To our knowledge, this is a unique study relating to the measurement of change in vessel caliber in anomalous coronaries during the cardiac cycle. We did not come across studies with similar intent and exploration in the literature. Anomalous coronary arteries have been reported to cause various cardiac symptoms and mechanisms have been hypothesized as to the pathophysiology. Physical exertion in such individuals can lead to accentuation of precarious hemodynamics leading to restricted myocardial blood flow, even myocardial ischemia and sudden death. [11–14] However, some patients with this entity may remain entirely asymptomatic. It is imperative to identify the patients at risk of potential myocardial ischemia, as surgical intervention is beneficial only in such cases. [15–17] In this study we have assessed the anomalous location of ostium of coronary vessels, the variation in the systolic and diastolic diameter and area of their interarterial segments to identify individuals at risk of myocardial ischemia.
Since slit-like ostium and acute angle at take-off were more frequently seen in patients with high take off anomalous coronary artery, these anatomical configurations may be assumed to be the indicator for higher risk. However, the occurrence of chest pain and positive TMT findings did not show statistically significant differences between the two groups.
The significant percentage change in mean area and diameter of the artery between cases of HIC and LIC concurs with the hypothesis by Lee et al, which proposes that hemodynamic significance of AORL with an interarterial course differs according to the location of the anomalous RCA ostium due to greater compression of the interarterial segment of anomalous coronaries with high origin.[5] However, HIC and LIC did not show significant correlation with TMT findings. Additionally, significant positive correlation was seen between change in vessel caliber in the interarterial course of coronary arteries in the cardiac cycle and positive TMT findings. This points to an important fact that anatomical classification into HIC and LIC doesn’t adequately categorize the ischemic risk, but the absolute percentage of compression does. Therefore, it is imperative to assume that it is not only the type of IAC, but also the degree of compression that should be taken into consideration when predicting risk assessment, thus, guide the decision on the management strategies in patients with interarterial coursing of coronaries.
Specific anatomic characteristics of patients with IAC of coronary arteries on CT coronary angiogram and relation between major adverse cardiac events have been studied earlier to distinguish patients at risk of adverse events. [16, 18] However, there are no relevant literature on the assessment of change in vessel caliber during the cardiac cycle in patients with IAC of coronary arteries and clinical significance. Hence, we believe that results of our study bridge the earlier lacunae, providing a more comprehensive basis for the patient management. This element of information should be carefully explored while deciding the treatment of anomalous coronary artery arising from the opposite sinus.
Ashrafpoor et al. assessed in their study, the relation between major adverse cardiac events and anatomical criteria determined by coronary computed tomography angiography. A significantly smaller minimal lumen area was seen in patients with adverse coronary events ( 3.6 mm2 vs 9.0 mm2 )18. In our study, the difference in minimal lumen area (systolic phase lumen) was not significant (5.4 mm2 vs 7.4 mm2). In fact, only three patients in our study had a minimal lumen area ≤3.6 mm2, one had negative TMT, second had positive TMT (borderline symptoms) and the third had a positive TMT (symptomatic, minimal lumen area of 1.7mm2 and area difference of 55% and 35% change in diameter), He underwent reinsertion of the anomalous RCA onto right coronary cusp and improved clinically. Hence, we are of the opinion that an absolute single measurement of the interarterial segment as suggested in earlier study, does not provide adequate assessment.
Many studies have assessed the anatomic parameters of ACAIAC particularly in young patients. Study by Lee et al comparing the ‘‘high-risk’’ morphologic characteristics of anomalous aortic origins of RCA vs left coronary artery showed no significant differences with respect to any morphologic features between the symptomatic and asymptomatic patients with ACIAC.[19] To prognosticate future adverse cardiac events, we need to look at factors which places them at higher risk. Adding dynamic coronary imaging in the CCA protocol is first step towards this direction.
Though traditionally believed that slit like course and ostial angulation were significant risk factors in SCD, our study did not show positive correlation of ostial angulation with positive stress testing. Similar observations were made in the study by Palmieri et al. [20] We also found a higher correlation of percentage change in caliber with stress testing results. Though we could not arrive at an absolute cut-off that would serve as a deciding factor in choosing management options, higher percentage of change in caliber in symptomatic individuals, along with anatomical factors could be added in establishing risk factor in SCD.
The positive TMT findings in patients with significant change in vessel caliber is an indication that the increased ventricular output during exertion, adds to vascular compromise, leading to increased risk of myocardial ischemia and SCD. As surgery is currently indicated only in symptomatic patients, identifying the patients who would benefit from surgery in a timely manner is critical to the management.[15, 16] There is also great variability in the existing guidelines for treatment of ACIAC in asymptomatic patients with wide ranging recommendations – from global recommendation of surgical repair in all teenagers to a very small subset of patients with defined criteria requiring intervention.[21–24] Though exercise testing is routinely performed in ACIAC, an positive exercise test does not provide significant reassurance. Adverse cardiac events occur even in previously asymptomatic patients as well.[25] It is imperative that we follow-up cases of borderline risk, and equally important to reassure patents in low risk or no increased risk regarding their management strategy. Risk stratification thus seems essential to the management. We hope that including criterion of dynamic assessment of interarterial segment caliber offer much needed information in solving the management dilemma.