Rationale and Objectives
Pilot study to determine whether among subjects receiving coronary computed tomography angiography (CTA), the combination of high-sensitivity troponin I (hsTnI) and coronary artery calcium score (CACS) identifies a low-risk population in whom CTA might be avoided.
Materials and Methods
A cross-sectional study of 314 symptomatic patients receiving CTA as part of their acute coronary syndrome evaluation was conducted. hsTnI was measured with Abbott Laboratories’ hsTnI assay. CACSs were calculated via the Agatston method. Patients were followed for at least 30 days after discharge for the occurrence of major adverse cardiac events (MACEs; all-cause mortality, acute coronary syndrome, and revascularization).
Results
Of 314 subjects studied, 213 (67.8%) had no coronary artery stenosis, and 67 (21.3%), 28 (8.9%), and 6 (1.9%) had maximal coronary artery stenosis of 1%–49%, 50%–69%, and 70% or greater, respectively. All MACEs occurred during index hospitalization and include one myocardial infarction and four revascularizations. Sixty-two percent (189/307) of subjects had zero CACS, and 24% (76/314) of subjects had undetected hsTnI. No subjects with undetectable hsTnI or zero CACS had an MACE. A strategy of avoiding further testing in subjects with undetectable initial hsTnI, performing CACS on subjects with detectable initial hsTnI but nonincreased hsTnI (less than 99th percentile), and obtaining CTA in subjects with Agatston greater than 0 will have a negative predictive value of 100.0% (95% confidence interval, 98.2%–100.0%). This strategy will avoid CTA in 63% (198/314) of subjects.
Conclusions
In this pilot study, the addition of CACS to hsTnI improves the identification of low-risk subjects in whom CTA might be avoided.
Emergency Department (ED) evaluation of patients with suspected acute coronary syndromes (ACSs) is time consuming and costly . Many patients with symptoms suggestive of ACS, including low-risk patients, undergo extensive evaluation. Recently, coronary computed tomography angiography (CTA)-based strategies have been shown to identify suspected ACS patients who can be discharged expeditiously . However, CTA involves exposure to ionizing radiation and is costly if used indiscriminately .
A number of investigators have suggested that patients with suspected ACS who have zero coronary artery calcium score (CACS) might be a group that could be discharged home without the need for further diagnostic testing . However, in a pooled analysis of six studies a small number of patients with zero CACS had an adverse outcome. Of note, half of those with zero CACS and an adverse outcome had increased troponin measured by conventional assays .
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Methods
Study Design and Setting
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Selection of Participants
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Methods and Measurements
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Coronary CT Angiography
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Outcomes
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Statistical Analysis
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Results
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Table 1
Demographic Characteristics of Study Population ( n = 314)
Characteristic Number (%) Median age in years (interquartile range) 51.1 (45.5–58.5) Gender Female 177 (56.4) Male 137 (43.6) Ethnicity Non-Hispanic Black 218 (69.4) Non-Hispanic White 73 (23.2) Hispanic 7 (2.2) Asian 4 (1.3) Native-American 11 (3.5) Native-Hawaiian 1 (0.3) Insurance Medicare 55 (17.5) Medicaid 82 (26.1) Commercial 135 (43.0) HMO 10 (3.2) VA 3 (1.0) None 29 (9.2) Transportation Self-transport 259 (82.5) Ambulance 45 (14.3) Transfer from other facility 10 (3.2) Current cigarette smoker 131 (41.7) Current cocaine use 14 (4.5) Family history of AMI or sudden cardiac death 100 (31.8) History of hypertension 168 (53.5) History of diabetes 60 (19.1) History of high cholesterol 99 (31.5) History of congestive heart failure 10 (3.2) History of stroke 20 (6.4)
AMI, Acute Myocardial Infarction; HMO, Health Maintenance Organization; VA, Veterans Affairs.
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hsTnI and CACS Measurements
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Outcomes
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Using hsTnI Only to Define a Low-risk Population
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Table 2
Diagnostic accuracy Measures for Models Examined
Model Sensitivity (95% CI) Specificity (95% CI) PPV (95% CI) NPV (95% CI) Outcome: significant CAD (≥50% stenosis) CACS only 93.9 (79.8–99.3) 68.5 (62.6–74.0) 26.5 (18.8–35.4) 98.9 (96.2–99.9) HsTnI only 93.9 (79.8–99.3) 27.1 (21.9–32.7) 13.5 (9.3–18.6) 97.4 (90.8–99.7) HsTnI and CACS 100 (89.4–100) 22.0 (17.2–27.4) 13.4 (9.4–18.3) 100 (94.0–100) Outcome: major adverse cardiac event CACS >0 100 (47.8–100) 62.6 (56.9–68.1) 4.2 (1.4–9.6) 100 (98.1–100) HsTnI > LOD 100 (47.8–100) 25.2 (20.4–30.5) 2.2 (0.7–5.0) 100 (95.3–100) HsTnI >0 and CACS >0 100 (47.8–100) 19.4 (15.2–24.3) 2.0 (0.6–4.5) 100 (94.0–100)
CACS only, coronary artery calcium score only model recommends CTA for CACS >0; CAD, coronary artery disease; CI, confidence interval; CTA, coronary computed tomography angiography; HsTnI only, high-sensitivity troponin I only model recommends CTA for hsTnI > LOD; HsTnI and CACS, this model recommends CTA only in those with either hsTnI > LOD or CACS >0; LOD, limit of detection (1.2 ng/L); NPV, negative predictive value; PPV, positive predictive value.
Illustrative algorithm = initial testing with hsTnI, CACS in fourth quintile hsTnI, and CTA in CACS >0 or fifth quintile hsTnI.
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Using CACS Only to Define a Low-risk Population
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Combining hsTnI and CACS Values to Define a Low-risk Population
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Table 3
Diagnostic Strategies for Safely Avoiding CTAs
Diagnostic Evaluation Strategy CTAs Avoided Missed Significant CAD Missed MACE Measure hsTnI and CACS in all subjects and perform CTA in CACS >0 or detectable hsTnI 60 (19%) 0 0 Measure hsTnI in all subjects and perform CTA in subjects with detectable hsTnI 76 (24%) 2, All with negative nuclear stress test 0 Measure hsTnI in all subjects; measure CACS in subjects with detectable hsTnI and perform CTA in subjects with CACS >0 198 (63.1%) 4, All with negative nuclear stress tests 0
CACS, coronary artery calcium score; CTA, coronary computed tomography angiography; hsTnI, high-sensitivity troponin I; LOD, limit of detection (1.2 ng/L); MACE, major adverse cardiac event.
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Discussion
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Limitations
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Conclusions
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Supplementary data
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Supplemental Table 1 and Legend for Supplemental Figure 1
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