Acute myocardial infarction: myocardial salvage assessment

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Acute myocardial infarction: myocardial salvage assessment

Primary coronary revascularization by means of percutaneous coronary intervention(PCI) is a highly effective treatment of acute myocardial infarction re-establishing coronary perfusion and stopping the ongoing necrosis in the dependent myocardium. Single-photon emission computed tomography(SPECT) is the most widely used modality assessing myocardial salvage as the difference between the acute perfusion defect before intervention and the remaining scar size measured in a second scan several days after the event. SPECT allows quantification of area at risk(AAR) and final infarct size(FIS) by tracer injection prior to revascularization and after 1 month, respectively. SPECT provides the most validated measure of myocardial salvage and has been utilized in multiple randomized clinical trials. However, SPECT is logistically challenging, expensive, and includes radiation exposure. More recently, a large number of studies have suggested that cardiac magnetic resonance(CMR) can determine salvage in a single examination by combining measures of myocardial oedema in the AAR exposed to ischaemia reperfusion with FIS quantification by late gadolinium enhancement.

acute myocardial infarction; area at risk; myocardial salvage; final infarct size; cardiac magnetic resonance; review

1 Introduction

Salvage of threatened myocardium is the principal mechanism by which patients with acute myocardial infarction(AMI) benefit from reperfusion. The combination of interventional and medical treatment has reduced mortality and morbidity significantly. Consequently, large patient numbers are required in clinical trials that aim at demonstrating improved survival of a new treatment. To diminish the need for large population sizes, numerous trials have used surrogate endpoints, including imaging measures of infarct size after coronary revascularization and indirect estimates of tissue damage by release of biomarkers, resolution of ST-segment elevation and myocardial blush grade[1-2].More recent clinical studies have used FIS and myocardial salvage as the primary endpoint[3-6]. The electrocardiogram may be used to estimate area at risk(AAR), but not final infract size(FIS)[7].Indirect measures of salvage can be calculated from angiographic estimates of AAR combined with estimates of FIS by imaging techniques or biochemical markers. Echocardiography is the preferred clinical method for evaluation of left ventricular(LV) function in patients with AMI. However, there are currently no specific echocardiographic measures of myocardial salvage. Single-photon emission tomography(SPECT) and cardiovascular magnetic resonance(CMR) provide the assessment of myocardial salvage, using paired quantification of AAR and FIS either from two separate studies before and after revascularization, or retrospectively in one step when the patient has been treated and stabilized.

2 Myocardial salvage

Several randomized single-centre trials have used myocardial salvage by SPECT as end point[8]. The trials are proof-of-concept studies testing the potential efficacy of new therapeutic approaches in smaller study groups. Subsequent larger trials are required to clarify whether the results are associated with clinical outcome. It has been demonstrated that increased salvage is associated with improved LV function after remote conditioning during transportation to primary PCI in STEMI patients[9-12]. Delineation of AAR prior to reperfusion therapy requires tracer availability in the catheterization laboratory on a 24 h basis and technical support for imaging within the following few hours. Because of the demanding set-up, efforts are made to develop methods for reliably estimating initial myocardium at risk after reperfusion therapy. Sciagra et al. recently published a small study of 36 AMI patients successfully treated with primary PCI[13-17]. Comparing function and perfusion 5 days after revascularization, they found a close correlation between salvage index by the functional wall ‘thickening’ and the conventionally performed ‘perfusion’ salvage index—data supporting a previous BRAVE-2 sub study[14].

3 Direct comparison of AAR between CMR and SPECT

The immediate benefits of CMR compared with SPECT include the absence of radioactive tracers and a minor logistical challenge because CMR can potentially determine the AAR retrospectively from 24 h to several days after the infarction. Compared with SPECT, CMR has higher spatial resolution, allowing delineation of the transmural extent of myocardial infarction. In contrast to SPECT, the CMR technology enables homogenous tissue signal from the entire field of view alleviating tissue attenuation as a limitation[15-17]. Consequently, both anterior and inferior myocardial infarctions are equally well depicted. There are relatively few direct comparisons between CMR and SPECT for quantification of AAR. In selected STEMI patients with a totally occluded coronary artery at arrival to the catheterization laboratory, a reasonable agreement was found between T2-weighted CMR and SPECT for the assessment of AAR and also between contrast-enhanced CMR and SPECT[18-20].

4 Conclusion

Myocardial salvage estimated by 99mTc-Sestamibi SPECT is a validated measure for comparing the efficacy of different treatment modalities. Translation of increased myocardial salvage into a clinical benefit should be considered in light of the fact that a large salvage is usually associated with a small FIS. The resultant LV dysfunction determines subsequent major adverse cardiac events and mortality after STEMI Myocardial salvage is a valid surrogate endpoint for comparison of the efficacy of cardioprotective strategies. 99m Tc-Sestamibi SPECT for quantification of AAR and FIS remains the best validated method at present but the method is logistically challenging and expensive. CMR may represent an applicable future alternative.

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NSENGIYUMVA Pierre1,CHEN Li-juan2,MA Gen-shan2

(1.SchoolofMedicine,SoutheastUniversity,Nanjing210009,China; 2.DepartmentofCardiology,ZhongdaHospital,SoutheastUniversity,Nanjing210009,China)

MA Gen-shan E-mail: magenshan@hotmail.com

format] NSENGIYUMVA PIERRE, CHEN Li-juan, MA Gen-shan. Acute myocardial infarction:myocardial salvage assessment[J].J Southeast Univ( Med Sci Edi),2015,34(3)：482-485.

R543.3 [Document code] A [Article ID] 1671-6264(2015)03-0482-04

10.3969/j.issn.1671-6264.2015.03.039

[Received date] 2014-10-29 [Revised date] 2014-11-14

[Biographies] NSENGIYUMVA Pierre (1983-),M,Burundian,Burundi,Postgraduate student.E-mail:nsengipre@yahoo.fr