Myocardial blood flow and metabolism in patients with hypertrophic cardiomyopathy--a study with carbon-11 acetate and positron emission tomography

Myocardial radionuclide imaging in patients with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is defined as a primary and familial cardiac disorder characterized by heterogeneous expression, unique pathophysiology and considerable diversity in clinical presentation. Clinical diagnosis was mainly based on the performance of ECG. In addition, cardiovascular MRI or ECG plays an important role in the diagnosis. Nevertheless, myocardial radionuclide imaging, which could provide detailed information on myocardial perfusion, metabolism and neurological function, is a valuable method for exploring the inter-relationship between the morphological, pathophysiological and functional changes in hypertrophic cardiomyopathy. It is also helpful in evaluating the effect of transcoronary ethanol septal ablation and prognosis in patients with hypertrophic cardiomyopathy, which suggests that it is an important imaging method in the comprehensive evaluation of hypertrophic cardiomyopathy.

Development of PET radiopharmaceuticals and their clinical applications at the Positron Medical Center

The Positron Medical Center has developed a large number of radiopharmaceuticals and 36 radiopharmaceuticals have been approved for clinical use for studying aging and geriatric diseases, especially brain functions. Positron emission tomography (PET) has been used to provide a highly advanced PET-based diagnosis. The current status of the development of radiopharmaceuticals, and representative clinical and methodological results are reviewed.

Determinants of myocardial energetics and efficiency in symptomatic hypertrophic cardiomyopathy

PURPOSE

Next to hypertrophy, hypertrophic cardiomyopathy (HCM) is characterized by alterations in myocardial energetics. A small number of studies have shown that myocardial external efficiency (MEE), defined by external work (EW) in relation to myocardial oxidative metabolism (MVO(2)), is reduced. The present study was conducted to identify determinants of MEE in patients with HCM by use of dynamic positron emission tomography (PET) and cardiovascular magnetic resonance imaging (CMR).

METHODS

Twenty patients with HCM (12 men, mean age: 55.2 + or - 13.9 years) and 11 healthy controls (7 men, mean age: 48.1 + or - 10 years) were studied with [(11)C]acetate PET to assess MVO(2). CMR was performed to determine left ventricular (LV) volumes and mass (LVM). Univariate and multivariate analyses were employed to determine independent predictors of myocardial efficiency.

RESULTS

Between study groups, MVO(2) (controls: 0.12 + or - 0.04 ml x min(-1) x g(-1), HCM: 0.13 + or - 0.05 ml x min(-1) x g(-1), p = 0.64) and EW (controls: 9,139 + or - 2,484 mmHg x ml, HCM: 9,368 + or - 2,907 mmHg x ml, p = 0.83) were comparable, whereas LVM was significantly higher (controls: 99 + or - 21 g, HCM: 200 + or - 76 g, p < 0.001) and MEE was decreased in HCM patients (controls: 35 + or - 8%, HCM: 21 + or - 10%, p < 0.001). MEE was related to stroke volume (SV), LV outflow tract gradient, NH(2)-terminal pro-brain natriuretic peptide (NT-proBNP) and serum free fatty acid levels (all p < 0.05). Multivariate analysis revealed that SV (ss = 0.74, p < 0.001) and LVM (ss = -0.43, p = 0.013) were independently related to MEE.

CONCLUSION

HCM is characterized by unaltered MVO(2), impaired EW generation per gram of myocardial tissue and subsequent deteriorated myocardial efficiency. Mechanical external efficiency could independently be predicted by SV and LVM.

Myocardial perfusion and sympathetic innervation in patients with hypertrophic cardiomyopathy

OBJECTIVES

This study assessed left ventricular myocardial perfusion and sympathetic innervation and function in hypertrophied and nonhypertrophied myocardial regions of patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Patients with HCM often have clinical findings consistent with increased cardiac sympathetic outflow. Little is known about the status of sympathetic innervation specifically in hypertrophic regions.

METHODS

We conducted positron emission tomographic (PET) scanning using the perfusion imaging agent 13N-ammonia (13NH3) and the sympathoneuronal imaging agent 6-[18F]-fluorodopamine (18F-FDA) in 8 patients with HCM and 15 normal volunteers. Positron emission tomographic data corrected for attenuation and the partial volume effect were analyzed using the region-of-interest technique.

RESULTS

Myocardial 13NH3-derived radioactivity was similar in hypertrophied and nonhypertrophied regions of patients with HCM and in normal volunteers. At all time points, the 18F:13N ratio was lower in hypertrophied than in nonhypertrophied regions of HCM patients and in the septum of normal volunteers (p = 0.001). Trends in 18F-FDA-derived radioactivity over time were normal in both hypertrophied and nonhypertrophied myocardium.

CONCLUSIONS

The results are consistent with decreased neuronal uptake of catecholamines in hypertrophied but not in nonhypertrophied myocardium of patients with HCM. Other aspects of cardiac sympathoneural function seem normal. Decreased neuronal uptake could reflect local relative hypoinnervation, decreased numbers of neuronal uptake sites, or metabolic limitations on cell membrane transport. By enhancing norepinephrine delivery to adrenoceptors for a given amount of sympathetic nerve traffic, decreased neuronal uptake can explain major clinical features of HCM.

BMIPP compared with PET metabolism

I-123 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (BMIPP) was introduced as an approved radiopharmaceutical in Japan in 1993. This article reviews our clinical comparisons between BMIPP and PET metabolism conducted at Kyoto University. BMIPP uptake was suggested to reflect exogenous fatty acid utilization in the myocardium. By the comparison between FDG PET and BMIPP SPECT, reduced uptake of BMIPP relative to thallium was considered metabolically damaged but viable myocardium in ischemic coronary artery disease. In hypertrophic cardiomyopathy, reduction of BMIPP uptake was shown to precede suppression of oxidative or glucose metabolism. Occasionally we encounter subjects with absent myocardial BMIPP uptake. The majority of these subjects showed metabolic switching from normal free fatty acid metabolism to abnormally enhanced glucose metabolism in the fasting state. Thus, BMIPP provides us with the valuable metabolic information which is unattainable using a perfusion tracer.