Coronary computed tomography angiography in suspected acute coronary syndrome patients with intermediate high-sensitivity cardiac troponin I levels: a valuable diagnostic tool

Introduction

Coronary computed tomography angiography (CCTA) has long been acknowledged as an invaluable tool for assessing patients with suspected acute coronary syndrome (ACS) in the era of conventional troponin. However, with the advent of high-sensitivity cardiac troponin assays (1), the role of CCTA in contemporary clinical practice demands further investigation. The updated 2023 European Society of Cardiology (ESC) guidelines (2) do not advocate CCTA as a level I option for suspected ACS patients. The primary reason is that CCTA does not significantly impact 1-year clinical outcomes (3). Notably, the suspected ACS population is highly heterogeneous. Even after excluding myocardial infarction (MI), further risk stratification can be achieved using high-sensitivity cardiac troponin I (hs-cTnI) (4-6).

hs-cTnI levels below the functional detection threshold of 5 ng/L can effectively identify a subgroup of suspected ACS patients at low risk. These patients can be safely discharged from the emergency department (ED), with a negative predictive value exceeding 99.6% for MI or cardiac death within 30 days (5,7). Intermediate hs-cTnI concentrations, ranging from 5 ng/L to the 99^th percentile, are associated with an increasing prevalence and severity of coronary atherosclerosis, as well as a potential elevated risk of adverse cardiac events (5,7,8). For this specific group of suspected ACS patients with intermediate hs-cTnI concentrations and MI ruled out, the best clinical decision remains a pressing concern for ED clinicians. Resolving this concern is essential for optimizing cost-effective patient treatment and efficiently allocating medical resources.

This study pioneers the exploration of the utility of CCTA for suspected ACS patients with intermediate hs-cTnI levels (5 ng/L to sex-specific 99^th percentile) who have had MI ruled out upon presenting at the ED. By shedding light on the practical challenges and gaps in care, this research endeavors to provide more substantial evidence regarding the management approach for suspected ACS patients in the ED. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-1649/rc).

Methods

Participants

This research retrospectively investigated two prospective, multicenter cohort studies (ChiCTR1800018661 and NCT03734796). From November 2017 to January 2019, five hospitals across China participated. All hospitals were equipped with cardiology services, cardiac catheterization labs, echocardiographic capability, and cardiology training programs.

Patients diagnosed with suspected ACS were included. Treating physicians made the adjudication based on admission symptoms, electrocardiogram (ECG) findings, and hs-cTnI levels (9,10). Among the 3,657 patients, 392 had been previously reported (11). The prior article indicated that the lipid core burden on CCTA independently predicted patients and plaques at a higher risk for future non-revascularized plaque-related major adverse cardiac events (MACEs). Our focus was on patients presenting to the ED with suspected ACS, who had intermediate hs-cTnI levels and had MI ruled out (Figure 1). For suspected ACS patients with intermediate hs-cTnI concentrations ranging from 5 ng/L to the 99^th percentile, we recommended either CCTA or invasive coronary angiography (ICA). The final decision regarding whether to perform CCTA or ICA was based on the patient’s symptoms, known history of coronary artery disease (CAD), patients’ wishes, and the advice of clinical doctors. We measured the plasma hs-cTnI concentration (ARCHITECT STAT troponin I assay; Abbott Laboratories, Longford, Ireland) at presentation and 3 hours after presentation. Additionally, we recommended that all included patients return to the hospital for a follow-up CCTA 1 year later. Local clinical doctors adjudicated acute MI according to the Third Universal Definition of Myocardial Infarction (9). The detailed inclusion and exclusion criteria are provided in Appendix 1. All participating centers followed the STROBE guidelines (12). This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The institutional ethics committee of Fuwai Hospital approved this retrospective research (Nos. 2016-809 and 2017-926 for the ChiCTR1800018661 and NCT03734796 cohort studies, respectively). Individual informed consent was waived due to the retrospective nature of the study.

Figure 1 Flow diagram. ACS, acute coronary syndrome; CABG, coronary artery bypass grafting; CCTA, coronary computed tomography angiography; ED, emergency department; hs-cTnI, high-sensitivity cardiac troponin I; PCI, percutaneous coronary intervention.

Risk stratification

For patient risk stratification, our study utilized the modified HEART score (chest pain history, ECG, age, risk factors) (13) to determine the proportion of suspected ACS patients at low risk and non-low risk in the ED who had MI ruled out.

CCTA

The CCTA protocol is described in detail in Appendix 1, and the entire CCTA procedure complied with the Society of Cardiovascular Computed Tomography (SCCT) guidelines (14). We retrieved the CCTA findings from the picture archiving and communication system (PACS). Visual diameter stenosis rates were classified as follows: normal or coronary stenosis <50% (0–49%); moderate obstructive lesions (50–69%); obstructive lesions (≥70% in one or more major epicardial arteries or ≥50% in the left main stem).

Study outcomes

The primary outcomes were the rates of ICA and revascularization within 30 days, and other findings on CCTA. Secondary outcomes included a composite of time to MACEs, including all-cause death, acute MI, and unplanned revascularization from discharge to 1 year. Unplanned revascularization was defined as either percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) that was unforeseen. Patient follow-up data were obtained from electronic medical records and telephone interviews.

Statistical analysis

Continuous variables were analyzed using the Student’s t-test, and categorical variables were assessed using the Chi-squared test, as appropriate. Continuous variables were presented as mean ± standard deviation (SD) or median [interquartile range (IQR)], and categorical variables were presented as frequencies and percentages.

Patients were divided into two groups: the CCTA group (patients who underwent CCTA) and the no-CCTA group (patients who did not). To address the non-random allocation of participants and minimize potential confounding between the two groups, we applied propensity score matching (PSM) at a ratio of 1:3 within a caliper of 0.05. The matching was based on clinical characteristics such as sex, age, hs-cTnI, body mass index (BMI), smoking status, hypertension, hyperlipidemia, diabetes, cerebrovascular disease, peripheral vascular disease, and family history of CAD. These baseline characteristics for matching were selected based on previous relevant study (15) and clinical relevance. After matching, the balance of the matched variables between the two groups was evaluated using the standardized mean difference (SMD). The rates of ICA and revascularization in the CCTA group were compared with those in the no-CCTA group using logistic regression modeling. The rates of MACEs were compared using the Kaplan-Meier survival curves and the log-rank test. Cox proportional hazards model analysis was performed to evaluate the impact of CCTA on MACEs in the matched patients. We also conducted subgroup analysis restricted to patients with known CAD (defined as those with a previous diagnosis of angina and MI) and those without known CAD.

All statistical analyses were conducted using SPSS (version 27; IBM) and R (version 4.3.1; The R Foundation). A two-tailed P<0.05 was considered to indicate a statistically significant difference.

Results

Baseline characteristics

Following PSM, 540 suspected ACS patients, who had MI ruled out and presented with intermediate sex-specific hs-cTnI concentrations, were identified in the ED. Among them, 136 patients were assigned to the CCTA group, and 404 to the no-CCTA group. Table 1 showcases the baseline characteristics of the study participants. Except for a higher prevalence of polypnea in the no-CCTA group [38.6% (156 out of 404 patients) compared to 24.3% (33 of 136 patients); P=0.003], there were no significant differences between the two groups. According to the modified HEART scores, the number of non-low risk individuals was greater, but no difference was observed between the two groups after PSM (P=0.455). The prevalence of known CAD was 36.8% in the CCTA group and 44.8% in the no-CCTA group (P=0.124). After PSM, 107 (79%) patients in the CCTA group were diagnosed with unstable angina, while 335 (83%) patients in the no-CCTA group received the same diagnosis (P=0.267). The rates of obstructive CAD diagnosis were similar in both groups (71.3% in the CCTA group vs. 73.8% in the no-CCTA group, P=0.58) (Table 2). Figure S1 presents the baseline hs-cTnI levels and the change in hs-cTnI values between baseline and 3 hours for the 540 patients.

CCTA findings

Especially, in the CCTA group, 90% of the patients (123 out of 136) had notable findings. These included obstructive CAD in 97 (71.3%), acute aortic dissection in six (4%), pulmonary embolism in four (3%), cardiomyopathy in two (2%), deep cardiac muscle bridge in eight (6%), and valvular heart disease in six (4%), as visualized in Figure 2.

Figure 2 Observations within the CCTA group. CAD, coronary artery disease; CCTA, coronary computed tomography angiography.

Follow-up and clinical outcomes

All patients were successfully followed up either through phone interviews or a review of electronic hospital records. Complete follow-up data regarding clinical outcomes were available for every participant. The detailed frequencies and types of events are elaborated in Table 3 and graphically represented in Figure 3. The temporal occurrences of events are illustrated in Figures 4,5. In the matched cohort, a significantly lower proportion of patients in the CCTA group underwent ICA compared to the no-CCTA group [66.9% vs. 91.1%, odds ratio (OR) =5.06, P<0.001]. Nevertheless, there was no significant difference in the rates of coronary revascularization between the two groups (62.5% in the CCTA group vs. 69.6% in the no-CCTA group, OR =1.37, P=0.13) (Table 3 and Figure 3). The 1-year incidence of MACEs was similar between the CCTA group [12 events (8.8%), including two deaths, one MI, and nine revascularizations] and the no-CCTA group [35 events (8.7%), including eight deaths, one MI, and 26 revascularizations]. The unadjusted hazard ratio was 0.98 (95% confidence interval: 0.51 to 1.89, P=0.96) (Figure 4 and Table 3).

Figure 3 Comparative analysis of primary outcomes between the CCTA group and the no-CCTA group. CCTA, coronary computed tomography angiography; ICA, invasive coronary angiography.

Figure 4 Cumulative MACEs rates in CCTA and no-CCTA groups. CCTA, coronary computed tomography angiography; CI, confidence interval; MACEs, major adverse cardiac events (including all-cause mortality, myocardial infarction, unplanned revascularization).

Figure 5 Cumulative MACEs rates in the CCTA and no-CCTA groups, stratified by CAD status-unknown (left) and known (right). CAD, coronary artery disease; CCTA, coronary computed tomography angiography; CI, confidence interval; MACEs, major adverse cardiac events (including all-cause mortality, myocardial infarction, unplanned revascularization).

Subgroup analysis

There was no significant difference in the 1-year incidence of MACEs between patients with known CAD and those with unknown CAD (Figure 5). In patients with unknown CAD, there was no difference in the proportion of obstructive lesions (60% vs. 67%, OR =1.486, P=0.157) and 30-day revascularization (56% vs. 65%, OR =1.647, P=0.071) between the CCTA group and the no-CCTA group. However, the 30-day ICA rate was significantly lower in the CCTA group (64% in the CCTA group compared to 90% in the no-CCTA group, OR =6.116, P<0.001) (Table S1).

Medications prescriptions

Upon admission, the CCTA group (39.7%) had a higher frequency of calcium blocker treatment compared to the no-CCTA group (22.5%) (P<0.001) (Table 1). Post-diagnostic evaluation demonstrated an increase in the prescription of preventive medications, such as aspirin, statin, P2Y₁₂ inhibitor, angiotensin-converting enzyme inhibitors or angiotensin-II receptor blockers, beta-blocker, oral anticoagulant, and nitrates agents in both groups (all P<0.05). The changes in medication prescription were consistent between the CCTA group and the no-CCTA group, as detailed in Table 4.

Case presentation

A representative case with normal intermediate hs-cTnI concentration (ranging from 5 ng/L to the 99^th percentile), ST-T depression on ECG, and moderate obstructive CAD is presented in Figure 6.

Figure 6 Case presentation. A 59-year-old male patient presented with non-typical angina and a normal intermediate high-sensitivity cardiac troponin I concentration of 21 ng/L (the 99^th percentile value being 34 ng/L). CCTA images shown the presence of calcified plaques (indicated by a white arrowhead) in the anterior descending artery (A); and the right coronary artery exhibited both calcified and mixed plaques (arrowhead), with a degree of stenosis approaching 50% (C). ICA performed within one week confirmed no significant stenosis in the anterior descending artery (B) and nearly 50% stenosis (arrowhead) in the right coronary artery (D), which was consistent with the findings from CCTA. CCTA, coronary computed tomography angiography; ICA, invasive coronary angiography.

Discussion

In this multicenter, register-based retrospective investigation, our primary objective was to evaluate the clinical utility of CCTA in managing and predicting outcomes for suspected ACS patients, who had MI ruled out and presented with intermediate hs-cTnI concentrations (ranging from 5 ng/L to the 99^th percentile reference range) in the ED. Our findings indicated that the primary benefits of CCTA were in clarifying diagnoses and reducing the necessity for ICA within 30 days, rather than decreasing the rate of MACEs at 1 year.

Deciding whether to use non-invasive CCTA for suspected ACS patients who have had MI ruled-out and possess normal troponin concentrations remains a challenge for ED clinicians. In our study, the CCTA group demonstrated a lower rate of ICA at 30 days compared to the no-CCTA group. This suggests that CCTA may reduce unnecessary ICA without affecting the rate of coronary revascularization. In line, the Rapid Assessment of Potential Ischemic Heart Disease with Computed Tomography Coronary Angiography (RAPID-CTCA) study (3), which focused on intermediate-risk patients, found that CCTA was associated with significantly lower rates of ICA and subsequent non-invasive testing for CAD and myocardial ischemia compared to standard care. Our study, like RAPID-CTCA, included more non-low risk patients. Both the RAPID-CTCA and our study emphasized the importance of selecting appropriate candidates for CCTA examination. In our CCTA group, 5.1% (7/136) of patients were not diagnosed with obstructive lesions by CCTA, including six moderate obstructive lesions and one with coronary stenosis <50%. However, ICA was still clinically applied further, indicating that some clinicians had more confidence in ICA than CCTA. This highlights the need to enhance the understanding in clinical practice that the strength of CCTA lies in its high negative predictive value for CAD. Had we discouraged ICA when the CCTA scan showed no obstruction, the rate of ICA would have been further reduced.

In contrast, the Better Evaluation of Acute Chest Pain with Computed Tomography Angiography (BEACON) trial found no difference in the rates of ICA and coronary revascularization at 30 days between CCTA and standard optimal care (16). The BEACON trial enrolled a highly selective and relatively low-risk cohort, which highlights the potential limitation of CCTA in low-risk patients. It also reminds us that low-risk patients, possibly similar to those with low-concentration (<5 ng/L) troponin, weakens the value of CCTA. A hs-cTnI concentration of less than 5 ng/L can ensure safe discharge from the ED with a negative predictive value of over 99.6% for MI or cardiac death at 30 days (5). Within the normal 99^th percentile reference range, an intermediate hs-cTnI concentration is three times more likely to indicates CAD on CCTA compared to concentrations below 5 ng/L (17). Furthermore, the Prospective RandOmised Trial of Emergency Cardiac Computerised Tomography (PROTECCT) enrolled patients with high-sensitivity cardiac troponin T (hs-cTnT) ranging from 5 to 50 ng/L. They concluded that CCTA did not reduce the ICA rate, mainly because only 8% of their study population had obstructive CAD. Patients with little or no disease diluted the beneficial impact of CCTA. Additionally, the definition of intermediate concentration hs-cTnT (5–50 ng/L) in this study differed from ours. This is a crucial point that cannot be overlooked. The 5 ng/L of hs-cTnI in our study is a functional limit value identified by professor Mill’s team in a large cohort study (5). This highlights the importance of using hs-cTnI concentrations with consistent detection methods (18) as a reliable marker for risk stratification in the ED. Moreover, troponin I is more sensitive than troponin T and more closely associated with cardiogenic diseases (19).

To the best of our knowledge, our study is the first to highlight the potential additional diagnostic value of CCTA in identifying the causes of intermediate elevated levels of hs-cTnI not attributable to MI or obstructive CAD in suspected ACS population. These findings are clinically significant as they aid in identifying non-coronary causes of suspected ACS symptoms. Our results offer a novel perspective on the application of CCTA in evaluating suspected ACS patients with intermediate hs-cTnI levels. On one hand, CCTA facilitated a more accurate differential diagnosis. On the other hand, suspected ACS patients with intermediate hs-cTnI concentrations in the ED have a potentially high risk of obstructive CAD (17). For these patients who did not undergo CCTA, the differential diagnosis and final diagnosis may have been less precise, potentially leading to a greater need for subsequent ICA, and corresponding medical therapies may have been erroneously missed.

Despite its diagnostic advantages, the application of early CCTA did not impact the cumulative rates of MACEs at 1 year, a finding in line with the 2023 ESC guidelines (2). Overall, CCTA is diagnostically consistent with and prognostically equivalent to ICA in patients with non-ST-segment elevation ACS (20,21). However, the rationality of using the 1-year endpoint as a determinant for the implementation of CCTA remains to be verified. The Cardiac-CT in the Treatment of Acute Chest Pain (CATCH) study supported the notion that early CCTA could improve clinical outcomes over a longer-term follow-up of 18 months in patients with acute chest pain and normal cardiac troponin concentration (22). Additionally, CCTA reflects the overall plaque burden of coronary artery tree, yet there is no data on its impact on the long-term prognosis of suspected ACS with intermediate hs-cTnI concentrations.

Our study was pragmatic and mirrored the real-world scenario where our population included both those with and without a final diagnosis of CAD. In two distinct subgroups (known CAD and unknown CAD), there were no statistically significant differences in the 1-year MACEs rates between the CCTA group and the no-CCTA group. Notably, in the unknown CAD group, the 1-year MACEs rate curve for the CCTA group was higher than that for the no-CCTA group. Through data review, we found that this phenomenon occurred because, in the CCTA group, four patients who experienced MACEs had obstructive lesions in their CCTA results but declined intervention treatment upon admission. After discharge, all these patients were hospitalized due to sudden angina and subsequently underwent PCI treatment. This underscores the pivotal role of CCTA as a gatekeeper for the catheter room.

In the high-sensitivity troponin era, there is a pressing need to optimize clinical decision pathways to enable more rapid decisions in the ED. The goal is to increase the rate of rapid ED discharges without the need for additional diagnostic tests while safeguarding patient safety (6). For suspected ACS patients in the ED with intermediate hs-cTnI concentrations, we recommend performing CCTA testing. In the future, rather than relying solely on dichotomous hs-cTnI for risk assessment, a more comprehensive approach would integrate absolute changes in serial high-sensitivity cardiac troponin concentrations, relevant clinical indicators, and significant CCTA features into a novel cardiovascular risk scoring system. Such a system would augment existing guidelines, providing ED physicians with a robust foundation for clinical practice and allowing more patients to benefit from enhanced secondary prevention measures.

Study limitations

Our cohort had a high proportion of obstructive CAD. We believe that there are several main reasons for this: first, suspected ACS patients with intermediate hs-cTnI concentrations are at a potentially high risk of CAD (17); second, our cohort included a certain proportion of patients with known CAD; third, our patients mainly came from a leading cardiovascular medical center in China, where patients’ coronary manifestations were relatively severe. In the real world, the number of suspected ACS with intermediate hs-cTnI is small. Compared with other studies, the sample size in our study, though not large, is sufficient. This indirectly attests to the value of our data and results. Despite our rigorous efforts to retrospectively recruit all potentially eligible candidates, some selection biases may still exist. To counteract this, we used PSM statistical methods to ensure balanced baseline characteristics between the two groups. A randomized controlled trial is needed to validate our results. Additionally, our study did not incorporate information from CT-fractional flow reserve (CT-FFR), plaque burden, or peri-coronary fat density to aid in clinical decision-making.

Conclusions

Our study emphasizes the crucial role of CCTA in managing suspected ACS patients with intermediate hs-cTnI concentrations who have been ruled out for MI. CCTA not only reduces the need for invasive angiography but also clarifies the underlying causes of slight hs-cTnI elevation in patients without obstructive CAD. Although our findings indicate that CCTA does not significantly alter 1-year clinical outcomes, its deployment in this specific patient group is proved to be both safe and reliable.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-1649/rc

Funding: This study was supported by the National Natural Science Foundation of China (No. 82102036), CAMS Innovation Fund for Medical Sciences (CIFMS) (No. 2023-I2M-C&T-B-065), the Ministry of Science and Technology of China, the National Key Research and Development Project (No. 2016YFC1300403), the Chinese Academy of Medical Sciences and Peking Union Medical College (No. 2021-I2M1-008), and the National Key R&D Program of China (No. 2023YFC2413001).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-1649/coif). The authors have no 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. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The institutional ethics committee of Fuwai Hospital approved this retrospective research (Nos. 2016-809 and 2017-926 for the ChiCTR1800018661 and NCT03734796 cohort studies, respectively). Individual informed consent was waived due to the retrospective nature of the study.

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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