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Biomedical subjects

T Lewalter

Publications and source records attributed to T Lewalter.

At least 19 recordsLinked to original sources
PubMed2001

Prevalence of left atrial chamber and appendage thrombi in patients with atrial flutter and its clinical significance.

OBJECTIVES: The study was done to assess the prevalence of left atrial (LA) chamber and appendage thrombi in patients with atrial flutter (AFl) scheduled for electrophysiologic study (EPS), to evaluate the prevalence of thromboembolic complications after transesophageal echocardiographic (TEE)-guided restoration of sinus rhythm and to evaluate clinical risk factors for a thrombogenic milieu. BACKGROUND: Recent studies showed controversial results on the prevalence of atrial thrombi and the risk of thromboembolism after restoring sinus rhythm in patients with AFl. METHODS: Between 1995 and 1999, patients with AFl who were scheduled for EPS were included in the study. After transesophageal assessment of the left atrial appendage and exclusion of thrombi, an effective anticoagulation was initiated and patients underwent EPS within 24 h. RESULTS: We performed 202 EPSs (radiofrequency catheter ablation, n = 122; overdrive stimulation, n = 64; electrical cardioversion, n = 16) in 139 consecutive patients with AFl. Fifteen patients with a thrombogenic milieu were identified. All of them had paroxysmal atrial fibrillation (AF). Transesophageal echocardiography revealed LA thrombi in two cases (1%). After EPS no thromboembolic complications were observed. Diabetes mellitus, arterial hypertension and a decreased left ventricular ejection fraction were found to be independent risk factors associated with a thrombogenic milieu. CONCLUSIONS: The findings of a low prevalence of LA appendage thrombi (1%) in patients with AFl and a close correlation between a history of previous embolism and paroxysmal AF support the current guidelines that patients with pure AFl do not require anticoagulation therapy, whereas patients with AFl and paroxysmal AF should receive anticoagulation therapy. In addition, the presence of clinical risk factors should alert the physician to an increased likelihood for a thrombogenic milieu.

Aged↗
PubMed2001

Interference with cardiac pacemakers by magnetic resonance imaging: are there irreversible changes at 0.5 Tesla?

The safety and feasibility of magnetic resonance imaging (MRI) in patients with cardiac pacemakers is an issue of gaining significance. The effect of MRI on patients' pacemaker systems has only been analyzed retrospectively in some case reports. Therefore, this study prospectively investigated if MRI causes irreversible changes in patients' pacemaker systems. The effect of MRI at 0.5 Tesla on sensing and stimulation thresholds, lead impedance and battery voltage, current, and impedance was estimated during 34 MRI examinations in 32 patients with implanted pacemakers. After measurements at baseline and with documentation of intrinsic rhythm and modification of the pacing mode, patients underwent MRI. The rest of the function time of the pacemaker was calculated. Measurements were again performed after 99.5 +/- 29.6 minutes (mean +/- SD), immediately after MRI examination, and 3 months later. Lead impedance and sensing and stimulation thresholds did not change after MRI. Battery voltage decreased immediately after MRI and recovered 3 months later. Battery current and impedance tended to increase. The calculated rest of function time did not change immediately after MRI. MRI affected neither pacemaker programmed data, nor the ability to interrogate, program, or use telemetry. Surprisingly, in the gantry of the scanner, temporary deactivation of the reed switch occurred in 12 of 32 patients when positioned in the center of the magnetic field. Missing activation of the reed switch through the static magnetic field at 0.5 Tesla is not unusual. MRI at 0.5 Tesla does not cause irreversible changes in patients' pacemaker systems.

Contraindications↗
PubMed2000

Clinical experience with implantable atrial and combined atrioventricular defibrillators.

UNLABELLED: The high prevalence of atrial fibrillation (AF) and its clinical complications, the poor efficacy of medical therapy for preventing recurrences, and dissatisfaction with alternative modes of therapy stimulated interest in implantable atrial and combined atrioventricular defibrillators. In a multicenter study, the safety and efficacy of a stand alone implantable atrial defibrillator, the Metrix system, were evaluated. The device was implanted in 51 patients with highly symptomatic episodes of AF refractory to pharmacological treatment. During a follow-up of 9 months, 96% of 227 spontaneous AF episodes were successfully converted to sinus rhythm in 41 patients. In 62 episodes (27%), several shocks and/or additional drug treatment were required to maintain stable sinus rhythm because of early recurrences of AF. A total of 3719 shocks were delivered and no induction of ventricular proarrhythmia or inaccurately synchronized shocks occurred. The AF detection algorithm exhibited a 100% specificity for the recognition of sinus rhythm and a 92.3% sensitivity for the detection of AF. The combined atrioventricular defibrillator, Jewel AF 7250, was evaluated in a multicenter, randomized, cross-over trial. The primary study objectives included: overall safety as determined by complications-free survival at 6 months, efficacy of tiered atrial pacing and defibrillation therapies for termination of spontaneous atrial tachycardias (AT) and AF, and relative sensitivity of a new dual-chamber detection algorithm. The device was implanted in 211 patients with either a history of ventricular tachyarrhythmias (VT/VF) alone or with a history of both AT/AF and VT/VF. During a mean follow-up of 4.5 months, it has been shown that the Jewel AF is safe and effective in treating atrial and ventricular tachyarrhythmias. Pace termination of 85% of AT episodes were achieved with painless delivery of antitachycardia pacing; additional 35% of AT episodes were terminated by high frequency burst pacing. CONCLUSIONS: The stand alone implantable atrial defibrillator may be safe and clinically useful in selected patients for the treatment of highly symptomatic, drug resistant recurrences of AF. The combined atrioventricular defibrillator may be particularly indicated in patients presenting with both a history of atrial and ventricular tachyarrhythmias.

Aged↗
PubMed2000

Predictors of success in radiofrequency catheter ablation of atrial flutter.

Radiofrequency catheter ablation of typical atrial flutter at the isthmus between the tricuspid annulus and the inferior vena cava is established. However in selected patients, the creation of a continuous linear lesion at the targeted isthmus requires a lengthened procedure or is not feasible at all and atrial flutter recurrences are common. In a retrospective analysis, we found that an intraoperatively determined distance between the tricuspid annulus and the inferior vena cava of <.2.5 cm is an independent predictor of a lengthened or failed ablation procedure. Additional equipment, e.g., long introducer sheaths, adapted ablation catheter design, or irrigated tip ablation, as well as alternative ablation approaches, e.g., linear lesions between the tricuspid annulus and Eustachian ridge, have been invented in order to increase the acute success rate or decrease fluoroscopy and procedure time. In a prospective study on the effects of various conduction properties at the isthmus between tricuspid annulus and inferior vena cava following radiofrequency ablation of atrial flutter, we showed previously that others than a complete bidirectional conduction block predicts a high recurrence rate of atrial flutter. For determination of transisthmal conduction properties following ablation, established mapping approaches are documentation of double potentials at the ablation line and right atrial activation sequence following posteroseptal and low lateral right atrial pacing. Novel threedimensional mapping systems, i.e., Carto(R) and EnSite(R), may further enhance the accuracy of conventional mapping techniques.

Atrial Flutter↗
PubMed2000

Comparison of spontaneous atrial fibrillation electrogram potentials with the P-wave electrogram amplitude in dual chamber pacing with unipolar atrial sensing.

AIMS: Although bipolar sensing is recommended and desirable in patients with dual chamber pacemakers (DDD) and intermittent atrial fibrillation (AF) it is a clinical reality that some patients who are given unipolar atrial leads without a prior history of AF may develop intermittent AF during follow-up. It was therefore the purpose of this prospective study to compare the electrogram amplitudes of AF potentials with sinus rhythm P-wave potentials as a relevant factor for appropriate mode switching in dual chamber pacing with unipolar atrial sensing. METHODS AND RESULTS: Forty-two patients with dual chamber pacemakers, unipolar atrial leads and intermittent AF were studied. Aside from measuring the P-wave potential, it was possible in 14 patients (4 women, 10 men; mean age: 61.8 (+/- 13.3) years) additionally to document spontaneous AF electrogram potentials using pacemaker telemetry. A prospective survey study was performed including a 6 month follow-up period with an outpatient clinic visit every 2-3 weeks. The mean P-wave electrogram amplitude was 3.4 (+/- 1.8) mV (range: 1.4-7.4) compared with the mean amplitude during AF of 2.04 (+/- 1.26) mV (range: 0.8-5.2 mV) indicating a significant attenuation of 40% during AF (P < 0.0001). A linear correlation regression analysis revealed that there was a significant correlation between the P-wave and the AF amplitude (P < 0.0001), with a correlation coefficient of r = 0.867. CONCLUSION: Once it is known that a substantial reduction exists in electrogram amplitude, compared with the P wave electrogram potential, an estimate can be made of whether AF potentials will be sensed, if the programming of atrial sensitivity is congruent with the P-wave characteristics and the presence or absence of myopotential triggering.

Atrial Fibrillation↗
PubMed1999

Hemodynamic and cardiorespiratory function following internal atrial defibrillation for chronic atrial fibrillation.

Internal atrial defibrillation (IAD) is able to restore sinus rhythm in patients with chronic atrial fibrillation (AF) and failed external electrical and/or pharmacologic cardioversion. To assess whether cardiorespiratory and hemodynamic function improve after IAD, 35 patients were prospectively investigated during constant workload exercise by spiroergometry and Doppler echocardiography before IAD, and 1 day and 1 month after IAD. Oxygen uptake kinetics, ventilation, left atrial mechanical function, and pulmonary artery pressure were determined simultaneously at rest and during steady state. During the serial follow-up, 20 patients maintained sinus rhythm. The time interval for achieving the steady state (146 +/- 53 vs 132 +/- 42 seconds; p = 0.5) and the oxygen deficit (645 +/- 190 vs 670 +/- 174 ml; p = 0.7) were not different before and 1 day after IAD, but decreased significantly after 1 month (98 +/- 16 seconds, p = 0.01 and 487 +/- 72 ml, p = 0.02). Exercise pulmonary artery systolic pressures were 38 +/- 13 mm Hg before IAD, increased significantly to 46 +/- 11 mm Hg on day 1 (p = 0.03), and decreased below baseline values at 1 month to 31 +/- 12 mm Hg (p = 0.07). Peak A-wave velocities increased from 0.51 +/- 0.1 m/s after 1 day to 0.67 +/- 0.2 m/s after 1 month (p = 0.03). Restoration of sinus rhythm in patients with AF resistant to external electrical and/or pharmacologic cardioversion improves hemodynamic and cardiorespiratory function at daily activity exercise levels.

Atrial Fibrillation↗
PubMed1999

Radiofrequency ablation of atrial flutter due to administration of class IC antiarrhythmic drugs for atrial fibrillation.

In selected patients, atrial fibrillation (AF) converts to atrial flutter (AFI) due to treatment with class IC antiarrhythmic drugs. In this study, we prospectively investigated the effects of AFI ablation and continuation of drug therapy in patients with AF who developed AFI due to long-term administration of class IC antiarrhythmic drugs. The study population consisted of 187 patients from an AF registry with paroxysmal AF who were orally treated with flecainide (n = 96) or propafenone (n = 91). Twenty-four patients (12.8%) developed AFI during the course of treatment. In 20 of these patients (10.7%), electrophysiologic study revealed typical AFI. These patients underwent radiofrequency ablation of AFI. Ablation failed in 1 patient. All patients continued preexisting drug treatment. Recurrence of AF was assessed by ambulatory Holter monitoring and serial questionnaires. During a mean follow-up of 11 +/- 4 months, the incidence of AF episodes was significantly lower in patients with a combined therapy (2.7 +/- 3.6 per year) than in control subjects with a sole drug treatment (7.8 +/- 9.2 per year, p <0.05) and than before therapy (10.2 +/- 5.4 per year, p <0.001). Subgroup analysis revealed that 7 patients (36.8%) remained symptom free with no evidence of atrial tachyarrhythmia. Eight additional patients (42.1%) had ongoing paroxysmal AF, however, with a significantly lower incidence of AF episodes than before therapy (2.3 +/- 1.6 per year vs 11.5 +/- 5.0 per year, p <0.001). In the remaining 4 patients (14.7%), no beneficial effect of AFI ablation was found. It is concluded that in patients with AF who develop typical AFI due to administration of class IC antiarrhythmic agents, a combined therapy with catheter ablation of AFI and continuation of drug treatment is highly effective in reducing occurrence and duration of atrial tachyarrhythmias.

Administration, Oral↗
PubMed1999

Transverse conduction capabilities of the crista terminalis in patients with atrial flutter and atrial fibrillation.

OBJECTIVES: In this study, the transverse conduction capabilities of the crista terminalis (CT) were determined during pacing in sinus rhythm in patients with atrial flutter and atrial fibrillation. BACKGROUND: It has been demonstrated that the CT is a barrier to transverse conduction during typical atrial flutter. Mapping studies in animal models provide evidence that this is functional. The influence of transverse conduction capabilities of the CT on the development of atrial flutter remains unclear. METHODS: The CT was identified by intracardiac echocardiography. The atrial activation at the CT was determined during programmed stimulation with one extrastimulus at five pacing sites anteriorly to the CT in 10 patients with atrial flutter and 10 patients with atrial fibrillation before and after intravenous administration of 2 mg/kg disopyramide. Subsequently, atrial arrhythmias were reinduced. RESULTS: At baseline, pacing with longer coupling intervals resulted in a transverse pulse propagation across the CT. During shorter coupling intervals, split electrograms and a marked alteration of the activation sequence of its second component were found, indicating a functional conduction block. In patients with atrial flutter, the longest coupling interval that resulted in a complete transverse conduction block at the CT was significantly longer than that in patients with atrial fibrillation (285 +/- 49 ms vs. 221 +/- 28 ms; p < 0.05). After disopyramide administration, a transverse conduction block occurred at longer coupling intervals as compared with baseline (287 +/- 68 ms vs. 250 +/- 52 ms; p < 0.05). Subsequently, a sustained atrial arrhythmia was inducible in 15 of 20 patients. This was atrial flutter in three patients with previously documented atrial fibrillation and in eight patients with history of atrial flutter. Mapping revealed a conduction block at the CT in all of these patients. CONCLUSIONS: It was found that the CT provides transverse conduction capabilities and that the conduction block during atrial flutter is functional. Limited transverse conduction capabilities of the CT seem to contribute to the development of atrial flutter.

Aged↗
PubMed1999

Oxygen uptake to work rate relation throughout peak exercise in normal subjects: relevance for rate adaptive pacemaker programming.

The oxygen uptake to work rate (VO2/WR) relationship observed throughout peak exercise testing is already being applied for rate adaptive pacemaker programming. However, the detailed curve design of VO2/WR with respect to the anaerobic threshold (AT) has not yet been investigated. It was the purpose of this study to determine the VO2/WR slope below and above the AT in a healthy control group. Seventy-eight healthy control subjects (45.9 +/- 17.4 years; 34 women: 49.9 +/- 18.6 years 44 men: 43.6 +/- 16.6 years) were exercised on a treadmill with "breath-by-breath" gas exchange monitoring using the symptom limited "ramping incremental treadmill exercise" (RITE) protocol. The slope of the VO2/WR relationship from rest to peak exercise (r-p), rest to AT (slope A), and AT to peak exercise (slope B) in mL oxygen uptake per watt of external treadmill work was determined by linear regression analysis. [table: see text] The oxygen uptake to work rate relationship throughout peak exercise in the entire study group generated a significant slope change at the AT (31%, P < 0.0001) with a decreasing slope during higher work load intensities. Female subjects demonstrated a greater percentage of slope change at AT (43%), as compared to men (22%, P < 0.01). When using the oxygen uptake to work rate relationship for the programming of the pacemaker's rate response to exercise, the significant slope change at the AT should be considered to more appropriately pace during higher work intensities supported by anaerobic metabolism. Female pacemaker patients should be programmed to generate a steeper VO2/WR slope below AT with a greater slope change at AT, as compared to men. Abnormally high oxygen uptake to work rate ratios above the AT may be possibly used as an indicator of overpacing.

Adult↗
PubMed1999

Verification of linear lesions using a noncontact multielectrode array catheter versus conventional contact mapping techniques.

INTRODUCTION: Creation of linear lesions is an established ablation goal. Verification of complete conduction block at the ablation line is required to determine ablation success. Conventional mapping techniques are sequential endocardial activation mapping and documentation of double potentials. Recently, a noncontact multielectrode array catheter was developed that allows instantaneous three-dimensional mapping by simultaneous reconstruction of > 3,000 electrograms. In this study, we prospectively compared the accuracy of noncontact mapping to identify discontinuities in linear lesions and to verify a conduction block with that of conventional mapping techniques. METHODS AND RESULTS: In 12 patients with atrial flutter, radiofrequency pulses were applied between the tricuspid annulus and either the inferior vena cava or the eustachian ridge. Following each application, pulse propagation at the ablation line was determined during pacing by conventional mapping techniques. The findings were compared to high-density isopotential mapping using the noncontact multielectrode array catheter. It was found that noncontact mapping reliably distinguished conduction delays from a conduction block as defined by contact mapping. In addition, noncontact mapping instantaneously identified the area where a discontinuity in the line of block was present. In these patients, complete conduction block was achieved by radiofrequency pulses guided by the noncontact mapping system. CONCLUSION: Noncontact mapping is highly accurate in distinguishing conduction delays from a complete conduction block. By providing an instantaneous high-density propagation vector at all sites along the ablation line, three-dimensional isopotential mapping is helpful in localizing discontinuities of linear lesions and, thus, may facilitate the creation of a complete conduction block.

Adult↗
PubMed1998

[QT syndrome: new diagnostic possibilities].

Electrocardiographic and clinical characteristics are currently used as diagnostic criteria for the long QT-syndrome. In borderline electrocardiographic findings associated with unclear syncope, it is often difficult to ensure or exclude long QT-syndrome. Schwartz and coworkers therefore created a point system as a guide in clinical decision making. In recent years genetic diagnostics have entered the arena of long-QT assessment. Aside from new insights into the pathophysiology of the long QT-disorder, it is expected that genetic diagnostics will offer substantial help to ascertain long QT-syndrome in patients with borderline electrocardiographic and clinical findings and improve risk stratification in long-QT family members. Performing linkage analysis, coupling of autosomal-dominant congenital long QT-syndrome (Romano-Ward Syndrome) to chromosomes 11 (LQT1/11p15.5), 3 (LQT3/3p21), 7 (LQT2/7q35), and 4 (LQT4/4q25-27) was demonstrated. More recently, the disease genes in long QT-syndrome 1, 2, and 3 could be identified. Analysis of the base-pair sequence allowed detection of several different mutations in different families illustrating genetic heterogeneity. Aside from diagnostic aspects, molecular genetics may also guide pharmacological therapy by identifying the specific ion-channel disorder leading to QT-prolongation and sudden death.

Chromosome Mapping↗
PubMed1998

[MRI diagnosis of right ventricular dysplasia].

PURPOSE: Right ventricular dysplasia (RVD) represents an important cause of sudden death and ventricular arrhythmias in young patients. The aim of this study was to describe diagnostic diagnostic criteria and the MR-tomographie aspects of the disease. METHODS: 34 patients with clinically suspected RVD were examined by 0.5-T MRI (cardiac-gated T1-weighted spin echo sequences and cine gradient echo sequences). RVD was confirmed in 16 patients and ruled out in 18 patients. MR images were evaluated for presence of: 1. right myocardial fatty infiltration, 2. dilatation of the right ventricle, 3. dilatation of the right ventricular outflow tract, and 4. localised right ventricular aneurysm. RESULTS: Right myocardial fatty infiltration was detected by MRI in 11 of 16 patients (69%) with RVD. Dilatation of the right ventricle was seen in 5 patients, dilatation of the right outflow tract in one patient, and localised right ventricular aneurysm in two patients with RVD. CONCLUSIONS: MRI is able to demonstrate fatty replacement of right ventricular myocardium in most cases and plays an important role in the diagnosis of RVD.

Adipose Tissue↗
PubMed1998

Acute and long-term effects of consecutive radiofrequency applications on conduction properties of the subeustachian isthmus in type I atrial flutter.

INTRODUCTION: Bidirectional conduction block at the subeustachian isthmus predicts long-term efficacy of atrial flutter ablation. Limited data are available on the incidence and outcome of minor conduction changes such as unidirectional or incomplete block. This prospective study sought to systematically assess discrete acute and long-term alterations of bidirectional conduction prior to a complete conduction block. METHODS AND RESULTS: In 41 patients with type I atrial flutter, pulse propagation through the subeustachian isthmus during low lateral and proximal coronary sinus pacing was documented and analyzed following each consecutive radiofrequency (RF) application. In cases of altered conduction properties and noninducibility of atrial flutter, patients were followed-up for 12 months. Three sets of results were found. First, following RF application, 23 patients presented a progressive conduction delay prior to a complete conduction block. Second, RF application did not always affect counterclockwise and clockwise conduction simultaneously or to the same extent. In 13 patients, an initial alteration of counterclockwise conduction was present before an alteration of clockwise conduction; in 5 patients, clockwise conduction was primarily affected. Third, the recurrence rate of typical atrial flutter was 9% (2/22) in patients with a complete bidirectional conduction block, 54% (7/13) in patients with unidirectional conduction block, and 100% (6/6) in patients with sole bidirectional conduction delay. CONCLUSION: In 50% of the patients, consecutive RF applications resulted primarily in a progressive conduction delay rather than a sudden conduction block. Since counterclockwise and clockwise conduction were not always affected simultaneously or to the same extent, lateral as well as septal pacing is recommended for improvement of bidirectional conduction block. Normalization of primarily altered conduction and, therefore, recurrence of atrial flutter are high in all patients without bidirectional block.

Adult↗