Single injection double acquisition a doubleedg

Authors: Ernst E van der Wall Yves G America Arthur J Scholte Jeroen J Bax

Publish Date: 2008/07/24

Volume: 24, Issue: 8, Pages: 837-839

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Abstract

In the clinical arena detection of myocardial viability is currently based on the use of nuclear techniques which show preserved tracer uptake and metabolism in viable myocardium 1 2 Assessment of myocardial viability and ischemia continues to be an issue in patients with coronary artery disease and left ventricular dysfunction in particular in patients following a myocardial infarction 3 Nuclear imaging has long played an important role in this field Especially PET imaging using 18Ffluorodeoxyglucose FDGPET has been regarded as the metabolic gold standard of tissue viability which has been supported by a wide clinical experience 4 Viability assessment using SPECT techniques has gained more widespread clinical acceptance than PET because it is more widely available at lower cost 5 Moreover technical advances in SPECT technology such as gated SPECT imaging further improve the diagnostic accuracy of the test 6 7 8 9During the past decade progress in the field of myocardial perfusion imaging has resulted in a myriad of choices for perfusion imaging protocols including choices in types of stressor imaging modality perfusion tracer method of analysis and a wide range of choices of imaging protocols 10 11 12 More recently the peculiar contribution of gated SPECT in the assessment of myocardial ischemia and viability has been demonstrated with the potential to evaluate in a single myocardial perfusion study the presence of preserved tracer uptake and the amount of contractile reserve through the acquisition of gated SPECT during inotropic stimulation with dobutamine 13 14 15 16 In 1999 Everaert et al did already study changes in global and regional left ventricular function in response to dobutamine infusion assessed in 10 healthy volunteers using sequential gated SPECT myocardial perfusion acquisitions 13 The authors concluded that changes in wall thickness induced by infusion of lowdose dobutamine can be assessed by sequential gated SPECT myocardial perfusion studies Based on this study it was suggested that the stress gated SPECT protocol proposed in their study might be helpful to distinguish viable from scar tissue in patients with coronary artery disease by demonstrating a preserved inotropic response in hypoperfused myocardiumIn 2000 Narula et al evaluated dualisotope gated SPECT imaging combined with low and high dose dobutamine as a single test for the characterization of various types of altered myocardial dysfunction 14 They studied 54 patients with ischemic cardiomyopathy using rest and 4 hredistribution thallium201 imaging and dobutamine technetium99m sestamibi SPECT and showed that this new imaging technique allowed the characterization of dysfunctional myocardium as stunned hibernating remodeled and nonviable Over the past years the gated SPECT imaging protocols have been refined 15 16 and recently a new technique has been developed consisting of threedimensional registration of CT coronary angiography CTCA and ECGgated myocardial perfusion SPECT 17 This technique of registration may assist the integration of information from gated SPECT and CTCA and may have clinical application for the diagnosis of ischemic heart disease 17 18 19In the current issue of this journal Fallahi et al studied 51 patients using a single injection double acquisition gated SPECT—low dose dobutamine protocol SIDAGSLDD representing a new way to establish the presence of viability and coronary artery disease 20 In this novel protocol the rest phase of the routine technetium99m SPECT protocol was substituted by another phase of image acquisition under continuous infusion of lowdose dobutamine immediately after the initial phase of stress imaging The new protocol was compared to the standard stress/rest gated SPECT protocol double injection double acquisition and the stressonly gated SPECT protocol single injection single acquisition The SIDAGSLDD protocol demonstrated a good agreement with the standard protocol and proved to be superior to for the assessment of viability in patients following myocardial infarction The protocol was also superior to the gated imaging stressonly protocol in detecting more defect reversibility Procedural advantages of the protocol are the absence of the need for a second injection of the tracer reducing the duration of the imaging study therewith decreasing the costs and radiation burden to both patients and personnelAlthough the novel protocol offers new perspectives for better streamlining imaging procedures there are several caveats to the protocol some of them also recognized by the authors In the present study by Fallahi et al 20 the main focus was on defect reversibility rather than on functional parameters wall motion/thickening left ventricular ejection fraction implying that only one side of the spectrum of viability has been highlighted In addition only the standard stress/rest method allows the true assessment of defect reversibility whereas the single injection protocols have to rely on a ‘reversibility equivalent’ as a marker of reversibility Consequently it remains difficult in the single injection protocols to accurately assess whether a perfusion defect is truly reversible Next it has been previously shown that it is useful to employ different imaging strategies depending on the history of the patient 21 In the study by Schroeder et al 21 patients without a previous myocardial infarction showed a normal stress SPECT study in almost onethird 32 of patients compared to only 4 in patients with a previously myocardial infarction As a result patients with a stress defect at Tc99m sestamibi/tetrofosmin SPECT imaging should always undergo a resting SPECT study irrespective of the clinical and stress electrocardiographic findingsA further caveat is that in patients with an earlier myocardial infarction who undergo gated SPECT imaging left ventricular function LVEF poststress may not always represent true resting left ventricular function 22 23 24 25 In patients with clinically important stressinduced perfusion abnormalities the LVEF after stress might be significantly lower than the LVEF at rest both with sameday reststress and stressrest imaging protocols These observations again justify the stratification of patients before starting the gated SPECT study underscoring that in patients with a previous myocardial infarction the gated acquisition should preferably be performed during the rest study Lastly the results of the present study have to be weighed against a true gold standard of viability such as FDGPET and evaluation postinterventionThis article is published under an open access license Please check the Copyright Information section for details of this license and what reuse is permitted If your intended use exceeds what is permitted by the license or if you are unable to locate the licence and reuse information please contact the Rights and Permissions team

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