bluuebunny/crossref_metadata_2025 huggingface dataset:
A “Dysautonomic” Head‐Up Tilt Test Pattern in Elderly Patients with Neurocardiogenic Syncope
Authors: BECK LIONEL , PONS MAXIME , PIOT CHRISTOPHE , LECLERCQ FLORENCE , MESSNER‐PELLENC PATRICK , FERRIÈRE MARC , DAVY JEAN‐MARC
Published: July 2006

The characteristics of neurocardiogenic syncope (NCS) in elderly patients remain unclear. We compared the hemodynamic profiles of young and older patients with consecutive and positive head‐up tilt tests (HUT). Continuous, noninvasive, and reliable monitoring of arterial pressure (AP) and heart rate (HR) was done throughout 46 consecutive positive HUTs of symptomatic patients. The population (12–82 years old) was divided into two groups: younger patients, Y (n = 25, ≤ 65 years), and older patients, O (n = 21). Changes in AP and HR after the first minute of tilting, during the stable orthostatic phase and during syncope were compared. Except for systolic pressure, baseline hemodynamic parameters were similar in Y and O. No difference appeared in the mean time elapsed before syncope (19 ± 9 vs 22 ± 2 min). Asymptomatic hypotension was observed, only in O, 1 minute after tilting, followed by a progressive fall in the mean AP before syncope (0 ± 0.9 vs −1 ± 0.7 mmHg/min) without HR increase (0.7 ± 1 vs 0 ± 0.6 beats/min). This pressure slope was strongly related to age (r = 0.54, P < 0.001). Hemodynamic recording during HUT identifies a dysautonomic pattern in elderly patients with NCS and the abnormal AP/HR responses to orthostasis may be a feature specific to this population. Although the central mechanism of NCS is common to all ages, the age‐related characteristics of the trigger event may indicate the need for specific management at different ages.
Time Dependence of Anodal and Cathodal Refractory Periods in Cardiac Tissue
Authors: BENNETT JONATHAN A. , ROTH BRADLEY J.
Published: July 2006

Mehra et al. (PACE 1980; 3:526) observed that immediately after implantation of a pacing electrode in a dog heart, the anodal refractory period (RP) is shorter than the cathodal RP, but after several weeks the anodal RP becomes longer than the cathodal RP. We examine this experiment using numerical simulations based on the bidomain model of cardiac tissue and a Beeler‐Reuter membrane. Our hypothesis is that accumulation of inexcitable tissue around the electrode following implantation causes the effective size of the electrode to increase and that this increase is the mechanism underlying the change in RP. We calculate that the anodal RP is shorter than the cathodal RP for both large and small electrodes. However, for large electrodes the threshold for anode “break” stimulation is greater than 8 mA. Mehra et al. defined RP experimentally as the interval at which the threshold stimulus strength becomes greater than 8 mA. If we restrict the stimulus current in our calculations to less than 8 mA, we exclude anode break stimulation from our calculation of the RP. In that case, our results are consistent with Mehra et al. and suggest that their observation resulted from their definition of RP.
Vasoactive Peptide Release in Relation to Hemodynamic and Metabolic Changes During Rapid Ventricular Pacing
Authors: YLITALO KARI , UUSIMAA PAAVO , VUOLTEENAHO OLLI , RUSKOAHO HEIKKI , PEUHKURINEN KEIJO
Published: July 2006

Plasma atrial natriuretic peptide (ANP) concentration increases during ventricular arrhythmias and rapid ventricular pacing but less is known about plasma brain natriuretic peptide (BNP) and endothelin (ET‐1). In the present study concentrations of ANP, the amino terminal part of the proANP (NT‐proANP), BNP, and ET‐1 were measured in the coronary sinus and femoral artery before and at the end of rapid ventricular pacing in 15 patients with coronary arterial disease. The changes were compared with the changes in mean arterial blood pressure, pulmonary capillary wedge pressure (PCWP), transcardiac differences in pH, pCO2, lactate, and norepinephrine. There was an increase in PCWP and a transient decrease in blood pressure after initiation of pacing. Pacing caused a decrease in ST‐segment, transcardiac difference of norepinephrine, lactate extraction, pCO2 difference, and an increase in pH difference. Concentration of ANP in the coronary sinus and femoral artery and its transcardiac difference increased during pacing (P < 0.001), whereas changes in NT‐proANP were small and BNP and ET‐1 levels remained unchanged. The change in transcardiac ANP difference correlated with the change in lactate (r = 0.53, P < 0.05) but not that of norepinephrine, PCWP, or blood pressure. The results show that the plasma concentration of ANP increases more than that of NT‐proANP during rapid ventricular pacing. Ischemia‐induced release of ANP and its diminished elimination may contribute to the increased plasma ANP level.
Clinical Surveillance of a Tined, Bipolar, J‐Shaped, Steroid‐Eluting, Silicone‐Insulated Atrial Pacing Lead
Authors: GLIKSON MICHAEL , HYBERGER LINDA K. , HITZKE MARY K. , KINCAID DANIEL K. , HAYES DAVID L.
Published: July 2006

Since 1990, 558 Medtronic 5524 bipolar, silicone‐insulated, J‐shaped, tined, steroid‐eluting atrial leads have been implanted at the Mayo Clinic (Rochester, MN, USA) and the Midelfort Clinic (Eau Claire, WI, USA). Implantation data were favorable, with pacing thresholds at implantation (median threshold, 0.6 V) better than most published data on other atrial leads. The rate of acute lead‐related complications (dislodgment and diaphragmatic pacing) necessitating reoperation or electrical abandonment of the atrial lead was 0.9%. This rate is lower than that in most published series of atrial leads. Over a median follow‐up time of 17.5 months (up to 69 months), there were no chronic lead‐related complications and no definite or suspected failures of lead material. This rate is much lower than that with other atrial leads studied previously. We conclude that the Medtronic 5524 atrial lead combines the reliability of silicone insulation with a lack of chronic complications and high thresholds due to its steroid elution and with stability in the atrium due to its J shape despite a passive fixation mechanism. There is no evidence of lead material failure during up to 6 years of follow‐up.
Arrhythmogenic Right Ventricular Dysplasia in an American Indian Woman
Authors: GALLOWAY JAMES M. , KOEPKE LAURA , OTT PETER , MARCUS FRANK I.
Published: July 2006

Arrhythmogenic right ventricular (RV) dysplasia consists of a dilatation of the right ventricle with a reduction of RV ejection fraction with fibrofatty replacement of the RV myocardium in the face of a well‐preserved left ventricular systolic function. Arrhythmogenic RV dysplasia, which is a cause of sudden unexpected death, has been reported from many geographic areas, including the United States, Europe, and the Far East. This case report presents the first case of arrhythmogenic RV dysplasia in an American Indian (Native American) patient.
Coronary Artery Bypass Grafting and Defibrillator Implantation in Patients with Ventricular Tachyarrhythmias and Ischemic Heart Disease
Authors: GEELEN PETER , PRIMO JOAO , WELLENS FRANCIS , BRUGADA PEDRO
Published: July 2006

In patients with sustained ventricular tachyarrhythmias and myocardial ischemia due to multivessel coronary artery disease, it remains unclear whether revascularization is enough to control the arrhythmias or whether additional implantation of a defibrillator is indicated. We therefore reviewed our clinical strategy of performing both bypass surgery and implantation of a defibrillator in patients with syncopal ventricular tachycardia or fibrillation and significant multivessel coronary artery disease. We retrospectively reviewed the outcome of 18 patients with malignant ventricular tachyarrhythmias, significant multivessel coronary artery disease, and signs of myocardial ischemia who underwent both bypass surgery and defibrillator implantation. Data on these patients were compared to data from 232 other defibrillator patients with respect to baseline clinical variables, cardiac events, and mortality during follow‐up. Except for underlying pathology, no other important differences in baseline characteristics were noted between the study patients and the other defibrillator patients. The cumulative occurrence of shocks during follow‐up was comparable in both groups (66% vs 67%). The cumulative survival from all‐cause mortality was 94% in the study patients and 78% in the others (P = NS). Pre‐ and postoperative electrophysiological testing was not useful to predict arrhythmia recurrences. In this population of patients with ventricular tachyarrhythmias and ischemia due to multivessel coronary artery disease, bypass surgery alone would not have prevented recurrences of arrhythmias. An excellent survival and a high incidence of shocks after both bypass surgery and defibrillator implantation were observed.
Single Center Experience with Femoral Extraction of Permanent Endocardial Pacing Leads
Authors: JARWE MOUSTAPHA , KLUG DIDIER , BEREGI JEAN PAUL , LE FRANC PIERRE , LACROIX DOMINIQUE , KOUAKAM CLAUDE , GUÉDON‐MOREAU LAURENCE , ZGHAL NAZIH , KACET SALEM
Published: July 2006

Between March 1995 and June 1997, 128 leads were extracted from the hearts of 28 women and 50 men, 69 ± 15 years of age (mean ± SD, range 22–92 years). The indications for the procedure were: Accufix lead in 18 patients (14%), dysfunction or incompatibility with ICD in 16 (12%), endocarditis on the lead in 41 (32%), pulse generator pocket infection in 28 (22%), and pulse generator and/or lead erosion in 25 patients (19%). The extraction was performed with a snare (lasso), via a femoral vein as a first approach in 116 leads, and as an alternate approach, after extraction from the original site of implantation had failed, in 12 leads. The leads had been implanted for 62 ± 48 months (range 1–205 months). A Cook sheath was used in 7, and a femoral approach traction in 20 instances. Of the 128 leads, 122 (95%) were completely extracted, and 2 (2%) were partially extracted (the distal electrode remaining attached to the myocardium), and 4 (3%) could not be removed. Four complications occurred: 2 tears of the tricuspid valve without clinical consequences, one separation of the lead's distal electrode which migrated into the hypogastric vein, and one hemorrhage at the femoral puncture site. There was no death or serious complication caused by lead extraction in this series.
Electrophysiological and Clinical Comparison of Two Temporary Pacing Leads Following Cardiac Surgery
Authors: HALLDORSSON ARI O. , VIGNESWARAN WICKII T. , PODBIELSKI FRANCIS J. , EVANS DIANA M.
Published: July 2006

Temporary pacing leads are invaluable in diagnosis and treatment of arrhythmia after cardiac surgery. The ideal lead possesses reliable pacing and sensing capabilities throughout the postoperative period. Ease of handling and a low complication rate are essential. This study compares a new lead (Medtronic model #6492) to a temporary pacemaker lead established in clinical use (Medtronic model #6500). One lead of each type was placed in the right atrium and ventricle in 33 patients undergoing elective coronary revascularization. Pacing function was measured on the first and fourth postoperative days. Lead complications were documented. On day 1, there was no statistical difference between lead types in terms of pacing (voltage threshold, current threshold), impedance, or sensing (P wave amplitude, R wave amplitude). On day 4, both leads showed an increase in pacing threshold and a decrease in sensing ability. The only statistical difference between lead types was in atrial sensing on day 4, as measured by the P wave amplitudes (1.95 ± 0.18 V for model 6492 vs 1.40 ± 0.14 V for model 6500, P < 0.05). Two leads of each model failed to pace in the ventricular position and one lead in each model in the atrial position. There were no complications attributable to either pacemaker lead. We found that both lead types were reliable and functioned well. The Medtronic Model #6492 lead demonstrated better long‐term sensing, although in this study the difference was not clinically significant.
The Effect of Biphasic Defibrillation on the Immediate Pacing Threshold of a Dedicated Bipolar, Steroid‐Eluting Lead
Authors: WELCH PATRICK J. , JOGLAR JOSE A. , HAMDAN MOHAMED H. , NELSON LAUREN , PAGE RICHARD L.
Published: July 2006

It is apparent that pacing threshold increases following an ICD shock, although the degree of change observed is dependent on the method used to assess pacing and the lead design used. We previously demonstrated a rise in postshock pacing threshold using a lead with integrated bipolar pacing in which the distal shocking coil also serves as the pacing anode. In this study, we sought to investigate whether the postshock pacing threshold increased significantly in an endocardial, steroid‐eluting lead with dedicated bipolar pacing electrodes. Twenty patients (16 men, 4 women; median age 73, ejection fraction [EF] 0.17–0.58) were studied during pectoral ICD implantation (Medtronic active can model 722lCx or 7223Cx with model 6932–65 lead). The diastolic pulse width pacing threshold at 1 or 2 V was determined. Pacing rate was set ≥ 100/min at twice diastolic threshold output to assess pacing immediately following the first DFT test shock. For subsequent shocks, the output was adjusted to establish postshock thresholds as 1, 2, 3, or 4 times the diastolic threshold. The postshock threshold was defined as the output yielding 100% capture ≥ 2.5 seconds following a shock. In 8 of 20 patients (ratio 0.40 ± 0.11), a rise in the post‐shock threshold was shown by failure of consistent capture when pacing at 2 times diastolic threshold ≥ 2.5 seconds after a DFT test shock. Two of these patients failed at 3 times threshold, but none failed at 4 × threshold. Five of 12 patients with successful capture at 2 times threshold failed to capture at threshold. The postshock threshold increased by a mean factor of 2.83 ± 0.83 in the group of patients with a threshold rise. Following ICD shock in an active can, steroid‐eluting lead system with dedicated bipolar pacing, the post‐shock threshold increases significantly. Our studies suggest a need for postshock pacing to be set at least 4 × threshold regardless of the lead design.
Results from the Use of a Preshaped Lead for Single‐Pass VDD/DDD Stimulation
Authors: ISRAEL CARSTEN WALTER , KRUSE IB MUNKSGAARD , VAN MECHELEN ROBERT , KROES GUUS , HEYNEN HENRY , LOKHOFF NICO
Published: July 2006

Main criticisms about single‐pass VDD stimulation in patients with AV block and normal sinus node function concern atrial undersensing in a lead with floating atrial electrodes, and loss of AV synchrony if sinus node dysfunction develops after implantation. We evaluated the concept of a preshaped single‐pass lead designed to place the atrial ring electrodes in a constant position close to, or in contact with, the atrial wall. A preshaped lead (Model 2775, Medtronic Inc.) was implanted in 14 patients and followed for up to 2 years. Mean P wave amplitudes (PWAs) were 3.1 mV at implantation, 1.2 mV at predischarge, and 1.3 mV after 12 months. In all patients, minimal PWAs were well above maximal atrial sensitivity of the pacemaker in all body positions during the complete follow‐up; atrial undersensing was not observed. Effective atrial stimulation was possible in all patients at implantation (mean stimulation threshold 2.5 V at 0.50 ms), in 11 patients on the first day after implant (mean stimulation threshold 0.22 ms at 5.0 V), in 10 patients after 1 month (mean stimulation threshold 0.57 ms at 5.0 V), and in 10 patients after 1 year (mean stimulation threshold 0.65 ms at 5.0 V). Intermittent phrenic nerve stimulation could be provoked in six patients. In conclusion, the concept of a preshaped single‐pass lead facilitated implantation, improved atrial sensing performance, and allowed atrial stimulation in some patients. Still, further improvements are necessary to decrease the atrial stimulation thresholds to acceptable values in all patients.
Paradigm Shift in Lead Design
Authors: IRNICH WERNER
Published: July 2006

During the past 30 years there has been a tremendous development in electrode technology from bulky (90 mm2) to pin‐sized (1.0 mm2) electrodes. Simultaneously, impedance has increased from 110 Ω to > 1 kΩ, which has been termed a “paradigm shift” in lead design. If current is responsible for stimulation, why is its impedance a key factor in saving energy? Further, what mechanism is behind this development based on experimental findings and what conclusion can be drawn from it to optimize electrode size? If it is assumed that there is always a layer of nonexcitable tissue between the electrode surface and excitable myocardium and that the electric field (potential gradient) produced by the electrode at this boundary is reaching threshold level, then a formula can be derived for the voltage threshold that completely describes the electrophysiology and electrophysics of a hemispherical electrode. Assuming that the mean chronic threshold for porous steroid‐eluting electrodes is 0.6 V with 0.5‐ms pulse duration, thickness of nonexcitable tissue can be estimated to be 1.5 mm. Taking into account this measure and the relationship between chronaxie and electrode area, voltage threshold, impedance, and energy as a function of surface area can be calculated. The lowest voltage for 0.5‐ms pulse duration is reached with r0= 0.5 d, yielding a surface area of 4 mm2 and a voltage threshold of 0.62 V, an impedance of 1 kΩ, and an energy level of 197 nJ. It can be deduced from our findings that a further reduction of surface areas below 1.6 mm2 will not diminish energy threshold substantially, if pulse duration remains at 0.5 ms. Lowest energy is reached with t = chronaxie, yielding an energy level < 100 nJ with surface areas ≤ 1.5 mm2. It is striking to see how well the theoretically derived results correspond to the experimental findings. It is also surprising that the hemispheric model so accurately approximates experimental results with differently shaped electrodes that it can be concluded that electrode shape seems to play a minor role in electrode efficiency. Further energy reduction can only be achieved by reducing the pulse duration to chronaxie. A real paradigm shift will occur only if the fundamentals of electrostimulation in combination with electrophysics are accepted by the pacing community.
Prediction of Optimal Atrioventricular Delay in Patients with Implanted DDD Pacemakers
Authors: ISHIKAWA TOSHIYUKI , SUMITA SHINICHI , KIMURA KAZUO , KIKUCHI MIYAKO , KOSUGE MASAMI , KUJI NAOMITSU , ENDO TSUTOMU , SUGANO TERUYASU , SIGEMASA TOMOHIKO , KOBAYASHI IZUMI , TOCHIKUBO OSAMU , USUI TAKASHI
Published: July 2006

In patients with an implanted DDD pacemaker (PM), the atrial contribution may be interrupted by too short an atrioventricular (AV) delay, and filling time may be shortened by too long an AV delay. The AV delay at which the end of the A wave on transmitral flow coincides with complete closure of the mitral valve may be optimal. The subjects were 15 patients [70.3 ± 12.3 (SD) years old] with an implanted DDD PM. Cardiac output (CO) and pulmonary capillary wedge pressure (PCWP) were measured by Swan‐Ganz catheter. Transmitral flow was recorded by pulsed Doppler echocardiography. AV delay was prolonged stepwise by 25 msc. When the AV delay was set at 155 ± 26 ms, the end of the A wave coincided with complete closure of the mitral valve. When the AV delay was prolonged 25, 50, 75, and 100 ms from this AV delay, the interval between the end of the A wave and complete closure of mitral the valve was prolonged 16 ± 5, 39 ± 6, 65 ± 4 and 88 ± 5 ms, respectively (r = 0.97, P < 0.0001) and diastolic mitral regurgitation was observed during this period. Thus, the optimal AV delay may be predicted as follows: the slightly prolonged AV delay minus the interval between the end of the A wave and complete closure of the mitral valve. When the AV delay was set at 215 ms, there was a significant positive correlation between the predicted optimal AV delay (166 ± 23 ms) and the optimal AV delay (CO: 161 ± 26 msec, r = 0.93, P < 0.0001. PCWP: 161 ± 28 msec, r = 0.95, P < 0.0001). In conclusion, optimal AV delay can be predicted by this simple formula: slightly prolonged AV delay minus the interval between end of A wave and complete closure of mitral valve at the AV delay setting.
The Costs of Recurrent Syncope of Unknown Origin in Elderly Patients
Authors: NYMAN JOHN A. , KRAHN ANDREW D. , BLAND PATRICIA C. , GRIFFITHS STEPHEN , MANDA VEN
Published: July 2006

Although syncope has been shown to reduce quality‐of‐life, its impact on resource costs has not been documented. The objective of this study was to quantify the annual medical costs of caring for elderly patients with syncope, especially recurrent syncope of unknown origin. Administrative data from the Health Care Financing Administration were obtained on 7,959 Medicare patients who had at least one inpatient admission with a diagnosis of syncope in 1993. The costs of any inpatient admissions, outpatient procedures, or physician visits with an ICD‐CM‐9 diagnosis for syncope were summed for a 365‐day period from the date of the initial hospitalization for syncope. Patients who had at least two hospitalizations with admission and discharge diagnosis of syncope were deemed to have recurrent syncope of uncertain origin. To better estimate syncope costs for those whose syncope costs could have been attributed to other diagnoses, a regression analysis was performed including variables representing the most frequent secondary diagnoses. The average annual costs of those who were admitted with syncope but who were discharged with another diagnosis was $4,942 in 1993. The average annual cost of patients with recurrent syncope deemed to be of unknown origin was $5,165. For those patients with secondary diagnoses of atherosclerosis, urinary tract infections, or hypokalemia, the annual costs of syncope averaged $6,820, $7,013, or $7,949, respectively.
Transesophageal Echocardiographic Visualization of Left Ventricular Malpositioned Pacemaker Electrodes: Implications for Lead Extraction Procedures
Authors: ORLOV MICHAEL V. , MESSENGER JOHN C. , TOBIAS SERGE , SMITH CLYDE W. , WAIDER WINFRIED , WINTERS REX , SCHANDLING ADRIAN , CASTELLANET MARK
Published: July 2006

Two cases of malpositioned LV electrodes are presented. Transesophageal echocardiography (TEE) allowed for a careful inspection of left‐sided leads and for tracking their course. One LV and two right‐sided leads were safely retrieved with TEE monitoring. One chronic LV lead was left in place as it was heavily fibrosed. TEE was helpful in the inspection and monitoring of the extraction and also in guided traction efforts. This is the first published report of echocardiographic visualization of the lead retrieval procedure.
Evaluation of Direct Respiratory Modulation of the QT Interval Variability
Authors: EMORI TETSURO , OHE TOHRU
Published: July 2006

To investigate the direct respiration‐mediated vagal modulation of the QT interval variability, spectral analyses of the RTp interval (from the R wave peak to the T wave peak) variability (RTpV) and the RR interval variability (RRV) were performed in 12 subjects with normal ventricular repolarization under three conditions while the respiration frequency was kept at 0.2 Hz: during sinus rhythm, during fixed atrial pacing, and during fixed atrial pacing with autonomic blockade. The cross‐spectrum between the RRV and RTpV was quantified by the squared coherence. During sinus rhythm the RRV power spectrum showed two peaks: a broad peak in the low frequency (LF) band and a sharp peak at 0.2 Hz which corresponded to the controlled respiration frequency. The RTpV power spectrum showed corresponding peaks to the RRV peaks in both the LF and high frequency (HF) bands with high coherence (mean maximum values of the squared coherence in the LF band 0.59 ± 0.22, and in the HF band 0.74 ± 0.14). During atrial pacing mean total power of the RTpV decreased from during sinus rhythm (from 16.3 ± 5.6 ms2 to 12.9 ± 5.4 ms2, P < 0.05) and the RTpV spectral peaks were abolished in both the LF and HF bands concordant with disappearance of the RRV peaks. Autonomic blockade gave no additional change to the RTpV power spectrum independently of the RRV during fixed atrial pacing. The present study suggested that the direct respiration‐mediated vagal modulation may not affect the short‐term variability of the QT interval in subjects without repolarization abnormality.
Energy Steering of Biphasic Waveforms Using a Transvenous Three Electrode System
Authors: LEONELLI FABIO M. , WANG K.E. , KING CHARLES , BREWER JAMES , DONOHOO ANN M. , KROLL MARK W.
Published: July 2006

The optimal electrode configuration for endocardial defibrillation is still a matter of debate. Current data suggests that a two pathway configuration using the right ventricle (RV) as cathode and a common anode constituted by a superior vena cava (SVC) and a pectoral can (C) is the most effective combination. This may be related to the more uniform voltage gradient created by shocks delivered using this configuration. We hypothesized that more effective waveforms could be obtained by varying the distribution of the shock current between the two pathways of a three electrode endocardial defibrillation system. In 12 pigs, we compared the characteristics and the defibrillation efficacy of six biphasic waveforms discharged using either a two (RV → C) or a three (RV → SVC + C) electrode combination with the following configurations: Configuration 1 (W1): the RV apical coil was used as a cathode and the subcutaneous C as anode (RV → C). Configuration 2 (W2): The RV was used as cathode and the combination of the atriocaval coil (SVC) and the subcutaneous C as anode (RV → SVC + C). Configuration 3 (W3): The RV → C was used for the first 25% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 4 (W4): The RV → C was used for the first 50% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 5 (W5): The R V → C was used for the first 75% off + and RV → SVC + C for the remainder of the discharge including f 2. Configuration 6 (W6): The RV → C was used for f + and RV → SVC + C for f2. As an increasing fraction of the waveform was discharged using the RV → SVC + C pathways, the impedance and the pulse width decreased while the tilt, the peak, and the average current significantly increased. The waveforms delivered using the RV → SVC + C configuration for 100% or 75% of their duration had significantly lower stored energy DFT than the other waveform. Current distribution between three endocardial electrodes can be altered during the shock and generates waveforms with different characteristics. Shocks with 75% or more of the current flowing to the RV → SVC + C required the lowest stored energy to defibrillate. This method of energy steering could be used to optimize current delivery in a three electrodes system.
Effect of Adenosine and Verapamil in Catecholamine‐Induced Accelerated Atrioventricular Junctional Rhythm: Insights into the Underlying Mechanism
Authors: LEE KATHY L. , CHUN HINGSON M. , LIEM L. BING , SUNG RUEY J.
Published: July 2006

Accelerated AV junctional rhythm is postulated to he due to enhanced automaticity of a high AV junctional focus. The adenosine response of this rhythm was tested in 17 patients (7 males, 12‐83 years). The indications of electrophysiology study were nonspecific palpitation (n = 5), unexplained syncope (n = 6), postablation of accessory pathways (n = 4), and postmodification of AV nodal reentry tachycardia (n = 2). The sinus node and AV nodal functions were normal. Pacing and programmed electrical stimulation failed to induce anv arrhythmia at baseline. The accelerated junctional rhythm (cycle length = 553 ± 134 ms) was initiated spontaneously in all patients after isoproterenol infusion (1‐2 μg/min). It was not suppressible bv overdrive pacing. Cessation of isoproterenol infusion terminated the rhythm in all patients. Adenosine (6 mg) reproducibly terminated the accelerated functional rhythm in all patients. In six patients, adenosine suppressed the junctional rhythm without producing AV nodal block. In the other 11 patients, the junctional rhythm was terminated prior to the occurrence of AV nodal block. Verapamil was tested in ten patients and 5 mg of intravenous verapamil terminated the junctional rhythm in all patients. In conclusion, the mechanism of catecholamine‐induced accelerated AV junctional rhythm is most likely enhanced automaticity, and catecholamine‐induced accelerated AV functional automaticity is sensitive to adenosine and verapamil. Adenosine appears to have differential effects on catecholamine‐enhanced AV junctional automaticity and AV nodal conduction. This suggests that, under catecholamine stimulation, adenosine may have different mechanisms of action on AV nodal conduction and automaticity.
Thoracoscopic Epicardial Radiofrequency Ablation for Vagal Atrial Fibrillation in Dogs
Authors: CHEVALIER PHILIPPE , OBADIA JEAN‐FRANçOIS , TIMOUR QUADIRI , BUI‐XUAN BERNARD , FATEMI MARJAREH , KIRKORIAN GILBERT , TABIB A. , LOIRE R. , TOUBOUL PAUL
Published: July 2006

Epicardial radiofrequency catheter ablation of the atria in the open‐chest dog has been shown to reduce inducibility of atrial fibrillation. Video‐assisted endoscopic techniques decrease the operative trauma in adult thoracic surgery. We report our results of video‐assisted thoracoscopic radiofrequency catheter ablation of the atria for the prevention of atrial fibrillation induction in canines. In 12 consecutive anesthetized dogs, induction of sustained atrial fibrillation was reproducibly obtained by burst pacing and cervical vagal stimulation. In six dogs, biatrial ablation was performed through right and left minithoracotomies and guided by video‐assisted endoscopic techniques. The remaining six dogs underwent a video‐guided left atrial procedure. Long continuous and transmural lesions were produced using epicardial temperature controlled radiofrequency energy delivered according to a simplified maze approach. Transmural lesions were demonstrated at the end of the study by examination of the heart. Sustained atrial fibrillation was still inducible after the right atrial ablation but sustained atrial fibrillation could not be induced following left atrial ablation. In acute canine studies: (1) epicardial radiofrequency catheter ablation of the atria is feasible using video‐assisted endoscopic techniques; (2) ablation extended or confined to the left atrium appears to be effective in preventing the inducibility of sustained vagal atrial fibrillation; and (3) ablation of the right atrium alone had no antiarrhythmic effect.
Diagnosis of Atrial Undersensing in Dual Chamber Pacemakers: Impact of Autodiagnostic Features
Authors: WIEGAND UWE K.H. , BODE FRANK , SCHNEIDER REGINA , BRANDES AXEL , HAASE HENNING , KATUS HUGO A. , POTRATZ JÜRGEN
Published: July 2006

Atrial undersensing occurs in a considerable number of patients, both with single lead VDD pacemakers and with DDD devices. The aim of this study was to investigate the diagnostic efficacy of electrocardiographic methods and autodiagnostic pacemaker features to detect atrial sensing dysfunction. Two hundred and thirty‐one patients with AV block received single lead VDD pacemakers or DDD devices. Atrial sensitivity was programmed to 0.1 or 0.18 in VDD devices and to 0.5 mV in DDD devices; the rate limits were set to 40 and 160 beats/min. Twelve‐lead ECG recording for 1 minute during deep respiration and change of body position, 24‐hour Holter ECG recording, and treadmill exercise were performed 2 weeks and 15 months after pacemaker implantation. AV synchrony and, if available, P wave amplitude histogram were sampled by autodiagnostic pacemaker features and compared to electrocardiographic findings. Atrial undersensing was assumed, if AV synchrony was below 100% or if minimal P wave amplitude (PWA) was equal to the programmed atrial sensitivity. Intermittent atrial undersensing occurred in 20.7% of patients. The diagnostic sensitivities of the various methods used to detect atrial sensing failures were: 24‐hour Holter monitoring 97.5%, P wave amplitude histogram 90.0%, stored AV synchrony 68.0% without significant difference between the various devices, treadmill exercise testing 58.8%, and 12‐lead ECG recording 21.3%. In one patient, atrial undersensing was exclusively detected by exercise testing. In conclusion, autodiagnostic pacemaker features facilitate the evaluation of atrial sensing performance. However, to exclude intermittent atrial malsensing, routine Holter monitoring and treadmill exercise are still needed.
Change of Atrial Refractory Period after Short Duration of Rapid Atrial Pacing: Regional Differences and Possible Mechanisms
Authors: LEE SHIH‐HUANG , CHEN SHIH‐ANN , YU WEN‐CHUNG , CHENG JUN‐JAGK , KAUN PEILIANG , HUNG GHI‐REN , CHANG MAU‐SONG , LIN FANG‐YUE
Published: July 2006

It is unknown whether there are regional differences in the cimnge of atrial effective refractory period (EBP) after a short duration of rapid atriai pacing. Furthermore, the effects of calcium channel and potassium channel on this phenomenon have not been extensively investigated. In opened‐chest dogs, the endocardial monophasic action potential duration at 90% repolarization (APD90) from the right atrial appendage, and ERP from seven atrial sites were measured before and after rapid atrial pacing at 800 beats/min for 30 minutes. Both atrial ERP and APD90 significantly shortened after rapid atrial pacing. The postpacing atria EBP and APD90 shortening persisted for 1.19 ± 3 and 123 ± 4 seconds after cessation of pacing, respectively. There was no significant difference in the magnitude or recovery course of atrial ERP shortening after pacing among the seven atrial sites. Pretreatment with nicorandil and d‐sotalol had no effects on the magnitude or recovery course of atrial EBP shortening after pacing. However, the degree of ERP and APD90shortening after pacing was significantly atten uated in the verapamil and ryanodine groups; furthermore, the recovery of ERP and APD90 after cessation of pacing was faster in the two groups. In conclusion, shortening of atrial EBP induced by short‐duration rapid atrial pacing was uniform in both atria. Both the adenosine triphosphatase (ATP) dependent potassium current and rapid component of the delayed rectifier did not significantly influence this phenomenon, but both the verapamil and ryanodine could significantly attenuate the degree of atrial ERP and APD90 shortening.
Symptomatic Atrioventricular Dual Pathway Double Responses: A Role for Slow Pathway Ablation
Authors: SORBERA CARMINE , COHEN MARTIN , DHAKAM SAJID , FAZIO JANNELLE
Published: July 2006

Two patients with symptomatic fast/slow pathway double responses were evaluated with electrophysiology studies. Chronic palpitations were resistant or worsened by medical therapy. No reentry tachycardias were induced. A nonreentrant paroxysmal supraventricular tachycardia was documented, Radiofrequency ablation of the slow pathway was safely and successfully performed. Patients remain asymptomatic for 16‐18 months. Ablation of the slow pathway for this substrate is a viable option.
Early Proarrhythmia During Intravenous Amiodarone Treatment
Authors: TOMCSáNYI JáNOS , MERKELY BéLA , TENCZER JóZSEF , PAPP LAJOS , KARLóCAI KRISTóF
Published: July 2006

We present a case of early (within the first 24 hours) development of malignant torsades de pointes (TdP) associated with intravenous amiodarone tberapy. After correction of predisposing factors (heart failure, hypokalemia, digoxin) amiodarone again resulted in torsades. This observation suggests that in patients who have experienced amiodarone‐induced proarrhythmia, amiodarone administration under different, more stable clinical conditions may still be hazardous.
Litter production and forest floor nutrient dynamics in pine and hardwood stands of New Brunswick, Canada
Authors: MacLean David A. , Wein Ross W.
Published: July 2006

Biomass and nutrient transfer (N, P, K, Ca, Mg) of overstory (branches and leaves) and understory litter fall were examined over a two year period in four jack pine stands aged 16, 29, 49 and 57 years and four mixed hardwood stands aged 7, 17, 20 and 29 years. Relative amounts of the five nutrients in litter fall for both series of stands were N > K ≷ Ca > P = Mg. Return of mineral elements to the forest floor was generally twice as high on the hardwood stands as for similarly aged pine stands. Overall return of nutrients plotted versus stand age generally exhibited a plateau relationship, with relatively little difference among stands; however, some exceptions occurred. Understory contribution to litter fall was very important on these stands, since in most cases the nutrient mass in understory litter was usually similar to or higher than that from the tree layer. Data on forest floor biomass, nutrient distribution and turnover rates of these stands were also presented; mobility of nutrients in the forest floor was in the order K > Mg ≥ P ≥ Ca ≥ N.
Life histories and distribution of British Trichoptera, excluding Limnephilidae and Hydroptilidae, based on the Rothamsted Insect Survey
Authors: Crichton M. I. , Fisher D. , Woiwod I. P.
Published: July 2006

Catches of Trichoptera from 67 light traps in Great Britain are studied. Two families are excluded: the Limnephilidae because they have been considered in an earlier publication, and the Hydroptilidae.

Catches from 148 complete year records, from 1965 to 1971, are grouped in three areas: A. Scotland, 15 sites; B. Wales and Northern England. 18 sites; C. Southern England, 34 sites. The total of over 146000 caddis flies includes 60 of the 109 British species from 14 families.

Small or nil catches are explained by limited distribution or dispersal, short adult lives and day‐flying habits. The flight periods are related to published information on life cycles. Most species are univoltine, but some small species are bivoltine. In contrast to Limnephilidae, there is no evidence of a summer adult diapause, median weeks for flight periods tend to be earlier in the south, and few species are autumnal fliers. Density distribution maps, produced by computer, are given for six species.
Vegetation of a snow bed at Godhavn, West Greenland
Authors: Philipp Marianne
Published: July 2006

The vegetation of a snow bed has been described by a pin‐point method and a modified Raunkiær frequency analysis. The thawing of the snow has been followed and some soil properties have been investigated. It is concluded that the composition of the vegetation in the snow bed is influenced mainly by the duration of the growth period, but locally the density and the species composition are determined by the downward flow of the melt water.
Spot‐distribution in Maniola jurtina (Lepidoptera) on small islands in southern Sweden
Authors: Bengtson Sven‐Axel
Published: July 2006

The Meadow Brown Butterfly, Maniola jurtina L., which is polymorphic for spotting on hind wings, was studied for five years on four small (0.15–1.0 km2) islands off the south coast of Sweden. Samples of females and males were unimodal for 0 and 2 spots, respectively. Spot‐distributions remained unaltered in 1973–1974 but changed significantly in 1975 only to be restored again in 1976 and 1977. The change in 1975 was assumed to be associated with an unusually dry and warm summer and the results are discussed in terms of natural selection.
The local climate of the Øvre Heimdalen valley
Authors: Johannessen T. Werner
Published: July 2006

Owing to the high altitude of Øvre Heimdalen and the complex topography within the valley, climatic conditions are complicated. The valley is situated in a mountain region with a subarctic or tundra macroclimate, which exists over the lake itself and on the SSW‐valley side. However, the favourable combination of slope angle and exposure of the NNE‐valley side gives a radiation or continental type of local climate on this side.

The large net input of radiant energy onto the NNE‐valley side during the summer results in higher air temperatures, greater precipitation and higher air humidity than elsewhere in the valley. This is clearly reflected in the luxuriant vegetation on this side. Thus, the climate of the Øvre Heimdalsvatn area is strongly influenced by terrain irregularities and shows how fundamentally different growth possibilities due to local climates may be over short distances in the uppermost valleys on the eastern side of the central mountain chain.
Physical and chemical properties of the waters of Øvre Heimdalen
Authors: Kloster Asbjørn Elias
Published: July 2006

The paper describes abiotic factors of basic importance for the biological research carried out simultaneously in the lake Øvre Heimdalsvatn.
The life cycle dynamics and production of zooplankton in Øvre Heimdalsvatn
Authors: Larsson Petter
Published: July 2006

The zooplankton in Øvre Heimdalsvatn was studied from May 1969 to Aug 1973 in order to obtain knowledge about their functioning and role in the lake ecosystem. The paper concentrates on the main species: Holopedium gibberum, Bosmina longispina, Cyclops scutifer. Heterocope saliens, Conochilus unicornis, Polyarthra vulgaris and Kellicottia longispina but Megacyclops gigus, Daphnia longispina and ciliated cells are also considered. The development of the populations was fairly synchronized and made it possible to determine life cycles, development times, growth, reproduction and production from field data. The total production of the multicellular zooplankton was 2–3 mg dry wt m−2 yr−1. The cladocerans dominated and their share of the total was 84–92% compared to the copepods 5–8% and the rotifers 3–8%. The ciliate production was not estimated, but their biomass exceeded that of the copepods and rotifers. The spring spate, June temperatures, food availability and invertebrate predation were found to be the most important regulatory factors for life cycle dynamics and production. Allochthonous organic matter was found to be a necessary food resource in addition to algae.
The Mollusca of the exposed zone of Øvre Heimdalsvatn
Authors: Brittain John E.
Published: July 2006

The molluscan fauna was surveyed monthly in 1972 during the ice free period. Densities were low and the most common species were the gastropods Gyraulus acronicus (Férussac) and Lymnaea peregra (Müll.).
The aquatic Coleoptera of Øvre Heimdalsvatn
Authors: Brittain John E.
Published: July 2006

The species composition, seasonal and spatial distribution, and biomass of the coleopteran Fauna of the exposed zone of Øvre Heimdalsvatn in 1972 are presented. Individual weight data are given for the 8 species present in the lake: Haliplus fulvus F., Hydroporus palustris L., Deronectes alpinus Payk., D. multilineatus, Flkstr., D. rivalis Gyll., Platambus maculatus L., Colymbetes dolabratus Payk. and Helophorus glacialis Villa. Deronectes alpinus occurred in highest densities, but P. maculatus, on account of its higher individual weight, was the major contributor to the coleopteran biomass.
The invertebrate fauna of the streams in Øvre Heimdalen
Authors: Lillehammer Albert , Britain John E.
Published: July 2006

The lotic communities in Øvre Heimdalen were completely dominated by insects. The species distribution of stoneflies (Plecoptera), mayflies (Ephemeroptera) and caddisflies (Trichoptera) is given together with autecological notes on the Plecoptera and certain other major species. The species distribution of these groups, especially the Plecoptera, was clearly related to the deciduous vegetation along the streams. There was a reduction in species parallel to a reduction in Salix vegetation.

The main inlet stream to the lake, Øvre Heimdalsvatn, the outlet and the outlet stream had different faunal compositions. The inlet fauna consisted to a large extent of winter growing species, mainly detritus feeders, while the outlet and outlet stream had a fauna dominated by summer growing species, several of which were filter feeders.
The dynamics and exploitation of the brown trout population of Øvre Heimdalsvatn
Authors: Jensen Kjell W.
Published: July 2006

The very dense trout population in the lake was substantially reduced by heavy fishing. The resulting changes in growth, age distribution and population density were examined. Fishing efforts with 32 mm nets gave the highest sustainable yield. With a yearly effort of 1600 nights with these nets the predicted sustained yield would be 5.7 kg ha−1 of trout with a mean weight of 269 g.
The energy budget of the brown trout population of øvre Heimdalsvatn
Authors: Lien Leif
Published: July 2006

Energy pathways of a natural brown trout Salmo trutta population were constructed. The main subjects taken into account were: the biomass, calorific values and production of the population, natural mortality and annual yield, energy intake, calorific values and composition of the food, efficiency of food absorption, spawning and migration of young trout. The specific energy value of trout increased with increasing weight of the fish. An energy decrease of almost 50% was demonstrated for the spawning trout of both sexes, and the calorific values prior to spawning were not reached before the next summer. Energy intake was estimated to 6.87, 10.31, 8.42 and 9.15 kcal m−2 lake surface for the years 1969, 1970, 1971 and 1972 respectively. Although a great number of food items were found in the trout stomachs, the four groups Gammarus lacustris, Lepidurus arcticus, Trichoptera and Chironomidae accounted for 2/3 of the total consumption. The efficiency of food absorption varied between 42 and 53%. The mean age of trout entering the lake from the nursery streams was ca. 3 yr. The annual amount of this immigration was estimated to be 0.28 and 0.24 kcal m−2 lake surface for 1969 and 1970 respectively. Annual production of trout in the take was estimated to be 1.46 and 2.66 kcal m−2 respectively for the same years. For both these years balance was found between biomass at the beginning of the year plus immigration of young and total production, minus catch by man, natural mortality and spawning on the one hand and biomass at the end of the year on the other hand.
Energy consumption of ducks on øvre Heimdalsvatn
Authors: Lien Leif
Published: July 2006

The energy consumption of the ducks is based on estimates of bird density and discovery chance together with juvenile production, metabolic rate and assimilation efficiency given in the literature. The approximate values for food energy consumed were 230000, 143000 and 165000 kcal in 1970, 1971 and 1972 respectively, or in terms of lake surface between 0.2 and 0.3 kcal m−2 yr−1.
Morphological variations in the preputial gland of wild bank voles, Clethrionomys glareolus
Authors: Christiansen Erik , Wiger Richard , Eilertsen Einar
Published: July 2006

The size and appearance of the preputial glands of Clethrionomys glareolus showed variations which were associated with season, sex and maturation. The glands were by far largest in mature males followed by mature females, and subadult males and females, in that order. There was a positive relationship between the length, fresh weight and dry weight of the glands. The possible role of the preputial glands in relation to territorially, social status and sexual attraction is discussed.
Resistance to anoxia of Chironomus plumosus and Chironomus anthracinus (Diptera) larvae
Authors: Nagell Björn , Landahl Carl‐Christer
Published: July 2006

Survival of the midge larvae Chironomus plumosus and C. anthracinus in anoxia at 4°C was investigated. C. plumosus survived about twice as long as C. anthracinus. The corresponding LT 50 values were ca 205 and 100 d. There was no statistically significant difference between the survival in anoxia and in aerated water, which indicates that the main reason for death in anoxia is not the absence of oxygen. This main reason is presumed to be starvation. The presence of undissociated H2S in low concentrations (ca 1.2 mg 1−1) did not influence the survival. In anoxia the larvae were usually motionless and did not feed but they increased in weight due to uptake of water. During 43 d C. plumosus and C. anthracinus increased ca. 10%.