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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Shock Polarity on Biphasic Defibrillation Thresholds Using an Active Pectoral Lead System (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 9 (1998), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Polarity and Biphasic Defibrillation Thresholds. Introduction: The downsizing of implantable defibrillator pulse generators has made pectoral placement routine. A further reduction of defibrillation thresholds (DFTs) may simplify implantation defibrillation testing and allow for smaller, lower output pulse generators while maintaining an adequate defibrillation safety margin. One factor that may affect defibrillation efficacy is shock polarity. Methods and Results: Sixty consecutive patients undergoing dual-coil, active left pectoral defibrillator implantation were evaluated. Paired, biphasic DFTs were measured in normal (RV apex = cathode) and reverse (RV apex = anode) polarity with order of testing randomized. Reverse polarity conferred a 15% reduction of mean DFTs (8.5 ± 5.0 J normal. 7.2 ± 4.6 J reverse polarity. P = 0.02). The effect of polarity appeared most pronounced among the patients with a high DFT (〉 15 J) resulting in a 31% reduction with reverse polarity (16.7 ± 2.5 J normal, 11.5 ± 5.9 J reverse, P = 0.03). Conclusion: Reversing shock polarity results in significantly lower biphasic DFTs with an active pectoral lead system, particularly in the subgroup of patients with a high normal polarity threshold. Reversing polarity in these patients may simplify acute defibrillation testing and allow for lower output devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1998.tb00923.x
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of QRS Duration on the Prognostic Value of T Wave Alternans (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: T Wave Alternans and QRS Duration. Introduction: T wave alternans (TWA) is a promising new noninvasive marker of arrhythmia vulnerability that quantifies beat-to-beat changes in ventricular repolarization. Secondary repolarization abnormalities are common in subjects with wide QRS complexes. However, the relationship between TWA and QRS prolongation has not been evaluated. The goal of this study was to determine if QRS prolongation influences the prevalence or prognostic value of TWA. Methods and Results: The study consisted of 108 consecutive patients with coronary artery disease and left ventricular ejection fraction ≤40% who were referred for electrophysiologic studies. Patients underwent TWA testing using bicycle ergometry in the absence of beta-blockers or antiarrhythmic drugs. The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The prognostic value of TWA was assessed in the entire cohort and in two subgroups: QRS 〈 120 msec (normal, n = 62) and QRS ≥ 120 msec (prolonged, n = 46). TWA (hazard ratio 2.2, P = 0.03) and QRS prolongation (hazard ratio 2.2, P = 0.01) were both significant and independent predictors of arrhythmic events. QRS prolongation had no effect on the prevalence of positive TWA tests (QRS 〈 120 msec: 48%, QRS ≥ 120 msec: 50%, P = NS). TWA was a highly significant predictor of events in patients with a normal QRS (hazard ratio 5.8, P = 0.02). In contrast, TWA was not useful for risk stratification in subjects with QRS prolongation (hazard ratio 1.1, P = 0.8). Conclusion: TWA is useful only for risk stratification in the absence of QRS prolongation. The presence of QRS prolongation and left ventricular ejection fraction ≤40% may be sufficient evidence of an adverse prognosis that additional risk stratification is not useful or necessary.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.00770.x
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  • 3
    Electronic Resource
    Electronic Resource
    Advanced Rhythm Discrimination for Implantable Cardioverter Defibrillators Using Electrogram Vector Timing and Correlation (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Electrogram Vector Timing and Correlation. Introduction: Discrimination of ventricular and supraventricular arrhythmias remains one of the major challenges for appropriate implantable defibrillator (ICD) therapy delivery. The electrogram vector timing and correlation (VTC) algorithm was developed for such rhythm discrimination. The VTC algorithm differentiates normally conducted supraventricular beats from abnormally conducted ventricular beats by comparing the timing and correlation of rate and shock channel electrograms. Methods and Results: Rate and shock channel electrograms of sinus rhythm and induced arrhythmias were collected from 93 patients during ICD placement. The algorithm was developed using data from 50 patients and prospectively tested in a software model with the remaining 43 patients. A sinus rhythm reference was formed by averaging complexes of the shock channel signal aligned by the peak amplitude of the rate channel. Eight features measuring the amplitude and timing of shock channel signal characteristics were extracted from the reference for comparison. When a high-rate rhythm was detected, the VTC algorithm computed the correlation of the arrhythmia complex features with the reference. Rhythms with a sufficient number of uncorrelated beats were classified as ventricular tachycardia (VT). In a dual-chamber implementation, the VTC algorithm is integrated with ventricular and atrial rate comparison (V 〉 A) and stability above an atrial fibrillation rate threshold. The test set consisted of 117 arrhythmias. Dual-chamber sensitivity was 100% (81/81 VT) and specificity was 97% (35/36 supraventricular tachycardia). Single-chamber analysis demonstrated 99% sensitivity and 97% specificity. Conclusion: The VTC algorithm demonstrated high sensitivity and specificity in discriminating between ventricular and supraventricular arrhythmias.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.01092.x
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  • 4
    Electronic Resource
    Electronic Resource
    Enhanced Detection of Arrhythmia Vulnerability Using T Wave Alternans, Left Ventricular Ejection Fraction, and Programmed Ventricular Stimulation: (2004)
    350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 15 (2004), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Introduction: In previous studies, the prognostic value of T wave alternans (TWA) was similar to that of programmed ventricular stimulation (PVS). However, presently it is unclear if TWA and PVS identify the same patients or provide complementary risk stratification information. In addition, the effects of left ventricular ejection fraction (LVEF) on the prognostic value of TWA are unknown. The aim of this study was to determine if combined assessment of TWA, LVEF, and PVS improves arrhythmia risk stratification. Methods and Results: This was a prospective study of 144 patients with coronary artery disease and LVEF ≤40% who were referred for PVS for standard clinical indications. The endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator (ICD) therapy. TWA (hazard ratio 2.2, P = 0.03) and PVS (hazard ratio 1.9, P = 0.05) both were significant predictors of endpoint events, and TWA was the only independent predictor. LVEF markedly influenced the prognostic value of TWA, which was a potent predictor of events in subjects with LVEF between 30% and 40% (event rates: TWA+ 36%, TWA- 0%, P = 0.001) but did not predict events in subjects with LVEF 〈30% (hazard ratio 1.1, P 〉 0.5). PVS successfully identified additional low-risk patients within the cohort with negative or indeterminate TWA results (hazard ratio 4.7, P = 0.015) but did not provide incremental prognostic information for TWA+ patients (hazard ratio 0.9, P 〉 0.5). Conclusion: The combined use of TWA, LVEF, and PVS is a promising new approach to arrhythmia risk stratification that permits identification of high-risk and very-low-risk patients. (J Cardiovasc Electrophysiol, Vol. 15, pp. 170-176, February 2004)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2004.03428.x
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  • 5
    Electronic Resource
    Electronic Resource
    The Effect of Procainamide on T Wave Alternans (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 10 (1999), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Procainamide and T-Wave Alternans. Introduction: The measurement of microvolt level T wave alternans (TWA) is a technique for detecting arrhythmia vulnerability. Previous studies demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of antiarrhythmic drugs on TWA are unknown. Methods and Results: This was a prospective evaluation of intravenous procainamide on TWA in 24 subjects with inducible sustained ventricular tachycardia (VT). Measurements of TWA were performed at baseline in the drug-free state and after procainamide loading (1,204 ± 278 mg). Recordings were made in normal sinus rhythm, and during atrial pacing at 100 heats/min and 120 heats/min. The magnitude of TWA in the vector magnitude lead was decreased by procainamide at all heart rates: 0.6 ± 0.8 to 0.3 ± 0.4 μV in sinus rhythm, 2.0 ± 1.6 to 0.7 ± 0.7 μV at 100 beats/min, and 3.0 ± 2.0 to 1.7 ± 1.8 μV at 120 beats/min (P 〈 0.001 by analysis of variance). The sensitivity of TWA for the induction of VT at baseline was 5% in sinus, 60% at 100 beats/min, and 87% at 120 beats/min, while it decreased with procainamide to 5%, 19%, and 60%, respectively. Decreases in TWA in response to procainamide were independent of the antiarrhythmic effects on VT inducibility. Conclusions: These results indicate that the magnitude of TWA decreases with acute procainamide loading and this effect decreases the sensitivity of TWA for the induction of sustained VT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1999.tb00241.x
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  • 6
    Electronic Resource
    Electronic Resource
    Postentrainment Activation Sequence: Diagnostic of the Supraventricular Tachycardia Mechanism? (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.00410.x
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  • 7
    Electronic Resource
    Electronic Resource
    Lack of Benefit of an Active Pectoral Pulse Generator on Atrial Defibrillation Thresholds (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Effect of an Active Can on Atrial DFTs. Introduction: Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator leads, which has led to the development of combined atrial and ventricular devices. For ventricular defibrillation, use of an active pectoral electrode (active can) in the shocking pathway markedly reduces defibrillation thresholds (DFTs). However, the effect of an active pectoral can on atrial defibrillation is unknown. Methods and Results: This study was a prospective, randomized, paired comparison of two shock configurations on atrial DFTs in 33 patients. The lead system evaluated was a dual-coil transvenous defibrillation lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and proximal atrial coil (lead) or between the right ventricular coil and an active can in common with the atrial coil (active can). Delivered energy at DFT was 4.2 ± 4.1 J in the lead configuration and 5.0 ± 3.7 J in the active can configuration (P = NS). Peak current was 32% higher with an active can (P 〈 0.01), whereas shock impedance was 18% lower (P 〈 0.001). Moreover, a low threshold (〈 3 J) was observed in 61% of subjects in the lead configuration but in only 36% in the active can configuration (P 〈 0.05). There were no clinical predictors of the atrial DFT. Conclusion: These results indicate that low atrial DFTs can be achieved using a transvenous ventricular defibrillation lead. Because no benefit was observed with the use of an active pectoral electrode for atrial defibrillation, programmable shock vectors may be useful for dual-chamber implantable cardioverter defibrillators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.00332.x
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  • 8
    Electronic Resource
    Electronic Resource
    Optimization of Atrial Defibrillation with a Dual-Coil, Active Pectoral Lead System (2004)
    350 Main Street , Malden , MA 02148-5018 , USA , and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 15 (2004), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Introduction: Atrial defibrillation can be achieved with standard implantable cardioverter defibrillator (ICD) leads, but the optimal shocking configuration is unknown. The objective of this prospective study was to compare atrial defibrillation thresholds (DFTs) with three shocking configurations that are available with standard ICD leads. Methods and Results: This study was a prospective, randomized, paired comparison of shocking configurations on atrial DFTs in 58 patients. The lead system evaluated was a transvenous defibrillation lead with coils in the superior vena cava (SVC) and right ventricular apex (RV) and a left pectoral pulse generator emulator (Can). In the first 33 patients, atrial DFT was measured with the ventricular triad (RV → SVC + Can) and unipolar (RV → Can) shocking pathways. In the next 25 patients, atrial DFT was measured with the ventricular triad and the proximal triad (SVC → RV + Can) configurations. Delivered energy at DFT was significantly lower with the ventricular triad compared to the unipolar configuration (4.7 ± 3.7 J vs 10.1 ± 9.5 J, P 〈 0.001). Peak voltage and shock impedance also were significantly reduced (P 〈 0.001). There was no significant difference in DFT energy when the ventricular triad and proximal triad shocking configurations were compared (3.6 ± 3.0 J vs 3.4 ± 2.9 J for ventricular and proximal triad, respectively, P = NS). Although shock impedance was reduced by 13% with the proximal triad (P 〈 0.001), this effect was offset by an increased current requirement (10%). Conclusion: The ventricular triad is equivalent or superior to other possible shocking pathways for atrial defibrillation afforded by a dual-coil, active pectoral lead system. Because the ventricular triad is also the most efficacious shocking pathway for ventricular defibrillation, this pathway should be preferred for combined atrial and ventricular defibrillators. (J Cardiovasc Electrophysiol, Vol. 15, pp. 790-794, July 2004)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2004.03684.x
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  • 9
    Electronic Resource
    Electronic Resource
    T Wave Alternans: Predictor of Arrhythmic Events? Fact or Fiction (2002)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2002.00513.x
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of Heart Rate on T Wave Alternans (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 9 (1998), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Heart Rate and T Wave Alternans. Introduction: T wave alternans (TWA) is a promising technique for detecting arrhythmia vulnerability. Previous studies in animals demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of heart rate on TWA in humans and the clinical relevance of this effect remain controversial. Methods and Results: This was a prospective evaluation of pacing rate and monitoring lead configuration on TWA in subjects undergoing electrophysiologic study. Measurements of TWA were performed on 45 patients in the absence of antiarrhythmic drugs. Recordings were made in normal sinus rhythm and during atrial pacing at 100 and 120 beats/min. Sustained monomorphic ventricular tachycardia (VT) was induced in 29 patients with programmed stimulation. TWA in the vector magnitude lead increased with heart rate, independent of VT inducibility (0.4 ± 0.7 μ V, 1.6 ± 1.9 μ V, and 2.4 ± 2.1 μ V in sinus rhythm and at 100 and at 120 beats/min, respectively; P 〈 0.001). In addition, the diagnostic performance of TWA for inducible VT was dependent on heart rate (sensitivity 4%, 42%, and 65%, and specificity 100%, 93%, and 63% at 77, 100, and 120 beats/min, respectively). By analyzing orthogonal leads rather than the vector magnitude lead, the sensitivity is increased from 42% to 59% at 100 beats/min, but the specificity is reduced from 93% to 72%. Conclusion: These results indicate that TWA in humans is strongly dependent on heart rate with regard to both magnitude and diagnostic performance. The optimal heart rate for the measurement of TWA is between 100 and 120 beats/min and multiple leads should be monitored.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1998.tb00957.x
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