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An asymptomatic 21 year old man with non-obstructive hypertrophic cardiomyopathy (HCM) was referred for radionuclide myocardial perfusion imaging for risk assessment.
Adenosine was infused at 140 μg/kg/min over six minutes with submaximal bicycle exercise and thallium-201 (80 MBq) was injected intravenously at three minutes. Stress images were acquired five minutes after injection and rest images one hour after subsequent resting injection of thallium-201 (40 MBq). Conventional emission tomographic imaging techniques were used.
The stress images (left hand panel) show inhomogeneity of tracer uptake in the septum but septal hypertrophy is not obvious and the images might be interpreted as normal. The rest images (right hand panel), however, show that the septum is hypertrophied with high tracer uptake. The ratio of counts in the septum and lateral walls reverses between the stress and rest images. The overall appearance is of a severe inducible perfusion abnormality in the hypertrophied septum, and this is presumably related to impaired perfusion reserve in the region of hypertrophy rather than obstructive coronary disease.
Risk assessment for sudden cardiac death is an integral part of the management of HCM. A high incidence of fixed and inducible perfusion abnormalities has been reported and these may lead to chest pain. However, the association between inducible ischaemia and sudden cardiac death is uncertain. Because stress uptake of tracer may appear normal in a region of hypertrophy, even if there is relative hypoperfusion, stress and rest images should always be compared in patients with known or suspected HCM who undergo radionuclide myocardial perfusion imaging.