European Journal of Cardiovascular Medicine

Coronary artery anomalies (CAAs), also known as rare congenital conditions affecting the coronary arteries, can present with various clinical symptoms. In adults, the occurrence of these conditions is typically around 1%, although there are variations observed in angiographic and autopsy studies. Angiographic investigations have reported an incidence ranging from 0.6% to 5.64%, while autopsy series indicate an approximate incidence of 0.3%.^1,2 Most individuals with CAAs are asymptomatic and generally have a benign course. However, a small percentage may experience clinical symptoms such as angina, dyspnea, syncope, acute coronary syndrome, heart failure, ventricular arrhythmias, and sudden cardiac death (SCD). ^3,4

The use of 64-slice dual-source multi-detect computerised tomography coronary angiography (MDCT-CA), which provides superior non-invasive 3D imaging of the coronary arteries, has proven to be reliable in detecting CAAs. 256 multi-slice spiral computed tomography are next generation MSCT scanners with faster gantry rotation, higher spatial, temporal resolution and can correct for artefacts brought on by arrythmias or faster heart rates. There are fewer studies on prevalence of CAAs using 256 MSCT from India. Hence this study planned to find the prevalence and pattern of coronary artery anomalies and variants in adult population from western part of India, which can provide valuable insights into the disease burden and the contribution of CAAs to cardiovascular diseases, which are a significant cause of mortality in India.⁵

Study setting, design and population: A prospective observational study was conducted at Kiran Multi Super Specialty Hospital, a tertiary care hospital in western India, between April 2023 and April 2024. An adult patients aged 18 years or older, attending the health checkup OPD and underwent 256 MSCT coronary angiography were included in the study. However, individuals having any absolute contraindications to CT or intravenous contrast agents, CT suboptimal images, and serum creatinine concentrations greater than 1.5 mg/dL were excluded.  Procedure: The CTCA scans were carried out using a Brilliance iCT 256-Slice CT scanner (Philips, Eindhoven). ECG gating was utilized to ensure a resting heart rate (HR) of less than 80 beats per minute (BPM) without the use of beta blockers or prior treatment. The scanning process covered a region approximately 1 cm below the tracheal bifurcation and at the level of the diaphragm in a cranio-caudal direction. A circular zone of interest with a diameter of 10 mm was placed within the lumen of the ascending aorta using an unenhanced scan taken at the level of the aortic root. Subsequently, a 25-mL bolus of saline was administered followed by the injection of a non-ionic contrast medium (IOHEXOL) based on the patient's weight (1 mL/kg) and HR (HR< 60 bpm, less than 5mL, and HR > 80 bpm, >5 mL) at a flow rate of 5 mL/second. Another 25-mL bolus of saline was administered using a dual-head injector (Optivantage, Mallinckrodt, Taco Health Care, and Canada). Inspiratory breath-hold scanning was initiated with an average duration of approximately 16 seconds (ranging from 11 to 23 seconds), and the intensity level (calcification density) within the most significant area reached approximately 110 Hounsfield units. The 256-slice scanner included instantaneous arrhythmia management, allowing the X-ray capture to be paused at the same axial point when sinus rhythm was restored in the event of ectopy during a prospective ECG-gated scan.

A soft-tissue convolution kernel of medium firmness was utilized along with an estimated reconstruction increment of 0.5 mm and a slice thickness of 0.9 mm to regenerate the images. The resulting reconstructed matrix had dimensions of 512 by 512. The field of vision was individually adjusted to include the cardiovascular system. Subsequently, each image was transferred to a separate workstation equipped with post-processing software (Philips Extended Brilliance WorkSpace 4.0). Retroactively ECG-gated observations were conducted using the following variables: a detector collimation of 128 x 0.625 mm, a dynamic Z-focal point for double sampling in the 256 x 0.625 mm slice collimation, and a gantry rotation time of 270 ms. When employing the typical half-scan reconstruction approach, a temporal resolution as low as 135 ms was achievable. For patients with a heart rate (HR) of 62 bpm or below, the HR-dependent pitch was set to 0.16, while for those with an HR higher than 62 bpm, it was set to 0.18. The tube current provided ranged from 471 mA to 860 mA, depending on the patient's weight, with a tube voltage of 120 kV. To attain optimal image quality using the retrospective approach, the ECG-based tube current regulation was disabled for each participant.

Image analysis: Two radiologists conducted a thorough examination of each CT scan independently. To capture the intricate anatomy of the coronary artery branches in three dimensions, advanced post-processing technologies such as multiplanar reconstructions (MPR), curved MPR (cMPR), maximum intensity projections (MIP), and volume reading (VR) were utilized to analyze every piece of information.

The Angelini method, which has been modified to allow for exceptions in cases where no instances have been recorded, and was utilized to categorize CAA.^6,7 In the upper to middle portions of the left and right coronary sinuses, the coronary ostia are anticipated to be located in a typical coronary artery system. The right coronary artery (RCA) and left main (LM) coronary artery originate from the aforementioned locations, respectively. Each proximal segment of the aortic wall is expected to be angled between 45 and 90 degrees. The course of the coronary artery must be extramural and sub-epicardial from the ostia to its endpoint. It should provide branches to the dependent myocardium, including the left ventricular (LV) free wall, antero-septal region, and right ventricular (RV) free wall throughout its territory. Using a threshold of 2 mm, the thickness of the surrounding cardiac muscle was employed to categorize myocardial bridging as either superficial or deep. Myocardial bridging (MB) is defined as a segment of the coronary artery that travels in an intramural path. Age distribution, gender distribution, presence or absence of disease in the area of interest in all individuals with anomalies, and the coronary dominance pattern, described as right: left: co-dominant (R: L: CD), were also noted.

Data analysis: Demographic data (age, gender), presence of any cardiac symptom and CTCA report based on Angelini method were recorded in a self-designed proforma. The gathered information was imported into an Excel spreadsheet. Categorical variables were presented as frequency and percentage, while continuous variables were represented as means and standard deviations (SD). This information sheet was then exported and analyzed using SPSS version 25. Results were expressed applying descriptive statistics. Prior to commencing the study, approval from the institutional ethics committee and informed consent were obtained from the institution and patient respectively.

Out of 612 participants, maximum number of participants were in 50 – 59 year age group, with mean age of study cohort 49.0±6.1 years. Male : female ratio of the cohort was 1.8:1. CAAs were detected in 39 participants with estimated prevalence of 6.37%. No age or gender significance was observed with regard to detection of CAAs. (Table 1). Among the participants with CAAs detection, 4 (10.3%) were symptomatic, while 35 (89.7%) were asymptomatic.

The assessment of coronary artery circulation dominance among the participants with CAAs revealed that the RCA was dominant in 28 (71.7%) of cases, followed by the both artery co-dominance in 6 (15.3%) while left coronary artery dominance in 5 (12.8%). Among 39 participants with CAAs, the least common type of left anterior descending artery (LAD) observed was type IV (5.1%) which supplies the cardiac apex and 25% of the inferior wall; followed by type I (7.6%) that does not supply the left ventricular (LV) apex; type II (23%) that provides blood circulation only to a part of the apex, and type III  (64%) that supplies the centre of the cardiac apex. No significant difference between type of LAD and CAAs were found. (Table 2)

Table 3 provides a comprehensive breakdown of the different types of CAAs. The majority of these anomalies, accounting for about half of the cases (n = 19, 3.1%), were attributed to anomalies of the course. Myocardial bridging was seen in 16 (2.6%) patients. The common variants related to course of the coronaries observed were myocardial bridging of the LAD (n=6, 1%) and the intra-atrial wall course of the mid-RCA (n=6, 1%). (figure 4). CAAs related to origin were seen in 18 (2.9%) individuals. The LCX originating from the RCA and the anomalous origin of the RCA from the left cusp, coursing between the aorta and pulmonary artery, had the highest prevalence at 0.5% each. This was followed by the absence of the LM with a separate origin of the LAD, LCX originating from the left cusp (Fig. 1), RCA arising just above the sinotubular junction, and the anomalous origin of the RCA noted from the left cusp (between RVOT and aorta) (figure 2), each accounting for 0.3% individually. Two (0.3%) patients had coronary termination anomalies, one of them had the coronary arteriovenous fistula and in another patient distal RCA was not visualised.

Table 1: Age and Gender distribution (N = 612)

         χ2= Chi-squared value

Table 2. Distribution of Coronary artery dominance and LAD type with CAAs

Table 3. CAAs types and variants detected with 256 MSCT coronary angiography.

LCx = left circumflex; LM= left main; LAD= left anterior descending; RCA= right coronary artery; LV= left ventricle; RVOT= right ventricular outflow tract; D1= diagonal 1; R=right; L=left; CD = co-dominance.

Figure 1. Separate origin of LAD & LCx from left cusp

Figure 2. Anomalous RCA origin from left cusp

Figure 3. Shepherd crook RCA

Figure 4. Myocardial bridging

An abnormality of the coronary arteries refers to any pattern of the coronary arteries that is uncommon in the general population and is characterized by features such as origination, course, and termination. ⁸ The definitions of normalcy and irregularity in this context are currently unclear, and there is no widely accepted categorization for these abnormalities. ⁹ Various methods of classifying CAAs have been proposed, but the Angelini classification is widely used. This classification utilizes four categories to define anomalies of origin and course, which are considered to be the most clinically significant in terms of difficulties encountered during angiography and surgery. ⁶ The inclusion or exclusion of myocardial bridging (MB) in the literature significantly affects the prevalence of CAAs, as some researchers consider MB to be a typical variety while others view it as an abnormality.^10-12 The incidence of CAAs ranges from approximately 0.5% to 3.0% when MB is not included, but increases to 7.9% to 18.4% when MB is included.¹³ In this study, we have utilized both the Angelini classifications and the MB to report the prevalence of these anomalies individually and comprehensively.  In the current study, the prevalence of CAA's, including MB, was determined to be 6.3%, which is in agreement to the finding of Rafiq S et al (5.6%). ¹⁴ Von Ziegler et al¹⁵ and Chaosuwannakit N et¹⁶ al reported 3.2% and 3.7% prevalence of CAAs in their study while Rao et al¹⁷ from India reported 10% prevalence of CAAs among adults having coronary artery disease (CAD).

Common coronary variants reported in literature includes left coronary artery dominance (10%), codominance (2 – 20%), shepherd’s crook RCA (5%), Ramus intermedius (10 - 15%) and variation in atrioventricular or sinoatrial node arterial supply. ¹⁸ Among the CAAs, commonest is separate origin of LAD & LCx (0.41%), LCx from right sinus (0.37%) and RCA from left sinus, reported from various studies in India.^18,19  The prevalence of separate origin of LAD & LCx was 3.93% and 0.59% respectively, while that of LCx from right sinus was 3.3% and 0.55% respectively by rao et al and Cademartini et al.^17,20. The common variants found in present study were codominance in 49 (8%) and shepherd’s crook RCA in 3 (0.5%). Among the CAAs, LCx anomalous origin (n=8,1.3%) was the commonest anomaly found in present study. Of these 3 patients had LCx originating from RCA and 3 had separate origin of LAD & LCx with absent LMCA. Both of these anomalies involving LCx are usually benign, however LCx from right sinus can pose technical issues during coronary intervention or surgery. ¹⁹Anomalous origin of RCA was found in 7 (1.1%), of which 5 had RCA originating from left cusp. Anomalous origin of RCA, particularly with course between aorta and pulmonary artery is frequently associated with sudden death.¹⁸ This anomaly was seen in 3 of our patients. Though most of the variants and anomalies are of benign nature, they may complicate cardiac surgery, percutaneous cardiac intervention if unrecognised. ¹⁸

Prevalence of myocardial bridge has a wide range from 0.15% to 25% angiographically and 5% to 86% at autopsy. Proximal LAD is the most commonly involved coronary with MB. ¹⁸ Anomalies of MB was observed in 2.6% of our cohort, out of which MB with mid LAD and intra atrial course was seen in 6 patients each. Most patients with MB are asymptomatic, however Morales et al revealed incidence of MI in patients with MB, possible mechanism is systolic compression of intramural LAD leading to impaired coronary flow and precipitation of ischemia. ²¹ Ferreria et al further explained occurrence of atypical angina in patients having deep MB as compared to superficial MB.²²

CT angiography is a non-invasive imaging modality, which describes the origin and course of coronary arteries in detail with a 3-dimensional anatomic information compared to suboptimal findings of conventional angiography. ¹⁹.   In a clinical practice a stepwise approach starting with non-invasive modality should be the ideal one.

STUDY LIMITATION

Considering that only the intermediate risk group has been included, it is possible that the prevalence of CAD in the CAA population might not be accurately represented. The primary constraint of the present study is the size of the population, as a more extensive cohort from the study population should be conducted in upcoming studies, particularly for the prevalence analysis.

The prevalence of CAAs including MB in present study is consistent with established ranges found in different studies. Though most of the CAAs are benign, association of some of them with difficult coronary intervention and sudden death underscores the importance of differentiation between hemodynamically serious and relatively benign anomalies. MSCTCA is helpful non-invasive modality in defining coronary artery anatomy, including origin, course, and termination.

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