Nova técnica para pesquisa de viabilidade miocárdica com 18F-fluoro-desoxi-glicose utilizando dieta restrita em carboidratos: estudo comparativo com o clamp hiperinsulínico euglicêmico

INTRODUCAO: Em pacientes com infarto do miocardio (IM) e disfuncao cardiaca, a evidencia de viabilidade miocardica e primordial, e o exame tomografico por emissao de positrons com 18F-fluoro-desoxi-glicose (18FDG-PET) e o padrao-ouro para essa identificacao. Existe preferencia, na literatura, pela realizacao do clamp hiperinsulinico euglicemico (CLAMP) antes da injecao de 18FDG para estimular todo o miocardio a consumir glicose (GLI), garantindo assim a sua captacao pelas areas de miocardio hibernado (MH). No entanto, essa tecnica e trabalhosa, alem do risco de hipoglicemia durante a realizacao. Desenvolvemos uma nova tecnica na qual o paciente e submetido a uma dieta restrita em carboidratos (DIETA) por 24 horas antes do exame, sem a necessidade de CLAMP, com o objetivo de diminuir os niveis de insulina e aumentar acidos graxos livres (AGL), estimulando o miocardio normal a consumir AGL, e nao GLI. A area de MH, porem, nao consegue realizar o metabolismo oxidativo de AGL, mantendo o consumo de GLI. OBJETIVOS: comparar o PET apos DIETA (PET-DIETA) com o PET apos CLAMP (PET-CLAMP), para a pesquisa de viabilidade miocardica. METODOS: Trinta pacientes com IM previo e hipocinesia na area infartada foram submetidos a cintilografia de perfusao miocardica com 99mTc-sestamibi (MIBI), PET-CLAMP e PET-DIETA. A DIETA limitava-se a 15-20g de carboidratos por dia. Os exames foram submetidos a analise visual e classificados por escores (0 a 4). Foram consideras areas de mismatch (MH) aquelas com hipoperfusao ao MIBI e captacao presente no PET-CLAMP ou no PET-DIETA, em um modelo de 17 segmentos, alem da analise por parede, territorio arterial e por paciente. A analise por segmentos foi realizada ainda dividindo-se os pacientes em diabeticos (DM) e nao diabeticos (NDM). O PET-DIETA tambem foi submetido a analise automatica (por percentual de captacao) RESULTADOS: Durante o CLAMP, seis (20%) pacientes apresentaram hipoglicemia. Nenhum paciente apresentou hipoglicemia... BACKGROUND: In patients with myocardial infarction and left ventricular dysfunction, the evidence of myocardial viability has important clinical implications. Positron emission tomography (PET) using 18F-fluoro-desoxi-glucose (18FDG) is considered the gold standard for viability detection. The euglycemic hyperinsulinemic clamping (CLAMP) before 18FDG injection stimulates uptake of both glucose and 18FDG in the myocardium, including areas of hibernating myocardium (MH), and it is the most used protocol. However, this imaging protocol has an increased risk for hypoglycemia and is relatively time-consuming. We developed a new protocol using a 24 hours low-carbohydrate diet (DIET), aiming to reduce insulin levels and increase free fatty acids (FFA). This protocol stimulates the normal myocardium to use FFA, not glucose, but the area of hibernating myocardium (viable area) may not use oxidative metabolism with FFA, keeping glucose uptake and becoming a hot spot at PET images. The aim of this study was to compare both techniques by segments, regions, vascular territories and patients. METHODS: Thirty patients with previous myocardial infarction and left ventricular dysfunction were studied. All of them underwent into a SPECT perfusion scan with 99mTc-sestamibi and two 18FDG PET studies to asses myocardial viability, one with CLAMP (PET-CLAMP) and another using a 24 hours low-carbohydrate diet (PET-DIET). For the analysis, the myocardium was divided into 17 segments, 5 regions and 3 vascular territories. A visual and an automatic semi-quantitative analysis (only for PET-DIET) were carried out according to the following score indicating radiotracer uptake: 0 = normal to 4 = absent. Myocardial viability was defined as the presence of normal or mildly reduced FDG uptake in an area with reduced perfusion (99mTc-sestamibi uptake). We also performed subgroup analyses in diabetes (DM) and non-diabetic patients (NDM). RESULTS: While using CLAMP protocol, six (20%) patients...