In patients with acute myocardial infarction, routine implantation of a stent has clinical benefits beyond those of primary coronary angioplasty alone.

Bioenergetic abnormalities in remodeled myocardium are related to the severity of LV dysfunction, which, in turn, is dependent on the severity of the initiating myocardial infarction.

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This study examined whether alterations in myocardial creatine kinase (CK) kinetics and high-energy phosphate (HEP) levels occur in postinfarction left ventricular remodeling (LVR). Myocardial HEP and CK kinetics were examined in 19 pigs 6 wk after myocardial infarction was produced by left circumflex coronary artery ligation, and the results were compared with those from 9 normal pigs. Blood flow (microspheres), oxygen consumption (MV˙o 2), HEP levels [31P magnetic resonance spectroscopy (MRS)], and CK kinetics (31P MRS) were measured in myocardium remote from the infarct under basal conditions and during dobutamine infusion (20 μg ⋅ kg−1 ⋅ min−1iv). Six of the pigs with LVR had overt congestive heart failure (CHF) at the time of study. Under basal conditions, creatine phosphate (CrP)-to-ATP ratios were lower in all transmural layers of hearts with CHF and in the subendocardium of LVR hearts than in normal hearts ( P < 0.05). Myocardial ATP (biopsy) was significantly decreased in hearts with CHF. The CK forward rate constant was lower ( P < 0.05) in the CHF group (0.21 ± 0.03 s−1) than in LVR (0.38 ± 0.04 s−1) or normal groups (0.41 ± 0.03 s−1); CK forward flux rates in CHF, LVR, and normal groups were 6.4 ± 2.3, 14.3 ± 2.1, and 20.3 ± 2.4 μmol ⋅ g−1 ⋅ s−1, respectively ( P < 0.05, CHF vs. LVR and LVR vs. normal). Dobutamine caused doubling of the rate-pressure product in the LVR and normal groups, whereas CHF hearts failed to respond to dobutamine. CK flux rates did not change during dobutamine in any group. The ratios of CK flux to ATP synthesis (from MV˙o 2) under baseline conditions were 10.9 ± 1.2, 8.03 ± 0.9, and 3.86 ± 0.5 for normal, LVR, and CHF hearts, respectively (each P < 0.05); during dobutamine, this ratio decreased to 3.73 ± 0.5, 2.58 ± 0.4, and 2.78 ± 0.5, respectively ( P = not significant among groups). These data demonstrate that CK flux rates are decreased in hearts with postinfarction LVR, but this change does not limit the response to dobutamine. In hearts with end-stage CHF, the changes in HEP and CK flux are more marked. These changes could contribute to the decreased responsiveness of these hearts to dobutamine.

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To investigate the dynamic control of cardiac ATP synthesis, we simultaneously determined the time course of mitochondrial oxygen consumption with the time course of changes in high-energy phosphates following steps in cardiac energy demand. Isolated isovolumically contracting rabbit hearts were perfused with Tyrode's solution at 28°C (n=7) or at 37°C (n=7). Coronary arterial and venous oxygen tensions were monitored with fast-responding oxygen electrodes. A cyclic pacing protocol in which we applied 64 step changes between two different heart rates was used. This enabled nuclear magnetic resonance measurement of the phosphate metabolites with a time resolution of =2 seconds. Oxygen consumption changed after heart-rate steps with time constants of 14±1 (mean±SEM) seconds at 28°C and 11±1 seconds at 37°C, which are already corrected for diffusion and vascular transport delays. Doubling of the heart rate resulted in a significant decrease in phosphocreatine (PCr) in inorganic phosphate (Pi) content, although oxygen supply was shown to be nonlimiting. The time constants for the change of both Pi and PCr content, =5 seconds at 28°C and 2.5 seconds at 37°C, are significantly smaller than the respective time constants for oxygen consumption. The changes in phosphate metabolites during changes in oxygen consumption suggest that regulation of oxidative phosphorylation could occur partly via products of ATP hydrolysis, but the unequal time constants of PCr and oxygen consumption suggest that other regulatory mechanisms also play a role. These dissimilar time constants further suggest that there might be an appreciable transient contribution of nonaerobic, presumably glycolytic, ATP synthesis to buffer the high-energy phosphates during fast transitions in cardiac work. (Circ Res. 1994;75: 751-759.) Key Words * myocardial energy metabolism * rabbit hearts * mitochondrial control * 31P nuclear magnetic resonance spectroscopy * oxidative phosphorylation changes in high-energy phosphates and Pi despite increases in myocardial oxygen consumption suggested that the phosphate metabolites may not be the primary regulators of cardiac mitochondrial respiration.The absence of a change in ATP or phosphocreatine (PCr) after a change in metabolic demand would also mean that mitochondrial ATP production and hence oxygen consumption must adapt immediately to a change in cytosolic ATP hydrolysis. In the isolated perfused rabbit heart, this is not the case, because oxygen consumption adapts to a new work load with a mean response time of at least 6 seconds.

During moderate reductions of blood flow, the myocardium downregulates contractile function and ATP utilization to result in reduced but stable ATP levels, recovery or stability of (reduced) creatine phosphate (CP), and preservation of myocyte viability. The intent of this study was to determine the influence of the level of ischemic blood flow and the major determinants of myocardial O2 consumption (MVO2) (heart rate and systolic blood pressure) on recovery of CP during prolonged moderate myocardial hypoperfusion. 31P-nuclear magnetic resonance spectroscopy was used to measure CP, ATP, and Pi in the subepicardium (Epi) and subendocardium (Endo) of 13 open-chest dogs. Wall thickening was measured with sonomicrometry. A coronary stenosis reduced mean myocardial blood flow (microspheres) from 1.10 +/- 0.07 to 0.71 +/- 0.06 ml.g-1.min-1 (P < 0.01) and the Endo-to-Epi blood flow ratio from 1.12 +/- 0.07 to 0.59 +/- 0.06 (P < 0.01), and dyskinesis developed. Coronary blood flow and systolic wall thickening did not change significantly during 4 h of hypoperfusion. Epi CP and ATP fell to 80 +/- 4% (P < 0.05) and 93 +/- 3% of control, respectively, at 30 min. Epi CP then recovered to 87 +/- 5% while ATP decreased further to 83 +/- 5% of baseline by the end of the 240-min ischemic period. Endo CP and ATP fell to 53 +/- 4 and 77 +/- 5% of control, respectively, at 30 min; then Endo CP recovered to 85 +/- 6% while ATP decreased further to 68 +/- 6% of baseline at 240 min of hypoperfusion. ADP levels were significantly increased at 30 min but recovered to baseline by 240 min of hypoperfusion. delta Pi/CP increased significantly (Endo > Epi) at the onset of ischemia and then progressively decreased. At 30 min, mild myocardial acidosis was observed in some hearts with variable pH recovery during continuing hypoperfusion. The data demonstrate that variations in blood flow cannot account for the magnitude of the initial fall in CP or for the final extent of recovery. However, the rate at which CP recovered was significantly correlated with the level of blood flow. Variations in the determinants of MVO2 did not account for differences in CP recovery.