Dynamic Remodeling from Reversible Ischemia and Sudden Cardiac Arrest Sudden cardiac arrest (SCA) from ventricular fibrillation (VF) is a major public health problem affecting Veterans and the majority of victims have severe, asymptomatic coronary artery disease. Many patients developing VF have no evidence of a myocardial infarction and the link between ischemia and SCA remains unclear. Our completed work in swine with chronic hibernating myocardium has demonstrated that reversible ischemia leads to intrinsic myocardial adaptations that protect myocytes from injury yet increase vulnerability of the heart to spontaneous VF. Chronic telemetry has failed to identify ST changes indicative of ischemia but has re- vealed QT shortening and elevated left ventricular (LV) end-diastolic pressure during sympathetic activation immediately preceding VF. This differs from survivors and is not present the week before SCA. Limited myo- cardial proteomic profiling has demonstrated reductions in multiple glycolytic enzymes that contrast with their upregulation in survivors with hibernating myocardium. These changes could promote lethal ventricular ar- rhythmias by reducing glycolytically derived ATP, opening ATP-dependent potassium channels (resulting in QT shortening) and reducing SR calcium ATPase activity (elevating cytosolic calcium and LV end-diastolic pres- sure). Our central hypothesis is that ischemia-induced adaptations resulting from the progression of a coronary stenosis leads to dynamic molecular remodeling that transiently increases the vulnerability to VT/VF during sympathetic activation. We will initially determine whether there is a functional impairment of glycolysis (reduced enzyme activity and PET FDG uptake) in swine rescued from SCA with an ICD. Candi- date plasma biomarkers will be evaluated to identify if they are differentially elevated prior to SCA. These stud- ies will be complimented with discovery-based proteomic approaches employing quantitative label-free ion cur- rent-based LC/MS profiling of tissue and blood. This will allow us to more completely identify additional myo- cardial mechanisms that are impaired as well as identify novel circulating plasma biomarkers that are elevated in animals developing VT/VF vs. survivors. We will accomplish this by addressing two Specific Aims:
Specific Aim 1 - Using an implantable cardiac defibrillator to abort SCA, determine whether there is differential ischemia-induced protein remodeling in comparison to animals that survive with hibernating myocardium. Hypothesis 1A - The activity of myocardial glycolytic enzymes is upregulated in survivors but down- regulated at the time that VT/VF develops. Hypothesis 1B - Reductions in glycolytic proteins and enzyme activity will be accompanied by reductions in FDG uptake vs. increased uptake in survivors with hibernating myocardium. Hypothesis 1C - Discovery-based label free ion current-based LC/MS tissue proteomic profiling will identify additional novel protein changes that are altered in animals developing VT/VF vs. survivors.
Specific Aim 2 -Determine whether a candidate biomarker panel or serum proteomic profiling can identify novel biomarkers that selectively predict the risk of VT/VF before SCA develops. Hypothesis 2A - While tissue necrosis based on CK-MB will be absent, serum TnI and BNP will be- come transiently elevated prior to SCA as compared to survivors. Hypothesis 2B - Discovery based serum proteomic profiling will identify novel biomarkers predicting the risk of SCA vs. animals with hibernating myocardium that survive. The project has high translational relevance since it employs a preclinical model to study SCA that has many of the features of chronic coronary artery disease. Identifying transient targets of molecular myocyte remodeling as well as novel circulating biomarkers that can predict the risk of SCA before an event would fill a critical knowledge gap and lead to improved risk stratification and prevention of SCA.
Cardiovascular disease continues to be the leading cause of death and health care burden for Veterans and many succumb to sudden cardiac death from ventricular fibrillation. CPR has advanced the treatment after an event occurs but the factors that precipitate a lethal heart rhythm disturbance in asymptomatic individuals have not been identified. While patients with sudden death have severely narrowed coronary arteries, many are asymptomatic and have no evidence of an acute heart attack or heart failure. Thus, identifying those at risk before an event continues to be a major clinical problem. This project will determine whether transient changes in cardiac muscle proteins that develop as the heart adapts to repetitive episodes of reduced blood flow can lead to vulnerability to cardiac arrest in the absence of a heart attack. In paralle, blood samples will be analyzed to identify circulating protein biomarkers indicative risk before an event. Our long-term goal is to develop new approaches to identify Veterans at highest risk of sudden death before a fatal event occurs.
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