Comparison of maximal myocardial blood flow during adenosine infusion with that of intravenous dipyridamole in normal men

AbstractObjective. This study compared quantitatively the efficacy of intravenous adenosine and dipyridamole for pharmacologic induction of myocardial hyperemia.Background. Pharmacologic vasodilation is used increasingly for induction of myocardial hyperemia in conjunction with radionuclide imaging of myocardial blood flow. Although both intravenous dipyridamole and adenosine have been used, the magnitude of hyperemia induced by these agents and the hyperemia to baseline blood flow ratios have not been quantified and compared.Methods. Twenty normal volunteers were studied with dynamic positron emission tomography (PET) and intravenous nitrogen-13 ammonia. Myocardial blood flow was quantified with a two-compartment tracer kinetic model.Results. Myocardial blood flow at rest averaged 1.1 ± 0.2 ml/min per g and increased significantly to 4.4 ± 0.9 ml/min per g during adenosine and 43 ± 1.3 ml/min per g after dipyridamole administration. Hyperemia to baseline flow ratios averaged 4.3 ± 1.6 for adenosine and 4.0 ± 1.3 for dipyridamole. The average flow ratios and the maximal flows achieved were similar for both agents, but there was considerable variation in the individual response to these agents, as indicated by the range of hyperemia to baseline flow ratios (from 2.0 to 8.4 for adenosine and from 1.5 to 5.8 for dipyridamole). in addition, the hyperemic responses to dipyridamole and to adenosine differed by > 1 ml/min per g in nine subjects.Conclusions. Despite these inter- and istraindividual differences, we conclude that both agents are equally effective in producing myocardial hyperemia

On Using Feedforward Neural Networks for Clinical Diagnostic Tasks

In this paper we present an extensive comparison between several feedforward neural network types in the context of a clinical diagnostic task, namely the detection of coronary artery disease (CAD) using planar thallium-201 dipyridamole stress-redistribution scintigrams. We introduce results from well-known (e.g. multilayer perceptrons or MLPs, and radial basis function networks or RBFNs) as well as novel neural network techniques (e.g. conic section function networks) which demonstrate promising new routes for future applications of neural networks in medicine, and elsewhere. In particular we show that initializations of MLPs and conic section function networks---which can learn to behave more like an MLP or more like an RBFN---can lead to much improved results in rather difficult diagnostic tasks. Keywords: Feedforward neural networks, neural network initialization, multilayer perceptrons, radial basis function networks, conic section function networks; thallium scintigraphy, angiog..

Safety of Concomitant Potassium-sparing Diuretics in Angiotensin-converting Enzyme-inhibitor Therapy in Severe Congestive-heart-failure

The safety of concomitant use of angiotensin-converting enzyme (ACE) inhibitors and potassium-sparing diurectics (PSD) in severe heart failure remains a controversial issue. The database of the recently reported double-blind international trial, ''Xamoterol in Severe Heart Failure,'' was investigated to elucidate this question. Of 516 patients with New York Heart Association (NYHA) class III-IV, despite diuretics and ACE inhibitor therapy, 352 were randomized to xamoterol, a beta(1) partial agonist, and 164 were randomized to placebo. During the 13-week study, 28% of all patients (xamoterol, 104; placebo, 42) received potassium-sparing diuretics. All groups were comparable in hemodynamics and dose of other diuretics. At study end, patients with or without PSD showed no significant differences in serum K+ or creatinine, independent of xamoterol or placebo therapy

Assessment of myocardial viability by dobutamine echocardiography, positron emission tomography and thallium-201 SPECT Correlation with histopathology in explanted hearts

AbstractObjectives. We examined the relationship among viability assessment by dobutamine echocardiography (DE), positron emission tomography (PET) and thallium-201 single-photon emission computed tomography (Tl-SPECT) to the degree of fibrosis.Background. DE, PET and Tl-SPECT have been shown to be sensitive in identifying viability of asynergic myocardium. However, PET and Tl-SPECT indicated viability in a significant percentage of segments without dobutamine response or functional improvement after revascularization.Methods. Twelve patients with coronary artery disease and severely reduced left ventricular function (EF 14.5 ± 5.2%) were studied with DE prior to cardiac transplantation: 5 had additional PET and 7 had Tl-SPECT studies. Results of the three techniques were compared to histologic findings of the explanted hearts.Results. Segments with >75% viable myocytes by histology were determined to be viable in 78%, 89% and 87% by DE, PET and Tl-SPECT; those with 50–75% viable myocytes in 71%, 50% and 87%, respectively. Segments with 25–50% viable myocytes showed response to dobutamine in only 15%, but were viable in 60% by PET and 82% by Tl-SPECT. Segments with <25% viable myocytes responded to dobutamine in 19%; however, PET and Tl-SPECT demonstrated viability in 33% and 38%, respectively. Discrepant segments without dobutamine response but viability by PET and SPECT had significantly more viable myocytes by pathology than did those classified in agreement to be nonviable but had significantly less viable myocytes than those classified in agreement to be viable (p < .001).Conclusions. These findings suggest that contractile reserve as evidenced by a positive dobutamine response requires at least 50% viable myocytes in a given segment whereas scintigraphic methods also identify segments with less viable myocytes. Thus, the methods may provide complementary information: Nuclear techniques appear to be highly sensitive for the detection of myocardial viability, and negative tests make it highly unlikely that a significant number of viable myocytes are present in a given segment. Conversely, dobutamine echo may be particularly useful for predicting recovery of systolic function after revascularization