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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
    Electronic Resource
    Electronic Resource
    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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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Unipolar Electrogram. Introduction: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventricular activation. The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave. However, the accuracy of this technique is unknown. Methods and Results: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature depolarization site of origin. Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients. No R waves were detected at the ventricular premature depolarization site of origin. R waves were detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode. An R wave was not observed at distances ≤ 11 mm from the site of tachycardia origin in 13 of 20 patients (65%). Conclusions: While an R wave in the unipolar electrogram can he seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.
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  • 8
    ISSN: 1542-474X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Background:The implantable cardioverter defibrillator (ICD) has underscored the limitations of our methods of risk assessment. ICDs should be available to patients at high risk for arrhythmic death, but because of the potential for adverse effects and high cost it should be scrupulously avoided in patients whose lives will not be prolonged. Unfortunately, discrimination between these two groups of patients remains a challenge. Recent clinical trial results have not only shown that electrophysiological studies (EPS) in combination with other risk stratifiers identify patients with ischemic heart disease at high risk for arrhythmic death, but they have linked the efficacy of ICD therapy to the results of EPS. However, to perform EPS in all potential candidates for ICD therapy would be a time-consuming and costly burden to medical services and would expose many patients to the risks and discomfort of an invasive procedure. Noninvasive identification of appropriate candidates is therefore essential to successful application of EPS. Methods:Nonsustained ventricular tachycardia (NSVT) and a reduced left ventricular ejection fraction (EF) was used to select patients for EPS in two important trials, but it is not certain that these are the optimal tests or that the optimal thresholds 〈inlineGraphic alt="geqslant R: gt-or-equal, slanted" extraInfo="nonStandardEntity" href="urn:x-wiley:1082720X:ANEC434:ges" location="ges.gif"/〉 1 episode of NSVT 〈inlineGraphic alt="geqslant R: gt-or-equal, slanted" extraInfo="nonStandardEntity" href="urn:x-wiley:1082720X:ANEC434:ges" location="ges.gif"/〉 3 beats; EF 〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:1082720X:ANEC434:les" location="les.gif"/〉 0.35 or EF 〈inlineGraphic alt="leqslant R: less-than-or-eq, slant" extraInfo="nonStandardEntity" href="urn:x-wiley:1082720X:ANEC434:les" location="les.gif"/〉 0.40) were used. A number of studies have addressed the accuracy of clinical factors for predicting the results of EPS and a number of noninvasive tests have been proposed including the signal-averaged electrocardiogram, heart rate variability, T-wave alternans, and high spatial resolution (multilead) electrocardiography. In some contexts, combinations of factors provide significant improvements in accuracy. However, the populations studied were often highly selected, which makes comparisons between techniques or prediction of responses in the populations that would require screening difficult. Results from recently completed and ongoing clinical trials should provide important new information. A greater problem is that EPS has not been shown to consistently provide accurate discrimination of patients with nonischemic cardiac disorders. Conclusions:Effective widespread application of ICD therapy will require greater precision of patient selection. Noninvasive tests under investigation demonstrate considerable promise in selecting appropriate candidates for EPS. However, because the most precise methods of risk assessment are likely to be those most closely linked to the mechanisms of fatal arrhythmias, it is important that further development of noninvasive techniques incorporates advances in basic cardiac electrophysiology. A.N.E. 1999;4(4):434–442
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  • 9
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Impedance Versus Temperature Monitoring. Introduction: The purpose of this study was to prospectively compare the value of impedance and temperature monitoring during accessory pathway ablation. Temperature and impedance monitoring can be used during radiofrequency ablation of accessory pathways to titrate power to achieve adequate but not excessive tissue beating. Methods and Results: One hundred thirty-two patients with a single accessory pathway were randomly assigned to undergo ablation using either impedance monitoring or temperature monitoring. During impedance monitoring, the endpoint for titration of power was a 5-to 10-Ω decrease in the measured impedance while for temperature monitoring the endpoint was to achieve a temperature of 58° to 62°C. Two protocols were used. In protocol 1 (90 patients), impedance monitoring was performed with a nonthermistor catheter and temperature monitoring was performed with a thermistor catheter. In protocol 2 (42 patients), a thermistor catheter was used in all patients. In protocol 1, the success rate (93% vs 93%; P = 1.0), ablation procedure duration (57 ± 56 vs 41 ± 41 min), fluoroscopy time (48 ± 29 vs 41 ± 23 min; P = 0.3), number of applications (6.2 ± 4.7 vs 5.7 ± 4.6; P = 0.8), and the number of applications associated with coagulum formation (0.1 ± 0.3 vs 0.3 ± 0.6; P = 0.1) were similar in the two groups. In protocol 2, as in protocol 1, there were no differences in the success rate (91% vs 95%; P = 1.0), ablation procedure duration (49 ± 37 vs 62 ± 55 min; P = 0.4), fluoroscopy time (46 ± 24 vs 49 ± 36 min; P = 0.8), number of applications (6.8 ± 7.0 vs 7.8 ± 12.1; P = 0.7), or number of applications associated witb coagulum formation (0.3 ± 0.6 vs 0.2 ± 0.7; P = 0.6) between the impedance and temperature monitoring groups. Conclusion: Temperature and impedance monitoring are equally effective in optimizing the results of accessory pathway ablation.
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  • 10
    Electronic Resource
    Electronic Resource
    350 Main Street , Malden , MA 02148 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Pacing for Postoperative AF. Introduction: Recent studies have reported the use of temporary epicardial atrial pacing as prophylaxis for postoperative atrial fibrillation (AF). The aim of this study was to assess the effect of pacing therapies for prevention of postoperative AF using meta-analysis. Methods and Results: Using a computerized MEDLINE search, eight pacing prophylaxis trials with 776 patients were included in the meta-analysis. Trials compared control patients to patients randomized to right atrial, left atrial, or biatrial pacing used in conjunction with either fixed high-rate pacing or overdrive pacing. Overdrive biatrial pacing (OR 2.6, CI 1.4–4.8), overdrive right atrial pacing (OR 1.8, CI 1.1–2.7), and fixed high-rate biatrial pacing (OR 2.5, CI 1.3–5.1) demonstrated a significant antiarrhythmic effect for prevention of AF after open heart surgery. Furthermore, studies investigating overdrive left atrial pacing and fixed high-rate right atrial pacing have been underpowered to assess efficacy. Conclusion: Biatrial overdrive and fixed highz-rate pacing and right atrial fixed high-rate pacing reduced the risk of new-onset AF after open heart surgery, and the relative risk reduction is approximately 2.5-fold. These results imply that various pacing algorithms are useful as a nonpharmacologic method to prevent postoperative AF. (J Cardiovasc Electrophysiol, Vol. 14, pp. 127-132, February 2003)
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