Correlation of Cerebral Metabolites With Clinical Outcome Among Patients With Severe Congestive Heart Failure

atients with severe congestive heart failure have de- ranged cognition,1,2 and their ability to manage every- day problems is impaired.3 Cardiovascular reflexes, as well as autonomic and endocrine functions that may involve the central nervous system, are also profoundly disrupted. It is therefore of the utmost importance to understand the consequences of severe congestive heart failure for brain function and metabolism. In vivo proton magnetic resonance spectroscopy (1H MRS) is generating interest for 2 reasons. First, 1H MRS provides a new probe of cerebral function that measures important brain metabolites by detecting the hydro- gen nuclei in these molecules. Furthermore, this examination is becoming widely available, and the patient's experience is virtually identical to that with conventional MRI. See p 2784 A large number of biochemical intermediates, neurotrans- mitters, peptides, and structural molecules could, in principle, be detected by MRS; however, biological factors and current limitations on the MRS experiment limit the number of different signals that may be observed in routine clinical examinations. For example, the concentration of the metab- olite must be high, which means that important neurotrans- mitters (such as dopamine or serotonin) and low- concentration metabolites cannot be observed. Another factor is the molecular weight and physical environment of the compound: ideally, the molecular weight is low and the molecule is freely diffusing in aqueous solution. Large molecules, such as relatively immobile membrane lipids or proteins, do not contribute discrete resonances in the clinical 1 H magnetic resonance spectrum. Another factor is the chemical structure itself. Organic molecules contain many hydrogen nuclei in different positions that interact with one another through spin-spin coupling. This effect is exploited for structure analysis by MR spectroscopists, but the phenom- enon reduces the height of any single resonance from that molecule. Therefore, hydrogen nuclei in simple chemical groups (such as methyl hydrogens) are more easily detected. For all of these reasons, the 1H MR spectrum of the human