Search Results
Results 451 - 500 of 1146
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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 ...
Lee S H - - 1997
We present here, the case of a 22-year-old male suffering from persistent tachycardia for the past 3 years. His resting pulse rate was rarely below 100 beats/min, and it frequently increased to as high as 150 beats/min even after a minimal of activity. Associated symptoms included palpitation, chest tightness, dyspnea ...
Vardas P E - - 1997
The aim of this study was to compare AAIR and DDDR pacing at rest and during exercise. We studied 15 patients (10 men, age 65 +/- 6 years) who had been paced for at least 3 months with activity sensor rate modulated dual chamber pacemakers. All had sick sinus syndrome ...
Stark G - - 1997
OBJECTIVE: It has been well established that class III antiarrhythmic drugs can also induce ventricular arrhythmias. Marked changes in the QT interval are correlated with an increased dispersion of repolarization which is an important factor for the induction of ventricular arrhythmias. The aim of the present study was to investigate ...
Tai C T - - 1997
BACKGROUND: Although typical atrioventricular nodal reentrant tachycardia (AVNRT) with discontinuous AV node function curves has been well studied, there has been a lack of any significant information about AVNRT without evidence of dual AV nodal pathway physiology during atrial extrastimulus testing or atrial pacing. METHODS AND RESULTS: Group 1 included ...
Verduyn S C - - 1997
OBJECTIVE: The mechanism of acquired torsade-de-pointes arrhythmias (TdP) is not clear but is suggested to be based on several parameters including early afterdepolarizations (EADs) and/or dispersion of repolarization (delta APD). In our animal model of TdP (anaesthetized dogs with chronic AV block), we assessed the relevance of interventricular dispersion for ...
Sheahan R G - - 1997
This case report concerns an adverse device-device interaction between a replacement ICD and a dual chamber rate responsive pacemaker. It was observed that subtle changes in the design of sensing circuits between an older first-generation ICD and the newer third-generation ICD device led to unexpected and dramatic changes in the ...
Pandozi C - - 1997
BACKGROUND: Atrial fibrillation (AF) is considered to be maintained by multiple reentrant circuits without or with a very short excitable gap. However, the possibility of local atrial capture has been shown recently in experimental AF or induced AF in humans. METHODS AND RESULTS: This study was undertaken to evaluate the ...
Sanner B M - - 1997
A 40-year-old man-as well as 15 more participants of the same meal-suddenly experienced vomiting and watery diarrhea four hours after having eaten a meal of grouper in the Dominican Republic. Symptoms persisted for four hours and were followed by a generalized pruritus and paresthesias of the lips, tongue, palms, and ...
Celiker A A Department of Pediatric Cardiology, Hacettepe University Medical School, Ankara, - - 1997
Dual sensor pacemakers were developed to obtain more appropriate responses to activity. We evaluated ten children with dual sensor pacemakers in different sensor blending circumstances using exercise testing to assess which ratio was optimal. Ten patients with several bradydysrhythmias (ages 6-16 years; mean 10.1 years) were included in the study. ...
Yu W C - - 1997
OBJECTIVES: This study evaluated the effect of high intensity drive train (S1) stimulation on the atrial effective refractory period (ERP) and its relation to the autonomic nervous system. BACKGROUND: High intensity S1 stimulation was demonstrated to shorten the ventricular ERP and to increase dispersion of refractoriness. These effects may be ...
Payne G - - 1997
A three phase relation has been demonstrated between increasing heart rate and cardiac output at rest. Phase I with cardiac output increasing with increasing heart rate, phase II a plateau, and phase III decreasing cardiac output with any further increase in heart rate. The "optimal rate" can be defined as ...
Fisch C - - 1997
OBJECTIVES: The objective of this study was to correlate electrocardiographic (ECG) PR interval changes during normal sinus rhythm with recent observations regarding the anatomy and physiology of the dual, slow and fast atrioventricular (AV) pathways. BACKGROUND: The least common manifestation of dual AV conduction is an abrupt PR interval change ...
Anyukhovsky E P - - 1997
We studied the effects of nibentan on transmembrane action potentials of canine Purkinje fibers (PF), ventricular epicardial and endocardial tissues and atrial tissue. Nibentan (1 x 10(-8) to 5 x 10(-6) M) had no effects on maximum diastolic potential of all tissues and produced a modest concentration- and use-dependent decrease ...
Bishop J W - - 1997
OBJECTIVE: Second cervical smears obtained at short time intervals often exhibit a lesser degree of abnormality than the first smear. We studied the effect of time interval between smears on diagnoses in two large, distinctive cohorts. STUDY DESIGN: Patients with two or more satisfactory smears with at least one smear ...
Langford E J - - 1997
In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in ...
Yuzuki Y - - 1997
In this report we describe 2 patients with exercise-induced, second-degree atrioventricular (AV) block. Case 1 was a 49-year-old man with normal AV conduction at rest but who developed dyspnea on exertion. Treadmill testing showed an exercise-induced 2:1 AV block. Electrophysiologic study (EPS) demonstrated rate-dependent, presumably intrahissian, AV block. Case 2 ...
Yu W C - - 1997
This study demonstrates that the fast-slow form of atrioventricular nodal reentrant tachycardia is usually catecholamine-sensitive and its electrophysiologic characteristics are significantly different from those of the slow-fast form. However, radiofrequency catheter ablation is a safe and effective treatment for patients with the fast-slow form of atrioventricular nodal reentrant tachycardia.
Santini M - - 1997
OBJECTIVES: We sought to analyze in patients with chronic atrial fibrillation (AF) the change in the intracardiac atrial defibrillation threshold (ADT) at rest and during exercise, to quantify the effective risk of low energy endocavitary cardioversion during the effort and to compare the ADT of chronic and reinduced AF. BACKGROUND: ...
Buys E M - - 1997
OBJECTIVE: To evaluate exercise capacity of patients with chronic atrial fibrillation in whom His bundle ablation followed by ventricular rate response pacing (VVIR) was carried out because of drug refractoriness. DESIGN: Prospective study. PATIENTS: 25 consecutive patients, all with chronic symptomatic drug refractory atrial fibrillation, underwent His bundle ablation. Before ...
Tsai W C - - 1997
Torsade de pointes is a serious ventricular arrhythmia which is usually associated with a long QT interval. It is important to recognize the possible predisposing factors for the management of this arrhythmia. Prolongation of the QT interval and torsade de pointes has been reported in patients with an overdose of ...
Hirose M - - 1997
Pituitary adenylate cyclase-activating polypeptide (PACAP) receptors exist, but the physiologic role of PACAP is unclear in the heart in situ. We investigated effects of PACAP-38 on sinus rate and on the negative chronotropic response to acetylcholine (ACh) or stimulation of the intracardiac parasympathetic nerve fibers to the sinoatrial nodal region ...
Wyse D G - - 1997
Measurements were made in 12 normal subjects and during induction of sustained ventricular tachyarrhythmias in 31 patients with remote myocardial infarction. QT interval measurements were made semiautomatically with computer assistance and the total QT interval was divided into early (QT1) and late (QT2) components. QT intervals and QT interval dispersion ...
Hasegawa A - - 1997
Our objective was to determine the adequate pacing rate during exercise in ventricular pacing by measuring exercise capacity, cardiac output, and sinus node activity. Eighteen patients with complete AV block and an implanted pacemaker underwent cardiopulmonary exercise tests under three randomized pacing rates: fixed rate pacing (VVI) at 60 beats/min ...
Ostermaier R H - - 1997
BACKGROUND: Atrial fibrillation (AF) is a common cardiac arrhythmia, affecting approximately 1.5 million patients in the United States. HYPOTHESIS: This study was designed to determine the effect of AF and the ventricular rate control during AF on cardiovascular performance as measured by exercise endurance on a standard Bruce protocol. METHODS: ...
Abildskov J A - - 1997
Pause dependent onset of torsades de pointes is characteristic in acquired long QT syndromes, and the probable mechanism is reentry facilitated by increased disparity of refractoriness following a long cycle. Adrenergic dependent onset is usual in familial long QT syndromes, and the mechanism is uncertain. In this study with a ...
Banks R W - - 1997
1. A combined physiological, histological and computer modelling study was carried out on muscle spindles of the cat tenuissimus muscle to examine whether there was any correlation between the functional interaction of putative encoding sites, operated separately by static and dynamic fusimotor neurones, and the topological structure of the preterminal ...
Kligfield P - - 1996
OBJECTIVES: This study sought to develop a regression-based method for characterization of QT interval behavior during exercise and to define the normal range of the resulting "dynamic" measures of repolarization during submaximal treadmill testing in men and women. BACKGROUND: The Bazett-corrected QT (QTc) interval during exercise has been used as ...
Ismer B - - 1996
Using telemetry, right atrial electrogram (RA), and marker channel of atrial sense events (MA) in combination with the left atrial electrogram (LA), recorded by a filtered bipolar esophageal lead, interatrial conduction during submaximal exercise and at rest was examined in 46 DDD pacemaker patients. The RA-LA and MA-LA conduction times ...
Kamalvand K - - 1996
The new SMARTracking (SMT) algorithm was evaluated in seven patients with the Intermedics Relay DDDR pacemakers and a history of atrial tachyarrhythmias. The SMT algorithm uses the sensor calculated rate to define a physiological band whose upper limit is defined by the SMT rate. Pacemakers were programmed to DDDR with ...
Delay M - - 1996
The SmarTracking (ST) algorithm (Marathon 294-09, Intermedics Inc.) uses the sensor-calculated rate (SCR) to define a "variation band" for the intrinsic sinus rate. If the sinus rate exceeds the upper limit of the band, the ventricular pacing rate is limited by the ST rate (STR) and Wenckebach behavior is observed. ...
Gessman L - - 1996
The AddVent pacemaker generator and model 1328C AV single-pass lead is a new pacemaker system capable of VDD or VDDR modes. The purpose of this study was to present the initial experience with AddVent in the United States and Canada. Between May 10, 1995 and May 3, 1996, 53 devices ...
Leung S K - - 1996
A dual sensor DDDR pacemaker (DX2 Model 7970, Medtronic Inc.) has integrated the rate response of minute ventilation (MV) and activity (ACT) sensors. False rate acceleration by the ACT (constrained upper rate) and MV (cross-checked by ACT) is reduced. We examined the rate response profile and rate kinetics of the ...
Darpö B - - 1996
The aim of the present study was to assess the frequency dependency of the effects of almokalant, a selective class III antiarrhythmic drug, on ventricular repolarization using recordings of monophasic action potentials and measurements of ventricular paced QT intervals. Twenty male volunteers were studied during almokalant infusion aiming at plasma ...
Lau C P - - 1996
The normal sinus rhythm remains the gold standard to compare the rate response of a rate adaptive pacemaker. The aim of this study was to assess an automatically optimized dual sensor system by continuous comparison of the normal sinus (SR) and sensor indicated rates (SIR). Twelve patients with complete heart ...
Lazarus A - - 1996
From November 1994 to October 1995, 63 patients (average age 66 years; 41 men) from 15 centers implanted with the Biotronik Dromos DR and Ergos TC 03 pulse generators were prospectively screened with an exercise test in the DDD mode for the presence of chronotropic incompetence (CI). Both pulse generators ...
Ricci R - - 1996
To evaluate the safety and efficacy of a new algorithm for automatic mode switching (AMS) from DDD-DDDR to DDIR, 26 patients, 16 females and 10 males, mean age 73 +/- 6 years of age, affected by sinus node disease, chronotropic incompetence, and recurrent paroxysmal atrial fibrillation (PAF) received the Medtronic ...
Viitasalo M - - 1996
The dynamics and homogeneity of the QT interval have been used as indicators of susceptibility to ventricular arrhythmias. We determined the relationship between QT intervals and heart rate during exercise testing and subsequent recovery in 18 healthy children. The QT intervals were measured to the apex (early QT), to the ...
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