Diagnostic performance of coronary computed tomography (CT) angiography without electrocardiographic (ECG)-gating: comparison with invasive coronary angiography

Introduction

Coronary artery disease (CAD) remains one of the leading causes of mortality and disability globally, and early, accurate diagnosis is essential for improving clinical outcomes (1,2). Invasive coronary angiography (ICA) has long been regarded as the gold standard for detecting coronary artery stenosis; however, its invasiveness, high cost, and associated risks limit its routine use in clinical practice (3,4). In contrast, with high spatial resolution and rapid imaging performance, coronary computed tomography angiography (CCTA) has become the preferred noninvasive technique for initial CAD evaluation and screening (5,6).

Nonetheless, traditional CCTA relies on electrocardiographic (ECG-gating) to mitigate cardiac motion artifacts, which presents several limitations in clinical application (7). First, its adaptability to patients is limited: ECG-gating requires a stable heart rhythm, and image quality is often substantially degraded in patients with high heart rate (HR) variability, such as those with atrial fibrillation or frequent premature beats (8). Second, radiation exposure is relatively high: retrospective ECG-gating involves coverage of the entire cardiac cycle, resulting in an average radiation dose of 3–5 mSv (9,10). Third, the technique is operationally complex, requiring real-time ECG monitoring and specialized expertise from both the equipment and operators.

To address these limitations, ECG-less CCTA has been developed as an alternative approach. This technique takes advantage of rapid volumetric scanning enabled by wide-detector computed tomography (CT) systems (e.g., 256-row or greater), along with deep learning-based image reconstruction, artificial intelligence-driven motion correction, and automated phase selection. These innovations allow image acquisition to be completed within a single cardiac cycle, significantly reducing scanning time (11). Our previous research demonstrated that ECG-less CCTA yields comparable objective image quality and subjective assessments to ECG-gated CCTA; however, its diagnostic performance—particularly its ability to detect lesions with ≥50% stenosis—has not been comprehensively evaluated (12).

Therefore, this study aimed to validate the diagnostic capability of ECG-less CCTA for detecting obstructive CAD using ICA as the reference standard. We present this article in accordance with the STARD reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1338/rc).

Methods

Patients

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This retrospective, single-center study was approved by the Institutional Review Board of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine (No. 2025-2258-01), with a waived requirement for informed consent due to the retrospective nature. Consecutive patients with suspected CAD who underwent ECG-less CCTA between June 2024 and March 2025, followed by ICA within 30 days [median 14 days, interquartile range (IQR), 7–21 days], were included. No intervening coronary revascularization procedures or acute coronary syndromes occurred between the CCTA and ICA examinations. The exclusion criteria were as follows: (I) a known history of CAD; (II) history of ICA; (III) history of coronary artery bypass grafting or stenting; (IV) suspected acute coronary syndrome; (V) age below 18 years; (VI) severe renal insufficiency, defined as an estimated glomerular filtration rate (eGFR) <30 mL/min/1.73 mm²; (VII) severe coronary calcification, defined as an Agatston score >2,000 (13) assessed on non-contrast CT (120 kV, 3 mm slice thickness) and semi-automated scoring software (SmartScore, GE Healthcare, Madison, WI, USA); and (VIII) a history of iodine contrast allergy, or suspected pregnancy. The study workflow is illustrated in Figure 1.

Figure 1 Patient enrollment flow chart. CAD, coronary artery disease; CCTA, coronary computed tomography angiography; ECG, electrocardiogram; ICA, invasive coronary angiography; IQR, interquartile range.

Image acquisition and reconstruction

All patients underwent ECG-less CCTA using a 256-row CT scanner (Revolution Apex Expert, GE Healthcare, USA). Scans were automatically selected with a tube voltage of 80, 100, and 120 kV according to the scout of patients, automatic tube current modulation, and preset noise index of 20 Hounsfield units (HU). The data acquisition window was set to 300–500 ms. A simulated ECG signal was generated based on the HR estimate (gathered before the CCTA through pulse), with no ECG leads placed on the patient. This simulated ECG signal was used for virtual gating of the CT data acquired through one full heart cycle. The optimal reconstruction phase was automatically selected by a proprietary algorithm (Smart Phase, GE Healthcare) which identifies the cardiac phase with minimal coronary motion, typically in mid-to-late diastole, based on the simulated cardiac cycle. This phase selection was subsequently refined using a motion correction algorithm (SnapShot Freeze 2, GE Healthcare), which synthesizes data from adjacent phases within the single cardiac cycle to compensate for residual coronary motion. The application of this motion correction algorithm has been previously validated for improving image quality in single-beat acquisitions (14). We positioned the bolus tracking region of interest (ROI) at the aortic root with a 180 HU trigger threshold and 4-second scan delay.

Contrast injection utilized bolus tracking with Iopromide (370 mgI/mL; Bayer, Leverkusen, Germany) at 0.6 mL/kg body weight over 10 seconds. An equal-volume saline flush was followed at an identical flow rate. Patients received neither beta-blockers nor nitroglycerin before the CCTA examination.

Optimal reconstruction phases were selected by an automatic phase selection software (Smart Phase), with a reconstruction slice thickness and interval of 0.625 mm. A coronary motion correction algorithm (SnapShot Freeze 2, SSF2) combined adjacent cardiac phases data within a single cardiac cycle to account for and compensate for coronary motion, improving image quality. This technology was specifically applied to vessel segments with significant motion artefacts. All images were reconstructed using deep learning image reconstruction algorithm (TrueFidelity^TM, GE Healthcare) combined with SSF2, ensuring minimal motion artifacts in the selected phases (14,15). An experienced cardiovascular radiologist objectively quantified CCTA image quality by measuring ascending aorta attenuation (HU) at the the pulmonary bifurcation level. Image noise was calculated as the standard deviation (SD) of attenuation values within an ascending aorta ROI.

Assessment of coronary artery stenosis

Two independent observers (with 7 and 10 years of experience in cardiac CT imaging, respectively) evaluated the ECG-Less CCTA images based on the 18-segment Society of Cardiovascular Computed Tomography (SCCT) model (16,17). Both observers were blinded to the results of ICA and all clinical data of the patients during the CCTA image analysis. All segments ≥1.5 mm in diameter were evaluated. Evaluable segments were assessed independently for the presence of significant coronary artery lumen stenosis, defined as a diameter narrowing ≥50%. Stenosis was evaluated on a per-segment, per-vessel, and per-patient level. Vessel-level analysis included left main coronary artery (LM), left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA). Disagreements regarding the stenosis degree between two radiologists were resolved in consensus during a joint reading session. Non-evaluable coronary artery segments were considered as positive findings for diagnostic purposes. The observers were ignorant of the ICA results when evaluating the CCTA image.

ICA

ICA followed the standard protocols with ≥2 projections per vessel. An experienced interventional cardiologist blinded to CCTA data and clinical history evaluated angiograms using the identical 18-segment model. Obstructive CAD was defined as ≥50% diameter stenosis, consistent with CCTA criteria.

Radiation dose

Per-patient volume CT dose index (CTDIvol) and dose-length product (DLP) values were recorded. The effective radiation dose (ED) was derived using the standard formula ED = κ × DLP, where κ = 0.014 mSv/(mGy·cm) (18).

Statistical analysis

Statistical analyses were performed using the software SPSS 26.0 (IBM Corp., Armonk, NY, USA). Continuous variables were expressed as mean ± SD or median with IQR, whereas categorical variables were presented as percentages. Diagnostic performance metrics, including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy, were calculated with 95% confidence intervals (CIs) using the Wilson score method. Subgroup analyses were conducted based on HR [stratified as ≤75 vs. >75 beats per minute (bpm)] and coronary calcification burden (Agatston score ≤400 vs. >400). Comparisons between subgroups were performed using the chi-square test or Fisher’s exact test, as appropriate, with a two-sided P value <0.05 considered statistically significant. Inter-observer agreement for stenosis grading was evaluated using Cohen’s kappa (κ) coefficient, where κ >0.80 indicated excellent agreement.

The sample size for this retrospective diagnostic accuracy study was determined pragmatically by including all consecutive patients meeting the inclusion criteria during the study period. A final cohort of 110 patients was achieved, which aligns with recommendations in the STARD guidelines and provides sufficiently stable estimates for diagnostic performance metrics.

Results

Patient characteristics

A total of 110 consecutive patients (mean age 64.2±9.5 years; 57.3% male) were included in the final analysis. Baseline clinical characteristics and cardiovascular risk factors are summarized in Table 1. Hypertension (68.2%) and hyperlipidemia (49.1%) were the predominant cardiovascular risk factors, whereas diabetes mellitus was present in 34.5% of patients. The median Agatston calcium score was 320 (IQR, 85–780), with 12 patients (10.9%) excluded due to severe calcification (Agatston score >2,000). The mean HR prior to CCTA was 76.8±14.2 bpm (range, 55–112 bpm), and no beta-blockers or nitroglycerin were administered. The mean contrast media volume was 64.2±13.1 mL, injected at a rate of 4.5±0.7 mL/s over a fixed 10-second duration, followed by a 35 mL saline flush.

Image quality and radiation dose

The mean attenuation of the ascending aorta was 438±72 HU, with image noise measured as 19.6±4.1 HU (Table 2). Among the 1,980 coronary segments evaluated, 93.6% (1,854/1,980) demonstrated diagnostic image quality, whereas non-evaluable segments (6.4%, 126/1,980) were predominantly due to motion artifacts (4.1%, 81/1,980) or heavy calcification (2.3%, 45/1,980).

Radiation dose parameters included a CTDIvol of 10.1±5.0 mGy and a (DLP of 101.4±50.5 mGy·cm. The ED, calculated using the conversion factor, was 1.4±0.5 mSv.

Diagnostic performance

Using ICA as the reference standard, ECG-less CCTA demonstrated robust diagnostic performance across patient-, vessel-, and segment-level analyses (Figure 2, Table 3).

Figure 2 A 72-year-old male with suspected CAD underwent ECG-less CCTA. High-quality images without motion artifacts revealed significant stenoses in the proximal (A) and mid-LAD (C), later confirmed by ICA (B,D). Red arrows indicate sites of significant stenosis (≥50%). CAD, coronary artery disease; CCTA, coronary computed tomography angiography; ECG, electrocardiogram; ICA, invasive coronary angiography; LAD, left anterior descending artery.

At the per-patient level, sensitivity and specificity were 92.1% (95% CI: 85.6–96.2%) and 91.5% (82.3–96.4%), respectively, with a PPV of 92.3% and an NPV of 93.5%, yielding an overall accuracy of 91.8%. Vessel-level analysis showed improved specificity (93.6%, 90.2–96.0%) and NPV (95.1%, 91.8–97.3%), whereas segment-level specificity further increased to 96.2% (94.8–97.3%) with an NPV of 97.2% (95.7–98.3%). However, segment-level sensitivity slightly declined to 89.5% (85.3–92.7%), likely due to challenges in assessing calcified or motion-affected segments.

Non-evaluable segments and inter-observer agreement

Non-evaluable coronary segments (6.4%, n=126), primarily due to motion artifacts or heavy calcification, were conservatively classified as positive for stenosis to avoid underestimation of disease prevalence. This conservative approach, however, may contribute to an overestimation of stenosis prevalence and a consequent reduction in specificity. This approach slightly reduced specificity in per-segment analysis but maintained clinical relevance for ruling out significant CAD. Inter-observer agreement was excellent (Cohen’s κ =0.89, 95% CI: 0.85–0.93).

In addition to the primary analysis where non-evaluable segments were conservatively classified as positive, we performed a sensitivity analysis excluding these segments (n=126). This exclusion resulted in a segment-level sensitivity of 86.8% (558/643 evaluable segments with true stenosis) and specificity of 97.1% (1,297/1,335 evaluable segments without stenosis), compared to 89.5% and 96.2% in our primary analysis. The minimal variation between approaches supports the robustness of our findings, whereas the primary conservative approach aligns with clinical priorities for ruling out significant CAD.

Subgroup analysis

Subgroup analyses stratified by HR (≤75 vs. >75 bpm) and calcium burden (Agatston score ≤400 vs. >400) (19) revealed nuanced trends (Table S1). In patients with HRs >75 bpm (n=48), sensitivity (89.7% vs. 94.1%, P=0.12) and specificity (88.3% vs. 93.8%, P=0.08) were marginally lower compared to the low HR group, though differences were not statistically significant. Conversely, patients with Agatston scores >400 (n=35) exhibited significantly reduced specificity (84.6% vs. 94.1%, P=0.02), aligning with prior reports that heavy calcification compromises stenosis assessment accuracy (20).

Discussion

This study demonstrates that ECG-less CCTA offers high diagnostic performance for the detection of obstructive CAD using ICA as the reference standard, achieving a sensitivity and specificity of 92.1% and 91.5% (Figure 3), respectively, at the patient level, while maintaining a low radiation dose of 1.4 mSv. These findings highlight the potential of integrating advanced technologies—wide-detector CT, motion correction algorithms, intelligent phase selection, and deep learning-based image reconstruction—to overcome traditional limitations of ECG-gated protocols, particularly in patients with arrhythmias or in emergent clinical settings.

Figure 3 Comparison of ICA and CCTA in identifying obstructive CAD. (A) Per patient. ICA diagnosed 52 cases as non-obstructive CAD, among which 4 cases were diagnosed as obstructive CAD by CCTA; 58 cases were diagnosed as obstructive CAD, among which 5 cases were diagnosed as non-obstructive CAD. (B) Per vessel. ICA diagnosed 209 cases as non-obstructive CAD, among which 13 cases were diagnosed as obstructive CAD by CCTA; 231 cases were diagnosed as obstructive CAD, among which 21 cases were diagnosed as non-obstructive CAD. (C) Per segment. ICA diagnosed 1,350 cases as non-obstructive CAD, among which 51 cases were diagnosed as obstructive CAD by CCTA; 630 cases were diagnosed as obstructive CAD, among which 66 cases were diagnosed as non-obstructive CAD. CAD, coronary artery disease; CCTA, coronary computed tomography angiography; ICA, invasive coronary angiography.

The diagnostic performance of ECG-less CCTA observed in our study is comparable to that reported for contemporary prospective ECG-gated CCTA protocols, which typically achieve sensitivities and specificities in the ranges of 95–99% and 80–90%, respectively (21,22). The streamlined workflow of ECG-less CCTA, eliminating the need for ECG electrode placement, HR optimization with β-blockers, and complex gating setup, can significantly reduce the preparation and total examination time. This is particularly advantageous in the emergency department for the rapid triage of patients with acute chest pain, and for patients with contraindications to β-blockers.

It should be noted that sublingual nitroglycerin was not administered in this study, in line with our aim to streamline the protocol for potential emergency and arrhythmic populations. Although this omission simplifies the workflow, it might theoretically limit maximal coronary vasodilation and potentially affect the evaluation of intermediate stenoses. However, the primary objective of detecting obstructive (>50%) stenosis was achieved with high accuracy.

The high diagnostic performance and streamlined workflow of ECG-less CCTA position it as a valuable alternative to conventional ECG-gated protocols in specific clinical scenarios. Primarily, this technique is ideally suited for emergency department triage of patients presenting with acute chest pain. In this fast-paced setting, where rapid rule-out of obstructive CAD is critical, ECG-less CCTA eliminates the time-consuming processes of ECG lead placement, HR optimization with β-blockers, and complex gating planning, thereby accelerating time-to-diagnosis without compromising accuracy, as evidenced by its high NPV (93.5% at patient-level) (11). Furthermore, ECG-less CCTA offers a significant advantage for patients with arrhythmias (e.g., atrial fibrillation, frequent ectopy) or those with contraindications to β-blockers [e.g., asthma, severe chronic obstructive pulmonary disease (COPD), hypotension]. These patient groups have traditionally been challenging for ECG-gated CCTA and often required direct referral to ICA. It is important to note that ECG-gated CCTA remains the preferred protocol for comprehensive plaque characterization in stable, elective patients where ultra-high spatial resolution is desired (23). Thus, ECG-less CCTA should be viewed as a powerful complementary tool that expands access to robust coronary CT angiography for populations and settings where the traditional approach is suboptimal.

The diagnostic accuracy observed in this study aligns with recent advancements in CT hardware and algorithms. The 256-row detector CT scanner, combined with volumetric acquisition within a single heart cycle, minimizes motion artifacts, even at elevated HRs (mean 76.8 bpm). This is further enhanced by the SnapShot Freeze 2 motion correction algorithm, which synthesizes data from adjacent cardiac phases to compensate for residual motion, a technique validated by Yamaguchi et al. (15). The integration of deep learning-based image reconstruction (TrueFidelity™) not only reduces image noise but also preserves vessel wall details, enabling precise stenosis quantification (24). Such innovations explain the high specificity at the segment level (96.2%), which is critical for excluding non-obstructive lesions in acute chest pain triage. It is important to note that our conservative approach of classifying non-evaluable segments as positive, although clinically safe and maximizing sensitivity, inherently increases the likelihood of false-positive findings and contributes to a slight reduction in the observed specificity. This is a recognized trade-off in studies adopting this analytical methodology.

Recent studies using similar wide-detector systems have reported comparable results. For instance, Wang et al. (11) demonstrated a sensitivity of 93.3% and specificity of 97.5% for ECG-less CCTA in a prospective cohort, underscoring the reproducibility of this approach. Importantly, our radiation dose (1.4 mSv) is 60% lower than conventional prospective ECG-gated protocols in a 256-row wide-detector volume CT and approaches the low-dose benchmarks set by high-pitch dual-source CT (21,22). This reduction is achieved through automated tube voltage selection, automated tube current modulation and deep learning-based image reconstruction, aligning with the ALARA (As Low as Reasonably Achievable) principle. It is important to acknowledge that our achieved dose of 1.4 mSv exists within a broader context of modern low-dose CT imaging. State-of-the-art prospective ECG-gated protocols, particularly those utilizing high-pitch spiral acquisition on dual-source CT systems combined with advanced iterative reconstruction, have also demonstrated the capability to achieve effective doses well below 1 mSv (25). The choice between an ECG-gated and an ECG-less strategy should therefore be guided by a combination of factors, including the clinical question, patient-specific characteristics (especially HR and rhythm), and the available scanner technology. The value of our ECG-less approach lies not solely in its low dose, but in its ability to achieve this low dose while simultaneously overcoming the limitations of ECG-dependent acquisition.

A key strength of this technique is its applicability to patients with irregular heart rhythms, a population often excluded from conventional CCTA due to ECG-gating constraints. In the study by Uehara et al. (26), conventional ECG-gating protocols maintained diagnostic accuracy in atrial fibrillation patients with a sensitivity of more than 90%. The results of our study were similar, even in the high HR subgroup (>75 bpm), the sensitivity remained strong (89.7%), supporting its use in diverse clinical scenarios. Furthermore, the streamlined protocol avoids β-blocker administration, reducing patient preparation time and contraindication-related exclusions. This is particularly relevant for elderly or comorbid patients, who may not tolerate HR-lowering medications.

Despite these advancements, moderate to severe coronary calcification (Agatston score >400) reduced specificity to 84.6%, consistent with challenges reported in prior studies (20). Calcified plaques introduce blooming artifacts that obscure lumen assessment, a limitation not fully resolved by current spatial resolution or reconstruction algorithms. This finding suggests that in patients with known high calcium burden, the interpretation of ECG-less CCTA (and indeed, all CCTA) should be undertaken with caution, acknowledging the potential for reduced specificity. In such cases, alternative approaches such as CT-derived fractional flow reserve (CT-FFR) could be considered to improve diagnostic specificity, or direct referral to ICA may be appropriate. Future integration of plaque characterization tools, such as dual-energy CT or photon-counting detectors, may improve differentiation between calcification and true stenosis. Additionally, combining CCTA with CT-FFR could enhance functional assessment, particularly in ambiguous lesions (27).

This study has several limitations. First, its retrospective, single-center design may introduce selection bias, and the exclusion of severely calcified cases (Agatston >2,000) limits generalizability to complex CAD populations. Second, the simulated ECG signal relies on pulse-derived HR estimation. In patients with highly irregular non-sinus rhythms (e.g., atrial fibrillation with rapid ventricular response), which were excluded from this cohort, the accuracy of phase prediction might be compromised, potentially leading to phase misregistration and motion artifacts. Furthermore, it is important to acknowledge that although our technique eliminates the need for physical ECG leads and significantly reduces dependency on ECG-gating, it still utilizes a surrogate cardiac signal for motion correction and phase selection. Finally, the sample size (n=110) necessitates validation in larger, prospective, multicenter cohorts. Future studies should also explore the integration of this anatomical assessment with functional evaluation using CT-FFR to improve diagnostic specificity, particularly in cases with ambiguous lesions or heavy calcification.

Conclusions

ECG-less coronary CT angiography achieves high diagnostic accuracy (sensitivity 92.1%, specificity 91.5%) for detecting obstructive CAD, with a significantly reduced radiation dose. Its streamlined workflow eliminates β-blocker administration and ECG lead placement, making it particularly valuable in emergency settings or for patients without severe arrhythmias for rapid triage of acute chest pain.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STARD reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1338/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1338/dss

Funding: This study was supported by the Medical Engineering Research Program of the National Institute of Hospital Administration, NHC (No. 2024MEB315), Medical and Health Research Project of Zhejiang Province (2023KY802) and Medical Scientific Research Foundation of Zhejiang Province (grant No. 2021KY291).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1338/coif). All authors report that this study was supported by the Medical Engineering Research Program of the National Institute of Hospital Administration, NHC (No. 2024MEB315), Medical and Health Research Project of Zhejiang Province (2023KY802) and Medical Scientific Research Foundation of Zhejiang Province (grant No. 2021KY291). A.S. was employed by GE Healthcare China. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This retrospective study was approved by the Institutional Review Board of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine (No. 2025-2258-01), and the requirement for informed consent was waived due to the retrospective nature.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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