The Helmholtz Total Artificial Heart Labtype

Abstract: To perform the first experimental tests for validation of a new gear unit concept, the pump chamber, diaphragm, and pusher plate design of an orthotopic electromechanical total artificial heart (TAH) (Helmholtz Labtype) was manufactured. In its early stage of development, it provides some of the most important features of the conceptual final artificial heart. The new gear unit transforms a uniform unidirectional rotational motor movement into translatory pusher plate movements, with resting phase in the end–diastolic position, and the angled pump chamber orientation determines the available space for the motor and gear unit. Furthermore, this labtype provides flexibility with regard to use of different types of structural parts for experimental investigations. The first in vitro test results, obtained with specially designed circulatory mockloops that simulate physiological preload and afterload conditions, are presented. They comprise pressure and flow generation, motor performance, efficiency, and energy consumption. The results prove the feasability of the new gear unit concept for an electromechanical artificial heart and allow a reliable determination of the necessary performance of the future brushless DC motor for the first in vivo TAH model.     

Clinical Experience with Expanded Polytetrafluoroethylene Gore-Tex® Surgical Membrane for Pericardial Closure: A Study of 110 Cases

Complete closure of the pericardium after cardiac operations has the advantage of avoiding injury of the heart and great vessels during reoperation. Between 1985 and 1987, the pericardium was closed with Gore-Tex Surgical Membrane (SM) in a selected series of 110 patients 1 month to 76 years of age. Fifty-three patients had congenital heart lesions and 57 patients had acquired heart disease. Overall hospital mortality was 3/110 cases. In no instance was there a relationship between occurrence of death and pericardial closure with SM. There was one episode of cardiac tamponade on the seventh postoperative day. One patient developed fever and leukocytosis due to a mediastinal hematoma. During a mean follow-up of 15 months, four patients had to be reoperated upon three, four, eight weeks, and eight months after primary operation. The anterior wall of the heart had no adhesion with the SM and the other parts of pericardium could be dissected easily. Scanning electron microscopic examination of the explanted SM patches showed neither cellular ingrowth nor immunocompetent cellular elements. The Gore-Tex Surgical Membrane has the advantages of easy availability and lack of reaction between its surface and the epicardium and pericardium. We believe its routine use should be encouraged in patients with high probability of reoperation after repair of complex cardiac anomalies, implantation of bioprostheses, coronary revascularization for one- or two-vessel disease, and repair of degenerative disease of the ascending aorta.     

Radiofrequency Ablation of Symptomatic but Benign Ventricular Arrhythmias

Two cases are presented where ablation of severely symptomatic ventricular arrhythmias not responding to medical therapy was accomplished with radiofrequency current application. After a routine programmed stimulation protocol, a quadripolar ablation catheter with a 4-mm tip was advanced percutaneously into the left ventricle in one case and into the right ventricle in the second case; and after precise pace mapping, the arrhythmogenic focus was successfully ablated using radiofrequency current. The postablation ambulatory recording revealed virtual eradication of ventricular ectopy in both cases. In conclusion, in severely symptomatic cases of "benign" ventricular arrhythmias, radiofrequency ablation offers an effective therapeutic alternative.     

Visual spatial attention to stimuli presented on the vertical and horizontal meridian: An ERP study

In the first experiment, 48 subjects carried out a visual spatial attention task. Stimuli were presented at the vertical meridian, either above or below a fixation dot, and the subjects were instructed to attend to one of these stimulus positions and ignore the other position. In three different conditions, the distances between stimulus positions and fixation were 0.5°, 0.9°, and 1.3°. Subjects searched for the presence of prememorized target letters at the attended location: memory load was one or four items in different conditions. The P1/N1 enhancement typically found on the horizontal dimension was not observed on the vertical dimension. Instead, a positive shift of the attended compared with the unattended stimuli was found, which was most prominent at anterior electrodes. This positivity showed effects of the distance manipulation. The N2b-P3a effect of attention and the effect of memory load (search negativity) normally present in this kind of selective search task were also found. Reaction times were faster when attention was directed above fixation than when it was directed below fixation. The event-related potential data suggested that this difference could be attributed to a more efficient neglecting of irrelevant stimuli presented below fixation. In Experiment 2, we examined whether the absence of the P1/N1 enhancement as the result of spatial attention in Experiment 1 could be attributed to (a) the presentation of stimuli along the vertical meridian instead of along the horizontal meridian, (b) the use of midline electrodes instead of lateralized electrodes, and (c) the relatively small spatial separation between the relevant and irrelevant stimuli. Twelve subjects searched for the presence of a single target letter at an attended position in three different conditions. In two of the conditions the letters were presented to the left or right of fixation. The distance between fixation and the stimulus positions was 1.3° in one of these conditions and 3° in the other condition. In the third condition, the stimuli were presented at 3° above or below fixation. In all three conditions effects similar to those in Experiment 1 were observed. In addition, in all three conditions an enhancement of the P1 and N1 components was found at two lateral occipitotemporal electrodes.     

Signal Averaging in Patients withCoronary Artery Disease:

Late Potentials in CAD. In patients who have survived acute myocardial infarction, thepresence of ventricular late potentials using the high resolution signal-averaged KCG indicatesareas of slow conduction and delayed activation that may potentially serve as a substrate lormalignant ventricular arrhythmias. Although detection of late potentials is technique specific, signal-averaged analysis in the time or frequency domain may he a useful index for riskstratification with regard to ventricular tachycardia or sudden cardiac death. The sensitivityand specificity of late potentials for this purpose may he enhanced by comhination with othervariables, such as left ventricular ejection fraction and presence of complex ventricular ectopy, Therefore, the presence of ventricular late potentials in postmyocardial infarction patients, particularly in those patients with impaired left ventricular function, identifies those patienlswho are at high risk of malignant ventricular tachyarrhythmias, However., (he strategies forprevention of serious arrhythmia complications during follow-up need to be established, Thenegative predictive value of late potentials is very high. Thus, the absence of late potentialsindicates a low propensity to sustained ventricular tachycardia or sudden death, even in thepresence of complex ventricular ectopy. Interventions may therefore not be necessary orshould even he avoided, The incidence of late potentials in patients with spontaneous orinduced ventricular fibrillation is lower and, if present, less pronounced than in those with sustained monomorphic ventricular tachycardia. This presumably is due to a lower degree of conduction delay, which serves as a substrate for reentry. Therefore, the ability of the signal-aver-aged ECG to predict a propensity to ventricular fibrillation is limited, Despite these limitations, the signal-averaged ECG may be used as a risk predictor in evaluation of patients aftermyocardial infarction. Unfortunately, at least as far as time domain analysis is concerned, itcannot be used as an efficacy predictor for response to pbarniacologic interventions, Furtherstudies will determine whether other modes of signal-averaged analysis can predict theresponse to drugs.     

Urticaria in association with etiocholanolone fever

A 17-year-old girl is reported with a history of recurrent febrile episodes during her menstrual bleeding accompanied by a generalised exanthem. Increased plasma levels of unbound etiocholanolone were noticed during the febrile attacks. Both the fever and the skin eruption could be suppressed by oral contraceptives.