NMR Spectroscopy of the Human Heart

Magnetic resonance spectroscopy (MRS) of the human heart has focused on the noninvasive detection of high-energy metabolites—phosphocreatine (PCr), and adenosine triphosphate (ATP), which fuels muscular contraction—using the 31P nucleus. New applications of 1H MRS to measure total creatine (CR) and myocardial lipids are emerging, while the potential use of hyperpolarized 13C to image cardiac glycolytic metabolism is on the horizon. The value of MRS lies in providing reliable quantitative measures of parameters that index metabolic reserve. The range of techniques used to spatially localize 31P, 1H, and 13C MRS signals to the heart, along with the methods developed to reproducibly quantify the PCr/ATP ratio, absolute metabolite concentrations, and the forward reaction rate of generating ATP from PCr via the creatine – kinase (CK) reaction, are all reviewed. Using the body of published work, literature average values for PCr/ATP, [PCr], [ATP], [CR], intracellular pH, pseudo first-order CK reaction rate, and CK flux, in the normal healthy human heart are reported herein. Then, the quantitative changes in metabolic parameters seen in myocardial infarction, myocardial ischemia, in dilated and hypertrophic cardiomyopathy, in failing heart, valve disease, transplanted hearts, and in patients with diabetes and other disorders that affect the human heart, are presented and discussed. MRS provides noninvasive access to endogenous human cardiac energy metabolism that contributes unique information to our understanding of the physiology of the normal heart, its disease processes, and the evaluation of metabolic responses to therapy.