The American Journal of Medicine
Volume 122, Issue 4 , Pages 387-391, April 2009

Impact of 64-Slice Multidetector Computed Tomography on Other Diagnostic Studies for Coronary Artery Disease

Division of Cardiovascular Medicine, Department of Internal Medicine, The Ohio State University College of Medicine, Columbus

Article Outline

Abstract 

Background

The clinical role of cardiovascular multidetector computed tomography (CT) remains in evolution, and application varies widely. Understanding its impact on the utilization of other cardiovascular diagnostic modalities could help define best practices.

Methods

Utilization of diagnostic testing was examined for the initial 1053 consecutive patients who underwent cardiovascular multidetector CT examinations after scanner installation in 2005. Yearly procedural volumes in the invasive catheterization and noninvasive stress laboratories were assessed before and after the introduction of multidetector CT.

Results

Ninety-one patients (8.6%) of the 1053 required invasive diagnostic catheterization; of these, nearly half subsequently underwent percutaneous or surgical intervention. Diagnostic catheterization and interventional volumes maintained their previous rates of annual increase, while the volume of stress testing decreased once multidetector CT became available.

Conclusions

The major impact of multidetector CT in initial cardiovascular practice is on the need and frequency of stress testing, with far less impact on utilization of cardiac catheterization and coronary interventions.

Keywords: Cardiac catheterization, Clinical cardiology, Computed tomography, Coronary artery disease, Percutaneous coronary intervention, Stress testing

 

The technical evolution of multidetector computed tomography (CT) has resulted in the ability to visualize the coronary arteries in motion. Sixty-four-slice multidetector CT, introduced in 2004, produces images with sub-millimeter isotropic spatial resolution obtained in synchronization with the cardiac cycle. This modality has shown favorable results in the assessment of coronary artery disease compared with invasive coronary angiography and intravascular ultrasound, and a negative study reliably excludes significant luminal obstruction.1, 2, 3, 4 Multidetector CT also has been validated as a useful tool to assess coronary artery bypass grafts and determine patency of coronary stents.5, 6, 7, 8, 9 In addition to evaluation of coronary artery disease, multidetector CT provides accurate quantification of right and left ventricular size and systolic function,10, 11 and comprehensive visualization of the complex 3-dimensional malformations of congenital heart disease during a single breath-hold.12, 13

Clinical Significance

 


•The introduction of cardiac computed tomography (CT) did not alter the volume of cardiac catheterization or coronary interventions in its first year.

•The overall volume of stress testing decreased after the introduction of cardiac CT.

•Because cardiac CT requires exposure to iodinated contrast and radiation, patients should be selected by balancing risk versus probability of obstructive coronary disease.

•The strength of cardiac CT is its high negative predictive value.

While multidetector CT has proven revolutionary in the comprehensive assessment of cardiovascular structure and function, important questions remain about utilization. Recently published appropriateness criteria provide some guidance, although clinical use remains heterogeneous.14 The purpose of this study was to analyze its impact on other cardiovascular diagnostic procedures used to diagnose and treat coronary artery disease at a major university medical center.

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Methods 

Study subjects consisted of consecutive patients with clinical suspicion of obstructive coronary artery disease who were referred by cardiovascular medicine faculty for multidetector CT angiography. Patients were scanned using a 64-slice Siemens Somatom multidetector CT (Siemens Medical Solutions USA Inc., Malvern, PA) located within the Richard M. Ross Heart Hospital's noninvasive cardiovascular imaging center, and studies were interpreted by Level 3 cardiovascular CT faculty15 in the Division of Cardiovascular Medicine. All CT scans were performed and interpreted before invasive coronary angiography, negating the need for blinding of CT interpreters. Data from these clinically billed cardiac multidetector CT procedures were retrospectively analyzed utilizing the electronic database for cardiovascular procedures at The Ohio State University (MedInfo CS®, Computerized Fiscal Planning, Inc., Columbus, OH) for the calendar year 2005. The diagnostic findings were recorded and tabulated (eg, coronary artery disease, previous coronary revascularization procedures such as percutaneous stenting, or coronary bypass surgery). Cardiovascular procedures in addition to multidetector CT also were recorded, including diagnostic invasive coronary angiography, percutaneous coronary intervention, or surgical revascularization. Annual procedural volumes for invasive diagnostic angiography, stress testing (stress echocardiography, nuclear perfusion imaging, and pharmacologic stress cardiovascular magnetic resonance), and percutaneous coronary intervention were tabulated for the 5 years preceding introduction of 64-slice multidetector CT as well as for the year 2005. The study protocol was approved by our institution's Human Subjects Committee.

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Results 

Clinical Utilization of MDCT 

For the 2005 calendar year, there were a total of 1053 cardiovascular multidetector CT procedures performed on the 64-slice scanner for coronary artery angiography (70%) and coronary artery and bypass graft angiography (30%). Patients were primarily male (58%), white (82%), and had a mean age of 52.8 ± 15.1 years. Of these 1053 patients, 91 (8.6%) subsequently underwent invasive coronary angiography with or without intravascular ultrasound and with or without hemodynamic assessment (pressure recordings). Within this cohort, 64 patients (70%) had native coronary artery disease alone and 27 (30%) had both native and bypass graft atherosclerotic disease.

Percutaneous and Surgical Interventions in Patients Undergoing Multidetector CT 

Of the 91 patients who proceeded to undergo invasive diagnostic catheterization, nearly half (48%) required percutaneous or surgical intervention. Surgical procedures in 23 patients included coronary artery bypass graft (52%), bypass graft and valve intervention (3%), bypass graft and aortic root/arch surgery (2%), aortic root/arch surgery alone (3%), valve surgery alone (1%), and heart failure-specific device placement (1%). Twenty-one patients underwent percutaneous coronary interventions, 10 (47.6%) in patients with only native vessel disease and 11 (52.4%) in native vessels in patients with previous bypass grafts. Three of these 21 percutaneous coronary intervention patients had previous interventions.

Impact of Multidetector CT on Invasive Diagnostic Procedures 

From 2000 through 2004, diagnostic invasive coronary angiography volume underwent an average yearly increase of 8.7% (Figure 1). With the introduction of multidetector CT in 2005, there was no significant change in this rate of increase as diagnostic catheterization volume still increased by 7%. When yearly totals of diagnostic invasive coronary angiography (3293, 3356, 3391, and 4093, respectively) were normalized by dividing by overall outpatient total visits within the division of cardiovascular medicine (13,177, 14,607, 13,907, and 15,564, respectively), the indexed volume was stable during the first 4 years of the study period (3533.25/14,313.75 = average 0.24 invasive coronary angiography procedures/outpatient visits) until 2004, when a decrease in total outpatient visits (13,225) led to a relative increase (0.34). The following year, the indexed volume returned to nearly the same value as 2003 (0.23).

  • View full-size image.
  • Figure 1. 

    Invasive coronary angiography, percutaneous coronary interventions, and total stress test volume by year. Bar graphs represent volume of patients undergoing procedure, and data points represent numbers indexed to total yearly outpatient volumes. The introduction of MDCT in winter 2004 is indicated under the 2005 data. Cath = invasive coronary angiography; Stents = percutaneous coronary interventions; MDCT = multidetector computed tomography.

Before multidetector CT, the amount of percutaneous coronary interventions underwent an average yearly increase of 15.2%. The year of its introduction, total volume increased by 15%, consistent with the prior annual rate of increase (Figure 1). When yearly totals of coronary interventions were normalized by dividing by overall outpatient visits, the indexed volume exhibited no significant change from 2003 (0.076) to 2005 (0.074), with a relative increase in 2004 (0.094) due to a decreased outpatient volume (Figure 1).

Impact of Multidetector CT on Noninvasive Diagnostic Procedures 

Over the same time period, stress testing performed at the University Medical Center and outpatient facilities increased at an average annual rate of 5.8% (Figure 1). This annual rate increased substantially in the year coinciding with multidetector CT availability, rising 10.9% from 2005 to 2006. Annual volumes normalized for total outpatient visits resided at an average of 0.374, with an average yearly decrease of 4.3% from 2000 through 2003. After a relative increase in 2004 due to a decreased outpatient volume, the indexed volume for 2005 decreases 30% when compared with the next earliest data point from 2003 (Figure 1).

Overall Volumes of Diagnostic Testing for the Division of Cardiovascular Medicine 

Comprehensive data demonstrating potential volume-determining factors for multidetector CT utilization are shown in Figure 2, with non-normalized totals for invasive coronary angiography, percutaneous coronary intervention and stress testing totals, and size of the total clinical and interventional faculty within the Division of Cardiovascular Medicine during each of the years from 2000 through 2005. These data serve as the background context in which to place and assess multidetector CT utilization during the overall continued growth in clinical patient encounters and faculty numbers.

  • View full-size image.
  • Figure 2. 

    Ohio State University Division of Cardiovascular Medicine diagnostic testing and faculty totals from 2000 through 2005. ICA = invasive coronary angiography; PCI = percutaneous coronary intervention; MDCT = multidetector computed tomography.

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Discussion 

The results of this study indicate that the incorporation of 64-slice multidetector CT at a large university medical center had no significant impact on volumes of diagnostic invasive coronary angiograms or percutaneous coronary interventions during its first year of deployment, but the volume of stress testing decreased. This is contrary to initial expectations that its ease of use and high-quality images would lead to a substantial reduction in the need for diagnostic invasive coronary angiography—perhaps even rendering it obsolete. In fact, we found that the normalized growth rates of diagnostic and interventional catheterization procedures during the first year of use were similar to those of the preceding 5 years.

Of all patients referred for multidetector CT, only a small percentage (8.6%) went on to undergo invasive catheterization. Within this subgroup, nearly half required percutaneous or surgical intervention. The reasons why 51% of the patients who had an invasive catheterization did not eventually require intervention likely are related to the known limitations of multidetector CT in the precise assessment of coronary artery lesions. Calcified coronary arteries and the resultant partial volume, or “blooming,” effect obscures visualization of the vessel lumen, leading to less accurate interpretation. Additionally, irregularities in heart rate and timing of acquisition with respect to intravenous contrast bolus administration and kinetics may further reduce the specificity of abnormal coronary artery appearance on multidetector CT.16

The diagnostic accuracy of multidetector CT compared with invasive coronary angiography revealed high sensitivity and negative predictive value, consistent with prior investigations. It is generally accepted that the strength of multidetector CT is to “rule out” significant coronary artery disease,1, 2, 3, 4 and our findings support this view. It is possible that long-term follow-up would reveal some of the studies deemed to have nonsignificant coronary artery disease to be “false negatives” as future clinical cardiovascular events occur, possibly altering our accuracy calculations. Because the patients in this cohort were not a specifically selected group beyond the clinical suspicion of obstructive coronary disease, variables such as high amounts of coronary calcium, higher-than-optimal heart rate, and obesity likely detract from the specificity and positive predictive value of multidetector CT.

These data also prompt the question of whether the patients who underwent multidetector CT may have done so purely “because the test was available” when other diagnostic evaluation, such as stress testing, may have sufficed. As such, did multidetector CT then serve a cost-effective role, acting as a less-expensive alternative to conventional angiography in patients who would have otherwise undergone catheterization, or did it result in higher overall costs? In a brief analysis of clinical billing for diagnostic cardiovascular procedures in our division, multidetector CT is significantly less expensive than both stress echocardiography and nuclear stress myocardial perfusion imaging. With our data indicating that introduction of multidetector CT led to fewer stress tests (96.7% of them included myocardial imaging), it is a likely possibility that multidetector CT may, in fact, contribute to lowering some costs associated with diagnostic testing.

Study Limitations 

This study was primarily limited by incomplete characterization of the patient cohort who underwent multidetector CT scanning. Ideally, quantified cardiovascular risk utilizing verified criteria (such as the Framingham Risk Score), description of patient symptoms, correlation of diagnostic testing, and long-term clinical follow-up would strengthen our results. Consequently, our data demonstrating a decrease in stress testing without clear effects on catheterization laboratory volumes may be difficult to interpret and extrapolate to other medical centers. If the majority of study subjects were at low to intermediate risk for coronary disease leading to cardiac ischemia, referring cardiologists would likely have ordered a stress test before the availability of multidetector CT. Conversely, if our cohort contained patients with an intermediate to high suspicion of obstructive coronary disease, then our results might have demonstrated a decrease in diagnostic invasive coronary angiography. The same issues apply to the size of the patient subgroup that underwent invasive coronary angiography after multidetector CT was found to be abnormal.

Because these data predate publication of appropriateness criteria for the use of multidetector CT,14 patient selection was determined by the referring physician's perception of the technology's abilities and limitations in the context of their pretest probability for coronary artery disease. If applied in retrospect, the multidetector CT appropriateness criteria would likely classify our patient cohort in 1 of 3 categories: intermediate pretest probability of coronary disease with an interpretable electrocardiogram and ability to exercise; uninterpretable or equivocal stress test; or evaluation of coronary anatomy and bypass grafts. Of these categories, patients with a prior equivocal stress test are considered to have the strongest indication for multidetector CT, while the others received a mid-range score (5-6 of 9), resulting in an “uncertain” indication. The majority of studies (68%) were ordered in patients without known coronary disease, clearly reflecting clinician understanding of multidetector CT's strong negative predictive value.2, 3 While the role of multidetector CT to evaluate patients after coronary artery bypass graft is currently labeled as “uncertain,” its ability to determine gross patency of bypass grafts has been reliably demonstrated5, 6, 9 and may yet become a standard alternative to conventional angiography.

The importance of proper patient selection is even more relevant when weighing risks of radiation and iodinated contrast exposure against the clinical benefits of obtaining diagnostic images. Young women, in particular, stand to receive significant breast exposure in the face of lower pretest probability for coronary disease compared with men.17 Overall, despite mathematical models predicting elevated cancer risk associated with multidetector CT,18 in properly chosen patients it may, in fact, result in lower total radiation exposure when utilized as a single, highly accurate diagnostic test instead of multiple modalities (stress nuclear perfusion with subsequent invasive coronary angiography) that often yield equivocal information. Future scanning techniques, such as prospective gating, are likely to improve upon the current model of electrocardiogram-triggered dose modulation, further lowering the radiation dose received during multidetector CT.

In summary, these data represent how the introduction of multidetector CT angiography affected diagnostic cardiovascular invasive and noninvasive procedural volumes at a university medical center. The intent was to specifically detail the first year of use, understanding that trends in imaging referrals, resultant interventions, procedural volumes, billing/reimbursement issues, and data delineating appropriate use will continue to evolve. Further analyses are warranted to follow the impact of this technology over time.

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References 

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 Funding: None.

 Conflicts of Interest: None.

 Authorship: All authors had access to the data and played a role in writing this manuscript.

PII: S0002-9343(08)01179-0

doi:10.1016/j.amjmed.2008.10.031

The American Journal of Medicine
Volume 122, Issue 4 , Pages 387-391, April 2009

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