Search PubMed⌕ Search

Biomedical subjects

G Steinbeck

Publications and source records attributed to G Steinbeck.

At least 109 records · Page 6Linked to original sources
PubMed1994

Biological effects of shock waves: induction of arrhythmia in piglet hearts.

During lithotripsy by electrohydraulic or electromagnetic lithotripters, the application of extracorporeal shock waves has to be synchronized with the electrocardiogram to reduce the induction of arrhythmias. The relation between the refractory period of the cardiac cycle and arrhythmia induction by shock waves, and the underlying mechanism have so far not been examined. In this experiment, the cardiac response to shock waves administered at 20 kV by an electrohydraulic lithotripter was assessed in nine piglets. The focus was positioned 5, 10 and 15 cm caudal to the apex of the left ventricle, and in some piglets also at the apex. The interval following the R-wave was determined during which the heart was refractory to shock wave stimulation by either single discharges or shock-wave bursts, i.e., groups of discharges separated by 10 ms intervals. This mechanical refractory period was compared to its electrical counterpart, which was determined by transvenous intracardiac atrial stimulation. As a result, mechanical refractory periods following the R-wave were at 5 cm distance 60 ms for single discharges and 70 ms for bursts (medians; range 10-180 ms); both stimulation modes were highly correlated (r = 0.88). While a similar result was obtained with the focus positioned directly at the cardiac apex, at 10 cm distance from it, bursts elicited a cardiac response significantly more often (in nine vs. two piglets). At 15 cm distance, no response was obtained at all. Both mechanical and electrical atrial refractory periods were in a similar range.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1994

A rapid assay for the quantification of myoglobin: evaluation and diagnostic relevance in the diagnosis of acute myocardial infarction.

We evaluated a new, fast, quantitative, turbidimetric assay (TurbiTimeSystem, Behringwerke AG, Marburg, Germany) for the determination of myoglobin concentration in serum. Within-run imprecision (n = 10) was < 3.7% in controls ranging from 81.1 to 621.4 micrograms/l and between-day imprecision (n = 50) was < 6% in controls ranging from 69.5 to 623.4 micrograms/l. The assay is linear over the measuring range and interfering substances such as bilirubin, haemoglobin or haptoglobin do not interfere but triacylglycerol-rich samples are only measurable after brief ultracentrifugation. EDTA- or citrate-treated samples display depressed myoglobin concentration when compared with serum samples. The upper reference limit for apparently healthy individuals (n = 100, 50 female and 50 male) is 61.5 micrograms/l. Comparison with nephelometry revealed a good correlation (r = 0.982) between the two methods with the regression equation: turbidimetric assay = 5.53 + 1.02x nephelometric assay. Serial determination of myoglobin concentration and creatine kinase in 18 patients with proven acute myocardial infarction showed in general an equal diagnostic significance for both analytes. In the first 4 hours after onset of chest pain, the determination of myoglobin can have an advantage, since it is released into the blood stream at an earlier stage, but thereafter myoglobin can lead to false negative diagnosis. Therefore, determination of creatine kinase and its isoenzyme MB is still the diagnostic strategy of choice in the diagnosis of acute myocardial infarction.

Citrates↗
PubMed1994

[The use of digitalis glycosides in atrial fibrillation].

The role of cardiac glycosides for conversion of atrial fibrillation to simus rhythm is controversially discussed. In a prospective study, 45 patients with paroxysmal atrial fibrillation were randomly assigned to one of three treatment groups (of 15 patients each). Group I received oral digoxin, three times 0.125 mg up to twice 0.25 mg daily; group II oral digoxin twice 0.125 mg and quinidine hydrogen sulphate 750-1000 mg daily; group III oral digoxin three times 0.125 mg and flecaimide 200-300 mg daily. During a mean observation period of 11 months, digoxin alone was significantly less effective (p < 0.05) in reducing or suppressing paroxyms of atrial fibrillation than digoxin plus quinidine or flecainide. The use of digoxin remains a mainstay of treatment for rate control in atrial fibrillation. To convert atrial fibrillation to sinus rhythm, however, the addition of a type I or III antiarrhythmic agent is necessary.

Administration, Oral↗
PubMed1994

[Quality assurance in cardiology: ergometry/long-term ECG].

Besides routine Ecg, exercise testing and Holter monitoring represent the most frequently applied non invasive cardiological examinations, performed not only within the hospital and by practising cardiologists, but most frequently by general practitioners as well as internists. Recommendations for standards of these methods have been published by Working Groups of the European Society of Cardiology as well as the American College of Cardiology and the American Heart Association. Based on these recommendations, this manuscript gives a survey about the prerequisites (equipment, staff), indications, "lege artis"-procedure, as well as interpretation of the results of both techniques. These recommendations can be used to set certain standards; furthermore, possibilities for the control of these quality standards are outlined.

Arrhythmias, Cardiac↗
PubMed1994

[Inadequate therapeutic effects of implantable cardioverter/defibrillators: etiology, therapy and prevention].

With the increasing number of implantable cardioverter-defibrillator (ICD) implantations in patients with sustained ventricular tachyarrhythmias, there is a growing interest in typical complications associated with this therapy. We analyzed the reasons and the incidence of inadequate therapy deliveries in 100 patients with epicardial (n = 27) or transvenous (n = 73) ICDs during a follow-up period of 10 +/- 8 months. A total of 21 of 100 patients received inadequate therapies. The most common reason was sinus tachycardia in eleven patients. Additional unnecessary shocks were avoided by reprogramming and application of beta-blockers. Lead failures caused the erroneous detection and defibrillation of ventricular fibrillation without any preceding clinical symptoms in four patients with an epicardial and in one patient with a transvenous ICD. All patients underwent successful surgical revision of their system. Atrial fibrillation with rapid ventricular response triggered inadequate shocks in four patients. Following digoxin administration no patient had additional inadequate shocks. In one patient non-sustained tachycardias caused unnecessary defibrillations. These results demonstrate that inadequate defibrillations are a common complication in patients after ICD-placement. The performance of x-ray, stress testing, and Holter monitoring on a regular basis may facilitate early diagnosis of possible reasons for unnecessary therapy deliveries. The improvement of detection and memory functions in future ICD-generations appears to be mandatory as well.

Adolescent↗
PubMed1993

Hemodynamic changes due to intraoperative testing of the automatic implantable cardioverter defibrillator: implications for anesthesia management.

During the insertion of an automatic implantable cardioverter defibrillator, repeated induction of ventricular tachycardia or ventricular fibrillation and subsequent defibrillation is performed to determine the defibrillation threshold. In this study, the influence of these testing episodes on myocardial function was investigated in 13 patients under general anesthesia. Preoperative ejection fraction (EF) was 41 (14 to 84) % (median and range). Testing was performed 3 (2-5) times. During these testing episodes the patients received a total of 4 (2-8) countershocks. Patients with a preoperative EF < 30% (N = 5) showed a significant reduction of cardiac index (CI) from 2.2 (1.5-3.3) L/min/m2 before testing to 1.5 (1.3-2.3) L/min/m2 after the last testing episode, and of left ventricular stroke work index (LVSWI) from 32 (14-53) g.m/m2 before testing to 22 (7-43) after the last testing episode. These changes were not related to the total fibrillation time or the cumulative defibrillation energy. Patients with a preoperative EF > 30% (N = 8) showed no significant changes of CI (2.15 [1.8-3.0] L/min/m2 v 2.15 [1.7-3.0] L/min/m2) or LVSWI (35 [28-48] g.m/m2 v 33.5 [27-52] g.m/m2). Comparison of the two patient groups revealed similar hemodynamic baseline values, but significant differences in LVSWI after the last testing episode. Defibrillation testing may produce a further reduction in myocardial performance in patients with preexisting poor cardiac function.

Adolescent↗
PubMed1993

Temperature-controlled radiofrequency catheter ablation of AV conduction: first clinical experience.

A new technique for catheter ablation of atrioventricular (AV) conduction, using temperature-controlled radiofrequency energy and a bipolar asymmetrical electrode configuration, was applied to 12 patients (mean age, 48 +/- 15 years; range, 18-69 years) with medically refractory atrioventricular nodal reentrant tachycardia (AVNRT) or rapid atrial rhythms. The energy source was a 500 kHz generator with automatic power regulation to a preselected temperature of 80 degrees C. A specially designed 7 F bipolar asymmetric thermo-catheter was used for ablation in all cases. The endpoints of the procedure were: first-degree AV block in patients with AVNRT and third-degree block in patients with atrial fibrillation or flutter. Energy was applied over a range of 1-14 times per patient. After a mean follow-up of 8 +/- 4 months, third- or first-degree AV block persisted in eight patients. In comparison to constant-power radiofrequency ablation, where impedance rises are commonly observed, no impedance rise or coating of the electrode occurred during any of the 97 energy applications in this study. Variable wall contact of the electrode was identified in 20 of 97 applications by a slow temperature rise or a drop in temperature and frequent power adjustments. Thus, monitoring temperature and automatic power regulation may help to reduce the total delivered energy. Temperature control during radiofrequency energy avoids coagulum formation and consequently the associated potential hazards of constant-power application.

Adolescent↗
PubMed1993

Randomized crossover comparison of the electrophysiologic and antiarrhythmic efficacy of oral cibenzoline and sotalol for sustained ventricular tachycardia.

We compared the electrophysiologic and clinical effects of oral cibenzoline and sotalol in 12 patients with spontaneous and inducible sustained ventricular tachycardia (VT), using a randomized, open-label, cross-over study. Electrophysiologic studies were performed in the control state, after oral cibenzoline and after oral sotalol, using an incremental dose-titration protocol. Therapy with cibenzoline at the maximum dose level (130-390 mg/day) resulted in complete suppression of VT in 1 of 12 patients (8%). Sotalol (160-320 mg/day) prevented induction of VT in 4 of 12 patients (33%). The effective refractory period (ERP) of the right ventricle was more significantly prolonged with sotalol (p < 0.001) as compared with cibenzoline (p < 0.05). Neither drug prolonged QT duration corrected for frequency (QTc) and cycle length of induced VT, as compared with the control study. Three patients experienced spontaneous VT after cibenzoline administration, and 2 patients experienced incessant VT during programmed electrical stimulation. No patient had a proarrhythmic effect while receiving oral sotalol treatment. Chronic sotalol therapy maintained long-term arrhythmia suppression in all 4 responders at 1-year follow-up. Sotalol appears to have greater efficacy than and a safety profile superior to that of cibenzoline. Drug-related proarrhythmic effects of oral cibenzoline therapy occurred with greater frequency than that associated with other antiarrhythmic drugs. Based on these findings, cibenzoline cannot be recommended for use in patients with VT.

Administration, Oral↗
PubMed1993

Should radiofrequency current ablation be performed in asymptomatic patients with the Wolff-Parkinson-White syndrome?

The exiting new method of ablation of accessory pathways using radiofrequency current applied by catheters will dramatically change our therapeutic decisions in these patients in the near future. This brief survey reviews the existing literature about the risk of the disease as well as of the procedure of catheter ablation. From these data, the risk of sudden death appears to be extremely low in asymptomatic Wolff-Parkinson-White (WPW) individuals. Side effects of catheter ablation may result from the invasive procedure as well as from radiation exposure (the latter to the patient as well as to operating physicians). While the complication rate in experienced centers is extremely low, a multicenter registry of the success and complication rate is urgently needed in view of the many centers starting with catheter ablation. Based on a subjective benefit-to-risk analysis, asymptomatic WPW individuals should be offered catheter ablation only under special circumstances (high risk profession, athletes, family history of sudden death). On the other hand, catheter ablation need not be and should not be considered generally in asymptomatic individuals with WPW pattern. Finally, this author cannot imagine that the energy, time, and money spent for mass screening and eventual catheter ablation of asymptomatic WPW individuals with its attending risks can be outweighed by the potential benefits for these asymptomatic individuals.

Catheter Ablation↗
PubMed1993

[Ventricular tachyarrhythmia in acute and chronic myocardial ischemia: value of diagnostic procedures].

The analysis of the outcome of patients after myocardial infarction in general, as well as of studies to predict the outcome of asymptomatic post-myocardial infarction patients by non-invasive methods, leads to the following conclusions: 1) The incidence of ventricular fibrillation and mortality after acute myocardial infarction has been declining since the 1970s (2); the causes for this reduction are presumably multifactorial (thrombolysis of acute infarction, administration of ACE-inhibitors and increasing prescription of beta-blockers, improvement of intensive care medicine, rigorous correction of risk factors). 2) Development of ventricular tachycardia, electrocardiographically documented ventricular fibrillation or successful reanimation due to sudden circulatory arrest in clinical studies of post-myocardial infarction patients are endpoints which in future studies must be differentiated from each other. 3) In contrast to previous assumptions, the outcome of patients with primary ventricular fibrillation after acute myocardial infarction, that is, without preceding symptoms is guarded, so that such an event should prompt invasive diagnostic evaluation (coronary arteriography, programmed stimulation (?)). 4) Newer methods for risk stratification after myocardial infarction during the chronic phase, such as programmed stimulation, late potential analysis from the body surface as well as programmed ventricular stimulation appear to be superior to more conventional methods such as long-term ECG monitoring as well as exercise testing. It is recommended that all methods which determine the arrhythmogenic substrate are combined with a parameter of left ventricular ejection fraction because of the paramount importance of left ventricular pump function.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Nervous System↗
PubMed1993

[Electrotherapy of supraventricular tachycardia (atrial fibrillation/atrial flutter)].

Contrary to patients with the WPW-syndrome and AV nodal reentry in whom radiofrequency catheter ablation is the therapy of first choice for cure from these arrhythmias instead of life-long medical therapy, pharmacologic therapy of atrial fibrillation and atrial flutter remains the treatment of choice in these patients. If, however, atrial fibrillation with rapid atrioventricular conduction is medically intractable and associated with severe haemodynamic impairment, these patients may be offered catheter ablation of AV conduction by radiofrequency energy. Compared to DC ablation, this approach is associated by an acceptable complication rate. Including the left ventricular approach in cases where it is not possible to ablate AV conduction using the venous approach, the success rate to achieve third degree AV block approaches 100%. With the development of temperature-controlled radiofrequency catheter ablation, a further reduction of side effects is anticipated. A disadvantage of this approach is the need for permanent pacemaker implantation (usually rate-adaptive VVI stimulation) after induction of complete AV block. Therefore, the advantage of normalization of ventricular rate by ablation of AV conduction has to be weighed against the risk of life-long pacemaker treatment for complete AV block in every patient. Patients with medically intractable typical atrial flutter may be offered the following alternative modes of electric treatment: selective ablation of the area of slow conduction sustaining circus movement in the right atrium underlying atrial flutter, by radiofrequency energy without interrupting AV conduction, implantation of a permanent antitachycardia pacemaker with electrodes positioned in the right atrium, radiofrequency catheter ablation of AV conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Fibrillation↗
PubMed1992

Prognosis of patients with sustained ventricular tachycardia and of survivors of cardiac arrest not inducible by programmed stimulation.

The aim of this study was to analyze the long-term clinical outcome of 60 prospectively studied patients with documented sustained ventricular tachyarrhythmia that was not inducible during baseline programmed ventricular stimulation: 39 with cardiac arrest due to noninfarction ventricular fibrillation (VF) and 21 with mild hemodynamically compromising sustained ventricular tachycardia (VT). Left ventricular ejection fraction was 55 +/- 14% in the VF group and 50 +/- 13% in the VT group (difference not significant). Patients were discharged without conventional antiarrhythmic drugs and received only empirical beta-blocker therapy. During a mean follow-up period of 21 +/- 16 months (mean +/- SD), 10 of 60 patients (17%) died suddenly. The actuarial incidence of sudden death at 1 and 4 years was similar in both groups (VF group, 10 and 20%; VT group, 16 and 16%) (p = 0.48). The actuarial incidence of sudden cardiac death was significantly higher in patients with left ventricular ejection fraction < or = 40% than in those with > 40% (1-year incidence in VF group, 40 vs 0%; VT group, 50 vs 0%) (p = 0.005 and p = 0.01, respectively). Multivariate regression analysis identified left ventricular ejection fraction < or = 40% and previous myocardial infarction as the only independent predictor of sudden cardiac death. The occurrence of frequent ventricular pairs during Holter monitoring was the only independent predictor of sustained VT recurrences. It is concluded that patients with sustained ventricular tachyarrhythmia in whom arrhythmia was non-inducible during baseline ventricular stimulation and not treated with antiarrhythmic therapy have a favorable outcome if left ventricular ejection fraction is high.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1992

A comparison of electrophysiologically guided antiarrhythmic drug therapy with beta-blocker therapy in patients with symptomatic, sustained ventricular tachyarrhythmias.

BACKGROUND: Antiarrhythmic drug therapy guided by invasive electrophysiologic testing is now widely used in patients with symptomatic, sustained ventricular tachyarrhythmias. METHODS: We conducted a prospective, randomized trial in 170 patients to investigate whether this approach would improve long-term outcome. Patients whose arrhythmia was inducible by programmed electrical stimulation were assigned to treatment with electrophysiologically guided drug therapy based on serial testing (61 patients) or with metoprolol (54 patients). Electrophysiologically guided therapy consisted of serial testing of antiarrhythmic agents to identify the first one that rendered the arrhythmia noninducible. The 55 patients whose arrhythmia was noninducible during the initial electrophysiologic test were also treated with metoprolol. RESULTS: During a mean (+/- SD) follow-up period of 23 +/- 17 months, recurrent, nonfatal arrhythmia occurred in 44 patients and sudden death due to cardiac factors in 27. The incidence of symptomatic arrhythmia and sudden death combined was virtually the same in the two groups with inducible arrhythmia after two years of observation (electrophysiologically guided therapy vs. metoprolol therapy, 46 percent vs. 48 percent). The outcome was more favorable in the patients with noninducible arrhythmia at base line (75 percent had neither adverse event) than in those with inducible arrhythmia who were assigned to metoprolol therapy (P = 0.009 by log-rank test). Only 6 of the 29 patients (21 percent) with inducible arrhythmia that became noninducible during drug therapy had recurrent arrhythmia or sudden death, as compared with 21 of the 32 patients (66 percent) with arrhythmia that continued to be inducible (P less than 0.001). A multivariate regression analysis identified continued inducibility of the arrhythmia as an independent predictor of recurrent arrhythmia or sudden death (relative risk, 7.3; 95 percent confidence interval, 2.3 to 23.2; P less than 0.001). CONCLUSIONS: As compared with metoprolol therapy, electrophysiologically guided antiarrhythmic drug therapy did not improve the overall outcome of patients with sustained ventricular tachyarrhythmias. However, effective suppression of inducible arrhythmia by antiarrhythmic drugs was associated with a better outcome than was lack of suppression.

Adrenergic beta-Antagonists↗
PubMed1992

Biophysical parameters of radiofrequency catheter ablation.

Radiofrequency catheter ablation has been shown to be an effective treatment for patients with accessory pathways in Wolff-Parkinson-White syndrome and other supraventricular tachycardias. However, the biophysical parameters used so far in vivo did not correlate to the size of myocardial lesions and provided no information about the myocardial wall contact of the electrode. In this study 104 radiofrequency applications were performed on excised pig myocardium in circulating heparinized pig blood as well as in blood alone, and root mean square (rms) voltage, root mean square current and phase angle were measured using a specially developed device. The calculated effective power and output power differed by only 2-7% when measured at the point of maximum current during coagulation. A drop of current following a rise in impedance led to a phase displacement of more than 80 degrees and thereby to a drop of effective power to 17% of the output power. Hence, apparent output power consists mainly of ineffective power. The time dependent variations of phase angle, impedance and current were found to be useful for distinguishing between the media blood and myocardium. These results show that physical parameters measured during radiofrequency catheter ablation may help to control electrode position in the clinical situation and reduce the number and duration of ineffective energy applications.

Animals↗