0322 : High consistency in left ventricular MR spectra in rats in vivo allows detecting small variations in energy status and early energy defects

Phosphorus magnetic resonance spectroscopy (31P-MRS) makes a unique and valuable contribution to our understanding of heart energetics, by giving the cardiac energy status from the concentrations of ATP and phosphocreatine (PCr). Changes in PCr/ATP ratio allow detecting energy imbalance that predicts disease and mortality. However, localized MR techniques in vivo are often challenged by tissue contamination and poor signal-to-noise ratio, especially in small animals.Here we purposely aimed at demonstrating good consistency in localized cardiac 31P-MR spectra obtained from left ventricle of rats in vivo with a surface probe at 9.4T. For that, 3-min MR spectra and short-axis cine-MRI frames were obtained in sinus rhythm during nine consecutive weeks in control and hypertensive rats (SHR) just before the apparition of severe pathology in the later. Then a severe tachycardia was acutely induced by isoproterenol injection (10μg/kg) and the PCr/ATP response kinetically analyzed.Along 9 weeks, we showed highly reproducible, steady and similar PCr/ATP ratios in each group in spite of progressive ventricular hypertrophy in SHR rats. Isoproterenol induced a similar tachycardia in each group (Control: 439bpm ±7, SHR: 411bpm±7) but altered responses of the energetics were noted in SHR rats: higher decrease in PCr/ATP ratio (–17.1%±0.75 vs. –4.7%±0.4, P<0.05) associated with longer recovery time (time constant of exponential fit 23.9 ±10.8 vs. 7.3±1.15min, P