A gating ³¹P NMR method triggered by pulses for cardiac pacing

Abstract

A new gating NMR technique triggered by pulses for the cardiac pacing of isolated, perfused rat heart is described. This technique is suitable for obtaining spectra at the same positions over the cardiac cycle with the same RF pulse repetition time and with constant heart rate. Accordingly, each recovered magnetization level at these positions during the cycle can be kept constant. It also allows a qualitative analysis of the myocardial energy level during the cycle under the condition of the same or different cardiac workload (rate pressure product, HR x LVP). This method was used to observe cyclical changes in the concentration of adenosine triphosphate (ATP), phosphocreatine (PCr), P(i), and in pH during the cardiac cycle, and confirmed that the levels of ATP and PCr showed reversible decreases, and P(i) showed an antiphasic increase at the peak systole. On the other hand, no significant changes in pH were noted during the cardiac cycle. This pacing-gated technique is an improvement over other gated NMR techniques triggered by the blood pressure or by ECG traces.

Cyclical Changes in High-Energy Phosphates During the Cardiac Cycle by Pacing-Gated 31P Nuclear Magnetic Resonance

“…The peak height of the extracellular Pi was nearly constant during the experiment. 10 In the present experiments, a splitting of the Pi peak was not observed because of low S:N ratios and because of the saturation effect using short repetition time. The chemical shift of the observed Pi peak and pH that was obtained by comparing the chemical shift of Pi peak relative to PCr almost agreed with that obtained by the intracellular Pi peak.…”

“…Details of the pacing-gated 31 P NMR techniques have been described elsewhere. 10 Fig 1 shows a schematic diagram of time between the RF pulse and the pacing pulse used. During this method, the NMR observation RF pulse was triggered by the pulses for cardiac pacing.…”

“…Under the condition of short repetition time, almost the same relative cyclical changes in ATP, PCr, and Pi were noted during the cycle as were seen when the long repetition time was used. 10 Accordingly, the saturation effects were not corrected because relative metabolite levels were also expressed as a ratio of peak area. When the long repetition time was used, a splitting of the Pi peak was observed because of the chemical shift difference between the intracellular Pi and the extracellular Pi from the buffer.…”

“…Cyclical changes in the concentration of adenosine triphosphate (ATP), phosphocreatine (PCr), and inorganic phosphate (Pi) during the cardiac cycle have also been studied using the subject's blood pressure or electrocardiogram (ECG)-gated 31 P NMR techniques. Several studies have demonstrated that cyclical changes in ATP, PCr, and Pi arise in vitro [8][9][10] and in vivo 11 in rat hearts. However, some investigators have not observed any cyclical changes in energy-related phosphate levels in in vitro 12 and in vivo 5,[13][14][15] hearts.…”

“…10 This is a suitable method for determining cyclical changes in energy-related phosphate compounds in the cardiac cycle because the heart rate and the RF pulse repetition time maintain a constant relationship with pacing. The purpose of the present study was to determine whether cyclical changes in energy-related phosphate levels arise during the cardiac cycle in isolated rat hearts and are affected by differences in myosin isozyme composition.…”