bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Restitution and Conduction Intervals of Ventricular Premature Beats in Man: Influence of Heart Rate
Authors: ENDRESEN KNUT , AMLIE JAN P.
Published: July 2006

Influence of Heart Rate. Monophasic action potentials (MAP) were obtained /rom the outflow tract of the right ventricle during apical pacing in 20 patients with coronary artery disease. The electrical restitution was studied hy interpolation of extrasystoles with various coupling intervals to the preceding steady‐state heat at basic paced cycle lengths (CL) of 700, 600, and 500 msec. At higher frequencies the ventricuiar effective refractory periods (V‐ERP) and duration of MAPs became shorter and the electrical restitution curves were displaced downwards (P < 0.001). With increasing diastolic intervals preceding the extrasystole up to a maximum of 100 msec, the duration of premature MAPs increased at all frequencies. An obvious hump of the electrical restitution curve was observed at coupling intervals of 100 msec due to a later transient decrease (P < 0.01) in duration of MAPs at the basic CL of 500 msec. No significant hump was observed at lower heart rates. Thus, a different time course of the electrical restitution was observed at various CLs. The intraventricular conduction intervals were shorter at the shorter basic CLs when compared to the 700 msec cycles (P < 0.05). The conduction intervals were also modified by the coupling interval between the interpolated stimulus and the preceding steady‐state action potential (AP). The premature beats elicited 30 msec or earlier after refractoriness were conducted more slowly at all basic cycle lengths (P < 0.005), and those between 60 and 150 msec after the V‐ERP more rapidiy (P < 0.01) than the steady‐state beats. These observations have implications for the protocols used for introducing two or more frequencies during programmed stimulation in man. Furthermore, the conduction pattern in vivo cannot be interpreted from single ceil studies.
“Clockwise” and “Counterclockwise” Bundle Branch Reentry as a Mechanism for Sustained Ventricular Tachycardia Masquerading as Supraventricular Tachycardia
Authors: WANG PAUL J. , FRIEDMAN PETER L.
Published: July 2006

A 35‐year‐old man presented with a regular tachycardia having a typical right bundle branch block morphology. Electrophysiological testing revealed inducible tachycardia exhibiting counterclockwise as well as clockwise bundle branch reentry, leading to left and right bundle branch block morpbologies. The disappearance of spontaneous episodes of these tachycardias following resolution of right bundle branch block in the resting electrocardiogram suggested that slow conduction in the right bundle branch played an essential role in the tachycardia circuit.
Exercise Electrophysiology Testing: The Effect of Exercise on the Induction of Ventricular Arrhythmias by Programmed Ventricular Stimulation
Authors: THOMAS GREGORY S. , GARAN HASAN , DAVIS MICHAEL J.E. , CURFMAN GREGORY D. , DEC G. WILLIAM , BOUCHER CHARLES A. , SLATER WILLIAM R. , MCGOVERN BRIAN , RUSKIN JEREMY N.
Published: July 2006

In order to assess the effect of acute, reversible myocardial ischemia on (he outcome of programmed ventricular stimulation (PVSJ, ventricular stimulation was performed at rest, during exercise, and during recovery in 10 patients with coronary artery disease. Of these ten patients, four were tested while off antiarrhythmic drugs and six were tested on antiarrhythmic drug therapy. Nine of the ten patients developed acute myocardial ischemia during exercise PVS. However, in only two of these ten patients ventricular arrhythmia could be induced by PVS, one during exercise and one during recovery.
Lack of Triggered Automaticity Despite Repolarization Abnormalities due to Bepridil and Lidoflazine
Authors: CAMPBELL ROBERT M. , WOOSLEY RAYMOND L. , IANSMITH DAVID H.S. , RODEN DAN M.
Published: July 2006

Bepridil and lidoflazine are calcium channel antagonists that also prolong action potential duration, produce QT interval prolongation on the surface EGG, and have been associated with the distinctive form of ventricular tachycardia, torsade de pointes. It has been demonstrated that quinidine, which also prolongs QT interval and induces torsade de pointes, produces early afterdepolarizations and triggered activity in canine Purkinze fibers driven at slow rates. The effects of bepridil (1‐10 μM) and of lidoflazine (5‐15 μM) on the transmembrane action potential from canine Purkinze fibers were therefore studied. At long cycle lengths, unlike with quinidine, triggered activity arising during phase 3 was rare; phase 3 secondary plateaus (early afterdepolarizations) were, however, common. Arrest of transmembrane potential between ‐50 and ‐60 mV during stimulation at long cycle lengths was also frequently observed (7/20 of bepridil and 3/15 of lidoflazine‐treated fibers). In preparations with prominent phase 3 secondary plateaus, addition of epinephrine resulted in triggered activity; similarly, epinephrine caused automaticity from a depolarized membrane potential in 8/9 fibers quiescent at ‐50 to ‐60 mV. Thus, the calcium channel blocking drugs bepridil and lidoflazine produced striking repolarization changes at slow stimulation rates, but unlike quinidine, triggered activity was rare. The effect of epinephrine on these drug‐treated fibers suggests that the slow inward calcium current plays a role in the generation of triggered activity in the presence of prolonged repolarization.
Effects of Filtering on Right Ventricular Electrograms Recorded from Endocardial Catheters in Humans
Authors: KLITZNER THOMAS S. , STEVENSON WILLIAM G.
Published: July 2006

Criteria for identifying electrically abnormal myocardium based on analysis of electrogram, amplitude, duration, and morphology have recently been proposed as an aid to catheter mapping in humans. Electrogram characteristics are likely to be influenced by analog filtering and the distance between recording electrodes. These parameters can be varied and differ among electrophysiol‐ogy laboratories. To determine the magnitude of the effect of low pass and high pass filtering and intere‐lectrode distance on human bipolar right ventricular electrograms eight patients were studied. The signal from a single bipolar electrode pair was recorded simultaneously on five channels with variable filtering. As the high pass filter frequency increased above 10 Hz, the electrogram duration and amplitude decreased. The decrease in amplitude was described by a monoexponential function with a 30% decrease in amplitude at a filter setting of 30 Hz and a 69% decrease at a filter setting of 100 Hz. As the low pass filter frequency decreased from 2,500 to 250 Hz, electrogram characteristics were not significantly altered. Low pass filtering at 300 Hz decreased electrogram amplitude slightly. Neither high nor low pass filter settings or interelectrode distance affected electrogram timing. However, filtering could markedly alter electro‐gram morphology, introducing the possibility for errors in visual assessment of electrograms. Electrogram duration increased linearly with increasing distance between recording electrodes. The effects of filtering on electrograms were similar regardless of interelectrode spacing. Thus, varying the high pass filter setting over a range that is used clinically (from 1 to 100 Hz) can substantially alter electrogram duration, amplitude, and morphology. Low pass filtering at 250 Hz and above had no effect on these electrograms although it is possible that alterations would be observed in signals from areas of slow conduction that we did not study. The filter setting and interelectrode distance must be considered when applying proposed criteria for distinguishing normal from abnormal electrograms.
Pacemaker Syndrome Evaluated by Cardiopulmonary Exercise Testing
Authors: FUJIKI AKIRA , TANI MASANAO , MIZUMAKI KOICHI , ASANOI HIDETSUGU , SASAYAMA SHIGETAKE
Published: July 2006

Two patients who presented with dyspnea on effort, persisting after insertion of a fixed rate ventricular demand pacemaker (VVI) for sick sinus syndrome, were evaluated by cardiopulmonary exercise testing. During VVI pacing a heightened ventilatory response to exercise and a fluctuation of ventilation occurred. The high ventilatory equivalent for CO2 throughout exercise with VVI pacing suggests that the patients had ventilation‐perfusion mismatching due to an increase in the pulmonary capillary wedge pressure caused by 1:1 ventriculoatrial conduction. Rate responsive ventricular (VVIR) pacing associated with intact 1:1 ventriculoatrial conduction exaggerated the exertional dyspnea, while rate responsive atrial (AAIR) pacing improved the ventilatory response to exercise. We suggest that a heightened ventilatory response to exercise due to ventilation‐perfusion mismatching may be an important factor causing the pacemaker syndrome, and that cardiopulmonary exercise testing is useful in identifying the exercise‐induced symptoms with ventricular pacing.
Relation between Spontaneous Atrial Fibrillation and Atrial Vulnerability in Patients with Wolff‐Parkinson‐White Pattern
Authors: GAITA FIORENZO , GIUSTETTO CARLA , RICCARDI RICCARDO , MAZZA ANTONIO , MANGIARDI LUCIA , ROSETTANI ERENNIO , BRUSCA ANTONIO
Published: July 2006

An intracavitary electrophysiological study was carried out on 103 patients with Wolff‐Parkinson‐Whire (WPW), 23 symptomatic patients had documented episodes of atrial fibrillation, 54 symptomatic patients had atrioventricular reentrant tachycardias, and 26 asymptomatic. Patients were examined for the relation between spontaneous atrial fibrillation and atrial vulnerability, defined as the possibility to induce sustained (> 1 minute) episodes of atrial fibrillation with a stimulation protocol excluding atriai bursts. Atrial fibrillation induction was attempted by single and double atriai extrastimuli during pacing at two different cycle lengths and incremental atrial pacing. Sustained atrial fibrillation was induced in 65% of the patients with spontaneous atrial fibrillation, and in 13% of the symptomatic patients with documented episodes of atrioventricular reentrant tachycardias and in 15% of the asymptomatic patients (P < 0.0005). Atrial vulnerability was higher in patients with spontaneous atrial fibrillation than in patients without this arrhythmia. No significant difference was observed between symptomatic without atrial fibrillation and asymptomatic patients.
Propafenone Induced Acute Variation of Chronic Atrial Pacing Threshold: A Case Report
Authors: MONTEFOSCHI NICOLA , BOCCADAMO ROBERTO
Published: July 2006

A marked increase of chronic atrial pacing threshold resulting in Joss of atrial capture, induced by propafenone, is reported in a patient with bradycardia‐tachycardia syndrome. After atrial pacemaker implant, the atrial threshold had been measured repeatedly noninvasively and shown to be stable. The threshoJd rise and loss of atrial capture occurred after 7 days of treatment with propafenone at the dosage of 450 mg daily; drug withdrawal resulted in resumption of atrial capture and a return to prior pacing thresholds.
Cardiomyopathy and the Use of Implanted Cardio‐Defibrillators in Children
Authors: KAMINER SHARON J. , PICKOFF ARTHUR S. , DUNNIGAN ANN , STERBA RICHARD , WOLFF GRACE S.
Published: July 2006

Children and adults with Cardiomyopathy and ventricular dysrhythmias have a uniformly poor prognosis, despite medical therapy. The use of automatic implantable cardio‐defibrillators in adult patients with medically resistant ventricular dysrhythmias has resulted in a positive impact on survival. Because of its size and former Jack of programmability, the device has been used rarely in children. Four patients with Cardiomyopathy, in whom refractory ventricular dysrhythmias were managed with automatic implantable cardio‐defibrillators, are presented. Two of these children are the youngest and smallest known in whom the device has been used; one of them received the first programmable model. The use of the automatic implantable cardio‐defibrillator may enhance survival in selected young patients.
Permanent Pacemaker Placement in Chronic Atrial Fibrillation Associated with Intermittent AV Block and Cerebral Symptoms
Authors: SAXON LESLIE A. , ALBERT BRIAN H. , URETZ EUGENE F. , DENES PABLO
Published: July 2006

We examined the hypothesis that a ≥2 second pause detected on 24‐hour Holter monitoring in patients with persistent atrial fibrillation and complaints of syncope or dizziness lacked sufficient specificity to warrant implantation of a permanent pacemaker. We retrospectively reviewed cases from our 24‐hour electrocardiographic (Holter) monitoring data base. A total of 411 consecutive Holter monitoring records demonstrating persistent atrial jibrillation obtained during a 5‐year period (1982 to 1987) were examined. One hundred and five (26%) patients had cerebral symptoms (dizziness or syncope) as a primary indication for monitoring 80 (76%) patients were identified with documented ventricular pauses of ≥2 seconds. Three hundred and six patients (74%) underwent 24‐hour monitoring without cerebral symptoms as an indication and 209 (68%) patients had ≥2‐second pauses. Clinical information was available in 164 (50 symptomatic and 114 asymptomatic) patients. There were no significant differences in the clinical or Holter findings between the two groups. Of the 50 symptomatic patients, 15 (30%) underwent permanent pacemaker placement and the remaining 35 (70%) were managed conservatively during a mean follow‐up of 23 ± 5 months. Eleven of 15 paced (73%) and 31 of 35 (89%) nonpaced patients experienced resolution of their cerebral symptoms (NS). The sensitivity of Holter monitoring in detecting pauses of ≥2 seconds in patients with cerebral symptoms was high (76%), but the specificity (32%) and positive predictive values (28%) were low. In conclusion, the finding of a 2‐second pause interval on Holter monitoring lacks sufficient specificity to identify symptomatic patients with persistent atrial fibrillation. In addition, there is a high rate of spontaneous resolution of cerebral symptoms in this group without the use of a pacemaker. These findings suggest that in patients with persistent atrial fibrillation in the presence of a 2‐second pause on a Holter recording, a clear association between cerebral symptom and the pause interval is necessary before the use of a permanent pacemaker is recommended.
The Use of Signal‐Averaged Electrocardiography in Predicting Patients at High Risk for Sudden Death
Authors: SEALE WALTER L. , GANG ELI S. , PETER C. THOMAS
Published: July 2006

Delayed and inhomogeneous ventricular depolarization is found in patients with ventricular tachycardia. This abnormal activity may be discerned as a ventricular late potential (LP) fay applying special signal‐averaging techniques to the surface electrocardiogram. The presence of LPs after acute myocardial infarction (AMI) is associated with an increased risk of serious ventricular arrhythmias and sudden cardiac death during the subsequent year. Thus the signal‐averaged EGG (SAECG) can identify a high risk subset of patients following AMI for whom more intensive diagnostic and/or therapeutic measures are indicated. Patients with findings ordinarily indicative of a relatively poor prognosis, such as reduced left ventricular ejection fraction, may be more precisely classified into high or low risk based on the presence or absence of LPs. The SAECG may be helpful in selecting patients with other types of presentations, such as syncope, who are likely to benefit from eJectrophysiological testing.
Atrial Standstill: An Indication For Rate Responsive Pacing
Authors: SOLTI FRANCIS , RÉNYI‐VÁMOS FRANCIS , GYÖNGY TIBOR
Published: July 2006

Atrial standstill (atrial paralysis) is a rare reason for permanent bradycardia. A case of atrial standstill is presented. A 35‐year‐old man had suffered from bradycardia since his childhood. For 2 years he had complaints (diminishment of his working capacity, and dyspnea occurred with effort) as well. On admission, a slow (38/min) functional escape rhythm could be detected. There were no signs of atrial mechanical activity (atrial contraction) according to chest x ray, echocardiography, and the atrial pressure curve. The electrophysiological study revealed that the atria could not be electrically stimulated, and no P wave (A wave) could be recorded on right atrial electrograms. The patient received a rate responsive pacemaker. After pacemaker implantation, he became symptom‐free; his working capacity improved markedly and his heart size decreased. Owing to the permanent bradycardia and the lack of atrial stimulation, the atrial standstill represents an indication for ventricular rate responsive pacing. Atrial standstill, permanent bradycardia, and the inability to stimulate the atrium are indications for ventricular rate responsive pacing.
The Ventricular Excitability‐Interval Relationship in Early Diastole in Humans: The Influence of the Electrode Configuration During Bipolar Stimulation
Authors: TOIVONEN LAURI K. , KADISH ALAN H. , KOU WILLIAM H. , MORADY FRED
Published: July 2006

The purpose of this study was to determine the relationship between ventricular excitability and the extrasfimulus (S2) coupling interval in early diastole in humans. The influence of the electrode configuration during bipolar stimulation was examined. Ventricular strength‐interval curves were constructed using an eight beat drive train at a cycle length of 600 msec, 2‐msec decrements in the S2 coupling interval, and 0.2‐mA increments in the current intensity of S2 at each coupling interval. A transient dip in the excitation threshold was observed in early diastole during bipolar pacing when the distal electrode was the anode in six of 17 patients (35%). In contrast, this type of dip was not observed when the distal electrode was the cathode. The excitation threshold at the trough of the dip ranged from 1.0 to 2.2 mA. Unipolar strength‐interval curves indicated that a dip occurred with anodal but not cathodal pacing. We postulated that the dip might interfere with the accurate determination of the ventricular effective refractory period by resulting in transient loss of ventricular capture during decremental scanning of diastole with S2. A gap in ventricular capture was produced in all six patients who demonstrated a dip in the bipolar strength‐interval curve by selecting an S2 current intensity that fell within the dip. In conclusion, the bipolar strength‐interval curve may display an early diastolic dip in the excitation threshold, depending on the electrode configuration. During determination of the ventricular effective refractory period, if the stimulus intensity falls within the range of current intensities encompassed by the dip, a transient early diastolic gap in ventricular capture will be observed as diastole is scanned with S2. If this type of gap is not recognized, the ventricular effective refractory period may be overestimated.
A New Steroid‐Eluting Epicardial Lead: Experience with Atrial and Ventricular Implantation in the Immature Swine
Authors: KUGLER JOHN D. , FETTER JOE , FLEMING WILLIAM , KILZER KAREN , STOEHR DAWN , FELIX GARY , RADIO STANLEY
Published: July 2006

The first study with investigational steroid epicardial leads was carried out in mature canine with prototype leads. Because the demand for epicardial leads is highest in small infants and the prototype steroid‐eluting lead has been redesigned, this study was carried out in immature swine to evaluate the newly designed lead. Six immature swine (2 at 5 weeks of age and 4 at 6 weeks) underwent epicardial implantation of four porous platinized tip leads: one steroid and one non‐steroid on the right atrium; one steroid and one nonsteroid on the right ventricle. At implantation, the lead terminals were connected to a percutaneous access device subcutaneously placed in the right lateral neck. This allowed chronic measurements by using an insulated needle connected with a cable to the pacing systems analyzer. Measurements were obtained at implantation and weekly for 3 weeks. Compared to the nonsteroid atrial leads, the steroid atrial leads had lower mean thresholds (P < 0.01) at 1,2, and 3 weeks after implantation. The mean threshold values from ventricular steroid leads were also lower and exhibited little increase from implant with the highest mean threshold of only 1.02 V, however, a statisticly significant difference between steroid and nonsteroid was not reached. This newly designed steroid epicardial lead provided favorable results for continual human clinical study.
Reversible Myocardial Depression in Survivors of Cardiac Arrest
Authors: DEANTONIO HARRY J. , KAUL SANJIV , LERMAN BRUCE B.
Published: July 2006

Three patients under 40‐years old who survived cardiac arrest due to ventricular fibrillation were originally diagnosed as having idiopathic dilated cardiomyopathy. Shortly after cardiac arrest, assessment of myocardial function revealed a globally dilated left ventricle in each patient with an estimated ejection fraction between 20% and 30%. Serial assessment of myocardial function, however, showed either normal or near‐normal function by 2 weeks postevent. These findings suggest that myocardial stunning due to hypoperfusion during ventricular fibrillation or the effects of transthoracic shocks may result in profound, reversible myocardial depression in survivors of cardiac arrest. Serial evaluation of left ventricular function may be of value in selected survivors of cardiac arrest in order to evaluate time‐dependent resolution of myocardial dysfunction and may prevent misdiagnosis of idiopathic dilated cardiomyopathy.
Relationship of the Effective Refractory Period and Monophasic Action Potential Duration after a Step Increase in Pacing Frequency
Authors: MORGAN JOHN M. , CUNNINGHAM A. DAVID , ROWLAND EDWARD
Published: July 2006

Adaptation of effective refractory period (ERP) and monophasic action potential (MAP) shortening after a step increase in drive frequency was determined at adjacent endocardial sites in the right ventricle of six patients without myocardial disease. EFIP and MAP shortening occurred simultaneously. ERP shortening and MAP shortening were similar in time course in individuals, although the degree of shortening varied between individuals as the size of the step increase in pacing frequency varied. Shortening of both ERP and MAP was complete after a mean of 67 ± 7.5 seconds. To allow group analysis, the percent change from baseline of action potential duration and ERP was calculated for each patient at intervals during adaptation and mean percent change for the group plotted against lime from the beginning of the step rate increase. A mean step increase in pacing frequency of 49.3% of baseline for the group caused the ERP to shorten by a mean of 18.12% and MAP90 by 17.43% of baseline. There was no significant difference (P = 0.05) between the action potential and ERP adaptation curves of the group. We conclude that in normal myocardium, there is a close relationship between shortening of ventricular ERP and action potential duration after a change in rate.
Long‐Term Antitachycardia Pacing Experience for Supraventricular Tachycardia
Authors: DEN DULK KAREL , BRUGADA PEDRO , SMEETS JOEP LRM , WELLENS HEIN JJ
Published: July 2006

A pacemaker was used to control drug‐resistant reentrant Supraventricular tachycardia (SVT) in 40 patients. An antitachycardia pacemaker was impJanted in 37 for SVT; in one for ventricular tachycardia that could also be used to terminate SVT; in one SVT could be terminated with an activity rate variable pacemaker; and in one a DDD pacemaker was used for prevention and termination of SVT. Twenty patients had AV nodal reentrant tachycardias, eight had tachycardias due to a concealed accessory pathway, eight had a Wolff‐Parkinson‐White syndrome, three had reentrant atrial tachycardias, and one hud atrial gutter. Twenty‐two patients were paced from the right atrium, five from the coronary sinus, ten from the right ventricle, and three had a DDD pacemaker. During a total follow‐up period of 1,503 (mean 38) months an estimated 16,240 episodes of tachycardia were terminated promptly at home, 58 required several attempts, 57 episodes lasted longer than 30 minutes but did not require medical attention, and 11 required hospital admission. Hospital admission for SVT decreased from one per patient‐month (in the 3 months before implantation) to 1 per 137 patient‐months after implantation. Additional reentrant tachycardias occurred in 13 patients. Antiarrhythmic drug therapy in combination with a conservative antitachycardia pacing mode was required in four patients paced from the atrium to avoid pacing induced atrial fibrillation. Antiarrhythmic drug therapy was used in 42% of patients to help control SVT. Conclusions; (1) Drug‐resistant SVTs can be safely and effectively managed on the long‐term with antitachycardia pacemakers. (2) Rapid termination of SVT improved the quality‐of‐life significantly by avoiding prolonged episodes of tachycardia and repetitive hospital admissions.
Benefits of Intracardiac Electrograms and Programmable Sensing Polarity in Preventing Pacemaker Inhibition Due to Spurious Screw‐In Lead Signals
Authors: NALOS PETER C. , NYITRAY WILLIAM
Published: July 2006

False inhibition of ventricular output due to spurious signals from a bipolar Oscor Medical lead (PY58BV) is reported following implantation of a Pacesetter Synchrony DDDR 2020T. Telemetered bipolar and distal unipolar intracardiac electrograms revealed 20 mV spurious signals coming from the distal screw‐in electrode, Reprogramming the sensing channel to unipolar ring prevented inhibition of pacemaker output.
Feasibility of Long‐Term Electrocardiographic Monitoring with an Implanted Device for Syncope Diagnosis
Authors: MURDOCK CHALLON J. , KLEIN GEORGE J. , YEE RAYMOND , LEITCH JAMES W. , TEO WEE SIONG , NORRIS CARO
Published: July 2006

Patients with infrequent recurrent syncope undiagnosed after extensive noninvasive and invasive testing pose a diagnostic and therapeutic dilemma. The purpose of this pilot study was to assess the feasibility of using an implanted, long‐term monitor as an aid to diagnosis in these patients. This was done using commercially available pacemakers with monitoring functions. Sixteen patients (eight males and eight femaiesj, aged 59.7 ± 17 years who had unexplained syncope despite a 12‐lead electrocardiogram, repeated Holter monitoring, exercise testing, echocardiography, an eJectro‐physioJogical study, and a tiJf test (n = 6), were entered into the study. Patients had experienced a mean of 3.3 ± 1 episodes of syncope in the 12 months prior to the study. All provided a history suggestive of Stokes‐Adams attacks and were referred for consideration of pacemaker implantation. Two patients had ischemic heart disease and one patient had a long QT interval. Patients had an Intermedics Nova II or Medtronic Quintech DPG pulse generator capable of recording sensed and paced events implanted with a single right ventricular lead. Syncope or presyncope occurred in ten patients (62%) 4.9 ± 4.2 months after pacemaker implantation. Bradycardia was detected in six patients and four patients had no arrhythmia. In addition to bradycardia, one patient also had tachycardia detected. Pacing therapy resulted in symptom relief in all six patients with syncope or presyncope due to bradycardia. Complications of pacemaker implantation (lead insulation failure) occurred in two patients. One of these patients subsequently had an infection of the generator pocket with associated systemic sepsis. Although the devices used in this study have serious limitations, the results suggest that continuous long‐term electrocardiographic monitoring can be useful in patients with recurrent syncope and a negative diagnostic work‐up. A smaller device with self‐contained electrodes designed for this purpose would be required for wider applicability.
Transthoracic Defibrillation Using Sequential and Simultaneous Dual Shock Pathways: Experimental Studies
Authors: KERBER RICHARD E. , BOURLAND JOE D. , KALLOK MICHAEL J. , HITE PAMELA , PRITCHARD BRUCE , CHARBONNIER FRANCIS , BIRKETT CLAY , FOX‐EASTHAM KAREN , KIESO ROBERT A.
Published: July 2006

Dual pathway sequential DC shocks reduce energy requirements for internal defibrillation. Our purpose was to determine if dual pathway shocks similarJy reduce energy requirements or improve shock success in transthoracic (external) defibrillation. We studied 39 closed‐chest anesthetized mongrel dogs. The dual pathways used were ie/t chest to right chest and left chest to posterior. In eight dogs we also assessed dual shock pathways oriented orthogonally, left lower chest to right upper chest and left upper chest to right lower chest. Four different dual pathway groups were studied: group 1: simultaneous shocks, sinusoidal waveform; group 2: sequential shocks, sinusoidal waveform, 100‐msec shock separation, orthogonal shock pathways; group 3: sequential shocks, sinusoidal waveform, 100 msec shock separation; and group 4: sequential shocks, rectangular waveform (sequential shocks: 2 pulses, 2.5 msec each, 0.1‐msec separation; single shock: 1 pulse, 5 msec). Shocks were given at 50 (J) joules, 100 J and 150 J and curves of energy versus success compared for dual pathway shocks versus single shocks. We found that the highest mean success rates (96 ± SD 9%) were achieved by simultaneous sinusoidal waveform dual pathway shocks at 100 J; this was identical to results achieved by the single pathway sinusoidal waveform comparison shocks at 100 J. Sequential dual pathway sinusoidal shocks separated by 100 msec achieved a mean success rate of 79 ± 31% at 150 J; the comparison single pathway mean success rate was similar: 81 ± 22% at 150 J, Thus, dual pathway sequential or simultaneous transthoracic shocks did not demonstrate clear superiority over single pathway shocks.
Cardiac Electrophysiological Experiments in Numero, Part II: Models of Electrophysiological Processes
Authors: MALIK MAREK , CAMM A. JOHN
Published: July 2006

This article is the second part of a three article series reviewing computer simulation models of the heart, in particular of cardiac electrophysiology. The previous section of the review discussed the methodological principles of the construction und application of computer models. This article overviews the development of mathematical and computer modeling studies applied to cardiology. The models are classified according to the physiological processes that were simulated: this article distinguishes models oriented to cardiac mechanics, hemodynamics, and electrophysiology. The electrophysiology models are discussed in more detail and the review classifies them into four main categories: models of cellular processes, models of tissue behavior, models of the ventricular electric field, and models of macroconduction disturbances. In each category, the historical development of the models and their key achievements are described.
Triggered Activity As a Possible Mechanism for Arrhythmias in Ventricular Hypertrophy
Authors: CHARPENTIER FLAVIEN , BAUDET STÉPHANE , LE MAREC HERVÉ
Published: July 2006

To study the cellular mechanisms of arrhythmias occurring in cardiac hypertrophy, we performed standard microelectrode studies on pupillary muscles isolated from control (group N) and hypertrophied ferrets right ventricles. Different stages of hypertrophy, induced by pulmonary banding, were studied: 10–22 days (group H1), 4–6 weeks (H2), and 51/2–6 months (H3). During the development of hypertrophy, under p‐adrenergic stimulation, triggered activity (TAJ induced by delayed afterdepolurizalions appeared in 2 of 5 muscles in group H1 and 8 of H in group H2. This arrhythmia was absent in N muscles, as well as in H3, despite a pronounced prolongation of the action potentials at 50% (100 ± 9.3 msec in group H3 vs 67 ± 5.7 msec in H2; P < 0.01) and 90% of repolarization (225 ± 8.7 in H3 vs 185 ± 7.4 msec in H2; P < 0.02). The presence of TA was associated with an increase in the intracellular calcium activity (144 ± 60 nM in H2 vs 47 ± 9 nM in N; P < 0.05). TA properties were as follows. Triggering frequency increased as p‐adrenergic stimulation increased, as pacing cycle length (PCL) decreased, and as duration of the prestimulative pause increased. The duration of salvos of TA increased as duration of the prestimulative pauses increased (NS). The coupling interval of the first triggered beat decreased as PCL decreased (P < 0.001). The minimal cycle length of salvos of TA was not modified by these parameters. It is concluded that delayed afterdepolarizations‐induced TA may occur under β‐adrenergic stimulation during the first stages of ventricular hypertrophy. This could partly explain the occurrence ofadrenergic‐dependent arrhythmias in ventricular hypertrophy.
The Mythology of Threshold Variations as a Function of Electrode Surface Area
Authors: STOKES KENNETH B. , BIRD TERI , GUNDERSON BRUCE
Published: July 2006

It has been established that the chronic thresholds of cardiac pacing leads vary as a function of the (spherical) electrode's radius or (geometric) surface area and the thickness of fibrotic encapsulation.1,2 Where the radius of the electrode is equal to the thickness of the fibrous capsule (about 0.7 to 1 mm for polished surfaces), threshold should be at a minimum.1 Where the radius of the electrode is larger or smaller than the thickness of the fibrous capsule, then thresholds should increase since the electric field strength required to stimulate decreases as the square of the distance between the electrode's surface and stimulatable tissue.1 In addition, it has become (incorrectly) accepted that small electrodes do not sense well.3 About 8‐mm2 electrodes, therefore, became the “standard” surface area, providing the best tradeoffs between pacing and sensing. Analysis of 18 years of canine data in our laboratory, however, suggest that these relationships may be overemphasized for the surface areas of clinical interest. In fact, new small porous and steroid‐eluting electrodes do not have high thresholds, are efficient, and their sensing is excellent.
A New Approach to the Prevention of Endless Loop Tachycardia in DDD and VVD Pacing
Authors: ROGNONI GIORGIO , OCCHETTA ERALDO , PERUCCA ANTONELLO , MAGNANI ANDREA , FRANCALACCI GABRIELLA , AUDOGLIO ROBERTO , ROSSI PAOLO
Published: July 2006

Endless loop tachycardia (ELT) is a possible complication in dual chamber pacing; it is usually prevented by programming the atrial refractory period (PVARP) longer than the retrograde ventriculoatrial (VA) conduction interval; this in some patients limits the upper rate. In 15 patients with a DDD (nine patients) or a single‐pass lead VDD pacemaker (six patients) and retrograde atrial activation, telemetric recording documented a significant difference in amplitude of antegrade, and retrograde atrial potentials (VDD 1.21 ± 0.32 mV vs 0.56 ± 0.23 mV, P = 0.008; DDD 2.7 ± 1 vs 1.8 ± 1 mV, P ‐ 0.038; Student's t‐test for paired data). In 3/15 patients ELT stopped after programming of atrial sensitivity to a value. greater than the retrograde P wave amplitude; in 11/15 patients this occurred at a sensing value lower than or equal to retrograde P wave amplitude with a high pass band filter operating. One patient required PVARP lengthening. Holter monitoring showed no more ELTs. In most patients with a DDD or single‐pass lead VDD pacemaker with widely programmable sensing amplitude and Hi/Low bandpass filters. individual programming of atrial channel sensitivity prevents ELT without affecting the PVARP and, consequently, upper rate limit.
Comparison of Titanium‐Mesh and Porous Disc Electrodes for Epicardial Defibrillation
Authors: RUBIN LEO , ROSENBERG DAVID , PARSONNET VICTOR , VILLANEUVA ALEXANDER , FERRARA‐RYAN MICHELLE
Published: July 2006

The object of this study was to compare the effectiveness of chronically implanted porous electrodes with that of smooth mesh titanium electrodes of the same diameter but smaller effective surface area. The criteria used in evaluating the electrodes were (1) acute, subacute, and chronic resistance and (2) acute, subacute, and chronic defibrillation thresholds. Electrode pairs 2.5 cm in diameter were implanted in each of 17 dogs (ten mesh and seven porous). One electrode of each pair was sutured to the right ventricle and one to the left ventricle near the cardiac apex. Defibrillalion threshold energy and total resistance were measured at the time of implantation and again 6 and 12 weeks after implantation. The mean initial resistance of the titanium electrodes was 131.7 Ω; the mean defibrillation values /or the porous electrode implant were 96.9 Ω and 7,5 joules, respectively. Three to 6 weeks after implantation, the values for the titanium mesh electrode were 88.9 Ω and 12.0 joules, while those for the porous electrode were 59.9 Ω and 8.0 joules. In the chronic state, the figures for the titanium mesh electrode were 78.1 Ω and 13.0 joules, while those for the porous electrode were 64.3 Ω and 8.3 joules. We conclude that defibrillation can be achieved successfully with small epicardial electrodes. The findings suggest that a porous electrode, with its larger effective surface area, has lower electrode/tissue interface resistance in the acute and chronic phases, and, therefore, provides lower defibrillation threshold energy.
When Is it Safe not to Replace an Implantable Cardioverter Defibrillator Generator?
Authors: TCHOU PATRICK , AXTELL KATHY , ANDERSON ALFRED J. , KEIM STEPHEN , SRA JASBIR , TROUP PAUL , JAZAYERI MOHAMMAD , AVITALL BOAZ , AKHTAR MASOOD
Published: July 2006

In most reports on patients receiving implantable cardioverter defibrillators. shocks were received mainly during the first 2 to 3 years. Thus, the question had been raised as to the need for device replacement after 3 or 4 years if no shocks had been received. In order to answer this question, shock experience in 184 putients receiving the implantable cardioverter defibrillator was analyzed. Patients were followed for a mean of 24 ± 18.7 months. A patient's shock was judged to be appropriate if there was electrocardio‐graphic documentation of sustained ventricular tachyarrhythmia at the time of shock or if it was preceded by sudden onset of presyncopal or syncopal symptoms. The majority of patients had coronary artery disease. In approximately two‐thirds of patients, left ventricular ejection fraction was below 40%. One hundred fourteen patients had inducible sustained monomorphic ventricular tachycardia. On follow‐up, there were 29 deaths, five of which were sudden. Sixty‐eight patients received an appropriate shock during follow‐up (37%). Over 90% of these 68 received their first shock within the 2 years after implant. The actuarial risk of receiving an appropriate shock by the fifth year after implant was 69%. Conversely, 31% of patients who survived 5 years had not received an appropriate shock. Hazard analysis indicates that there is a high incidence of first appropriate shock during the year following implant. Subsequently, the incidence dropped to a relatively steady rate with a rise in this rate during the fifth year. This analysis suggested a bimodal distribution of appropriate shocks. The results indicate that implantable cardioverter defibrillator generators should be replaced even up to the fifth year despite the fact that a patient had not received an appropriate shock.
A New Approach Towards Defibrillation Electrodes: Highly Conductive Isotropic Carbon Fibers
Authors: ALT E. , THERES H. , HEINZ M. , ALBRECHT K. , GEORG H. , BLOEMER H.
Published: July 2006

A new carbon fiber material was studied for its potential benefit in defibrillation electrodes. Miniaturization of the fiber production can result in small strands with extremely large surface areas. Two carbon fiber patches and a single carbon fiber bundle were used for the purposes of this study, and the results were compared to those obtained with conventional titanium/mesh patch electrodes. Tests performed in a saline filled tank revealed considerably lower resistances through the carbon material when compared to standard mesh electrodes. There was also a higher peak current flow with lower voltage. The carbon fibers exhibited lower impedance for defibrillation and this may be related to low polarization known to occur with carbon materials. This new carbon material may prove to be useful and further research is required.
A Comparison of Intravenous Propafenone and Flecainide in the Treatment of Tachycardias Associated with the Wolff‐Parkinson‐White Syndrome
Authors: O'NUNAIN SEAN , GARRATT CLIFFORD J. , LINKER NICHOLAS J. , GILL JASWINDER , WARD DAVID E. , CAMM A. JOHN
Published: July 2006

We compared the electrophysiological effects of intravenous propafenone andflecainide on accessory pathway conduction by a randomized crossover study in 16 patients with Wolff‐Parkinson‐While syndrome. The antegrade refractory period of the pathway increased from 256 ± 18 msec at baseline to 288 ± 13 msec on propafenone (P < 0.05) find to 296 ± 2 7 msec on flecainide (P = 0.075). The minimum preexcited HR interval during atrial fibrillation or incremental atrial pacing was prolonged from 225 ± 37 msec to 262 ± 22 msec by propafenone (P < 0.05) and to 301 ± 31 msec by flecainide (P < 0.005). The prolongation was significantly greater with flecainide than propafenone (P < 0.05). Both drugs increased tachycardia cycle length (TCL) from 310 ± 35 msec to 354 ± 37 msec (propafenone P < 0.005) and to 352 ± 37 msec (flecainide P < 0.01). Both propafenone and flecainide blocked antegrade conduction in the pathway in five patients. Both drugs rendered atrial fibrillation noninducifale in seven patients and orthodromic tachycardia nonindudble in five patients. Conclusions: (1) Fiecainide causes a greater prolongation of minimum preexcited RR interval than propafenone; (2) There is no significant difference between propafenone and flecainide on the inducibility of arrhythmias, TCL, or incidence of antegrade conduction block.
Sensing Through the Esophagus for Temporary Atrial Synchronous Ventricular VDD Pacing
Authors: VROUCHOS GEORGE TH. , VARDAS PANOS E.
Published: July 2006

The purpose of this study was to evaluate the effectiveness and safety of temporary VDD pacing using an esophageal electrode for sensing of the atrial electrogram. We studied 15 patients, 8 men and 7 women, aged 77 ± 2 years (mean ± SE, range 61–90), with severe atriovenfricular (AV) conduction disturbances. A 24‐hour beat‐to‐beat ECG analysis was used to evaluate the effectiveness of the pacing system and special tests were performed to test the stability of pacing and sensing. The system performed satisfactorily in 12 of the 15 patients. The 24‐hour Holter ECG monitoring revealed the following percentages of beats: 96.32 ± 0.5 VDD, 2.92 ± 0.6 VVI, and 0.14 ± 0.05 paced beats resulting from pseudosensing. All the latter were single, with no bigeminy or salvos. The results of the stability tests were as follows: the percentage of VDD beats was significantly lower than the 24‐hour mean when the patient lay on his right side (92.8 ± 0.5, P < 0.001), during the swallowing of liquids (91.26 ± 0.4, P < 0.001) and soft foods (84.2 ± 1.4, P < 0.001), and during coughing (94.2 ± 0.6, P < 0.001). The percentage of VVI type beats increased in these four cases (6.7 ± 0,5, 7.2 ± 0.3, 13.2 ± 1.2 and 4.8 ± 0.4, respectively, P < 0.001 in each case). The percentage of ectopic beats due to pseudosensing did not change significantly during any of the tests. These results indicate that the method described is a safe and effective technique for temporary VDD pacing.
Loss of Atrial Signal Detection with Increasing Sensitivity Settings: A Software Problem and its Practical Solution
Authors: FRÖHLIG GERD , SCHWERDT HOLGER , BERG MONIKA , SPITZER STEFAN , SCHIEFFER HERMANN
Published: July 2006

A logic error in the software of Cosmos II results in apparent malsensing of atrial signals at high rather than low sensitivity settings. The paradoxical function was found in 54 out of 87 units tested (= 62%) if the atrial sensitivity was increased and the ventricular refractory period was lengthened beyond critical limits that could be defined individually. The problem inherent in both unipolar (66%) and bipolar systems (54%) is attributed to a summation of a physiological signal and internal noise, which has to be detected at the atrial level within a specific timing window to disable atrial sensing for the next pacing cycle. The malfunction virtually disappears if the ventricular refractory period does not exceed 210 msec. It is recommended, therefore, that Cosmos II pacemakers be left at their nominal ventricular refractory value (200 msec).
Right‐sided Infective Endocarditis with Acquired Tricuspid Valve Stenosis Associated with Transvenous Pacemaker: A Case Report
Authors: ENIA FRANCESCO , MAURO RENATO LO , MESCHISI FRANCESCO , SABELLA FRANCESCO PAOLO
Published: July 2006

Five years prior to presentation, a 29‐year‐old woman received a (ransvenous pacemciker (DDD) for sick sinus syndrome and nodo‐hisian pathology. After pacemaker insertion, she complained of recurrent febrile episodes. Her pacemaker related endocarditis was quite unusual for the infecting organism (a micrococcus) and for an acquired tricuspid valve stenosis, The suspected cause was confirmed at surgery.
A Prospective Study of Changes in Right Ventricular dP/dt During Ventricular Tachycardia
Authors: KAPADIA KETAN A. , WOOD MARK A. , LU BIN , VALENTA HARRY , ELLENBOGEN KENNETH A.
Published: July 2006

The automatic implantabie cardioverter defibrillator (AICD) has significantly decreased mortality in high risk ventricular tachycardia (VT) patients. The AICD provides treatment based on ventricular rate, sometimes leading to high energy shocks in conscious patients with stable VT, or patients with sinus or supraventricular tachycardia. Other physiological parameters, such as maximal positive and negative systolic right ventricular (RV) dP/dt (RV +dP/dfmax, RV ‐dP/dtmax, respectively), may be included in detection algorithms for future implantabie defibrillators. We studied frequency band limited positive and negative RV dP/dtmax before, during, and after 13 episodes of VT lasting at least 40 beats in duration in nine male patients. The mean (± SEM) RV + dP/dtmax, dropped by 120 ± 28 mmHg/sec (P < 0.001) during the first five beats of VT. RV +dP/dtmax then slowly rose toward baseline levels until a significant overshoot occurred during the first ten beats following VT termination (δ= 234 ± 58 mmHg/second, P < 0.002). RV +dP/dtmax correlated poorly with mean arterial pressure (r = 0.32, P > 0.1), systolic blood pressure (r = 0.19, P > 0.1), and VT cycle length (r == 0.34, P > 0.1). Conversely, RV ‐ dP/dtmax rose during the first ten beats of VT (74 ± 27 mmHg/sec, P > 0.05) and then slowly drifted back toward baseline levels. Like RV + dP/dtmax, RV ‐dP/dfmax overshot baseline levels during the recovery phase (‐ 108 ± 48 mmHg/sec, P < 0.05). RV ‐dP/dtmax also did not correlate well with mean arterial pressure (r = 0.06, P > 0.1), systolic blood pressure (r = 0.077. P > 0.1), or VT cycle length (r = 0.064, P > 0.1), We conclude that frequency band limited measurement of positive and negative RV dP/dtmax poorly reflect hemodynamic stability during VT and would probably not be useful as a hemodynamic sensor in AICDs.