Beneficial effect of residual anterograde flow on tissue viability as assessed by positron emission tomography in patients with myocardial infarction

With the advent of therapeutic interventions to restore bloodflow in patients with acute infarction, early identificationof salvageable myocardium has gained clinical importance. Itwas the purpose of this study to define regional blood flowand glucose metabolism in patients with acute myocardial infarctionas assessed by positron emission tomography (PET) and to correlatethese findings with coronary anatomy. In 15 patients blood flowas determined by N-13 ammonia was reduced in 37 left ventricularsegments. In 20 segments there was a similar decrease in FDGuptake, consistent with tissue necrosis. In contrast, 17 segmentswith reduced blood flow revealed maintained FDG uptake suggestingresidual viability in the electrocardiographically defined ‘infarctsegment’. PET viability and necrosis was significantlyassociated with presence or absence of anterograde flow in theinfarct artery. Evaluation of regional wall motion did not distinguishsegments with PET criteria for viability from segments withnecrosis. Thus, in patients without thrombolytic therapy duringevolving myocardial infarction, spontaneous reperfusion appearsto be beneficial for tissue survival. PET offers the uniquepossibility to assess tissue viability early after the ischaemicinjury where evaluation of wall motion fails to identify salvageablemyocardium.     

Exonic MHC-DRB Polymorphisms and Intronic Simple Repeat Sequenees: Janus'Faces of DNA Sequence Evolution

The evolution of highly polymorphic gene loci is following routes that cannot be extrapolated from the existing knowledge of single copy genes. In addition, interpreting the evolution of the most polymorphic loci in vertebrates requires a plethora of data from different taxa. We evaluate here the rules for the evolution of Major Histocompatibility Complex (MHC-)DRB genes recently established in humans and other primates on the basis of sequences from several artiodactyl species. MHC genes encode essential molecules for self/altered-self/non-self discrimination in the interaction of the organism with its environment. The necessity to effectively present various different antigens to immunocompetent cells causes positive selection pressure on the variability of these genes in the population. Artiodactyls represent the third mammalian order in which this phenomenon was evidenced independently. A further incentive to investigate also the surroundings of MHC-DRB loci was the presence of a particular repetitive sequence stretch in the vicinity of the polymorphic exon - in addition to the evolutionarily old alleles, ancient polymorphisms and the mechanisms for their generation and/or maintenance. Besides their utility for indirect gene diagnosis (MHC-DRB typing), the closely linked stretches of simple repetitive DNA in the neighborhood of the highly polymorphic MHC-DRB genes are also interesting remains of the evolutionary history. Evolutionary developmenl is different in genetically inert intron-ic DNA compared to the exonic counterparts, despite their close vicinity. The persistence of these simple repeats over nearly 100 million years in one location preserving the same basic motif structure is startling. Indirect evidence is weighed that biological meaning should be considered for these elements. The combined analysis of the polymorphic DRB genes and the (highly variable but persistent) simple repeat stretches deepen our understanding of the complexities within a unique genomic compartment encoding essential molecules for self/non-self dif-ferentiation in the interaction of the organism with its environment.     

Does Radiofrequency Catheter Ablation Induce a Deterioration in Sympathetic Innervation? A Positron Emission Tomography Study

Radiofrequency catheter ablation (RFCA) is an effective treatment for the interruption of accessory bypass tracts in WPW syndrome or the modification of the Ay-nodal conduction system in patients with A V-nodal tachycardias. However RFCA may also damage cardiac innervation. The purpose of this pilot study was to assess possible changes in sympathetic innervation after RFCA as evaluated by the cathecholamine analog carbons-11- hydoxyephedrine (HED) positron emission tomography (PET) which allows the visualisation of sympathetic nerve terminals. We investigated nine patients with supraventricular tachycardias before and two to six weeks after RFCA. Myocardial perfusion was depicted by n-I3-ammonia-PET. In addition to visual analysis, HED retention was quantified in the myocardial quadrant distal to the location of intervention; these results were compared with values in remote areas. Before RFC A, myocardial perfusion showed homogenous distribution in 8 of 9 patients. One patient showed a perfusion defect in the posterior wall. HED retention matched perfusion distribution in all patients. After RF'CA there was no significant change observed either in ammonia or in HED distribution. Quantitative HED retention data showed no significant change before versus after RFC A. Thus, HED-PET does not demonstrate any abnormalities of tracer uptake indicating integrity of sympathetic nerve terminals after radiofrequency ablation therapy.     

Beneficial effect of residual anterograde flow on tissue viability as assessed by positron emission tomography in patients with myocardial infarction

With the advent of therapeutic interventions to restore bloodflow in patients with acute infarction, early identificationof salvageable myocardium has gained clinical importance. Itwas the purpose of this study to define regional blood flowand glucose metabolism in patients with acute myocardial infarctionas assessed by positron emission tomography (PET) and to correlatethese findings with coronary anatomy. In 15 patients blood flowas determined by N-13 ammonia was reduced in 37 left ventricularsegments. In 20 segments there was a similar decrease in FDGuptake, consistent with tissue necrosis. In contrast, 17 segmentswith reduced blood flow revealed maintained FDG uptake suggestingresidual viability in the electrocardiographically defined ‘infarctsegment’. PET viability and necrosis was significantlyassociated with presence or absence of anterograde flow in theinfarct artery. Evaluation of regional wall motion did not distinguishsegments with PET criteria for viability from segments withnecrosis. Thus, in patients without thrombolytic therapy duringevolving myocardial infarction, spontaneous reperfusion appearsto be beneficial for tissue survival. PET offers the uniquepossibility to assess tissue viability early after the ischaemicinjury where evaluation of wall motion fails to identify salvageablemyocardium.