Abstract

The ability to measure myocardial blood flow (MBF) offers significant advantages in interpreting the phenomena underlying myocardial ischemia. Nuclear cardiology using hybrid positron emission tomography/computed tomography (PET/CT) systems allows accurate measurement of MBF using noninvasive techniques. Short- or very short-lived radiopharmaceuticals are now available, as well as standardized analytical models and software for clinical use. The incremental value of quantitative measurement of MBF in the pathophysiologic assessment of ischemic heart disease compared with anatomic variables or qualitative or semi-quantitative assessment by single-photon emission computed tomography (SPECT) with gamma-emitting tracers will be analyzed. The clinical role of MBF, myocardial flow reserve (MFR), and coronary flow capacity (CFC) will be clarified. However, the widespread availability of this technology is limited by the need for on-site cyclotron tracer production or the purchase of expensive radionuclide generators. The ability to obtain quantitative measurements using newer SPECT with cadmium-zinc-telluride technology and technetium-labeled tracers may offer the possibility of extending MBF measurement to most nuclear cardiology units in the near future.

OBJECTIVE: To study the quantitative changes in intramyocardial blood vessels in rats in whom nitric oxide synthesis was inhibited. METHODS: Four groups of 10 rats were studied: control (C25 and C40) and L-NAME (L25 and L40). The animals L25 and L40 received L-NAME in the dosage of 50mg/kg/day for 25 and 40 days, respectively. On days 26 and 41 the animals in groups 25 and 40 were sacrificed. Analysis of the myocardium was performed using light microscopy and stereology. RESULTS: Arterial blood pressure and heart weight increased 74.5 and 57.8% after 25 days and 90.2 and 34.6% after 40 days, respectively. Comparing the L-NAME rats with the respective controls revealed that vessel volume density decreased 31.3% after 40 days, and the vessel length-density decreased 53.5% after 25 days and 25.7% after 40 days. The mean cross-sectional area of the vessels showed an important reduction of 154.6% after 25 days. The intramyocardial vessels decreased significantly in length- density in the L-NAME animals. The mean cross-sectional area of the vessels, which normally increases during heart growth between 25 and 40 days, showed a precocious increase by the 25th day in the L-NAME rats. This suggests an increase of the size of the heart, including blood vessels. CONCLUSION: The inhibition of the NO synthesis provokes rarefaction in the intramyocardial vessels that progresses with the time of administration of L-NAME.