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Regional myocardial blood flow and glucose utilization in symptomatic patients with hypertrophic cardiomyopathy
C A Nienaber1, S S Gambhir, F V Mody
1Department of Radiological Sciences, UCLA School of Medicine, Los Angeles, CA 90024.
Insights
Symptomatic hypertrophic cardiomyopathy patients show myocardial ischemia, indicated by reduced blood flow and normal glucose utilization. This blood flow-metabolism mismatch is more pronounced in younger individuals, suggesting age-related differences in disease severity.
Area of Science:
- Cardiology
- Nuclear Medicine
- Medical Imaging
Background:
- Previous studies indicated myocardial ischemia in symptomatic hypertrophic cardiomyopathy (HCM).
- Positron emission tomography (PET) allows noninvasive measurement of myocardial blood flow and glucose metabolism.
- This technique is suitable for detecting altered glucose utilization in HCM, aiding pathomechanism elucidation.
Purpose of the Study:
- To investigate myocardial blood flow and glucose metabolism in symptomatic patients with hypertrophic cardiomyopathy.
- To determine if quantitative PET imaging can identify ischemia and its relation to metabolism in HCM.
- To explore the pathomechanism of ischemia in hypertrophic cardiomyopathy.
Main Methods:
- Utilized positron emission tomography with N-13-ammonia and F-18 deoxyglucose.
- Measured regional myocardial blood flow and glucose utilization at rest and during exercise in 13 HCM patients.
- Compared flow and metabolism in hypertrophied versus normal myocardium.
Main Results:
- At rest, hypertrophied myocardium showed significantly lower blood flow (0.78 mL/min/g) than normal myocardium (0.99 mL/min/g).
- Glucose utilization rates were similar between hypertrophied and normal myocardium at rest.
- Blood flow-metabolism mismatches, indicative of ischemia, were observed in three patients at rest and three of four during exercise, characterized by reduced flow with maintained glucose uptake.
- This disparity was more pronounced in younger patients.
Conclusions:
- Diminished blood flow with normal/elevated glucose utilization suggests myocardial ischemia in symptomatic HCM.
- The age-dependent disparity indicates differences in pathophysiology or disease severity.
- Quantitative PET imaging is valuable for assessing ischemia in hypertrophic cardiomyopathy.
Background:
Previous studies suggested the presence of myocardial ischemia in symptomatic patients with hypertrophic cardiomyopathy. Positron emission tomography, a technique that can identify metabolic consequences of ischemia in coronary artery disease, permits the noninvasive measurements of regional myocardial blood flow and glucose metabolism. This new quantitative imaging approach should therefore be suitable for detecting a possible enhancement of glucose utilization in myocardium of patients with hypertrophic cardiomyopathy and thus may help to elucidate the pathomechanism of ischemia in this disease.
Methods And Results:
In 13 symptomatic patients with hypertrophic cardiomyopathy, myocardial blood flow and glucose utilization were measured with intravenous N-13-ammonia and F-18 deoxyglucose at rest and, in four patients, again during supine bicycle exercise. At rest, blood flow was significantly lower in hypertrophied than in normal myocardium (0.78 +/- 0.19 versus 0.99 +/- 0.13 mL.min-1.g-1, p < 0.025), whereas rates of glucose utilization were similar (0.88 +/- 0.31 versus 0.87 +/- 0.35 mumol.min-1.g-1). With exercise, blood flow and glucose utilization failed to increase in hypertrophic and normal segments but became more heterogeneously distributed throughout the left ventricular myocardium. Blood flow-metabolism mismatches indicative of myocardial ischemia were noted in three patients at rest and in three of the four patients during exercise and were due to reduced flow in the presence of maintained glucose uptake. The discordance between flow and glucose metabolism in hypertrophied myocardium was significantly more prominent in younger than in older patients.
Conclusions:
Normal or even elevated rates of glucose utilization and the presence of diminished blood flow in hypertrophied relative to normal myocardium suggest the presence of myocardial ischemia in symptomatic hypertrophic cardiomyopathy. The age dependence of blood flow metabolism disparity suggests differences in the underlying pathophysiology or severity of disease.