The acute effects of intravenously administered L-acetylcarnitine (LAC) were evaluated with single-photon emission computed tomography (SPECT) and 99mTc-hexamethylpropyleneamine oxime in 30 demented patients (21 with a clinical diagnosis of Alzheimer’s dementia and 9 with mixed-type dementia). Two SPECT scans were performed: in basal conditions, and 30 min after the administration of 500, 1,000, 1,500, or 2,000 mg LAC intravenously. Tracer activity ratios were determined in 10 pairs of cerebellar, cortical and subcortical regions. After administration of the lowest dose of LAC, no changes from the basal values were observed in any of the regions examined. The higher doses of the drug significantly elevated the tracer activity in cortical regions, particularly in the parietal lobe, which showed an impaired regional cerebral blood flow in the basal study. These effects of LAC and their relation with the cholinomimetic properties of the drug are discussed.

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Thirty-four demented patients, 19 with Alzheimer’s and 15 with multi-infarct dementia, were studied using single photon emission computed tomography, and ^99mTc-hexamethyl-propylenemine oxime as a tracer of regional cerebral perfusion. Tracer activity ratios, determined in cortical and subcortical regions, were compared with those of 11 age-matched controls. In both groups of demented patients, most of the cortical regions showed significant declines in tracer uptake from control values, with the greatest reductions in the parietal cortex. Significantly lower parietal indexes were found in the Alzheimer’s patient group as compared both to the control values and to the group of multi-infarct dementia patients. A positive correlation was found between the magnitude of the parietal deficits and the severity of dementia.

Atrial Excitation Assuming Uniform Propagation. Introduction:We investigated the spread of the excitation wave over the atria following initiation in a given focus in an atrial model containing its overall geometry only, i.e., without atrial bundles.Methods and Results: The propagation velocity of the excitation wave was taken to be uniform, and the wall thickness was discarded. The timing of excitation of any point on the atrium thus becomes directly proportional to its shortest distance over the atrial wall to the focus. Despite these gross simplifications, the general nature of the excitation sequence found corresponded closely to clinical data reported in the literature. This suggests that the complex overall geometry of the atria dominates the timing of the excitation. A highly intriguing observation from this study was that, when looking at the pathways from the sinus node to all other points on the atrium, prominent routes became visible even though no such pathways formed part of the model of the atrial geometry used. The locations of these prominent routes coincide with those of various distinct bundles in the atria. Possible inferences of these observations are discussed.Conclusion: Based upon comparison with data from other studies, it is concluded that, during stable heart rhythms, propagation of the atrial excitation wave is well approximated by an assumption of uniform velocity, even though no atrial bundles were included in the model. The overall geometry seems to be the dominant factor in the spread