Original Article
Incremental prognostic value of coronary flow reserve assessed with single-photon emission computed tomography

https://doi.org/10.1007/s12350-011-9345-4Get rights and content

Abstract

Background

We assessed the prognostic value of coronary flow reserve (CFR) estimated by single-photon emission computed tomography (SPECT) in patients with suspected myocardial ischemia.

Methods and Results

Myocardial perfusion and CFR were assessed in 106 patients using dipyridamole/rest Tc-99m sestamibi SPECT and follow-up was obtained in 103 (97%) patients. Four early revascularized patients were excluded and 99 were assigned to normal (summed stress score <3) vs abnormal myocardial perfusion and to normal (≥2.0) vs abnormal CFR. During the follow-up (5.8 ± 2.1 years), 28 patients experienced a cardiac event (cardiac death, nonfatal myocardial infarction, and late revascularization). Abnormal perfusion (P < .01) and abnormal CFR (P < .05) were independent predictors of cardiac events at Cox proportional hazard regression analysis. Also in patients with normal perfusion, abnormal CFR was associated with a higher annual event rate compared with normal CFR (5.2% vs 0.7%; P < .05). CFR data improved the prognostic power of the model including clinical and myocardial perfusion data increasing the global chi-square from 18.6 to 22.8 (P < .05). Finally, at parametric survival analysis, in patients with normal perfusion the time to achieve ≥2% risk of events was >60 months in those with normal and <12 months in those with abnormal CFR.

Conclusions

Myocardial perfusion findings and CFR at SPECT imaging are both independent predictors of cardiac events. Estimated CFR provides incremental prognostic information over those obtained from clinical and myocardial perfusion data, particularly in patients with normal perfusion findings.

Introduction

Myocardial perfusion imaging with single-photon emission computed tomography (SPECT) is an established diagnostic and prognostic method for evaluation of patients with suspected or known coronary artery disease (CAD).1 This technique has proven to be useful in prognostic stratification and provides information for the clinical decision-making process.2 Normal stress SPECT imaging is associated with a very low event rate (≤1%/year), leading to a negative predictive value of more than 99%.3 In contrast, abnormal SPECT increases the annualized event rate by a factor of 7, and the risk of events is related to the severity of perfusion abnormalities.4 However, the limitations of relative perfusion imaging by SPECT suggest that patient care might be enhanced by the use of quantitative measures of perfusion reserve.5,6 Although positron emission tomography (PET) imaging is the gold standard to measure CFR in non-invasive way, attempts have been recently made to obtain quantitative CFR by dynamic SPECT imaging.7, 8, 9, 10 This approach is potentially open to implementation in most nuclear cardiology laboratories and it could be adapted for general application.11 A good correlation between CFR values estimated by SPECT and those measured by intravascular Doppler ultrasound has been reported.8,10 This technique has been also validated by comparison with PET, despite some underestimation at higher flow rate.9 These findings support the concept that SPECT may compete with other modalities for CFR estimation.1,11 However, no data are currently available on the predictive value of SPECT estimated CFR. Therefore, the aim of this study was to assess the long-term prognostic value of CFR estimated by SPECT imaging in patients with suspected myocardial ischemia.

Section snippets

Patients

The study population included 106 consecutive patients who underwent stress SPECT imaging because of suspected myocardial ischemia; 29 of these patients had known CAD. In all patients, beta-blockers and calcium antagonists were withheld for 48 h and long-acting nitrates for 12 h before testing. Cardiovascular risk factors such as hypertension, diabetes mellitus, dyslipidemia, smoking, or positive family history for CAD were assessed at the time of SPECT imaging by reviewing patient charts. The

Results

SPECT imaging was performed in 106 patients. Follow-up data were complete in 103 (97% of the total) patients. Of these, four patients were excluded due to early revascularization (<60 days), leaving 99 patients (80 men, mean age 59 ± 11 years) available for the analysis.

Discussion

To the best of our knowledge, this is the first study assessing the long-term prognostic value of CFR estimated by SPECT imaging in patients with suspected myocardial ischemia. The main result of the study is that CFR is a strong independent predictor of major adverse cardiovascular events and provides incremental prognostic information over those obtained from clinical and myocardial perfusion data.

The quantitative assessment of CFR may be useful for the functional evaluation of CAD, allowing

Conclusions

Myocardial perfusion findings and CFR at SPECT imaging are both independent predictors of cardiac events. In this pilot study, estimated CFR using myocardial retention index appears to provide prognostic information along with myocardial perfusion data. The findings of this study support further evaluation in larger investigations to establish the prognostic value of CFR estimated by SPECT imaging.

Acknowledgment

The authors have indicated they have no financial conflicts of interest.

References (26)

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