We conducted an observational, retrospective, single-center study to evaluate the differences in the topography of CAD in the right as opposed to the left coronary arterial system in a large dataset of 17,323 patients who underwent coronary angiography during a 20-year period. The present study is the first large scale registry to demonstrate that LCA-only disease was more frequent than RCA-only disease. Our results of higher angiographic localization of atherosclerosis in LCA as compared to RCA further confirm previous findings derived from histopathologic (n = 2,964) , angiographic (n = 302) , intravascular ultrasound (n = 262)  and computed tomography (n = 102)  data. Furthermore, our results are in agreement with clinical evidence that isolated right ventricular or left posterior infarction, which are basically attributed to RCA lesions, are less common than left ventricular infarctions [1, 2].
Local hemodynamic and anatomic particulatiries of LCA vs RCA may be responsible for the predilection of atherosclerosis development in the left coronary system [12, 13]. First, the right coronary flow is more uniform during the cardiac cycle as compared to the left, which experiences a remarkable systolic decline accompanied by a significant diastolic increment [12, 14, 15]. As a result the local endothelial shear stress (ESS) in LCA is lower and more oscillatory, especially in atherosclerosis-prone regions, as compared to RCA . Low and oscillatory ESS shift the endothelial cell function and structure to a pro-atherosclerotic phenotype promoting atherosclerosis [12, 13, 16]. Second, increased wall stress is another potent atherogenic stimulus . LCA segments are exposed to higher wall stress during systole than RCA. This is a result of the different contractile properties of the left versus right ventricle [12, 17]. The greater wall stress throughout the cardiac cycle in LCA may form an atherogenic stimulus . Third, RCA and LCA have differences in anatomy. Left anterior descending artery exhibits twice the torsion of RCA . Torsion may play a major role in generating helical flow patterns, which may promote atherosclerosis progression [13, 19, 20]. Finally, the increased branching of the LCA as compared to the RCA contributes to the development of disturbed flow in the respective regions thus rendering a more atherosclerosis-susceptible environment in the LCA .
Our finding of a higher probability of men to present with concomitant RCA and LCA disease may indicate that male sex is prone to a more widespread form of atherosclerosis . On the other hand, the increased likelihood of women to present with LCA-only disease may in part explain their worse prognosis after a coronary event .
Concerning the effects of age in the localization of CAD, our findings suggest that concomitant RCA and LCA disease is found at older ages than isolated RCA or LCA involvement. This comes into consistence with previous autopsy studies exhibiting an increased prevalence of CAD with the progression of age [4, 5]. In women however, all three categories of CAD were most prevalent in an older age group than in men, and this is attributed to the established tendency for women to develop CAD at a later age than men .
Several limitations apply within our study. First, it was performed to a specific group of patients referred for coronary angiography; thus, the generalizability of our results to the general population is limited and the real prevalence of the localization of CAD in the community remains unknown. Also, a referral bias regarding the clinical presentation of the patients cannot be excluded as the study was conducted in a tertiary care center. Detailed information on the medical history of the subjects was not available due to heterogeneity of cases studied in terms of the cardiology center they were referred from and due to the lack of electronic patient records for the first years of the study. These, in association with the large number of study subjects and the long period in the past our report extends to, render not feasible to investigate on potential differences with regards to coronary artery disease risk factors. Also, we were unable to assess variations in the localization of atherosclerosis within the proximal or distal parts of the coronary arteries, although there is evidence that most thin-cap fibroatheromas and ruptured plaques are found in the proximal third of the coronaries . The burden of CAD in human coronaries was based on data from conventional angiography, although newer imaging modalities, such as intravascular ultrasound, have been proved more accurate in imaging of the anatomy and extent of CAD . Finally, the unavailability of follow up data did not permit us to evaluate the long-term outcome of CAD in relation to its localization.