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  • 1
    ISSN: 1572-8595
    Keywords: implantable cardioverter-defibrillator ; defibrillation threshold ; defibrillation energy requirement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Introduction: A variety of factors, including the number of defibrillation electrodes and shocking capacitance, may influence the defibrillation efficacy of an implantable defibrillator system. Therefore, the purpose of this study was to compare the defibrillation energy requirement using a 125 uF two-electrode defibrillation system and a 90 uF three-electrode defibrillation system. Methods and Results: The defibrillation energy requirements measured with both systems were compared in 26 consecutive patients. The two-electrode system used a single transvenous lead with two defibrillation coils in conjunction with a biphasic waveform from a 125 uF capacitor. The three-electrode system used the same transvenous lead, utilized a pectoral implantable defibrillator generator shell as a third electrode, and delivered the identical biphasic waveform from a 90 uF capacitor. The two-electrode system was associated with a higher defibrillation energy requirement (10.8±5.5 J) than was the three-electrode system (8.9±6.7 J, p 〈 0.05), however, the leading edge voltage was not significantly different between systems (361±103 V vs. 397±123 V, P = 0.07). The two-electrode system also had a higher shocking resistance (49.0±9.0 ohms vs. 41.4±7.3 ohms, p 〈 0.001) and a lower peak current (7.7±2.6 A vs. 10.1±3.7 A, p 〈 0.001) than the three-electrode system. Conclusions: A three-electrode defibrillation system that utilizes a dual coil transvenous lead and a subcutaneous pectoral electrode with lower capacitance is associated with a lower defibrillation energy requirement than is a dual coil defibrillation system with higher capacitance. This finding suggests that the utilization of a pectoral generator as a defibrillation electrode in conjunction with smaller capacitors is a more effective defibrillation system and may allow for additional miniaturization of implantable defibrillators.
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  • 2
    ISSN: 1572-8595
    Keywords: Radiofrequency Energy ; PSVT ; Catheter Ablation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Temperature monitoring may be helpful for ablation of accessory pathways, however its role in ablation of atrioventricular nodal reentrant tachycardia (AVNRT) using the slow pathway approach is unclear. Therefore, the purpose of this study was to prospectively compare slow pathway ablation for AVNRT using fixed power or temperature monitoring. The study included 120 patients undergoing ablation for AVNRT. Patients were randomly assigned to receive either fixed power at 32 watts, or to temperature monitoring with a target temperature of 60°C. The primary success rate was 72% in the fixed power group and 95% in the temperature monitoring group (p=0.001). The ablation procedure duration (35±29 min vs 35±30 min; p=0.9), fluoroscopic time (32±17 vs 35±19 min; p=0.4), mean number of applications (10.2±8.1 vs 8.4±7.9; p=0.2), and coagulum formation per application (0.2% vs 0.5%; p=0.6) were statistically similar in the fixed power and temperature monitoring groups, respectively. The mean temperature (47.3±4.8°C vs 48.6±3.8°C; p〈0.01), and the temperature associated with junctional ectopy (48.2±3.8°C vs 49.3±3.6°C, p〈0.01) were less for the fixed power than the temperature monitoring group. In the temperature monitoring group, only 31% of applications achieved an electrode temperature of 60°C. During follow up of 6.6±3.6 months there were two recurrences in the fixed power group and one in the temperature monitoring group (p=1.0). In summary, power titration directed by temperature monitoring was associated with an improved primary procedural success rate. Applications of energy were associated with a temperature of approximately 50°C with both techniques, suggesting that there is a low efficiency of heating in the posterior septum.
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  • 3
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Lack of AVNRT Induction. 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, each with one and two extrastimuli, in 103 patients with AVNRT. The stimulation protocol was repeated 10 times in the baseline state, during isoproterenol infusion, and after atropine administration, or until AVNRT was induced in 7 of 10 attempts. The mechanisms responsible for 〈 7 of 10 inductions were classified as: (1) the inability to achieve critical AH prolongation; (2) fast pathway block; and (3) slow pathway block. The induction endpoint was achieved in 90 patients: 55 in the baseline state, 34 during isoproterenol infusion, and 1 after atropine. Tbe mechanism of noninducibility in the baseline state (n = 48) was the inability to achieve a critical AH interval in 20%, fast pathway block in 49%, and slow pathway block in 31% (P = 0.02). During isoproterenol administration (n = 14) and after atropine administration (n = 13), the three mechanisms were equally responsible for nonreproducible induction of AVNRT. Conclusions: The induction of AVNRT is poorly reproducible in approximately 10% of patients. In the baseline state, the most common reason for the inability to reproducibly induce AVNRT is fast pathway block. In the presence of isoproterenol or atropine, each of the three mechanisms was equally responsible for noninducibility of AVNRT.
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  • 4
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Slow Pathway Ablation. Introduction: Successful radiofrequency ablation of an accessory pathway has been demonstrated to be associated with an electrode-tissue interface temperature of approximately 60°C or an impedance change of −5 to −10 Ω. However, the temperature and impedance changes associated with ablation of AV nodal reentrant tachycardia (AVNRT) using the slow pathway approach have not been reported. Therefore, the purpose of this study was to define the temperature and impedance changes achieved during ablation of AVNRT. Methods and Results: The study included 35 consecutive patients with AVNRT undergoing radiofrequency ablation of the slow pathway with a fixed power output of 32 W, and using a catheter with a thermistor bead embedded in the distal 4-mm electrode. The procedure was successful in each patient. The steady-state electrode-tissue interface temperature during successful applications of energy was 48.5 ± 3.3°C (range 42° to 56°C), and the steady-state temperature during ineffective applications was 46.8°± 5.5°C (P = 0.03). The mean impedance change during all applications of energy was −1.4 ± 2.8 ω, and did not differ significantly during effective and ineffective applications. Coagulum formation resulted during five applications (2.7%) in two patients (5.7%). There were no recurrences during 114 ± 21 days of follow-up. Conclusions: Successful ablation of AVNRT using fixed power output is achieved at an electrode-tissue interface temperature of approximately 48°C and is associated with a drop in impedance of 1 to 2 ω. These findings suggest that slow pathway ablation requires less heating at the electrode-tissue interface than does accessory pathway or AV junction ablation.
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  • 5
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    350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
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  • 6
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Biventricular Pacing. Introduction: The aim of this study is to describe implantation techniques and lead performance for biventricular pacing, dual-chamber implantable cardioverter defibrillators (ICDs). Methods and Results: A dual-chamber ICD with biventricular pacing was implanted in 87 patients with congestive heart failure (ejection fraction: 0.21 ± 0.09), prolonged QRS duration (161 ± 22 msec), and an indication for ICD therapy. Left ventricular pacing was achieved with a thoracotomy approach (n = 21) or a nonthoracotomy approach (n = 66). With a thoracotomy, biventricular devices were implanted successfully in all patients. During follow-up (17 ± 11 months), 9 patients died (43%), 2 underwent transplantation, and 2 required left ventricular lead revision. At last follow-up, biventricular sensing and capture threshold were 11 ± 5 mV and 1.5 ± 0.8 V, respectively. For nonthoracotomy procedures, two types of coronary sinus (CS) leads were implanted: an over-the-wire lead (n = 45) and a shaped lead (n = 21). The rate of successful implantation (overall: 89%) (over-the-wire 93% vs shaped 81%; P = 0.1) and durations for CS lead placement (66 ± 50 vs 58 ± 34 min, P = 0.6) and the procedure (133 ± 58 vs 129 ± 33 min, P = 0.8) were not different between the two CS leads. During follow-up (11 ± 9 months), 9 patients died (14%), and the shaped CS lead dislodged in 3 patients (3 shaped vs 0 over-the-wire, P = 0.01). At last follow-up, biventricular sensing and capture threshold were 10 ± 4 mV and 1.8 ± 0.7 V, respectively, and there was no difference between over-the-wire and shaped leads. By multivariate analysis, mortality was associated with absence of spironolactone therapy but not procedural features. Conclusion: Nonthoracotomy CS lead implantation is feasible, with a success rate of about 90% and few adverse events. For the remaining 10%, a thoracotomy approach can be completed safely in these ill patients without increased risk for death.
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  • 7
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Sinus Node Remodeling. Introduction: The purpose of this study was to investigate the effect of ablation of right atrial flutter upon sinus node function in humans. Methods and Results:This study enrolled 35 patients. Twenty-four patients (16 men and 8 women; age 68 ± 11 years) were referred for ablation of persistent atrial flutter (duration 8 ± 11 months). After ablation, there was abnormal sinus node function defined as a corrected sinus node recovery time (CSNRT) 〉 550 msec. The control group consisted of 11 patients who were undergoing pacemaker implantation for sinus node disease but did not have a history of atrial dysrhythmias or ablation. Within 24 hours of ablation or pacemaker implantation, baseline maximal CSNRT was measured through a permanent pacemaker by AAI pacing at six cycle lengths: 600, 550, 500, 450, 400, and 350 msec. CSNRT then was measured in the same manner at 48 hours, 14 days, and 3 months after ablation/pacemaker implantation. P wave amplitude and duration, and percent atrial sensing also were assessed at the same intervals. For patients undergoing atrial flutter ablation, there was progressive temporal recovery of CSNRT (1,204 ± 671 msec at baseline vs 834 ± 380 msec at 3 months; P 〈 0.001) and a significant increase in the percent atrial sensing and P wave amplitude at 3 months compared with baseline (P 〈 0.001). In control subjects, there was no change in the CSNRT, percent atrial pacing, or P wave amplitude. Conclusion: After ablation of persistent atrial flutter, there is temporal recovery of CSNRT and increase in spontaneous atrial activity. These findings suggest that atrial flutter induces reversible changes in sinus node function.
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  • 8
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Patients with ICDs are commonly advised to quit industrial jobs because of concerns that strong electromagnetic fields operating in the industrial environment might interfere with ICD functions. This study was done to assess interactions between industrial equipment and ICDs, and to devise a simple low risk screening protocol. We studied 18 patients carrying nine different ICD models who were met at their workplace by a clinical technician and were asked to walk through their workplace and perform typical duties while sensing status was monitored by listening to the ICD's beeper. All devices were interrogated at the completion of testing. At follow-up, patients were contacted by phone and were asked about employment status and history of ICD discharges or syncope. One hundred eighty-four contacts with 114 types of industrial equipment in 13 different industrial facilities (including 31 contacts with arc welding machines) were monitored. Interference with ICD's function occurred in only one contact (0.5%), when ICD therapy was temporarily suspended while a worker was attaching a huge electromagnet to a crane. At follow-up 46.0 ± 6.0 months after testing, 7 patients (41%) are still holding the same job, 7 have retired because of reasons unrelated to their ICD, and 3 patients were transferred to a nonindustrial job. None of the patients had either an ICD shock or syncope during work. The use of a simple screening procedure can safely identify sources of electromagnetic interference that may affect ICD operation, and can predict long-term safety of working in an industrial workplace for ICD patients. (PACE 2003; 26:1675–1678)
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  • 9
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The chronic defibrillation energy requirement (DER) is believed to remain clinically stable in patients with defibrillators. Six patients (two with an epicardial and four with a nonthoracotomy system) were identified with a rise in their chronic DER, which eliminated a 10-J safety margin, thus necessitating a defibrillator lead system revision. The mean increase in DER was 14.7 ± 4 J and was discovered at a mean of 16.0 ± 18 months (range 2-41) following implantation. Management included placement of a defibrillator with a biphasic waveform, placement of an additional defibrillation electrode, or both. At 2 months following revision of the defibrillation system, a 10-J DER safety margin was present in each patient. In some patients, there is a progressive increase in the chronic DER with elimination of a 10-J safety margin necessitating revision of the defibrillation system. Routine reevaluation of the chronic DER, therefore, is necessary to identify these patients.
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  • 10
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Low-Energy Defibrillation. Introduction: In patients undergoing defibrillator implantation, an appropriate defibrillation safety margin has been considered to be either 10 J or an energy equal to the defibrillation energy requirement. However, a previous clinical report suggested that a larger safety margin may be required in patients with a low defibrillation energy requirement. Therefore, the purpose of this prospective study was to compare the defibrillation efficacy of the two safety margin techniques in patients with a low defibrillation energy requirement. Methods and Results: Sixty patients who underwent implantation of a defibrillator and who had a low defibrillation energy requirement (≤ 6 J) underwent six separate inductions of ventricular fibrillation, at least 5 minutes apart. For each of the first three inductions of ventricular fibrillation, the first two shocks were equal to either the defibrillation energy requirement plus 10 J (14.6 ± 1.0 J), or to twice the defibrillation energy requirement (9.9 ± 2.3 J). The alternate technique was used for the subsequent three inductions of ventricular fibrillation. For each induction of ventricular fibrillation, the first shock success rate was 99.5%± 4.3% for shocks using the defibrillation energy requirement plus 10 J, compared to 95.0%± 17.2% for shocks at twice the defibrillation energy requirement (P = 0.02). The charge time (P 〈 0.0001) and the total duration of ventricular fibrillation (P 〈 0.0001) were each approximately 1 second longer with the defibrillation energy requirement plus 10 J technique. Conclusion: This study is the first to compare prospectively the defibrillation efficacy of two defibrillation safety margins. In patients with a defibrillation energy requirement ≤ 6 J, a higher rate of successful defibrillation is achieved with a safety margin of 10 J than with a safety margin equal to the defibrillation energy requirement.
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