bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation in P Wave Amplitude Immediately After Pacemaker Implantation: Possible Mechanism and Implications for Early Programming
Authors: SHANDLING ADRIAN H. , CASTELLANET MARK J. , THOMAS LAVERGNE A. , MULVIHILL DANIEL F. , FEUER JOSHUA M. , MESSENGER JOHN G.
Published: July 2006

SHANDLING, A.H., et al.: Variation in P Wave Amplitude Immediately After Pacemaker Implantation: Possible Mechanism and Implications for Early Programming The P ivave amplitude (PWA) plays an important role in doterirnning atrial sensing capabilities. To assess early PWA change, we compared lhe unipolar PWA in 43 patients at the time of atrial lead placement, measured by a pacing systems analyzer, to the unipolar PWA recorded at the end of pacemaker surgery, from telemetered airial endocardial electrograms. Individual PWA varied from a decrease of 5.2 mV lo an increase of 2 mV (−63% to 267%). In 33 patients with active fixation leads, the implant PWA was 1.96 ± 0.99mV versus 2.4 ± 1.4 mV after surgery. In 11 patients with passive fixation leads, the implant PWA was 2.8 ± 1.9 mV versus 1.9 ± 0.8 mV after surgery. The PWA change, measured as the difference between the postsurgical and implant PWA was 0.43 ± 0.8mV in active versus −0.86 ± 1.6 mV in the passive fixation lead groups (P < 0.05). Considerable change in individual P wave ampiitude can therefore occur very early after pacemaker implantation. The direction differs significantly between active (predominantly positive) and passive fixation groups (predominantly negative). These data suggest that an adequate margin of safety is important when initially programming atrial sensitivity, particularly when using passive fixation leads.
Efficacy of Nadolol Alone or in Combination with a Type IA Antiarrhythmic Drug in Sustained Ventricular Tachycardia: A Prospective Study
Authors: MUNSIF ANAND N. , SAKSENA SANJEEV
Published: July 2006

MUNSIF A.N., et al.: Efficacy of Nadolol Alone or in Combination with a Type IA Antiarrhythmic Drug in Sustained Ventricular Tachycardia A Prospective Study. We examined the clinical efficacy and safety of intravenous nadolol acutely, as well as chronic nadolol alone or combined with a type IA antiarrhythmic drug in 19 patients with sustained ventricular tachycardia and heart disease, mean age 62 ± 15 years, and mean left ventricular ejection fraction 39 ± 8%. Patients underwent electrophysiological studies in the drug‐free state (control), after intravenous nadolol (dose = 0.05 mg/kg), and oral nadolo) (dose = 80 mg/day) for 5 days alone or in combination with a type IA antiarrhythmic drug. Electrocardiographic and electrophysiological effects as well as ventricu/ar tachycardia induction at electrophysiological study were analyzed. Long‐term therapy with oral nadolol alone or in combination with a type IA antiarrhythmic drug was evaluated in responders. Intravenous nadolol prolonged RH and QRS intervals but had no effect on PR and QTc intervals. Oral nadolol alone tended to prolong RR intervals (P = 0.08). Oral nadolol with type IA antiarrhythmic drug prolonged RR and QTc intervals (P < 0.001). The mean right ventricular effective refractory period tended to prolong after intravenous nadolol alone (from 251 ± 29 to 263 ± 25 msec, P = 0.08). Oral nadolol and type IA antiarrhythmic drugs did not prolong right ventricular effective refractory period (P = 0.3). Eighteen patients had inducible sustained ventricular tachycardia at control electrophysiological study. After intravenous nadolol, ventricular tachycardia was no longer in‐ducible in seven patients. Ventricular tachycardia did not recur and remained noninducible in two of six patients who tolerated oral nadolol alone. Mean right ventricular effective refractory period prolonged from baseline values (from 249 ± 30 to 271 ± 30 msec, P < 0.02) in patients who became noninducible on intravenous nadolol. In patients who remained inducible. mean right ventricular effective refractory period remained unchanged (from 253 ± 29 to 258 ± 22 msec, P > 0.2). In nonresponders to intravenous or oral nadolol, oral nadolol, and type IA antiarrhythmic drug suppressed ventricular tachycardia induction in two often patients. During follow‐up, three patients continued on oral nadolol alone (one patient) or oral nadolol and type IA antiarrhythmic drug (two patients). Adverse effects resulting in nadolol discontinuation occurred in five patients. Therefore, we concluded that intravenous nadolol is effective in acute suppression of inducible ventricular tachycardia in selected patients. Oral nadolol alone or in combination with type IA antiarrhythmic drug is infrequently effective and poorly tolerated by this patient population. In addition, electrophysiological studies on intravenous nadolol do not predict the outcome of oral nadolol therapy.
Metabolic Changes and Mitochondrial Dysfunction Early Following Transthoracic Countershock in Dogs
Authors: TROUTON T.G. , ALLEN J.D. , YONG L.K. , ROONEY J.J. , ADGEY A.A.J.
Published: July 2006

TROUTON, T.G., et al.: Metabolic Changes and Mitochondrial Dysfunction Early Following Transthoracic Countershock in Dogs The mechanisms of myocardial injury and necrosis /ollon'ing transfhoracic shocks from a direct current cardiac defibrillator were investigated in adult greyhounds. Myocardial lactate extraction became negative maximally at 1 minute, following two (mean –22%± SEM 23) or five (–193%± 135) shocks and returned to baseline in 6–15 minutes. Myocardial necrosis assessed at 4 hours following the shock period was 0.05 g (± 0.03) after two shocks, 6.69 g (± 1.76) after five shocks and zero in controls. In further experiments, dogs received five or zero (dummy) shocks and mitochondria were isolated from their hearts following excision within 1 minute of receiving the final shock. Maximal oxygen consumption in right ventricular mitochondria was lower than the unshocked controls ivith both giutamate (66.9 ± 9.4 nanoatoms of oxygen/mg per minute, n = 9 vs 86.6 ± 13.6 nanoatoms/mg per minute, n = 7) and succinate (96.2 ± 8.7 nanoatoms/mg per minute, n ‐ 9 vs 119.5 ± 14.4 nanoatoms/mg per minute, n = 7) as substrates. Using electron spin resonance spectroscopy, an increase in a peroxyl‐free radical with g = 2.031 was detected in myocardial tissue after two internal shocks (50 joules stored energy, 0.5‐minute intervals). We conclude that mitochondria) dysfunction and free‐radical generation are likely contributors to cellular injury following multiple countershocks.
Left Atrial Herniation Through a Partial Pericardial Defect: A Rare Cause of Syncope
Authors: HOORNTJE JAN C. A. , MOOYAART EDUARD L. , MEUZELAAR KOOS J.
Published: July 2006

HOORNTJE, J.C.A., et al.: Left Atrial Herniation Through a Partial Pericardial Defect: A Rare Cause of Syncope A case of herniation of the left atrial auricle through a partial congenital pericardial defect is presented. The main symptoms were short periods of syncope that were not related to the presence of an incidental type II Wenckebach block. Intravenous digital subtraction angiography established the diagnosis and is regarded as superior to catheterization of the heart in uncomplicated cases.
The Electrocardiographic Manifestation of Combined AV Nodal Wenckebach Periodicity and Reentry
Authors: SCHWEITZER PAUL
Published: July 2006

SCHWEITZER, P.: The Electrocardiographic Manifestation of Combined AV Nodal Wenckehach Periodicity and Reentry Presented are three patients with Wenckebach type second degree AV block that was complicated with AV nodal reentry producing different arrhythmias. The common presentation of manifest AV nodal reentry is an incomplete Wenckebach periodicity, whereby the retrograde impulse interrupts the Wenckebach cycle; rarely, the retrograde impulse initiates an AV junctional reentrant tachycardia. The documentation of concealed AV nodal reentry is more difficult and should be considered if there is a sudden increase of the PR interval in the Wenckebach cycle.
Catecholamine Sensitive Right Ventricular Outflow Tract Tachycardia: Intraoperative Mapping and Ahlation of a Free‐Wall Focus
Authors: WILBER DAVID J. , BLAKEMAN BRADFORD M. , PIFARRE ROQUE , SCANLON PATRICK J.
Published: July 2006

WILBER, D.J., et al.: Calecholamine Sensitive Right Ventricular Outflow Tract Tachycardia: Intraoperative Mapping and Ablation of a Free‐Wall Focus A patient with catecholamine‐sensitive right ventricular ouiflow tract tachycardia refractory to pharmacological therapy underwent intraoperative mapping and cryoablation. Epicardial and endocardial mapping demonstrated earliest ventricular activation in the free‐wall of the outflow tract, and cryoablation of the area resulted in surgical cure. No histologic abnormalities at the site of tachycardia origin were detected. Catecholamine sensitivity does not appear to result from a diffuse myocardial process, and permanent ablation of the tachycardia in this group of patients with a regional procedure is feasible,
Short‐Term and Long‐Term Changes of Left Ventricular Volumes During Rate‐Adaptive and Single‐Rate Pacing
Authors: SEDNEY MEREDITH I. , WEIJERS ERIC , VAN DER WALL ERNST E. , ADIPRANOTO JEEEREY D. , CAMPS JAN , BLOKLAND JACOBUS A.K. , PAUWELS ERNEST K.J. , SCHIPPERHEIJN JOHANNES J. , BUIS BEERT , BRUSCHKE ALBERT V.G.
Published: July 2006

SEDNEY, M.L, et al.: Short‐Term and Long‐Term Changes of Left Ventricular Volumes During Rate‐Adaptive and Single‐Rate Pacing To evaluate the adaptation of the heart to exercise during pacing, 15 patients with permanent endocardial pacemakers were studied; nine patients had atrioventricular universal (DDD) pacemakers (Symbios 7005) and six patients had activity detecting rate‐responsive ventricular (WIR) pacemakers (Activitrax 8403). Left ventricular function in each patient during rate variable pacing was compared to ventricular function during VVI single‐rate pacing. End‐systolic and end‐diastolic volume changes during exercise were measured by radionuclide angiography and the amount of volume change was used to assess left ventricular function. Both short‐term (within 4 hours) and long‐term measurements (after at least 4 weeks) were made at rest and at 50% of the maximal exercise capacity in DDD or VVIR mode and were compared with VVI single‐rate pacing. All patients, when changed from DDD or VVIR mode to VVI single‐rate pacing showed a significant increase of the end‐diastolic volume during exercise, which increased even more after long‐term VVI pacing. During long‐term rate variable pacing, there was no increase of the end‐diastolic volume during exercise. DDD or VVIR pacing initially showed a substantial increase of the end‐systolic volume during exercise combined with a decrease of left ventricular ejection fraction, suggesting a decrease of the left ventricular contractility. After 4 weeks, contractility improved both with DDD and VVIR pacing. We conclude that short‐term DDD and VVIR pacing induces a temporary impairment of left ventricular function that improves after 4 weeks, whereas long‐term VVI pacing is associated with left ventricular dilatation even at moderate levels of exercise.
Programmed Ventricular Stimulation During Variant Angina: Report of a Case
Authors: LEMERY ROBERT , GERSH BERNARD J.
Published: July 2006

LEMERY, R., et al.: Programmed Ventricular Stimulation During Variant Angina: Report of a Case Programmed ventricular stimulation was performed in a 74‐year‐old patient who had a history of syncope following chest pain. In the baseline state, ventricular tachycardia was not inducible. Immediately following the study protocol, the patient complained of her usual chest pain and ST elevation was documented in lead II with reciprocal ST depression in leads AVF and V1, Programmed ventricular stimulation was repeated (presumobly during the occlusive phase of coronary spasm) and a polymorphic rentricular tachycardia with a cycle length of 200 msec was repeatedly induced. Following intravenous nitroglycerin and resolution of chest pain, ventricular tachycardia was not inducible. Coronary angiography with ergonovine testing confirmed coronary spasm of the right coronary artery. We speculate that syncope was caused by ventricular tachycardia following coronary artery spasm. During a 12‐month follow‐up with calcium blockers and nitrates, there has been no recurrence of chest pain or syncope.
Bradycardia‐Dependent Block and Fatigue Phenomenon of the His‐Purkinje System Manifested During Upright Tilt
Authors: HERNANDEZ ROSA , MANN DAVID E. , REITER MICHAEL J.
Published: July 2006

HERNANDEZ, R., et al.: Bradycardia‐Dependent Block and Fatigue Phenomenon of the His‐Purkinje System Manifested During Upright Tilt Atrioventricular (AV) block occurring in the His‐Purkinje system may occur sporadically and can be difficult to document. In this article, we describe two patients with spontaneous episodes of AV biock, in whom the use of upright tilt during electrophysiological testing led to a diagnosis of His‐Purkinje disease. In both cases, testing in the supine position only uncovered mild or no abnormalities of infra‐nodal conduction. In the first case, high grade block distal to the His occurred and the mechanism appeared to be bradycardia‐dependent block. In this case, increased sympathetic tone due to upright tilt may have enhanced the slope of phase 4 depolarization in abnormal His‐Purkinje cells, leading to block. In the second case, high grade block distal to the His was seen with upright tilt and the mechanism of block appeared to be fatigue phenomenon in the His‐Purkinje system. These cases empha size the elusive nature and varied mechanisms of His‐Purkinje block and illustrate the utility of electrophysiological testing in the upright position in patients with suspected conduction system disease.
Closed Loop Control of Rate Adaptive Pacing: Clinical Assessment of a System Analyzing the Ventricular Depolarization Gradient
Authors: PAUL VINCE , GARRATT CLIFFORD , WARD DAVID E. , CAMM A. JOHN
Published: July 2006

PAUL, V., et al.: Closed Loop Control of Rate Adaptive Pacing: Clinical Assessment of a System Analyzing the Ventricular Depolarization Gradient Closed loop control of rate adaptive pacing has theoretical advantages over current rate responsive pacemakers. The first available system (which senses the ventricular depolarization gradient) has been evaluated in ten patients. The pacing response to a variety of exercise and nonexercise stimuli was assessed. Response to isotonic exercise was prompt and proportional to the exertion involved while isometric exercise and mental stress produced obvious but more gradual increases in pacing rate. In seven patients, comparison between the intrinsic P wave and pacing rate showed a high correlation during exercise (r = 0.91) and mental activity (r = 0.87). Postural changes induced a paradoxical response. Closed loop rate responsive pacing based upon analysis of the ventricular depolarization gradient produces a fast and appropriate rate response to most physiological stimuli.
Discordant Effects of Carotid Sinus Massage and Intravenous Adenosine in Atypical (Fast‐Slow) Atrioventricular Nodal Reentrant Tachycardia
Authors: MILCHAK MARK A. , GREENBERG MARK L.
Published: July 2006

MILCHAK, M.A., et al.: Discordant Effects of Carotid Sinus Massage and Intravenous Adenosine in Atypical (Fast‐Slow) Atrioventricular Nodal Reentrant Tachycardia The precise mechanism underlying supraventricular tachycardia with a long R‐P interval is often difficult to assess noninvasively. Carotid sinus massage has been used traditionally to produce transient AV nodal conduction delay at the bedside, and may be of diagnostic or therapeutic benefit. More recently, adenosine has also been shown to be useful in this situation. We report the case of a patient with an incessant long R‐P tachycardia in whom the response to CSM was misleading while the response to adenosine was diagnostic. The electrophysiologic responses to both maneuvers are displayed, and a mechanism for the discordant responses is proposed.
Impaired Activity Rate Responsiveness of an Atrial Activity‐Triggered Pacemaker: The Role of Differential Atrial Sensing in its Prevention
Authors: SHANDLING ADRIAN H. , CASTELLANET MARK J. , THOMAS LAVERGNE , RYLAARSDAM ARLENE , VALIKAI KEN , MESSENGER JOHN C. , ELLESTAD MYRVIN H.
Published: July 2006

SHANDLING, A.H., et al.: Impaired Activity Rate Responsiveness of an Atrial Activity‐Triggered Pacemaker: The Role of Differential Atrial Sensing in its Prevention The physiological benefit of rate responsive, single‐chamber cardiac pacing is well documented. We studied the activity response of nine atrially placed Activitrax II pacemakers. Seven patients were noted to have an inadequate activity‐rate response with maximal pacing rates of 85 to 101 beats/min. Marker Channel(tm) analysis revealed that the upper rate timeout was reset by far‐field R wave sensing, even when sensing occurred in the atrial refractory period. These 9 pacemakers were tested by atrial sensitivity adjustment for ability to exclude far‐field R wave sensing, while preserving P wave sensing. Unipolar implantation data were then examined for predictors of this differential far‐R and P‐wave sensing. Differential atrial sensing occurred in 4/9 pacemakers (2/2 bipolar in the right atrial appendage; 0/1 bipolar in the coronary sinus; and A/9 unipolar). An empirically developed index utilizing unipolar implant parameters discriminated outcomes for 8/9 unipolar pacemakers. We conclude that; (1) the rate responsiveness of the atrial Activitrax II pacemaker is limited by far‐field R wave sensing even when this occurs during atrial channel refractoriness; (2) reprogramming atrial sensitivity to differentially sensed P and far‐field R waves may restore appropriate rate responsiveness; and (3) although a unipolar implant discriminant index may correctly identify adequacy of future rate responsiveness, the atrial application of the Activitrax II pacemaker is cautioned until further validation is forthcoming, particularly when used in unipolar and coronary sinus applications.
Induced Sustained Ventricular Tachycardia in Nonischemic Dilated Cardiomyopathy: Dependence on Clinical Presentation and Response to Antiarrhythmic Agents
Authors: CONSTANTIN LUIS , MARTINS JAMES B. , KIENZLE MICHAEL G. , BROWNSTEIN SHELDON L. , MCCUE MICHAEL L. , HOPSON ROSANNE C.
Published: July 2006

Thirty‐one patients with nonischemic dilated cardiomyopathy either idiopathic or due to regurgitant valvular disease were studied in the cardiac electrophysiology lab. The indications for study were sustained ventricular tachycardia (VT) in 26, ventricular fibrillation (VF) in 11, and syncope of unknown etiology in 4. Sustained VT was reproducibly induced in 17 patients, including 12 with a history of sustained VT, 2 with VF and 3 with syncope. Of 15 patients undergoing serial antiarrhythmic drug studies, sustained VT was rendered noninducible or nonsustained in 23. Three had recurrent arrhythmic events while on therapy predicted to be effective. One of 2 patients discharged on a regimen predicted to be ineffective had a recurrence of sustained VT that resulted in cardiac arrest. Of 14 patients in whom sustained VT could not he reproducibly induced, 2 subsequently had spontaneous occurrences of sustained VT, and 2 experienced aborted sudden death. These results suggest the following; (1) the induction of sustained VT in the setting of nonischemic dilated cardiomyopathy is dependent on the clinical presentation; (2) antiarrhythmic drugs frequently render sustained VT noninducible or nonsustained; (3) antiarrhythmic drug suppression of inducible sustained VT predicts long‐term prevention of spontaneous recurrences; and (4) noninducibility of sustained VT in the baseline state does not predict freedom from subsequent episodes of VT or sudden death.
Determination of Myocardial Depolarization and Repolarization Times Using the Unipolar Ventricular Evoked Potential: Contrasting Effects of Stimulus Interval and Isoprenaline in the Isolated Perfused Rahhit Heart
Authors: WALTON CHRISTOPHER , ECONOMIDES APOLLO PLATO , GERGELY STEPHEN
Published: July 2006

The effects of changes in stimulus interval and the infusion of isoprenaline upon myocardial depolarization and repolarization times have been determined using the unipolar ventricular evoked potential. An isolated perfused rabbit heart was the experimental vehicle and the stimulus‐to‐R wave (St‐R) and R wave‐to‐end (R‐E) of complex time intervals were used as measures of depolarization and repolarization times, respectively. Variation in the stimulus interval was shown to have highly statistically significant effects upon both of the parameters of the unipolar paced evoked potential that were investigated. Myocardial repolarization time is increased at longer intervals, while activation time is reduced. Isoprenaline was found to reduce the duration of the R‐E interval of the unipolar ventricular evoked potential when infused at a constant rate at a fixed stimulus interval. At the maximum concentration of the drug, when stimulus interval was just shorter than the intrinsic RR interval, it was estimated that one third of the total change in the R‐E interval was due purely to the effects of decreased stimulus interval. It proved impossible to identify any effect of isoprenaline infusion upon the St‐R interval. The absence of any effect of isoprenaline on the St‐R interval of the evoked potential suggests that it may serve as a monitor of purely stimulus interval dependent variations of the signal.
Deduction of Biphasic Phase Response Curves from Ventricular Parasystole
Authors: ÅHLFELDT H. , NILSSON G. , BANDH S. , JONASON T. , AHREN T. , RINGQVIST I.
Published: July 2006

The mechanisms behind ventricular premature beats may be divided into two main categories, reentry and modulated parasystole. Although it is relatively easy to distinguish among arrhythmia generating mechanisms on the cellular level, it is far more difficult in the clinic. Modulation of ventricular parasystole by sinus beats has been shown to result in a biphasic phase response curve. Two cases are reported where the deduction of such phase response curves from long‐term ECG recordings is discussed and described as a stepwise procedure.
Design Dependent Loss of Telemetry: Uplink Telemetry Hold
Authors: LINDENBERG BARRY S. , HAGAN CATHERINE A. , LEVINE PAUL A.
Published: July 2006

Bidirectional telemetry in cardiac pacing is the ability of the programmer to communicate with the pacemaker and vice versa. It is an essential capability if one is to interrogate the pacemaker as to its programmed parameters and to access the diagnostic capabilities incorporated in the present generation pacemakers. Pacemaker to programmer telemetry capability was lost in two Medtronic SymbiosRpacemakers due to a design eccentricity termed “uplink telemetry hold”. It is initiated by a complex sequence of spontaneous sensed and internal timing events, once activated it cannot be reversed in the clinical setting. It is potentially dangerous in that the subsequent application of a magnet over the pacemaker can result in total output inhibition. The initiating sequence of events included activation of the “cancel magnet” command. If that command is not activated, “uplink telemetry hold” cannot occur. Once telemetry uplink hold does occur, the pulse generator should be replaced.
Chronic Lung Collapse: A Predictable Impediment to Ipsilateral Lead Placement
Authors: III F. EARL FYKE
Published: July 2006

Implantation of a permanent transvenous pacemaker was undertaken in a patient with longstanding, complete collapse of the right lung. Unanticipated distortion of the lead path prevented entirely introduction of a right subclavian sheath and rendered lead placement from a right cephalic venotomy extremely difficult An angioplasty guidewire substituted for the standard stylets proved useful in positioning the lead. This report describes the predictable venous deformity, illustrates the consequent impediment to ipsilateral lead placement, and discusses why contralateral entry sites should be superior in cases of massive loss of lung volume.
Respiratory Pump Failure and its Treatment
Authors: SHNEERSON J.M.
Published: July 2006

The activity of the nervous system determines the respiratory pattern, although the degree of alveolar ventilation also depends on the mechanical properties of the chest wall and Jungs. Failure to ventilate the lungs adequately may be due to defects in respiratory control or the respiratory muscles or to an increase in the work that the muscles have to perform. The selection of the best method of treatment of respiratory pump failure requires an exact knowledge of its cause. Phrenic nerve stimulation or mechanical assistance by positive and negative pressure ventilators or by a rocking bed, can be very effective. Each of these methods has a place in the long‐term management of ventilatory failure.
Electrical Techniques for Stimulation of the Phrenic Nerve to Pace the Diaphragm: Inductive Coupling and Battery Powered Total Implant in Asynchronous and Demand Modes
Authors: HOGAN JAMES F. , KODA HIROYUKI , GLENN WILLIAM W. L.
Published: July 2006

A review of the electrical design of a rf inductively coupled phrenic nerve stimulator for the diaphragm developed in our laboratories will be discussed. Modifications of the original circuit are based on long‐term laboratory and clinical studies. A total implant battery powered stimulator was designed exclusively for animal studies to evaluate fhe effects of several stimulating parameters on diaphragm fatigue and neuromuscular structure. On the basis of these studies the optimum current level, stimulus frequency, respiratory rate, electrode configuration, and waveform were selected for clinical use to pace the diaphragm. A multiprogrammable dual output stimulator responsive to interrogation has been constructed and used in the experimental laboratory in anticipation of clinical application. There was an insignificant difference between the effect on neural structure or diaphragm function of stimulation with pulse width modulated constant voltage or with amplitude‐modulated constant current. Demand pacing: maintenance of normal PACO2 by monitoring ET PACO2 with feedback to the diaphragm pacemaker to adjust the pacing rate has been successful in the experimental animal.
Effects of Chronic Cerebellar Stimulation (CCS) Setting on the Gait and Speech of a Spastic Cerebral Palsy Adult
Authors: HERSHLER C. , UPTON A.R.M. , DEBRUIN H. , BURCEA I. , KING R.N. , ZOGHAIB C.
Published: July 2006

A single (N = 1) spastic cerebral palsy adult who had experienced Chronic Cerebellar Stimulation (CCS) for 9 years without any change in the stimulator settings was assessed at six different stimulator settings. These voitage settings varied from 0 volts to 40 volts and frequencies of stimulation from 0 to 200 Hz. Stimulation was with bipolar rectangular pulses with less than 0.2 C/mm2 charge per phase. Responses measured at each setting were quantitative gait, speech, and somatosensory evoked potential measurements. Additional clinical assessments were done by a neurologist and speech therapist. Alteration in stimulator settings occurred 1 week apart to allow for stabilization and all assessments were completed in the same sequence each day. None of the individual stimulator settings were known to any of the assessors or to the patient. The results showed consistently that the patient's gait and speech were poorest when the stimulator was switched off completely. Switching on the stimulator caused improved function according to all assessments. There was consistent improvement in gait and speech when the rate of the cerebellar stimuli was high (for voltages between 0 and 40 V). Changing the voltage (within the range 0 to 40 V), while keeping the frequency of stimulation constant, did not appear to have as much effect. This preliminary evaluation suggests that the technique of CCS is safe and can improve function in a measurable manner.
The Impact of a Manufacturer's Revision of Pacemaker Service Life on the Workload of a Large Pacing Center
Authors: LLEWELLYN MICHAEL J. , BENNETT DAVID H. , SHEARER KENNETH S. , SLAVEN YVONNE M.
Published: July 2006

In certain batches of a manufacturer's pacemakers, inadequate insulation of the battery cell feed‐through mechanism led to internal short‐circuiting and premature battery depletion. We describe the impact of the consequent reduction in service life and recommended close supervision of these generators on the follow‐up clinics and inpatient workload at a large pacing center. One‐hundred and ninety patients had Cordis Gamma series pacemakers implanted between September 1981 and July 1985; 135 have had to undergo premature generator replacement. Eleven of these pacemakers had developed early depletion of rate and 12 no‐output failure. Within 3 months of their generator change, 12 patients developed wound sepsis, three of them requiring fiirther system replacement. We calculate that at least 540 extra outpatient appointments, 400 in‐hospital patient days and 12 full working days in one of our catheterization laboratories were required to deal with the problems. The pacemaker industry, as well as doctors and technicians involved in pacemaker purchase and implantation, should be aware of the consequences of a major recall not only on workload but also on patient morbidity and anxiety.
Pacing Failure Due to Markedly Increased Stimulation Threshold 2 Years after Implantation: Successful Management with Oral Prednisolone: A Case Report
Authors: NAGATOMO YOSHITATSU , OGAWA TSUNEO , KUMAGAE HARUHITO , KOIWAYA YASUSHI , TANAKA KENJIRO
Published: July 2006

In a 53‐year‐old male who had undergone transvenous permanent pacing, infracardiac potential reduced progressively over a 2‐year period and exit block developed, while the stimulation threshold was markedly increased. After oral prednisolone for 5 months, the stimulation threshold reduced gradually along with an increase in intracardiac potential, culminating in no recurrence of exit block for the ensuing 2 years. The clinical course suggests that progressive reduction in intracardiac potential may have presaged the late development of exit block, and that oral prednisolone may be a therapeutic approach for the restoration of ventricular capture even 2 years after implantation.
Stability of Electrophysiological Parameters after Acute Amiodarone Loading: Implications for Patient Management
Authors: GREENBERG MARK L. , LERMAN BRUCE B. , HAINES DAVID E. , BARON JOHN A. , DIMARGO JOHN P.
Published: July 2006

The appropriate timing of electrophysiological study in patients treated with amiodarone is uncertain. Twenty patients with coronary artery disease in whom sustained ventricular tachycardia was still inducible after 9 ± 1 days of amiodarone loading (1,200‐1,400 mg/day) underwent repeat electrophysiological testing after an additional month of maintenance therapy (400 mg/day). Compared with baseline, both short‐ and long‐term amiodarone therapy caused significant changes in QTc, right ventricular elective refractory period, and ventricular tachycardia cycle length. However, there was no significant change in electrophysiological parameters between the end of the acute amiodarone loading period and 1 month of additional therapy. Sustained ventricular tachycardia remained inducible in 19 of 20 patients after 1 month of maintenance therapy. Amiodarone and desethylamiodarone plasma concentrations remained stable after amiodarone loading, but did not correlate with the magnitude of electrophysiological changes from baseline. These data suggest that electrophysiological testing after 9 days of high dose amiodarone therapy may accurately reflect long‐term electrophysiological effects.
P Wave Tracking Above the Maximum Tracking Rate in a DDDR Pacemaker
Authors: HIGANO STUART T. , HAYES DAVID L.
Published: July 2006

Dual‐chamber, rate‐modulated pacemakers have recently become available. These devices, whose rate response is determined by the combined input from the intrinsic atrial rate and the sensor‐driven rate, have led to some unexpected upper rate behaviors. In the case presented, with the maximum sensor pacing rate at 150 ppm, multiple episodes of apparent P wave tracking occurred above the maximum P wave iracking rate of 100 ppm. This behavior is explained by P waves thai inhibit sensor‐driven atrial output; inhibition may result in variable maximum tracking rates that are equal to the current sensor‐driven rate. This effect appears to have minimal physiological consequence. Its importance lies in its recognition as normal DDDR function so that searches for pacemaker malfunction will not be made.
Atrial Pacing: Efficacy and Safety
Authors: KERR CHARLES R. , TYERS G. FRANK O. , VORDERBRUGGE SHIRLEY
Published: July 2006

Atrial pacing has the advantages of simplicity, maintenance of AV synchrony, and economy. The major detraction has been the potential for deterioration of atrioventricular conduction. In this study, we followed 43 patients with sick sinus syndrome treated with atrial (AAI) pacing. Excellent initial implant parameters were obtained in all. Three early lead repositionings were required. Minor sensing and pacing problems could all otherwise be handled by reprogramming. FoIIow‐up for a mean of 25 ± 20 months demonstrated excellent performance of the pacing systems. Pacing and sensing thresholds and lead impedance indicated excellent lead performance. There were no late lead failures. Nine patients have had mild deterioration in atrioventricular conduction and one of these had a change to DDD pacing at the time of elective battery change. All patients are asymptomatic. Thus, chronic atrial pacing in selected patients is safe and reliable with good chronic lead performance and low risk of subsequent conduction system disease.
The Tricuspid Valve: An Unusual Site of Endocardial Pacemaker Lead Fracture
Authors: CLARKE BERNARD , JONES SUSAN , GRAY HUON H. , ROWLAND EDWARD
Published: July 2006

Two patients are described in this article who developed fractures of transvenous endocardial pacing leads at the point of passage across the tricuspid valve. In one case life‐threatening asystole occurred, emphasizing the potential seriousness of this complication.
Temporal Relationship Between Exercise and QT Shortening in Patients with QT Pacemakers
Authors: HORSTMANN ECKHARD , KOENN BIRGIT
Published: July 2006

The present study was undertaken to examine the temporal relationship between exercise and QT interval shortening as one of the principal determinants for the functioning of QT pacemakers. Ten patients (mean age of 72.6 years) with implanted QT pacemakers were subjected to supine bicycle exercise with two different slopes, 90% and 80%. The QT interval as seen by the pacemaker was monitored by telemetry and stored on magnetic tape. After the beginning of exercise QT prolongation of a few msec occurred up to 40 sec in most patients. The earliest QT shortening of 4 msec was noted after 63.4 sec with 90% slope and 75.7 sec with 80% slope. The difference was not significant. The further time course was dependent on slope and pacemaker algorithm. Maximal QT shortening was 65.9 msec with 90% and 69.8 msec with 80% slope. It was seen 29.2 sec after termination of exercise with 90% slope and 69.5 sec with 80% slope (P < 0.05). There was no correlation of the measured delays with age. Earliest rate response in QT driven pacemakers is determined by earliest QT shortening on one hand and by the slope setting of the pacemaker on the other, where the limiting parameter appears to be QT shortening, which occurs after the first minute of exercise.
Pericardial Tamponade Associated with Pacemaker Catheter Manipulation
Authors: SANDLER MANFRED A. , WERTHEIMER JOHN H. , KOTLER MORRIS N.
Published: July 2006

Three patients developed cardiac tamponade following postpacemaker catheter manipulation. Although regarded as a rare complication, this entity has to be recognized immediately on clinical grounds and confirmed by echocardiography. Prompt recognition and urgent pericardial drainage is lifesaving in this acute cardiac emergency.
Oscillations of Diastolic Interval and Refractory Period Following Premature and Postmature Stimuli in Canine Cardiac Purkinje Fibers
Authors: WATANABE MARI , ZIPES DOUGLAS P. , GILMOUR ROBERT F.
Published: July 2006

The effective refractory period (ERP) of His Purkinje tissue is known to oscillate following sudden changes in stimulus frequency. It has been proposed that the oscillation of ERP is caused by oscillation of the diastolic interval. This hypothesis was tested in vitro in canine cardiac Purkinje fibers superfused with normal and hyperkalemic (10 mM KC1) Tyrode's solution. The ERP of responses to premature stimuli, responses to postextrastimuli, and responses to postmature stimuli were measured. ERP of premature responses and postextrasystolic responses oscillated in normal Tyrode's solution. Oscillations of ERP of premature responses and postextrasystolic responses were damped in hyperkalemic Tyrode's solution. Determinations of the restitution of ERP as a function of diastolic interval revealed that oscillation of ERP of premature and postextrasystolic responses was for the most part predictable from the diastolic interval during superfusion with normal Tyrode's solution. In contrast, both hyperkalemic Tyrode's solution and postmature stimuli shifted the restitution curves, resulting in ERPs that were markedly longer than those predicted from the diastolic interval alone. Shifts in the restitution curves completely accounted for damping of the oscillation of ERP in hyperkalemic Tyrode's solution and with postmature stimuli. These data may relate to operations of refractoriness during sudden changes in ventricular rate, such as occur during atrial fibrillation or ventricular tachycardia.
Deduction of Triphasic Phase Response Curves from Ventricular Parasystole
Authors: ÅHLFELDT H. , NILSSON G. , BANDH S. , JONASON T. , AHREN T. , RINGQVIST I.
Published: July 2006

Modulation of ventricular parasystole by sinus beats has been shown to result in a biphasic phase response curve. Some reports also indicate that the modulation effect could be described by a triphasic response with an early phase of acceleration, which would correspond to the supernormal phase of excitability. Two cases of such triphasic phase response curves are reported. The coexistence of ventricular couplets and parasystole is also discussed. The second beat of the couplet has often been explained by reentry or reflection, but could also be interpreted as due to supernormal modulation, resulting in an accelerated second ectopic response. (PACE, Vol. 12, July 1989 parasystole, phase response curve, triphasic, couplets, supernormality, computer simulation
The Ventricular Depolarization Gradient: Effects of Exercise, Pacing Rate, Epinephrine, and Intrinsic Heart Rate Control on the Right Ventricular Evoked Response
Authors: CALLAGHAN FRANK , VOLLMANN WILLIAM , LIVINGSTON ANDREA , BOVEJA BIRINDER , ABELS DEBRA
Published: July 2006

A new pacing technique is described that permits high fidelity recording of the paced ventricular evoked response, including cardiac depolarization. Integration of the paced R wave yields the ventricular depolarization gradient (GD), which is dependent on activation sequence and the spatial dispersion of activation times. GDwas studied in 27 dogs to determine the ejects of treadmill exercise at fixed rate pacing (n = 10), elevation of heart rate in the absence of stress (n = 20), epinephrine at fixed rate (n = 6), and exercise in the presence of normal chronotrophic response (n = 7). Low level exercise (1 mph, 2 min, 15°) at a fixed heart rate produced significant (P < 0.0005) decreases in GDthat averaged —‐10.8 ± 4.0% (mean ± SD). The rate of change in GDwas faster at the onset of exercise than at its cessation (P < 0.0005). Artificial elevation of heart rate at rest produced significant (P < 0.0005) increases in GD; mean sensitivity of GDto rote was 0.27 ± 0.12%/beats/min. Intravenous injection of epinephrine produced significant (P < 0.001) decreases in GD at two dosage levels (2.5 and 5.0 μg/kg) when evaluated at two baseline pacing rates (150 and 190 beats/min); mean changes in GDwere –20.64 ± 0.53% (2.5 μ/kg at 150 beats/min), –25.19 ± 4.20% (5.0 μ/kg at 150 beats/min), –14.18 ± 5.19% (2.5 μ/kg at 190 beats/min), and –24.22 ± 4.94% (5.0 μ/kg at 190 beats/min). Sensitivity of GDto epinephrine was dose‐dependent (P < 0.01) at each baseline rate, but was independent (P > 0.05) of the rate itself. In the presence of a normal chronotropic response. GD remained unchanged (P > 0.5) during exercise in spite of significant elevation in heart rate (105.0 to 167.1 beats/min, P < 0.001). These data suggest the presence of an intrinsic negative‐feedback control mechanism that maintains GDconstant in the healthy heart during homeostatic disturbance. Applications in closed‐loop rate adaptive pacing are described.
Ultrasonic Assisted Permanent Pacing in a Patient with Severe Pulmonary Tuberculosis
Authors: LAU CHU‐PAK , WONG CHEUK‐KIT , LEUNG WING‐HUNG , CHENG CHUN‐HO
Published: July 2006

A 67‐year‐old male patient with previous history of pulmonary tuberculosis presented with syncope due to complete heart block. Collapse of the right lung and deviation of the heart to the right chest had prevented visualization of the cardiac silhouette by fluoroscopy. Successful endocardial permanent pacing using a passive fixation electrode was achieved with the help of ultrasonic visualization of the cardiac chambers.
The Effect of Electrode Design on the Efficiency of Delivery of Radiofrequency Energy to Cardiac Tissue In Vitro
Authors: BLOUIN LEONARD T. , MARCUS FRANK I.
Published: July 2006

Four types of electrodes were studied with respect to efficiency of delivery of radiofrequency energy (HFE) and characteristics of the lesions produced in dog ventricular muscle in vitro. An imbeddable needle electrode was found to be the most efficient of the four types studied, with a lesion volume/energy‐delivered ratio of 1.10 mm3joule at an optimum power level of 2.8 watts and power density at the electrode surface of 0.45 watt/mm2. Lesion volume was linearly related to energy delivered at all power levels used below a power density of 0.64 watt/mm2, at and above which tissue impedance increased abruptly. The electrode catheter typically used for RFE ablations was the least efficient at 0.15 mm3/joule and a power density at the electrode surface of 0.50 watt/mm2 at 6.27 watts. Masking 2/3 of the electrode surface with electrically insulating epoxy caused the RFE current to be directed into the tissue, resulting in a threefold increase in efficiency (0.46 mm3/joule) at less than half the power (2.79 watts). A flat, thermally insulated electrode with larger (10 mm2) contact area approached the efficiency of the imbedded electrode with a ratio of 0.69 mm3/joule at a low power density of 0.19 watt/mm2 and 1.85 watt power level. Characteristics of an “ideal” electrode for RFE lesion production in cardiac tissue are discussed.
Impedance Changes During Catheter Ablation and Their Relationship to Electrical Arcing and Clinical Efficacy
Authors: CUNNINGHAM DAVID , AHSAN ARIF J. , ROWLAND EDWARD , RICKARDS ANTHONY F.
Published: July 2006

This study has used high energy ablative shocks in saline and in man to characterize the complex, energy dependent behavior of the impedance at the electrode‐tissue interface. In vitro shocks showed a fall in impedance when an arc was formed, due to formation around the electrode of a vapor globe rendered conductive by the arc. Following arc extinction, this same vapor globe insulates the electrode, and subsequently collapses, forming a shock wave, and allowing current flow to resume. Shocks delivered to tissue specimens exhibited progressively higher impedance and less insulation as contact pressure was increased. In vivo, lesser degrees of insulation during arcing shocks were associated with greater clinical efficacy.
Electrophysiological Studies on Cardiac Catheter Ablation
Authors: MOORE E. NEIL , SCHAFER WILLIAM , KADISH ALAN , HANICH ROBERT F. , SPEAR JOSEPH F. , LEVINE JOSEPH H.
Published: July 2006

Clinical and animal investigations have pointed out that high energy electrical shocks are associated with the development of cardiac arrhythmias and with variable success in permanent ablation. The effects of electrode configuration and location on the size of the recorded electrogram was investigated to help explain variable catheter ablation results. We analyzed the cellular effects of catheter ablation shocks and found depression of resting potential, action potential amplitude, dV/dt and action potential duration. The most severe effects were noted with high current densities in tissues located between the cathode and anode. Damage was worse nearest the cathode. Similar cellular studies were completed using argon laser photoablation. Again, there was a decrease in resting potential, action potential amplitude and dV/dt. Laser energy led to a more focal region of myocardium void of action potentials and the border zone of injury was smaller. We also investigated the effects of lower energy shocks)1 to 10 joule) on cardiac tissues. Using microelectrodes, we observed that the membrane potential can “hang up” at the depolarized levels for varying periods of time and that conduction is altered during this membrane “hang‐up” period. The duration and membrane hang‐up level correlated with shock intensity and shock duration. Sequential shocks resulted in additive membrane “hang‐up”. We believe that membrane hang‐up may be associated with brief arrhythmias observed following catheter ablation since conduction, refractoriness and excitability are all altered.
Catheter Ablation of Canine Myocardium with Radiofrequency Energy
Authors: FRANKLIN JAY OLEN , LANGBERG JONATHAN J. , OEFF MICHAEL , FINKBEINER WALTER E. , HERRE JOHN M. , GRIFEIN JERRY C. , SCHEINMAN MELVIN M.
Published: July 2006

High energy direct‐current shocks delivered via an electrode catheter have been used to ablate the atrioventricular junction since 1981.1 This technique has also been adapted for ablation of other cardiac tissues including the atrium, posterior interatrial septum and ventricular myocardium. The limitations of this technique include inadequate control of the energy source, poor understanding of the mechanisms of myocardial injury, and untoward complications possibly related to barotraumatic injury. Radiofrequency energy has been shown to create ablative injury when delivered lo the myocardium via standard electrode catheters. This report will review our experience with radiofrequency catheter ablation of the canine myocardium with specific emphasis on the biophysical aspects of lesion formation.