bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison of Two Stab‐On Unipolar Epicardial Pacing Leads in Children
Authors: HAMILTON ROBERT M. , CHIU CHRISTINE , GOW ROBERT M. , WILLIAMS WILLIAM G.
Published: July 2006

The Oscor MP52V and Medtronic 4951 leads have similar construction and intended application. To determine if one of these designs was more suited to pediatric pacing, we reviewed implant, 3 month, and 12 months follow‐up thresholds for all 18 MP52V implants at our institution from December 1989 to April 1991 and compared them to the 4951 implants from fanuary 1982 to October 1989. Lead suirival for tbe MP52V implants was compared to the most recent 36 4951 implants. Patients ranged in ages from 2 days–16 years (median = 4 years) and required antibradycardia pacing for congenital or acquired heart disease. Patients were compared for weigbt and proportion ofatrial leads in each group by t‐test and Fisher exact tests respectively. Energy thresholds were assessed in μJ and compared by t‐test. Lead survival was defined hy abandonment or replacement for any reason. Kaplan 8‐ Meier survival curves were plotted and compared by Gehan's Wilcoxan Test There were no significant differences between the MP52V and 4951 groups for age at implant (53 months vs 80 months) or proportion of atrial implants (5/18 vs 11/36). Lead survival was poor but did not differ significantly (70% vs 78% cumulative survival at 3 vears), usuallv failing by exit block. Implant and follow‐up thresholds did not differ significantly between leads. The MP52V did not provide significant improvement in performance over the 4951. New epicardial lead designs are needed to improve lead survival and thresholds in children.
Spatial Resolution and Role of Pacemapping During Ablation of Accessory Pathways
Authors: MOLIN FRANCK , SAVARD PIERRE , DUBUC MARC , KUS TERESA , TREMBLAY GAÉTAN , NADEAU RÉGINALD
Published: July 2006

The objectives of this study were: (1) to evaluate quantitatively the spatial resolution of pacemapping: and (2) to assess the predictive value and role of pacemapping for the catheter ablation of overt APs. Sixty‐three unipolar leads were used instead of the standard 12‐lead ECG to acquire more information and assess the intrinsic accuracy of pacemapping. Spatial resolution was evaluated in 19 patients for whom data were recorded during bipolar ventricular pacing near the AV ring using the three electrode pairs of a quadripolar ablation catheter with a 5mm interelectrode spacing. The predictive value was assessed in 27 patients with overt APs who underwent HF ablation: their data were recorded during pacing at the site of successful ablation and at one or two sites where HF energy delivery was ineffective. Data from different beats were compared visually by using body surface potential maps and quantitatively by computing average correlation coefficients (r). Heproducibility was high for paced beats (r = 0.98 ± 0.02). Displacements of 5 mm of the pacing site could be detected with a sensitivity of 90% and a specificity of 87%. Correlation between pacing at successful ablation sites and preexcited sinus rhythm was low (r = 0.79 ± 0.11) and the ablation outcome could be predicted with a negative prediction accuracy of 87% and a positive prediction accuracy of 49%. Despite an excellent spatial resolution, pacemapping is of limited value for the identification of successful AP ablation sites, probably because APs can be interrupted at some distance from their ventricular insertion point.
Tolerance to Lower Body Negative Pressure Exposure: Comparison Between Patients with Neurocardiogenic Syncope and Controls
Authors: RUIZ G. AURORA , MADOERY CRISTIAN , SOCAS ARIEL G. , SCAGLIONE JORGE , TENTORI CRISTINA
Published: July 2006

Lower body negative pressure exposure (LBNPE) produces hemodynamic modifications similar to those produced by head‐up tilt test (HUT). Patients with vasovagal syncope are more susceptible to HUT than healthy persons. The supine position during LBNPE would facilitate the simultaneous performance of complementary methods. The aim of this study was to compare tolerance to LBNPE between a group of patients with vasovagal syncope and a group of healthy volunteers. Eleven patients with vasovagal syncope and positive HUT and 13 healthy volunteers without prior history of syncope and negative HUT were included. The following protocol was used: −10 mmHg, 1 minute; −20 mmHg, 1 minute; −30 mmHg, 3 minutes, and −40, −50, −60, and −70 mmHg, 5 minutes for each stage. Tolerance was expressed as: maximum tolerated negative pressure (Max NP), maximum tolerated time (Max T), and Σ P × T, where P = pressure and T = time. Syncope or presyncope during the test was considered positive LBNPE. LBNPE was positive at −50 or −60 mmHg in 8 of 11 patients (73%). One healthy volunteer had presyncope after 5 minutes at −70 mmHg. Tolerance, as expressed by any of the three parameters, was significantly higher for the healthy volunteers (Max NP: −59.1 ± 7.9 vs −70, P < 0.01; Max T: 19.1 ± 4.2 vs 24.4 ± 0.3, P < 0.01; Σ P × T: 836.3 ± 269.5 vs 1214.6 ± 18, P < 0.01). We conclude that patients with neurocardiogenic syncope have a significantly lower tolerance to LBNPE than subjects with no previous history of syncope.
Methods Other Than Tilt Testing for Diagnosing Neurocardiogenic (Neurally Mediated) Syncope
Authors: BRIGNOLE MICHELE , MENOZZI CARLO
Published: July 2006

The recording of spontaneous episodes of bradycardic neurocardiogenic syncope (NCS) has shown that: a prolonged ventricular asystole seems necessary to cause syncope; asystole is preceded by other bradyarrhythmias in the vast majority of cases; some warning symptoms precede the loss of consciousness in most cases; conventional dual‐chamber pacing is efficacious both in patients with a positive response to carotid sinus massage (CSM) and eyeball compression test (EBC) and in those with a positive response to tilt‐testing (TT). CSM, EBC, and TT are established tools for diagnosing NCS, when the recording of spontaneous syncope is lacking. When combined together, they are probably able to correctly identify most patients affected by NCS. Nevertheless, whether the type of reflex induced by the cardiovascular reflexivity maneuvers correlates with that of the spontaneous syncope is largely unknown. Our knowledge suggests that the correlation may be unsatisfactory, owing to the following: the variability of the mechanism of spontaneous syncope from patient to patient and also, in the same patient, from one episode to another; the discordance of the type of response when 2 or 3 tests are positive in the same patient, the response being more frequently asystolic with CSM and EBC and more frequently vasodepressor with TT; the different timing between hypotension induced by CSM (in which it follows the bradycardia) and that induced by TT (in which it usually precedes the bradycardia) and the uncertainty about the timing of hypotension during the spontaneous syncope; the good reproducibility of the spontaneous event by CSM and EBC, but not by TT, when cardiac asystole is the manifestation of NCS: and the fairly high rate of false‐positive results of cardiovascular reflexivity maneuvers. Hypotension is the main reason for the failure of pacemaker therapy in all the forms of neurocardiogenic syncope (NCS), whether diagnosed by CSM, EBC, or TT. Thus, the need arises to correctly identify the magnitude of the hypotensive reflexes of spontaneous events.
Detecting Incipient Vasovagal Syncope: Intraventricular Acceleration
Authors: BRIGNOLE MICHELE , MENOZZI CARLO , CORBUCCI GIORGIO , GARBEROGLIO BRUNO , PLICCHI GIANNI
Published: July 2006

The peak endocardial acceleration (PEA) caused by ventricular isometric contraction can be measured with an implantable microaccelerometer located inside the tip of a normal unipolar pacing lead. It has been shown that PEA correlates with myocardiai contractility and the maximum rate of rise of ventricular pressure (peak dP/dt) of the left ventricle. A PEA measuring system was temporarily inserted into the apex of the right ventricle in seven patients affected by syncope of uncertain origin. Each patient subsequently underwent 60 tilt testing with three different protocols: without pharmacological challenge (baseline); potentiated with sublingual trinitroglycerin (at a dose of 0.3 mg); and with isoproterenol infusion (at a dose of 3 μg/min). Each phase lasted 20 minutes. Syncope was induced in 1 patient during the baseline phase, in 3 patients during the trinitrin phase, and in 4 patients during the isoproterenol phase. Six patients had a negative response during the baseline phase and served as a control group. From the beginning of upright posture to the time of maximum heart rate, PEA increased by about the same amount in both positive and negative patients, but absolute values were from two‐ to three fold higher with isoproterenol (from 1.2 ± 0.5 G to 1.6 ± 0.8 G, from 0.8 ± 0.2 G to 1.2 ± 0.4 G, and from 2.8 ± 1.8 G to 3.6 ± 1.8 G, respectively, for negative, positive baseline or trinitrin, and positive isoproterenol tests). At the time of syncope, PEA values fell to baseline values. PEA changes were inversely correlated with blood pressure changes and directly correlated with heart rate changes. Thus, tilt induced syncope occurred both at low and high levels of left ventricular contractility. Whether spontaneous syncopes occur at low or high PEA behavior remains to be established. Since heart rate correlates well with changes in PEA and is far easier to measure, it is unlikely that a PEA measurement system or, in general, a contractility‐based system, might become an ideal sensing parameter for the introduction of devices to combat vasovagal syncope.
Tilt Testing: A Useful Screen for Rate‐Drop Response
Authors: GAMMAGE MICHAEL DENNIS
Published: July 2006

Tilt testing is accepted as the main tool for the diagnosis of neurocardiogenic syncope, particularly in the “malignant” vasovagal form. As a result of experience with tilt testing, the cardiovascular responses to head‐up tilting in patients with malignant vasovagal syncope (MVVS) have been defined in respect of the vasodepressor (hypotensive) and cardioinhibitory (bradycardic) components. Pacing therapy has been of limited value in the past, with controversy about its role, even in the cardioinhibitory form of MVVS. With the advent of more sophisticated algorithms for pacing (i.e., rate‐drop response [RDR], Thera DR) in response to the onset of bradycardia in MVVS, however, this therapy is being reexamined. This article examines the blood pressure and heart rate responses to head‐up tilt in patients with MVVS and examines the role of this test in screening such patients for the benefits of pacing with RDR. Careful analysis of the pattern of blood pressure and heart rate response during the tilt test may allow selection of those patients likely to respond to RDR and may provide useful information for initial programming of the algorithm.
Modification of Patient Driving Behavior After Implantation of a Cardioverter Defibrillator
Authors: CONTI JAMIE BETH , WOODARD DAVID A. , TUCKER KELLY J. , BRYANT BETH , KING LEANN C. , CURTIS ANNE B.
Published: July 2006

Driving habits among recipients of ICDs have not been well characterized previously, yet such information may have implications for development of national policy. This study was undertaken to characterize driving behavior after defibrillator implantation in our patient population. From 1988–1993, 82 ICDs were implanted at the University of Florida. All patients received defibrillator teaching preoperatively and postoperatively with particular emphasis placed on driving restrictions. A standardized questionnaire was developed to ascertain driving behavior, compliance with restrictions, and occurrence of motor vehicle accidents following implantation. The patients were divided into two groups according to whether or not they had received a shock from their device since implantation. Group I patients did, and Group II patients did not. Fifty‐two out of 82 (63%, Group I) patients had at least one shock. The remaining 30 patients had received no shocks. Mean age and gender were no different between the two groups. Mean time since implantation was 6 ± 1.3 years in Group I, compared to 4 ± 1.5 years In Group II (P = 0.001). Forty‐seven out of 52 (90%) and 26 out of 30 (87%) in Groups I and II, respectively, resumed driving after defibrillator implantation. There was no difference in the amount of time that passed prior to resumption of driving. Group I patients drove more, 20.5 ± 27 miles/day compared to patients in Group II, 8.3 ± 9.7 miles/day (P = 0.02). No patient experienced device discharge during driving; likewise, no patient was involved in a motor vehicle accident secondary to their device firing. Sixty‐seven out of 82 (82%) patients complied with the instructions they thought they heard; seven patients in Group I and eight patients in Group II deliberately did not follow our advice. The majority of patients do comply with physician instructions, although the instructions they remember are not always the instructions given. If a national policy is created to prohibit driving after ICD implantation, effective enforcement may be difficult.
Global Electrophysiological Mapping of the Atrium: Computerized Three‐Dimensional Mapping System
Authors: RODEFELD MARK D. , BRANHAM BARRY H. , SCHUESSLER RICHARD B. , HAND DWIGHT E. , GAMACHE CAROLYN M. , PLATT JOHN W. , LABARBERA STEVEN P. , COX JAMES L. , BOINEAU JOHN P.
Published: July 2006

The atria are anatomically complex three‐dimensional (3‐D) structures. Impulse propagation is dynamic and complex during both normal conduction and arrhythmia, Atrial activation has traditionally been represented on two‐dimensional surface maps, which have inherent inaccuracies and are difficult to interpret. Interactive computerized 3‐D display facilitates interpretation of complex atrial activation sequence data obtained from form‐fitting multipoint electrodes. Accordingly, the purpose of this article is to describe the application of 3‐D form‐fitting electrode molds to the 3‐D mapping and display system developed in this laboratory for the study of complex cardiac arrhythmias. Computer generated 3‐D surface models are created from a database of serial cross‐sectional anatomical images. Points chosen on endocardial and epicardial surfaces in each cross‐sectional image are processed to create polygons defining myocardial wall boundaries. The polygons from adjacent serial images are then combined, to create a 3‐D surface model. The discrete anatomical locations of unit electrodes on multipoint electrode templates are then assigned in the proper position on the surface model. Computer analysis of simultaneous activation data from each unit electrode is performed based on parameters set by the user. Activation data from each unit electrode site are displayed on the computer surface model in a color spectrum correlating with a user‐defined time scale. Activation sequence maps can be visualized as static isochrone maps, interval maps, or as dynamic maps at variable speeds, from any 3‐D perspective. Thus, an interactive computerized 3‐D display system is described, which allows anatomically superior analysis and interpretation of complex atrial arrhythmias.
Clockwise and Counter‐Clockwise Circulation of Wavefronts around an Anatomical Obstacle as One Mechanism of Two Morphologies of Sustained Ventricular Tachycardia in Patients after a Corrective Operation of Tetralogy of Fallot
Authors: CHINUSHI MASAOMI , AIZAWA YOSHIFUSA , KITAZAWA HITOSHI , TAKAHASHI KAZUYOSHI , WASHIZUKA TAKASHI , SHIBATA AKIRA
Published: July 2006

Two different monomorphic VTs were observed in two patients after a corrective operation for tetralogy of Fallot. The activation pattern of the wavefronts of the two VTs were different: in a counter‐clockwise direction around the anatomical obstacle due to a ventriculotomy of the right ventricle in one VT; and in a clockwise direction around the same obstacle in the other VT. The different revolutions of the wavefronts could be the mechanism for the different morphologies of VT.
Permanent Pacing from the Coronary Sinus in a Patient with an Implantable Defibrillator
Authors: PETERS ROBERT W. , KAVESH NEAL , PELINI MICHAEL , GOLD MICHAEL R.
Published: July 2006

A woman with an ICD underwent permanent pacemaker implantation for bradycordia‐tachycardia syndrome. Despite multiple right atrial positions, oversensing secondary to “double counting” was always noted. A coronary sinus pacing catheter was inserted and left atrial pacing was accomplished with acceptable pacing and sensing characteristics. The patient has since done well without further shocks.
Idiosyncratic Pacing with a Commercial Pacing System Analyzer
Authors: ZWEIBEL STEVEN , GOEL SATISH , CALDERON EVELIO , BIOLSI ROBERT , NEGLIA JOHN , GROSS JAY
Published: July 2006

An idiosyncratic response of the Medtronic AV Pacing System Analyzers (models 5311 [unipolar] and 5311B [bipolar]) during high output AAI pacing is reported. Using the bipolar analyzer with unipolar cables and a 2734 adaptor, ventricular capture was noted during high output AAI pacing when the ground was displaced from the patient. Using the unipolar analyzer with bipolar cables also resulted in ventricular capture with high output AAI pacing. Implanting physicians should be aware of this phenomenon to avoid false conclusions.
Pseudoatrial Flutter: Artifact Simulating Atrial Flutter Caused by a Transcutaneous Electrical Nerve Stimulator (TENS)
Authors: WEITZ STEVEN H. , TUNICK PAUL A. , McELHINNEY LILLIAN , MITCHELL TERESA , KRONZON ITZHAK
Published: July 2006

A patient with previous actual atrial flutter had what appeared to be atrial flutter seen on Holter monitoring during treatment with a transcutaneous electrical nerve stimulation (TENS) unit. This proved to be artifact caused by the unit rather than a true arrhythmia. The artifact was reproduced in a normal volunteer by application of a TENS unit.
Syncope: The Diagnostic Value of Head‐Up Tilt Testing
Authors: ORIBE EMILIO , CARO SUSANA , PERERA ROHAN , WINTERS STEPHEN L. , GOMES J. ANTHONY , KAUFMANN HORACIO
Published: July 2006

To determine the usefulness of prolonged head‐up tilt in the diagnosis of neurally mediated syncope, 201 patients with history of syncope of unknown cause and 102 age and gender matched control subjects underwent a 40 minute 60 degree head‐up tilt test. Head‐up tilt elicited syncope (i.e., was positive) in 74 of the 201 patients (37%) with a history of unexplained syncope and in only 6 of the 102 controls (6%). The specificity of the test was 100% in patients 60 years of age and older. Symptoms during tilt‐induced syncope were identified by the patients as similar to those they had suffered during their spontaneous episodes. All 80 subjects who had tilt‐induced syncope recovered without sequelae. The positive predictive value of a positive response to head‐up tilt was 93% and the negative predictive value was 43%. The results indicate that the prolonged head‐up tilt test is a very specific procedure of high diagnostic value in patients with a history of unexplained syncope. It is particularly useful in the elderly age groups who have a high incidence of syncope.
Effects of an Angiotensin II Antagonist on Reperfusion Arrhythmias in Dogs
Authors: MATSUO KUNIHIRO , KUMAGAI KOICHIRO , ANNOURA MIYUKI , YAMANOUCHI YOSHIO , HANDA KOICHI , NAKASHIMA YOSHIYUKI , HIROKI TADAYUKI , ARAKAWA KIKUO
Published: July 2006

Losartan, an angiotensin II receptor antagonist with no bradykinin potentiating property, provides the opportunity to study the consequences of blocking angiotensin II. The objective of this study was to evaluate the antiarrhythmic responses of reperfusion arrhythmia to hsartan in dogs. The effects of losartan on ventricular tachyarrhythmias induced during occlusion and reperfusion of the left anterior descending coronary artery were investigated in 30 dogs. The animals were randomized to receive either losartan (n = 15) or saline (n = 15). The VF inducing threshold was measured before occlusion and after reperfusion. Losartan (50 μg/kg per min) or saline was intravenously administered 5 minutes before occlusion and continued throughout the entire study period. The incidence of ventricular tachyarrhythmias during reperfusion was lower in the losartan group than in the control group (4/15 vs 6/15). There was no significant change in VF inducing threshold between the period before occlusion and during reperfusion in the losartan group (10.9 ± 5.7 vs 11.1 ± 5.7mA, P = NS), whereas there was a significant decrease in the control group (15.5 ± 4.4 vs 7.7 ± 3.9 mA, P < 0.01). Blockade of the angiotensin II receptor has beneficial effects on reperfusion arrhythmias.
Role of Sympathovagal Balance in the Initiation of Idiopathic Ventricular Tachycardia Originating from Right Ventricular Outflow Tract
Authors: HAYASHI HIDEKI , FUJIKI AKIRA , TANI MASANAO , MIZUMAKI KOICHI , SHIMONO MAYUMI , INOUE HIROSHI
Published: July 2006

VT originating from the right ventricular outflow tract (RVOT) is prone to occur when sympathetic nervous activity is increased. β‐Blockade is, therefore, effective in suppressing this VT. The purpose of this study was to determine the role of sympathovagal balance assessed by heart rate variability (HRV) in the spontaneous initiation of repetitive premature ventricular contractions (PVCs) and VT (five or more consecutive PVCs) arising from RVOT in seven patients without structural heart diseases. Frequency‐domain measures of HRV were determined by analyzing 24‐hour Holter electrocardiographic recording with the maximum entropy method over α 1,280‐second period immediately before the onset of 35 single PVCs, 26 episodes of 2‐4 consecutive PVCs, and 21 episodes of VT. High frequency component (HF: 0.15–0.40 Hz) was used as an index of parasympathetic activity, and the ratio of low frequency component (LF: 0.04–0.15 Hz) to HF (LF/HF ratio), as an index of sympathovagal balance. NN50(%), a time‐domain variable of parasympathetic activity, was also determined. Mean RR interval and any measures of HRV did not change significantly before single PVCs. Mean RR interval shortened and HF decreased prior to repetitive PVCs and VT. The LF/HF ratio, however, increased only before the onset of VT. NN50(%) tended to decrease before repetitive PVCs and decreased significantly before VT. With propranolol (30–60 mg/day), frequency of repetitive PVCs was suppressed from 2,048 ± 1,201 to 746 ± 658/day and VT was totally abolished, but frequency of single PVCs did not change significantly. In conclusion, sympathetic predominance plays an important role in the initiation of repetitive PVCs and VT originating from RVOT in patients without structural heart diseases.
A Simple Electrocardiographic Algorithm for Detecting Ventricular Tachycardia
Authors: COHEN TODD J. , COLDNER BRUCE , MERKATZ KENNETH , JADONATH RAM , ADLER HEATHER , EHRLICH JASON C.
Published: July 2006

The purpose of this study wus to determine whether a simple ECG algorithm could be developed for predicting susceptibility to ventricular tachyarrhythmias (VT) as defined by sustained spontaneous or inducible VT. Two different QT dispersion algorithms were determined by the difference between the longest and shortest QT interval measured in three orthogonal leads (I, aVF, V1; QTD3), and at least 11 of 12 leads (QTDl2) from the 12‐lead ECG. These QT dispersion algorithms were investigated (with and without the QRS duration from the 12‐lead EGG) and compared to the signal‐averaged ECG (SAEGG) in order to determine their sensitivity and specificity for detecting VT. Only patients who underwent SAECC and were referred for programmed electrical stimulation were included in this study. A positive SAECG was defined by filtered QRS duration > 114 ms, and/or low amplitude signal duration > 38 ms, and/or root mean square voltage in the last 40 ms of < 20 μV. Sixty patients were enrolled in this study with a mean age of 63 ± 2 years. Eifty‐five percent of the patients had coronary artery disease. A simple ECG algorithm consisting of the sum of QTD3 plus the QBS duration had a sensitivity and specificity of 90% and 63%. respectively, whereas the SAECG had a sensitivity and specificity of 60% and 63%. respectively (P = 0.022). We conclude that a simple EGG algorithm is more sensitive than the SAEGG for predicting VT. This algorithm combines two easily measured variables obtained from the 12‐lead EGG, and can easily be performed without expensive computer equipment.
Optimizing the AV Delay in DDD Pacemaker Patients with High Degree AV Block: Mitral Valve Doppler Versus Impedance Cardiography
Authors: KINDERMANN MICHAEL , ERÖHLIG GERD , DOERR THOMAS , SCHIEFFER HERMANN
Published: July 2006

In DDD‐pacemaker patients with high degree A V block, Doppler echocardiography of transmitral blood flow can be used to find the individually optimal AV delay (AVO) for left heart AV synchronization. This study tried to validate a Doppler method (ECHO) recently proposed to optimize left ventricular filling by comparing it to stroke volume data derived from impedance cardiography (ICG). It should be further elucidated if optimizing the AV delay (AVD) by means of this method is superior to fixed AVD settings and which differential AVD (pace‐sense‐offset) should be programmed for atrially triggered (A TP) and A V sequential (A VP) pacing, respectively. A VO as measured in 53 patients showed a linear correlation between ECHO and ICC for both ATP (r = 0.66, P < 0,00001) and AVP (r = 0.53, P < 0.005). The mean deviation in AVO between ECHO and ICC was ± 26 ms (ATP) and ± 30 ms (AVP), respectively, with a tendency to longer AVDs with the Doppler method. ECHO limitations could mainly be attributed to: (1) restrictions of AVD programming options (which may be compensated for by slight modification of the proposal); and (2) to pathophysiological mechanisms that alter mitral valve dynamics. Optimization of the AVD by Doppler produced a stroke volume that was significantly higher (19%) than with a fixed AVD (150 ms in ATP; 200 ms in AVP). There was a wide scatter in pace‐sense‐offsets between ‐7 and 134 ms, which was reflected by both methods. It is concluded that AVO determinations by ECHO are valid provided that methodological pitfalls and limitations caused by the disease are recognized. Tailoring AVD with respect to diastolic filling improves systolic function and is superior to nominal AVD settings. Fixed differential AVDs as offered by some manufacturers are far from being physiological. Thus modern pulse generators should offer free programmability over a wide range of AV delays.
Effect of Ventricular Pacing on Coronary Blood Flow in Patients with Normal Coronary Arteries
Authors: TAKEUCHI MASAAKI , NOHTOMI YUICHI , KUROIWA AKIO
Published: July 2006

Although ventricular pacing is thought to produce impairment of left ventricular function by altering the sequence of ventricular activation and AV dyssynchrony, little is known about the effect of ventricular pacing on coronary blood flow. We measured coronary blood flow and coronary flow reserve in the left anterior descending coronary artery during sinus rhythm, and during both atrial and ventricular pacing at a rate of 100 ppm in 14 patients with normal coronary arteries. The double product increased significantly during both types of pacing. Coronary arterial diameter during ventricular pacing significantly increased compared to that during both sinus rhythm and atrial pacing. Coronary flow velocity during ventricular pacing was significantly lower compared to that during both sinus rhythm and atrial pacing. Coronary blood flow increased significantly during atriai pacing (30.7%± 12.1%; P < 0.001), but not significantly during ventricular pacing (23.6%± 47.0%; P = ns). While coronary flow re‐serve during both atrial (3.9 ± 1.3) and ventricular pacing (3.8 ± 0.9) was lower compared to its value during sinus rhythm (4,5 ± 1.5), the difference was not significant. There was a significant positive correlation between the coronary flow reserve during sinus rhythm and the increase of coronary blood flow during ventricular pacing (R2= 0.78; P < 0.001). We concluded that an increase in coronary blood flow during ventricular pacing is not a common finding regardless of the increase in metabolic demand. The increase of coronary blood flow during ventricular pacing was less in patients with a reduced coronary flow reserve. These findings suggest that preservation of AV synchrony and the presence of a normal sequence of ventricular activation may play an important role in preserving coranary blaod flow in this subset of patients.
False‐Positive Behavior with the dP/dt Sensing Pacemaker: A Rare Complication of a Physiological Sensor
Authors: CROSSLEY GEORGE H. , KIGER LISA A. , HAISTY WESLEY K. , SIMMONS TONY W. , ZMIJEWSKI MATT , FITZGERALD DAVID M.
Published: July 2006

As with “nonphysiological” devices, sensors that directly measure physiological variables bave the potential to measure unexpected signals and for the physiological parameter being measured to respond in an unexpected manner. We present tbe case of a dP/dt sensing pacing system that functioned normally for 2 months and then developed upper rate behavior due to the sensing of a high frequency artifact on the pressure recording. Our case and others cited reinforce the need for future physiological rate responsive pacemakers to incorporate a second sensor to provide for backup rate response in cases of inappropriate rate response.
Radiofrequency Ablation of a Posteroseptal Accessory Pathway Via the Middle Cardiac Vein in a Six‐Year‐Old Child
Authors: O'CONNOR BRIAN K. , CASE CHRISTOPHER L. , GILLETTE PAUL C.
Published: July 2006

Although radiofrequency ablation is highly successful in patients with the Wolff‐Parkinson‐White syndrome, certain patbways remain refractory to ablation. In particular, subepicardial pathways often fail ablation via an endocardial approach. In adult patients, left‐sided subepicardial pathways bave been treated successfully using energy delivery within the coronary sinus. To document the safety and efficacy of this approach in children, we present the case of a 6‐year‐old boy who underwent radiofrequency ablation of a posteroseptal pathway via energy delivery within tbe middle cardiac vein. Follow‐up study showed no evidence of recurrence or gross coronary vascular injury.
Analysis of Clinical Follow‐up Databases: Risk Stratification Studies and Prospective Trial Design
Authors: MALIK MAREK
Published: July 2006

Design of new prospective studies should utilize detailed retrospective evoluotions of clinicaldata. For this purpose, clinical data are needed containing both prospectively recorded values of risk factors and follow‐up events. A concept of a new trial can then be modeled within the existing data‐set. The development of such a model consists of the following steps: (a) the distribution of values of risk factors has to be investigated in the whole recorded population and the statistical association of the risk factors with follow‐up events has to be established; (b) the stratification characteristics (sensitivity, specificity, and predictive accuracies) have to be evaluated for individual risk factors and for their multivariate combinations; (c) the stratification characteristics have to be converted into estimates of mortality reduction expected within the high risk group and used for the optimum trial design in terms of screened and randomized patient numbers. In this review, the strategy of designing a new trial is demonstrated using data of 644 survivors of acute myocardial infarction with available 3‐year follow‐up during which 74 patients died. A model of a new trial is considered involving reduced left ventricular ejection fraction, increased 24‐hour mean heart rate, and depressed 24‐hour heart rate variability as risk stratifiers.
Factors Predisposing to the Development of Atrial Fibrillation
Authors: LÉVY SAMUEL
Published: July 2006

Atrial fibrillation (AF) is in most patients (approximately 70%) associated with organic heart disease including valvular heart disease, coronary artery disease, hypertension, hypertrophic cardiomyopathy, dilated cardiomyopathy, and congenital heart disease, mostly atrial septal defect in adults. In many chronic conditions, determining whether AF is the result or is unrelated to the underlying heart disease, remains unclear. The list of possible etiologies also include cardiac amyloidosis, hemochromatosis and endomyocardial fibrosis. Other heart diseases, such as mitral valve prolapse (without mitral regurgitation), calcifications of the mitral annulus, atrial myxoma, pheochomocytoma, and idiopathic dilated right atrium may present with AF. Atrial fibrillation may occur in the absence of detectable organic heart disease, the so‐called “lone AF”, in about 30% of cases. The term “idiopathic AF” implies the absence of any detectable etiology including hyperthyroidism, chronic obstructive lung disease, overt sinus node dysfunction, and overt or concealed preexcitation (Wolff‐Parkinson‐White syndrome), only to mention a few of other uncommon causes of AF. The autonomous nervous system may contribute to the occurrence of AF in some patients. AF occurs commonly. In patients with valvular heart disease, AF is common, particularly when the mitral valve is involved. The occurrence of AF is unrelated to the severity of mitral stenosis or mitral regurgitation but is more common in patients with enlarged left atrium and congestive heart failure. In patients with coronary artery disease, AF occurs predominantly in older patients, males, and patients with left ventricular dysfunction. Important predictive factors of AF include hypertension, left ventricular hypertrophy and diabetes. The risk of the development of AF, in an individual patient, is often difficult to assess. Increasing age, presence of valvular heart disease, and congestive heart failure increase the risk of atrial fibrillation.
Risk of Ventricular Arrhythmias in Survivors of Myocardial Infarction
Authors: ANDRESEN DIETRICH , BRÜGGEMANN THOMAS , BEHRENS STEFFEN , EHLERS CHRISTOPH
Published: July 2006

The most recent studies have made it clear that the prognosis of asymptomatic post‐MI patients has significantly improved in the last two decades. Holter monitoring as well as a low LyEF still is an important method for the risk stratification in the thrombolytic era of patients with post‐MI. Patients with normal noninvasive tests do have a good prognosis. The electrophysiological stimulation seems to be the clinically most valuable single method to predict arrhythmic events. However, as an invasive procedure it is not suitable as a screening test for a large cohort. The stepwise risk stratification technique using first noninvasive followed by invasive procedures seem to be most suitable and effective for identifying asymptomatic infarct survivors which incidence of arrhythmic events is as high as the recurrence rate of patients who had been resuscitated from ventricular fibrillation. Consequently, prophylactic implantation of a defibrillator in asymptomatic MI patients, whose positive predictive value is around 30% becomes more and more interesting.
Arrhythmias in Hypertrophic Cardiomyopathy
Authors: KUCK KARL‐HEINZ
Published: July 2006

Supraventricular and ventncular arrhythmias, particularly nonsustained ventricular tachycardia, and ventricular premature beats are a common finding in patients with hypertrophic cardiomyopathy. Several investigations have demonstrated that nonsustained ventricular tachycardia on Holter monitoring is associated with an increased risk of sudden cardiac death. It has been a long lasting controversial discussion whether suppression of these arrhythmias with drugs, such as amiodarone is capable to reduce the incidence of sudden cardiac death. While recent studies have indicated that nonsustained ventricular tachycardia in asymptomatic patients without additional risk factors, such as a positive family history of sudden cardiac death or syncope should not be treated prophylactically with amiodarone. Symptomatic patients with sustained ventricular tachycardias and/or syncope related to ventricular arrhythmias should undergo ICD implantation. The implantation of an ICD in asymptomatic patients should be limited to those who have several risk factors for sudden cardiac death. It is questionable whether other risk stratifiers, such as programmed electrical stimulation may be helpful to identify asymptomatic patients who are at risk to die suddenly. Moreover, whether the demonstration of electrocardiogram fractionation during electrophysiological study is superior to the induction of sustained ventricular arrhythmias for risk stratification, needs further investigation.
Management of Patients with Life‐Threatening Ventricular Tachyarrhythmias in the Defibrillator Era: The Need to Differentiate
Authors: STEINBECK G. , HABERL R. , HOFFMAN E.
Published: July 2006

Patients with a history of sustained ventricular tachyarrhythmias form an extremely inhomogeneous group with respect to presenting arrhythmia, underlying cardiac disease, and therefore, risk of dying suddenly. Eor subgroups such as ventricular tachycardia in the absence of underlying cardiac disease, radiofrequency catheter ablation offers cure. In others, implantation of a cardioverter defibrillator already appears to have gained the therapy of first choice, leaving only a secondary role to antiarrhythmic drugs. It must be emphasized however, that these new therapeutic strategies have their pros and cons like the older, seemingly outfashioned approaches of noninvasively or invasively guided antiarrhythmic drug therapy or empiric amiodarone treatment. Until the advent of controlled randomized trials comparing the implantable cardioverter defibrillator (ICD) with the best other, usually medical form of treatment, physicians must continue to base their individual therapeutic decisions on circumstantial published and personal experience. In doing so, the recent achievements of catheter ablation and defibrillator implantation have definitely improved patient care, but have not made antiarrhythmic drugs jobless. With all the alternatives at hand, it remains a challenging task to weigh the benefits and risks of the various approaches against each other in an attempt to tailor the antiarrhythmic intervention to the very individual need of the patient.
Ventricular Tachycardia in Healing Canine Myocardial Infarction: Evidence for Multiple Reentrant Mechanisms
Authors: KANAAN NABIL , ROBINSON NIKKI , ROTH SANDFORD I. , YE DINGZHONG , GOLDBERGER JEFFREY , KADISH ALAN
Published: July 2006

Prior studies have demonstrated that unimorphic VT, sometimes due to epicardial reentry, can be induced in healing canine MI; however, the characterization of the types of reentry involved has differed among prior studies. The purpose of this study was to further characterize the spectrum of epicardial reentrant circuits during induced VT in experimental canine MI. Experimental MI was created by total occlusion of the LAD in dogs. Five days later, programmed stimulation was used to induce VT, which was mapped on the epicardium using a combination of vector and isochronol techniques. Pathological analysis was used to determine regions of transmural MI. Epicardial reentrant circuits were identified in eight dogs. The mean cycle length of induced VT was 212 ± 32 ms. In 3 of 8 experiments, a region of transmural MI was present, which formed at least a portion of a central zone of block around which reentrant impulses circulated. In five experiments, reentry was functional in nature, although the characteristics of the region of functional conduction block were variable. Long lines of functional block, short lines of block with slow conduction transverse to fiber orientation, and leading circle reentry were each observed in different experiments. Although a zone of slow conduction was identified in seven of the experiments, slow conduction transverse to fiber orientation appeared crucial in maintaining reentry in only three experiments. Multiple reentrant mechanisms of VT may be present in this single canine infarction model. Although a zone of slow conduction is usually present, the characteristics of the region of block are highly variable. However, epicardial reentry accounted for only a minority of induced arrhythmia episodes.
Inappropriate Rate Change in Minute Ventilation Rate Responsive Pacemakers Due to Interference by Cardiac Monitors
Authors: CHEW ENG WOOI , TROUGHEAR RICHARD H. , KUCHAR DENNIS L. , THORBURN CHARLES W.
Published: July 2006

Observations of inappropriate rate increase in five patients with minute ventilation rate responsive implanted pacemakers (Telectronics Meta) are reported. Pacing rate increases were observed immediately upon connection of the resting patients to two brands of widely used cardiac monitors, and one commonly used echocardiograph. In some circumstances, the rate increase remained until monitor disconnection; in others the rate increase was transient, lasting about 20 seconds. A hardware thoracic resistance variation simulator was constructed and connected to one of the pacemakers to test sensitivity to rate modifying interference from external sources. This demonstrated that the sensitivity to interference is dependent upon the frequency of the interfering signal and is highest in the range 10–60 kHz. that peak currents as low as 10 μA can cause maximum rate increase, and that the signals injected into patients by several cardiac monitors, for purposes of lead‐off detection or respiratory monitoring, fall into the frequency range at which the pacemaker is most susceptible to interference.
Morphological Variation of Nonreentrant Idiopathic Ventricular Tachycardia Originating from the Right Ventricular Outflow Tract and Effect of Radiofrequency Lesion
Authors: CHINUSHI MASAOMI , AIZAWA YOSHIFUSA , TAKAHASHI KAZUYOSHI , KOUJI OHIRA , KITAZAWA HITOSHI , WASHIZUKA TAKASHI , ABE AKIRA , SHIBATA AKIRA
Published: July 2006

RF catheter ablation was performed in 16 patients with nonreentrant idiopathic VT originating from the RVOT. All documented VT was monomorphic, but subtle morphological variation in the VT‐QRS complex was observed in 10 (63%) of 16 patients. Through endocardial mapping, VT origin was determined within a narrow site (< 0.5 ± 0.5 cm) in 4 of the 10 patients with the morphological variation. In the other 6 of 10 patients, the origin extended to an area of > 0.5 ± 0.5 cm. In VT with morphological variation, the local electrogram at the site of VT origin also showed variation in morphology and activation sequence. For VT of narrow origin, RF application to the site eliminated the VT. However, in VT from a wide arrhythmogenic area, RF current had to be delivered to 3–7 distinct sites to cover the possible origin, and specific QRS configuration of VT and/or PVC was ablated at each of the earliest activation site. All but one VT were successfully ablated by RF current. Subtle morphological variation was frequent in this type of VT, and about half were associated with a wide arrhythmogenic area. Precise mapping and analysis of the efficacy of each BF application might be helpful to better understand the relationship between subtle changes of VT‐QRS morphology and their origins.
On the Mechanism of Ventricular Defibrillation
Authors: WALGOTT GREGORY P. , KNISLEY STEPHEN B. , ZHOU XIAOHONG , NEWTON JONATHAN G. , IDEKER RAYMOND E.
Published: July 2006

The mechanism of ventricular defibrillation can be considered at many different levels. The highest level is considered the strength of the shock given through the defibrillation electrodes. At the next level, the mechanism of defibrillation can be examined in terms of the electrical field that the shock produces throughout the ventricles. Other levels include the effects this electric field has on the activation sequences and on the cellular action potentials that either initiate or inhibit the early sites of activation following the shock. Yet another level considers the mechanism by which the shock field initiates new action potentials or prolongs the action potential by changing the transmembrane potential during the shock. Finally, the subcellular level is considered, which involves the response of the individual ion channels to the shock. This review gives a brief overview of some salient features of defibrillation at each of these mechanistic levels.
Mechanism of Lethal Proarrhythmia Observed in the Cardiac Arrhythmia Suppression Trial: Role of Adrenergic Modulation of Drug Binding
Authors: PACKER DOUGLAS L. , MUNGER THOMAS M. , JOHNSON SUSAN B. , CRAGUN KEVIN T.
Published: July 2006

A variety of recent in vivo studies have sought to clarify the mechanism underlying the proarrhythmic response to flecainide in the Cardiac Arrhythmia Suppression Trial (CAST). Increased inducibility of relatively stable ventricular arrhythmias in subacute and chronic postinfarction models has been universally observed. The arrhythmogenesis has been explained in part by drug induced modulation of anisotropic conduction in persistently ischemic tissue, increased durations of vulnerable windows, enhanced generation of unidirectional block with the introduction of extrastimuli, variability of repolarization within the ventricular wall, and the creation of stable reentrant circuits with narrow central zones of propagation. While these data explain arrhythmo‐genesis in general, malignant ventricular arrhythmia capable of producing the excess sudden or arrhythmic death mortality in the CAST trial have not been universally observed, nor have the proported beneficial effects of β‐blockade seen in the CAST trial and other studies been explained. Additional studies examining the adrenergic modulation of flecainide binding have shown reversal of flecainide effects in normal tissue, but paradoxical amplification of flecainide induced conduction slowing in depolarized tissue. This variable effect in normal versus abnormal tissue produces significant dispersions of conduction with an expected increased propensity for conduction failure in response to ectopy, increased liminal length for impulse propagation, enhanced vulnerability to premature extrastimuli, and completed reentrant circuits in regions of depressed membrane potentials. This, along with the decrease in action potential duration and accompanying refractoriness in the setting of adrenergic modulation may favor more malignant double wavelet or unstable ventricular arrhythmias.
The ESVEM Trial: Impact on Treatment of Ventricular Tachyarrhythmias
Authors: REITER MICHAEL J.
Published: July 2006

The ESVEM (Electrophysiologic Study Versus Electrocardiographic Monitoring) trial was a prospective, randomized study, initiated in 1983, to compare the outcome of patients in whom antiarrhythmic therapy was guided by serial electrophysiological study with the outcome of patients in whom therapy was guided hy electrocardiographic monitoring. In a surprising finding, there was no difference in rates of arrhythmia recurrence or mortality between the two methods. Subsequent reanalyses using more stringent criteria for both methods or a combined assessment have not significantly improved the predictive accuracy of guided therapy. Because drug therapy in each limh was also randomized, a comparison of specific antiarrhythmic agents was also possible: sotalol therapy and the absence of previous antiarrhythmic drug therapy were associated with a reduction in arrhythmia recurrence. Survey data suggest that the results of this trial have influenced clinical practice.