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Biomedical subjects

G Steinbeck

Publications and source records attributed to G Steinbeck.

At least 91 records · Page 5Linked to original sources
PubMed1997

Influence of anodal electrode position on transvenous defibrillation efficacy in humans: a prospective randomized comparison.

Nonthoracotomy lead systems for implantable cardioverter defibrillators (ICDs) have reduced operative mortality and morbidity as compared to epicardial lead systems but are usually associated with higher defibrillation thresholds (DFTs). The purpose of this prospective randomized trial was to investigate if the second defibrillation electrode in the left subclavian vein can increase defibrillation efficacy and decrease DFT as compared to the superior vena cava (SVC) position in nonthoracotomy lead systems for ICDs. Seventeen patients (mean age: 49.9 +/- 11.3 years, mean ejection fraction: 46.1% +/- 15.8%) were implanted with an investigational unipolar electrode (Medtronic 13001) used as the defibrillation anode. DFT testing was started in the SVC (n = 10, group A) or the left subclavian vein (n = 7, group B), and repeated in the alternative position starting at the DFT of the initial position. Fifteen patients were eligible for analysis (group A: n = 9, group B: n = 6). With the electrode in the SVC, ventricular fibrillation could be successfully terminated in 9 out of 15 patients (60%). In the left subclavian vein the success rate was 100% (P < 0.01). Mean DFT in the SVC was 13.0 +/- 5.2 J and in the left subclavian vein 10.2 +/- 4.9 J. DFTs in the left subclavian vein were either lower (group A: n = 5/9, group B: n = 5/6) or equal to the results in the SVC position (P < 0.001). Thus, the left subclavian vein appears to be a superior alternative for positioning of the defibrillation anode as compared to the SVC for nonthoracotomy lead systems using two separate leads.

Defibrillators, Implantable↗
PubMed1997

The combined transvenous implantation of cardioverter defibrillators and permanent pacemakers.

We developed criteria for implantation and programming of permanent endocardial pacemakers in patients with a nonthoracotomy ICD system. These criteria were prospectively used in 10 patients who recieved an ICD prior to (n = 5) or following (n = 5) implantation of a dual chamber (n = 6) or ventricular (n = 4) pacemaker with a unipolar (n = 4) or bipolar (n = 6) lead configuration. All patients were tested for interactions or malfunctions. Undersensing of ventricular fibrillation by the atrial sense amplifier and inadequate atrial pacing occurred in one patient with a unipolar dual chamber system programmed to AAIR but didn't impair ICD sensing. Transient or permanent loss of capture or sensing of the pacemaker was not observed after ICD shocks with the output programmed to double pulse width and voltage of stimulation threshold and the sensitivity to 50% of the detected R wave. One episode of transient reprogramming occurred without clinical consequences. One unipolar ventricular pacemaker lead had to be exchanged against a bipolar lead because of oversensing of the pacing artifact by the ICD. There was no failure of an ICD to detect ventricular arrhythmias due to inadequate pacemaker activity. During a follow-up period of 21 +/- 11 months, a total of 78 ventricular arrhythmias were effectively treated in six patients. Thus, a combined use of transvenous ICD and pacemaker is possible despite the close vicinity of pacing and defibrillations leads. Optimized programming different to the common settings is required. As interactions occurred only in unipolar pacemaker leads bipolar systems should be used in these patients.

Aged↗
PubMed1997

Management of patients with life-threatening ventricular tachyarrhythmias in the defibrillator era: the need to differentiate.

Patients with a history of sustained ventricular tachyarrhythmias form an extremely inhomogeneous group with respect to presenting arrhythmia, underlying cardiac disease, and therefore, risk of dying suddenly. For subgroups such as ventricular tachycardia in the absence of underlying cardiac disease, radiofrequency catheter ablation offers cure. In others, implantation of a cardioverter defibrillator already appears to have gained the therapy of first choice, leaving only a secondary role to antiarrhythmic drugs. It must be emphasized however, that these new therapeutic strategies have their pros and cons like the older, seemingly out-fashioned approaches of noninvasively or invasively guided antiarrhythmic drug therapy or empiric amiodarone treatment. Until the advent of controlled randomized trials comparing the implantable cardioverter defibrillator (ICD) with the best other, usually medical form of treatment, physicians must continue to base their individual therapeutic decisions on circumstantial published and personal experience. In doing so, the recent achievements of catheter ablation and defibrillator implantation have definitely improved patient care, but have not made antiarrhythmic drugs jobless. With all the alternatives at hand, it remains a challenging task to weigh the benefits and risks of the various approaches against each other in an attempt to tailor the antiarrhythmic intervention to the very individual need of the patient.

Amiodarone↗
PubMed1997

[A comparison of ultrafast computed tomography, magnetic resonance angiography and selective angiography for the detection of coronary bypass patency].

PURPOSE: Validation of ultrafast-CT and MR-angiography (MRA) in comparison with angiography for detection of early postsurgical arterial and venous coronary artery bypass graft (CABG) patency. METHODS: 21 patients with a total of 55 CABG (34 venous and 21 arterial) were studied with angiography, ultrafast-CT (EBT), and MRA. RESULTS: With EBT, patency of 43/45 angiographically patent CABG could be correctly assessed (sensitivity: 96%). With MRA 26 CABG (17 venous and 9 arterial) were identified as patent (sensitivity: 67%). It was not possible to quantify proximal stenosis of three grafts (> 40%) and to evaluate the distal bypass anastomosis with both EBT and MRA. CONCLUSIONS: Ultrafast-CT is a promising minimal invasive screening method for the evaluation of venous and arterial CABG patency. The diagnostic significance of MRA is remarkably reduced.

Aged↗
PubMed1997

Competitive RT-PCR for studying gene expression in micro biopsies.

The technique of RT-PCR has become a powerful method for studying gene expression in various species and tissues. Here we present a competitive PCR for quantitative measurement of absolute levels of mRNA molecules for the regulatory alpha 2/delta subunit of the high-voltage-activated dihydropyridine sensitive human cardiac L-type calcium channel. With the method described the dynamic process of cardiac gene expression can be studied in human endomyocardial biopsies in different patient collectives and even in the individual.

Avian Proteins↗
PubMed1996

Regional differences in current density and rate-dependent properties of the transient outward current in subepicardial and subendocardial myocytes of human left ventricle.

BACKGROUND: Recordings of outward currents in human ventricular myocytes revealed the presence of a large calcium-insensitive transient outward current. This current has been suggested to contribute significantly to regional electrophysiological heterogeneity in myocardial cells and tissue of several animal species and to cause electrical gradients across the ventricular wall. METHODS AND RESULTS: The patch-clamp technique was used to record action potentials and outward currents in myocytes enzymatically isolated from thin subepicardial and subendocardial layers of human nonfailing and failing left ventricle. In all subepicardial cells studied, a calcium-insensitive transient outward current (Ito1) could be recorded with large density (10.6 +/- 1.08 pA/pF at 40 mV), whereas current density of Ito1 in subendocardial cells was fourfold smaller (2.63 +/- 0.31 pA/pF, P<.0001, nonfailing myocardium). In failing hearts, the density of Ito1 was significantly smaller in subepicardial cells (7.81 +/- 0.53 pA/pF, P=.012) but not different in subendocardial myocytes (2.01 +/- 0.23 pA/pF, P=.25). Rate-dependent reduction of peak Ito1 at a 2-Hz depolarization rate was minimal in subepicardial cells (to 92.3 +/- 1.9%), whereas peak Ito1 in subendothelial myocytes was almost suppressed at 2 Hz (reduction to 13.2 +/- 2.1%, P<.0001). The different rate-dependent reduction of the transient outward current was due to a much slower time course of recovery from inactivation in subendocardial cells. Kinetic data, including action potentials recorded at 35 degree C, allow assessment of the role of the transient outward current for electrical activity and transmural voltage gradients in human left ventricle. CONCLUSIONS: Marked regional differences in density and rate-dependent properties of the transient outward current exist in subendocardial and subepicardial layers in human left ventricular myocardium, causing transmural electrical gradients that are important for normal and pathological electrical behavior of the human heart. The difference in recovery rates of the transient outward current is a distinguishing feature between subepicardial and subendocardial myocytes.

Action Potentials↗
PubMed1996

Comparison of a unipolar defibrillation system with a dual lead system using an enlarged defibrillation anode.

The unipolar system for transvenous defibrillation, consisting of a single right ventricular lead as the cathode and the device shell as anode, has been shown to combine low defibrillation thresholds (DFTs) and simple implantation techniques. We compared the defibrillation efficacy of this system with the defibrillation efficacy of a dual lead system with a 12-cm long defibrillation anode placed in the left subclavian vein. The data of 38 consecutive patients were retrospectively analyzed. The implantation of an active can system was attempted in 20 patients (group 1), and of the dual lead system in 18 patients (group 2). Both groups had comparable demographic data, cardiac disease, ventricular function, or clinical arrhythmia. The criterion for successful implantation was a DFT of < or = 24 J. This criterion was met in all 18 patients of group 2. The active can system could not be inserted in 3 of the 20 group 1 patients because of a DFT > 24 J. In these patients, the implantation of one (n = 2) or two (n = 1) additional transvenous leads was necessary to achieve a DFT < or = 24 J. The DFTs of the 17 successfully implanted group 1 patients were not significantly different from the 18 patients in group 2 (12.3 +/- 5.7 J vs 10.8 +/- 4.8 J). The defibrillation impedance was similar in both groups (50.1 +/- 6.1 omega vs 48.9 +/- 5.2 omega). In group 1, both operation duration (66.8 +/- 17 min vs 80.8 +/- 11 min; P < 0.05) and fluoroscopy time (3.3 +/- 2.1 min vs 5.7 +/- 2.9 min; P < 0.05) were significantly shorter. Thus, the active can system allows reliable transvenous defibrillation and a marked reduction of operation duration and fluoroscopy time. The dual lead system, with an increased surface area defibrillation anode, seems to be a promising alternative for active can failures.

Defibrillators, Implantable↗
PubMed1996

[Incidence and localization of apoptosis bodies in human arteriosclerosis lesions].

Increased density of smooth muscle cells is an accepted feature of human restenosis after angioplasty. In addition to migration and proliferation, deregulated forms of programmed cell death may represent pathogenic mechanisms which lead to increased intimal cellularity. The goal of the present study was (i) to demonstrate programmed cell death in human plaque tissue by the detection of apoptotic bodies and to distinguish it from cellular necrosis, (ii) to evaluate the frequency and the localization of apoptotic bodies, and (iii) to compare restenotic and primary lesions for different expression patterns. To this end, coronary and peripheral atherectomy specimens from 14 restenotic and 25 primary lesions were examined by electron microscopy and morphometric analysis. Apoptotic bodies were distinguished from cellular necroses due to distinct morphological features, and were observed extracellularly, isolated or cell membrane-bound, as well as intracellularly in smooth muscle cells and macrophages. The main finding of this study is that hypercellular restenotic tissue from both coronary and peripheral lesions contains fewer apoptotic bodies than hypocellular plaques from primary lesions (p < 0.01 and p < 0.05, respectively). Most importantly, a highly significant, inverse correlation was seen between the density of apoptotic bodies and intimal cellularity (r = -0.67; p < 0.0001). Especially in the extracellular matrix regions, restenotic lesions showed fewer apoptotic bodies (p < 0.001). Again, these plaques exhibited a smaller number of apoptotic bodies with intracellular or membrane-bound localization; however, this observation was without statistical significance compared to primary lesions. For both plaque types, apoptotic bodies were found more frequently (by the factor 4-10) in the presence of smooth muscle cells than with macrophages. With respect to the cellular composition of the plaques, apoptotic bodies were evenly detected in 15-28% of all smooth muscle cells and macrophages. Our results document a considerable intimal density of apoptotic bodies in high-grade human arteriosclerotic lesions and, in addition, reveal nearby smooth muscle cells and macrophages exhibiting intensive phagocytotic capacity. Differences in the density of apoptotic bodies and in cellularity, coincident with an inverse correlation between these determinants, were observed for restenotic and primary tissue. These findings strongly point to deregulated forms of programmed cell death as important pathogenic mechanisms involved in human restenosis.

Aged↗
PubMed1996

[Radiofrequency catheter ablation of an accessory atrioventricular conduction pathway with persistent left superior vena cava and hypertrophic cardiomyopathy].

A 43-year-old man with a 30-year history of WPW-syndrome and a hypertrophic cardiomyopathy developed acute heart failure after onset of atrial fibrillation with fast antegrade conduction, which could be converted to sinus rhythm with antiarrhythmic medication. Catheterization of the coronary sinus during EP testing demonstrated a persistent left superior vena cava. The accessory pathway could be localized at the orifice of an atypical epicardial vein. It was successfully abolished after subvalvular placement of the electrode catheter in the left ventricle. This constellation indicates a combined defect during the regression of the sinus venosus to the sinus coronarius with persistence of conducting muscle fibers. Successful RF ablation procedure provides an obvious risk reduction as a result of a lower frequency of atrial fibrillation and the eliminated risk of ventricular fibrillation due to rapid conduction via an accessory pathway. Beyond that, harmless therapeutic treatment of hypertrophic cardiomyopathy with a calcium-channel-blocker (verapamil type) can follow RF ablation.

Adult↗
PubMed1996

[The value of ultrafast computerized tomography in detection of the patency of coronary bypasses].

Bypass graft patency with ultrafast computed tomography (= Electron Beam Tomography, EBT) was examined in 72 bypass grafts (47 saphenous veins, 25 internal mammary arteries) in 30 patients and compared with coronary angiography. Angiography was performed a mean of 4.4 +/- 3.5 months (range 1-13) from the EBT examination. Contrast material (120 ml) was continuously administered via a peripheral vein and 40 axial slices (3 mm slice thickness, 110 ms scan time) without overlap sequences were obtained, ECG triggered with the single slice scanner mode. Imaging of internal mammary artery grafts began at the thoracic inlet, for saphenous vein grafts, at the undersurface of the aorta. Sixty of 63 angiographically patent bypass grafts were determined patent by EBT (sensitivity 95%), 8 bypass grafts could not be detected by EBT, and 9 were angiographically occluded (specificity 89%). Twenty-four of 25 internal mammary artery grafts were patent at EBT and coronary angiography, one was occluded. In 27 of the 30 patients (90%), all of the angiographically patent grafts could be confirmed as open with EBT. Obstructions of 10 grafts could not be visualized with EBT. Graft insertion into native coronary vessels could be visualized in axial slices, although morphologic quantification of graft insertion stenosis (75-90%) in two cases was not possible. Three dimensional reconstruction of the 40 axial slices allowed graft anatomy to be delineated. Visualization of bypass insertion into the native coronary vessel was less successful because of opacification of the left and right ventricle. Electron beam computed tomography is a minimally invasive procedure capable of evaluating the patency of saphenous vein and internal mammary artery grafts. The morphologic quantification of graft obstruction and visualization of the insertion of the bypasses into the native coronary vessels is less successful with present technology and imaging modalities.

Aged↗
PubMed1996

[Drug therapy of atrial fibrillation: control of heart rate versus establishing sinus rhythm].

Our knowledge about efficacy and safety of various therapeutic strategies is insufficient, especially with respect to the direct comparison of reestablishment of sinus rhythm by drugs in comparison to rate control. Therefore, an initiative of the German Working Group on Electrophysiology of the Deutsche Gesellschaft für Kardiologie--Herz- und Kreislaufforschung is urgently needed which will compare these strategies in a prospective controlled trial (pharmacologic intervention in atrial fibrillation PIAF: Reestablishment of sinus rhythm by the drug amiodarone, in addition DC-defibrillation if necessary; rate control with the calcium antagonist diltiazem). It is hoped that this study will give quantitative data about recurrences of arrhythmia, quality of life and exercise capacity. A much bigger study, presumably including 5300 patients, will be performed in the USA supported by the National Institute of Health (AFFIRM study: atrial fibrillation follow-up: investigation of rhythm management) which will assess the consequences of cardioversion and rate control of atrial fibrillation, not only on morbidity, but also on mortality. Until these study results are available, the physician will have to make his individual choice based on the preferences of the patient, a cost-benefit analysis, current data and experience.

Amiodarone↗
PubMed1995

Failures of epicardial and transvenous leads for implantable cardioverter defibrillators.

Lead failures constitute a major risk for patients with an implantable cardioverter defibrillator (ICD). However, data about the incidence and patterns of ICD-lead failures in a larger population are lacking. We analyzed the short-term and midterm performance of 27 epicardial and 103 nonthoracotomy ICD-lead systems during a follow-up period of 36 +/- 21 months and 22 +/- 10 months, respectively (p < 0.05). The failure rate was 5 (19%) of 27 in the epicardial and 6 (6%) of 103 in the nonthoracotomy group (p < 0.05). The most common symptom was erroneous detection of ventricular fibrillation from artifact sensing in five patients. Two patients had to be resuscitated because of failure to defibrillate. Loss of pacing and loss of sensing were seen in two patients. Only two asymptomatic lead fractures could be diagnosed on routine radiograph. In conclusion, there was a considerable rate of lead failures, especially in epicardial systems. Long-term studies addressing the longevity of ICD leads, mechanisms of their failures, and improved diagnostic facilities are important to further increase the safety of this therapeutic approach.

Defibrillators, Implantable↗
PubMed1995

Defibrillator implantation in a patient with a persistent left superior vena cava.

The implantation of a transvenous cardioverter defibrillator (PCD 7217B) was performed in a patient with a persistent left superior vena cava. The defibrillation electrodes were positioned in the right ventricle and the superior vena cava via the right subclavian vein. A subcutaneous patch had to be implanted at the left lateral chest wall to achieve sufficient defibrillation thresholds. Three weeks later the system had to be removed because of a generator pocket infection. During the second implantation we placed one electrode in the persistent left superior vena cava perpendicular to the electrode in the right ventricle. Using this configuration transvenous defibrillation was possible without an additional subcutaneous patch.

Adult↗
PubMed1995

The left subclavian vein as an alternative site for implantation of the second defibrillation lead.

The optimal placement for the second defibrillation lead in a two-lead system has never been addressed. We retrospectively reviewed the data of 33 patients with an average age of 59.2 years (range 41-78 years), predominantly male (n = 29), who underwent implantation of a cardioverter defibrillator (ICD) for treatment of ventricular tachycardia (n = 19) or ventricular fibrillation (n = 14). In all patients an attempt was made to implant an endovenous ICD device (leads only, no subcutaneous patch). In group I (n = 18) the defibrillation anode, a separate unipolar lead, was placed in the common position, the superior vena cava. In group II (n = 15) the lead was placed in the left subclavian vein. At least two consecutive shocks reverting ventricular fibrillation at energies < or = 24 J were required for implantation of the ICD device. All shocks were monophasic. The success rate of endovenous defibrillation was significantly higher in group II than in group I (67% vs 28%, P < 0.05). Thus, it could be demonstrated that the position of the defibrillation anode can influence the defibrillation efficacy in transvenous ICD systems. Prospective randomized trials are needed to investigate the optimal position for the second defibrillation electrode, which may gain increasing importance as soon as dual chamber ICDs become available.

Adult↗
PubMed1995

[Use of ultra-fast computerized tomography in diagnosis of coronary heart disease].

Ultrafast or electron beam tomography (EBT) permits acquisition of images in 50-100 ms. An artifact-reduced display of heart and vessel structures as well as calcifications can be achieved. Therefore, EBT can be used for the detection and quantification of coronary artery calcification. Thirty-two patients with known coronary artery disease (CAD) were studied by EBT with and without i.v. contrast enhancement and with conventional coronary angiography. Different scoring systems were applied in order to define the basis to compare the data. The results showed a high EBT sensitivity for detection of coronary artery stenosis of up to 94% but low specificity with a maximum of 75%, depending on the scoring system applied. With EBT, differentiation between significant CAD (> 75%) and low-grade CAD (0-75%) showed significant results. The scoring system is not yet completely satisfactory, and with the integration of other screening tests and continuous development of scoring systems, the significance and reliability of this method in evaluation of CAD are expected to increase.

Aged↗
PubMed1994

Hemodynamic deterioration during ICD implant: predictors of high-risk patients.

Defibrillation threshold (DFT) testing during implantation of the cardioverter defibrillator is associated with hemodynamic deterioration and pump failure in many patients. We investigated the influence of DFT testing on cardiac function intraoperatively using a balloon-tipped catheter. In 13 consecutive patients with a nonthoracotomy approach, a mean of 3.4 +/- 1.4 episodes of ventricular fibrillation were induced with an overall ischemic time of 87 +/- 54 seconds. At the end of DFT testing, patients with a left ventricular ejection fraction (EF) of < 30% had significant impairment of cardiac index (1.6 +/- 0.5 L/min/m2 after testing vs 2.2 +/- 0.6 L/min/m2 before the procedure). One patient with severely comprised ventricular function needed prolonged positive inotropic support. The left ventricular function of patients with a preoperative EF > or = 30%, however, was not changed (2.2 +/- 0.5 L/min/m2 after testing and 2.2 +/- 0.5 L/min/m2 before testing). The two groups did not differ with respect to the number of testing episodes, ischemic time, or DFT. Thus patients with a low preoperative EF (< 30%) are threatened by a severe left ventricular deterioration during ICD implantation. Close hemodynamic monitoring with a balloon-tipped catheter is recommended in these patients.

Cardiac Pacing, Artificial↗
PubMed1994

One-incision approach for insertion of implantable cardioverter defibrillators.

The placement of a transvenous implantable cardioverter defibrillator (ICD) system through a single infraclavicular skin incision has been a surgical goal for years. The development of a new investigational model of ICD with substantially reduced dimensions (volume, 83 cm3; mass, 132 g) has made the one-incision approach a clinical reality. Between March and September 1993, 4 female and 19 male patients (mean age, 60 +/- 9.6 years; range, 46 to 73 years) underwent implantation of this device for the treatment of ventricular fibrillation (n = 14) or ventricular tachycardia (n = 9). One transvenous lead was placed in the right ventricular apex and another in the left subclavian vein. A subpectoral pocket was formed in the infraclavicular area from the same incision to house the ICD generator and, if necessary, the subcutaneous patch. The mean operation time (81.5 +/- 32.7 minutes; range, 54 to 195 minutes) was significantly shorter than that noted for a previous series made up of patients undergoing traditional transvenous ICD implantations. In 20 patients (87%), endovenous defibrillation without a subcutaneous patch successfully caused externally induced ventricular fibrillation to revert with a mean minimum energy output of 21.9 +/- 3.5 J (range, 12 to 24 J). Endovenous defibrillation was more successful when biphasic (n = 16/17 [94%]) shocks rather than monophasic shocks (n = 4/6 [67%]) were used. No mortality, morbidity, or surgical complications were observed. These results indicate that the one-incision approach and the small size of the ICD generator can substantially facilitate ICD implantation and result in a reduction in the surgical trauma, the operation time, and the amount of material implanted.

Aged↗