[New technologies in the optimization of CRT programming]. / Neue Technologien zur Optimierung in der CRT-Programmierung.

After implanting a CRT device, consistent and scheduled patient follow-up is mandatory. Besides determining electrode parameters and reviewing arrhythmic episodes, these follow-ups focus on monitoring and optimizing congestive heart failure therapy. Therefore new CRT devices present methods for heart failure surveillance and telemetric transmission of the acquired data, which allows the physician to respond immediately to the varying needs of the respective heart failure patient. In addition to cardiac resynchronization, optimization of atrioventricular (AV) and interventricular (VV) delay provide major hemodynamic benefits. As echocardiographic optimization of AV and VV delay is time consuming it is often not feasible during daily clinical practice. Therefore implemented algorithms that automatically determine and adapt AV and VV delays with respect to the fluctuating needs of the patients are essential. This article presents the current state of monitoring and optimization methods in CRT devices.

Application of the Bogossian formula for evaluation of the QT interval in pacemaker patients with stimulated left bundle branch block.

BACKGROUND: The presence of left bundle branch block (LBBB) represents a particular challenge in properly measuring the QT interval. Here we demonstrate the applicability of the "Bogossian formula" in pacemaker patients with LBBB due to apical or nonapical right ventricular (RV) pacing and preserved left ventricular function. METHODS: A total of 163 patients with a cardiac one- or two-chamber pacemaker were included in this prospective, multicentre observational study. Twelve-lead ECG recordings were obtained during both intrinsic rhythm and RV pacing with induced LBBB. The QT interval measured during LBBB was corrected using the Bogossian formula to obtain the "modified QT" (QTm). The QTmc interval was calculated with the Bazett formula, and this was compared with the QTc interval during intrinsic rhythm. RESULTS: Eighty-three patients (78 ± 9 years; male n = 83) with apical and eighty patients (71 ± 13 years; male n = 80) with non-apical RV pacing were included in this study. In the apical group the QTmc was determined to be 444 ± 39 ms in paced rhythm and the QTc interval 413 ± 36 ms in intrinsic rhythm. In the non-apical group these values were 430 ± 34 ms in paced and 416 ± 32 ms in intrinsic rhythm. CONCLUSION: The Bogossian formula is a reliable tool for QTc interval evaluation in pacemaker patients with LBBB due to apical or non-apical RV pacing. However, an overestimation of 30 ms should be included in the calculation.

Catheter stimulation of cardiac parasympathetic nerves in humans: a novel approach to the cardiac autonomic nervous system.

BACKGROUND: Cardiac parasympathetic nerves run alongside the superior vena cava (SVC) and accumulate particularly epicardially adjacent to the orifice of the coronary sinus (CS). In animals, these nerves can be electrically stimulated inside the SVC or CS, which results in negative chronotropic/dromotropic effects and negative inotropic effects in the atria but not the ventricles. Parasympathetic nerve stimulation (PS) with 20 Hz in the CS, however, also excites the atria, thereby inducing atrial fibrillation. The present study overcomes this limitation by applying high-frequency nerve stimuli within the atrial refractory period. Using this technique, we investigated for the first time whether neurophysiological effects similar to those in animals can be obtained in humans. METHODS AND RESULTS: In 25 patients, parasympathetic nerves were stimulated via a multipolar electrode catheter placed in the SVC (stimulation with 20 Hz; n=14) or CS (pulsed 200-Hz stimuli; n=11). A significant sinus rate decrease and prolongation of the antegrade Wenckebach period was achieved during PS in the SVC. During PS in the CS, a graded-response prolongation of the antegrade Wenckebach interval was observed with increasing PS voltage until third-degree AV block occurred in 8 of 11 patients. The negative chronotropic/dromotropic effects started and terminated immediately after the onset and termination of PS, respectively. Atropine abolished these effects (n=11). CONCLUSIONS: Human parasympathetic efferent nerve stimulation induces reversible negative chronotropic and dromotropic effects. PS may serve as an adjunctive tool for the diagnosis/treatment of supraventricular tachycardias and may be beneficial for ventricular rate slowing during tachycardic atrial fibrillation in patients with congestive heart failure.

Telephonic transmission of 12-lead electrocardiograms during acute myocardial infarction.

To test the feasibility of a small and simple system for telephonic transmission of 12-lead electrocardiograms (ECGs), 70 patients with acute coronary syndrome admitted to the cardiac care unit (CCU) were included in a feasibility study. The transmission system consisted of a belt with multiple electrodes, which was positioned around the chest. The ECG signal was sent to a call centre via a standard telephone line. In parallel, a standard 12-lead ECG was recorded on site. In a retrospective analysis, each lead of the transmitted ECG was compared with the on-site 12-lead ECG with regard to ST-segment changes and final diagnosis. In all 37 patients with acute ST-elevation myocardial infarction, the diagnosis was correctly established on the basis of telephone-transmitted ECGs. In 96% of limb and 88% of chest leads, ST elevations which were visible in standard ECGs were correctly displayed on telephonically transmitted ECGs. In the remaining 33 patients no false-positive diagnosis was made using transtelephonic ECG analysis. A control group of 31 patients without apparent heart disease showed high concordance between standard ECGs and telephonically transmitted ECGs. Telephonically transmitted 12-lead ECGs interpreted by a hospital-based internist/cardiologist might allow a rapid and accurate diagnosis of ST-elevation myocardial infarction and may increase diagnostic safety for the emergency staff during prehospital decision making and treatment of acute myocardial infarction.

Glimepiride (Hoe490) inhibits the rilmakalim induced decrease in intracellular free calcium and contraction of isolated heart muscle cells from guinea pigs to a lesser extent than glibenclamide.

Glibenclamide is a potent inhibitor of the ATP-dependent potassium channel. Opening of the ATP-dependent potassium channel is regarded as a mechanism of ischemic preconditioning. This in vitro study examines the influence of glibenclamide and glimepiride, a new sulfonylurea, on the negative inotropic action of the potassium channel opener rilmakalim in isolated ventricular myocytes. Cardiac myocytes were isolated from adult guinea pig hearts by collagenase perfusion and incubated with rilmakalim (concentration range 0.1-12.0 microM), glibenclamide (concentration range 0.03-3.0 microM) plus rilmakalim (3.0 or 7.5 microM), and glimepiride (0.03-9.0 microM) plus rilmakalim (3.0 or 7.5 microM) and paced by electrical field stimulation. Contractility of the myocytes was evaluated by digital image analysis, intracellular free calcium was determined by means of fura-2 fluorescence measurements, and cell viability was assessed morphologically as well as by measurement of lactate dehydrogenase activity. Rilmakalim reduced the systolic intracellular free calcium and contractility of ventricular myocytes in a concentration dependent manner. This effect was antagonized by glibenclamide at lower concentrations (0.3 microM) than glimepiride (3.0 microM). The smaller antagonistic action of glimepiride on the negative inotropic effect of rilmakalim as compared with glibenclamide most likely reflects a less potent inhibition of ATP-dependent potassium channels by glimepiride.

[Stored electrograms in pacemakers and ICDs from Medtronic]. / Gespeicherte Elektrogramme in Schrittmachern und ICDs der Firma Medtronic.

Modern pacemakers and implantable defibrillators provide a multitude of technical algorithms and parameters, which can be programmed individually and can treat different forms of arrhythmias. Stored electrograms offer the possibility to obtain valuable information during follow-up (but also in real-time) about arrhythmias and device function or malfunction. This results in improved treatment of cardiac arrhythmias and heart disease. Due to constant innovation and development of these systems, it requires, however, profound biomedical and technical knowledge, since stored electrograms may display complex arrhythmias and device reactions that are not easy to interpret. Understanding of stored device information improves follow-up and facilitates individual care for the patient.

[Catheter ablation of accessory pathways and atrioventricular nodal reentry tachycardia]. / Katheterablation bei akzessorischen Leitungsbahnen und AV-Knoten-Reentrytachykardie.

Radiofrequency current catheter ablation has gained acceptance as primary long-term therapy for patients with symptomatic accessory pathways and symptomatic atrioventricular nodal reentrant tachycardia (AVNRT) with frequent recurrences. In both arrhythmias, curative treatment is possible in more than 90% of cases at a low complication rate although an incidence of about 1% complete AV block after slow pathway ablation has to be taken into account when this therapy is considered. The recurrence rate is 3-10% for accessory pathways and 0-15% for AVNRT. The high success rate of catheter ablation has already led to a shift in the indications for the procedure where the percentage of patients with accessory pathways is decreasing and there is an increase of patients with AVNRT and newer indications (atrial flutter, focal atrial tachycardias).

Verapamil prevents stretch-induced shortening of atrial effective refractory period in langendorff-perfused rabbit heart.

INTRODUCTION: Atrial dilation and rapid pacing reduce atrial effective refractory periods (AERPs), thereby increasing the susceptibility to sustained atrial fibrillation (AF) in Langendorff-perfused rabbit hearts. It is unclear whether similar pathophysiologic mechanisms are operative in short-term electrophysiologic changes caused by dilation and rapid pacing. Therefore, we analyzed whether both forms of short-term electrophysiologic changes are similarly affected by pharmacologic interventions acting on different potential mechanisms underlying these changes. METHODS AND RESULTS: Thirty Langendorff-perfused rabbit hearts underwent a protocol with stepwise increase of intra-atrial pressure from 0 to 12 cm H2O followed by 10 minutes of rapid pacing at 4 cm H2O. The protocol was repeated after addition of glibenclamide (10 micromol/L, n = 7), cariporide (1 micromol/L, n = 7), or verapamil (1 micromol/L, n = 9). In the basal state, increase of intra-atrial pressure from 0 to 12 cm H2O decreased AERPs from 85 +/- 11 to 55 +/- 9 msec (P < 0.01), rapid pacing at low intra-atrial pressure (4 cmH2O) decreased AERP to a similar extent, from 81 +/- 11 to 60 +/- 10 (P < 0.01). At higher intra-atrial pressure, decrease of AERP was more pronounced (10 cm H2O: 37 +/- 2 msec) (n = 7). Addition of verapamil decreased basal AERP from 86 +/- 10 msec to 68 +/- 11 msec (P < 0.05). Short-term electrophysiologic changes due to atrial dilation were abolished; changes due to rapid pacing were reduced but still present. Glibenclamide and cariporide had no significant effect. CONCLUSION: Langendorff-perfused rabbit heart is a suitable model for studying short-term electrophysiologic changes due to both rapid pacing and atrial dilation. AERPs are shortened to a similar extent by both mechanisms, whereas a combination of the two leads to more pronounced AERP reduction. Calcium overload plays a crucial role in short-term electrophysiologic changes caused by atrial dilation, whereas atrial ischemia or acidosis has no significant impact.