Receiver operating characteristics of perceptrons: Influence of sample size and prevalence

In many practical classification problems it is important to distinguish false positive from false negative results when evaluating the performance of the classifier. This is of particular importance for medical diagnostic tests. In this context, receiver operating characteristic (ROC) curves have become a standard tool. Here we apply this concept to characterize the performance of a simple neural network. Investigating the binary classification of a perceptron we calculate analytically the shape of the corresponding ROC curves. The influence of the size of the training set and the prevalence of the quality considered are studied by means of a statistical-mechanics analysis.

Selective perfusion of ischemic myocardium during coronary venous retroinjection: A study of the causative role of venoarterial and venoventricular pressure gradients

Coronary venous retroinjection is often associated with preferential distribution of flow to ischemic myocardium. The purpose of this study was to define the mechanism of such retrodistribution of flow. In 24 anesthetized open chest dogs, Monastral blue dye (10 ml) was injected by way of a balloon catheter in the distal great cardiac vein as a marker for retrograde flow distribution. The injection rate (0.6 to 2.4 ml/s) was adjusted such that systolic pressure in the anterior interventricular vein ranged between 60 and 85 mm Hg. In 11 dogs with no ischemia and normal myocardial perfusion pressure (96 ± 8 mm Hg), no myocardial staining occurred despite retrograde filling of epicardial veins. One minute after occlusion of the left anterior descending coronary artery, dye injections caused selective staining of the cyanotic area in 15 of 18 episodes, sparing the normal myocardium within the zone of retroperfused veins. In five dogs, with the arterial pressure <55 mm Hg, retroinjection resulted in homogeneous staining of all the myocardium drained by the retroperfused veins.Selective staining of the ischemic myocardium caused by retroinjection was associated with the following pressure gradients: during systole from the anterior interventricular vein to the occluded coronary artery, 31 to 58 mm Hg, and during diastole from the retroperfused veins to the left ventricular chamber, 9 to 28 mm Hg. There was no diastolic venoarterial gradient in the ischemic myocardium. In normal myocardium, retroinjection did not reverse the arteriovenous pressure gradient.In conclusion, retrograde flow is primarily directed to myocardium with low anterograde perfusion pressure. Selective retrograde penetration of acutely ischemic myocardium can thus be achieved by a mechanism consistent with the development of venoarterial and venoventricular pressure gradients

Electrocardiography and Outcome in Patients with Diabetes Mellitus on Maintenance Hemodialysis

Background and objectives: In hemodialysis, applicable guidelines recommend regular electrocardiogram (ECG) recordings. However, respective systematic evaluations are absent. Thus, the authors investigated whether routine ECG findings add prognostic information to standard risk assessment in hemodialysis

Subthreshold atrial pacing in patients with a left-sided accessory pathway: An effective new method for terminating reciprocating tachycardia

AbstractThis study investigated the possibility of terminating reciprocating atrioventricular (AV) tachycardia using subthreshold atrial pacing. Ten patients with a left-sided accessory pathway and sustained AV tachycardia underwent suhthreshold atrial pacing from the coronary sinus site closest to insertion of the accessory pathway. In seven of these patients, the tachycardia could be reliably terminated with subthreshold atrial overdrive pacing. When pacing at a cycle length of 80 ± 23% of the tachycardia cycle length, the minimal subthreshold current that was effective in tachycardia termination was 64 ± 14% of threshold current and the maximal ineffective current was 49 ± 17% of threshold (p < 0.05). In all cases, the tachycardia was terminated by one or two instances of atrial capture that resulted in a premature atrial impulse (20 ± 4% advancement of the atrial cycle) that blocked the AV node limb of the tachycardia. Anterograde conduction over the accessory pathway never occurred, either during the tachycardia or during subthreshold pacing after a return to normal sinus rhythm. No instances of atrial fibrillation were provoked by suhthreshold pacing. Possible explanations for the intermittent atrial capture with critically placed subthreshold impulses include supernormal atrial conduction or summation of impulses at the atrial insertion site of the accessory pathway.It is concluded that subthreshold pacing is effective in selected patients with AV tachycardia due to an accessory pathway. Furthermore, because neither atrial fibrillation nor anterograde conduction over the accessory pathway is seen with subthreshold pacing, this modality may hold significant promise for permanent antitachycardia pacing in these patients

Receiver Operating Characteristics of Perceptrons: Influence of Sample Size and Prevalence

. In many practical classification problems it is important to distinguish false positive from false negative results when evaluating the performance of the classifier. This is of particular importance for medical diagnostic tests. In this context, receiver operating characteristic (ROC) curves have become a standard tool. Here we apply this concept to characterize the performance of a simple neural network. Investigating the binary classification of a perceptron we calculate analytically the shape of the corresponding ROC curves. The influence of the size of the training set and the prevalence of the quality considered are studied by means of a statistical-mechanics analysis. PACS numbers: 87.10, 07.05, 05.90 1. Introduction Classification problems in general and medical diagnostic tests in particular are often well suited for the application of neural networks [1, 2, 3]. The rule how to classify an item is generally not available, but can be derived from examples, e.g. patients wit..

Effect of additional temporary glycoprotein IIb/IIIa receptor inhibition on troponin release in elective percutaneous coronary interventions after pretreatment with aspirin and clopidogrel (TOPSTAR trial).

OBJECTIVES: The Troponin in Planned PTCA/Stent Implantation With or Without Administration of the Glycoprotein IIb/IIIa Receptor Antagonist Tirofiban (TOPSTAR) trial investigated: 1) the amount of troponin T (TnT) release after nonacute, elective percutaneous coronary intervention (PCI) in patients pretreated with aspirin and clopidogrel; and 2) the effect of additional glycoprotein (GP) IIb/IIIa receptor inhibiton on postinterventional TnT release. BACKGROUND: No data are available yet as to whether additional administration of a GP IIb/IIIa receptor antagonist might be beneficial in patients undergoing elective PCI already pretreated with aspirin and clopidogrel. METHODS: After bolus application of the study medication (tirofiban [T] or placebo [P]), PCI was performed followed by an 18-h continuous infusion of T/P. Primary end point of the study was incidence and amount of TnT release after elective PCI after 24 h. RESULTS: A total of 12 h after PCI troponin release was detected in 63% of the patients receiving P and in 40% of the patients receiving T (p < 0.05), after 24 h in 69% (P) and 48% (T) (p < 0.05) and after 48 h in 74% (P) versus 58% (T) (p < 0.08) of the patients. No differences were observed regarding major bleeding, intracranial bleeding or nonhemorrhagic strokes. After nine months a reduction of combined death/myocardial infarction/target vessel revascularization could be observed in the tirofiban group ([T] 2.3% vs. [P] 13.04%, p < 0.05). CONCLUSIONS: Troponin T release occurs after successful intervention in 74% of the patients undergoing elective PCI after 48 h even after pretreatment with aspirin and clopidogrel. The GP IIb/IIIa receptor antagonist tirofiban is able to decrease the incidence of troponin release significantly in this patient population

Significance of psychosocial factors in cardiology: update 2018

Background Psychosocial factors in cardiovascular diseases are increasingly acknowledged by patients, health care providers and payer organizations. Due to the rapidly increasing body of evidence, the German Cardiac Society has commissioned an update of its 2013 position paper on this topic. The German version was published in 2018 and the current manuscript is an extended translation of the original version. Methods This position paper provides a synopsis of the state of knowledge regarding psychosocial factors in the most relevant cardiovascular diseases and gives recommendations with respect to their consideration in clinical practice. Results Psychosocial factors such as low socioeconomic status, acute and chronic stress, depression, anxiety and low social support are associated with an unfavorable prognosis. Psychosocial problems and mental comorbidities should be assessed routinely to initiate targeted diagnostics and treatment. For all patients, treatment should consider age and gender differences as well as individual patient preferences. Multimodal treatment concepts should comprise education, physical exercise, motivational counseling and relaxation training or stress management. In cases of mental comorbidities, brief psychosocial interventions by primary care providers or cardiologists, regular psychotherapy and/or medications should be offered. While these interventions have positive effects on psychological symptoms, robust evidence for possible effects on cardiac outcomes is still lacking. Conclusions For coronary heart disease, chronic heart failure, arterial hypertension, and some arrhythmias, there is robust evidence supporting the relevance of psychosocial factors, pointing to a need for considering them in cardiological care. However, there are still shortcomings in implementing psychosocial treatment, and prognostic effects of psychotherapy and psychotropic drugs remain uncertain. There is a need for enhanced provider education and more treatment trials