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  • 11
    ISSN: 1572-8595
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 12
    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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  • 13
    ISSN: 1572-8595
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Just as a stable defibrillation threshold is re-quired for implantable defibrillators to maintain efficacyand a margin of safety for the conversion of life-threateningventricular arrhythmias, a stable pacing threshold is alsorequired to provide bradycardia support and pacing to ter-minate ventricular tachycardias. This article reports thetemporal course of pacing thresholds in patients treatedwith a tripolar, tined endocardial defibrillator lead capableof bipolar sensing and pacing, and defibrillation. Seventeenpatients who underwent implantation of an implantabledefibrillator system using an integrated bipolar pac-ing/sensing system were prospectively studied over 18months. There were 16 males and one female, with a meanage of 69 ± 5 years (range 61–75 years). At implantation,predischarge, and every 2 months thereafter, the pacingpulse-width threshold was tested at both 2.5 and 5.0 Vstimulus amplitudes. After a mean follow-up of 363 ± 173days (range 34–597 days), the pacing threshold increasedfrom 0.08 ± 0.08 ms to 0.5 ± 0.3 ms at the 2.5 V amplitude(p≤0.01, CI-0.57 to -0.27) and from 0.04 ± 0.02 ms to 0.256 0.14 ms at the 5.0 V amplitude (p≤0.01, CI -0.28 to-0.14). Eight of the 17 patients (47%) received spontaneousimplantable defibrillator shocks for clinically detected ar-rhythmias, and the total number of joules delivered via theleads did not correlate with the pacing threshold changes.We conclude that the pacing threshold for the nonthoraco-tomy implantable defibrillator lead system studied is notstable and increases with time. This finding has implica-tions for defibrillator battery life in patients who use im-plantable defibrillators for bradycardia pacing.
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  • 14
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    ISSN: 1572-8595
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 15
    ISSN: 1572-8595
    Keywords: arrhythmia ; fibrillation ; and defibrillation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Background: The upper limit of vulnerability (ULV) is the stimulus strength above which ventricular fibrillation cannot be induced, even when the stimulus occurs during the vulnerable period of the cardiac cycle. Determination of ULV using T-wave shocks during ventricular pacing has been shown to closely correlate with the defibrillation threshold (DFT) at ICD implantation. However, there are no data correlating ULV determined in sinus rhythm at ICD implantation, with DFT determined at implantation or during long-term follow-up. This is of clinical importance since ULV may be used to estimate DFT during ICD implantation, both during ventricular pacing or sinus rhythm. Methods and Results: Twenty-one patients receiving a transvenous ICD system were studied prospectively. There were 16 males and 5 females, mean age 68 ± 15 years, with mean ejection fraction 37.4 ± 17.4%. All had structural heart disease. The ULV was defined as the lowest energy that did not induce ventricular fibrillation with shocks at 0, 20 and 40ms before the peak of the T-wave, using a step-down protocol. The initial energy tested was 15J and the lowest energy 2J. DFT was determined following a similar step-down protocol. The DFT was defined as the lowest energy that successfully defibrillated the ventricles. The linear correlation coefficient between ULV and DFT was r = 0.73 (p 〈 0.001). At implant, mean ULV was 9.2 ± 5J, not statistically different from mean DFT 9.4 ± 4J. ULV plus 5J successfully defibrillated 19 of 21 patients. During long-term follow-up of 10.1 ± 1.8 months in eight patients, DFT was 8.8 ± 5.8J, not significantly different than the DFT of 7.5 ± 4.1J or ULV of 8.0 ± 5.3 at implant. Conclusion: 1) When determined during normal sinus rhythm the ULV significantly correlates with DFT. 2) ULV testing might be used in lieu of standard DFT testing to confirm adequate lead placement thus minimizing or eliminating VF inductions, particularly in hemodynamically unstable patients. 3) Since ULV + 5J has a high probability of successful defibrillation in most patients, programming ICD first shock energy for VF at ULV + 5J may result in lower first shock energies compared to the standard methods of programming first shock energy at twice DFT. Condensed Abstract. The purpose of this study was to determine if the upper limit of vulnerability (ULV) determined during normal sinus rhythm correlates with the defibrillation threshold (DFT), as has been previously shown when determined during ventricular pacing. The linear correlation coefficient between the ULV and DFT was r = 0.73 (p 〈 0.001). Mean ULV at implant was 9.2 ± 5J, not statistically different from mean DFT of 0.4 ± 4J. During long-term follow-up of 10.1 ± 1.8 months in 8 patients, DFT was 8.75 ± 8J, not significantly different than the DFT of 7.5 ± 4.1J or ULV of 8.0 ± 5.3 at implant. Shocks energies of ULV + 5J successfully defibrillated 19 of 21 patients at implant and 8 of 8 at follow-up. This study indicates that the ULV determined in normal sinus rhythm closely correlates with the DFT, and that ULV + 5J defibrillated most patients. ULV testing could be used to predict DFT and reduce or eliminate the need for DFT testing and VF induction. Programming ICD first shock energy for VF to ULV + 5J will result in lower energy than that used with standard DFT testing.
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  • 16
    ISSN: 1572-8595
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 17
    ISSN: 1572-8595
    Keywords: pediatrics ; ablation ; tachycardia ; mitral insufficiency ; transseptal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The incidence of significant valvar insufficiency at late (〉6 month) follow-up was retrospectively evaluated in 27 young patients (age 4.0–18.0 years) undergoing 29 ablation procedures via the retrograde aortic approach for left-sided accessory connections in whom pre-ablation and post-ablation echocardiograms were available for review. Valvar insufficiency was graded using color flow techniques as absent, trivial, mild, moderate, or severe by blinded reviewers. Ablation was acutely successful via the retrograde approach in 25 of 29 procedures among these 27 patients. Successful ablation was ultimately achieved in all 27 patients. At baseline, 7 patients had evidence of trivial or mild mitral insufficiency, and no patient had aortic insufficiency. Three patients had evidence of impaired left ventricular systolic performance in the presence of manifest pre-excitation. At follow-up, pre-existing mitral insufficiency resolved in 5/7 patients, and persisted in 2 patients. New mitral insufficiency was evident in 3 patients, and new aortic insufficiency was transiently evident in 1 patient following ablation (all trivial). Institutional experience (mean rank 10 cases vs. 33 cases, p 〈 .0005), and lower patient weight (29.7 vs. 56.3 kilograms, p = .01) were the only factors associated with the development of new valvar insufficiency. Valvar insufficiency could not be detected by careful auscultation in any patient and was deemed clinically insignificant in all patients. We conclude that ablation of left-sided accessory connections can be performed via the retrograde aortic approach without creating clinically significant valvar insufficiency.
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  • 18
    ISSN: 1572-8595
    Keywords: atrial pacing ; AV pacing ; AV delay ; coronary blood flow velocity ; left anterior descending artery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract This study examined the effects of different atrioventricular (AV) intervals, during AV sequential pacing, on hemodynamics and coronary blood flow in individuals with normal hearts. Left anterior descending artery blood flow velocity was measured, using intracoronary Doppler, in 17 normal individuals. Five pacing tests were applied in random order for 5 min, at 15 beats/min above the sinus rate. Four tests using AV sequential pacing with AV intervals of 175, 150, 100, and 50 ms, and one using atrial pacing were applied. Mean flow velocity was 21 ± 9 cm/s, 20 ± 9 cm/s, 17 ± 7 cm/s, 17 ± 7 cm/s, and 22±10 cm/s, respectively (F = 8.87, p = .00001). The hemodynamic effects of these 5 pacing tests were assessed in 8 different normal subjects. Isovolumic relaxation time constant and left ventricular systolic pressure decreased, whereas right atrial pressure increased during AV sequential pacing with short AV intervals. Thus, during short-term AV sequential pacing at rest, coronary blood flow in a normal left anterior descending artery decreases with short AV intervals.
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  • 19
    ISSN: 1572-8595
    Keywords: Pacemaker lead ; lead extraction ; venous thrombosis ; balloon venoplasty ; superior vena cava syndrome
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Patients (pts) may present for lead extraction with symptomatic or asymptomatic subclavian vein or superior vena cava thrombosis. Replacement of permanent pacemaker leads (PPLs) in these pts may be difficult and may require accessing a new site. We examined the utility of replacing PPLs through completely occluded vessels using extraction sheaths as conduits through the total occlusion. Over six years, a total of 210 atrial and/or ventricular PPLs were extracted from 137 pts. Two pts presented with angiographically documented thrombotic occlusion of the subclavian vein. One additional pt, who had presented with a superior vena cava (SVC) syndrome, had a totally occluded innominate vein and SVC occlusion. Balloon venoplasty was used as an adjunct to dilate the SVC. In all pts, after PPLs were removed via a subclavian extraction sheath through the occluded vessel, the retained sheath was used to place a guide wire, then a peel away dilating sheath, to insert new PPLs, in each case on the side of total venous occlusion. Seven PPLs and two lead fragments were extracted, and five new PPLs replaced, ipsilateral to the venous occlusion. These data show that extraction of PPLs through thrombosed veins may be performed successfully and may not require replacing the leads through a new site. This technique spares the pt the need to access the opposite subclavian vein, and it avoids an excessive number of PPLs in the subclavian vein and SVC. The procedure illustrates an efficient means to reintroduce new PPLs with the potential to reduce associated morbidity, since repeat puncture of the subclavian vein is not required. Safety of the procedure as a whole must be considered with regard to the known risks of lead extraction, some complications of which may be substantial using current techniques.
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  • 20
    ISSN: 1572-8595
    Keywords: Wolff-Parkinson-White syndrome ; radiofrequency ablation ; tachycardia recurrence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The histological findings from a patient with Wolff-Parkinson-White syndrome (right superior paraseptal accessory pathway) who underwent successful radiofrequency ablation and had recurrence of tachycardia one month later in the absence of overt pre-excitation are reported. Histology revealed three small, oval to circular shaped, whitish, smooth areas on the right endocardial surface, the one being situated at the atrial free wall, and the other two being at the ventricular aspect. A very small hole was present in the interventricular component of the membranus septum. The accessory pathway band passed to either side of the small hole albeit disrupted by fibrous tissue in places. These findings indicate that multiple applications may cause penetration of the myocardium, and to achieve success, complete disruption of the pathway at some point along its course is required. Recurrence of retrograde accessory pathway conduction can be explained with the impedance mismatch hypothesis.
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