Search Results
Results 401 - 450 of 1133
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Wiegand U K - - 1999
Atrial undersensing occurs in a considerable number of patients, both with single lead VDD pacemakers and with DDD devices. The aim of this study was to investigate the diagnostic efficacy of electrocardiographic methods and autodiagnostic pacemaker features to detect atrial sensing dysfunction. Two hundred and thirty-one patients with AV block ...
Moleiro F - - 1999
BACKGROUND: Few studies have dealt with the behavior of the corrected (QTc) and uncorrected QT intervals during exercise and recovery. HYPOTHESIS: Based on previously published dynamics of the QT interval during treadmill testing, this study attempted to reevaluate the computer-proposed underlying mechanisms of these dynamics and to determine whether the ...
Mazgalev T N - - 1999
BACKGROUND: Postganglionic vagal stimulation (PGVS) by short bursts of subthreshold current evokes release of acetylcholine from myocardial nerve terminals. PGVS applied to the atrioventricular node (AVN) slows nodal conduction. However, little is known about the ability of PGVS to control ventricular rate (VR) during atrial fibrillation (AF). METHODS AND RESULTS: ...
Panou F K - - 1999
Fifteen hypertensive patients (13 men) with left ventricular hypertrophy, mean age 69 6 5 years, having complete heart block and paced in the DDD mode, were studied by two-dimensional and Doppler echo in 100 and 200 ms atrioventricular delays. ANF plasma levels were measured at rest and at peak exercise, ...
Clémenty J - - 1999
The gold standard for rate modulation is the sinus node. To improve the rate modulation provided by artificial sensors, new sensors have to be developed or 2 different sensor systems can be combined within a single device. Association combination of a sensor with a rapid-response fast-rate increase sensor (activity) and ...
Reiss R A - - 1999
Atrial fibrillation in young or middle-aged active patients can often be managed with medication. Evaluation should address associated conditions and predisposing factors such as idiopathic hypertrophic subaortic stenosis, Wolff-Parkinson-White syndrome, congenital heart disease, hyperthyroidism, excess alcohol or other drug use, and exercise-induced catecholamine release. Diagnostic studies may include an ECG, ...
Joglar J A - - 1999
Dry-electrode heart rate monitors allow display of heart rate by transmitting a signal to the receiving device, which typically is on the wrist or exercise machine, but due to the potential for electromagnetic interference, their use has been contraindicated in patients with pacemakers. In 12 patients, we found no adverse ...
Seki A - - 1999
1. The class Ic anti-arrhythmic agent, flecainide is known to inhibit the transient outward K current (Ito) selectively in human atrium. We studied the effects of propafenone, another class Ic antiarrhythmic agent, on K currents in human atrial myocytes using a whole-cell voltage-clamp method. 2. Propafenone inhibited both Ito and ...
Qian L - - 1999
Gastric pacing has received increasing attention recently. However, few studies have systematically assessed the effect of pacing on gastric dysrhythmias. The aims of this study were to investigate the effect of gastric pacing on gastric dysrhythmia and to explore whether the effect of gastric pacing was mediated via cholinergic nerves. ...
Tse H F - - 1999
Accurate detection of atrial fibrillation (AF) is essential for appropriate operation of an implantable atrial defibrillator (IAD). However, during episodes of sinus tachycardia, distinction between AF and sinus rhythm (SR) using the "quiet interval" and "baseline crossing" analysis in the detection algorithm of the IAD may be difficult. The efficacy ...
Ellenbogen K A - - 1999
Pacemaker lead technology has changed considerably over the past decades. The widespread use of low polarization highly porous electrodes and steroid elution electrodes has resulted in low chronic pacing thresholds, as well as a decrease in the incidence of exit block. Efforts to develop pacing leads with high impedance might ...
Barold H S - - 1999
Although changes in autonomic tone affect ventricular defibrillation, little is known about the effect of increased parasympathetic or sympathetic tone on the atrial defbrillation threshold. METHODS: To evaluate the effect of reflexly increased parasympathetic and increase alpha- and beta-adrenergic tone on the atrial defibrillation threshold (ADFT), atrial fibrillation was induced ...
de Chillou C - - 1998
BACKGROUND: Radiofrequency ablation of atrioventricular accessory pathway is widely used to cure patients with the Wolff-Parkinson-White syndrome. The site of successful ablation is determined using electrophysiological parameters, endocavitary bipolar electrogram measurements being the most commonly used. Interobserver reproducibility of these measurements may limit the reliability of ablation criteria based upon ...
Schwaab B - - 1998
In 42 patients (26 men, 16 women; mean age 69 +/- 10 years), who were paced and medicated with antiarrhythmic drugs for the bradycardia tachycardia syndrome, chronotropic response and AV conduction with rapid atrial pacing during exercise were studied. Patients were included if they had no second- or third-degree AV ...
Clémenty J - - 1998
The aim of this study was to assess the long-term performance of a new dual chamber rate responsive pacing system based on the dynamic measurement of the peak endocardial acceleration (PEA) index of cardiac contractility. Seventy patients who participated in the Multicenter European Clinical Evaluation were studied 1 year after ...
Sharp C T - - 1998
When developing an exercise program for pacemaker patients, basic information about the pacemaker must be understood. Atrial, ventricular, and dual-chamber devices can produce varying exercise responses and impact the exercise prescription. The type of rate adaptive sensor the pacemaker has will affect the nature of heart rate response, and therefore, ...
Bonnet J L - - 1998
The minute ventilation is known to be one of the most physiological indicators of exercise. A curvilinear relationship between VE and the normal sinus rhythm (NSR) has been demonstrated in healthy patients. The aim of this study is to show that a pacemaker based on a VE sensor can reproduce ...
Simantirakis E N - - 1998
This study examined the acute and long-term effects of DDD pacing on ergospirometric parameters and neurohormonal activity in patients with hypertrophic obstructive cardiomyopathy (HOCM). We studied eight patients (five males), aged 56 +/- 7 years, with HOCM refractory to drugs. In all patients a DDD pacemaker was implanted and programmed ...
Celiker A - - 1998
Rate adaptive pacemakers are used to achieve a better cardiac performance during exercise by increasing the heart rate and cardiac output. The ideal rate adaptive sensor should be able to mimic sinus node modulation under various degrees of exercise and other metabolic needs. Minute ventilation sensing has proven to be ...
Haenggeli A - - 1998
Some cochlear implant patients achieve better speech recognition with pulsatile electrical stimulation presented at high rates. The present study aimed to explore, in an animal model of cochlear implants, how the excitability of the cochlear nerve is affected by pulsatile electrical stimulation delivered at high rates, of up to 1,000-2,000 ...
Athill C A - - 1998
BACKGROUND: The characteristics of transmembrane potential (TMP) at the core of functional reentry in the atrium are not well understood. METHODS and RESULTS: In protocol 1 (11 dogs), isolated perfused canine right atria were mapped from the endocardial surface while simultaneous TMPs were recorded from the epicardial surface. Episodes of ...
Lampert Rachel - - 1998
Two strategies for treatment of atrial fibrillation in the elderly include rate control with anticoagulation, or cardioversion and maintenance of sinus rhythm. Rate controlling agents include digoxin, calcium blockers, and b-blockers, most effective during exercise, or nonpharmacologic control with AV nodal ablation and pacemaker implantation. Agents to maintain sinus rhythm ...
Staniforth A D - - 1998
OBJECTIVES: To compare the value of a series of cardiovascular measurements in patients with symptomatic disease receiving an effective treatment (rate responsive pacing). PATIENTS: 12 pacemaker dependent patients with VVIR units. INTERVENTIONS: Single blind crossover between VVI and VVIR. OUTCOME MEASURES: Exercise capacity was assessed by treadmill tests (modified Bruce ...
Haennel R G - - 1998
The effects of sensor selection and sensor blending on the cardiovascular response to graded exercise was evaluated in 10 patients (age 74 +/- 2 yrs; 7 men and 3 women) implanted with a dual sensor rate adaptive VVIR pacemaker (Vitatron Topaz model 515). Patients underwent three graded exercise tests (GXT) ...
Leung S K - - 1998
The use of combined sensors and advanced algorithms using different principles can improve rate performance over a single sensor system. Combinations of sensors and more sophisticated algorithms, however, invariably increase the complexity of pacemaker programming. An automatically optimized combined minute ventilation and activity DDDR pacemaker was developed to minimize repeated ...
Morsi A - - 1998
The purpose of this paper is the assessment of sinus node competence over time in patients with isolated atrioventricular block (AV block). Patients implanted with AV synchronous pacemakers for isolated AV block between December 1993 and June 1995 were prospectively evaluated at predischarge, 6 weeks, and subsequent 6 months follow-up ...
Danilovic D - - 1998
The aim of the study was to investigate pacing impedance (PI) behavior in ambulatory patients. Eighteen atrial and 18 ventricular tined steroid eluting leads with 1.2-mm2 and 5.6-mm2 electrodes were implanted in 20 patients. At 9-27 months after implantation PI was measured automatically by means of additional algorithms downloaded via ...
Constable P - - 1998
Cardiac chamber enlargement and hypertrophy are normal physiologic responses to repetitive endurance exercise activity in human beings and domestic dogs. Whether similar changes occur in wild animals as a consequence of increased activity is unknown. We found that free-ranging gray wolves (Canis lupus, n = 11), the archetypical endurance athlete, ...
Windecker S - - 1998
Mixed venous oxy-hemoglobin saturation (MVO2) is a physiological variable with several features that might be desirable as a control parameter for rate adaptive pacing. Despite these desirable characteristics, the long-term reliability of the MVO2 sensor in vivo is uncertain. We, therefore, designed a study to prospectively evaluate the long-term performance ...
Wilkie M - - 1998
The life cycle of the sea lamprey (Petromyzon marinus) is characterized by a terminal upstream spawning migration that may be associated with brief bursts of high-intensity swimming. Such activity usually leads to pronounced blood acid-base disturbances in fishes, but lampreys rapidly correct these perturbations within 1 h. In the present ...
Carmouche D G - - 1998
The normal heart rate is linearly related to oxygen consumption during exercise. The maximum heart rate of the normal sinus node is approximated by the formula: HRmax = (220-age) with a variance of approximately 15%. However, the nominal upper rate of most permanent pacemakers is 120 beats/min, a value that ...
Swan H - - 1998
OBJECTIVES: To improve the diagnostic criteria of the congenital long QT syndrome in borderline cases we examined rate adaptation of ventricular repolarization phases during exercise and subsequent recovery in children with the long QT syndrome and controls. METHODS: Nineteen children with definite long QT syndrome and 19 healthy controls underwent ...
Lau C P - - 1998
To assess the effect of right ventricular pacing on rate regularity during exercise and daily life activities, 16 patients with sinoatrial disease and chronic atrial fibrillation (AF) were studied. Incremental ventricular pacing was commenced at 40 beats/min until > 95% of ventricular pacing were achieved during supine, sitting, and standing. ...
Tovar O H - - 1998
Clinical studies suggest that epinephrine facilitates ventricular fibrillation (VF) although mechanisms remain unclear. We tested the hypothesis that epinephrine increases the probability of inducing VF and stabilizes VF in association with shortening of fibrillation action potential duration. VF was induced in isolated, New Zealand White rabbit hearts (n=16) under control ...
Geller C - - 1998
An increase in sinus rate has been previously described in patients with AV node reentry (AVNRT) following successful AV node modification. This increase could either be a specific sign of elimination of slow pathway conduction or it could be a consequence of energy application in the posteroseptal area. Thus, we ...
Roukema G - - 1998
An increased spatial dispersion of ventricular repolarization duration (QT dispersion) is associated with an increased vulnerability to arrhythmias. This study was designed to examine the effect of exercise on QT dispersion in ischemic heart disease (IHD). QT dispersion, corrected QT dispersion, and percentage change in uncorrected and corrected QT dispersion ...
Faerestrand S - - 1998
A VDD pacing system with bipolar single-pass leads, were implanted in 36 consecutive patients (average age 72 +/- 2 years) with high degree atrioventricular block and normal sinus node function. At implant the atrial signal amplitude was 2.6 +/- 0.2 mV measured by a pacing system analyser (PSA), 1.8 +/- ...
Ayusawa M - - 1998
A 52-year-old woman exhibited Mobitz type II atrioventricular block with right bundle branch block and 1:1 atrioventricular conduction at or slower than 80 beats/min. Electrophysiologic study revealed transient HV interval block followed by recovery from the block at shorter coupling intervals without prolongation of the H1H2 and H2V2 intervals, suggesting ...
Leung S K - - 1998
Although multisensor pacing may compensate the inadequacy of rate adaptation in a single sensor system, the clinical role of multisensor driven rate adaptive pacing remains unclear. We compared the performance between single sensor and dual sensor driven pacemakers using exercise cardiac output (CO) as a marker of cardiac performance. Eight ...
Gaspo R - - 1997
BACKGROUND: Rapid atrial activation causes electrical remodeling that promotes atrial fibrillation (AF), but underlying mechanisms are incompletely understood. We applied epicardial mapping to evaluate atrial electrophysiology and AF duration in dogs subjected to rapid atrial pacing (400/min). METHODS AND RESULTS: Dogs paced for 1 (P1, n=7), 7 (P7, n=13), or ...
Ikeda T - - 1997
BACKGROUND: The purpose of this study was to test the hypothesis that a single meandering functional reentrant wave front can result in rapid and irregular electrogram activity in human atrial tissues. METHODS AND RESULTS: The study used the explanted hearts of five human cardiac transplant recipients. Three right and two ...
Kautzner J - - 1997
The effect of phenylephrine-induced reflex parasympathetic stimulation on QT interval and its dispersion was studied in 16 healthy subjects with a history of paroxysmal supraventricular tachycardia, both during sinus rhythm and during atrial pacing. Results demonstrate that rapid reflex parasympathetic stimulation does not influence QT interval duration or QT dispersion, ...
Xiao X H - - 1997
Glibenclamide has been shown to prevent ischemia-induced shortening of action-potential duration (APD) and to prolong effective refractory period (ERP). Glibenclamide also has been shown to prolong APD under normal conditions. The aim of this study was to test the hypothesis that glibenclamide would prolong APD and ERP in the nonischemic ...
Abildskov J A - - 1997
Effects of heart rate on refractory period (RP) duration and disparity have opposing actions on vulnerability to fibrillation. Both bradycardia and tachycardia have been reported to increase vulnerability to fibrillation, and the role of their effects on RP duration and disparity in producing that effect is uncertain. That role has ...
Cuomo S - - 1997
The autonomic tone has been shown to influence the duration of the QT interval, however the independent contribution of sympathetic and parasympathetic tone is not fully elucidated. The influence of autonomic tone on QT duration was studied in 10 young healthy volunteers by evaluating the changes in QT and RR ...
Zabel M - - 1997
INTRODUCTION: The exact electrophysiologic mechanism of torsades de pointes (TdP) is under intense investigation. No isolated animal heart model of this particular arrhythmia exists. METHODS AND RESULTS: In isolated rabbit hearts, TdP was induced by means of bradycardia in the presence of a high concentration of d-sotalol (10(-4) M) and ...
Krahn A D - - 1997
BACKGROUND: The diagnosis of the long-QT syndrome (LQTS) may be difficult to establish in patients with normal or borderline prolongation of the QT interval. Noninvasive markers are needed to identify patients with LQTS. METHODS AND RESULTS: Fourteen patients with known LQTS, 9 unaffected family members, and 40 control subjects underwent ...
Santini M - - 1997
AIMS: The aim of this Italian multicentre study was to evaluate the haemodynamic and antiarrhythmic effects of DDIR versus DDI pacing mode in sick sinus syndrome with chronotropic incompetence. METHODS: Seventy-nine patients were implanted with a dual chamber rate-responsive pacemaker (Medtronic 7075) and centrally randomised to DDI or DDIR pacing ...
Cohen TJ - - 1997
Exercise causes enhanced sympathetic discharge and results in physiologic tachycardia. However, in certain patients with a diseased conduction system, exercise can precipitate heart block. The sinus and atrioventricular nodes are innervated by the autonomic nervous systems. The His-Purkinje system is relatively devoid of autonomic nerve supply. Hence the former and ...
Hohnloser S H - - 1997
INTRODUCTION: Evidence is accumulating that microvolt T wave alternans (TWA) is a marker of increased risk for ventricular tachyarrhythmias. Initially, atrial pacing was used to elevate heart rate and elicit TWA. More recently, a noninvasive approach has been developed that elevates heart rate using exercise. METHODS AND RESULTS: In 30 ...
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