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  • 1
    ISSN: 1540-8191
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background and Aim: Surgical resection of myocardium that acutely reduces left ventricular (LV) volume in patients with advanced heart failure (HF), the so-called “Batista Operation,” remains controversial. We examined the effects of acute LV reduction with the Acorn Cardiac Support Device (CSD) in dogs with HF (LV ejection fraction 〈 30%). Methods: HF was produced in 15 dogs by intracoronary microembolization. In nine dogs, intravenous dobutamine was administered to reduce LV end-diastolic dimension (LVEDD) by 10%-25%. While on dobutamine infusion, the CSD, a preformed knitted polyester device, was surgically placed around the ventricles, anchored to the arteriovenous (AV) groove, and tailored anteriorly to fit snugly over the ventricles. Dogs were then weaned off dobutamine. Results: On average, the procedure reduced LVEDD by 7 ± 1 mm (range 5–12 mm). Of the nine dogs, two died before completion of the study and seven survived for the entire period. Six dogs did not undergo device placement and served as controls. All were followed for 3 months prior to sacrifice. In controls, LV end-diastolic volume increased after 3 months (66 ± 5 mL vs 77 ± 6 mL; p = 0.007), while in CSD-treated dogs (n = 7), it decreased (80 ± 5 mL vs 60 ± 3 mL; p = 0.002). In controls, LV ejection fraction (EF) decreased after 3 months (27 ± 1% vs 23 ± 1%; p = 0.001) but was unchanged in CSD-treated dogs (25 ± 1% vs 26 ± 1%; p = 0.66). Compared to controls, CSD-treated dogs showed improved LV diastolic dysfunction and chamber sphericity, decreased wall stress, and no functional mitral regurgitation (MR). Conclusion: In dogs with advanced HF, acute LV reduction with the Acorn CSD prevents progressive global LV dilatation and ameliorates functional MR.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Annals of noninvasive electrocardiology 3 (1998), S. 0 
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background: The mean ventricular rate is known to be, on average, higher during episodes of paroxysmal atrial fibrillation (AF) than during the sinus rhythm. The data on other statistical parameters of ventricular periods are less known, especially in the respect of atrial premature beats, which are frequent in paroxysmal AF patients while in sinus rhythm.Methods: This study investigated distinction between paroxysmal AF and sinus rhythm based on statistical parameters of 60-second segments of RR interval series from paroxysmal AF and sinus rhythm episodes. The data of the study were taken from 54 long-term Holter recordings of 31 paroxysmal AF patients. For each segment, the mean, standard deviation, skewness, and kurtosis of RR intervals were computed. The values obtained from segments of paroxysmal AF and sinus rhythm were used in attempts to distinguish both rhythms. The distinction was evaluated using: (1) statistical comparison of each parameter in each tape; and (2) receiver operator characteristics (ROCs) (dependency of specificity on sensitivity) computed in each tape for each individual parameter as well as for multivariate combinations of all four parameters.Results: The comparison found the mean RR to be the most powerful discriminator of all statistical parameters used in the distinction of paroxysmal AF and sinus rhythm. The standard deviation of RR intervals differentiated significantly the segments of sinus rhythm and paroxysmal AF in pool data. However, when applied to individual Holter recordings, the distinction between paroxysmal AF and sinus rhythm based on standard deviation of RR intervals (assessed with ROC) was the worst among all investigated parameters.Conclusions: The study suggests that an automatic distinction between paroxysmal AF and sinus rhythm episodes is highly problematic, mainly because of the frequent atrial premature beats that pollute sinus rhythm episodes in patients with paroxysmal AF.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Reentry Site and Defibrillation Waveform Efficacy. Introduction: Unsuccessful defibrillation shocks may reinitiate fibrillation by causing postshock reentry. Methods and Results: To better understand why some waveforms are more efficacious for defibrillation, reentry was induced in six dogs with 1-, 2-, 4-, 8-, and 16-msec monophasic and 1/1- (both phases 1 msec) 2/2-, 4/4-, and 8/8-msec biphasic shocks. Reentry was initiated by 141 ± 15 V shocks delivered from a defibrillator with a 150- μ F capacitance during the vulnerable period of paced rhythm (183 ± 12 msec after the last pacing stimulus). The shock potential gradient field was orthogonal to the dispersion of refractoriness. Activation was mapped with 121 electrodes covering 4 × 4 cm of the right ventricular epicardium, and potential gradient and degree of recovery of excitability were estimated at the sites of reentry. Defibrillation thresholds (DFTs) were estimated by an up-down protocol for the same nine waveforms in eight dogs internally and in nine other dogs externally. DFT voltages for the different waveforms were positively correlated with the magnitude of shock potential gradient and negatively correlated with the recovery interval at the site at which reentry was induced by the waveform during paced rhythm for both internal (DFT = 1719 + 64.5 ∇ V − 11.1RI; R2= 0.93) and external defibrillation (DFT = 3445 + 150 ∇ V − 22RI; R2= 0.93). Conclusion: The defibrillation waveforms with the lowest DFTs were those that induced reentry at sites of low shock potential gradient, indicating efficacious stimulation of myocardium. Additionally, the site of reentry induced by waveforms with the lowest DFTs was in myocardium that was more highly recovered just before the shock, perhaps because this high degree of recovery seldom occurs during defibrillation due to the rapid activation rate during fibrillation.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 9 (1998), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The effects of digoxin on ventricular response during atrial fibrillation (API and consequent effects on arrhythmic symptoms have still not been fully explained. This study investigated whether the treatment by digoxin contributes to mid– and long–term stabilization of ventricular cycles in patients with paroxysmal AF. A population of 45 patients with paroxysmal AF underwent 24–hour ECG recordings during each arm of a randomized crossover trial comparing digoxin and placebo. This yielded 30 Holter recordings from 22 patients that contained AF episodes lasting in excess of 2 minutes and with acceptably low Holter noise. Each AF episode was divided into nonoverlapping segments of 30 seconds and the distribution of RR intervals in each segment was compared with the distribution of all other AF segments in the same recording using the Kolmogorov–Smimov test. The percentage of tests that revealed significant differences at levels of P ≤ 0.01, and P ≤ 0.001 were sorted according to the time between the segments compared. The comparisons of these results were performed between: (a) all recordings on placebo (n = 16) and all recordings on digoxin (n = 14), and (b) between recordings on placebo and on digoxin in 8 patients in whom paired analysis was possible. Adjacent AF segments (distance 0) differed significantly only in 〈 30% of both recordings on placebo and on digoxin. However, with increasing the distance between segments, the proportion of the significant differences between RR interval distributions increased more with placebo than with digoxin (P 〈 10−300, Chi-square test). Paired data revealed larger differences between placebo and digoxin with increasing distance between segments. Thus in patients with paroxysmal AF, digoxin leads to more reproducible patterns of ventricular cycles that may be better tolerated clinically.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Left atrial (LA) dilatation is a common finding in patients with chronic atrial fibrillation (AF). Progressive dilatation may alter the atrial defibrillation threshold (ADFT). In our study, epicardial electrodes were implanted on the LA free wall and right ventricular apex of eight adult sheep. Large surface area, coiled endocardial electrodes were positioned in the coronary sinus and right atrium (RA). LA dilatation was induced by rapid ventricular pacing (190 beats/min) for 6 weeks and echocardiographically assessed weekly along with the ADFT (under propofol anesthesia). LA effective refractory period (ERP) was measured every 2–3 days using a standard extra stimulus technique and 400 ms drive. The AF cycle length (AFCL) was assessed from LA electrograms. During the 6 weeks of pacing the mean LA area increased from 6.1 ± 1.5 to 21.3 ± 2.4 cm2. There were no significant changes in the mean ADFT (122 ± 15 V), circuit impedance (46 ± 5 Ω), or LA AFCL (136 ± 23 ms). There was a significant increase in the mean LA ERP (106 ± 10 ms at day 0, and 120 ± 13 ms at day 42 of pacing). In this study, using chronically implanted defibrillation leads, the minimal energy requirements for successful AF were not significantly altered by ongoing left atrial dilatation. This finding is a further endorsement of the efficiency of the coronary sinus/RA shock vector. Furthermore, the apparent stability of the AF present may be a further indication of a link between the type of AF and the ADFT.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 7 (1996), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Automatic Atrial Defibrillator. Atrial fibrillation is a common arrhythmia, accounting for more consumption of medical resources than any other arrhythmia. The impact of the disease results from the combination of a loss of atrial contraction, and atrial control over cardiac rate. Studies in animals demonstrated the basic feasibility of atrial defibrillation using electrodes passed intravenously. Subsequent studies in patients confirmed that low-energy shocks were effective in converting atrial fibrillation and were safe if delivered synchronous to the R wave in the absence of a short preceding RR interval. Preliminary experience suggests that a small implanted device might provide beneficial therapy for patients with recurring episodes of persistent, drug-refractory, atrial fibrillation.
    Type of Medium: Electronic Resource
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