bluuebunny/crossref_metadata_2025 huggingface dataset:
Communicating with the Public: Community‐Based Nursing Research and Practice
Authors: Flynn Beverly C.
Published: May 2007

Abstract This paper presents examples of community‐based nursing research in relation to selected health care trends that affect practice and considers ways the media can help community health nurses be more effective communicators with the public. Research provides evidence that community‐based nursing practice includes quality services that can control costs; a focus on disease prevention and health promotion: the organization of services where people live, work, and learn; partnerships and coalitions; service to people across the life span; services to culturally diverse populations; access to services for at‐risk populations; development of the community's capacity for health; work with policy makers for policy change; and efforts to make the environment healthier. Two approaches to communication with the public through the media, social marketing and media advocacy, are compared. It is recognized that community health nurses are well prepared and suited for media advocacy. Media advocacy can be used to not only communicate the effectiveness of community‐based nursing practice but also to support the community's voice for public health.
Benefits and Barriers to Well‐Child Care: Perceptions of Mothers in a Rural State
Authors: Earle Leigh Powell , Burman Mary E.
Published: May 2007

Abstract Though preventive health care can be beneficial, many children do not receive regular well‐child care. To gain insight into the reasons for the underuse of well‐child care, this qualitative study elicited consumers' views by examining how mothers in a rural state perceive well‐child care, its benefits, and barriers to obtaining it. Twenty‐one women in two Wyoming counties were interviewed about their knowledge and beliefs about well‐child care and the care their children had received. Five categories of responses for the definition of well‐child care, 10 categories of benefits, and seven categories of barriers were identified. Most of the informants valued well‐child care as providing maternal reassurance, information, identification of problems, developmental testing, preventive care, and health maintenance, and would obtain the recommended care if the barriers they perceived, such as financial limitations and inconvenience, were removed or reduced. Primary care providers can promote the use of well‐child care in numerous ways, including educating consumers on the purposes, benefits, and schedule for preventive care, providing services that consumers value, providing high quality care, and providing cues‐to‐action to prompt consumers to make and keep appointments.
Severity of Abuse To Pregnant Women and Associated Gun Access of the Perpetrator
Authors: McFarlane Judith , Soeken Karen , Campbell Jacquelyn , Parker Barbara , Reel Sally , Silva Concepcion
Published: May 2007

AbstractTo investigate the relationship between abuse to pregnant women and gun access by the abuser, an ethnically stratified cohort of 199 pregnant abused women (70 African‐Americans, 63 non‐Hispanic Anglo‐American, and 66 Hispanic women were interviewed using: (1) The Index of Spouse Abuse, a measure of the severity of physical and nonphysical abuse: (2) The Danger Assessment Scale, a measure of potential danger of homicide; and (3) The Severity of Violence Against Women Scale, a measure of threats of violence and actual violence. There were no significant differences by ethnicity among the 41.2% of the abused women who reported that their male partner had access to a gun. Among these same women reporting gun access, 17% reported the abuser kept the gun on his body. Women reporting gun access by the abuser reported higher levels of abuse on all scaled instruments (P= < 0.01). To protect women's safety and prevent further trauma and potential homicide, routine assessment for abuse and gun access is recommended. Additionally, policy initiatives to remove firearms from abuse perpetrators may reduce the severity of violence experienced by abused women.
The Significance of Sense of Coherence for the Perceptions of Task Characteristics and Stress During Interruptions Amongst a Sample of Public Health Nurses in Hong Kong: Implications for Nursing Management
Authors: Shiu Ann Tak‐Ying
Published: May 2007

Abstract The study aimed to investigate the significance of sense of coherence (SOC) for the perceptions of task characteristics and for stress perceptions during interruptions of public health nurses (PHNs) with children in Hong Kong. The research design employed the experience sampling method. Convenience sampling was used to recruit 20 subjects. During stage one of the study a watch was worn that gave a signal at six random times each day for seven days to complete an experience sampling diary. PHNs on average responded to 34 signals (80%) to complete the diaries which collected data on work and family juggling, task characteristics, and their effects on mood states. At stage two respondents completed the SOC scale which measured confidence in life as comprehensible, manageable, and meaningful. Two major findings provide the focus for this paper. First, results indicate that there was positive correlation between SOC and perceived task characteristics. Second, results reveal that when interruptions occurred, PHNs with high SOC had higher positive affect and lower negative affect than PHNs with low SOC. These results suggest that SOC as a salutogenic model helps PHNs to cope with the family and work juggling as well as the occupational stress. Implications for nursing management on strengthening SOC of PHNs are discussed.
Family Nursing Practice in Public Health: Finland and Utah
Authors: Duffy Mary E. , Vehvilainen‐Julkunen Katri , Huber Debra , Varjoranta Pirjo
Published: May 2007

Abstract This exploratory study of family nursing practice in public health care was conducted in Finland and Utah. Staff nurses were interviewed in focus groups and asked to describe their practice of family nursing, the factors promoting and restraining practice, and the impact of the changes in health care delivery on practice. Thirty‐six Finnish and 30 Utah nurses participated. Pressure to do more activities with fewer nurses and resources, changes in family problems, and skill level of the nurses were common themes. However, differences were evident. Finnish public health nurses used emotional support and information to help families empower themselves to use resources and to strengthen their family unit. Utah nurses focused first on individual level goals and then family cohesion and health. Nurseinitiated referrals and direct physical care were the primary intervention strategies of Utah nurses. Unlike the U.S. health care system, access for all in maternal and child health care and school health allowed Finnish nurses to develop long‐term relationships with families, thus advancing family nursing practice. This study identifies several potential variables for further study particularly related to the organization of health care and nurse‐family relationships.
Exploring Seniors' Views on the Use of Assistive Devices in Fall Prevention
Authors: Aminzadeh Faranak , Edwards Nancy
Published: May 2007

Abstract Falls are a common barrier to independent living among elderly persons. In recent years, growing awareness of the incidence of falls has led to the development of many community based fall prevention programs for older adults. However, the potential impact of these programs is diminished by the lack of research on factors that may influence older persons' decisions to adopt or reject fall prevention behaviors. This exploratory descriptive study employed a focus group approach to elicit qualitative data on seniors' views on the use of assistive devices in fall prevention. Four focus group interviews were conducted with a convenience sample of 30 community‐living older adults from Italian‐ and British‐Canadian backgrounds in Ottawa, Canada. The interviews documented personal experiences with and the meaning of falls, aging, and assistive device use for older adults. The findings have important implications for the public health nursing practice in the realms of individual counseling, social marketing, and policy change to prevent falls among elderly persons. The study also provides direction for future research on this topic.
Domestic Violence Among Patients at Two Rural Health Care Clinics
Authors: Hightower Nikki R. Van , Gorton Joe
Published: May 2007

ABSTRACTDespite a growing body of knowledge concerning family abuse, there is little research focusing on domestic violence in rural settings. Likewise, there is a paucity of research on family abuse among Hispanics. This study examined the prevalence of spousal abuse among predominately low income Hispanic patients of two rural health care clinics. The correlation of certain social factors to domestic violence also was examined. Survey data was collected from 155 adult female patients. Findings revealed a 19% prevalence rate. This rate corresponds to recent measures of domestic abuse nationwide. A bivariate analysis showed a significant positive relationship between spousal abuse and drug/alcohol use by victims' intimate partners. Abuse also was significantly related to the community location of the health care clinics. The article concludes by discussing implications of the study for rural domestic violence intervention, treatment, and research.
The Obesity Paradox and Discrepancy Between Peak Oxygen Consumption and Heart Failure Prognosis—It's All in the Fat
Authors: Artham Surya M. , Lavie Carl J. , Milani Richard V. , Ventura Hector O.
Published: May 2007

The authors present the case of an obese patient with advanced heart failure that demonstrates the paradox between obesity and heart failure prognosis. In addition, the authors discuss the rationale for the correction of cardiopulmonary stress data (used as predictors of survival and listing for cardiac transplantation) for lean weight (as opposed to total body weight), a consideration that may be particularly important in obese patients with a high percentage of body fat.
Arrhythmogenic Effects of Quinidine on Catecholamine‐Induced Delayed Afterdepolarizations in Canine Atrial Fibers
Authors: WIT ANDREW L. , TSENG GEA‐NY , HENNING BERTHOLD , HANNA MICHAEL S.
Published: May 2007

Arrhythmogenic Effects of Quinidine on Catecholamine‐induced Delayed Afterdepolarizations. We studied the effects of quinidine and tetrodotoxin (TTX), two drugs that block Na+ channels, on delayed afterdepolarizations (DAD) caused by norepinepbrine in atrial fibers of the canine coronary sinus. At long stimulus cycle lengths of 10 seconds, quinidine increased the amplitude of the afterdepolarizations and caused triggered activity within 1–2 minutes. Simultaneously, action potential duration (APD) was lengthened but upstroke velocity was not decreased. Prolonged exposure to quinidine eventually decreased upstroke velocity but DAD amplitude remained larger than control and triggered activity was still induced more easily. The effects of quinidine to increase afterdepolarizations was partially related to its prolongation of the APD since shortening APD with repolarizing current decreased DAD amplitude. However, DAD amplitude remained larger than control indicating that quinidine caused triggering by other mechanisms as well. TTX, on the other hand, which blocks Na+ channels but shortens APD, decreased DAD amplitude and triggered activity. Part but not all of these effects resulted from the shortening of APD by TTX since prolongation of APD with depolarizing current only partially restored DAD amplitude. Anti‐arrhythmic drugs, therefore, may have effects on DADs that partly result from changes in the APD. Quinidine may cause cardiac arrhythmias by virtue of its effects to potentiate triggered activity.
Effect of Interelectrode Distance on the Bipolar Strength‐Interval Relationship and Ventricular Effective Refractory Period in Humans
Authors: MORADY FRED S. , KADISH ALAN H , SCHMALTZ STEPHEN , SUMMITT JONI , ROSENHECK SHIMON
Published: May 2007

Effect of Interlectrode Spacing The purpose of this study was to compare the effects of interelectrode distaices of 1 cm and 0.5 cm on the ventricular effective refractory period (VERP) and the strength‐interval relationship during bipolar cathodal pacing. A quadripolar electrode catheter with an interelectrode spacing of 0.5 cm was positioned at the right ventricular apex in 30 subjects, and the VERP was measured in 2‐msec steps at twice the late diastolic threshold using bipolar cathodal pacing, first with an electrode spacing of I cm, then 0.5 cm. With the technique used in this study, there was up to 4 msec of variability in the measured VERP. Therefore, a change in the VERP of at least 6 msec was required before concluding that the interelectrode distance had affected the measured VERP In 15 subjects (group 1), the VERP was not affected by a change in electrode spacing; in nine subjects (group 2) the VERP was 6–10 msec longer with the 0.5 cm spacing than with the 1‐cm spacing, and in six subjects (group 3) the VERP was 6–12 msec longer with the 1.0‐cm spacing than with the 0.5‐cm spacing. Determination of unipolar strength‐interval curves in ten other subjects demonstrated that anodal curves can be distinguished from cathodal curves by the presence of an early diastolic dip and by the occurrence of the ascent of the curve at a longer extrastimulus coupling interval. These features were used as markers of an anodal contribution to the bipolar strength‐interval curves in groups 1, 2, and 3. In subjects in whom there was a difference in the VERP with the two electrode spacings, an anodal contribution to the bipolar strength interval curve was always identifiable in the curve generated with the electrode spacing that had yielded the longer VERP With the bipolar configuration that yielded the longer VERP, the unipolar stimulation threshold at the anode was always ≤ 1.6 mA and was always lower than the anodal threshold of the bipolar configuration that yielded the shorter VERP. In conclusion, the VERP may either lengthen or shorten by up to 10–12 msec when the interelectrode distance is changed from 1 to 0.5 cm during bipolar cathodal pacing. The effect of electrode spacing on the measured VERP is attributable to position‐dependent effects on the unipolar anodal stimulation threshold. A lower anodal threshold may result in a greater degree of anodal contribution during bipolar pacing, manifest by the occurrence of the ascent of the strength‐interval curve later in diastole and a corresponding increase in the VERP measured at a current strength of twice the late diastolic threshold. (J Cardiovasc Electrophysiol, Vol. 1. pp. 103–115, April 1990)
Effects of Myocardial Ischemia on Triggered Activity in Hamster Atrial Transplants
Authors: GILMOUR ROBERT F. , ZIPES DOUGLAS P.
Published: May 2007

Effects of Ischemia on Triggered Activity. The effects of acute myocardial ischemia on delayed afterdepolarizations and triggered activity were determined in vascularized hamster atrial cheek pouch transplants. Triggered activity was initiated in eight normally perfused transplants by spontaneous or paced action potentials. During control, bursts of triggered activity lasted 14.4 ± 2.S sec (mean ± SEM), had an average cycle length of 456.6 ± 33.8 msec, and terminated following a subthreshold delayed afterdepolarization having an amplitude of 13.8 ± 0.5 mV. Interruption of blood flow to the transplants initially suppressed induction of triggered activity by spontaneous action potentials, shortened bursts of triggered activity initiated by pacing, and tended to prolong the cycle length during triggered bursts. Complete suppression of triggered activity occurred after 15–70 minutes of ischemia. Despite a reduction of delayed afterdepolarization amplitude during ischemia, the membrane potential at the peak of the afterdepolarization became less negative, secondary to ischemia‐induced reductions of resting membrane and takeoff potentials. Thus, suppression of triggered activity during ischemia appeared to be caused by a shift of the voltage threshold to less negative membrane potentials, rather than by a reduction in delayed afterdepolarization amplitude. (J Cardiovasc Electrophysiol, Vol. 1. pp. 139–144, April 1990)
Underlying Heart Rhythm after Catheter Ablation of the Atrioventricular Conduction System
Authors: VIJGEN JOHAN , ECTOR HUGO , GEEST HILAIRE DE
Published: May 2007

Underlying Heart Rhythm after Catheter Ablation of the Atrioventricular Conduction System. Catheter fulguration was used to treat 30 patients with refractory supraventricular arrhythmias. Persistent complete heart block was achieved in 23 patients (77%). Two patients (6%) have intermittent complete heart block, and remain asymptomatic without additional drug therapy. In one patient, AV conduction resumed, but the patient became asymptomatic with previously ineffective drugs. The procedure was ineffective in four patients (13%). To assess the long‐term stability of the subsidiary escape rhythm, we describe the underlying heart rhythm, after pacemaker inhibition by chest wall stimulation, on 125 occasions in 25 patients with complete heart block. The mean follow‐up period was 30 months (range: 2–79 months). Ten patients (40%) did have an escape rhythm on every assessment. The cycle length of the subsidiary escape rhythm was 1,380 ± 421 msec (mean $ SD). Catheter ablation of the AV junction should only he used as a last resort, hecause of the possible induction of a pacemaker dependent state. A reliable escape rhythm was present in only 40% of the patients. (J Cardiovasc Electrophysiol, Vol. 1, pp. 209–213, June 1990)
Cardiac Sarcoidosis: A Report of Four Cases with Ventricular Tachycardia
Authors: BECKER DAVID , BERGER ERIC , CHMIELEWSKI CHESTER
Published: May 2007

Cardiac Sarcoidosis: A Report of Four Cases with Ventricular Tachycardia. Four patients with systemic sarcoidosis who presented with ventricular tachycardia are described. Three of the four patients had biopsy proven cardiac involvement while the fourth had systemic sarcoidosis and fixed thallium scan defects without evidence of coronary artery disease. Antiarrhythmic therapy for these patients was guided by means of electrophysiological testing. Two patients received an automatic implantable cardioverter defibrillator (AICD), one following ineffective ablative surgical treatment. Two other patients had presumed effective drug therapies determined by electrophysiological testing. One of these patients died suddenly 21 months after therapy was initiated. This patient did not have inducible sustained ventricular arrhythmias during baseline electrophysiological study, but was treated for inducible nonsustained arrhythmias. This report expands the number of patients with cardiac sarcoidosis and arrhythmias in the literature and illustrates the difficulty in guiding therapy. Because sarcoid infiltration and subsequent scarring of the myocardium may be progressive, the long‐term effectiveness of surgery, antiarrhythmic medications and corticosteroids may not be predictable. AICD implantation has the potential to remain an effective therapy despite the emergence of new tachyarrhythmias. (J Cardiovasc Electrophysiol, Vol. 1. pp. 214–219, June 1990)
Effects of Drug Metabolism, Metabolites, and Stereoselectivity on Antiarrhythmic Drug Action
Authors: TURGEON JACQUES , MURRAY KATHERINE T. , RODEN DAN M.
Published: May 2007

Metabolism, Stereoselectivity, and Antiarrhythmic Drug Action. The notion that variability in response to a desired antarrhythmic drug therapy can he reduced by adjusting doses to produce a desired plasma concentration is well established. However, unexplained toxicity or efficacy at low plasma concentrations, or suhstantial variahility in concentration‐effect relations can still occur. This review addresses two major potential sources of such responses: stereoselective drug action and the formation of active drug metaholites. Intensive study of the role of these phar‐macokinetic factors can not only improve patient care hut also can provide major clues to the fundamental determinents of drug‐macromolecule interactions which mediate drug effects in man. (J Cardiovasc Electrophysiol, Vol. 1, pp. 238–260, June 1990)
An Analysis of Beat‐By‐Beat Recording of Late Potentials and His‐Purkinje Signals in a Hospital Environment
Authors: YANG WEIQUN , HORAN LEO G. , FLOWERS NANCY C.
Published: May 2007

Beat‐by‐Beat Recording of Low‐Level Potentials. Due to the excessive electrical and magnetic noise in a hospital environment, the utility of low‐amplitude electrocardiographic signals has been greatly impeded. In order to record surface ventricular late potentials and His‐Purkinje potentials on a beat‐by‐beat basis outside a shielded environment, a new system was implemented with a microcomputer. In the case of late potential recording, six bipolar orthogonal leads (two along each axis) were high‐pass filtered, spatially averaged, and finally combined into vectormagnitude complexes on an every beat basis. Bidirectional filters and finite impulse response filters with linear phase response were used to prevent filter ringing in the terminal QRS. Late potentials were recorded on a heat‐by‐beat hasis in patients who exhibited late potentials in the signal‐averaged electrocardiogram (ECG). His‐Purkinje potentials were recorded using spatial averaging and channel selection algorithms that discriminate the signal from noise. All the recordings were performed in a clinical environment without using a shielded room. Magnetic fields of 60 Hz and its harmonics were the major sources of interference, and interference‐free recordings could he obtained if the field was smaller than 6.6 × 10−8 Tesla (T) at 60 Hz. The study indicates that with appropriate instrumentation and care during acquisition, it is feasible to acquire high quality data and analyze late potentials and His‐Purkinje potentials on a beat‐hy‐heat hasis in a clinical environment. Interested investigators are cautioned against basing clinical decisions on marginal quality and noisy data. (J Cardiovasc Elec‐trophysiol. Vol. 1, pp. 486–495 December 1990)
The Relation Between Contraction and Intracellular Sodium in Voltage‐Clamped Sheep Purkinje Fibers
Authors: LEVI ALLAN J. , BOYETT MARK R.
Published: May 2007

Contraction and Intracellular Sodium. Intracellular sodium activity (aiNa) and contraction were simultaneously recorded in voltage‐clamped sheep Purkinje fibers while the sodium‐potassium pump was inhibited with strophanthidin or low potassium. Exposures to low (1.5×10−7M) and high (10−5M) doses of strophanthidin resulted in aiNa and contraction increasing together. However, when strophanthidin was washed off, aiNa recovered more slowly than contraction. Due to this lag of aiNa behind contraction, there was hysteresis in the relation between contraction and aiNa. We compared strophanthidin exposures in voltage‐clamped fibers to those in unclamped fibers with action potentials. The lack of association between contraction and aiNa was less when fibers were clamped. We conclude that some of the dissociation previously reported in unclamped fibers was due to changes of membrane potential with strophanthidin. Using voltage clamp, we also compared the effect of different doses of strophanthidin applied to the same fiber. Higher doses of strophanthidin caused a larger rise of contraction for a similar increase of aiNa. Higher doses, which inhibit the Na‐K pump to a greater extent, also resulted in a faster rate of rise of aiNa. Inhibition and reactivation of the Na‐K pump with bathing potassium (or rubidium) also resulted in hysteresis between contraction and aiNa. A greater reduction of potassium caused a larger rise of contraction for a similar rise of aiNa. Lower potassium inhibits the Na‐K pump more completely and results in a faster rate of rise of aiNa. Although the absolute rise of aiNa with strophanthidin or low potassium is related to the increase of contraction, we conclude that this is not the only factor. The inotropic effect of these agents is also related to the rate at which aiNa rises; when the rate of rise is large, a given level of aiNa is associated with a larger contraction. Such behavior may be compatible with the presence of aiNa gradients from the subsarcolemmal space to the bulk cytoplasm during pump inhibition.
Vagal Stimulation of the Heartbeat: Muscarinic Receptor Hypothesis
Authors: PAPPANO ACHILLES J.
Published: May 2007

“For the best and safest method of philosophizing seems to be, first diligently to investigate the properties of things and establish them by experiments, and then later seek hypotheses to explain them… For hypotheses ought to be fitted merely to explain the properties of things and not attempt to predetermine them except so far as they can be an aid to experiments.” (I. Newton, Opera, Vol. IV, p. 314; From The Metaphysical Foundation of Modern Science. E.A. Burtt, Doubleday & Company, Inc., Garden City, New York, 1932; p.215.)
Ionic Current in Sinoatrial Node Cells
Authors: IRISAWA HIROSHI , HAGIWARA NOBUHISA
Published: May 2007

Ionic Current in Sinoatrial Node Cells. In this article, we report our current understanding of ionic mechanisms of the spontaneous rhythm of the mammalian sinoatrial pacemaker cells obtained from whole‐cell voltage clamp studies. Various ionic currents that underlie the pacemaker potential are discussed. Calcium (Ca) current, delayed‐rectifier potassium (K) current, and hyperpolarization‐activated inward current were found to be the major time‐dependent currents responsible for the pacemaker depolarization. Together with these time‐dependent currents, a time‐independent background current may also contribute to generation of pacemaker activity.
A Review of Surgery for Atrial Fibrillation
Authors: COX JAMES L. , BOINEAU JOHN P , SCHUESSLER RICHARD B. , FERGUSON T. BRUCE , LINDSAY BRUCE D. , CAIN MICHAEL E. , CORR PETER B. , KATER KATHY M. , LAPPAS DEMETRIOS G.
Published: May 2007

A Review of Surgery for Atrial Fibrillation. Atrial fibrillation is the most common of all sustained cardiac arrhythmias, yet it has no effective medical or surgical therapy. During the past decade, multipoint computerized electrophysiologic mapping systems were used to map both experimental and human atrial fibrillation. On the basis of these studies, a new surgical procedure was developed for atrial fibrillation. Between September 25, 1987, and July 1, 1991, this procedure was applied in 22 patients with paroxysmal atrial flutter (n = 2), paroxysmal atrial fibrillation (n = 11), or chronic atrial fibrillation (n = 9) of 2 to 21 years duration. All patients were refractory to all antiarrhythmic medications, and each patient failed to receive the desired therapeutic benefits of an average of five drugs administered preoperatively. There were no operative deaths and all perioperative morbidity resolved. All 22 patients have been successfully treated for atrial fibrillation with surgery alone. Preservation of atrial transport function has been documented in all patients postoperatively, and all have experienced marked clinical improvement.
Currently Known Mechanisms Underlying Direct Current External and Internal Cardiac Defibrillation
Authors: WITKOWSKI FRANCIS X. , KERBER RICHARD E.
Published: May 2007

Mechanisms of Cardiac Defibrillation. Cardiac defibrillation is currently the only available successful therapy for ventricular fibrillation. Despite the wide application of this effective clinical tool, controversy exists concerning the electrophysiologic mechanisms by which the passage of electrical current through the heart terminates ventricular fibrillation. The development and application of clinically useful implantable cardioverter defibrillators has been accelerated by the generic nature of electrical therapy and by frustration in finding pharmacologic means of improving mortality. The current concepts that explain the mechanisms for the pernicious stability of ventricular fibrillation, and how external and internal defibrillation alter this rhythm disturbance, are presented.
CNS Regulation of Cardiac Rhythm and the Potential for Pain‐Induced Arrhythmia
Authors: GILLIS RICHARD A. , MANDAL ALOKE K. , GATTI PHILIP J. , NORMAN WESLEY P. , QUEST JOHN A.
Published: May 2007

CNS Control of Cardiac Rhythm. The purpose of our studies was to determine brain areas that influence cardiac rhythm. Studies were performed in anesthetized cats and indicate that a yet undetermined site in the hindbrain involving GABAergic mechanisms has a major influence over cardiac rhythm. In addition, a serotonergic mechanism involving 5‐HT2 receptors in the subretrofacial nucleus is responsible for selective activation of sympathetic neurons to the ventricle of the heart. Our data also indicate that neurons in the area postrema exert a major effect on cardiac rhythm. Finally, the question of whether pain‐induced changes in cardiovascular function involves neurons in the subretrofacial nucleus is also addressed.
Stress‐Specific Influences of Opioids on Cardiac Electrical Stability
Authors: VERRIER RICHARD L. , CARR DANIEL B.
Published: May 2007

Opioids and Arrhythmias. Evidence is provided indicating that the action of opioids on cardiac electrical stability is contingent on the nature of the stress that impinges on the myocardium. This concept is illustrated by the studies of three clinically relevant conditions, namely, acute behavioral stress, hemorrhage, and myocardial ischemia. During aversive conditioning in dogs, morphine sulfate has been found to prevent the stress‐induced reduction in cardiac electrical stability. This protective effect is significantly blunted by administration of atropine, indicating that enhanced vagal activity plays a major role. However, there is a remaining component of morphine's action, which is probably due to reduced perception of the aversive stress. In the context of hemorrhage, the mu‐selective agonist fentanyl substantially reduces the profibrillatory effect of this physiological stress. The main mechanism involved in this condition is amplification of baroreceptor sensitivity leading to inhibition of cardiac sympathetic drive. Full activation of mu receptors with fentanyl is also effective in reducing vulnerability to fibrillation during acute coronary artery occlusion. This effect was due to vagal efferent activation and not to enhanced baroreceptor responsiveness as in the case of hemorrhage. Administration of the partial mu‐agonist buprenorphine does not exert an antifibrillatory action. Collectively, these results not only demonstrate the potent stabilizing influence of opioids on cardiac rhythm but also the stress specificity of the intermediary mechanisms.
Antinociceptive States and Hypertension
Authors: RANDICH ALAN , THURSTON CINDY L.
Published: May 2007

Antinociception and Hypertension. A review of available data indicates that acute and chronic increases in arterial blood pressure (ABP) are associated with antinociception in animals and hypoalgesia in humans. The primary issues of concern are whether increases in ABP are directly responsible for altered nociceptive function, and the extent to which carotid sinus, aortic depressor, and/or vagal afferents contribute to the changes in nociceptive function.
Incidence of Atrial Fibrillation Following Ventricular Defibrillation with Transvenous Lead Systems in Man
Authors: JONES GREG K. , JOHNSON GEORGE , TROUTMAN CHARLES , BUONO GRACE , GARTMAN DAVID M. , KUDENCHUK PETER J. , POOLE JEANNE E. , DOLACK G. LEE , BARDY GUST H.
Published: May 2007

Atrial Fibrillation After Ventricular Defibrillation. Introduction: The induction of atrial fibrillation (AF) following implantable defibrillator therapy of ventricular fibrillation carries multiple risks. The frequency of shock‐induced AF may be more problematic in patients with transvenous defibrillators because current is often delivered through atrial tissue. Thus, the purpose of this study was to determine the incidence of AF following transvenous ventricular defibrillation.

Methods and Results: Atrial electrograms were recorded before and after energy delivery in patients undergoing intraoperative testing of transvenous defibrillation lead systems. A total of 114 tracings were examined from 21 patients following ventricular defibrillation. Transvenous deflbrillation shock strength ranged between 200–800 volts (2–40 joules). Bipolar atrial electrograms were obtained from atrial electrodes with 1‐cm interelectrode spacing located on one of the defibrillation catheters. The timing of the ventricular defibrillation shock was expressed as a percentage of the preceding sinus PP interval. Three of the 114 transvenous shocks (2.6%) generated AF. Each episode of AF occurred in a different patient. The shocks responsible for AF occurred at 21%, 43%, and 84% of the preceding sinus PP interval. No relation was found between AF induction and the timing of pulse delivery, pulse strength, or pulse number.

Conclusion: We conclude that transvenous ventricular defibrillation infrequently causes AF and that timing shock delivery to the atrial cycle is likely to be of marginal or no benefit in the prevention of shock‐induced AF. (J Cardiovasc Electrophysiol, Vol. 3, pp. 411–417, October 1992)
Transient Manifestation of Antegrade Conduction Over a Kent Bundle After Ventricular Pacing
Authors: YAMASHITA TAKESHI , INOUE HIROSHI , NOZAKI AKIRA , AJIKI KOHSUKE , OIKAWA NAOKI , KUO TSONGTEH , USUI MASAHIRO , MURAKAWA YUJI , SUGIMOTO TSUNEAKI
Published: May 2007

Postventricular Pacing Preexcitation. Antegrade conduction over a Kent bundle was transiently manifested after the cessation of ventricular overdrive pacing in two patients; otherwise, the heart behaved as if it had a concealed accessory pathway. Conventional electrophysiologic study suggested either a longitudinal dissociation of an accessory pathway or closely located double accessory pathways. The mechanism of the transient manifestation of ventricular preexcitation was discussed. (J Cardiovasc Electrophysiol, Vol. 3, pp. 423–430, October 1992)
Transcatheter Endocardial Ablation: Acute Effects of Direct Current Countershock on Regional Myocardial Blood Flow
Authors: TCHOU PATRICK , REEVES WILLIAM , AKHTAR MASOOD , HARE JOHN , RIEDER MICHELLE , CHRISTENSEN CARL
Published: May 2007

Effect of DC Shock Ablation on Myocardial Blood Flow. Introduction: High energy direct current ablative shocks delivered through endocardial electrode catheters have been used as a treatment for various cardiac arrhythmias including ventricular tachycardia. Frequently, these shocks result in depression of myocardial function, at least transiently.

Methods and Results: This study assessed the effect of a 200‐joule direct current shock delivered endocardially to the apex of the heart in ten adult mongrel dogs. Arterial blood pressures were monitored continuously. Myocardial contraction was monitored via two‐dimensional echocardiography. Regional myocardial blood flows were measured using radionuclide labeled microspheres before delivery of the shock, 30 seconds after delivery of the shock, and at 5 and 10 minutes after the shock. The results of the study demonstrated that there was a marked drop in arterial blood pressure immediately after the shock that gradually recovered over a 20‐minute period. Regional myocardial blood flow at the site of catheter ablation was severely depressed immediately after the shock. The degree of myocardial blood flow depression was inversely related to the distance from the site of ablation. At 5–10 minutes after ablation there was a marked hyperemic response in areas that suffered from depressed flow immediately after the shock. Two‐ dimensional echocardiography demonstrated depressed contractile function immediately after the shock with gradual recovery over a 10‐ to 20‐minute period. The catheter shock also generated prominent echo densities within the myocardium surrounding the ablative site. In contrast to the intracavitary echo densities that cleared quickly, the intramyocardial densities cleared much more slowly.

Conclusion: The results of the study confirm the clinical observation that human left ventricular function is depressed acutely following a high‐energy ablative shock delivered to the left ventricular endocardium. Our results also demonstrated for the flrst time the effect of such ablative shocks on regional myocardial blood flow. Such depressions of blood flow may help explain the sudden drop in contractile function of the heart. The persistent intramyocardial echoes seen after the shock probably represented generation of intramyocardial bubbles that could obstruct arterial flow as well as disrupt cellular function. (J Cardiovasc Electrophysiol, Vol. 3, pp. 40–47, February 1992)
Propagation of Electrical Activity in Ischemic and Infarcted Myocardium as the Basis of Ventricular Arrhythmias
Authors: JANSE MICHIEL J. , KLÉBER ANDRÉ G.
Published: May 2007

Impulse Propagation in Ischemia. The disturbances in impulse propagation in the heart with regional ischemia and the heart with chronic infarction, which underlie the initiation and perpetuation of arrhythmias, are briefly reviewed. Evidence is presented that reentry is responsible for ventricular tachycardia in both conditions. During acute ischemia, reentrant excitation is characterized by unstable functional reentrant circuits, the properties of which are determined by the changes in transmembrane action potential. Tachycardia is caused by a single unstable reentrant circuit. Fibrillation ensues when a single circuit is broken up into many independent reentrant wavelets. In contrast, ventricular excitation during sustained monomorphic tachycardia in hearts with a healed infarct is characterized by stable reentrant circuits determined by the architecture of surviving myocardial cell bundles within the infarct. In acutely ischemic myocardium, conduction velocity is reduced to about half of the value in normal myocardium, due to the reduced action potential amplitude and upstroke velocity. After about 5–10 minutes ischemic cells become inexcitable at resting membrane potentials of ‐50 to ‐60 mV. An important characteristic of ischemic cells is the dependence of the action potential upstroke on cycle length mainly because of the markedly prolonged recovery from inactivation of the fast Na+ current in partially depolarized cells. Changes in transmembrane potentials do not occur homogeneously throughout the ischemic zone, and small differences in resting potential (associated with small differences in local K+ accumulation) of depolarized cells result in large local differences in refractory periods. The time dependence of refractoriness explains why an increase in sinus rate, or a single premature beat, may produce conduction block at certain sites, and allow conduction in adjacent areas, thus setting the stage for reentry. A decrease in electrical cell‐to‐cell coupling, which also is a factor in decreasing conduction velocity, only occurs after 15–20 minutes of ischemia. Its role in the type 1B arrhythmias, which coincide with the period when uncoupling begins, remains to be elucidated. The cellular electrophysiology of myocardial cells surviving in the subendocardium of infarcts in human hearts is close to normal. Conduction slowing may be caused by “zigzag” conduction along small bundles that are separated by fibrous tissue, and that merge and divide over small distances. (J Cardiovasc Electrophysiol, Vol. 3, pp. 77–87, February 1992)
Dantrolene Sodium‐Induced Purkinje Fiber Action Potential Duration Prolongation and Its Relation to the Geometry of the Preparation
Authors: WAXMAN MENASHE B. , ASTA JOHN A.
Published: May 2007

Dantrolene‐Induced Purkinje Fiber Action Potential Prolongation. Introduction: The purpose of this study was to investigate the influence that the mode of drug administration and preparation geometry exerted on the ability of dantrolene to prolong sheep and canine Purkinje fiber (PF) action potential duration (APD).

Methods and Results: Sheep PF with attached muscle were superfused with dantrolene 3–5 μg/mL for 90 minutes (group A), while identical preparations were incubated in dantrolene 33.3 μg/mL for 5 minutes, then washed for 60 minutes (group B). Additional preparations were incubated with dantrolene (as in group B) for 5 minutes, then washed for 60 minutes: sheep PF (group C); sheep PF attached to muscle at one end but tied off from the muscle (group D); PF as in group D with a freshly cut branch (group E); freshly cut canine PF (group F); and sheep PF attached to muscle at one end were placed in a partitioned bath and each side incubated with dantrolene separately and then washed for 60 minutes (group G). Superfusion (group A) or incubation (group B) with dantrolene prolonged PF APD by 93% and 83%, respectively (NS). Sealed PF of groups C and D: APD prolonged by 10% and 34%, respectively (compared to A, P < 0.01). Freshly cut PF in groups E and F: APD lengthened by 78% and 74%, respectively (compared to A, NS). Dantrolene administration to the PF side and to the muscle side in group G prolonged the PF APD on either side similarly.

Conclusion: Thus, dantrolene is effective by prolonged superfusion or short incubation. Dantrolene penetrates sealed PF poorly, but readily penetrates freshly cut PF or ventricular muscle. In vitro geometry greatly influences dantrolene's effect on Purkinje fibers. (J Cardiovasc Electrophysiol, Vol. 3, pp. 119–127, April 1992)
Catheter Ablation with Radiofrequency Energy: Biophysical Aspects and Clinical Applications
Authors: KALBFLEISCH STEVEN J. , LANGBERG JONATHAN J.
Published: May 2007

Radiofrequency Catheter Ablation. Radiofrequency catheter ablation techniques are becoming increasingly accepted as the therapy of choice for selected patients with symptomatic arrhythmias. The ability to titrate the power output using radiofrequency current has allowed these ablative techniques to be applied safely in a variety of arrhythmias. In many institutions, radiofrequency catheter ablation has now become standard therapy for controlling medically refractory atrial arrhythmias using atrioventricular (AV) junction ablation and for curing AV nodal reentrant tachycardia and supra ventricular tachycardia due to accessory AV connections. This technology is also being used to treat some forms of ventricular tachycardia such as bundle branch reentry ventricular tachycardia, ventricular tachycardia in structurally normal hearts, and with limited success in patients with ventricular tachycardia and coronary artery disease. Advancements in catheter design and energy delivery systems may further expand the use of this form of therapy. (J Cardiovasc Electrophysiol, Vol. 3, pp. 173–186, April 1992)
On the Mechanism of Inhibition of KATP Channels by Glibenclamide in Rat Ventricular Myocytes
Authors: RIPOLL CRISTINA , JON LEDERER W. , NICHOLS COLIN G.
Published: May 2007

Glibenclamide Block of KATP Channels. Introduction: The mechanism by which glibenclamide inhibits KATP channel activity has been examined in membrane patches from isolated rat ventricular cells. Methods and Results: Inside‐out patches were exposed to zero, or low, [ATP] to activate KATP channels. Glibenclamide did not affect single channel conductance, but reversibly reduced channel open probability from either side of the membrane. Internal (cytoplasmic) glibenclamide inhibited with half‐maximal inhibitory [glibenclamide] = 6 μM, Hill coefficient = 0.35. Complete channel inhibition was not observed, even at 300 μM [glibenclamide]. The response to step increases of internal [glibenclamide] could be resolved into two phases of channel inhibition (t1/2, fast, < 1 sec, t1/2, slow= 10.5 ± 0.9 sec, n = 8). Step decrease of [glibenclamide] caused a single resolvable phase of reactivation (t1/2= 20.4 ± 0.7 sec, n = 16). Channel inhibition by internal glibenclamide could be relieved by ADP, but only in the presence of Mg2+.

Conclusion: Glibenclamide can inhibit KATP channels from either side of the membrane, with block from one side being competitive with block from the other. Internal MgADP antagonizes the blocking action of glibenclamide. Glibenclamide inhibition of cardiac KATP channels differs quantitatively and qualitatively from the inhibition of pancreatic KATP channels.
Reentrant Circuits and the Effects of Heptanol in a Rabbit Model of Infarction with a Uniform Anisotropic Epicardial Border Zone
Authors: Ph.D. GERALD NASSIF. , DILLON STEPHEN M. , RAYHILL STEVEN , WIT ANDREW L.
Published: May 2007

Reentry in Rabbit Ventricles. Introduction: The purpose was to study reentry in a rabbit model of infarction.

Methods and Results: A model of an infarct epicardial border zone was produced in Langendorff perfused rabbit hearts by freezing the inner two thirds of the left ventricular wall, allowing only a thin epicardial muscle layer to survive. Reentrant circuits causing stable ventricular tachycardia occurred in the surviving rim of epicardial muscle as shown by mapping impulse propagation with a 196–electrode array. The circuits were functional, and reentry did not occur around an anatomical obstacle. Slow conduction in the circuits was caused by the anisotropic properties of the epicardial muscle. Activation in the circuits was slow transverse to the long axis of the fiber bundles and rapid parallel to the long axis. Other features of the circuits, including orientation of the central functional line of block parallel to the fiber long axis, and an oval shape are also characteristic of anisotropic reentry. Since the slow conduction causing reentry is a result of poor transverse intercellular coupling, we determined whether the “uncoupler” heptanol would cause block in the circuits and terminate tachycardia. Heptanol in concentrations up to 1.2 mM slowed conduction in the transverse and longitudinal directions in the circuits and sometimes extended the central line of functional block. It did not, however, stop reentry because the reentrant impulse was still able to conduct around the ends of the block line.

Conclusion: Drugs that decrease intercellular coupling may not be effective antiarrhythmic agents when uniform anisotropy causes functional reentry.