bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Body Position on Defibrillation Thresholds of Nonthoracotomy Implantable Defibrillators:
Authors: SCHAUERTE PATRICK , DIEM BJÖRN , ZIEGERT KATHRIN , FRANKE ANDREAS , HANRATH PETER , STELLBRINK CHRISTOPH 
Published: April 2007

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.
Differential Effects of Bupivacaine on Cardiac K Channels: Role of Channel Inactivation and Subunit Composition in Drug—Channel Interaction
Authors: LIPKA LESLIE J. , JIANG MIN , TSENG GEA‐NY 
Published: April 2007

Mechanisms of Bupivacaine's Actions on K Channels.Introduction: We examined the effects of a nonspecific ion channel blocker, bupivacaine, on K channels encoded by hERG, rKvl.4, rKv4.3, and hKvLQTI along with hIsK. Their native counterparts in the heart are important for the function of IKr, Ito, and IKsand, thus, play an important role in repolarization.Methods and Results: To elucidate the mechanisms and sites of bupivacaine's actions, we correlated the voltage and time dependencies of drug effects with those of channel gating. We also studied the effects of altering the C‐type (hERG) or N‐type (rKvl.4) inactivation process or the subunit composition (hKvLQT1 with or without hIsK) on bupivacaine's actions. The results suggest that, except for hKvLQT1 co‐expressed with hIsK, bupivacaine binding occurred at depolarized voltages coinciding with channel activation. With hKvLQT1 co‐expressed with hIsK, bupivacaine bound preferentially at negative voltages when channels were in the closed state, and unbound at depolarized voltages when channels opened. The C‐type inactivation of hERG enhanced, whereas the N‐type inactivation of rKv1.4 hindered, bupivacaine's effects.Conclusion: We propose that bupivacaine's actions on these K channels can be described as a nonspecific pore blockade in the inner mouth region. However, the apparent binding affinity and voltage dependence of binding can be differentially influenced by the inactivation processes occurring at two ends of the pore (C‐type inactivation at the outer end and N‐type inactivation at the inner end), or by the interaction between hIsK and hKvLQT1 subunits.
Myopotential Sensing by a Dual Chamber Implantable Cardioverter Defibrillator:
Authors: DESHMUKH PRAMOD , ANDERSON KATHY 
Published: April 2007

Myopotential Oversensing by a Dual Chamber ICD. Introduction: Inappropriate discharges and/or improper inhibition of bradycardia pacing due to oversensing of extraneous signals in implantable cardioverter defibrillators (ICDs) have been described. With one exception, no previous report involving an intact lead system bas cited myopotential oversensing as the cause. Methods and Results: Two case reports of myopotential oversensing by a dual chamber ICD system are reported. In the first patient suffering from chronic pulmonary obstructive disease, intermittent myopotential seasing during labored respiration resulted in episodic inhibition of bradycardia pacing. In the second patient, oversensing of sustained myopotentials generated during strenuous isometric activity resulted in an inappropriate ICD discharge. For both, the ICD system consisted of a CPI model 1810 Ventak AV used in conjunction with a model 0125 Endotak lead, incorporating integrated bipolar sensing. Conclusion: Although modern ICDs have proven to be highly effective in detecting and terminating malignant tachyarrhythmias, the opportunity for improving their detection specificity remains.
Ischemia‐Induced Changes of the Signal‐Averaged Electrocardiogram:
Authors: STEINBIGLER PETER , HABERL RALPH , STEINBECK GERHARD 
Published: April 2007

Late Potential Changes with Ischemia. Introduction: The influence of myocardial ischemia on the detection of an arrhythmogenic substrate with the signal‐averaged ECG is unclear. Methods and Results: In 80 patients with single vessel coronary artery disease and a critical stenosis of the left anterior descending vessel selected after coronary angiography in whom percutaneous transluminal coronary angioplasty (PTCA) was planned, we retrospectively investigated the signal‐averaged ECGs in the time domain before, during, and after occlusion of the coronary artery by the PTCA balloon. Forty patients were resuscitated from ventricular fibrillation (VF group), and 40 patients had no ventricular arrhythmia (non‐VF group). Late potentials were seen at rest in 26 of 40 patients in the VF group. During ischemia, the duration of the filtered QRS complex and the duration of low‐amplitude signals < 40 μV increased significantly. In another 14 patients in the VE group, late potentials were observed only during ischemia. In 4 of 26 patients in the VE group without prior infarction hut with severe ischemia present at rest, successful PTCA eliminated preexistent late potentials. In the non‐VF group, one patient had late potentials present at rest. In two patients with prior infarction, late potentials were provokable only during transmural ischemia. Conclusion: Myocardial ischemia is able to modify detection of an arrhythmogenic substrate with the signal‐averaged ECG.
No Evidence of Chaos in the Heart Rate Variability of Normal and Cardiac Transplant Human Subjects
Authors: COSTA MADALENA , PIMENTEL IVETA R. , SANTIAGO TERESA , SARREIRA PEDRO , MELO JOÃO , DUCLA‐SOARES EDUARDO 
Published: April 2007

Heart Rate in Normal and Cardiac Transplant Subjects. Introduction: The variability observed in the heart rate may reflect fundamental aspects of cardiac activity. It has been under discussion whether heart rate variability (HRV) is due to noise or chaos, which is irregular behavior occurring in deterministic nonlinear systems. Methods and Results: Using chaos analysis techniques, we analyzed HRV of five normal and five human cardiac transplant subjects at rest. HRV is studied using the beat‐to‐beat RR interval time series extracted from the ECG. The cardiac transplant subjects exhibited a much smaller HRV than the normal subjects because of heart denervation. We present the map and correlation dimension estimation for the RR time series. To test for nonlinear correlations in the dynamics, we built surrogate time series that have the same power spectra as the experimental time series, but also have randomized phases. The experimental and the surrogate data were compared using the correlation integral. No correlation dimension was found for the RR time series of either the normal or the cardiac transplant subjects. Nevertheless, nonlinear correlations were detected in the HRV of the normal subjects but not in HRV of the cardiac transplant subjects. For the latter, no significant changes were observed in the correlation integral as a function of time after transplantation. Conclusion: We found no evidence of low‐dimensional chaos in the HRV of normal and cardiac transplant subjects. However, some nonlinear correlations were detected in the HRV of the normal subjects, which may be associated with autonomic nervous system influence.
Inspiration Induced by Phrenic Nerve Stimulation Increases Internal Defibrillation Energy Requirements
Authors: EULER DAVID E. , WHITMAN TERESA A. , KALLOK MICHAEL J. 
Published: April 2007

Active Inspiration Affects Defibrillation. Introduction: The purpose of this study was to systematically evaluate the effects of active inspiration induced by phrenic nerve stimulation on the energy required for 50% successful defibrillation (E50). Methods and Results: Shocks (95‐μF biphasic waveform) were delivered after 10 seconds of ventricular fibrillation between a right ventricular coil and left pectoral test can in ten anesthetized pigs (25 to 37 kg). Using a 1‐J step size, the E50 was determined with an up/down, three‐reversal method. Positive‐pressure ventilation was halted just before fibrillation, and shocks were delivered during expiration or at the end of 2 seconds of bilateral phrenic stimulation (50 Hz, 0.3 msec, 5 to 6 V). Phrenic stimulation produced inspiratory volumes that were 15.3 ± 1.7 mL/kg (mean ± SD). The E50 was 9.8 ± 1.9 J during expiration and increased to 13.0 ± 1.7 during inspiration (P = 0.001). The leading‐edge voltage at the K50 was 451 ± 46 V during expiration and 519 ± 33 V during inspiration (P = 0.001). The leading‐edge current at the E50 was 9.7 ± 1.0 A during expiration and increased to 11.3 ± 1.4 A during inspiration (P = 0.002). The average impedance was 47.8 ± 2.7 Ω during expiration and 47.3 ± 3.3 Ω during inspiration (P = 0.12). Conclusion: Inspiration induced by phrenic stimulation results in a 31% increase in the E50 compared with expiration. The decrease in shock efficacy occurs in the absence of a change in impedance. Active inspiration may alter the distribution of the electrical field leading to a decrease in shock efficacy.
Insights into the Mechanism of Sustained Ventricular Tachycardia after Myocardial Infarction in a Closed Chest Porcine Model Using a Multielectrode “Basket” Catheter
Authors: GREENSPON ARNOLD J. , HSU STEVE S. , BORGE RICHARD , SMITH MICHAEL R , ELDAR MICHAEL 
Published: April 2007

Mechanism of Sustained VT. Introduction: Accurate analysis of the arrhythmia substrate is important for successful radiofrequency ablation of sustained ventricular tachycardia (VT) after myocardial infarction (MI). Methods and Results: A multielectrode “basket” catheter capable of endocardial recording and pacing was inserted percutaneously into the left ventricle of post‐MI swine for analysis of the mechanism of sustained VT. Sustained VT was induced in 42 of 61 pigs that survived an acute MI produced by percutaneous transluminal coronary angioplasty balloon occlusion of the left anterior descending coronary artery and injection of agarose gel beads. A multielectrode “basket” catheter (Constellation™) with 64 electrodes was inserted in 35 of these animals for analysis of the VT. Induced VT had a cycle length of 179 ± 25 msec at control and 230 ± 43 msec after administration of intravenous procainamide. Presystolic electrical activity was recorded from at least 1 of 32 bipolar pairs of electrodes at a mean 40.7 ± 23.6 msec prior to QRS onset. Isolated mid‐diastolic potentials were recorded in 26 of 35 animals. In 22 animals, there were multiple isolated potentials recorded from adjacent electrode pairs. Isochronal maps demonstrated that these potentials returned to the systolic site of origin. Resetting of sustained VT by single premature ventricular stimuli was observed in 6 of 12 animals. Entrainment with overdrive pacing was seen in 19 of 26 animals with induced VT. Concealed entrainment was observed in ten animals. The mean stimulus to QRS interval was 45 ± 28 msec. Concealed entrainment was observed from adjacent electrode pairs with different stimulus to QRS intervals. Conclusion: These data suggest that sustained VT in this model is due to reentry with an excitable gap. A multielectrode “basket” catheter is useful for analyzing the zone of slow conduction participating in the tachycardia circuit. Such analysis may provide useful information to guide successful catheter ablation of sustained VT after MI.
Transvenous Parasympathetic Cardiac Nerve Stimulation:
Authors: SCHAUERTE PATRICK N. , SCHERLAG BENJAMIN J. , SCHERLAG MICHAEL A. , GOLI SUNIL , JACKMAN WARREN , LAZZARA RALPH 
Published: April 2007

Transvenous Parasympathetic Cardiac Nerve Stimulation. Introduction: Epicardial electrical stimulation of parasympathetic nerves innervating the sinus node has been shown to decrease sinus rate. We investigated whether intravascular parasympathetic cardiac nerve stimulation (IPS) can be achieved over a relatively long‐term period to slow the supraventricular rate. Methods and Results: Fifteen dogs were investigated. IPS was performed with rectangular stimuli (0.05‐msec duration, 20 Hz) using a catheter with an expandable electrode basket. The catheter was positioned in the superior vena cava (SVC; n = 9) or right pulmonary artery (RPA; n = 6). The basket then was expanded to hold the catheter in place. Nonfluoroscopic identification of effective IPS sites was achieved within 5 minutes in the SVC. Increasing IPS voltage resulted in a graded response of supraventricular rate slowing. A 50% prolongation of the baseline atrial cycle length was achieved with 28 V in the SVC (1,056 ± 355 msec vs 489 ± 154 msec; P < 0.001) and 25 V in the RPA (1,181 ± 306 msec vs 518 ± 138 msec; P < 0.01). The rate slowing started immediately after IPS onset, terminated abruptly after IPS cessation, and could be maintained over 10 hours. A rate slowing effect also was observed when the sinus rate was increased by isoproterenol (SVC: 304 ± 8 msec/RPA: 341 ± 9 msec with isoproterenol vs SVC: 635 ± 12 msec with isoproterenol + IPS at 39 V/ RPA: 584 ± 16 msec with isoproterenol + IPS at 38 V; n = 6). Conclusion: IPS results in a significant supraventricular rate slowing that is stable over a relatively long period and may be applied to slow undesirable sinus tachycardia in acute ischemic syndromes or to counteract undesirable chronotropic effects of catecholamines during treatment of cardiogenic or septic shock and acute congestive heart failure.
Droperidol Lengthens Cardiac Repolarization due to Block of the Rapid Component of the Delayed Rectifier Potassium Current
Authors: DROLET BENOIT , ZHANG SHETUAN , DESCHÊNES DOMINIC , RAIL JIMMY , NADEAU SYLVIE , ZHOU ZHENGFENG , JANUARY CRAIG T. , TURGEON JACQUES 
Published: April 2007

Droperidol Blocks Cardiac IKr.Introduction: Torsades de pointes have been observed during treatment with droperidol, a butyrophenone neuroleptic agent. Our objectives were (1) to characterize the effects of droperidol on cardiac repolarization and (2) to evaluate effects of droperidol on a major time‐dependent outward potassium current involved in cardiac repolarization (IKr).Methods and Results: Isolated, buffer‐perfused guinea pig hearts (n = 32) were stimulated at different pacing cycle lengths (150 to 250 msec) and exposed to droperidol in concentrations ranging from 10 to 300 nmol/L. Droperidol increased monophasic action potential duration measured at 90% repolarization (MAPD90) in a concentration‐dependent manner by 9.8 ± 2.3 msec (73%± 0.7%) at 10 nmol/L but by 32.7 ± 3.6 msec (25.7%± 2.2%) at 300 nmol/L (250‐msec cycle length). Increase in MAPDW90also was reverse frequency dependent As noted previously, droperidol 300 nmol/L increased MAPD90by 32.7 ± 3.6 msec (25.7%± 2.2%) at a pacing cycle length of 250 msec but by only 14.1 ± 1.3 msec (13.6%± 2.3%) at a pacing cycle length of 150 msec. Patch clamp experiments performed in isolated guinea pig ventricular myocytes demostrated that droperidol decreases the time‐dependent outward K+current elicited by short depolarizations (250 msec; 1k250) in a concentration‐dependent manner. Estimated IC50for IK250, which mostly underlies IKr, was 28 nmol/L. Finally, HERG K+current elicited in HEK293 cells expressing high levels of HERG protein was decreased 50% by droperidol 32.2 nmol/L.Conclusion: Potent block of IKrby droperidol is likely to underlie QT prolongation observed in patients treated at therapeutic plasma concentrations (10 to 400 nmol/L) of the drug.
Transient QT Prolongation with Torsades de Pointes Tachycardia after Ablation of Permanent Junctional Reciprocating Tachycardia
Authors: GRIMM WOLFRAM , HOFFMANN JÜRGEN , MENZ VOLKER , MAISCH BERNHARD 
Published: April 2007

Torsades de Pointes after PJRT Ablation. Introduction: Catheter ablation with radiofrequency energy is a curative therapy in patients with permanent junctional reciprocating tachycardia (PJRT). Methods and Results: For the first time, we report a case of transient QT prolongation with torsades de pointes tachycardia 18 hours after successful radiofrequency energy ablation of PJRT in a 25‐year‐old woman with tachycardia‐induced cardiomyopathy. Of note, the torsades de pointes occurred in the absence of bradycardia, electrolyte disturbances, or QT‐prolonging drugs. This patient initially was thought to have a hereditary long QT syndrome that was unmasked by PJRT ablation. Therefore, the patient received an implantable defibrillator in addition to beta‐blocker therapy, which was discontinued 6 months later. Surprisingly, the QT interval completely normalized within 1 week after PJRT ablation, and the patient remained free of arrhythmias during a follow‐up period of 4.5 years. Conclusion: Patients with incessant tachyarrhythmias should undergo ECG monitoring for at least 24 hours following successful radiofrequency catheter ablation because transient QT prolongation with torsades de pointes may occur even in the absence of bradycardia, QT‐prolonging drugs, or electrolyte disturbances.
Electrophysiologic Characteristics of Accessory Atrioventricular Connections in an Inherited Form of Wolff‐Parkinson‐White Syndrome
Authors: MEHDIRAD ALI A. , FATKIN DIANE , DiMARCO JOHN P. , MacRAE CALUM A. , WASE ABDUL , SEIDMAN J.G. , SEIDMAN CHRISTINE E. , BENSON D. WOODROW 
Published: April 2007

EP Characteristics in Familial WPW. Introduction: A familial form of Wolff‐Parkinson‐White syndrome (WPW) occurs in association with hypertrophic cardiomyopathy and intraventricular conduction ahnormalities. This syndrome, demonstrating autosomal dominant inheritance and segregating with a high degree of penetrance but variable expressivity, has been genetically linked to chromosome 7q3. The purpose of this study is to detail the electrophysiologic characteristics of accessory atrioventricular connections (AC) in four members of a kindred with this syndrome. Methods and Results: We clinically evaluated 32 members of a single kindred and identified 20 individuals with ventricular preexcitation, abnormal intraventricular conduction including complete AV block and/or ventricular hypertrophy, Genetic linkage analysis mapped the disease gene in this kindred to the chromosome 7q3 locus (maximum logarithm of the odds score = 6.88, θ= 0); recombination events in affected individuals reduced the genetic interval from 7 centimorgans (cM) to 5 cM. Electrophysiologic study of four individuals with preexcitation, identified seven AC (1 right sided, 3 septal, and 3 left sided). All four individuals had inducible orthodromic tachycardia; while three had multiple AC. Bidirectional conduction was demonstrated in 6 of 7 AC. Successful ablation was accomplished in 5 of 7 AC. Conclusion: The electrophysiologic characteristics and location of AC in family members having this complex cardiac phenotype are similar to those seen in individuals with isolated WPW. Identification of WPW in more than one family member should prompt clinical evaluation of relatives for additional findings of ventricular hypertrophy or conduction abnormalities.(J Cardiovasc Electrophysiol. Vol. 10, pp. 629‐635, May 1999)
Low‐Power Radiofrequency Application and Intracardiac Echocardiography for Creation of Continuous Left Atrial Linear Lesions
Authors: ROITHINGER FRANZ X. , STEINER PAUL R. , GOSEKI YOSHINARI , LIESE KARL S. , SCHOLTZ DINA B. , SIPPENSGROENEWEGEN ARNE , URSELL PHILIP , LESH MICHAEL D. 
Published: April 2007

Prediction of Left Atrial Linear Lesions. Introduction: Continuity of radiofrequency (RF) lesions for a catheter‐based cure of atrial fibrillation is essential in order to avoid reentrant tachycardias. In the present study, we assessed the value of intracardiac echocardiography and preablation electrode‐tissue interface parameters for creation of left atrial linear lesions. Methods and Results: In six healthy dogs, two left atrial linear lesions (lesion 1, along the inferior posterior left atrium; lesion 2, from the appendage to the left atrial roof) were attempted via a transseptal approach using a deflectable catheter with six 7‐mm coil electrodes. In a randomized fashion, one lesion was performed under echocardiographic guidance and one with blinded echocardiographic monitoring. The following preablation parameters were assessed for every coil electrode: (1) mean atrial electrogram amplitude of six consecutive sinus beats; (2) diastolic pacing threshold; and (3) temperature response to application of 5 W for 10 seconds. After ablation (target temperature 70°C, maximum power 50 W, duration 60 sec), the excised left atrium was examined macroscopically and histologically for lesion length, continuity, and presence or absence of lesions associated with each coil.Out of 12 attempted RF lesions, 7 were continuous (length, 47 ± 5 mm, lesion 2, n = 6) and 5 were discontinuous (lesion 1, n = 5). Fifty‐two of 70 coil electrodes (74%) had pathologic evidence of lesion creation. Intracardiac echocardiography was superior to fluoroscopy with respect to the actual number of coil electrodes creating lesions, and lesion continuity was correctly predicted in 9 of 12 lesions. Intracardiac echocardiography was 85% sensitive and 54% specific in predicting lesions created by individual coils. The correlation between the mean 60‐second ablation temperature and the preablation parameters was 0.45 for the electrogram amplitude, ‐0.67 for the pacing threshold, and 0.81 for the temperature response to low‐power application. Sensitivity and specificity for prediction of lesions created by individual coils, respectively, were 84% and 48% for the electrogram amplitude. 90% and 68% for the pacing threshold, and 96% and 76% for the low‐power RF application. Conclusion: Long linear lesions can be safely and effectively performed in the canine left atrium, using a tip‐deflectable multielectrode catheter. Intracardiac echocardiography may be helpful for positioning the ablation catheter in some parts of the left atrium, and preablation parameters, especially a nontraumatic low‐power RF application, are able to predict ultimate lesion creation with high accuracy.