bluuebunny/crossref_metadata_2025 huggingface dataset:
Importance of Heart Rate Response During Exercise in Patients Using Atrioventricular Synchronous and Ventricular Pacemakers
Authors: MCMEEKIN JAMES D. , LAUTNER DAVID , HANSON SPENCER , GULAMHUSEIN SAJAD S.
Published: July 2006

Atrioventricular synchronous pacing offers advantages over fixed‐rate ventricular (VVI) pacing both at rest and during exercise. This study compared the hemodynamic effects at rest and exercise of ventricular pacing at a rate of 70 beats/mm, ventricular pacing where the rate was increased during exercise and duaJ chamber pacing. Ten patients, age 63.8 years, with multiprogrammable DDD pacemakers were studied using supine bicycle radionuclide ventriculography. RadionucJide data during dual chamber pacing was acquired at rest and during a submaximal workload of 200‐400 kpm/min. The pacemakers were then programmed to VVI pacing at a rate of 70 beats/min, and 1 week later, studies were repeated in the VVI mode at rest, during exercise at a rate of 70 beats/min, and during exercise with the WI pacemaker programmed to a rate adapted to the ODD pacing exercise rate. At rest, (he cardiac output was lower in the WI compared with the AV sequential mode (4.1 ±1.1 vs 5.7±1.1 1/mm, P < 0.01). During exercise, the cardiac output increased from resting values in the DDD and WI pacing modes, however cardiac output in the rate‐adapted WI mode was higher than in the WI mode with the rate maintained at 70 beats/min (8.1 ±1.5 vs 6.3 ±1.1 1/min, P = 0.02). Three patients completed lower workloads with WI pacing at 70 beats/min compared with AV synchronous pacing. At rest, AV sequential pacing was superior to WI pacing, suggesting the importance of the atrial contribution to ventricular filling. With WI pacing during exercise, cardiac output was improved with an increased pacemaker rate, suggesting that the heart rate response during exercise was the major determinant of the higher cardiac output.
Modification of Atrioventricular Conduction by Selective AV Nodal Artery Catheterization
Authors: WANG PAUL J. , SCHOEN FREDERICK J. , REAGAN KATHLEEN , HASAN HUSSEIN HASAN RIZK , GUO HONG SHENG , FRIEDMAN PETER L.
Published: July 2006

The effects of selective AV nodal artery embolization on AV nodal function was investigated in six closed‐chest adult dogs. Programmed atrial stimulation was performed to determine control values for AV nodal effective refractory period (AVN‐ERP) and the paced cycle length at which AV nodal Wenckebach conduction occurred (WCL). Using standard percutaneous femoral techniques of coronary artery catheterization, a flexible infusion catheter was positioned selectively in the AV nodal artery. Proper positioning of the catheter was confirmed angiographically and by selective acetylcholine (ACH) infusion into the AV nodal artery, which caused transient cornplele AV nodal block in three dogs, and for the group, caused lengthening of both AVN‐ERP and WCL Following cessation of ACH infusion and autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg, denervated recontrol values for AVN‐ERP and WCL were 192 msec and 243 msec, respectively. The AV nodal artery was then embolized with a suspension of cross‐linked collagen fibrils in either normal saline or absolute ethanol. Successful embolization of the AV nodal artery, confirmed angiographically, caused an acute increase in AVN‐ERP (243 msec, P < 0.05 compared to denervated control) and WCL (287 msec, P = 0.058 compared to denervated control). However, at a mean follow‐up of 37 days, only one animal exhibited a chronic increase in AVN‐ERP and WCL. Selective AV nodal artery cathelerization can be performed using standard percutaneous catheterization techniques. Selective administration of agents with direct cidal effects on the AV node using this technique may provide an alternative to conventional methods of catheter ablation of AV conduction in patients with drug‐resistant supra ventricular arrhythmias.
Termination of Macro‐Reentrant Tachycardia by a Single Extrastimulus Delivered During the ‘Effective’ Refractory Period: A Computer Modeled ‘Case Report’
Authors: MALIK MAREK , CAMM A. JOHN
Published: July 2006

A computer model of cardiac excitation sequences was used to reproduce atrioventricular (AV) reentrant tachycardia (AVRTJ and its termination by a single ‘on‐circuit’ exfrastimulus. The model simulated activation waves revolving along a one‐dimensional circular pathway, the portions of which represented the atrial. AV nodal, His‐Purkinje, ventricular, and accessory pathway sections of the tachycardia circuit. The modeled pathway was composed of 289 elements. The model distinguished only the depolarised and resting states of constituent elements, but introduced differential refractoriness and conduction velocity for each element. These values approximated the natural situation established in a patienl suffering from AVRT associated with the right bundle branch block. The results of the study suggest that: (A) the usual impression of a regular recovery wave and of a regular excitable window moving uniformly along the macro‐reentrant circular path is incorrect; (B) during the tachycardia, islands of repolarized cells appear which are surrounded by tissue that is still refractory; (C) an extrastimulus which captures the island of early repolarized tissue may cause an excitation restricted to a small part of the myocardium but the local refractoriness following such an extrastimulus may be sufficient to terminate the tachycardia.
Intermittent Ventricular Bigeminy as an Expression of Two‐Level Wenckebach Periodicity in the Reentrant Pathway of Extrasystoles
Authors: KINOSHITA SHINJI , KONISHI GO , KINOSHITA YORKO
Published: July 2006

A patient with intermittent ventricular bigeminy is reported in whom the presence of two‐level Wenckebach periodicity in the reentrant pathway of extrasystoles is suggested. When sinus arrest was caused by vagal stimulation, no ectopic QRS complex occurred. This indicated that ventricular bigeminy was not parasystolic bigeminy but ordinary extrasystolic bigeminy. Observations of the electrocardiogram suggested that Wenckebach block occurred at two different levels in the reentrant pathway of ventricular extrasystoles. When extrasystoles were noninterpolated, Wenckebach block occurred at the distal level of the pathway and caused termination of ventricular bigeminy. On the other hand, when extrasystoles were interpolated, Wenckebach block occurred at the proximal level of the pathway. This is the first report to suggest the presence of two‐level Wenckebach periodicity in a reentrant pathway of extrasystoles.
Clinical Evaluation of an Automatic Sensitivity Adjustment Feature in a Dual Chamber Pacemaker
Authors: WILSON JOHN H. , LOVE CHARLES J. , WETTENSTEIN ELIAS H.
Published: July 2006

The clinical evaluation of a new automatic sensitivity adjustment feature in the Cosmos fl, Model #284–05 is described. This feature, designed to maintain a 2:1 safety margin for sensing intrinsic signals, was activated by way of special programmer software in ten patients at two centers. While the feature worked satisfactorily in some cases, it did not perform as expected, and undersensing in both chambers was observed. This may have been due to biasing the adjustment toward maximum rather than minimum electrograms, This study suggested that electrograms may vary by more than 100% which underscores the importance of this feature, and reinforces the need for continued development.
Treatment of Encainide Proarrhythmia with Hypertonic Saline
Authors: GARDNER MARK L. , BRETT‐SMITH HELENA , BATSFORD WILLIAM P.
Published: July 2006

We report a case of successful treatment of encainide‐induced ventricuJar tachycardia with 3% hypertonic saline. To our knowledge, no other report exists in the literature of this treatment for proarrhythmic ventricular tachycardia from a type 1C agent. Metabolic consequences of the treatment included severe hypernatremia, hyperosmolarity, hypocalcemia, and hypophosphatemia, which were reversible over 24 hours. In spite of the risks, treatment of incessant ventricuJar tachycardia induced by type 1C agents with hypertonic saline may be life saving.
Radiofrequency Catheter Ablation: The Effect of Electrode Size on Lesion Volume In Vivo
Authors: LANGBERG JONATHAN J. , LEE MICHAEL A. , CHIN MICHAEL C. , ROSENQVIST MARTEN
Published: July 2006

Radiofrequency current is a promising alternative to high voltage direct current defibrillator discharges for catheter ablation of arrhythmias. However, lesions produced with radiofrequency current are relatively small and use of high power is limited by the impedance rise that occurs with desiccation of tissue and coagulum formation. The effect of electrode size on radiofrequency ablation was assessed by comparing results of radiofrequency application using a standard 6 French electrode catheter (distal electrode 2 mm in length) to those using catheters modified with longer distal electrodes (3, 4, 6, 8, and 10 mm in length). Radiofrequency ablation was performed at 47 left ventricular endocardial sites in 20 anesthetized dogs. A constant power of 13.3 ± 1.3 watts at 550 kHz was applied between the distal catheter electrode and a skin electrode until a total of 500 joules had been delivered or a rise in impedance occurred. Increasing electrode length from 2 to 4 mm more than doubled lesion volume from a mean of 143 to 326 mm3 (P = 0.025). Increasing electrode length beyond 4 mm produced progressively smaller lesions (157 mm3, 155 mm3, and 67 mm3 for 6‐, 8‐, and 10‐mm electrode lengths, respectively). Impedance rise was significantly less likely with larger electrodes and took longer to occur. Increasing the size of electrodes used for radiofrequency ablation allows application of higher power without an impedance rise. Optimizing electrode size (3 or 4 mm in this study) results in larger lesions and may improve the effectiveness of radiofrequency ablation of arrhythmias.
Alternate Methods for the Determination of Atrial Capture Threshold Utilizing the Telemetered Intracardiac Electrogram
Authors: FEUER JOSHUA M. , FLORID JOSEPH , SHANDLING ADRIAN H.
Published: July 2006

Periodic determination of pacemaker capture threshold is important to ensure appropriate pacemaker function. During dual chamber pacing, it is sometimes difficult to identify evidence of atrial depolarization on surface electrocardiography (ECG), and this can interfere with the ability to ascertain atrial capture. We describe new methods for determining atrial capture threshold using a standard telemetered endocardial atrial electrogram (AEGM). For the first method, the atrial output is decremented until loss of atrial capture is demonstrated by the appearance of native P wave activity on the AEGM. The atrial capture threshold can then be accurately determined as the point at which a stepwise increase in atrial output results in extinction of the native P wave activity. The second method uses the direct visualization of the AEGM recorded between the ring electrode and pacemaker generator during unipolar (lead tip electrode) pacing. This requires the presence of a bipolar lead. Using this method of recording, it is possible to identify a signal after the atrial pacing stimulus artifact during atrial capture, which disappears with loss of capture. This signal is consistent with a paced “evoked atrial potential” and allows verification of atrial capture. After validating the methods in two sets of test patients with dearly identifiable atrial depolarization on surface ECG, one method was successfully applied to a patient in whom atrial depolarization could not be reliably ascertained on surface ECG. These methods promise to be useful in selected patients in whom confirmation of atrial capture would otherwise be difficult.
Monophasic Versus Biphasic Cardiac Stimulation: Mechanism of Decreased Energy Requirements
Authors: KAVANAGH K.M. , DUFF H.J. , CLARK R. , ROBINSON K.V. , GILES W.R. , WYSE D.G.
Published: July 2006

The purpose of the present study was to examine the effects of monophasic and biphasic stimulation under conditions of full and incomplete repolarization in an in vivo dog model and in an in vitro rabbit ventricular single cell model. Strength‐interval curves were constructed with monophasic cathodal stimulation and biphasic subthreshold anodal followed by cathodal stimulation in dogs prior to and late after left anterior descending coronary artery occlusion. At the monophasic absolute refractory period plus 10 msec, less cathodaJ current was required for biphasic compared to monophasic stimulation (P = 0.04). Moreover, the biphasic absolute ventricular refractory period (116 ± 8 msec) was significantly shorter than the monophasic absolute ventricular refractory period (136 ± 15 msec) (P < 0.02). At coupling intervals > 30 msec after the monophasic absolute ventricular refractory period, there was no distinction between monophasic and biphasic stimuli. Similarly enhanced excitability was observed with biphasic stimuli in infarcted hearts. Voltage clamp measurements mimicking conditions of the in vivo studies demonstrated that when repolarization is incomplete, a hyperpoiarizing prepulse reactivates additional sodium current resulting in enhanced excitability. In conclusion, biphasic stimulation consisting of a hyperpolarizing anodal prepulse followed by a cathodal pulse decreases the current required for excitation compared to cathodal monophasic stimulation in a critical zone near the ventricular absolute refractory period.
The Bin Area Method: A Computationally Efficient Technique for Analysis of Ventricular and Atrial Intracardiac Electrograms
Authors: THRONE ROBERT D. , JENKINS JANICE M. , DICARLO LORENZO A.
Published: July 2006

Recent studies have reported a significant false positive rate in delivery of therapy by implantable antitachycardia devices utilizing detection algorithms based on sustained high rate. More selective decision schemes for the recognition of life‐threatening arrhythmias have been recently proposed that use analysis of the intrinsic electrogram rather than rate alone. Morphological discrimination of abnormal electrograms using correlation waveform analysis (CWA) has been proposed as an effective method of intracardiac electrogram analysis, but its computational demands limit its use in implantable devices. A new method for intracardiac electrogram analysis, the bin area method (BAM), was created to detect abnormal cardiac conduction with computational requirements of one‐half to one‐tenth those of CWA. Like CWA, BAM is a template matching method that is sensitive to conduction changes revealed in the electrogram morphology and is independent of amplitude and baseline fluctuations. Performance of BAM and CWA were compared using bipolar right ventricular and right atrial electrode recordings from 47 patients undergoing clinical cardiac electrophysiology studies. Nineteen patients had 31 distinct monomorphic ventricular tachycardias (VTs) induced (group I), thirteen patients had paroxysmal bundle branch block of supraventricular origin (BBB) induced (group II), and 19 patients had retrograde atrial activation during right ventricular overdrive pacing (group III). (One patient was common to all three groups, and two patients were common to groups II and III.) Using the ventricular electrogram, both BAM and CWA distinguished VT from sinus rhythm in 28/31 (90%) cases, and BBB from Normal Sinus Rhythm (NSR) in 13/13 (100%) patients. Using the atrial electrogram, both BAM and CWA distinguished anterograde from retrograde atrial activation in 19/19 (100%) patients. BAM achieves similar performance to CWA with significantly reduced computational demands, and may make real‐time analysis of intracardiac electrograms feasible for implantable pacemakers and antitachycardia devices.
Genesis of Sigmoidal Dose‐Response Curve During Defibrillation by Random Shock: A Theoretical Model Based on Experimental Evidence for a Vulnerable Window During Ventricular Fibrillation
Authors: HSIA PENG‐WIE , MAHMUD REHAN
Published: July 2006

The sigmoidal dose‐response curve (percent success vs shock energy) suggests a probabilistic nature of defibrillation. The mechanism is still largely unknown, however, random variation in the excitable state during ventricular fibrillation (VFJ is suspected. A canine defibrillation study was designed to determine whether random variation in absolute VF voltage (AVFVJ of crude marker of number of excitable cells) was related to success of defibrillufion, using a DC shock successful at the 50% level. The results were: (a) fransmyocardial resistance (73.4 ± 1.4 vs 73.6 ± 1.5 ohms) and delivered energy (6.1 ±1.2 vs 6.2 ± 1.2 joules) were similar; however, (b) AVFV 2 msec prior to DC shock was greater for successful as compared to unsuccessful attempts (0.5 ± 0.1 vs 0.3 ± 0.0 mV, P < 0.01). A mathematical model was subsequently developed based on fluctuation in the number of excitable cells. Variation in the state of excitability resulted in a cyclic window potentially vulnerable to defibrillation. The vulnerable window occurred at a point when the number of excitable cells was low, i.e., a higher state of total depolarization, which was in agreement with the experimental finding. For a given VF pattern, duration of the vulnerable window was regulated by the shock energy. A larger shock energy generated a wider vulnerable window and, in turn, a higher success rate. Finally, the sigmoidal dose‐response curve of defibrillafion was theoretically constructed by calculating the variable chances of a random DC shock occurring either in a vulnerable window or elsewhere during VF. It is concluded that a vulnerable window susceptible to defibrillation can be demonstrated in the early stages (10 sec) of VF. The mathematical model provides a theoretical basis for the vulnerable window and helps elucidate the probabilistic nature of defibrillation.
DDI Pacing in the Bradycardia‐Tachycardia Syndrome
Authors: BANA GILBERTO , LOCATELLI VINCENZO , PIATTI LUIGI , GEROSA CAMILLO , KNIPPEL MAURO
Published: July 2006

The bradycardia‐tachycardia syndrome is a subgroup within the larger category of sinus node dysfunction. Pacing is often required to treat either the protracted asystolic spells following the spontaneous termination of a paroxysmal supra‐ventricular tachyarhythmia or to protect the patient from pharmacologically exacerbated bradycardias. While the optimal pacing mode for this subset of patients remains debatable, recent reports have favored the use of atrial ventricular sequential pacing with intact atrial sensing (DDI). This paper reports our experience with a series of 30 consecutive patients in whom the DDI mode was utilized as part of the management of this syndrome. DDI pacing has been demonstrated to be safe, extremely effective, and easy to use in this group of patients.
Venous Obstruction Due to Permanent Transvenous Pacemaker Electrodes: Treatment with Percutaneous Transluminal Balloon Venoplasty
Authors: SPITTELL PETER C. , VLIETSTRA RONALD E. , HAYES DAVID L. , HIGANO STUART T.
Published: July 2006

Transvenous placement of permanent pacemaker leads is currently the most common method for permanent cardiac pacing. Venous abnormalities, in particular venous stenosis or thrombosis (or both) frequently have been described, although most patients remain asymptomatic because of the development of an adequate venous collateral circulation. Venous obstruction often first becomes apparent during pacemaker lead revision, when difficulty passing the new pacing lead is encountered. In this report, we present two cases of venous stenosis and thrombosis due to permanent transvenous pacemaker electrodes and the use of percutaneous transluminal balloon venoplasty to relieve the venous obstruction.
Clinical Assessment of the Right Ventricle Anterior Papillary Muscle Extrasystoles with Holter Recordings
Authors: LAZZARI JULIO O. , FACHINAT ARMANDO , TAMBUSSI ANA
Published: July 2006

To assess the short‐term behavior of the right ventricle anterior papillary muscle extrasystoles (APME) based on Holter recording and exercise data, 20 subjects (age 31.5 ± 13.7 years) with otherwise normal electrocardiogram were studied. APME was diagnosed when it resembled LBBB morphology, with downward oriented AQRS in the frontal plane, slurred r wave in lead V1, and an R/S ratio < 1 in this same lead. Except for palpitations in ten patients, there were no other symptoms related to the arrhythmia. Two Holter recordings, 30 to 330 days apart, were performed and their results compared. In the first Holter recording, the average rate of VPB/minute was 9,9 ± 2.5 (xg ± SD). Half of the patients had couplets and five had ventricular tachycardia, fn the second Holter recording, the average rate of VPB/minute was 8.7 ± 3. In eight cases, couplets were recorded, in half of which one or more episodes of ventricular tachycardia were also noted. Six patients showed another VPB morphology distinct from APME, Stress test suppressed VPB in 10/13 patients, couplets in 2/3 and ventricular tachycardia in the only one with this arrhythmia at the start of the test. Repetitive forms vs APME frequency and vs heart rate exhibited an inverse relationship. We conclude that APME is a clinical condition with both high and stable VPB levels, which can be found in subjects with otherwise normal hearts and in the short‐term has a spontaneous uncomplicated outcome.
Epicardial Mapping: How to Measure Local Activation?
Authors: PAUL THOMAS , MOAK JEFFREY P. , MORRIS CODY , GARSON ARTHUR
Published: July 2006

Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 electrodes. Maps were generated with a computer‐assisted mapping system using four different definitions of local epicardial activation: (1) maximal negative slope (intrinsic deflection) of the unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maximal amplitude of the bipolar elecirogram, and (4) first onset by 45° from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation ivas identical with maximal negative slope in the unipolar electrogram and maximal slope and maximal amplitude of the bipolar electrogram in all jive animals. Times of earliest and latest epicardial activation calculated witb maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each of the other three definitions of local activation, and in two of the five animals, first epicardial breakthrough was mapped to a different site than with the three other methods. Conclusions: (1) Maximal amplitude of the bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; (2) Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may be misinterpreted.
Daily Bedside Electrophysiological Testing Following Surgery for the WPW Syndrome
Authors: FISHER JOHN D. , KIM SOO G. , FERRICK KEVIN J. , ROTH JAMES A. , BRODMAN RICHARD F.
Published: July 2006

A simple technique is described that allows daily bedside evaluation of the results of surgery for the Wolff‐Parkinson‐White (WPW) syndrome, using standard postoperative myocardial wires, a single‐channel ECG machine, and a temporary pacer capable of rapid stimulation. Rate incremental atrial and ventricular ramp pacing was performed daily in 40 postoperative WPW patients. This technique, together with underdrive pacing in some individuals permits quick assessment of anterograde and retrograde conduction. Two surgical failures were identified in early postoperative days, and promptly returned to the operating room for successful reoperation. No additional failures were identified at formal predischarge electrophysiological testing or following discharge. The technique permits reassurance on a daily basis to apparent successes and early identification in the event of failure, permitting prompt intervention.
Analysis of the Morphology of the Unipolar Endocardial Paced Evoked Response
Authors: BROUWER JAN , NAGELKERKE DICK , DE JONGSTE MIKE J.L. , BOUTE WIM , DEN HEIJER PETER , LIE K.I.
Published: July 2006

In a retrospective study we analyzed the unipolar endocardial evoked response signal (ERS) of 103 patients prior to pacemaker implantation. The objective of this study was to give a complete description of the ERS morphology and to evaluate influences on this morphology of both various electrode characteristics and pacing rate. In addition, spontaneous endocardial signals were studied. The results demonstrate that acute leads had both higher R wave and T wave amplitudes and a faster downslope of the T wave. In the acute leads those with porous titanium carbon coated tips showed a more pronounced T wave. Pacing rate influences the R wave amplitude and the stimulus to T wave interval. Both stimulus to maximum and stimulus to minimum T wave interval show an exponential correlation with the stimulus interval. The interval between maximum and minimum of the T wave and the absolute amplitude of the T wave are not influenced by rate. Although there were significant correlations of the spontaneous endocardial signal with the ERS, the predictive value of the spontaneous signal for the ERS morpology is low. Prospective studies will be necessary to confirm the findings in this study.
Cycle Length Alternation During Supraventricular Tachycardia: Occurrence and Mechanism in a Canine Model of AV Reentrant Tachycardia
Authors: TALAJIC MARIO , VILLEMAIRE CHRISTINE , PAPADATOS DEMETRIOS , LEMERY ROBERT , ROY DENIS , NATTEL STANLEY
Published: July 2006

Cycle length alternation (CLA) is common by observed during Supraventricular tachycardia (SVT) onset and termination. The present study was designed to gain insights into the mechanism and potential clinical relevance of CLA by comparing computer simulations of tachycardia to directly observed behavior in a canine model of AV reentrant tachycardia (AVRT), The computer model was based on the hypothesis that CLA is secondary to feedback between AV nodal output during SVT and subsequent AV nodal input, and used the measured anterograde AV nodal recovery curve (AV vs A1A2) to predict sequential AV and RR intervals during SVT. Orthodromic AVRT was created experimentally in 11 open‐chested, autonomically‐blocked (atropine plus nadolol) dogs using a sensing and pacing circuit that mimicked a retrograde‐conducting accessory pathway. Steady‐state cycle length and AV interval during experimental AVRT closely paralleled predictions made by the computer model. CLA appeared consistently at the onset of experimental AVRT at programmed VA intervals ≤ 100 msec (corresponding to VA ≤ 150 msec as measured clinically) in all dogs. The amplitude and duration of CLA increased as the VA interval decreased, and closely paralleled predictions based on the computer model. Abrupt accelerations in arrial pacing to the same rate as AVRT did not result in alternation of cycle length. in conclusion, alternation of cycle length results from feedback between AV nodal output and subsequent AV nodal input at the onset of reentrant supraventricular tachycardia, and does not require changes in autonomic tone or dual AV nodal pathways. CLA occurrence, amplitude, and duration are predictable based on AV node recovery properties, and depend on retrograde conduction properties of the reentrant circuit. The presence of CLA suggests that the AV node is an integral component of the SVT reentry circuit, and may be useful clinically to identify the mechanism of supraventricular tachycardias.
The Defibrillation Success Rate Versus Energy Relationship: Part I‐Curve Fitting and the Most Efficient Defibrillation Energy
Authors: GLINER BRADFORD E. , MURAKAWA YUJI , THAKOR NITISH V.
Published: July 2006

The effect of applying an energy pulse to the heart during ventricular fibrillation is described by the probability of successful defibrillation or success rate. Seven to ten (8.60 ± 0.84: mean ± standard deviation) defibrillation trials per energy were randomly attempted at energies which span the defibrillation success rate versus energy curve. We obtained 70.0 ± 8.4 episodes per dog. We fit the defibrillation success rate versus energy relationship from ten dogs (20.5 y1.5 kg) to four types of curves: linear, exponential, profit transformed linear, and logic transformed linear. The correlation coefficients for each fit are 0.957 ± 0.057,0.944 ±0.014, 0.926± 0.051, and 0.889 ± 0.098. respectively. We therefore conclude that the exponential curve best describes the DSRE relationship. This suggests the existence of an energy below which defibrillation does not occur. At higher energies, the exponential curve asymptotically approaches a 100% success rate, which indicates that increasing the energy produces a diminishing benefit to defibrillation success rate. The estimated energies with a 0% defibrillation success rate are surprisingly consistent among dogs, with 2.072 ± 0.553 J. The estimated energy with an 80% defibrillation success rate is 5.217 ± 1.091 J. The estimated defibrillation success rate corresponding to the defibrillation threshold of 3.59 ± 3.06 J is consistent with 0.516 ± 0.144. The estimated energies with a 0% success rate correlate well with the defibrillation thresholds with R = 0.772; P = 0.0088. Since implant able defibrillators have a limited energy supply, we determined energy efficiency by dividing defibrillation success rate by the applied energy and energy consumption by dividing the applied energy by the defibrillation success rate. The most efficient defibrillation energy occurs at the maximum energy efficiency and the minimum energy consumption. The most efficient defibrillation energy of 4.34 ± 0.97 J determined from the exponential fit has a success rate of 0.70 ± 0.06. The most efficient defibrillation energy can be predicted from the defibrillation threshold. Clinically, a 70% success rate may not be adequate. We, therefore, compared the energy efficiency and consumption of energies with 90% and 95% success rates to the most efficient defibrillation energy. About a 50% increase in energy from the most efficient defibrillation energy is necessary for a 90% success rate which results in about a 33% loss in energy efficiency and about a 16% increase in energy consumption. About an 84% energy increase is necessary for a 95% success rate which results in about a 24% loss in energy efficiency and about a 33% increase in energy consumption. For these energies, the benefit to success rate may outweigh the decrease in energy efficiency and may be more appropriate clinically. A prudent choice of energy setting for the AICD must include careful consideration of energy efficiency and consumption.
Effect of the Intertrain Pause on the Ventricular Effective Refractory Period Measured by the Extrastimulus Technique
Authors: MORADY FRED , KADISH ALAN H. , ROSENHECK SHIMON , SCHMALTZ STEPHEN , DEBUITLEIR MICHAEL
Published: July 2006

This study determined the effect of the duration of the intertrain pause on the ventricular elective refractory period (VERP) measured by the extrastimulus technique using conventional eight‐beat basic drive trains. In 50 subjects, the VERP was measured using a basic drive train cycle length of 500 msec, 2‐msec steps in the extrastimulus coupling interval, and intertrain pauses of 0, 1, 4, 8, 20, 40, 60, or 380 seconds. The VERP increased significantly with each stepwise increment in the intertrain pause up to 20 seconds, then reached a plateau. The VERP measured with an intertrain pause of 20 seconds was a mean of 13 msec longer than when measured with a conventional 4‐second pause. The results of this study demonstrate a direct relationship between the VERP and the duration of the pause separating the eight‐beat basic drive trains used to measure the VERP. When the cycle length of the basic drive train is 500 msec, the VERP lengthens as the duration of the intertrain pause increases from 1 to 20 seconds, demonstrating that the basic drive trains exert a cumulative effect on the VERP when the intertrain pause is shorter than 20 seconds. A cumulative effect of the basic drive trains on the VERP is lost when the intertrain pause is 20 seconds or more.
Utility of Low Energy Test Shocks for Estimation of Cardiac and Electrode Impedance with Implantable Defibrillators
Authors: LEITCH JAMES W. , YEE RAYMOND , KLEIN GEORGE J. , JONES DOUGLAS L.
Published: July 2006

We assessed the value and safety of using a low voltage test shock to predict cardiac and electrode impedance during subsequent high voltage, transvenous, sequential pulse shocks. Two transvenous defibrillation catheters were inserted in 15 patients undergoing electrophys‐iology study for the evaluation of ventricular tachycardia/fibrillation. A sequential pulse test shock at stored voltage of 50 or 300 volts was delivered during sinus rhythm and high voltage therapeutic shocks were delivered during induced ventricular tachycardia/fibrillation. The test shocks were well tolerated and caused only minimal discomfort. Peak delivered voJtage for each pulse of the test shock ranged from 34 to 116 volts (mean 62 ± 27) and for each pulse of the therapeutic shocks from 186 to 778 volts (mean 435 ± 146). There was a very strong relationship between the impedance of the test shock and the mean impedance of the therapeutic shocks (R = 0.89, P < 0.001). The mean impedance of the test shock was slightly greater than the mean impedance of the test shock as slightly greater than the mean impedance of the therapeutic shocks (mean 90 ± 24 ohms compared to 77 ± 16 ohms, P < 0.001), with a maximum difference between test and therapeutic shock impedances of 39 ohms (mean difference 8.4 ± 10.3 ohms). There was a significant inverse relationship between impedance and peak current (R = ‐ 0.49, P = 0.001). Cardiac and electrode impedance during (ransvenous defibrillafion can be predicted reliably and safely by a low voltage test shock. This technique provides a safe and simple method to ensure appropriate connections and electrode function for subsequent countershock therapies.
Atrial Natriuretic Peptide During Different Pacing Modes in a Comparison with Hemodynamic Changes
Authors: BARATTO M.T. , BERTI S. , CLERICO A. , FOMMEI E. , DEL CHICCA M.G. , CONTINI C.
Published: July 2006

The study investigates the response of atrial nafriuretic peptide (ANP) to different cardiac pacing modes in comparison with hemodynamic changes. Ten patients underwent Swan‐Ganz catheterization during pacemaker implant. Atrioventricular and ventricular pacing were performed consecutively at three pacing rate levels (80, 100, and 110 ppm). Blood samples were taken from the pulmonary artery for ANP determination, both basally and at the end of each pacing period, Concomitantly, mean pulmonary capillary wedge pressure (PCWP) and mean pulmonary artery pressure (PAP) were measured. Cardiac output (CO) was determined by thermodilution both basally and during the 110 ppm steps. During atrioventricular pacing, whereas no significant changes were observed for ANP, PCWP and PAP, CO increased significantly (P < 0,0005), At the beginning of ventricular pacing hemodynamic parameters and ANP levels were comparable with those of baseline conditions. During subsequent ventricular pacing PCWP and ANP increased significantly at the 110 ppm rate step (P < 0.05). PAP did not change significantly, whereas CO decreased in all cases (P < 0.01). A positive correlation was observed between ANP and PCWP during ventricular (P < 0.001), but not atrioventricular pacing. The results, while confining the hemodynamic advantages of atrioventricular pacing, point to a major stimulation of ANP secretion during ventricular pacing. This fact, together with the observed drop in CO and the correlation between ANP and PCWP, suggest that the increase of ANP in ventricular pacing may be the expression of a compensatory mechanism to the hemodynamic disadvantages of atrioventricular asynchrony.
Mechanism of Double Ventricular Response to a Single Atrial Extrastimulus in Patients with Wolff‐Parkinson‐White Syndrome
Authors: MATSUHISA MOKUO , SHIMOMURA KATSURO , OHE TOHRU , KAMAKURA SHIRO , AIHARA NAOHIKO
Published: July 2006

The purpose of this sudy is to elucidate electrophysiological determinants of double ventricular response (DVR) to a single atrial extrastimulus in Wolff‐Parkinson‐White (WPW) syndrome. DVR was observed in 5 (3.4%) out of 146 consecutive patients with WPW syndrome. The site of accessory pathway was located in left lateral free wall in four patients and posterior septum in one. DVR was induced by extrastimulus from coronary sinus in four patients with left‐sided accessory pathway, and from both coronary sinus and high right atrium in a patient with septal accessory pathway. However, it was not possible to induce DVR from high right atrium in patients with left‐sided accessory pathway, because 50 to 80 ms are needed for intra‐atrial conduction from high right atrium to coronary sinus. Critical prolongation of normal AV conduction allowing DVR was seen in the slow pathway of AV node in four patients. In the remaining patients requisite conduction delay occurred in both AV node and His‐Purkinje system. Single right ventricular extrastimulus could easily elicit orthodromic AV reciprocating tachycardia or echo beat in four out of five patients and incremental ventricular stimulation induced it in the remaining patient, indicating the presence of retrograde block in the normal AV pathway. As requisites of DVR to a single atrial extrastimulus in WPW syndrome: (1) slow antegrade conduction and retrograde block in the normal AV pathway; and (2) stimulation site in the vicinity of accessory pathway, are needed.
Paroxysmal Bundle Branch Block of Supraventricular Origin: A Possible Source of Misdiagnosis in Detecting Ventricular Tachycardia Using Time Domain Analyses of Intraventricular Electrograms
Authors: THRONE ROBERT D. , DICARLO LORENZO A. , JENKINS JANICE M. , WINSTON STUART A.
Published: July 2006

Current implantable antitachycardia devices use several methods for differentiating sinus rhythm (SR)from Supraventricular tachycardia (SVT) or ventricular tachycardia (VT). These methods include sustained high rate, the rate of onset, changes in cycle length, and sudden onset. Additional methods for detecting VT include techniques based upon ventricular electrogram morphology. The morphological approach is based on the assumption that the direction of cardiac activation, as sensed by a bipolar electrode in the ventricle, is different when the patient is in SR as compared to VT. Whether paroxysmal bundle branch block of Supraventricular origin (BBB) can be differentiated from VT has not been determined. In this study, we compared the morphology of the ventricular electrogram during sinus rhythm with a normal QRS (SRNIQRS) or SVT with a normal QRS (SVTNIQRS) with the morphologies of BBB and VT in 30 patients undergoing cardiac electrophysiology studies. Changes in ventricular electrogram morphology were determined using three previously proposed time domain methods for VT detection: Correlation Waveform Analysis (CWA), Area of Difference (AD), and Amplitude Distribution Analysis (ADAJ. CWA, AD, and ADA distinguished VT from SRNIQRS or SVTNIQRS in 16/17 (94%), 14/57 (82%), and 12/17 (71%) patients, and BBB from SRNIQRS or SVTNIQRS in 15/15 (100%), 13/15 (87%), and 6/15 (40%) patients, respectively. However, the ranges of values during BBB using these methods overlapped with ranges of values during VT in all cases for CWA, AD, and ADA. Hence, BBB may be a source of misdiagnosis in detecting VT when these time domain methods are used for ventricular electrogram analysis.
Successful Treatment of Congenital Atrial Flutter with Antitachycardia Pacing
Authors: CASE CHRISTOPHER L. , GILLETTE PAUL C. , ZEIGLER VICKI L. , OSLIZLOK PAUL C.
Published: July 2006

Congential atrial flutter is a condition that rarely requires chronic pharmacological therapy. An unusual case of congenital atrial flutter is described which was resistant to medical therapy, yet responded well to antitachycardia pacing. While most experience with antitachycardia pacing in pediatrics has been with the postoperative congenital heart patient, patients such as the one described with unscarred atria may prove to be the most suitable pediatric candidates for this pacing modality.
Electrophysiological Effects of α‐Adrenergic Stimulation
Authors: TALAJIC MARIO , VILLEMAIRE CHRISTINE , NATTEL STANLEY
Published: July 2006

Autonomic blockade for in vivo electrophysiological studies generally involves atropine and beta blockers, ignoring the potential role of α‐adrenergic activity, To evaluate the importance, if any, of α‐adrenergic tone, the electrophysiological effects of incremental doses of phenylephrine were examined in eight chloralose‐anesthetized dogs. In order to study direct effects, all dogs were both beta blocked (with nadolol) and vagally blocked (with the combination of vagotomy and atropine). Results were also obtained after normalization of Wood pressure with nitroprusside or the α‐blocker, prazosin, Phenylephrine caused dose‐dependent increases in systolic and diustolic Wood pressure. This was accompanied by consistent but modest decreases in sinus cycle length (control RR interval 492 ± 34 msec vs 459 ± 29 msec after dose 1 of phenylephrine, P < 0.05, 516 ± 41 vs 484 ± 34 msec control versus dose 2. P < 0.05). These increases in automaticity were not prevented after normalization of arterial pressure by nitroprusside, but were reversed when concomitant α‐recepfor blockade was achieved with prazosin, suggesting that sinus node acceleration resulted directly from α‐receptor stimulation. No effects on atrial, AV nodal or His‐Purkinje conduction were noted. In addition, phenylephrine did not affect atrial, AV nodal, or ventricular refractoriness. In conclusion, conduction and refractoriness of normal cardiac tissue (other than the sinus node) are unaffected by direct α‐receptor stimulation. This justifies the use of combined beta and muscarinic blockers to achieve autonomic blockade under most circumstances.
Transarterial Permanent Pacing of the Left Ventricle
Authors: MAZZETTI HECTOR , DUSSAUT ALEJANDRO , TENTORI CRISTINA , DUSSAUT EDUARDO , LAZZARI JULIO O.
Published: July 2006

Clinical evaluation of a 64‐year‐old male patient with a permanent pacemaker showed a right bundle branch block in his EGG that led to the suspicion of catheter misplacement. A two‐dimensional echocardiogram and bilateral venogram demonstrated that the pacemaker lead was not in the venous system and that its course was from the axillary artery to the left ventricle passing through the aortic valve. Thirty‐three days after implant, replacement of the pacemaker lead through the venous system to stimulate the right ventricular endocardium was performed. At 7 month follow‐up the patient has had no complication from his previous arterial pacemaker implantation.
Catecholamine Levels and Pacing Behavior of QT‐Driven Pacemakers During Exercise
Authors: JORDAENS LUC , BACKERS JOS , MOERMAN EMMANUEL , CLEMENT DENIS L.
Published: July 2006

It is thought that increasing Catecholamine levels in the heart are partly responsible for shortening of the repolarization time and so indirectly for the pacing behavior of the QT driven pacemaker, Adrenaline and noradrenaline (NAJ plasma levels were determined at rest, during symptom‐limited exercise, and during recovery more than 1 month after the implantation of a 919 or a Rhythmyx pacemaker (Vitatron, The Netherlands) in eight patients (age 54–85 yrs). Significant increases were detected in NA level (from 0.57 ± 0.23 ng/mL to 2.15 ± 0.76 ng/mL), but not in the circulating adrenaline level. The correlation coefficient of the mean pacing rate and the mean NA level during exercise and recovery was 0.963 (P < 0.0001), the correlation coefficient with the mean oxygen consumption was 0.888 (P < 0.01). No correlation with the adrenaline level was observed. The correlation coefficient of the changes of pacing rate and the changes of NA level during exercise and recovery was 0.882 (P < 0.005). The pacing rate of the new generation of QT driven pacemakers is closely correlated with the noradrenaline spillover in the plasma, not with the adrenaline level. A short delay (<1 minute) is observed in the adaptation.
Persistent Functional Atrioventricular Block in Two Patients with Prolonged QT Intervals; Elucidation of the Mechanism of Block
Authors: VAN HARE GEORGE F. , FRANZ MICHAEL R. , ROGE CLAUDE , SCHEINMAN MELVIN M.
Published: July 2006

This article describes two infants with prolonged QT interval and intermittent second‐degree atrioventricular block. An asymptomatic 14‐month‐old child with persistent 2:1 atrioventricular conduction since birth underwent electrophysiology study including measurements with a contact monophasic action potential catheter. During 2:1 conduction, atrioventricular block occurred distal to the site of the His‐bundle recording. Monophasic action potential duration was closely related to prior RR intervals. Single premature atrial or ventricular depolarizations during 1:1 conduction followed by a pause, lead to monophasic action potential prolongation and subsequent 2:1 atrioventricular conduction, which was perpetuated by the resulting long RR intervals. Paired premature ventricular contractions or short bursts of ventricular pacing elicited monophasic action potential shortening and subsequent 1:1 atrioventricular conduction that was perpetuated by the resulting short RR intervals. A second infant presented at birth with a prolonged QT interval, ventricular tachycardia, and episodes of second‐degree atrioventricular block with persistent 2:1 atrioventricular conduction. The atrioventricular block was repeatedly elicited by single premature ventricular contractions and terminated by ventricular couplets. We conclude that the atrioventricular block in both patients is functional in nature and results from the interrelationships between ventricular rate, action potential duration, and His‐Purkinje system refractoriness.
Recurrent Symptoms after Ventricular Pacing in Unexplained Syncope
Authors: FITZPATRICK ADAM P. , TRAVILL CHRISTOPHER M. , VARDAS PANOS E. , HUBBARD WILLIAM N. , WOOD ANGUS , INGRAM ANN , SUTTON RICHARD
Published: July 2006

We report clinical and hemodynamic data in two cases of recurrent syncope. Both patients received permanent demand ventricular pacing (VVI) for unexplained syncope. Both patients experienced recurrent syncope after pacemaker implantation. They later underwent 60° head‐up tilt testing, initially noninvasively and then with hemodynamic profile. A vasovagul response fo lilt occurred with bradycardia and was complicated by the onset of ventricular pacing and retrograde atrioventricular conduction (RAVC) with hemodynamic deterioration and rapid reproduction of syncope. Limited intracardiac electrophysiofogical study (EPS) excluded atrioventricular (AV) conduction disease, sinus node disease, and carotid sinus syndrome, and confirmed RAVC. Both patients were upgraded to dual chamber pacing, DDI mode, with 50/80 rate hysteresis. One patient was asymptomatic at repeat tilt testing; the other experienced continued symptoms due to the vasodepressor component of vasovagal syncope. Cardiac pacing alone is ineffective treatment for this phenomenon, and no proven therapy is presently available. Ventricular pacing applied to patients with unexplained syncope may lead to an increase in or continuation of symptoms rather than an amelioration. There is a need for full investigation of such patients, which must include tilt testing, to allow for the most accurate diagnosis possible and guide the most appropriate therapy.