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Biomedical subjects

S Weyerbrock

Publications and source records attributed to S Weyerbrock.

9 recordsLinked to original sources
PubMed2001

Pseudotermination of intermittent atrial fibrillation by a pacemaker algorithm: antitachycardia pacing without capture miscounted as successful termination of fibrillation episodes.

A patient is described with intermittent AF and an implanted pacemaker which provides preventive pacing and overdrive stimulation designated to terminate atrial arrhythmias. The case highlights the possibility of false estimation of therapeutic efficacy and possible proarrhythmic effect of this therapeutic modality.

Algorithms↗
PubMed2001

Activation patterns in the left atrium during counterclockwise and clockwise atrial flutter.

INTRODUCTION: Activation of the left atrium (LA) in patients with isthmus-dependent right atrial flutter (AFL) has not yet been studied. The aim of this study was to analyze the activation patterns in the LA in patients with counterclockwise and clockwise AFL. METHODS AND RESULTS: The study population consisted of 12 patients (10 men and 2 women; mean age 61+/-13 years) with documented AFL and atrial fibrillation referred for ablation. The LA was mapped with a 64-electrode basket catheter inserted through a transseptal approach (10 patients) or an open foramen ovale (2 patients). In patients with counterclockwise AFL (10 episodes), the LA was activated for a mean of 133+/-28 msec. Two endocardial breakthroughs of earliest activity on the left side of the interatrial septum, separated in time by an interval of 38+/-15 msec, were observed in 9 episodes (90%). Two wavefronts originated from these breakthroughs, which activated the posterior and the anterior LA walls, respectively. In one patient, the entire LA was activated from the inferior breakthrough. In patients with clockwise AFL (five episodes), the LA activation time was 130+/-13 msec. During ongoing episodes, two early electrical breakthroughs, separated in time by an interval of 41+/-15 msec, appeared in the high anteroseptal and low posteroseptal LA regions. The superior wavefront that emerged from the high anterolateral LA region was the dominant activation pathway in 4 (80%) of 5 episodes. CONCLUSION: In patients with AFL, the LA is activated by two wavefronts originating from the high anterior and the low posterior regions of the interatrial septum. The sequence of activation of these interatrial connections in counterclockwise or clockwise AFL and the conductive properties of the LA conduction pathways determine the activation patterns in the LA.

Activation Analysis↗
PubMed1999

Clinical experience with a novel multielectrode basket catheter in right atrial tachycardias.

BACKGROUND: The complexity of atrial tachycardias (ATs) makes the electroanatomic characterization of the arrhythmogenic substrate difficult with conventional mapping techniques. The aim of our study was to evaluate possible advantages of a novel multielectrode basket catheter (MBC) in patients with AT. METHODS AND RESULTS: In 31 patients with AT, an MBC composed of 64 electrodes was deployed in the right atrium (RA). The possibility of deployment, spatial relations between MBC and RA, MBC recording and pacing capabilities, mapping performance, and MBC-guided ablation were assessed. MBC deployment was possible in all 31 patients. The MBC was left in the RA for 175+/-44 minutes. Stable bipolar electrograms were recorded in 88+/-4% of electrodes. Pacing from bipoles was possible in 64+/-5% of electrode pairs. The earliest activity intervals, in relation to P-wave onset, measured from the MBC and standard roving catheters were 41+/-9 and 46+/-6 ms, respectively (P=0.21). Radiofrequency ablation was successful in 15 (94%) of 16 patients in whom it was attempted, including 2 patients with polymorphic right atrial tachycardia (RAT), 2 with RAT-atrial flutter combination, 1 with macroreentrant AT, and 1 with focal origin of atrial fibrillation. CONCLUSIONS: These data demonstrate that MBC can be used safely in patients with right atrial arrhythmias. The simultaneous multielectrode mapping aids in the rapid identification of sites of origin of the AT and facilitates radiofrequency ablation procedures. The technique is especially effective for complex atrial arrhythmias.

Adult↗
PubMed1998

Frequency dependence in the action of the class III antiarrhythmic drug dofetilide is modulated by altering L-type calcium current and digitalis glucoside.

We investigated how modulation of L-type calcium current affects the class II antiarrhythmic effect of dofetilide. Action-potential duration (APD) was determined in guinea pig papillary muscle by microelectrode techniques at different stimulation frequencies (0.5-3 Hz). The APD-prolonging effect (deltaAPD) of 10 nM dofetilide was reversed frequency dependent; it was 51 +/- 6 ms at 0.5 Hz and lower at 3 Hz, 21 +/- 3 ms. Either 10 microM diltiazem or 0.1 microM Bay K 8644 (BayK) was added to decrease or increase L-type calcium currents. In the presence of dofetilide + diltiazem, deltaAPD was reduced to 32 +/- 4 ms at 0.5 Hz but not affected at 3 Hz. Conversely, dofetilide + BayK further prolonged deltaAPD to 78 +/- 10 ms at 0.5 Hz but not at 3 Hz. When 10 microM dihydroouabain, a digitalis glucoside, was added to dofetilide, deltaAPD was more pronounced at 0.5 Hz and reduced at 3 Hz. We conclude that the reversed frequency-dependent effect of dofetilide on APD can be modulated by altering L-type calcium currents. With reduced calcium current, the frequency profile is less reversed and more favorable. The similarity of BayK and dihydroouabain in aggravating the reversed frequency-dependent effect of dofetilide is in line with a contribution of intracellular calcium to this reversed rate-dependent profile in the guinea pig ventricle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1998

Intraoperative recordings of monophasic action potentials with chronically implantable pacemaker leads.

Since the development of fractally coated Iridium electrodes recordings of monophasic action potentials are possible. Intraoperative recordings of MAP from 15 pacemaker implantations were done after positioning the chronically implantable pacemaker leads (Biotronik, Berlin, Germany) in the right ventricle by using five screw-in electrodes and ten anchor electrodes. Intraoperative recordings of MAP are possible with all implanted pacemaker leads. The recordings of typical MAP signals were always accompanied with stable electrode positions and good sensing and pacing characteristics.

Action Potentials↗
PubMed1998

Does radiofrequency catheter ablation induce a deterioration in sympathetic innervation? A positron emission tomography study.

Radiofrequency catheter ablation (RFCA) is an effective treatment for the interruption of accessory bypass tracts in WPW syndrome or the modification of the AV-nodal conduction system in patients with AV-nodal tachycardias. However RFCA may also damage cardiac innervation. The purpose of this pilot study was to assess possible changes in sympathetic innervation after RFCA as evaluated by the cathecholamine analog carbon-11-hydoxyephedrine (HED) positron emission tomography (PET) which allows the visualisation of sympathetic nerve terminals. We investigated nine patients with supraventricular tachycardias before and two to six weeks after RFCA. Myocardial perfusion was depicted by n-13-ammonia-PET. In addition to visual analysis, HED retention was quantified in the myocardial quadrant distal to the location of intervention; these results were compared with values in remote areas. Before RFCA, myocardial perfusion showed homogenous distribution in 8 of 9 patients. One patient showed a perfusion defect in the posterior wall. HED retention matched perfusion distribution in all patients. After RFCA there was no significant change observed either in ammonia or in HED distribution. Quantitative HED retention data showed no significant change before versus after RFCA. Thus, HED-PET does not demonstrate any abnormalities of tracer uptake indicating integrity of sympathetic nerve terminals after radiofrequency ablation therapy.

Adult↗
PubMed1997

Rate-independent effects of the new class III antiarrhythmic agent ambasilide on transmembrane action potentials in human ventricular endomyocardium.

The electrophysiologic effects of ambasilide, a new class III antiarrhythmic drug reported to be a nonselective blocker of both components (I(Kr) and I(Ks)) of the delayed-rectifier potassium current (I(K)) and other repolarizing potassium currents (I(tol), I(so)), were studied in specimens of left ventricular endomyocardium of human hearts obtained from 10 patients undergoing either heart transplantation (n = 4) or mitral valve replacement (n = 6). We recorded transmembrane action potential (TAP) characteristics at different stimulation frequencies (0.5, 1, 1.5, and 2 Hz) and with different dosages of ambasilide (1, 10, and 50 microM) by using conventional microelectrode techniques. Beginning at a concentration of 10 microM ambasilide, the TAP duration at 90% repolarization (TAPD90) was significantly prolonged and independent of stimulation frequency with a mean percentage prolongation of 18% at 10 microM and 30% at 50 microM ambasilide. TAP duration at 50% repolarization was not significantly prolonged except for 10 microM ambasilide at 0.5 Hz (17%; p < 0.05). The frequency-independent action potential (AP) prolongation by ambasilide in human ventricular endomyocardium indicates that a nonselective block of repolarizing potassium currents seems to be more favorable than a selective block of I(Kr).

Action Potentials↗
PubMed1996

Differential class III antiarrhythmic effects of ambasilide and dofetilide at different extracellular potassium and pacing frequencies.

We studied the effect of two new class II antiarrhythmics, ambasilide and dofetilide, on the action potential duration (APD) of guinea pig right ventricular papillary muscle at different extracellular potassium concentrations ([K+e]) and pacing frequencies. Under normal [K+e], both drugs significantly prolonged APD90 (APD at 90% repolarization) at 0.5 Hz. The effect of ambasilide was well preserved at rapid pacing rates, independent of [K+e]. The effect of dofetilide was markedly reduced with increasing pacing rate, especially in high [K+e]. Therefore, ambasilide may be useful in treating tachyarrhythmias in normal, as well as in altered [K+e] conditions.

Action Potentials↗