Patients with mildly abnormal or equivocal results on myocardial perfusion imaging (MPI) typically undergo diagnostic angiography or receive medical management for coronary artery disease. Catheterization is often required for either appropriate diagnosis or management. With its very high negative predictive rate, coronary computed tomographic angiography (CCTA) has great potential to rule out clinically significant coronary artery disease in this setting. The aim of this study was to analyze the clinical utility and cost implications of CCTA before invasive angiography in patients with abnormal or equivocal results on MPI. Consecutive patients referred by their physicians to our center with abnormal or equivocal results on MPI were reviewed. Patients with histories of myocardial infarction or of revascularization (coronary artery bypass grafting or percutaneous coronary intervention) were excluded. All patients underwent CCTA. Of 241 participants, only 66 (27%) of the studies with abnormal or equivocal nuclear findings revealed obstructive disease on CCTA (>50% stenosis). Fifty-five of 241 patients had normal coronary arteries, 97 patients had nonsignificant disease (<30%), and 23 patients had mild disease (30% to 50% stenosis) on CCTA, leading to diagnoses of noncardiac chest pain. Selective catheterization (for >50% stenosis on CCTA) demonstrated an average cost reduction of $1,295 per patient. Sensitivity analysis revealed cost savings to be preserved even if up to 70% of the patient cohort underwent catheterization after CCTA and across a wide range of procedural costs. In conclusion, CCTA after equivocal or mild or moderate abnormal MPI findings results in significant cost savings and a robust reduction in the need for cardiac catheterization and excludes obstructive coronary artery disease in almost 75% of patients.
Coronary computed tomographic angiography (CCTA) has recently emerged as a method to safely and effectively evaluate for the presence of coronary artery disease (CAD). Notably, the Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography (ACCURACY) trial demonstrated high sensitivity and specificity for CAD in a low- to intermediate-risk patient population. When no stenosis >50% was detected on CCTA, the negative predictive value was extremely high (99%), essentially ruling out the presence of obstructive CAD by invasive coronary angiography (ICA). The implications from this study are clear: a patient with no or mild disease on CCTA can be treated with high confidence as not having obstructive CAD. In a recent study, Cole et al used CCTA in an algorithm to exclude CAD before diagnostic angiography in patients with mildly abnormal findings on nuclear scans, saving approximately $1,454 per patient. Further validation studies are needed to investigate the cost-effectiveness of CCTA in this setting. The aim of our study was to evaluate the cost implications of CCTA before diagnostic angiography in patients with atypical symptoms and low to intermediate risk for CAD with abnormal or equivocal findings on myocardial perfusion imaging (MPI).
Methods
Consecutive cases involving patients with abnormal or equivocal MPI scans who were referred for CCTA from December 2006 to September 2009 were reviewed. Inclusion criteria were age >40 years and the presence of atypical symptoms with ≥2 cardiac risk factors (hypertension, dyslipidemia, tobacco abuse, obesity, diabetes, and physical inactivity). These patients had to be referred specifically stated to be in lieu of diagnostic angiography. Patients with histories of myocardial infarction or of revascularization were excluded, as were patients with inadequate studies. All data were collected and maintained by a single investigator in a Health Insurance Portability and Accountability Act–compliant database. The examinations were performed according to the following protocol.
All coronary computed tomographic angiographic scans were performed using a 64–detector row LightSpeed VCT scanner (GE Healthcare, Milwaukee, Wisconsin). Patients with baseline heart rates >65 beats/min were administered oral β-blocker therapy as the preferred method for slowing the heart rate. Intravenous administration was allowed, using metoprolol in 5-mg increments to a total possible dose of 25 mg to achieve a rest heart rate <65 beats/min.
After a scout x-ray of the chest (anteroposterior and lateral), a timing bolus (using 10 to 20 ml of contrast) was performed to detect time to optimal contrast opacification in the axial image at a level immediately superior to the ostium of the left main artery. Nitroglycerin 0.4 mg sublingually was administered immediately before contrast injection. During CCTA, 60 ml of iodinated contrast (Visipaque; GE Healthcare) was injected using a triple-phase-contrast protocol: 40 ml iodixanol, followed by 40 ml of a 50:50 mixture of iodixanol and saline, followed by a 50-ml saline flush. Prospective electrocardiographically gated helical contrast-enhanced CCTA was performed, with scan initiation 10 mm above the level of the left main artery to 10 mm below the inferior myocardial apex. The scan parameters were 64 × 0.625 mm collimation, tube voltage of 100 to 120 mV, and effective tube current of 350 to 780 mA.
Using actual reimbursements for CCTA and cardiac catheterization, we modeled the costs of 2 clinical algorithms: (1) the standard approach using cardiac catheterization in all patients immediately after abnormal findings on MPI, in contrast to (2) our proposed approach of using cardiac catheterization only in select patients with abnormal findings on MPI and evidence of significant obstructive disease (>50% stenosis) on CCTA. Only direct costs were considered from the perspective of the individual buyer. Medicare reimbursement rates for 2006 were used for this cost analysis. Costs included all reimbursed physician services as well as associated hospital costs (outpatient observation admission and technical fees). For strategy 1, the total cost was calculated by multiplying 241, the total number of patients in the cohort, by the average rate for diagnostic angiography. For strategy 2, total costs included the sum of CCTA costs for all 241 patients plus the catheterization costs for all patients with obstructive disease on CCTA. We also estimated radiation doses for participants who underwent the 2 algorithms using the same calculations as the aforementioned cost calculations by substituting average radiation dose for average cost.
Normally distributed continuous variables were compared using Student’s t tests and are expressed as mean ± SD; continuous variables not normally distributed were compared using Mann-Whitney U tests and are expressed as medians and interquartile ranges. Categorical variables were compared using chi-square tests and are expressed as numbers and/or percentages.
Sensitivity analysis is a method to determine whether the conclusions of a given cost analysis remain valid as certain variables change. For this study, sensitivity analysis for the following variables was performed by analyzing each variable while keeping other variables at the measured values: percentage of patients who underwent catheterization, catheterization costs, and costs of CCTA. A final sensitivity analysis was performed to address the issue of changing costs if a higher percentage of patients were sent to CCTA than would have been sent to angiography. The precision of the diagnostic parameters is presented with 95% confidence intervals. A p value ≤0.05 was considered to indicate statistical significance. Statistical analyses were performed using PASW version 18.0.0 for Windows (SPSS, Inc., Chicago, Illinois).
Results
A total of 241 patients underwent CCTA for equivocal or abnormal findings on nuclear scans. Fifty-two percent of the cohort (126 of 241) were men, and the average age was 66 ± 11 years. Of the 241 studies performed ( Table 1 ), 55 revealed normal coronary arteries, 97 showed minimal disease (<30%), 23 showed mild disease (30% to 50% stenosis), and 66 showed obstructive disease (>50% stenosis). Overall, 63% of patients with abnormal or equivocal findings on nuclear tests were demonstrated to have no significant disease. Of the 66 patients with obstructive disease, 2 patients had significant left main artery disease, 37 had significant obstructive left anterior descending coronary artery disease, and 25 had multivessel disease. Only 3 studies (1%) (2 with significant motion artifacts and 1 with heavy calcification) were read as uninterpretable; 3 studies had mild motion artifacts noted, and 2 studies were deemed suboptimal because of body habitus.
| Result on CCTA | N (%) |
|---|---|
| Normal coronary arteries | 55 (23) |
| Nonsignificant disease (<30% stenosis) | 97 (40) |
| Mild disease (30%–50% stenosis) | 23 (10) |
| Obstructive disease (≥50% stenosis) | 66 (27) |
| Left anterior descending coronary artery disease (≥50% stenosis) | 37 (15) |
| Left main coronary artery disease | 2 (1) |
| Multivessel disease | 25 (10) |
For the baseline case, using average global (technical plus professional) Medicare reimbursement in 2006, the cost of CAD diagnosis confirmed by ICA was $2,532 per patient for the traditional pathway with MPI as the only gatekeeper to ICA and $1,237 per patient for the pathway with multidetector computed tomography as the gatekeeper to ICA after nuclear testing. This represented a 51% saving per patient using multidetector computed tomography as the gatekeeper to ICA and a total savings of $311,996 for the cohort of 241 patients with positive results on nuclear stress tests (a net savings of $1,295 per patient). The multidetector computed tomographic pathway provided cost savings compared to the nuclear pathway in each of the 1-way sensitivity analyses, with savings ranging from $781 to $2,111 per patient. Sensitivity analysis revealed cost savings to be preserved even if up to 70% of the patient cohort underwent catheterization after CCTA and across a wide range of procedural costs and reimbursements.
Using an average radiation dose of 3 mSv for CCTA and avoiding left-sided cardiac catheterization radiation doses (average dose 8 mSv ) in 73% of patients, we calculated that CCTA and selective cardiac catheterization results in reducing radiation exposure by 3.1 mSv per patient overall.
Results
A total of 241 patients underwent CCTA for equivocal or abnormal findings on nuclear scans. Fifty-two percent of the cohort (126 of 241) were men, and the average age was 66 ± 11 years. Of the 241 studies performed ( Table 1 ), 55 revealed normal coronary arteries, 97 showed minimal disease (<30%), 23 showed mild disease (30% to 50% stenosis), and 66 showed obstructive disease (>50% stenosis). Overall, 63% of patients with abnormal or equivocal findings on nuclear tests were demonstrated to have no significant disease. Of the 66 patients with obstructive disease, 2 patients had significant left main artery disease, 37 had significant obstructive left anterior descending coronary artery disease, and 25 had multivessel disease. Only 3 studies (1%) (2 with significant motion artifacts and 1 with heavy calcification) were read as uninterpretable; 3 studies had mild motion artifacts noted, and 2 studies were deemed suboptimal because of body habitus.
