European Journal of Cardiovascular Medicine

Coronary artery disease (CAD) continues to be one of the most significant public health concerns globally, and India has witnessed a marked rise in both its prevalence and overall disease burden over the past few decades (1). For patients with extensive multivessel involvement or anatomically complex coronary lesions, coronary artery bypass grafting (CABG) remains the revascularization strategy of choice, offering durable symptom relief and survival benefit. As postoperative survival improves, there is an increasing need for accurate, timely, and non-invasive assessment of graft patency. Early detection of graft stenosis or occlusion is essential for guiding clinical decision-making, preventing recurrent ischemia, reducing morbidity, and optimizing long-term patient outcomes.

Invasive coronary angiography (ICA) has long been regarded as the gold standard for evaluating graft anatomy and patency (2). However, ICA in post-CABG patients is technically challenging, often requiring longer procedural time, higher volumes of iodinated contrast, and significant radiation exposure for both patients and operators (2). Although relatively uncommon, complications such as arrhythmias, vascular injury, coronary dissection, stroke, and even death have been reported (3,4). These limitations emphasize the importance of safe, reliable, and non-invasive alternatives capable of accurately assessing bypass grafts while minimizing patient risk.

Cardiac computed tomographic angiography (CTA) has evolved considerably over the last two decades and now represents a powerful non-invasive modality for graft assessment. Early-generation multidetector CT (MDCT) scanners, particularly 16-slice and 64-slice systems, demonstrated encouraging diagnostic performance due to the relatively large diameter and limited motion of graft conduits (2,3,5). Advances in spatial and temporal resolution, as well as sophisticated 3-dimensional reconstruction algorithms, have further improved diagnostic accuracy and clinical utility (6,7). Studies utilizing 64-slice CTA have reported sensitivity and specificity approaching 100% for the detection of graft occlusion and significant stenosis (7). Moreover, CTA allows comprehensive visualization of both arterial and venous grafts and provides additional anatomical information that can be clinically valuable.

Nevertheless, certain limitations persisted with 64-slice CTA which include suboptimal imaging in patients with elevated heart rates, arrhythmias, heavy calcification or high body mass index. Motion artifacts and image degradation also affected the assessment of distal anastomoses, which are smaller, more mobile, and technically more challenging to evaluate (8). These constraints prompted the development of more advanced scanners, including 256-slice and 320-slice CT systems, which offer improved temporal resolution, wider z-axis coverage and faster acquisition times (8,9). Such technological advancements enhance image quality, reduce motion artifacts and potentially lower radiation exposure when combined with ECG-gating and radiation-saving techniques (11,12).

Despite the technological promise of 256-slice CTA, clinical data evaluating its diagnostic accuracy, practical advantages and overall clinical impact for post-CABG graft assessment remain relatively sparse, particularly in India, where CAD prevalence and CABG procedures continue to rise. The present study addresses this gap by assessing the performance of 256-slice CTA in evaluating graft patency in patients with prior CABG. We compare CTA findings with ICA, analyze image quality, and examine the influence of heart rate and heart rate variability (HRV), as well as radiation and contrast usage. To the best of our knowledge, this represents one of the earliest Indian studies systematically comparing 256-slice CTA with ICA for bypass graft evaluation aiming to inform clinical practice and optimize patient care.

Study Population

This prospective study included 100 consecutive patients with documented CAD who had undergone CABG at least one year earlier and were referred for evaluation of graft status. Exclusion criteria included hypersensitivity to iodinated contrast, history of drug allergies, renal dysfunction (serum creatinine >1.3 mg/dL or GFR <60 mL/min/1.73 m²), presence of implanted pacemaker or automatic implantable cardioverter-defibrillator, hemodynamic instability, severe cardiorespiratory illness (NYHA class III or IV), and pregnancy. All participants provided written informed consent. The institutional ethics committee approved the study protocol.

CT Coronary Angiography Protocol

Patients with pre-scan heart rates exceeding 70 bpm received intravenous metoprolol (3–5 mL of 1 mg/mL metoprolol), titrated to body weight, unless contraindicated. A 256-slice MDCT scanner (Brilliance iCT, Philips) was used. A stable three-lead ECG signal with clearly identifiable QRS complexes was required for retrospective ECG gating. Scanning was performed in a cranio-caudal direction, spanning from the aortic arch to the diaphragm for venous grafts and from the subclavian artery for internal mammary grafts. The system’s temporal resolution was 135 msec.

Contrast material (Iohexol 300 mg/mL) was injected via an 18-gauge cannula at 5.5 mL/s for a total of 75 mL, followed by a 30-mL saline flush. Bolus tracking at the ascending aorta (threshold: 150 HU) triggered image acquisition. Images were reconstructed at 0.9-mm slice thickness using a 512 × 512 matrix. Post-processing was performed using Extended Brilliance Workspace 4.5 with multiplanar reformation (MPR), curved planar reformation (CPR), maximum intensity projection (MIP), and 3D volume rendering.

Image Interpretation and Graft Segmentation

Two independent observers, aware of surgical graft details but blinded to HR and HRV data, analyzed the images using datasets acquired at 40%, 45%, 70%, 75%, 78%, and 80% of the R-R interval.

Each graft was divided into three segments:

• Proximal segment: first 1 cm and proximal anastomosis

• Middle segment: graft body

• Distal segment: terminal 1 cm including distal anastomosis

Image quality was graded on a 5-point scale:

1. Excellent

2. Good

3. Moderate

4. Poor

5. Non-diagnostic

Scores 1–3 were considered evaluable.

Image quality degradation caused by stepladder artifacts, surgical clip artifacts, respiratory artifacts, insufficient opacification or small distal anastomosis was recorded.

Grafts were classified as:

• Patent (<50% luminal narrowing)

• Stenosed (≥50% narrowing)

• Occluded (non-opacified or stump only)

Invasive Coronary Angiography

Patients with significant stenosis or occlusion on CTA underwent ICA within seven days. ICA employed standard Judkins technique via femoral access. All therapeutic decisions were based solely on ICA.

Heart Rate and Radiation Dose Evaluation

Mean HR and HRV (standard deviation of HR during acquisition) were calculated using workstation software.

Radiation dose was derived from dose-length product (DLP) and chest conversion factor (k = 0.014):

• Effective radiation dose (mSv) = Dose length product (mGy x cm) X 0.014

Statistical Analysis

CTA was analyzed on a per-graft, per-segment, and per-patient basis. ANOVA assessed associations between HR/HRV and image quality. Sensitivity, specificity, PPV, and NPV were calculated with ICA as reference. SPSS v19 was used, with significance set at p-value < 0.05.

Of the 100 patients enrolled, 99 (99%) successfully underwent CTA; one patient was excluded because of a technical acquisition error. The mean age of the cohort was 65.3 ± 8.6 years, and 88% were male. Typical or atypical angina were the most frequent presenting symptoms, while hypertension and diabetes were the predominant risk factors (Table 1).

Table 1. Baseline Characteristics (n = 99)

Graft Characteristics

As mentioned in Fig 1 & 2, total 276 grafts were evaluated, comprising 129 arterial (46.7%) and 145 venous (52.5%) grafts. 2 of the grafts were of unknown origin. CTA reported 193 (69.9%) grafts as patent, 11 (4.0%) as stenosed, and 72 (26.1%) as occluded. Arterial grafts exhibited significantly higher patency (82.9%) compared with venous grafts (57.9%).

Fig 1: Types of grafts

Fig 2: Graft patency

Image Quality and Heart Rate Findings

The mean heart rate (HR) during scanning was 63.7 ± 11.3 bpm, and mean heart rate variability (HRV) was 1.90 ± 1.15. A total of 606 graft segments from 202 grafts were analyzed for image quality:

• Score 1 (excellent): 467 segments (77.1%)
• Score 2 (good): 134 segments (22.1%)
• Score 3 (moderate): 5 segments (0.8%)
• No poor or non-diagnostic segments.
• The single patient with atrial fibrillation had fully interpretable images.

Distal segments demonstrated significantly lower image quality than proximal or mid segments (p < 0.05). HRV significantly affected distal segment quality (p < 0.001), while HR showed no significant correlation (Fig 3 & 4).

Fig 3: Correlation of image quality with mean heart rate

Fig 4: Correlation of image quality with heart rate variability

Correlation With Invasive Coronary Angiography (ICA)

20 of the 99 patients underwent ICA, providing comparison for 61 grafts (18 arterial and 43 venous). CTA showed excellent agreement with ICA except for one LIMA–LAD graft containing an in-situ stent, which CTA incorrectly classified as occluded (Table 4).

Table 4. CTA vs ICA: Graft Patency, Radiation Dose, and Contrast Volume

Radiation and Contrast Exposure

CTA was associated with higher radiation doses compared with ICA (16.5 ± 2.5 mSv vs. 10.0 ± 3.1 mSv; p < 0.05). However, CTA required substantially less contrast (75 mL vs. 180.5 ± 34.6 mL; p < 0.05).

Table 5. CTA Diagnostic Matrix for Detecting Stenosis/Occlusion

*Excluding the graft with an in-situ stent, CTA accuracy becomes 100%.

This study shows that coronary CT angiography (CTA) provides a reliable and accurate noninvasive method for evaluating graft patency in post-CABG patients, with a completion rate of 99% and consistently interpretable images. These findings parallel prior reports demonstrating high feasibility and diagnostic utility of modern multidetector CT systems in postoperative coronary assessment (1,2).

Graft Patency Patterns

Arterial grafts continued to outperform venous conduits, with significantly higher patency rates (Fig 1 & 2). This observation mirrors the well-recognized long-term durability of LIMA grafts described in earlier studies (3,4). The higher occlusion burden in venous grafts in our cohort reflects their known susceptibility to progressive atherosclerotic degeneration, reinforcing the importance of regular non-invasive surveillance (5).

Image Quality and Heart Rate Dynamics

Overall image quality was excellent, with more than three-quarters of all segments graded as optimal. Even in the single patient with atrial fibrillation, all segments were diagnostic, demonstrating the robustness of current scanning technology. Similar high-quality imaging in arrhythmia or variable heart rates has been noted with advanced scanners in previous work (6). As seen in earlier publications, distal anastomotic segments showed comparatively lower image quality (1,7). Our findings confirm that heart rate variability (HRV) — rather than absolute heart rate—has the most significant influence on distal segment quality. This is consistent with the work of Achenbach et al. & others who demonstrated degradation in image quality with increasing HRV (7,8).

Fig 1: 3D volumetric reconstruction depicting patent grafts (sapheno-venous graft to obtuse marginal & LIMA to left anterior descending artery. Also shown is blocked stump of Sapheno-venous graft to Posterior descending artery. Curved MPR showing - LIMA to left anterior descending artery  & sapheno-venous graft to obtuse marginal.

Fig 2: 3D volumetric reconstruction demonstrating patent LIMA to LAD graft & patent Radial artery graft between LIMA & PDA. Curved MPR showing patent LIMA to LAD graft & patent Radial artery graft between LIMA & PDA.

Correlation With Invasive Angiography

CTA correlated strongly with ICA, with only one discordant case involving a stented LIMA–LAD graft. Metallic stents are a known source of blooming artifact on CT, often leading to misinterpretation in heavily stented or calcified segments (9). After excluding this outlier, CTA reached 100% diagnostic accuracy, consistent with modern studies of 64 and 256-slice CT that report high sensitivity and specificity (2,10).
The strong agreement between CTA and ICA supports CTA as an effective initial tool for graft assessment, allowing ICA to be reserved for cases requiring intervention.

Radiation and Contrast Considerations

Although CTA demonstrated higher radiation exposure than ICA, it required substantially less contrast. Previous studies similarly report higher effective doses with retrospective gating but significantly lower iodinated contrast requirements for CTA (3,11). The reduced contrast volume is clinically advantageous, particularly in patients with compromised renal function. Technological advances such as dose-modulated scanning, high-pitch acquisition, and iterative reconstruction techniques have been shown to meaningfully reduce radiation dose in contemporary CT systems (11,12). Adoption of these strategies may help align CTA doses more closely with or even below those of ICA.

Clinical Implications

The study reinforces CTA as a practical and accurate first-line imaging modality in post-CABG patients presenting with recurrent symptoms. Its noninvasive nature, high negative predictive value and ability to evaluate both grafts and native coronary arteries provide substantial clinical benefit. CTA is especially valuable for centers managing large populations of surgical patients, facilitating early detection of graft failure and planning timely intervention.

Limitations

The main limitation is the relatively small proportion of patients who underwent ICA, which restricts the size of the comparative dataset. Nevertheless, the strong diagnostic performance observed is consistent with existing literature. Qualitative image grading, while clinically meaningful, may introduce observer variability. Finally, the misinterpretation of a stented graft highlights an area where technological refinement is still needed.

In conclusion, this study supports the use of 256-slice CTA as a highly effective and non-invasive method for evaluating post-CABG graft patency. The method offers high diagnostic accuracy and superior image quality as compared to previous generation CT. Given its ability to provide reliable graft assessment without the need for invasive procedures, 256-slice CTA is a valuable tool for routine post-surgical surveillance, especially in high-volume centers. Additionally, the reduced contrast dose as compared to ICA offers a major advantage for patients at risk of contrast-induced nephropathy, making CTA a safer option in this population. Future research with larger sample sizes and objective measures of image quality will help further validate the widespread use of 256-slice CTA in clinical practice.

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