Cardiac Evaluation: The CurrentStatus of Outcomes-Based Imaging 19

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Cardiac Evaluation: The Current Status of Outcomes-Based Imaging

Andrew J. Bierhals and Pamela K. Woodard

I. Does coronary artery calcification scoring predict outcome?

II. Special case: high-risk patients

III. Which patients should undergo coronary angiography?

IV. Which patients should undergo noninvasive imaging of the heart?

V. What is the appropriate use of coronary artery computed tomogra- phy and magnetic resonance?

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Issues

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A strong recommendation can be made for initial coronary angiogra- phy among high-risk patients and those who are post–myocardial infarction (MI) that was transmural or with ischemic symptoms (strong evidence).

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A strong recommendation can be made for performing a noninvasive imaging examination [e.g., single photon emission computed tomo- graphy (SPECT) or stress echo] prior to coronary angiography in low-risk patients and those who have had a non–Q-wave MI (strong evidence).

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Aside from coronary angiography, the appropriate usage of cardiac imaging studies remains unclear, and more research is required to evaluate the outcomes, as well as the cost-effectiveness of the afore- mentioned modalities (insufficient evidence).

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Coronary artery calcium scoring has been shown in asymptomatic patients to be predictive of coronary artery disease; however, there have been no data to support the position of added predictive value over and above the clinical Framingham model (insufficient evidence).

Key Points

Definition and Pathophysiology

The etiology of coronary artery disease (CAD) is multifactorial involving

both interaction of lifestyle and genetic predispositions. While some factors

are not modifiable, those risks that may be altered are often neglected until

there evidence of disease. As a result, a multitude of tests and clinical

assessment tools have been developed to risk stratify patients in order to direct short- and long-term treatments. The modifiable risk factors (e.g., hypertension, hyperlipidemia, and diabetes) have been on the rise over the past decade (1,2); therefore, a greater urgency has arisen to identify patients with CAD.

Coronary artery disease begins as fatty streaks in the coronary arteries that may begin as early as 3 years of age. The fatty streaks are composed of large cells with intracellular lipids (foam cells) that are located in the suben- dothelial region. As patients age, the fatty streaks develop into fibrous plaques that narrow the vessel lumen, reducing blood flow. The fibrous plaques over time may calcify, reducing vessel compliance and increasing fragility. This further reduces blood flow and increases the chance of the plaque rupturing, resulting in an acute coronary artery occlusion.

Epidemiology

Coronary artery disease is a nationwide epidemic involving 6.4% of the entire population (3,4) and is the largest cause of mortality, accounting for one in every five deaths (4). This translates into a death rate of 177.8 per 100,000 (based on 2001 estimates) (4). In the United States, over 1.5 million people will have a myocardial infarction, and the majority of the patients will initially present with symptoms in their 50s and 60s.

A large volume of literature has been generated investigating these modalities, but little has focused on the impact the modalities have on the patient outcomes even though there has been a steady increase in the use of costly diagnostic testing and treatment (5). This chapter reviews the literature on the outcomes research of cardiac imaging, and makes recommendations concerning the utilization of the techniques in patient management.

Overall Cost to Society

In the United States, the estimated 2004 cost of heart disease to society is

$238 billion, with over half secondary to CAD ($133 billion) (4,6). The cost of heart disease is substantial in comparison to other disease processes, such as cancers ($189 billion) and AIDS ($29 billion) (4,6). The costs of CAD include direct health care of $66 billion, and $67 billion in indirect costs (e.g., loss of productivity secondary to morbidity and mortality) (4,6).

The expenditures for health care are consistently increasing, because of

new technologies and the current medicolegal environment. An ever-

declining budget results in a need for clinicians to incorporate cost-

effective strategies in patient evaluations. However, cost-effective does not

mean withholding evaluations or always ordering the seemingly least

expensive test, but rather understanding what is most efficient with respect

to a specific clinical situation, based on current research. The purpose of

this approach is to direct a finite amount of resources and limit costs to

society without affecting the quality of health care. This chapter reviews

the cost-effectiveness and outcomes of various imaging modalities of heart

disease, and makes recommendations concerning these techniques in

patient care. Specifically, coronary artery calcification scoring, myocardial

SPECT, angiography, stress echocardiography, and cardiac magnetic reso-

nance (MR) and computed tomography (CT) will be evaluated in their potential roles in the evaluation of heart disease.

Goals

The goals of imaging related to CAD are based on the a priori risk to the patient. In a low-risk population, the goals of imaging are to identify those with early disease. Subsequently, interventions directed toward risk factors and lifestyle may be initiated in order to reverse disease or halt progres- sion before any long-term effects result. However, risk stratification becomes the goal of cardiac imaging among those patients who are con- sidered high risk. The imaging in the aforementioned population is to determine if any coronary artery intervention (i.e., endovascular or bypass graft) is required over and above medical management.

Methodology

The outcomes and cost-effectiveness literature was evaluated by perform- ing a literature review on Medline from 1999 to 2004 using a keyword search including the terms calcium scoring and outcomes and calcium scoring and cost-effectiveness. Of the over 2000 reports identified in the literature review, fewer than 50 addressed any issues concerning patient outcomes and not one evaluated cost-effectiveness.

A similar literature review was performed for coronary angiography using Medline. The keyword search from 1999 to 2004 included coronary angiography and outcomes and coronary angiography and cost-effectiveness.

Over 5000 reports were identified, with approximately 100 addressing patient outcomes and 10 evaluating cost-effectiveness.

Lastly, a literature review was performed on Medline from 1999 to 2004 for noninvasive techniques including SPECT, positron emission tomogra- phy (PET), echocardiogram, and coronary CT and MR using the same method, as described above. The review yielded over 100 articles address- ing patient outcomes and five evaluating cost-effectiveness; however, there were no reports that evaluated either topic for MR or CT angiography.

I. Does Coronary Artery Calcification Scoring Predict Outcome?

Summary of Evidence: Coronary artery calcium scoring has been shown in asymptomatic patients to be predictive of CAD; however, there have been no data to support the position of added predictive value over and above the clinical Framingham model. Therefore, coronary artery calcification scoring cannot be recommended as a screening tool at this time. The lack of cost-effectiveness data necessitates further investigations before a final position can be determined on the utility of calcium scoring (insufficient evidence).

Supporting Evidence: Coronary artery calcium scoring performed by com-

puted tomography (CT) has been utilized in asymptomatic patients to

assess their risk of an acute coronary event (7). However, the literature has

debated the utility of calcium scoring. Some researchers support its use

(8,9), while others are less enthusiastic concerning the utilization in patient care (10).

Computed tomography calcium scoring, despite conflicting reports, has been shown to be associated with a fourfold increased risk in myocardial infarction and coronary death in a meta-analysis by O’Malley et al. (11) in 2000. The study included nine reports that had a diverse asymptomatic population that was evaluated for coronary artery calcification by electron beam CT. The authors also reported a ninefold increased risk of coronary events (i.e., nonfatal MI, sudden death, or revascularization) among those with a coronary artery calcium score above the median. There is moderate evidence to suggest that coronary artery calcification score is predictive of coronary events.

More recent reports have echoed these results regarding the predictive value of CT calcium scoring. A 2003 study by Shaw et al. (8) developed a multivariate model on a sample of greater than 10,000 asymptomatic indi- viduals incorporating calcium score with typical clinical risk factors (i.e., hypertension, hypercholesterolemia, diabetes, age, and sex) to predict all- cause mortality. The results of the study indicated that calcium score pre- dicted all-cause mortality (p < .001) over and above the effects of other risk factors. The study also found that there was a trend with the coronary artery calcium score such that as the calcium burden increased there was a greater risk of all-cause mortality. The relative risk in patients with ele- vated calcium scores ranged from 1.6 to 4.0 above individuals with the lowest calcium burden; as the calcium burden increased, the risk increased (Fig. 19.1). Based on the results, the authors concluded that calcium scoring of the coronary arteries provides additional information in the prediction of all-cause mortality (8); however, morbidity and mortality secondary to

Figure 19.1. Graph shows risk stratification for each category of Framingham risk (from low to high) according to baseline calcium score. Event rate is predicted mor- tality at 5 years (8). Low risk <0.30 (no risk factors), intermediate risk <0.70 (one to two risk factors), and high risk <0.9 (three or more risk factors) probability of cardiac disease. [Source: Shaw et al. (8), with permission from the Radiological Society of North America.]

CAD was not specifically addressed. In addition, the authors did not inves- tigate if the added explanation would have any clinical impact and thus provide information that would have proved clinically important.

Other authors have found similar results in the prediction of mortality from calcium scoring. For example, Arad et al. (12) demonstrated that mod- erate calcium scores were associated with a 10 times increase in cardiac death or MI. In addition, a small study of 676 subjects demonstrated that coronary artery calcification scores incrementally predicted cardiac events (13). These studies, as with the aforementioned larger sample, were able to show that coronary artery calcification on CT predicted health out- comes (e.g., MI and mortality). But of all the studies that have been eval- uated, none has shown any extra value in risk stratification and patient management.

Aside from the earlier described reports, there has been a multitude of similar studies with varying patient population that have reached the same conclusion concerning the ability of coronary artery calcium scoring to predict heart disease and mortality (14–19). Other investigators utilized calcium scoring in conjunction with laboratory tests, such as C-reactive protein to model the mortality of heart disease (20), but no interactive effects were noted, although each independently predicted coronary events and mortality. However, a review of the literature to date has failed to iden- tify any direct data suggesting that calcium scoring has any clinical benefit over the current Framingham risk model (21).

Currently, coronary artery calcium scoring on CT is utilized as a risk stratification tool for CAD. The major proportion of the data to date has shown that calcium scoring can predict CAD as well as mortality related to heart disease among asymptomatic patients. A literature review did not uncover any data that show that calcium scoring adds any additional infor- mation over current clinical predictive models in the asymptomatic patient.

In addition, there have been no studies specifically evaluating the cost- effectiveness of coronary calcium scoring as a screening tool. As a result, calcium scoring, while predictive of CAD and mortality, has yet to be shown to add any additional information over and above current clinical models. Therefore, at this time there is insufficient data to recommend calcium scoring as a screening or risk stratification tool in the asympto- matic population. However, the dearth of cost-effectiveness data precludes stating that calcium scoring should not be preformed as a screening test.

Subsequently, additional cost-effectiveness studies should be instituted to evaluate the role of calcium scoring in the screening for CAD.

II. Special Case: High-Risk Patients

Summary of Evidence: Among high-risk symptomatic populations coro- nary artery calcium scoring on CT has failed to show any predictive value for a coronary event or mortality. Thus, among high-risk populations calcium scoring cannot be recommended for screening or risk stratification (Insufficient Evidence).

Supporting Evidence: The data in the asymptomatic populations consis-

tently indicated that coronary artery calcium scoring can predict cardiac

events and may be helpful in risk stratifying patients. However, the results

in populations with a known risk are not as straightforward. Qu et al. (22) evaluated calcium scoring in a diabetic population. The data showed that when adjusting for other risk factors in a diabetic sample, calcium scores did not predict coronary events, but calcium scoring was predictive among nondiabetics (Fig. 19.2). Although the results have not been as clear among an elderly population that coronary artery calcification is associated with the degree of CAD, some researchers have found that the calcium score has variability among an elderly population, and thus may have the poten- tial to discriminate risk within this group (23). However, other authors have concluded that there is limited utility of using calcium scoring among elderly patients (24,25) because of comorbidities limiting the effect of inter- ventions. Lastly, Detrano et al. (10) concluded that neither clinical risk assessment nor calcium scoring is an accurate predictor of cardiac events in a high-risk population, based on the Framingham model. Currently, there is insufficient evidence to recommend coronary artery calcium scoring in a high-risk population as a means of risk predicting coronary events (insufficient evidence).

III. Which Patients Should Undergo Coronary Angiography?

Summary of Evidence: Coronary angiography has been studied with a greater degree of rigor than the other modalities, with several studies investigating the cost-effectiveness. Based on the large amount of extant

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Figure 19.2. A: Relative risks (RRs), stratified by diabetes status, of nonfatal myocardial infarction (MI), or coronary death associated with calcium score risk groups (low, <2.8; medium, 2.8–117.8; high, >117.8). B: RRs, stratified by diabetes status, of nonfatal MI, coronary death, percutaneous transluminal coronary angio- plasty (PTCA), coronary artery bypass graft (CABG), or stroke associated with calcium score risk groups (low, <2.8; medium, 2.8–117.8; high, >117.8). [Source: From Qu et al. (22).]

data, a strong recommendation can be made for initial coronary angiogra- phy among high-risk patients and those who are post-MI that was trans- mural or with ischemic symptoms. Also, a strong recommendation can be made for performing a noninvasive imaging examination (i.e., SPECT or stress echo) prior to coronary angiography in low-risk patients and those who have had a non–Q-wave MI (Fig. 19.3) (strong evidence).

Supporting Evidence: Over the past 20 years, coronary angiography has been the mainstay in the diagnosis of acute occlusion of the coronary arter- ies as well as in the quantification of CAD to direct management, whether surgical, medical, or endovascular. Throughout this period, angiography has become the gold standard for the diagnosis of CAD, but unlike other imaging studies of the heart there is greater risk associated with the pro- cedure. Subsequently, the risk and technical factors preclude all patients from undergoing an angiogram.

Several cost-effectiveness models have been proposed to evaluate the role of coronary angiography in the diagnosis of coronary artery disease (26–28). Patterson et al. (27) utilized decision analysis to evaluate angiog- raphy versus other noninvasive modalities [i.e., SPECT, PET, exercise elec- trocardiogram (ECG)]. This model incorporated both direct and indirect costs as well as quality-adjusted life years (QALYs) to evaluate the differ- ent diagnostic modalities. The diagnostic evaluations included non- invasive testing followed by angiography (among those with an initial abnormal test) or angiography alone. The results of the study indicate that cost-effectiveness of the diagnostic modality is based on the initial pretest likelihood of disease. The authors found angiography was the most cost-effective modality in those with a high pretest probability (p > .70).

However, populations with low risk (p < .70) noninvasive testing was the most cost-effective with PET > SPECT > exercise ECG. In addition, the authors found that there was little impact on the cost-effectiveness

Figure 19.3. The recommended decision tree for the evaluation of CAD based on the patients’ initial clinical status. *Noninvasive study can represent SPECT or stress echo depending on the institutional performance characteristics of the imaging study.

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from the differing treatment modalities (i.e., surgical, medical, or endovas-

cular). Similar results have been described by Garber and Solomon (28).

Their decision analysis demonstrated that while stress echocardiography was the least costly per QALY saved, immediate angiography was an acceptable cost-effective alternative to SPECT and stress echocardiography among patients who are at high risk of cardiac disease. In their model, the relative cost-effectiveness for the modalities remained the same regardless of the patient’s age or gender (Fig. 19.4). There is strong evidence to rec- ommend that among low-risk populations a noninvasive cardiac imaging study should be performed prior to coronary angiography (strong evidence).

Coronary angiography seemingly has a specific role in the diagnosis and risk stratification of patients with heart disease and has been shown to be cost-effective in given populations (26–28); however, the data in post-MI populations is not as clear. In a decision analysis by Kuntz et al. (29), the decision analytic model incorporated clinical history and symptoms in the post-MI patient to evaluate the cost-effectiveness of angiography versus medial care. While the authors incorporated clinical elements into the analyses, there was a failure to account for type of MI to address the issue of noninvasive evaluation of cardiac perfusion (e.g., SPECT or stress echo).

Based on the model outcomes, angiography was found to be cost-effective in almost all patients in the post-MI setting, and among those at highest risk the cost-effectiveness ratios were less than $50,000 for each QALY saved. Only in those women at low to moderate risk for coronary disease was angiography found not to be cost-effective. Similar results on the patient survival and outcomes have been found in other studies that have included all post-MI patients (30,31), and the largest effects were among the patients with transmural infarctions. There is strong evidence to support the use of angiography in the transmural infarction while those with a nontransmural infarction should undergo a noninvasive study prior to angiography (strong evidence).

Several authors have evaluated low to moderate risk (probability of CAD < .7) subpopulations in the post-MI state to determine the cost- effectiveness and outcomes among those treated with noninvasive image guidance versus immediate angiography. Barnett et al. (32) utilized a randomized controlled trial to evaluate the cost-effectiveness of angiogra- phy versus selective angiography (i.e., performing angiography in patients with an abnormal finding on a noninvasive study) in a population with a non–Q-wave MI. The results indicate a conservative management program is more cost-effective than immediate angiography in patients with a non–Q-wave MI. In the acute setting, image-directed angiography resulted in a cost of $14,700 versus $19,200 for immediate angiography and per- sisted after 2 years of follow-up, at which time there was an approximate

$2100 difference in cost. In addition, the conservative group had a better

survival (1.86 years) over a 2-year follow-up relative to immediate

angiography (1.76 years). Thus, conservative management (i.e., noninva-

sive image-directed angiography) is the dominant strategy over angiogra-

phy in the non–Q-wave post-MI patient with resulting lower cost and

improved outcome. There is strong evidence to show that noninva-

sive testing prior to angiography is more cost-effective than angiography

alone in patients who have had a nontransmural infarction (strong

evidence).

Figure 19.4. A: Cost-effectiveness of tests for coronary artery disease, in thousands of 1996 U.S. dollars per quality-adjusted life year (QALY), for men at 50% pretest risk for disease. B: Cost-effectiveness of tests for coronary artery disease, in thou- sands of 1996 U.S. dollars per QALY, for women at 50% pretest risk for disease.

ECHO, stress echocardiography; ETT, exercise electrocardiography; PET, positron emission tomography; SPECT, single photon emission computed tomography.

[Source: Garber and Solomon (28).]

Figure 19.4. Continued

362 A.J. Bierhals and P.K. Woodard

An earlier report by Boden et al. (33) came to a supporting conclusion regarding patient outcome in the post-MI setting. They evaluated the impact of post-MI angiography in a population with non–Q-wave MIs.

Through 2 years of follow-up among the aforementioned patient popula- tion (Fig. 19.5), a noninvasive image-directed approach to patient man- agement was found to have a significantly lower mortality and reinfarction rates than those patients who had undergone an initial angiogram in the acute MI state. The findings have been supported by the recommendations of other groups and researchers (34,35).

Coronary angiography has a specific role in the evaluation of heart disease that is based on the patient’s clinical history and symptoms. The data support the position that in an asymptomatic population with a low clinical suspicion of heart disease, noninvasive testing should be per- formed prior to angiography (26–28,36), whereas in situations were there is a high clinical suspicion of CAD, angiography should be the initial test of choice. A similar picture develops in post-MI patients. For instance, individuals who have had a transmural MI or who have clinical signs of ischemia should undergo a coronary angiogram, but those with a non–Q- wave MI without clinical ischemia would best be evaluated by noninva- sive imaging (29–35). Therefore, the utilization of coronary angiography is based on the clinical situation and the initial use may not always be the most prudent or cost-effective method to manage patients who are sus- pected of CAD or recently in the post-MI state.

Figure 19.5. Kaplan-Meier analysis of the probability of survival according to strat- egy group during 12 to 44 months of follow-up. Death from any cause was included in this analysis. The Cox proportional-hazards ratio for the conservative as com- pared with the invasive strategy was 0.72 (95% confidence interval, 0.51–1.01).

[Source: Boden et al. (33).]

IV. Which Patients Should Undergo Noninvasive Imaging of the Heart?

Summary of Evidence: There is a moderate amount of support to suggest that stress echo should be recommended prior to coronary angiography in the low-risk patients. However, several authors have suggested that stress echo is highly operator dependent and at times SPECT may be a viable alternative. Both modalities have an acceptable cost-effectiveness profile;

as a result, there is insufficient evidence to recommend SPECT over stress echo. More comprehensive cost-effectiveness reports are needed to com- pletely evaluate these modalities (insufficient evidence).

Supporting Evidence: A few cost-effectiveness evaluations have been performed incorporating the aforementioned noninvasive studies that have had some conflicting results. A decision analysis was performed by Kuntz et al. (36) that modeled immediate angiography versus a stepwise approach to angiography. In this situation angiography would be per- formed only if the initial noninvasive test were positive. The analysis incor- porated SPECT, stress echocardiography, and stress electrocardiography.

The results indicated that stress echocardiography was more cost-effective than SPECT in the low-risk population with an incremental cost effective- ness ratio of $26,800/QALY versus $27,600/QALY, respectively. Although the model does assume an idealized performance of echocardiography, slight changes in sensitivity of either SPECT or echo affect the results of the model. Thus, decisions concerning the performance of a specific test should be based on the test characteristics at a given institution (36).

The model also supported the results of other angiographic studies in which immediate angiography is more cost-effective in the high-risk patient.

Another decision analysis performed by Garber and Solomon (28) included PET in their analyses along with angiography, stress echo, planar thallium, exercise electrocardiography, and SPECT. The results indicated that the initial use of stress echo was the most cost-effective followed by SPECT and angiography (Fig. 19.4). Positron emission tomography was not cost-effective in the diagnosis, resulting in higher cost without improved outcomes. The study also brings to the forefront the idea that there is variability in cost and performance of SPECT and stress echo; sub- sequently, SPECT may be the initial modality of choice in some regions (28,38).

However, a single study evaluating the cost-effectiveness of SPECT versus exercise electrocardiography was performed to evaluate any addi- tional prognostic value of SPECT (37). The authors found that SPECT pro- vided additional information, which translated into $5500 per level of risk reclassification.

Other researchers have also included PET in decision analysis along with

SPECT and angiography (26). The findings of this study contradicted the

prior model, such that PET was found to be the most cost-effective modal-

ity in diagnosing CAD among low-risk patients (28). Aside from the two

prior studies, no other reports were found in the literature review to eval-

uate the cost-effectiveness of PET in the diagnosis of CAD. Subsequently,

there is insufficient evidence to recommend PET in the evaluation of CAD

(insufficient evidence).

Similarly, only the previously described studies could be found to eval- uate the cost-effectiveness of stress echocardiography (28,36,38). However, several other studies evaluating the cost-effectiveness of SPECT were iden- tified in the literature review. In a small patient sample (n = 29), SPECT was found to increase the diagnostic ability in cardiologist who were treat- ing emergency room patients with acute chest pain (39). The study also found a decrease in hospitalizations and a savings of $800 per patient (39), although this study had a small sample size and did not rigorously eval- uate cost and outcomes. Lastly, Udelson et al. (40) assessed the effect of SPECT in the evaluation of acute chest pain in the emergency department.

There was a lower hospitalization rate among patients without coronary ischemia who had undergone a SPECT in the emergency department (42%) versus usual care (52%). The results suggest that SPECT may have an effect on decision making and possibly lower the costs by reducing hospitaliza- tion; however, to date there is insufficient evidence to recommend SPECT in the emergency setting.

In conclusion, multiple decision analyses and randomized studies agree that in a low-risk patient a noninvasive study should be preformed prior to an angiogram. Also, the models seem to support stress echocardiogra- phy as the most cost-effective, but also have suggested that SPECT may be as cost-effective depending on the institutional performance. Subsequently, there is little definitive data to use one of these studies over the other.

The use of SPECT or echo should be based on the institutional efficacy.

Although there is an early suggestion that SPECT may be useful in the emergent chest pain setting for patient triage, there is not enough data at this time to support this position. Lastly, there is conflicting evidence con- cerning the cost-effectiveness of PET in the diagnosis of CAD and ischemia;

more studies are needed to determine the role of PET in the cardiac eval- uation (insufficient evidence).

In symptomatic post-MI patients or those at high risk for CAD, coronary angiography is the most cost-effective method to evaluate, diagnose, and plan treatments. However, among those without symptoms, noninvasive modalities (i.e., PET, SPECT, and stress echocardiography) are the more cost-effective means to evaluate heart disease. But the research to date is somewhat unclear as to the utilization of the aforementioned modalities.

The current literature is somewhat limited in the cost-effective evaluations of noninvasive studies.

V. What Is the Appropriate Use of Coronary Artery Computed Tomography and Magnetic Resonance?

Summary of Evidence: The newer noninvasive modalities of cardiac MR and CT have a paucity of cost-effectiveness research and outcomes data available at this time and cannot be recommended for the evaluation of ischemic cardiac disease (insufficient evidence).

Supporting Evidence: In the past decade there have been advances in CT and MR in the evaluation of many aspects of the heart and heart disease.

The current literature has limited data on the performance of MR and CT with respect to evaluation of the coronary arteries or for assessment of ath- erosclerosis aside from calcium scoring. However, our literature review found no reports evaluating the cost-effectiveness of either modality.

364 A.J. Bierhals and P.K. Woodard

Huniak et al. (41) performed a decision analysis and developed a model incorporating current initial diagnostic modalities (i.e., SPECT and stress echo) prior to coronary angiography. In addition, coronary MR and CT were also included to determine those cost and performance characteris- tics necessary for the new modalities to possess in order to be cost- effective. For a new diagnostic study to be more cost-effective than stress echo, a cost of less than $1000 and a sensitivity and specificity greater than 89% and 88%, respectively, should be obtained. The results were similar for replacing SPECT, such that the new imaging study must have a sensi- tivity and specificity greater than 85% and 80%, respectively. Lastly, as would be expected, a new testing modality required a sensitivity and speci- ficity of 99% to replace angiography (41). While the prior study is a good start in the evaluation of the cost-effectiveness of coronary MR and CT, dedicated studies are required to fully evaluate these aspects of the imaging modalities, in order to have a complete understanding of their role in patient care.

In addition, as opposed to the traditional modalities, cardiac MRI can assess simultaneously a multitude of aspects of the heart and cardiac func- tion. Thus, a modality with such versatility may have higher costs that are offset by evaluating several cardiac dimensions at once, resulting in a greater cost-effective modality. Therefore, studies need to be designed to address cardiac MR’s role in a complete heart evaluation encompassing ejection fraction, wall motion, coronary arteries, perfusion, and valvular disease. All of these aspects of cardiac MR have been addressed, but no single study has encompassed all aspects to evaluate cost-effectiveness.

Studies have shown that cardiac perfusion abnormalities can be detected with similar sensitivity and specificity with MR, SPECT, and PET (42–44).

Cardiac MRI has been found to comparable to stress echo in the evalua- tion of wall motion (44,45). In addition, it is better than SPECT in the assess- ment of myocardial viability as it is of higher resolution and able to differentiate between subendocardial and transmural infarct. Cardiac MR has also been utilized to evaluate the coronary arteries for aberrant vessel course and bypass graft complications, all with a relatively high degree of sensitivity of about 90% (44). Cardiac MR has been found to correlate with Doppler ultrasound findings in the estimation of valvular area size (46,47).

Aside from the potential utilization for heart disease, cardiac MR has been shown to have applications for patients with congenital heart disease (48) that assist with surgical planning and medical management. The current cardiac MR data are extremely promising but remain limited and require further investigation regarding a future role in patient care.

Cardiac CT also suffers from a paucity of data evaluating the cost-

effectiveness in patient management; as a result, its role in patient care

remains unclear. Cardiac CT has made great strides over the past 5 years

with the introduction of multidetector scanners, which has improved res-

olution and speed, allowing for improved performance of multiphase and

arterial phase studies. These characteristics do provide some advantage

over MR in terms of speed and in the evaluation of stents and patients with

pacemakers. But due to the novelty of the modality, the literature remains

more limited than that for cardiac MR. Therefore, even before cost-

effectiveness studies can be performed, data must be generated on the per-

formance of cardiac CT. Preliminary studies have shown that cardiac CT

can evaluate coronary artery stents (49), and others have used cardiac CT

to evaluate congenital heart disease (50). Also, preliminary data have been

generated in the use of cardiac CT for coronary angiography (51); however, the sample sizes are not substantial enough to generate any accurate assessment of performance.

Recommended Imaging Protocols Based on the Evidence

Cardiac Catheterization

• Selective injection of left coronary artery with at least the projections anteroposterior (AP), left anterior oblique (LAO) cranial, and right ante- rior oblique (RAO) caudal is the minimum needed to cover the course of the left main anterior descending and circumflex arteries.

• Selective injection of the right coronary artery with at least the projec- tions lateral, RAO, LAO, and LAO cranial are required to evaluate the right coronary artery.

Stress Echo

In a nonpharmacologic stress echocardiogram, the target for an adequate study is similar to that of SPECT or a treadmill test. Failure to meet the stress limits the sensitivity of the examination. The heart rate should reach at least 85% of predicted. However, the study should be terminated if cardiac symptoms arise or there are ECG changes.

Cardiac SPECT

• In the nonpharmacologic stress SPECT, 85% of the maximum heart rate needs to be achieved to prevent limitations in sensitivity.

• Dipyridamole is infused at a rate of 0.6 mg/kg over 4 minutes. Then imaging with thallium 201 begins 10 minutes after infusion. No caf- feinated products or xanthines should be taken prior to the study as they will eliminate the effects of dipyridamole. This should not be given to asthmatics as it may precipitate bronchospasm.

• Adenosine is infused intravenously at 140 mg/kg/minute over 4 to 6 minutes. The thallium 201 is injected 3 minutes after infusion. Adenosine is contraindicated in individuals with heart block and bronchospasm.

Future Research

• In the future, cost-effectiveness research should focus on incorporating calcium scoring and clinical risk stratification in the screening for early heart disease. Coronary artery calcification scoring has been shown in the asymptomatic patient to predict a coronary event, but cost- effectiveness has not been adequately evaluated. By evaluating calcium scoring in this manner, a determination can be made concerning the modalities’ additional benefits as well as the cost that may be incurred.

• Future research should focus on the potential utilization and outcomes of novel coronary artery imaging modalities, such as CT and MRI. These modalities are promising for the evaluation of coronary arteries in mul- tiple clinical circumstances (52). Prior to any cost-effectiveness studies, an understanding of modality performance characteristics (e.g., sensi- tivity and specificity) is needed, along with evaluation of the impact on patient management and outcome.

366 A.J. Bierhals and P.K. Woodard

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