Verification of Agent-Based Artifact Systems

Artifact systems are a novel paradigm for specifying and implementing business processes described in terms of interacting modules called artifacts. Artifacts consist of data and lifecycles, accounting respectively for the relational structure of the artifacts’ states and their possible evolutions over time. In this paper we put forward artifact-centric multi-agent systems, a novel formalisation of artifact systems in the context of multi-agent systems operating on them. Differently from the usual process-based models of services, we give a semantics that explicitly accounts for the data structures on which artifact systems are defined. We study the model checking problem for artifact-centric multi-agent systems against specifications expressed in a quantified version of temporal-epistemic logic expressing the knowledge of the agents in the exchange. We begin by noting that the problem is undecidable in general. We identify a noteworthy class of systems that admit bisimilar, finite abstractions. It follows that we can verify these systems by investigating their finite abstractions; we also show that the corresponding model checking problem is EXPSPACE-complete. We then introduce artifact-centric programs, compact and declarative representations of the programs governing both the artifact system and the agents. We show that, while these in principle generate infinite-state systems, under natural conditions their verification problem can be solved on finite abstractions that can be effectively computed from the programs. We exemplify the theoretical results here pursued through a mainstream procurement scenario from the artifact systems literature.

Interactions between Knowledge and Time in a First-Order Logic for Multi-Agent Systems: Completeness Results

We investigate a class of first-order temporal-epistemic logics for reasoning about multi-agent systems. We encode typical properties of systems including perfect recall, synchronicity, no learning, and having a unique initial state in terms of variants of quantified interpreted systems, a first-order extension of interpreted systems. We identify several monodic fragments of first-order temporal-epistemic logic and show their completeness with respect to their corresponding classes of quantified interpreted systems.

[Detection and assessment of myocardial stunning with perfusion tomographic scintigraphy using gated SPECT]

BACKGROUND

Gated-SPECT using 99mTc-labeled flow tracers provides the simultaneous assessment of global and regional myocardial perfusion and function. The aim of this study was to identify patients with stress-induced postischemic stunning, among those with reversible stress perfusion defects, and patients with artifactual defects among those with fixed defects, in order to assess the value of the functional data provided by gated acquisition of perfusion imaging in the characterization of ischemia.

METHODS

We studied 221 consecutive patients who underwent conventional diagnostic dual day stress/rest gated-SPECT following injection of 925 MBq of 99mTc-tetrofosmin using a dual head SPECT camera, 115 of whom (52%) showed reversible perfusion defects, and 66 (30%) fixed defects. Perfusion was analyzed on ungated images using 20 segments scored on a 5-point scale (0 = normal, 4 = no uptake), while wall thickening was assessed visually on stress/rest end-systolic images using a 4-point score (0 = normal, 3 = absence of wall thickening). Left ventricular ejection fraction and volumes were calculated using an automatic algorithm (quantitative gated-SPECT). Fifty-two out of 221 (23.5%) patients underwent coronary angiography.

RESULTS

In 40/115 (35%) patients with reversible perfusion defects, post-stress left ventricular ejection fraction was > 5% lower than that at rest (Group A: stunned), whereas in the remaining 75 patients, post-stress left ventricular ejection fraction was either +/- 5% or greater than that at rest (Group B: non-stunned). Peak exercise angina and ischemic electrocardiographic response to exercise were present in 79 and 58% respectively of Group A patients and in 33 and 39% of Group B patients. The number of patients with multivessel disease was significantly higher in Group A compared to Group B (58 vs 41%, p < 0.05). The total stress and rest perfusion scores were significantly higher in Group A than in Group B (p < 0.01); even the total stress wall thickening score was significantly higher in Group A (p < 0.001). As for global parameters, post-stress end-systolic volume was significantly higher in the stunned group (p < 0.05). In 40 out of 66 (60.5%) patients without reversible ischemia fixed defects were judged to be ischemic (Group C), while in 26/66 (39.5%) they were attributed to attenuation artifacts (Group D). Eighty percent of Group C patients had a previous myocardial infarction against none of Group D. Stress/rest perfusion and wall thickening scores were significantly higher in Group C than in Group D.

CONCLUSIONS

Gated-SPECT myocardial perfusion evaluation allowed us to identify a subgroup of post-stress stunned coronary artery diseased patients. The post-stress left ventricular ejection fraction reduction in this population seems to be due to the increase in end-systolic volume. The stunned patients showed more severe perfusion defects and wall thickening abnormalities.

Effects of infusion of glucose-insulin-potassium on myocardial function after a recent myocardial infarction

We studied the effects of glucose, insulin, and KCl infusion (GIK), on regional myocardial perfusion and function by 99m-Tc-tetrofosmin-gated SPECT.

METHODS

We studied 21 male patients with their first uncomplicated acute myocardial infarction (AMI). All patients underwent a rest and submaximal stress before and after 24-hour infusion of GIK-solution (group A) or saline solution (group B).

RESULTS

Group A showed better stress tolerance and ischaemic threshold improvement after GIK infusion whilst no statistical differences were found between basal and post-infusion test in group B. At first the stress test in group A, of the 192 segments analysed, 52 (27%) showed reversible perfusion defect. In group B, of 144 segments analysed, 31 (21%) showed reversible perfusion defect. A post-infusion analysis in group A showed a post-GIK end-diastolic significant count improvement in 21 segments, and a post-GIK end-systolic count improvement in 22 segments. In group B, perfusion increase was observed only in 4 segments, whilst systolic thickening increase was observed only in 1 segment.

CONCLUSION

These data demonstrate the efficacy of GIK infusion to improve regional myocardial perfusion and function mainly in segments adjacent to the recently infarcted area.

[A comparison between attenuation-corrected and -uncorrected transmission-emission SPECT images obtained with Tl-201 in CAD patients]

BACKGROUND

The aim of this study was to evaluate the impact of attenuation correction (AC) on the diagnostic accuracy of conventional stress/red thallium SPECT studies.

METHODS

We studied 60 consecutive patients (36 males) who underwent conventional diagnostic stress/red study with and without AC (NAC) using a dual-head SPECT camera (Vertex ADAC) with a 153Gd source. The mean age of these patients was 60 years (30-80) and 29 of the subjects had a history of MI. Reconstructed images were visually analyzed using 20 segments scored on a 5-point scale (0 = normal, 4 = no uptake). Diagnostic accuracy was evaluated in 24 consecutive patients who underwent coronary angiography. Polar plots from each of the four reconstructed data sets per patient were normalized on the maximum and quantified using a nine segment model.

RESULTS

The comparison between the segmental stress score obtained with and without AC showed agreement in 1057 out of 1200 (88%) segments analyzed, K statistic value = 0.67. The number of fixed defects was significantly lower after AC. The diagnostic accuracy, evaluated in 24 patients (480 segs), was not significantly different between AC and NAC analysis (80 vs 84% respectively).

CONCLUSIONS

AC seems to reduce the number of fixed defects due to attenuation artefacts without improving diagnostic accuracy, probably because of the low number of subjects submitted to angiography and of the interpreting bias due to the expertise of the operators. In fact, in the rather small group of patients evaluated, no improvement in diagnostic accuracy was observed, probably because several attenuation defects were not considered pathological due to operator expertise.

[Myocardial scintigraphy by the gated SPECT method in coronary disease patients with postischemic stunning]

Gated SPECT using Tc-99m-labeled flow tracers provides simultaneous assessment of global and regional myocardial perfusion and function. The aim of this study was to evaluate whether regional wall thickening (WT) obtained after stress and at rest makes it possible to identify and analyze a subgroup of post-ischemic stunned patients.

METHODS

We studied 20 patients (18 males) who underwent conventional diagnostic dual-day stress/rest Gated SPECT following injection of 925 MBq of 99mTc-tetrofosmin using a dual-head SPECT camera (Vertex ADAC). The mean age of these patients was 59 years (38-71) and 10 of them had a history of previous acute myocardial infarction (AMI). Perfusion was analyzed on ungated images using 20 segments scored on a 5-point scale (0 = normal, 4 = no uptake), while WT and motion were assessed visually on stress/rest end-systolic images using a 4-point score (0 = normal, 3 = absence of WT/motion). Left ventricular ejection fraction (LVEF) and volumes were calculated. All patients underwent coronary angiography.

RESULTS

All patients showed at least one reversible defect with post-stress WT reduction and normal rest WT. The stunned group showed a significant post-stress reduction of LVEF and a statistically non-significant increase of end systolic volume (ESV). A good correlation was observed between global perfusion and WT score both at stress and rest conditions; LVEF showed a significant inverse correlation with global post-stress and rest perfusion and WT score. ESV and the global perfusion stress/rest score showed a good correlation, while end-diastolic volume did not correlate. In 44% of the segments with fixed defects, there was a normal WT and normal coronary-related vessel (false positives); 28% of reversible segments showed a post-stress pathological WT and five of them a rest pathological WT.

CONCLUSIONS

The gated SPECT myocardial perfusion evaluation allowed us to analyze a subgroup of post-stress stunned coronary artery disease patients. The post-stress LVEF reduction in this population seems to be due to the increase of end-systolic volume caused by endocardial ischemia. The stunned segments showed severe perfusion defects.

Effects of glibenclamide on ventricular fibrillation in non-insulin-dependent diabetics with acute myocardial infarction

BACKGROUND

Glibenclamide, a hypoglycemic sulfonylurea, has shown antiarrhythmic effects in acutely ischemic myocardium. The aim of the present study was to evaluate the effectiveness of the drug in preventing ventricular fibrillation in diabetic patients with acute myocardial infarction.

METHODS

We studied 232 patients with non-insulin-dependent diabetes mellitus (106 on glibenclamide, group A1; 126 treated with another hypoglycemic drug or with diet only, group A2) and 830 non-diabetic people. All the patients were admitted to our coronary care unit with their first myocardial infarction.

RESULTS

Ventricular fibrillation occurred in 1.9% of group A1, 7.9% of group A2, and 9.9% of the non-diabetic (A1 versus A2, P < 0.05; A2 versus the non-diabetic group, NS; A1 versus the non-diabetic group, P < 0.01). Sustained ventricular tachycardia was not significantly different among the groups.

CONCLUSIONS

The antiarrhythmic effectiveness of glibenclamide might be related to its blocking action on the ATP-dependent potassium channel, with consequent attenuation of the efflux of potassium induced by ischemia. We also observed a higher mortality rate resulting from heart failure in group A2 than in group A1 or the non-diabetic group. Since glibenclamide has never shown significant effects on myocardial contractility, this finding remains to be elucidated. Glibenclamide therefore appears to have an antifibrillatory effect in acute myocardial infarction; with respect to acute coronary events, the drug might be able to prevent ventricular fibrillation, which is most often fatal when it occurs before hospitalization.

Fourier amplitude image circumferential profile analysis in the evaluation of the dipyridamole test

The aim of this study was to evaluate a circumferential profile method of analysis (CPA) of the Fourier image of amplitude (FA), obtained by equilibrium gated radionuclide angiocardiography (EGRA) in the assessment of the response to the dipyridamole (DIP) test in patients with previous myocardial infarction. The changes in regional wall motion (RWM) induced by DIP in a group of 29 patients with previous MI were compared with those of a ten-patient control group. On the basis of SPECT thallium-201 standard stress-rest scintigraphy the infarcted patients were divided into 9 patients with fixed perfusion defects at four hours and 20 patients with both fixed and reversible perfusion defects. The quantitative CPA was carried out on the FA image normalized by the mean amplitude calculated for the left ventricle (LV) area. A circular ROI was drawn around the FA left ventricle image and two curves (basal and post-DIP) with 60 points were obtained. We compared this method with a five-sector method of analysis applied to the same FA images. An increase of 2 or more SD in the basal post-DIP ratio curve, compared with the average of the ratios in the control group, was found in 16 of 20 patients with reversible perfusion defects (sensitivity: 80%) and an increase in the same ratio was found in 2 of 9 MI patients with fixed perfusion defects (specificity: 78%). A sensitivity and specificity of 60% and 78% respectively were found using sectorial analysis.

Thallium-201 lung uptake: comparison of an automatic and a manual method of ROI drawing

An automatic method for ROI drawing to measure 201TI lung uptake after stress testing in planar and tomographic myocardial perfusion imaging, was compared with the more commonly used manual method. A linear correlation in the lung/heart ratio (LHR) and lung washout (LWO) data, obtained in planar and SPECT images with the two methods, was found. Pearson's correlation coefficient between the automatic and manual methods was highly significant both for LHR and for LWO. For LHR we found a high linear correlation between the two methods in the planar anterior (r = 0.71, p < 0.001), SPECT anterior (r = 0.84, p < 0.001), and SPECT LAO (r = 0.96, p < 0.001) views. The analysis of LWO data showed a good linear correlation for the planar anterior (r = 0.84, p < 0.001), SPECT anterior (r = 0.66, p < 0.005) and SPECT LAO (r = 0.79, p < 0.001) views. Furthermore, comparison by the student's t test of the averages of the LHR and LWO values obtained in the same views but with different methods was performed. The advantages and the critical issues associated with the automatic method are discussed; it appears to be quick and easy to perform and to be equivalent to the more time-consuming method based on a manual definition of left lung ROI.

Delayed effect of streptokinase on left ventricular function after acute myocardial infarction assessed by equilibrium gated radionuclide angiocardiography

A blind comparative study was conducted on 80 consecutive patients who were given Streptokinase (SK) or placebo between 3 and 6 hours after the onset of acute myocardial infarction (AMI). Left ventricular ejection fraction (LVEF), peak ejection rate (PER), peak filling rate (PFR) and regional wall motion (RWM) were evaluated by equilibrium gated radionuclide angiocardiography (EGRA) at 3-5 weeks and 6 months after the onset of AMI. In the anterior AMI SK-group, the mean LVEF values rose from 0.37 at one month to 0.43 at six months, PER (end-diastolic volumes per second) from 1.76 to 2.00, and PFR (end-diastolic volumes per second) from 1.46 to 1.75 (p = 0.01, p < 0.05, and p < 0.05, respectively). In the anterior non-SK group no improvement was seen in any of the LV function parameters. Only a slight improvement was observed in the inferior AMI group, with no significant difference between the treated and non-treated patients. The regional wall motion analysis was in agreement with the global function data. In conclusion, SK treatment given between three and six hours after the onset of anterior AMI may result in some improvement in LV function, which becomes fully appreciable only after the complete resolution of stunning, i.e. after more than one month.

Radionuclide assessment of left ventricular function in patients with myocardial infarction and diabetes mellitus

The aim of this study was to compare left ventricular function, assessed by radionuclide angiocardiography, in 54 diabetics and 194 non-diabetics with acute myocardial infarction (AMI). The most meaningful results concern the inferior AMI group, whose left ventricular ejection fraction (LVEF) and regional wall motion were significantly lower in diabetics than in non-diabetics (LVEF was 44.2 +/- 11 vs. 51.6 +/- 9%, P less than 0.005; the regional wall motion score was 0.46 +/- 1 vs. 1.56 +/- 1, P less than 0.01, respectively), while no significant difference was observed in the anterior AMI group. However, in the group as a whole, the LVEF was 41 +/- 13% in diabetics and 47 +/- 13% in non-diabetics (P less than 0.01), the number of abnormally contracting segments was 2.0 +/- 0.9 and 1.5 +/- 1, respectively, and the wall motion score was 0.2 +/- 1.1 and 1.0 +/- 1.4, respectively (P less than 0.01). These data could be explained by an underlying cardiac dysfunction in diabetes, in addition to AMI. The more marked difference between diabetics and non-diabetics in inferior AMI might be related to the smaller infarct size in this group.

[Flecainide and anti-arrhythmia therapy]

Flecainide is a benzenacetamide synthesised about a decade ago and only recently introduced into the treatment of arrhythmias. Its electrophysiological properties place it in Class IC of the anti-arrhythmia drugs. Flecainide has proved useful in the treatment of supraventricular arrhythmias, atrial fibrillation (especially in patients with Wolff-Parkinson-White disease), in reciprocating supraventricular tachycardias and in focal atrial tachycardias. The drug is also extremely effective in ventricular ectopias with a success rate of over 90%. Flecainide is therefore destined to be widely used in the treatment of arrhythmias and is indicated for both supraventricular and ventricular forms, particularly those resistant to other treatment. In addition the biological availability and long half life of Flecainide make it suitable for even very prolonged treatment.

[Right ventricular infarct and atrioventricular blocks]

Right ventricular infarction in inferior left ventricular infarction is very common. We have examined, by means of equilibrium gated radionuclide angiography, the relationship existing between right ventricular infarction and atrioventricular block. Seventy-two patients with inferior wall myocardial infarction were studied. Thirty-nine of them had ventriculographic evidence of right ventricular infarction. Fifteen of them (38%) had a-v block in the acute phase. Only 3 patients without right ventricular involvement (9%) had a-v block. The occurrence of a-v block is usually explained by the fact that the blood supply to the a-v node depends on the right coronary artery. In the patients with right ventricular involvement, the incidence of a-v block is high just because occlusion of the right coronary artery is proximal to the branch to the a-v node. However, the presence of collateral blood supply to the a-v node makes the occurrence of a-v node not so high as expected.