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Myocardial Oxidative Metabolism in Remote Normal Regions in the Left Ventricles with Remodeling After Myocardial Infarction: Effect of ß-Adrenoceptor Blockers

¹ Third Department of Internal Medicine, Nagoya City University Medical School, Nagoya, Japan
² Department of Cardiology and Radiology, Nagoya City Rehabilitation and Sports Center, Nagoya, Japan

In patients with myocardial infarction (MI), an expansion of the remote normal regions of the left ventricle is often observed. However, the characteristics of such regions are not fully understood. Thus, we investigated this issue from the standpoint of myocardial oxidative metabolism using ¹¹C-acetate PET. Methods: In 33 patients with recent MI (24 not receiving ß-blockers, 9 receiving ß-blockers) and 12 age-matched normal control subjects, ¹¹C-acetate dynamic myocardial PET scanning was performed at rest. Time-activity curves of ¹¹C-acetate in 5–7 regions of interest (ROIs) on the midventricular transaxial image in each subject were generated, and the clearance rate constant (K_mono) in each ROI was calculated by monoexponential fitting as an index of myocardial oxidative metabolism. The left ventricular (LV) end-diastolic volume index as an index of LV remodeling and the heart rate · pressure product were obtained in all subjects. Results: The LV end-diastolic volume index was significantly larger in patients with MI without ß-blockers than in normal control subjects (101 ± 22.5 vs. 61.6 ± 12.8 mL · m^-2; P < 0.001). There was no significant difference in the heart rate · pressure product between the patients with MI without ß-blockers and the normal control subjects (8,229 ± 1,503 vs. 8,311 ± 1,311 mm Hg · min^-1). The K_mono in remote normal regions was significantly greater in patients with MI without ß-blockers even when compared with the highest K_mono on the anteroseptal wall of the left ventricle in normal control subjects (0.078 ± 0.022 vs. 0.065 ± 0.007 min^-1; P < 0.01). In contrast, the heart rate · pressure product (6,911 ± 1,135 mm Hg · min^-1) and the K_mono (0.054 ± 0.009 min^-1) in remote normal regions were significantly less in patients with ß-blockers than in those without ß-blockers (P < 0.001). No significant difference in the LV end-diastolic volume index was found between the MI patients with and without ß-blockers. Multivariate regression analysis showed that ß-blockers significantly and directly decreased the K_mono in remote normal regions after adjusting the effect of the heart rate · pressure product, although the prime determinant of the K_mono in such regions was the heart rate · pressure product. Conclusion: Myocardial oxidative metabolism in remote normal regions is accelerated in the left ventricles with remodeling after acute MI. Therapy using ß-blockers normalizes the myocardial oxidative metabolism in such regions through the reduction of the heart rate · pressure product and their direct effect on the myocardium.

Key Words: acetate • ß-blocker • myocardial infarction • PET • remodeling

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