The added value of ECG-gating for the diagnosis of myocardial infarction using myocardial perfusion scintigraphy and artificial neural networks

To assess the value of ECG-gating for the diagnosis of myocardial infarction using myocardial perfusion scintigraphy (MPS) and an artificial neural network. A total of 422 patients referred for MPS were studied using a one day (99m)Tc-tetrofosmin protocol. Adenosine stress combined with submaximal dynamic exercise was used. The images were interpreted by one of three experienced clinicians and these interpretations regarding the presence or absence of myocardial infarction were used as the standard. A fully automated method using artificial neural networks was compared with the clinical interpretation. Either perfusion data alone or a combination of perfusion and function from ECG-gated images were used as input to different artificial neural networks. After a training session, the two types of neural networks were evaluated in separate test groups using an eightfold cross-validation procedure. The neural networks trained with both perfusion and ECG-gated images had a 4-7% higher specificity compared with the corresponding networks using perfusion data only, in four of five segments compared at the same level of sensitivity. The greatest improvement in specificity, from 70% to 77%, was seen in the inferior segment. In the septal and lateral segments the specificity rose from 73% to 77% and from 81% to 85%, respectively. In the anterior segment, the increase in specificity from 93% to 94% by adding functional data was not significant. The addition of functional information from ECG-gated MPS is of value for the diagnosis of myocardial infarction using an automated method of interpreting myocardial perfusion images.

The regulatory background of nuclear cardiology in Europe: a survey by the European Council of Nuclear Cardiology

PURPOSE

Nuclear cardiology is a well-validated, non-invasive imaging modality that is highly cost-effective as a diagnostic and prognostic tool in the evaluation of patients with known or suspected coronary artery disease. However, the number of procedures in Europe is very far from that which would be expected on the basis of epidemiological data, particularly when comparison is made with the USA. As a preliminary step for future action aimed at improving and increasing nuclear cardiology practice in Europe, the European Council of Nuclear Cardiology performed a survey to identify the regulatory issues and the training components pertaining to the practice of nuclear cardiology.

METHODS

a questionnaire was sent to 31 national nuclear medicine societies and to 40 national cardiology societies. The main areas covered by the survey were: (1) the license requirements, (2) the theoretical and practical aspects of training and (3) supervision of the stress test during a nuclear cardiology study.

RESULTS

The results show that, in a setting of wide heterogeneity of national regulations, education and professional practice, nuclear medicine is a restricted and closely regulated specialty. This situation guarantees the quality and safe use of radionuclides; at the same time, however, it limits integration of nuclear medicine into the clinical arena.

CONCLUSION

Cardiologists should become more involved in nuclear cardiology, to further stimulate the use of this powerful diagnostic and prognostic imaging modality.

EANM/ESC procedural guidelines for myocardial perfusion imaging in nuclear cardiology

The European procedural guidelines for radionuclide imaging of myocardial perfusion and viability are presented in 13 sections covering patient information, radiopharmaceuticals, injected activities and dosimetry, stress tests, imaging protocols and acquisition, quality control and reconstruction methods, gated studies and attenuation-scatter compensation, data analysis, reports and image display, and positron emission tomography. If the specific recommendations given could not be based on evidence from original, scientific studies, we tried to express this state-of-art. The guidelines are designed to assist in the practice of performing, interpreting and reporting myocardial perfusion SPET. The guidelines do not discuss clinical indications, benefits or drawbacks of radionuclide myocardial imaging compared to non-nuclear techniques, nor do they cover cost benefit or cost effectiveness.

Sequence, purification, and cloning of an intracellular serine protease, quiescent cell proline dipeptidase

We recently observed that specific inhibitors of post-proline cleaving aminodipeptidases cause apoptosis in quiescent lymphocytes in a process independent of CD26/dipeptidyl peptidase IV. These results led to the isolation and cloning of a new protease that we have termed quiescent cell proline dipeptidase (QPP). QPP activity was purified from CD26(-) Jurkat T cells. The protein was identified by labeling with [(3)H]diisopropylfluorophosphate and subjected to tryptic digestion and partial amino acid sequencing. The peptide sequences were used to identify expressed sequence tag clones. The cDNA of QPP contains an open reading frame of 1476 base pairs, coding for a protein of 492 amino acids. The amino acid sequence of QPP reveals similarity with prolylcarboxypeptidase. The putative active site residues serine, aspartic acid, and histidine of QPP show an ordering of the catalytic triad similar to that seen in the post-proline cleaving exopeptidases prolylcarboxypeptidase and CD26/dipeptidyl peptidase IV. The post-proline cleaving activity of QPP has an unusually broad pH range in that it is able to cleave substrate molecules at acidic pH as well as at neutral pH. QPP has also been detected in nonlymphocytic cell lines, indicating that this enzyme activity may play an important role in other tissues as well.

A novel apoptotic pathway in quiescent lymphocytes identified by inhibition of a post-proline cleaving aminodipeptidase: a candidate target protease, quiescent cell proline dipeptidase

The vast majority of lymphocytes in vivo persist in a quiescent state. These resting lymphocytes are maintained through a cellular program that suppresses apoptosis. We show here that quiescent PBMC, but not activated PBMC or transformed lymphocytes, die in the presence of highly specific post-proline aminodipeptidase inhibitors. This form of death has the hallmarks of apoptosis, such as phosphatidylserine externalization and loss of mitochondrial transmembrane potential. However, it differs from apoptosis induced by gamma irradiation in the same cells or by Fas ligation in transformed lymphocytes in terms of caspase involvement. In addition, the aminodipeptidase inhibitor-induced cell death, but not gamma-irradiation-mediated apoptosis, can be prevented by inhibition of the proteasome complex. The target of these inhibitors is not CD26/DPPIV, but probably a novel serine protease, quiescent cell proline dipeptidase, that we have recently isolated and cloned. These studies will yield a better understanding of the requirements and the mechanisms that mediate quiescent lymphocyte homeostasis in vivo.

Long-term (5 year) effects of transient (silent) ischaemia on left ventricular systolic function in stable angina. Clinical and radionuclide study

AIMS

(a) to assess short (1 year) and long-term (5 year) changes in left ventricular ejection fraction in patients with stable coronary disease with or without ECG evidence of transient ischaemia during daily life on routine therapy, and (b) to assess whether patients with recurrent transient ischaemic episodes have a particular propensity to gradual deterioration in left ventricular ejection fraction in the absence of infarction.

METHODS AND RESULTS

One hundred and forty eight patients (127 males; mean age 59 years), part of a natural history cohort of 172 patients who had undergone exercise testing, 48 h ambulatory ST monitoring, and resting radionuclide ventriculography at baseline, and who had not suffered any intervening cardiac event, underwent repeat radionuclide ventriculography at 1 year follow-up on identical or very similar medications. Furthermore, 56 patients (50 males; mean age 65 years) of this cohort, who had ischaemia both on exercise testing and ambulatory monitoring at baseline (n=33), or no ischaemia on either test at baseline (n=23), and who had suffered no intervening event, underwent repeat exercise testing, ambulatory monitoring and radionuclide ventriculography at a mean of 61.8 months follow-up. In 38 of these 56 cases, long-term testing mirrored baseline testing in terms of presence or absence of ischaemia (both tests +, n=25; both tests -, n=13). At one year there was no change in left ventricular ejection fraction, either for the whole group (n=148; left ventricular ejection fraction 47=11.6% - 47.13+11.07%, P=ns) or for subgroups with (n=62; left ventricular ejection fraction 48+12.1%-48.5+10.5%, P=ns) and without (n=86; left ventricular ejection fraction 46.2+10.4%-46.2+11.3%, P=ns) evidence of transient ischaemia at baseline. At 61 months, there was a small fall in mean left ventricular ejection fraction for the total study group (n=56; left ventricular ejection fraction 45.8+9.3%-42.1+8.8%, P<0.05); however, this fall was not significant for those patients with both baseline and 5 year evidence of transient ischaemia (n=25; left ventricular ejection fraction 44.9+8.7%-41.3+7.5%, P=0.056).

CONCLUSION

In medically treated stable coronary patients who do not suffer any intervening cardiac event, recurrent transient (silent) ischaemic episodes do not, in themselves, lead to gradual deterioration in left ventricular systolic function over a 1-5 year period.

A comparison of adenosine and arbutamine for myocardial perfusion imaging

We have compared our standard stress protocol (adenosine combined with exercise) with the new stress agent arbutamine, for thallium-201 myocardial perfusion imaging (MPI) in order to assess the comparative value of arbutamine. We studied 23 patients referred for MPI, and each patient had two studies (18 males, median age 66 years, five with previous myocardial infarction). Uptake scores were assigned to each of nine segments, and the extent and severity of defects were measured using a polar plot. Haemodynamic changes were greater with arbutamine (rate-pressure product increase 78% vs 51%, P = 0.003). Symptoms were experienced by 21 patients with arbutamine and 16 with adenosine (P = 0.07). Agreement between the techniques for classification of patients as normal or as having reversible, fixed or mixed defects was good (19 of 23 studies, 83%, kappa = 0.76). Agreement for similar classification of segments was also good (82%, kappa = 0.71). Segmental agreement for stress scores was good (86%, kappa = 0.77). However, mean size of stress defect was larger with adenosine (83+/-52 pixels vs 65+/-48 pixels, P<0.05), though severity and reversibility were similar (P = NS). We conclude that arbutamine provides comparable results to those obtained with adenosine and exercise and that the observed differences are not clinically significant.

Downregulation of immunodetectable connexin43 and decreased gap junction size in the pathogenesis of chronic hibernation in the human left ventricle

BACKGROUND

The regional wall motion impairment and predisposition to arrhythmias in human ventricular hibernation may plausibly result from abnormal intercellular propagation of the depolarizing wave front. This study investigated the hypothesis that altered patterns of expression of connexin43, the principal gap junctional protein responsible for passive conduction of the cardiac action potential, contribute to the pathogenesis of hibernation.

METHODS AND RESULTS

Patients with poor ventricular function and severe coronary artery disease underwent thallium scanning and MRI to predict regions of normally perfused, reversibly ischemic, or hibernating myocardium. Twenty-one patients went on to coronary artery bypass graft surgery, during which biopsies representative of each of the above classes were taken. Hibernation was confirmed by improvement in segmental wall motion at reassessment 6 months after surgery. Connexin43 was studied by quantitative immunoconfocal laser scanning microscopy and PC image software. Analysis of en face projection views of intercalated disks revealed a significant reduction in relative connexin43 content per unit area in reversibly ischemic (76.7+/-34.6%, P<.001) and hibernating (67.4+/-24.3%, P<.001) tissue compared with normal (100+/-30.3%); ANOVA P<.001. The hibernating regions were further characterized by loss of the larger gap junctions normally seen at the disk periphery, reflected by a significant reduction in mean junctional plaque size in the hibernating tissues (69.5+/-20.8%) compared with reversibly ischemic (87.4+/-31.2%, P=.012) and normal (100+/-31.5%, P<.001) segments; ANOVA P<.001.

CONCLUSIONS

These results indicate progressive reduction and disruption of connexin43 gap junctions in reversible ischemia and hibernation. Abnormal impulse propagation resulting from such changes may contribute to the electromechanical dysfunction associated with hibernation.