Assessment of myocardial viability by intracellular Na-23 magnetic resonance Imaging

Background - Because of rapid changes in myocardial intracellular Na+ (Na-i(+)) during ischemia and reperfusion (R), Na-23 magnetic resonance imaging (MRI) appears to be an ideal diagnostic modality for early detection of myocardial ischemia and viability. So far, cardiac Na-23 MRI data are limited and mostly concerned with imaging of total Na+. For proper interpretation, imaging of both Na-i(+) and extracellular Na+ is essential. In this study, we tested whether Na-i(+) imaging can be used to assess viability after low-flow (LF) ischemia.Methods and Results - Isolated rat hearts were subjected to LF (1%, 2%, or 3% of control coronary flow) and R. A shift reagent was used to separate Na-i(+) and extracellular Na+ resonances. Acquisition-weighted Na-23 chemical shift imaging (CSI) was alternated with Na-23 MR spectroscopy. Already during control perfusion, Na-i(+) could be clearly seen on the images. Na-i(+) image intensity increased with increasing severity of ischemia. During R, Na-i(+) image intensity remained highest in 1% LF hearts. Not only did we find very good correlations between Na-i(+) image intensity at end-R and end-diastolic pressure ( R = 0.85, P <0.001) and recovery of the rate-pressure product ( R = - 0.88, P <0.001) at end-R, but most interestingly, also Na-i(+) image intensity at end-LF was well correlated with end-diastolic pressure ( R = 0.78, P <0.01) and with recovery of the rate-pressure product ( R = - 0.81, P <0.01) at end-R. Furthermore, Na-i(+) image intensity at end-LF was well correlated with creatine kinase release during R ( R = 0.79, P <0.05) as well as with infarct size ( R = 0.77, P <0.05).Conclusions - These data indicate that Na-23 CSI is a promising tool for the assessment of myocardial viability.