances revealed calcified plaque in varying quantities in other segments of the RCA.
In the majority of instances involving MB in the RCA, clinical or radiographic indications of PHT, left ventricular hypertrophy, cardiomyopathy, and COPD have been documented [18]. Contrarily, our investigation identified PHT and COPD in only one distinct case each, with left ventricular hypertrophy observed at a comparatively low prevalence of 12.1%. These findings deviate from established literature. Nonetheless, to facilitate statistical analyses, further research with more extensive cohorts is warranted.
The intra-atrial or intracavitary trajectory of the RCA is characterized by the RCA's passage through the right atrial cavity [10]. Radiographically, this manifests as an RCA segment that is consistently enveloped by intracavitary contrast throughout all phases of the cardiac cycle. Although the literature includes case reports detailing IARCA instances, research series quantifying its prevalence remain scarce. Initially detected solely in post-mortem specimens and during heart surgeries, its observed frequency ranges from 0.1–1.8% [10, 11, 25]. IARCA's prevalence, as reported in autopsy or surgical cohorts is notably minimal [11]. MacAlpine et al. quantified a 0.1% prevalence in a thousand autopsy evaluations, and Ochsner et al. indicated a surgical prevalence of 0.09% [26, 27]. Krishnan et al. uncovered IARCA in six out of 331 autopsy dissections, noting a 1.8% occurrence rate [8], without finding any RCA origin anomalies. Opolski et al. elucidated the efficacy of CTA in recognizing IARCA within an extensive cohort of 9284 subjects, marking a 0.15% prevalence rate [28]. Hossain et al., with a 464 patient cohort, reported a 0.4% prevalence, while Ganga et al. found a 0.29% prevalence in a 7114 CTA case series [9, 11]. Buckley et al., across a 7847 CTA case series, identified IARCA in 17 individuals, documenting a 0.22% prevalence [29]. Given the escalating application of sophisticated cardiac imaging like CTA, an increase in the actual prevalence is anticipated. Our study also revealed an IARCA prevalence of 0.44%.
Consistent with the broader scholarly discourse, where sex disparities are generally not emphasized, Hossain et al. identified a predilection for IARCA occurrences in males [9]. Although a higher prevalence among males is noted in our cohort, with males constituting 4 of the 7 cases, the sample size is limited. Frey et al. documented the case featuring a concurrent dual RCA and IARCA, a rarity in medical literature [25]. Despite a small sample size in our investigation, we observed a relatively elevated incidence of dual RCA and IARCA coexistence at 42.8%. This suggests that the simultaneous presence of these rare anatomical variations may not be as infrequent as previously assumed.
Regarding the predominantly affected segment, while most literature cites the distal RCA as the frequent site, Ganga et al. highlighted the mid RCA. Our findings similarly emphasize the distal segment in 4 patients but also identified the mid-segment in 3 patients, without any instances affecting the proximal segment, underscoring the need for further investigation despite the absence of statistical analysis due to the small sample size. Ganga et al. delineated the average depth and length of IARCA as 2.57 mm and 14.85 mm, respectively. Contrastingly, our findings revealed an average depth of 5.1 mm and length of 37.9 mm, suggesting a significant deviation towards more pronounced anatomical manifestations. Literature scantily suggests a higher observation of right coronary dominance in IARCA cases [11]. Consistently, our study confirmed right coronary dominance across all instances, aligning with the extant observations on coronary dominance dynamics in IARCA presentations.
Kolodziej et al. delineated mild atherosclerosis affecting the intra-atrial segment in a subset of three individuals diagnosed with IARCA [30]. This contrasts with the broader literature, where no atherosclerotic conditions in IARCA segments are typically reported. Studies by Opolski et al., Krishnan et al., and Ganga et al. likewise indicated an absence of noteworthy atherosclerosis in the IARCA segments [8, 11, 28]. Our findings are similar to the literature in this respect. A singular case in our cohort showed mild coronary artery disease in segments of the RCA apart from the IARCA, with no instances of calcified atherosclerotic plaques within the RCA.
In our review of English-language literature, no investigations were found addressing comorbidities associated with IARCA. Our analysis extended to the exploration of concurrent conditions such as PHT, left ventricular hypertrophy, and COPD, none of which were detected across our patient cohort.
While IARCA manifestations are predominantly asymptomatic and considered benign, unrecognized presence prior to conducting invasive cardiac interventions can precipitate adverse outcomes. Challenges in pinpointing vessel localization arise during cardiovascular surgical revascularization and bypass graft operations. Furthermore, right heart catheterization procedures bear a risk of inflicting potential harm to the vessel. In electrophysiological interventions such as catheter ablation or lead device placements within the right atrium wall or right ventricular apex, there exists a direct risk to intracavitary coronary arteries, potentially culminating in inadvertent vessel damage [25]. The proximity between the electrode and artery during ablation, where thermal damage to tissues approximately 3–5 mm in proximity is a known risk, underscores a heightened injury risk post-ablation when IARCA is present [31]. Even though the RCA in scenarios of left-dominant circulation might influence a lesser extent of the myocardium, it remains susceptible to damage during the aforementioned procedures. Ganga et al. reported a predominance of right-sided dominance in 81% of their patient cohort [11]. While the literature largely omits discussions on coronary dominance, our analysis similarly observed right coronary dominance across all cases.