An approach to ventricular efficiency by use of carbon 11-labeled acetate and positron emission tomography

Left ventricular metabolism, function, and sympathetic innervation in men and women with type 1 diabetes

BACKGROUND

In type I diabetes (T1DM), alterations in LV function may occur due to changes in innervation, metabolism, and efficiency.

OBJECTIVES

We evaluated the association between sympathetic nerve function, oxidative metabolism, resting blood flow, LV efficiency and function in healthy diabetics, and assessed gender differences.

METHODS

Cross-sectional study of 45 subjects with T1DM, 60% females, age 34 ± 13 years, and 10 age-matched controls. Positron emission tomography (PET) imaging with [(11)C]acetate and [(11)C]meta-hydroxyephedrine was performed, in addition to cardiac magnetic resonance imaging.

RESULTS

There were no significant differences in LV function, innervation, or oxidative metabolism between T1DM and controls. Cardiac oxidative metabolism was positively associated with higher levels of sympathetic activation, particularly in women. Diabetic women had significantly lower efficiency compared with diabetic men. Resting flow was significantly higher in diabetic women compared with diabetic men, and tended to be higher in female controls as well.

CONCLUSIONS

Measures of myocardial function, metabolism, blood flow, and sympathetic activation were preserved in young, otherwise healthy, T1DM patients. However, T1DM women presented with greater myocardial oxidative metabolism requirements than men. Ongoing studies are evaluating changes over time.

[¹¹C]acetate PET/CT visualizes skeletal muscle exercise participation, impaired function, and recovery after hip arthroplasty; first results

Purpose

Based on skeletal muscle acetate physiology we aimed studying muscle function after hip arthroplasty with [¹¹C]acetate PET.

Procedures

Two male patients were investigated 3 and 12 weeks after hip arthroplasty with muscle [¹¹C]acetate PET/CT performed at rest and exercise. Median muscle SUV_mean were calculated on three non-consecutive transverse PET slices.

Results

The four exercise PET/CT showed, compared with rest, consistent increase in [¹¹C]acetate uptake in active muscles contralateral to surgery. On the arthroplasty side most muscles showed symmetric activity increase under exercise both at 3 and 12 weeks after surgery, but four muscles showed only minor activity increase at 3 weeks. At 3 months, functional recovery of the latter four muscles was observed.

Conclusion

Consistent increase in [¹¹C]acetate uptake in healthy muscles under exercise compared with rest was observed by PET/CT. Transiently impaired muscle function 3 weeks after surgery recovered at 3 months. These first observations merit further investigation.

The effects of beta(1)-blockade on oxidative metabolism and the metabolic cost of ventricular work in patients with left ventricular dysfunction: A double-blind, placebo-controlled, positron-emission tomography study

BACKGROUND

The mechanism for the beneficial effect of beta-blocker therapy in patients with left ventricular (LV) dysfunction is unclear, but it may relate to an energy-sparing effect that results in improved cardiac efficiency. C-11 acetate kinetics, measured using positron-emission tomography (PET), are a proven noninvasive marker of oxidative metabolism and myocardial oxygen consumption (MVO(2)). This approach can be used to measure the work-metabolic index, which is a noninvasive estimate of cardiac efficiency.

METHODS AND RESULTS

The aim of this study was to determine the effect of metoprolol on oxidative metabolism and the work-metabolic index in patients with LV dysfunction. Forty patients (29 with ischemic and 11 with nonischemic heart disease; LV ejection fraction <40%) were randomized to receive metoprolol or placebo in a treatment protocol of titration plus 3 months of stable therapy. Seven patients were not included in analysis because of withdrawal from the study, incomplete follow-up, or nonanalyzable PET data. The rate of oxidative metabolism (k) was measured using C-11-acetate PET, and stoke volume index (SVI) was measured using echocardiography. The work-metabolic index was calculated as follows: (systolic blood pressure x SVI x heart rate)/k. No significant change in oxidative metabolism occurred with placebo (k=0.061+/-0.022 to 0.054+/-0.012 per minute). Metoprolol reduced oxidative metabolism (k=0.062+/-0. 024 to 0.045+/-0.015 per minute; P:=0.002). The work-metabolic index did not change with placebo (from 5.29+/-2.46 x 10(6) to 5.14+/-2. 06 x 10(6) mm Hg. mL/m(2)), but it increased with metoprolol (from 5. 31+/-2.15 x 10(6) to 7.08+/-2.36 x 10(6) mm Hg. mL/m(2); P:<0.001).

CONCLUSIONS

Selective beta-blocker therapy with metoprolol leads to a reduction in oxidative metabolism and an improvement in cardiac efficiency in patients with LV dysfunction. It is likely that this energy-sparing effect contributes to the clinical benefits observed with beta-blocker therapy in this patient population.

Assessment of myocardial viability by use of 11C-acetate and positron emission tomography. Threshold criteria of reversible dysfunction

BACKGROUND

Dual positron emission tomography (PET) imaging with a perfusion tracer and 18F-fluorodeoxyglucose (FDG) can detect myocardial viability. This approach may be replaced by a single 11C-acetate study, which enables quantification of both regional blood flow and oxidative metabolism. The significance of acetate-derived indexes for myocardial viability is examined.

METHODS AND RESULTS

Thirty postinfarct patients with akinetic ventricular segments, a mean ejection fraction of 42 +/- 11%, and high-grade coronary obstructions were studied with serial 11C-acetate PET scanning before and 7 +/- 5 months after coronary revascularization. Acetate PET was tested against FDG and serial assessments of segmental wall motion. Sixty of 155 severely dysfunctional LV segments improved postoperatively, and regional blood flow increased. Flow estimates after revascularization suggested little fibrosis in reversible segments. At baseline, blood flows differed between normal myocardium, reversible dysfunction, and irreversible dysfunction (1.04 +/- 0.27, 0.73 +/- 0.18, and 0.43 +/- 0.18 mL.min-1.g-1, respectively; P < .001). Oxidative metabolic rates were reduced only in irreversibly injured LV segments. Multivariate analysis identified the acetate perfusion index as the only independent predictor of postoperative recovery. Its predictive accuracy was similar to that of FDG imaging but superior to indexes of flow-metabolic mismatch or oxidative metabolism.

CONCLUSIONS

After myocardial infarction, quantitative indexes of perfusion and oxidative metabolism from acetate PET indicate a critical threshold beyond which tissue is irreversibly injured. Findings support the use of blood flow as a marker of myocardial viability in chronic postinfarct patients with modestly reduced ejection fractions.