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  • 1
    Electronic Resource
    Electronic Resource
    Influence of Body Position on Defibrillation Thresholds of Nonthoracotomy Implantable Defibrillators: (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: DFT of Nonthoracotomy Defibrillators. Introduction: Defibrillation thresholds (DFTs) usually are determined with the patient in the supine position. However, patients may be in the upright position when a shock is delivered during follow-up, which may explain some first shock failures observed clinically. This study investigated whether body posture affects defibrillation energy requirements of nonthoracotomy implantable cardioverter defibrillators with biphasic shocks. Methods and Results: Using a step up-down protocol, DFTs were compared intraindividually in 52 patients (“active-can” systems in 41 patients, two-lead systems in II patients) for the supine and upright positions as achieved by a tilt table. The mean DFT was 7.3 ± 4.2 J in the supine versus 9.2 ± 4.8 J in the upright position (P = 0.002). Repeated comparison in reversed order 3 months after implantation in 22 patients revealed thresholds of 6.2 ± 2.5 J (supine) versus 8.4 ± 3.7 J (upright; P 〈 0.03) 1 week and 4.4 ± 2.4 J (supine) versus 6.2 ± 4.1 J (upright; P 〈 0.04) 3 months after implantation. DFTs decreased significantly for both body positions from 1 week to 3 months after implantation (P 〈 0.04). Conclusion:(I) DFTs for biphasic shocks delivered by nonthoracotomy defibrillators are higher in the upright compared to the supine body position. (2) Differences remain significant 3 months after implantation. For both body positions, DFT decreases significantly from 1 week to 3 months after implantation. These findings have important implications for programming first shock energy to lower than maximal values or for development of devices with lower maximal stored energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1998.tb00956.x
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  • 2
    Electronic Resource
    Electronic Resource
    Polarity Reversal Improves Defibrillation Efficacy in Patients Undergoing Transvenous Cardioverter Defibrillator Implantation with Biphasic Sbocks (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 20 (1997), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The purpose of this study was to determine the influence of polarity reversal on DFT in patients undergoing implantation of nonthoracotomy defibrillators with biphasic shocks. Previous studies have shown higher defibrillation efficacy with using the distal electrode as anode in implantation of nonthoracotomy defibrillators and monophasic shocks. However, it is as yet unclear whether biphasic shock defibrillation will also be influenced by polarity reversal. Using a transvenous lead system with a proximal electrode in the superior caval vein and a distal electrode in the RV apex, 27 patients undergoing defibrillator implantation were randomized to DFT testing with “initial” (distal electrode = cathode) or “reversed” polarity (distal electrode = anode). Defibrillation energy was reduced stepwise until defibrillation failure occurred. At this point, polarity was switched and testing continued until the lowest energy requirement was determined for both polarities. With reversed polarity, DFT was 11.1 ± 5.7 J versus 13.3 ± 5.8 J with initial polarity (P = 0.033). This means a 17% reduction of the DFT. In 10 patients, the threshold was lower with reversed, whereas in 3 patients it was lower with initial polarity. In conclusion, changing electrode polarity in transvenous implantable defibrillators with biphasic shocks may significantly influence defibrillation energy requirements. Therefore, polarity reversal should always be attempted before considering patch implantation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1997.tb06174.x
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  • 3
    Electronic Resource
    Electronic Resource
    Dilatation of the Pulmonary Veins in Atrial Fibrillation: (2003)
    350 Main Street , Malden , MA 02148-5018 , U.S.A . : Blackwell Publishing
    Pacing and clinical electrophysiology 26 (2003), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Ectopic beats originating from sleeves of atrial tissue within the pulmonary veins (PVs) can induce and sustain paroxysmal atrial fibrillation (AF). Left atrial stretch and dilatation favors the development of atrial ectopy and AF. Similarly, PV dilatation, if present, might trigger PV ectopy in patients with AF. This study was designed to evaluate whether PV dilatation is present in patients with nonfocal AF and whether the PV diameter correlates to the left atrial diameter (LAD). The diameters of the right superior (RSPV) and left superior PV (LSPV) were measured at the ostium and at a depth of 1 cm in 170 patients (AF, n = 75 ; sinus rhythm [SR], n = 95) using transesophageal echocardiography. The LAD was determined by transthoracic echocardiography. The diameters of the PVs were significantly larger in patients with AF than in patients with SR (LSPVostium: AF 13.6 ± 3.5 mm vs SR 10.6 ± 2.7 mm, P 〈 0.001 ; LSVP1cm: AF 12.5 ± 2.9 mm vs SR 10.2 ± 2.5 mm, P 〈 0.001 ; RSPVostium, AF 13.9 ± 3.5 mm vs SR 11.7 ± 2.9 mm, P 〈 0.001 ; RSVP1cm: AF 12.8 ± 2.8 mm vs SR 10.6 ± 2.6 mm, P 〈 0.05). Similarly, LAD was larger in patients with AF (44.7 ± 7.7 mm) as compared to patients with SR (38.8 ± 6.8 mm, P 〈 0.001). Neither for the SR nor the AF group did the PV size correlate to the LAD. AF is associated with a significant enlargement of the RSPV, LSPV, and LAD. There is no correlation between LAD and PV diameters. This raises the question whether PV dilatation in patients with AF is a cause or a consequence of AF and whether it may contribute to the development and perpetuation of AF. (PACE 2003; 26:1371–1378)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9592.2003.t01-1-00196.x
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  • 4
    Electronic Resource
    Electronic Resource
    Temporary Disturbances of the QT Interval Precede the Onset of Ventricular Tachyarrhythmias in Patients with Structural Heart Diseases (2002)
    Oxford, UK : Blackwell Futura Publishing, Inc.
    Pacing and clinical electrophysiology 25 (2002), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: DIEM, B.H. et al.: Temporary Disturbances of the QT Interval Precede the Onset of Ventricular Tach-yarrhythmias in Patients with Structural Heart Diseases. An increase in sinus rate prior to ventricular tachyarrhythmias has been demonstrated in previous studies. There is no clear data available concerning changes in ventricular de- and repolarization prior to ventricular tachyarrhythmias, especially in patients with structural heart disease. Therefore, the aim of this study was to analyze the QT and QTc interval (Bazett's formula immediately before the onset of ventricular tachyarrhythmias in stored electrograms of patients with ICDs. The study analyzed 228 spontaneous ventricular tachyarrhythmia episodes in 52 patients (mean age 64 ± 10 years, 49 men, 3 women) and compared them with 146 electrograms of baseline rhythm recorded during regular ICD follow-up. Mean ventricular cycle length (CL), QT interval, and QTc were measured before the onset of ventricular tachyarrhythmia and during baseline rhythm. Prior to ventricular tachyarrhythmias onset, CL was significantly shorter than during baseline rhythm (714 ± 139 vs 828 ± 149 ms, P 〈 0.0001). By contrast, the QT interval (430 ± 67 ms) and QTc interval (518 ± 67 ms) were significantly prolonged before the onset of ventricular tachyarrhythmias as compared to baseline rhythm (QT 406 ± 67 ms, QTc 450 ± 61 ms; P 〈 0.0001). CL, QT, and QTc changes were independent of concomitant treatment with antiarrhythmic drugs. Ventricular tachyarrhythmias are preceded by a significant prolongation of the QT and QTc intervals. This phenomenon may represent a greater than normal disparity of repolarization recovery times possibly facilitating the development of ventricular tachyarrhythmias.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9592.2002.01413.x
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of Polarity Reversal on de-fibrillation Success with Biphasic Shocks and a Transvenous/Subcutaneous Defibrillator System in a Porcine Animal Model (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 21 (1998), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Clinical studies show that polarity reversal affects de-fibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for de-fibrillation. We investigated in a porcine animal model whether polarity reversal influences de-fibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the de-fibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with “initial polarity” (IP, distal electrode = cathode) and “reversed polarity” (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative de-fibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P 〈 0.05) and insignificantly higher for 10.8 ms (52% vs 42%, P = n.s.). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 44 ± 8.4 vs RP: 37 ± 9.3 with 14.3 ms, P 〈 0.001 and IP: 44 ± 6.2 vs RP: 41 ± 7.6 Ω with 10.8 ms, P 〈 0.001) and the leading edge of pulse 2 (IP: 37 ± 5 vs RP: 35 ± 4.2 Ω with 14.3 ms, P = 0.05 and IP: 37.5 ± 3.7 vs RP: 36 ± 5 Ω with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal de-fibrillation using the distal coil as anode results in higher de-fibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1998.tb00215.x
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  • 6
    Electronic Resource
    Electronic Resource
    Postfibrillatory Enhancement of Left Atrial Contractility After Short Paroxysms of Atrial Fibrillation (2004)
    350 Main Street , Malden , MA 02148-5018 , USA and 9600 Garsington Road , Oxford OX4 2DQ , UK . : Blackwell Futura Publishing, Inc.
    Pacing and clinical electrophysiology 27 (2004), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Implantable cardioverter defibrillators and pacemakers detect an increasing number of silent episodes of AF. In a porcine model, the study evaluated the contractility of the left atrial appendage (LAA) during AF paroxysms as they may occur in patients. Peak outflow velocity of the LA and mean outflow velocity of the LAA (LAA-Voutmean) (n = 17) were measured before, during, and after induction of self-terminating AF. LAA-Voutmean was also measured during incremental pacing from different atrial sites using epicardial Doppler probes (n = 6) and during continuous recordings (n = 5) of 40 minutes of pacing maintained AF. Compared to baseline sinus rhythm, LAA-Voutmean increased during short AF episodes (41 ± 3 vs 35 ± 2 cm/s, P 〈 0.05). After termination of the AF episodes, LAA-Voutmean further increased (69 ± 15 cm/s, P 〈 0.001 vs baseline). This “postfibrillatory enhancement” maintained after repeated induction of short AF paroxysms. During prolonged AF episodes lasting 40 minutes, an initial hypercontractility (44 ± 2 vs 38 ± cm/s, P 〈 0.01) was followed by a hypocontractility after 20 minutes (29 ± 12 P 〈 0.05 vs SR) and a postfibrillatory enhancement after cessation of AF (56 ± 12 vs 27 ± 9 cm/s at 40 minutes AF, P 〈 0.001). L-type Ca channel blockade abolished the initial hypercontractility during AF and the postfibrillatory enhancement. Repetitive AF paroxysms up to 2 minutes did not decrease left atrial contractility. During maintained AF up to 40 minutes an initial hypercontractility and a consecutive hypocontractility, which is overcompensated by a postfibrillatory enhancement of atrial inotropy after cessation of AF, are present. The observed phenomenon seems to be related to an increased Ca2+ influx through the L-type Ca2+ channel. (PACE 2004; 27:579–585)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.2004.00490.x
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  • 7
    Electronic Resource
    Electronic Resource
    Optimized Pulse Durations Minimize the Effect of Polarity Reversal on Defibrillation Efficacy with Biphasic Shocks (1999)
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 22 (1999), S. 0 
    Details
    ISSN: 1540-8159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: There are conflicting results on the effect of polarity change on the defibrillation efficacy of biphasic shocks possibly caused by different shock durations. The goal of the present study was to investigate the influence of polarity reversal on defibrillation efficacy for different biphasic shock durations in a porcine animal model. In eight anesthesized pigs using a transvenous/submuscular lead system DFTs for 4 phase 1 durations were determined: 8.1 ms, 6 ms, 3.8 ms and 1.7 ms. The phase 1/phase 2 ratio was constant at 60%/40%. For cathodal shocks, the defibrillation coil in the right ventricular apex was the cathode during phase 1 and for anodal shocks it was the anode. For both polarities, the strength-duration curve revealed a DFT minimum at 3.8 ms (cathodal shocks: 21.3 ± 6.4 J, P 〈 0.001; anodal shocks: 21.9 ± 8 J, P = 0.05). For anodal shocks and phase 1 durations of 1.7, 3.8, and 6 ms there was no significant difference of the stored energy at the DFT compared to cathodal shocks. In contrast, significantly lower DFTs were observed for anodal shocks with a phase 1 duration of 8.1 ms (28.8 ± 6.4 J compared to 33.1 ± 5.9 J for cathodal shocks, P = 0.006). The effect of lower defibrillation energy requirements with polarity reversal depends on the total biphasic shock duration; for the pulse duration with the lowest DFT, polarity reversal does not increase defibrillation efficacy of biphasic shocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8159.1999.tb00545.x
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  • 8
    Electronic Resource
    Electronic Resource
    Regional and total myocardial blood flow and metabolism at rest, during pacing and after nitroglycerin in patients with coronary heart disease
    Amsterdam : Elsevier
    Journal of Molecular and Cellular Cardiology 9 (1977), S. 26-27 
    Details
    ISSN: 0022-2828
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0022-2828(77)80290-3
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  • 9
    Electronic Resource
    Electronic Resource
    Transcoronary Venous Radiofrequency Catheter Ablation of Ventricular Tachycardia (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 8 (1997), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Coronary Venous Ablation of VT. Ventricular tachycardias in coronary artery disease arise mostly from endocardial sites. However, little is known about the site of origin in other diseases. We present the case of an incessant, adenosine-sensitive ventricular tachycardia arising from the lateral wall of the left ventricle in a patient with mildly reduced left ventricular function. Intracardiac mapping suggested an epicardial origin, and the tachycardia was successfully ablated from a coronary sinus branch. After ablation, left ventricular function returned to normal. Transcoronary venous radiofrequency catheter ablation is a new approach for the treatment of ventricular tachycardia. Its value in the management of other types of ventricular tachycardia has yet to he determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-8167.1997.tb00853.x
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  • 10
    Electronic Resource
    Electronic Resource
    Verapamil Prevents Stretch-Induced Shortening of Atrial Effective Refractory Period in Langendorff-Perfused Rabbit Heart (2001)
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 12 (2001), S. 0 
    Details
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Verapamil Prevents Stretch-Induced AERP Shortening. Introduction: Atrial dilation and rapid pacing reduce atrial effective refractory periods (AERPs), thereby increasing the susceptibility to sustained atrial fibrillation (AF) in Langendorff-perfused rabbit hearts. It is unclear whether similar pathophysiologic mechanisms are operative in short-term electrophysiologic changes caused by dilation and rapid pacing. Therefore, we analyzed whether both forms of short-term electrophysiologic changes are similarly affected by pharmacologic interventions acting on different potential mechanisms underlying these changes. Methods and Results: Thirty Langendorff-perfused rabbit hearts underwent a protocol with stepwise increase of intra-atrial pressure from 0 to 12 cmH2O followed by 10 minutes of rapid pacing at 4 cmH2O. The protocol was repeated after addition of glibenclamide (10 μ mol/L, n = 7), cariporide (1 μ mol/L, n = 7), or verapamil (1 μ mol/L, n = 9). In the basal state, increase of intra-atrial pressure from 0 to 12 cmH2O decreased AERPs from 85 ± 11 to 55 ± 9 msec (P 〈 0.01), rapid pacing at low intra-atrial pressure (4 cmH2O) decreased AERP to a similar extent, from 81 ± 11 to 60 ± 10 (P 〈 0.01). At higher intra-atrial pressure, decrease of AERP was more pronounced (10 cmH2O: 37 ± 2 msec) (n = 7). Addition of verapamil decreased basal AERP from 86 ± 10 msec to 68 ± 11 msec (P 〈 0.05). Short-term electrophysiologic changes due to atrial dilation were abolished; changes due to rapid pacing were reduced but still present. Glibenclamide and cariporide had no significant effect. Conclusion: Langendorff-perfused rabbit heart is a suitable model for studying short-term electrophysiologic changes due to both rapid pacing and atrial dilation. AERPs are shortened to a similar extent by both mechanisms, whereas a combination of the two leads to more pronounced AERP reduction. Calcium overload plays a crucial role in short-term electrophysiologic changes caused by atrial dilation, whereas atrial ischemia or acidosis has no significant impact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1540-8167.2001.00085.x
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