Search Results
Results 501 - 550 of 1133
< 6 7 8 9 10 11 12 13 14 15 16 >
Strickberger S A - - 1996
INTRODUCTION: AV nodal reentrant tachycardia (AVNRT) is not always reproducibly inducible. The purpose of this study was to determine the mechanisms responsible for the lack of reproducible induction of AVNRT. METHODS AND RESULTS: The induction of AVNRT was assessed with atrial burst pacing, and with atrial and ventricular programmed stimulation, ...
Ma J - - 1996
OBJECTIVE: To investigate the exercise hemodynamic benefits of activity-sensing rate adaptive ventricular pacing (VVIR) over fixed rate pacing (VVI) mode. METHODS: Activity sensing rate adaptive pacemaker was implanted in 19 patients (13 males and 6 females, mean age 54.8 years) with bradycardia. All patients underwent symptom-limited upright bicycle exercise in ...
Theodorakis G N - - 1996
The aim of this study was to evaluate clinical, adrenergic and endocrine factors that could predict sinus rhythm maintenance after direct current cardioversion in chronic atrial fibrillation. Nineteen patients with chronic non-rheumatic atrial fibrillation (mean duration 6 +/- 5 months) were studied. They were exercised 24 h before cardioversion at ...
Fei H - - 1996
We used eight adjustable preparations in which the canine atrial tricuspid rings were cut and reconnected electronically by sensing activation on one side of the cut and pacing the other after an adjustable delay. A long delay resulted in a long cycle length (CL) and excitable gap (EG) during reentry. ...
Aizawa Y - - 1996
OBJECTIVE: Monomorphic sustained ventricular tachycardia (VT) can often be entrained and interrupted at a critical paced cycle length. The aim was to evaluate a possible determinant of this phenomenon by observing the action of mexiletine on the critical paced cycle length and other variables. METHODS: Nine consecutive patients with symptomatic ...
Rodefeld M D - - 1996
Intraatrial reentrant tachycardia, or atrial flutter, is a common postoperative problem after Fontan repair, which involves an atriopulmonary connection. A modification of Fontan repair, total cavopulmonary connection, minimizes the portion of the right atrium exposed to stretch and hypertension; however, atrial flutter continues to occur after this procedure. We postulated ...
Page R L - - 1996
This study examined the complex interaction between vagal enhancement and how a concealed atrial impulse alters atrioventricular (AV) nodal function. In theory, vagal augmentation could increase or decrease the effect that a premature atrial beat has on the subsequent beat. In 10 patients we established the AV nodal effective refractory ...
Stark U - - 1996
Detajmium (4--3'-diethylamino-2'-hydroxypropyl--ajmalin) is an Na(+)-channel-blocking drug with an extremely long recovery from use-dependent sodium channel block. The aim of the present study was to investigate the rate-dependent effects of detajmium on the intraventricular conduction of isolated, spontaneously beating, guinea pig hearts in comparison with the effects of propafenone. Detajmium (0.3 ...
Yamada A - - 1996
Direct cardiac effects of sematilide, a new class III antiarrhythmic drug, were compared with those of E-4031 and MS-551 in canine isolated blood-perfused heart preparations. Doses of sematilide, E-4031, and MS-551 causing a 10% decrease in the spontaneous sinoatrial beating rate were 58 +/- 15, 9 +/- 5, and 84 ...
Shapira Y - - 1996
The case of an endurance runner with moderate aortic stenosis, who had recurrent syncope, is reported. A Holter recording during syncope revealed asystole lasting 57 s. Head-up tilt table test with isoproterenol was abnormal. No important abnormality was found in sinus or atrioventricular nodal functions. It was postulated that the ...
Candinas R - - 1996
OBJECTIVE: The electrophysiological effects of intravenously administered pure (S)- and (R)-propafenone hydrochloride has been determined for the first time in humans-12 patients with supraventricular tachycardia. METHODS: Measurements were performed before and during drug therapy. RESULTS: (S)- and (R)-propafenone prolonged the AH interval from 82 to 107 ms and 75 to ...
Honda T - - 1996
It is believed that reciprocating tachycardia and accessory pathways play important roles in atrial fibrillation (AF) in patients with Wolff-Parkinson-White (WPW) syndrome. However, the mechanism by which AF occurs is not yet fully understood. This study was performed to evaluate the contribution of sympathoadrenal activity to the onset of AF ...
Scott C D - - 1995
The chronotropic response to exercise is abnormal in cardiac transplant recipients as a result of autonomic denervation. Differences in the response between recent transplant recipients and longer-term survivors have been described in previous cross-sectional studies. These changes have not been assessed directly using serial studies. The effect of sinus node ...
Hamer M E - - 1995
It is generally assumed that paroxysmal supraventricular tachycardia (PSVT) induced during invasive electrophysiological study reproduces the patient's spontaneous, clinical arrhythmia. Even in the absence of antiarrhythmic drugs, however, there may be significant differences in characteristics of the induced and spontaneous arrhythmias. We compared the heart rate of PSVT in 38 ...
Birkui P J - - 1995
Ventricular epicardial mapping was performed in six closed-chest anesthetized dogs to investigate the cardiac electrical response to external pacing. A right thoracotomy was performed, complete AV block was produced by formaldehyde injected into the AV node and a sock electrode array, comprised of 127 unipolar electrodes, was placed over the ...
de Groot S H - - 1995
BACKGROUND: In the intact heart, methodological difficulties hamper the direct visualization of delayed afterdepolarizations (DADs) responsible for triggered arrhythmias. Therefore, we tested the hypothesis that a combination of pacing and the recording of a monophasic action potential (MAP) could facilitate the recognition of ouabain-induced DADs and triggered arrhythmias by demonstrating ...
Shafik A - - 1995
OBJECTIVES: To study the electric activity of the vas deferens (VD), or electrovasogram (EVG), in 14 mongrel dogs. METHODS: The VD was exposed in the spermatic cord and three electrodes were applied to it. Synchronous transcutaneous EVG was also recorded by another three electrodes. The electric activity and intravasal pressure ...
Kowallik P - - 1995
INTRODUCTION: Evidence from animal experiments indicates that the autonomic nervous system may influence the sinus (SA) and atrioventricular (AV) nodes differently. We investigated, therefore, whether there are spontaneous functional differences in the innervation of the SA and AV nodes in man. METHODS AND RESULTS: This study was performed in 10 ...
Williamson J W - - 1995
Cardiac output (CO) responses to exercise can be altered by ventricular pacing in pacemaker-dependent patients. The relative contributions of CO and peripheral vascular resistance (PVR) toward the initial increase in blood pressure with the initiation of static exercise were investigated in eight otherwise healthy pacemaker-dependent subjects [age 24 +/- 2 ...
Kay G N - - 1995
BACKGROUND: Oxygen uptake during constant workload exercise increases exponentially from its resting value before reaching a steady state. The difference between the actual rate of oxygen consumption at the onset of exercise and the steady state is an oxygen deficit. Similarly, the normal sinus node increases its rate at the ...
Billette J - - 1995
The functional origin of atrioventricular nodal hysteresis was studied in isolated rabbit heart preparations. This hysteresis is characterized by asymmetric changes in nodal conduction time (NCT) occurring for symmetric changes in cycle length. The respective contribution of the nodal properties of recovery, facilitation, and fatigue to the beat-to-beat changes in ...
Hargreaves M R - - 1995
OBJECTIVE: To compare symptoms and exercise tolerance during dual chamber universal (DDD) and ventricular rate response (VVIR) pacing in elderly (> or = 75) patients. DESIGN: Randomised, double blind, crossover study. SETTING: Regional cardiac department. PATIENTS: Twenty elderly patients (mean age 80.5 (1) years) with high grade atrioventricular block and ...
Ovadia M - - 1995
BACKGROUND: Sensors of posture may improve rate-adaptive pacing in syndromes where syncope occurs in the upright posture, particularly in the young. No sensor of posture has been described to date. Previous studies suggest that two sensors currently under investigation (preejection period [PEP] and left ventricular ejection time [LVET] systolic time ...
Mehta A V - - 1995
Symptomatic sinus bradycardia, due to either sick sinus syndrome or vagotonia, can be familial, affecting several members of a family. We report an 18-year-old male patient with palpitations and limited exercise capacity who was noted to have severe sinus bradycardia. His resting heart rate was 40/min, with normal PR and ...
Goldberger J J - - 1995
BACKGROUND: Most studies evaluating the effects of high-intensity drive-train (S1) stimulation on the measurement of the ventricular effective refractory period (VERP) demonstrated a shortening of the VERP. Because this effect may be due to the local release of catecholamines, VERP shortening would be expected to occur only near the site ...
Alt E - - 1995
Fourteen patients were implanted with a single chamber dual sensor pacemaker (Legend Plus) that measures minute ventilation (VE) via variations in impedance between a bipolar lead and the pacemaker case, and activity via a piezoelectric crystal bonded to the pacemaker case. Chronotropic incompetent patients were exercised on a treadmill and ...
Crook B - - 1995
In this study, the intercepts and slopes of the regression lines of sinus heart rate response to exercise were examined as a possible means of assessing normal and abnormal chronotropic responses. The regressions were plotted for 223 normal subjects and 93 pacemaker patients during progressive bicycle exercise. The 93 pacemaker ...
Lee J U - - 1995
OBJECTIVES: The PR interval on the electrocardiogram represents conduction time from the onset of atrial activation through His-Purkinje conduction system during a normal cardiac cycle. While its behavior at rest and during exposure to various cardioactive drugs is well documented, there exist few reports which describe PR interval variations during ...
Leclercq C - - 1995
Pacing the right ventricle in the apex profoundly modifies the sequence of activation and thus the sequence of contraction and relaxation of the left ventricle. To evaluate the relative importance of preserving normal ventricular activation sequence and optimal atrioventricular (AV) synchrony in permanent pacing, we compared the effects of three ...
Davis T M - - 1995
OBJECTIVE: To investigate changes in the electrocardiographic QT interval during rapidly induced, sustained hypocalcaemia in healthy volunteers. DESIGN: Serial rate corrected QT measurements were made during and after a variable rate trisodium citrate infusion designed to "clamp" the whole blood ionised calcium concentration 0.20 mmol/l below baseline for 120 min. ...
Frielingsdorf J - - 1995
To determine the benefit of atrial contribution on work capacity in relation to left ventricular ejection fraction, we studied 17 patients (68 +/- 13 years) with dual chamber pacemakers (DDD) implanted for high degree atrioventricular (AV) block. In random order they were assigned to rate responsive ventricular (VVIR) and to ...
Rothman S A - - 1995
BACKGROUND: Sinus node dysfunction has been reported to occur in up to 50% of orthotopic heart transplant recipients, and oral theophylline has been used in an attempt to limit the morbidity associated with this abnormality. The purpose of this study was to evaluate the electrophysiologic effects of methylxanthines on sinus ...
Zile M R - - 1995
Chronic supraventricular pacing tachycardia (SVT) causes abnormalities in both ventricular and cellular relaxation. The mechanisms causing these abnormalities have not been fully determined. To examine two of the possible mechanisms, a decrease in restoring force or an impairment of the intrinsic myocardial relaxation process, cardiocytes were enzymatically isolated from the ...
Odell J A - - 1995
A 35-year-old male developed superior vena cava (SVC) obstruction due to multiple retained pacemaker leads. This caused cyanosis and suffusion of the head and neck during arm exercise, with desaturation from 99%-90% demonstrated by ear oximetry. The SVC was bypassed using a spiral vein graft because of worsening symptoms. Dramatic ...
Williamson J W - - 1995
R-R interval (RRI) changes were recorded from 15 healthy volunteers in response to volitional unloaded cycling and passively induced cycling (PC). PC was also combined with electrical stimulation (n = 5) to increase muscle mechanoreceptor activation. The electrocardiogram and leg electromyographic activity were continuously sampled by computer at 1,000 Hz, ...
Wang J A - - 1995
Although exercise testing has been advocated to unmask proarrhythmic potentials in patients receiving flecainide acetate, the effects of this drug on exercise parameters in individuals without structural heart disease have not been reported. This study was undertaken to assess the effects of flecainide on hemodynamics and electrocardiographic changes during exercise ...
Li H G - - 1995
INTRODUCTION: Absence of overt retrograde accessory pathway conduction may be related to low resting sympathetic tone in patients with apparent unidirectional anterogradely conducting accessory pathways (UACAP). METHODS AND RESULTS: To test this hypothesis, we studied the effect of isoproterenol on accessory pathway function and tachycardia induction in 18 patients (12 ...
Barrington W W - - 1995
Dual chamber, rate responsive (DDDR) pacing is felt to be superior to ventricular, rate responsive (VVIR) pacing since it more closely mimics the normal electrical and hemodynamic activity of the heart. This reasoning has been used to justify the higher initial costs and increased complexity of dual chamber system. This ...
van den Berg M P - - 1995
OBJECTIVE: To examine the effect of exercise on cycle length in atrial flutter. PATIENTS: 15 patients with chronic atrial flutter. Seven patients were taking digoxin and six verapamil; two were not taking medication. METHODS: All patients underwent bicycle ergometry. Flutter cycle length was measured at rest and at peak exercise. ...
Ovsyshcher I - - 1995
The LEGEND-PLUS, a new rate adaptive pacemaker that combines activity and minute ventilation sensing for automatic rate adaptation was implanted in the right ventricle (VVIR) in 11 patients (mean age 62 +/- 9 years). Initial programming was performed using the Programmer Exercise Protocol (a 3-minute walk). This programming was evaluated ...
Wysocki H - - 1995
Peripheral polymorphonuclear neutrophils (PMN) number, percent of PMN bearing IgG Fc receptors as well as PMN adherence were evaluated in 29 patients submitted to an exercise test. The peripheral PMN count significantly increased at the maximal work load. The increase in number of neutrophils bearing IgG Fc receptors was also ...
Alison J F - - 1995
BACKGROUND: Catheter ablation of the atrioventricular (AV) node with radiofrequency current (RFC) is associated with the short-term onset of a junctional escape rhythm (JER) in nearly all patients. However, the origin of the JER and short-term thermal effects of RFC on this junctional pacemaker activity are ill defined. METHODS AND ...
Pinney S P - - 1995
Torsades de pointes ventricular tachycardia (VT) has been reported in patients taking the nonsedating antihistamine, terfenadine. We performed electrophysiologic studies of 14 isolated guinea pig hearts using the Langendorff technique to assess whether terfenadine exerted actions that could be responsible for inducing the arrhythmia. Twelve hearts were perfused with an ...
Kligfield P - - 1995
A mathematic description of the behavior of the Bazett-corrected QTc interval during exercise was developed from the underlying relationship between the unadjusted QT interval and heart rate in 94 normal men. Measurements were made from digitized precordial lead V5 complexes that were averaged by computer over 20-second periods at upright ...
Lau C P - - 1994
Central venous oxygen saturation (SvO2) closely reflects cardiac output and tissue oxygen consumption. In the absence of an adequate chronotropic response during exercise, SvO2 will decrease and the extent of desaturation may be used as a parameter for rate adaptive cardiac pacing. Eight patients with sinoatrial disease received a DDDR ...
Lau C P - - 1994
Although differences in exercise performance have been observed between different rate adaptive modes, the relative impact of atrioventricular (AV) synchrony and rate adaptation on quality of life (QOL) have not been determined. Thirty-three patients with either sinoatrial disease (18) or complete atrioventricular (AV) block (15) received DDDR pacemakers (16 minute ...
Slade A K - - 1994
BACKGROUND: Minute volume is a truly physiological sensor for rate adaptive pacing that correlates with metabolic expenditure throughout the range of physical activity. Criticism has centered on the slow initial response compared to less physiological sensors. A new algorithm, consisting of rate augmentation factor and programmable speed of response, has ...
Faerastrand S - - 1994
A new rate adaptive pacemaker (Sensorithm) controlled by an activity sensor providing electrical signals induced by a magnetic ball moving freely in an elliptical cavity surrounded by two copper coils, was implanted in ten patients; mean age of 75 years (range 64-89). Six patients had atrioventricular block and four had ...
Sinha S - - 1994
Dual sensor pacemakers should respond more appropriately during differing exercise modes than a single sensor device. The Topaz model 515 (QT and activity count [ACT] sensing) pacemaker shows appropriate rate response during treadmill exercise testing. We postulated that adjustments to relative sensor contribution should allow fine tuning of the onset ...
Alt E - - 1994
A new generation of activity-based pacemakers incorporates an accelerometer sensitive to low frequency acceleration signals in the anteroposterior direction for sensing of bodily stress. The purpose of our investigation was to test a representative model of these new activity-based pacemakers (Relay) and compare it with current vibration- and housing pressure-sensing ...
< 6 7 8 9 10 11 12 13 14 15 16 >