Noninvasive prediction of sudden death and sustained ventricular tachycardia after acute myocardial infarction using a neural network algorithm.

BACKGROUND: The early and accurate noninvasive identification of postinfarction patients at risk of sudden death and sustained ventricular tachycardia (arrhythmic events) still remains an unsolved problem. The aim of the present study was to identify the combination of clinical and laboratory noninvasive variables, easy to obtain in most patients, that best predicts the occurrence of arrhythmic events after an acute myocardial infarction. METHODS: Four hundred and four consecutive patients with acute myocardial infarction were enrolled and followed for a median period of 21.4 months. In each patient, 61 clinical and laboratory noninvasive variables were collected before hospital discharge and used for the prediction of arrhythmic events using an artificial neural network. RESULTS: During follow-up, 13 (3.2%) patients died suddenly and 11(2.5%) had sustained ventricular tachycardia. The neural network showed that the combination best predicting arrhythmic events included: left ventricular failure during coronary care stay, ventricular dyskinesis, late potentials, number of ventricular premature depolarizations/hour, nonsustained ventricular tachycardia, left ventricular ejection fraction, bundle branch block and digoxin therapy at discharge. The neural network algorithm allowed identification of a small high-risk patient subgroup (12% of the study population) with an arrhythmic event rate of 46%. The sensitivity and specificity of the test were 96 and 93% respectively. CONCLUSIONS: These results suggest that, in postinfarction patients, it is possible to predict early and accurately arrhythmic events by noninvasive variables easily obtainable in most patients. Patients identified as being at risk are candidates for prophylactic antiarrhythmic therapy.

Thermal influences on optical properties of light-emitting diodes: a semiempirical model.

The application of LED technology to fields such as alphanumerical displays and traffic control is continuously increasing. Because the technology is used outdoors, it must be able to operate under various environmental conditions. Like all semiconductor devices, LED's have properties that change with temperature. We propose a semiempirical model, based on semiconductor solid-state theory, that predicts the changes in the emission spectrum including the effect of temperature changes on the optical properties of the LED, within a range appropriate for outdoor applications (0-40 degrees C). This model permits us to evaluate the changes in the output flux and the chromaticity coordinates of the LED. We checked this model with seven different LED's.

Modulation transfer function of translucent rough sheets.

Rough surfaces in translucent protective sheets are used in imaging systems, such as displays, to decrease specular reflections of external sources. However, they modify the quality of the images formed by transmission. Using a geometric approximation, we have modeled the behavior of rough surfaces in imaging systems. This model provides an analytical expression for the modulation transfer function of rough surfaces.

Value of programmed ventricular stimulation in predicting sudden death and sustained ventricular tachycardia in survivors of acute myocardial infarction.

To assess the prognostic value of the response to programmed ventricular stimulation in selected post-acute myocardial infarction (AMI) patients identified at risk of sudden death and spontaneous sustained ventricular tachycardia (VT) (arrhythmic events) by noninvasive, highly sensitive testing, 286 consecutive patients were evaluated prospectively and followed for 12 months. One hundred three patients (group 1) with either left ventricular ejection fraction < or = 40% or ventricular late potentials or spontaneous complex ventricular arrhythmias were considered at risk of late arrhythmic events and eligible for programmed ventricular stimulation; the remaining 183 patients (group 2) were discharged without any further evaluation. Electrophysiologic study was performed 11 to 20 days after AMI utilizing up to 2 extrastimuli and rapid ventricular burst pacing. At the end of the follow-up period, 10 patients in group 1 and 2 in group 2 died of cardiac causes; in addition, 10 patients in group 1 and 1 in group 2 had arrhythmic events. Sustained monomorphic VT was the only inducible arrhythmia related either to cardiac death (p <0.0005) or to arrhythmic events (p <0.0001). It was induced in 11 patients (3 died suddenly, and 3 had spontaneous VT). Multivariate analysis showed that such arrhythmia was the strongest independent predictor of arrhythmic events (F = 9.76; p <0.0001). In the entire study population, it allowed identification of patients at risk, with a sensitivity, specificity, and positive predictive value of 55%, 99%, and 67%, respectively. We conclude that programmed ventricular stimulation performed in selected post-AMI patients, utilizing a moderately aggressive stimulation protocol, is a specific but less sensitive procedure for predicting arrhythmic events; the induction of sustained monomorphic VT allows the accurate identification of patients who may profit by prophylactic antiarrhythmic therapy.

[The prognostic stratification of the risk of sudden death and sustained ventricular tachycardia after an acute myocardial infarct: which patients should undergo programmed ventricular stimulation?]. / Stratificazione prognostica del rischio di morte improvvisa e tachicardia ventricolare sostenuta dopo infarto miocardico acuto: quali pazienti dovrebbero essere sottoposti a stimolazione ventricolare programmata?

BACKGROUND: Programmed ventricular stimulation performed early after acute myocardial infarction allows to identify patients at risk of sudden death and sustained ventricular tachycardia with high degree of predictive accuracy. This procedure, however, because of its invasive nature, is not desirable as a screening test for large numbers of patients. Therefore, it should be performed on a smaller group of postinfarction patients preselected on the basis of noninvasive testing. The aim of the present study was to identify, early after acute myocardial infarction, any procedure among noninvasive testing, able to selected with the highest sensitivity patients at risk of sudden death and sustained ventricular tachycardia to submit to programmed ventricular stimulation. METHODS: Two hundred and sixty four consecutive patients with recent myocardial infarction were evaluated and followed during a period of 12 months. In each patient 48 epidemiological, clinical and laboratory variables were evaluated. Laboratory variables were acquired between the 7th and the 12th day after the acute event. RESULTS: Multiple linear regression analysis showed that only Killip class, the number of ventricular premature depolarizations per hour and the presence of ventricular late potentials were significantly and independently related to the occurrence of sudden death and sustained ventricular tachycardia (F = 18.7; p < 0.00001). Combinations of these variables, determined at cut off levels best discriminating two subgroups of patients at different risk of the end-point events, proved to be able to accurately predict the outcome of our patients. The presence of at least one of the following conditions: Killip class > or = 2, ventricular premature depolarizations > or = 30 per hour, ventricular late potentials allowed to identify a first subgroup of patients at risk with a sensitivity of 100% (p = 0.00007), whereas the presence, at the same time, of all the above mentioned parameters allowed to identify a second subgroup of patients at risk with a 44% of positive predictive value (p = 0.00007). CONCLUSIONS: Our findings suggest that the first subgroup of postinfarction patients selected on the basis of noninvasive testing should undergo programmed ventricular stimulation, the second might be treated by adequate antiarrhythmic therapy without undergo any further investigation, whereas the remaining patients (without late potentials, in Killip class 1 and with ventricular premature depolarizations < 30 per hour) might be discharged without any antiarrhythmic therapy.

[Supraventricular tachyarrhythmias during acute myocardial infarction: short- and mid-term clinical significance, therapy and prevention of relapse]. / Tachiaritmie sopraventricolari durante infarto miocardico acuto: significato clinico a breve e lungo termine, terapia e profilassi delle recidive.

Clinical significance, short and long-term prognostic value, and treatment of supraventricular tachyarrhythmias were evaluated in 208 patients with definite acute myocardial infarction (AMI). No patient received thrombolytic therapy. In Coronary Care Unit supraventricular tachyarrhythmias were detected by continuous electrocardiographic monitoring in 30 (14%) patients: 18 had atrial fibrillation, 1 atrial flutter, 9 paroxysmal atrial tachycardia and 2 non-paroxysmal junctional tachycardia. These episodes began within the first 48 hours of AMI in 93% of patients, and generally they were preceded by frequent or repetitive atrial premature beats. Supraventricular tachyarrhythmias were significantly associated with older age, higher incidence of overt left ventricular dysfunction (both p less than 0.05) and higher Peel Index (p less than 0.02). They caused severe hemodynamic consequences in 20% of patients. In 8 patients they were selflimiting, in 20 they were suppressed by means of medical therapy and in one by DC countershock. During hospitalization supraventricular tachyarrhythmias recurred in one patient; moreover, in this period cardiac death occurred in 26% of patients with supraventricular tachyarrhythmias and in 13% of the remaining (p: ns). Multivariate analysis showed that supraventricular tachyarrhythmias are not important factors in identifying patients at risk of cardiac death. At hospital discharge, patients with supraventricular tachyarrhythmias showed significantly higher values of left ventricular end-diastolic and end-systolic dimensions (both less than 0.05), and a greater use of digitalis-diuretics and/or vasodilators (p less than 0.03). By contrast, in patients with and without supraventricular tachyarrhythmias no significant difference was present with regard to the frequency of New York Heart Association functional classes III-IV for congestive heart failure, frequency of significant tachyarrhythmic events during 24-hour continuous electrocardiographic recording, X-ray cardiac size and left ventricular ejection fraction at rest. In the 2 years following AMI, survival curves showed no significant difference in the risk of cardiac death among patients with or without supraventricular tachyarrhythmias; in particular, in the first group only 2 patients had severe hemodynamic events and no patient showed recurrences of tachyarrhythmia. Our findings suggest that although supraventricular tachyarrhythmias complicating AMI frequently occur in patients with severe cardiac disease they are not related to a higher risk of cardiac death either during in-hospital period or in the 2 years following AMI; medical therapy is effective and safe to suppress these arrhythmias; a systematic use of specific antiarrhythmic drugs to prevent their recurrences is not necessary.

[Evaluation of left ventricular ejection fraction in coronary disease patients by the gated blood pool method and cineangiography. Critical analysis of divergences between the 2 methods]. / La valutazione della frazione di eiezione ventricolare sinistra in pazienti coronaropatici con "gated blood pool method" e con cineangiografia. Analisi critica delle divergenze tra i due metodi.

In order to assess the reliability of left ventricular ejection fraction as estimated by gated blood pool method, radionuclide angiography (LAO) and single plane (RAO) contrast cineangiocardiography were performed within 14 days in 60 patients with coronary artery disease. The mean value of radionuclide ejection fraction was found to be 55 +/- 16%; contrast cineangiographic ejection fraction was 57 +/- 15%; r = 0.92. In 23 patients with previous anterior myocardial infarction gated blood pool method was found to underestimate left ventricular ejection fraction when compared with contrast cineangiography. The observed underestimation was wide significant in 11 patients with previous anterior infarction, low (less than 50%) radioisotopic ejection fraction and septal akinesia and/or apical dyskinesia; radionuclide ejection fraction = 33 +/- 8%; contrast cineangiographic ejection fraction = 42 +/- 9%; r = 0,76. This study confirms that the values of left ventricular ejection fraction as estimated by gated blood pool method in coronary patients are quite reliable; moreover, the intrinsic variability of the data is low. This may be not true in patients with previous anterior myocardial infarction. The Authors discuss the possible causes of disagreement between radioisotopic and contrastographic ejection fraction in patients with previous anterior infarction and poor left ventricular function: physical problems of measuring ejection fraction by gated blood pool in dilated ventricles; possible mistakes in evaluating blood pool due to the low mobility of the blood mass nearest to the scintillation camera; inhability of contrast cineangiography in RAO to recognize the interventricular septum and evaluate its kinetic abnormalities; unreliability of the geometrical model of revolution elypsoid in calculating end-systolic volumes in ventricles with abnormal wall-kinesis.(ABSTRACT TRUNCATED AT 250 WORDS)