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.     

Bidirectional transvenous/subcutaneous defibrillation of ventricular fibrillation in dogs: success rates, energy requirements, currents, voltages and impedance

Four hundred and thirteen defibrillations of alternating current-inducedventricular fibrillation were performed in 10 halothane-anaesthetizeddogs (body weight: 24.5–30.5 kg). Success rates, energydemands, currents, peak voltages and impedance were determined.A transvenous catheter electrode system (Medtronic 6880, rightventricular apex and superior vena cava, distance 100 or 150mm) and subcutaneous patch electrodes (Intec 67 L, 2nd/3rd and/or3rd/4th left intercostal space) were used for bidirectionaldefibrillation. Loading voltages ranged from 600 to 850 V. Withan electrode distance of 100 mm and a pulse duration of 2 msseparated by 1 ms, success rates were 100%, 40% and 0% for 850,650 and 600 V, respectively. With a 3-ms pulse duration, thecorresponding rates were 100%, 60% and 50%. With a 2-ms pulseduration, successful defibrillation was achieved with energieslower than 15 J in 27%, with energies between 15 and 20 J in77%, and 100% with energies higher than 20 J. Defibrillationcurrents were 4.4–9.3 A for pulse 1 (superior vena cava/ventricularapex) and 6.3–13.4 A for pulse 2 (patch/ventricular apex),respectively. Effective peak voltages ranged from 510 to 787V and from 514 to 777 V and averaged 89.6% of the loading voltages.Impedance values (peak voltage/current) were 75.5–117.7(pulse 1) and 51.7–94.9 Ohms (pulse 2). Fifty consecutivedefibrillations in one animal resulted in a decrease of impedance(114.6 to 84.9 Ohms, pulse 1; 75.4 to 53.0 Ohms, pulse 2). Defibrillationof ventricular fibrillation can be achieved with acceptablylow energies using a bidirectional transvenous/subcutaneoussystem, avoiding thoracotomy and general anaesthesia for implantationof the defibrillation system.     

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.     

Temperature-controlled Radiofrequency Catheter Ablation of Accessory Pathways and Atrioventricular Nodal Reentrant Tachycardia: The 5-French Catheter Approach

Ablation with Temperature-Controlled 5-French Catheters. Introduction: In the present study, we assessed the feasibility of radiofrequency (RF) ablation of accessory pathways and AV nodal reentrant tachycardias with novel 5-French catheters with 4-mm tip electrodes using established mapping criteria and temperature-controlled power output control. Methods and Results: In this prospective study, 60 consecutive adult patients (mean age 36 ± 20 years) with accessory pathways (n = 37; 24 left-sided) or AV nodal reentrant tachycardia (n = 23) underwent RF catheter ablation. A 5-French catheter with a 4-mm tip electrode and an embedded thermistor was used for RF application. The surface of the tip electrodes was 26 mm2 compared to 38 mm² of 7-French catheters with 4-mm tip electrodes from the same catheter series. Power output was automatically and continuously adjusted according to the preset catheter tip temperature of 60° to 70°C. Pulse duration was 90 seconds. For left-sided accessory pathways, the retrograde route via the femoral artery was used. After removing the 5-French sheaths, only 4 hours of bed rest were advised. For ablation of AV nodal reentrant tachycardia, the so-called slow pathway was targeted for ablation. Acute success was achieved in 34 (92%) of 37 patients with accessory pathways and 23 (100%) of 23 patients with AV nodal reentrant tachycardia. A mean of 3 ± 4 RF pulses (median 2 pulses; range 1 to 20 pulses) was applied. The mean fluoroscopy time was 26 ± 21 minutes. No complete AV block or other procedure-related complications were observed. Recurrences occurred in 2 patients with accessory pathways and in 2 patients with AV nodal reentrant tachycardia during a follow-up of 9 ± 4 months. Conclusions: Temperature-controlled RF ablation of accessory pathways and AV nodal reentrant tachycardia in adults using 5-French catheters is feasible, effective, and safe. Ablation with 5-French catheters might help to reduce the complication rate of catheter ablation techniques.     

Radiofrequency Catheter Ablation of Idiopathic Left Ventricular Tachycardia:

Idiopathic Left Ventricular Tachycardia. Introduction: Idiopathic left ventricular tachycardia with a QRS pattern of right bundle branch block and left-axis deviation constitutes a rare but electrophysiologically distinct arrhythmia entity. The underlying mechanism of this tachycardia, however, is still a matter of controversy. This report describes findings in a 42-year-old man who underwent successful radiofrequency catheter ablation of idiopathic left ventricular tachycardia.
Methods and Results: On electrophysiologic study, the tachycardia was reproducibly induced and terminated with double ventricular extrastimuli. Intravenous verapamil terminated the tachycardia whereas adenosine did not. Detailed left ventricular catheter mapping during sinus rhythm revealed a fragmented delayed potential at the mid-apical region of the inferior site near the posterior fascicle of the left bundle branch. At the same site, continuous electrical activity throughout the entire cardiac cycle was recorded during ventricular tachycardia. Repeated spontaneous termination of this continuous electrical activity in late diastole was followed immediately by termination of the tachycardia. Single application of radiofrequency current for 20 seconds at this site completely abolished inducibility of the tachycardia. After catheter ablation, at the identical site of preablation recording of the fractionated potential during sinus rhythm, no fragmented delayed activity could be recorded. There was no complication from the ablation procedure.
Conclusion: The preablation recordings of fragmented delayed potentials during sinus rhythm and continuous diastolic electrical activity during tachycardia, together with ablation characteristics and previously reported electrophysiologic properties of this arrhythmia, may further support microreentry as the underlying mechanism in idiopathic left ventricular tachycardia.     

Radiofrequency Catheter Ablation of the Anterosuperior and Posteroinferior Atrial Approaches to the AV Node for Treatment of AV Nodal Reentrant Tachycardia

Catheter Ablation Techniques in AVNRT. Radiofrequency catheter ablation has been established as a first-line curative treatment modality in patients with symptomatic AV nodal reentrant tachycardia (AVNRT). The successful sites of stepwise catheter ablation approaches of the so-called fast and slow pathways strongly suggest that AVNRT involves the atrial approaches to the AV node. The typical fast pathway ablation sites are located anterosuperior toward the apex of the triangle of Koch, which also contains the compact AV node, whereas the usual slow pathway ablation sites are located posteroinferior toward the base of the triangle of Koch at a greater distance to the compact AV node and bundle of His. Accordingly, ablation studies with large patient cohorts have demonstrated that fast pathway ablation carries a higher risk of inadvertent complete AV block. Thus, the slow pathway is clearly the primary target site, and fast pathway ablation is rarely necessary. Different approaches for slow pathway ablation have been elaborated: anatomically oriented stepwise techniques, ablation guided by double potentials recorded within the area of the slow pathway insertion, and combined techniques. The modern concept of AVNRT suggests that this arrhythmia involves the highly complex three-dimensional nonuniform anisotropic AV junctional area. Accordingly, mapping and ablation studies demonstrated that the anterior approach is not identical with fast pathway ablation, and the posterior approach is not identical with slow pathway ablation. Therefore, it is essential for interventional electrophysiologists to familiarize themsdves with the anatomic and electrophysiologic details of this complex and variable specialized AV junctional region. In this review, the anatomic and pathophysiologic aspects of the AV junctional area as they relate to interventional therapy are summarized briefly, and the catheter techniques for ablation of the so-called fast and slow AV nodal pathways for the treatment of AVNRT are described.     

Erroneous Discharge of an Implantable Cardioverter Defibrillator Caused by an Electric Razor

We report an unusual case of the erroneous discharge of a third-generation multiprogrammable implantable Cardioverter defibrillator in a 64-year-old patient with a history of recurrent ventricular tachycardias caused by electromagnetic interference while shaving with an electric razor. Electromagnetic interference was related to a defect in the electrode's insulation and could not be provoked in an intact electrode .