Original Article
Diagnostic and clinical benefit of combined coronary calcium and perfusion assessment in patients undergoing PET/CT myocardial perfusion stress imaging

https://doi.org/10.1007/s12350-009-9159-9Get rights and content

Abstract

Background

A limitation of stress myocardial perfusion imaging (MPI) is the inability to detect non-obstructive coronary artery disease (CAD). One advantage of MPI with a hybrid CT device is the ability to obtain same-setting measurement of the coronary artery calcium score (CACS).

Methods and Results

Utilizing our single-center nuclear database, we identified 760 consecutive patients with: (1) no CAD history; (2) a normal clinically indicated Rb-82 PET/CT stress perfusion study; and (3) a same-setting CAC scan. 487 of 760 patients (64.1%) had subclinical CAD based on an abnormal CACS. Of those with CAC, the CACS was >100, >400, and >1000 in 47.0%, 22.4%, and 8.4% of patients, respectively. Less than half of the patients with CAC were receiving aspirin or statin medications prior to PET/CT imaging. Patients with CAC were more likely to be initiated or optimized on proven medical therapy for CAD immediately following PET/CT MPI compared to those without CAC.

Conclusions

Subclinical CAD is common in patients without known CAD and normal myocardial perfusion assessed by hybrid PET/CT imaging. Identification of CAC influences subsequent physician prescribing patterns such that those with CAC are more likely to be treated with proven medical therapy for the treatment of CAD.

Introduction

Detection of coronary artery disease (CAD) by stress myocardial perfusion imaging (MPI) requires the presence of a physiologically significant, flow-limiting stenosis. Thus, patients referred for stress MPI may have subclinical, non-obstructive CAD despite normal perfusion images. The most common method for diagnosing subclinical CAD is measurement of a coronary artery calcium score (CACS).1,2 The presence of CAC is indicative of coronary artery disease, and the extent of CAC is proportional to the total coronary artery plaque burden.3, 4, 5 Furthermore, the presence and extent of coronary calcification is prognostically important and adds incremental prognostic information beyond that of traditional cardiovascular risk factors.6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 Therefore, in patients suspected of having CAD, a combined evaluation of both stress MPI and CACS could incrementally add to their correct classification25, 26, 27, 28, 29, 30 and could significantly change clinical management.

Stress MPI utilizing positron emission tomography (PET) is increasingly utilized to diagnose patients with suspected CAD. First-generation cardiac PET MPI scanners utilized a germanium rod source to produce a transmission scan for attenuation correction purposes. Newer cardiac PET scanners are coupled with computed tomography (CT) which allows a low-intensity CT scan of the patient’s chest to be acquired as a part of the imaging protocol, and is used for an attenuation map. The availability of the CT scan allows for quantification of CAC as a part of the examination. There are few reports of findings when CACS is routinely performed in typical intermediate-likelihood patients referred for PET perfusion imaging, and how or whether the findings influence subsequent management.

The purpose of this study was to evaluate the presence and severity of subclinical CAD evidenced by abnormal coronary artery calcification in patients who: (1) had no prior diagnosis of CAD; (2) were referred for cardiac PET/CT MPI for the evaluation of suspected CAD; and (3) had normal myocardial perfusion. We analyzed the association between demographic/clinical variables and the presence/extent of coronary artery calcification. Additionally, we evaluated the impact of CAC identification on subsequent medical management of CAD by the referring physician.

Section snippets

Subjects

Between March 2007 and June 2008 all patients referred for PET/CT MPI at our institution (Cardiovascular Consultants, PA; Kansas City, Missouri), who had no history of CAD and underwent same-setting coronary artery calcification scoring where identifies. In our practice, patients who are referred for pharmacologic stress myocardial perfusion imaging are preferentially imaged using PET versus SPECT given the higher diagnostic accuracy of PET myocardial perfusion imaging. After obtaining patient

Results

Seven-hundred sixty patients were identified for inclusion in this analysis. The overall demographic and clinical characteristics of the patients are presented in Table 1. The majority of patients were female (n = 496, 65.3%); mean age of the entire cohort was 64.8 ± 12.8 years. Overall, 22.1% had diabetes mellitus, 72.6% had hypertension, 67.5% had hyperlipidemia, and 16.2% were current smokers. None of the patients had a prior diagnosis of CAD. The mean LV ejection fraction was similar in

Discussion

In this analysis, we found that subclinical coronary artery disease was present in the majority of patients (64.1%) with normal PET perfusion scans undergoing stress PET/CT MPI for evaluation of possible coronary artery disease. Of the patients with normal PET/CT MPI, 30.1% had an Agatston coronary calcium score >100. We also found that while CAC was more prevalent in those with higher FRS, a significant proportion of patients with intermediate and high FRS had little or no coronary

Limitations of this Study

The patients analyzed for this study were referred for vasodilatory stress using cardiac PET MPI testing. These patients may not be representative of those referred for vasodilatory SPECT imaging and are generally not representative of those undergoing exercise SPECT. However, we performed coronary artery calcium scoring on all consecutive patients referred for PET/CT MPI who did not have known coronary artery disease. Therefore, our study does not suffer from referral bias as do prior studies

Conclusions

Patients referred for vasodilatory myocardial PET/CT MPI for suspected coronary artery disease frequently manifest subclinical CAD detected by the presence of CAC, despite having normal myocardial perfusion images. Our findings support the concept that patients without known CAD undergoing stress PET/CT MPI should undergo a same-setting coronary calcification study. This practice will importantly lead to the diagnosis of subclinical CAD in many patients who would not have otherwise received

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    Kevin A. Bybee, Richard Markiewicz, and Timothy M. Bateman were involved in the conception, design, analysis, and interpretation of the data. They were participants in the drafting of the manuscript and approval of the manuscript in its final version. John Lee, Ryan Longmore, A. Iain McGhie, James H. O’Keefe, Bai-Ling Hsu, Kevin Kennedy, and Randall C. Thompson were involved in the design, analysis and interpretation of the data. They were participants in the critical revision of the manuscript for important intellectual content and approval of the manuscript in its final version.

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