Propagation of plane waves in nonlocal semiconductor nanostructure thermoelastic solid with fractional derivative due to ramp-type heat source

In this paper, propagation of thermoelastic waves in semi-conducting nanostructure medium is studied. First, the governing equations are formulated with the help of coupled nonlocal elasticity theory, thermoelastic three-phase-lag model, and equation of motion. Heat equation with fractional order is incorporated to study thermal effects on the propagation of wave. The problem is solved using Fourier series and Laplace transform to obtain the exact expressions of physical fields. The distributions of the nondimensional carrier density and stresses are obtained and illustrated graphically. The effects of nonlocal parameter, fractional order parameter, and time parameter on these wave characteristics are concerned and discussed in detail. Some semiconductor materials as Silicon (Si) and Germanium (Ge) are used to make the numerical simulation and some comparisons in different thermal memories are made.

P5658Incorporation of severity of left atrial enlargement in clinical risk factors improves identification of patients at risk for development of atrial fibrillation

Background

Early identification of patients at risk for atrial fibrillation (AF) is desirable to prevent its development and complications. Clinical predictors have been recognized but need refinement to improve predictability. We evaluated whether severity of left atrial enlargement (LAE) added to a scoring system (CHA2DS2VASC) in an unselected non-AF population improves risk stratification for incident AF.

Purpose

To assess the incremental benefit of LAE severity added to CHA2DS2VASc in predicting future AF in non-AF patients.

Methods

From 2012–2017, consecutive adult patients with an echocardiogram and no prior AF were identified. CHA2DS2VASc was used to define baseline AF risk, and the incremental risk of AF with addition of LAE was assessed through increased LA volume index (LAVI; moderate 42–48 ml/m2, severe >48 ml/m2). To quantify improvement in risk prediction, logistic regression model was fitted and odds ratios (OR) and ROC curves obtained.

Results

Out of 155,597 patients with no prior AF, 13.8% developed AF over 1.5±1.3 years. OR for AF with CHA2DS2VASc was 1.68 (95% CI 1.66–1.69). With addition of moderately or severely increased LAVI to the model, OR for AF increased to 2.3 (2.2–2.5) and 3.8 (3.6–4.0), respectively. ROC analysis showed c-statistics of 0.66 with CHA2DS2VASc, 0.63 with LAVI, and 0.71 with incorporation of both (Fig).

AF CHAD score

Conclusion(s)

In non-AF patients, predictability for future AF can be improved by using clinical factors (CHA2DS2VASc) and increased LAVI. This information may guide closer monitoring and initiation of therapies to prevent progression to AF or stroke.

Acknowledgement/Funding

None

P2822Seasonal variation in in-hospital cardiac arrest and associated mortality

Background

Previous reports have documented seasonal variation in out-of-hospital cardiac arrest (OHCA), with peak incidence in winter months, regardless of geographical region. However, seasonal variation in in-hospital cardiac arrest (IHCA) has not been well studied.

Purpose

To assess seasonal variation in incidence of in-hospital cardiac arrest, as well as gender and mortality differences.

Methods

We queried the 2014 National Inpatient Service (NIS) database for the total numbers of inpatient hospitalizations and in-hospital cardiac arrests for each month, as identified by ICD-9 codes (99.60 and 99.63). The trend for each month was plotted to assess seasonal variations in hospitalizations, IHCA, and mortality.

Seasonal Variations in IHCA

Results

The mean age of the study population was 57.3±0.2 years and 58.9% were female. Out of 29,717,872 total inpatient hospitalizations in 2014, the overall IHCA event for the year was 0.38%. Females were more likely to be hospitalized; however, males were more likely to have IHCA. These gender differences persisted throughout the year. Overall, more hospitalizations and IHCA were seen in the winter compared to the summer, and this trend was seen in both men and women. The highest incidence of in-hospital cardiac events occurred in January and the lowest incidence occurred in June. There was no seasonal variation in mortality in both male and female patients who suffered IHCA.

Conclusion(s)

In this observational study, seasonal variation is present in in-hospital cardiac arrest. Cardiac events are highest in the winter months as compared to the summer months; however, the mechanism of this variation is unknown and warrants further study.

Acknowledgement/Funding

None

Frequency, Awareness, and Symptoms of Chikungunya Among Patients in a Tertiary Care Hospital of Karachi: A Cross-Sectional Study

Background 

Chikungunya fever (CHIKF) is an infectious illness spread by the bite of mosquitoes and caused by an arbovirus known as Chikungunya virus (CHIKV). This disease has become an epidemic in Karachi and various other cities of Pakistan, affecting a large population, especially those from poor, socioeconomically underdeveloped areas. It is proving to be a severe and alarming cause of debility due to its prolonged detrimental effects on the joints. A significant number of cases are reported daily in different hospitals of Karachi, with Civil Hospital being one of the major tertiary care hospitals. The aim of this study is to determine the frequency and symptoms of chikungunya as well as to assess the participants’ awareness about the spread and preventive measures of this disease.

Methods

This is a cross-sectional study that was carried out in Civil Hospital Karachi by approaching patients in the out-patient department (OPD) and the emergency department with complaints of fever and joint pain. All the data was collected via a pre-coded questionnaire during May-June 2017 by taking prior informed verbal consent and were analyzed through Statistical Package for the Social Sciences (SPSS) version 22 software.

Results

The age group most affected by this disease was the 21-30 years range, which represented almost a quarter of the cases (n=83, 32.17%). Majority of the respondents (n=214, 82.95%) had heard of the disease, mainly due to their own prior experience with it (n=100, 38.76%). Lethargy (n=219, 84.88%), difficulty in walking (n=213, 82.56%), and headache (n=209, 81.01%) were the major symptoms reported apart from fever (n=258, 100.00%) and arthralgia (n=258, 100.00%).

Conclusion

CHIKF is proving to be a great threat to people as it impairs their quality of life to a great extent. The recent outbreak of chikungunya has victimized a considerable population of Karachi. This study mainly assessed the severity of the disease and its symptoms as well as the lack of awareness among patients. Proper and effective preventive measures can further help to eradicate this disease on a large scale and prevent future epidemics.

Predictors of 30-day mortality following hip/pelvis fractures

INTRODUCTION

With the cost of healthcare in the United States reaching $2.9 trillion in 2013 and expected to increase with a growing geriatric population, the Center for Medicare and Medicaid Services (CMS) and Hospital Quality Alliance (HQA) began publicly reporting 30-day mortality rates so that hospitals and physicians may begin to confront clinical problems and promote high-quality and patient-centered care. Though the 30-day mortality is considered a highly effective tool in measuring hospital performance, little data actually exists that explores the rate and risk factors for trauma-related hip and pelvis fractures. Therefore, in this study, we sought to explore the risk factors associated with 30-day mortality in trauma-related hip and pelvic fractures.

MATERIALS AND METHODS

Utilizing the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database, 341,062 patients undergoing orthopaedic procedures from 2005 to 2013 were identified through a Current Procedural Terminology (CPT) code search. A second CPT code search identified 24,805 patients who sustained a hip/pelvis fracture. Patient demographics, preoperative comorbidities, operative characteristics and postoperative complications were collected and compared using Chi-squared test, Wilcoxon-Mann-Whitney test and multivariate logistic regression analysis.

RESULTS

Preoperative and postoperative risk factors for 30-day mortality following a hip/pelvis fracture were found: ASA classification, ascites, disseminated cancer, dyspnea, functional status, history of congestive heart failure (CHF), history of chronic obstructive pulmonary disease (COPD), a recent blood transfusion, and the postoperative complications: pneumonia, myocardial infarction, stroke, and septic shock.

DISCUSSION

Several preoperative patient risk factors and postoperative complications greatly increased the odds for patient mortality following 30-days after initial surgery. Orthopaedic surgeons can utilize these predictive risk factors to better improve patient care.

LEVEL OF EVIDENCE

Retrospective study. Level IV.

Direct incorporation of the NKT-cell activator α-galactosylceramide into a recombinant Listeria monocytogenes improves breast cancer vaccine efficacy

Background:

Immune suppression in the tumour microenvironment remains a major limitation to successful immunotherapy of cancer. In the current study, we analysed whether the natural killer T cell-activating glycolipid α-galactosylceramide could overcome immune suppression and improve vaccination against metastatic breast cancer.

Methods:

Mice with metastatic breast cancer (4T1 model) were therapeutically treated with a Listeria monocytogenes-based vaccine expressing tumour-associated antigen Mage-b followed by α-galactosylceramide as separate agents, or as a complex of α-galactosylceramide stably incorporated into Listeria-Mage-b. Effects on metastases, tumour weight, toxicity and immune responses were determined.

Results:

Sequential treatments of mice with established 4T1 breast carcinomas using Listeria-Mage-b followed by α-galactosylceramide as a separate agent was highly effective at reducing metastases, but was accompanied by severe liver toxicity. In contrast, combined therapy using Listeria-Mage-b modified by incorporation of α-galactosylceramide resulted in nearly complete elimination of metastases without toxicity. This was associated with a significant increase in the percentage of natural killer T cells in the spleen, and an increase in natural killer cell activity and in T cell responses to Mage-b.

Conclusions:

Our results suggest that direct incorporation of α-galactosylceramide into a live bacterial vaccine vector is a promising non-toxic new approach for the treatment of metastatic breast cancer.

Single dose streptozotocin-induced diabetes: considerations for study design in islet transplantation models

Streptozotocin (STZ)-induced diabetes mellitus (DM) offers a very cost-effective and expeditious technique that can be used in most strains of rodents, opening the field of DM research to an array of genotypic and phenotypic options that would otherwise be inaccessible. Despite widespread use of STZ in small animal models, the data available concerning drug preparation, dosing and administration, time to onset and severity of DM, and any resulting moribundity and mortality are often limited and inconsistent. Because of this, investigators inexperienced with STZ-induced diabetes may find it difficult to precisely design new studies with this potentially toxic chemical and account for the severity of DM it is capable of inducing. Until a better option becomes available, attempts need to be made to address shortcomings with current STZ-induced DM models. In this paper we review the literature and provide data from our pancreatic islet transplantation experiments using single high-dose STZ-induced DM in NCr athymic nude mice with hopes of providing clarification for study design, suggesting refinements to the process, and developing a more humane process of chemical diabetes induction.

Comparison of arterial and venous blood gases and the effects of analysis delay and air contamination on arterial samples in patients with chronic obstructive pulmonary disease and healthy controls

BACKGROUND

Arterial blood gases (ABGs) are often sampled incorrectly, leading to a 'mixed' or venous sample. Delays in analysis and air contamination are common.

OBJECTIVES

We measured the effects of these errors in patients with chronic obstructive pulmonary disease (COPD) exacerbations and controls.

METHODS

Arterial and venous samples were analyzed from 30 patients with COPD exacerbation and 30 controls. Venous samples were analysed immediately and arterial samples separated into non-air-contaminated and air-contaminated specimens and analysed at 0, 30, 60, 90 and 180 min.

RESULTS

Mean venous pH was 7.371 and arterial pH was 7.407 (p < 0.0001). There was a correlation between venous and arterial pH (r = 0.5347, p < 0.0001). The regression equation to predict arterial pH was: arterial pH = 4.2289 + 0.43113 · venous pH. There were no clinically significant differences in arterial PO₂ associated with analysis delay. A statistically significant decline in pH was detected at 30 min in patients with COPD exacerbation (p = 0.0042) and 90 min in controls (p < 0.0001). A clinically significant decline in pH emerged at 73 min in patients with COPD exacerbation and 87 min in controls. Air contamination was associated with a clinically significant increase in PO₂ in all samples, including those that were immediately analyzed.

CONCLUSIONS

Arterial and venous pH differ significantly. Venous pH cannot accurately replace arterial pH. Temporal delays in ABG analysis result in a significant decline in measured pH. ABGs should be analysed within 30 min. Air contamination leads to an immediate increase in measured PO₂, indicating that air-contaminated ABGs should be discarded.

Characteristics of patients presenting with erythema nodosum and sarcoidosis

We explored the relationship between erythema nodosum (EN) and sex, age, serum angiotensin converting enzyme (ACE), bronchoalveolar lavage lymphocytosis (BAL-I), interstitial granulomas and radiological stage in patients presenting with pulmonary sarcoidosis in Ireland. Sixty-nine patients diagnosed with sarcoidosis between 2003 and 2006 were studied. Forty one patients (59%) were male. Sixteen patients (23%) presented with EN. Forty one patients of 65 (63%) had transbronchial biopsies demonstrating non-caseating granulomas. Patients with sarcoidosis presenting with EN were more likely to be female (p=0.042), younger (p=0.012) and have earlier stage pulmonary disease (p=0.02). There were no correlations between serum ACE, interstitial granulomas and disease stage. BAL-I did however predict increasing disease radiological stage (p=0.042). In this study, one quarter of patients with sarcoidosis presented with EN among their presenting features. These patients were more likely to be young females with early stage radiological disease.

Comorbid conditions and outcomes after percutaneous coronary intervention

OBJECTIVE

To evaluate whether adding comorbid conditions to a risk model can help predict in-hospital outcome and long-term mortality after percutaneous coronary intervention (PCI).

DESIGN

Retrospective chart review

SETTING

Academic medical centre.

PATIENTS

7659 patients who had 9032 PCIs.

INTERVENTIONS

PCI performed at Mayo Clinic between 1 January 1999 and 30 June 2004.

MAIN OUTCOME MEASURES

The Mayo Clinic Risk Score (MCRS) and the coronary artery disease (CAD)-specific index for determination of comorbid conditions in all patients.

RESULTS

The mean (SD) MCRS score was 6.5 (2.9). The CAD-specific index was 0 or 1 in 46%, 2 or 3 in 30% and 4 or higher in 24%. The rate of in-hospital major adverse cardiovascular events (MACE) increased with higher MCRS and CAD-specific index (Cochran-Armitage test, p<0.001 for both models). The c-statistic for the MCRS for in-hospital MACE was 0.78; adding the CAD-specific index did not improve its discriminatory ability for in-hospital MACE (c-statistic = 0.78; likelihood ratio test, p = 0.29). A total of 707 deaths after dismissal occurred after 7253 successful procedures. The c-statistic for all-cause mortality was 0.69 for the MCRS model alone and 0.75 for the MCRS and CAD-specific indices together (likelihood ratio test, p<0.001), indicating significant improvement in the discriminatory ability.

CONCLUSIONS

Addition of comorbid conditions to the MCRS adds significant prognostic information for post-dismissal mortality but adds little prognostic information about in-hospital complications after PCI. Such health-status measures should be included in future risk stratification models that predict long-term mortality after PCI.

K(ATP) channel therapeutics at the bedside

The family of potassium channel openers regroups drugs that share the property of activating adenosine triphosphate-sensitive potassium (K(ATP)) channels, metabolic sensors responsible for adjusting membrane potential-dependent functions to match cellular energetic demands. K(ATP) channels, widely represented in metabolically-active tissue, are heteromultimers composed of an inwardly rectifying potassium channel pore and a regulatory sulfonylurea receptor subunit, the site of action of potassium channel opening drugs that promote channel activity by antagonizing ATP-induced pore inhibition. The activity of K(ATP) channels is critical in the cardiovascular adaptive response to stress, maintenance of neuronal electrical stability, and hormonal homeostasis. Thereby, K(ATP) channel openers have a unique therapeutic spectrum, ranging from applications in myopreservation and vasodilatation in patients with heart or vascular disease to potential clinical use as bronchodilators, bladder relaxants, islet cell protector, antiepileptics and promoters of hair growth. While the current experience in practice with potassium channel openers remains limited, multitude of ongoing investigations aims at defining the benefit of this emerging family of therapeutics in diverse disease conditions associated with metabolic distress.

Potassium channel openers: therapeutic potential in cardiology and medicine

Potassium (K(+)) channel openers (KCOs) define a class of chemically diverse agents that share a common molecular target, the metabolism-regulated ATP-sensitive K(+) (K(ATP)) channel. In view of the unique function that K(ATP) channels play in the maintenance of cellular homeostasis, this novel class of ion channel modulators adds to existent pharmacotherapy with potential in promoting cellular protection under conditions of metabolic stress. Indeed, experimental studies have demonstrated broad therapeutic potential for KCOs, including roles as cardioprotective agents, vasodilators, bronchodilators, bladder relaxants, anti-epileptics, insulin secretagogues and promoters of hair growth. However, clinical experience with these drugs is limited and their place in patient management needs to be fully established.

Increased calcium vulnerability of senescent cardiac mitochondria: protective role for a mitochondrial potassium channel opener

In senescence, endogenous mechanisms of cardioprotection are apparently attenuated resulting in increased vulnerability to ischemia-reperfusion. In particular, mitochondria, which are essential in maintaining cardiac energetic and ionic homeostasis, are susceptible to Ca2+ overload, a component of metabolic injury. However, effective means of protecting senescent mitochondria are lacking. Here, mitochondrial function and structure were assessed using ion-selective mini-electrodes, high-performance liquid chromatography and electron microscopy. Aging decreased ADP-induced oxygen consumption and prolonged the time associated with ADP to ATP conversion, which manifested as a reduced rate of oxidative phosphorylation. Aging also reduced mitochondrial Ca2+ handling, and increased Ca2+-induced mitochondrial damage. Diazoxide, a potassium channel opener, reduced Ca2+ loading and protected the functional and structural integrity of senescent mitochondria from Ca2+-induced injury. In this way, the present study identifies the potential usefulness for pharmacotherapy in protecting vulnerable senescent mitochondria from conditions of Ca2+ overload, such as ischemia-reperfusion.

Intra-atrial conduction block along the mitral valve annulus during accessory pathway ablation: evidence for a left atrial "isthmus"

INTRODUCTION

We observed a change in the atrial activation sequence during radiofrequency (RF) energy application in patients undergoing left accessory pathway (AP) ablation. This occurred without damage to the AP and in the absence of a second AP or alternative arrhythmia mechanism. We hypothesized that block in a left atrial "isthmus" of tissue between the mitral annulus and a left inferior pulmonary vein was responsible for these findings.

METHODS AND RESULTS

Electrophysiologic studies of 159 patients who underwent RF ablation of a left free-wall AP from 1995 to 1999 were reviewed. All studies with intra-atrial conduction block resulting from RF energy delivery were identified. Fluoroscopic catheter positions were reviewed. Intra-atrial conduction block was observed following RF delivery in 11 cases (6.9%). This was evidenced by a sudden change in retrograde left atrial activation sequence despite persistent and unaffected pathway conduction. In six patients, reversal of eccentric atrial excitation during orthodromic reciprocating tachycardia falsely suggested the presence of a second (septal) AP. A multipolar coronary sinus catheter in two patients directly demonstrated conduction block along the mitral annulus during tachycardia.

CONCLUSION

An isthmus of conductive tissue is present in the low lateral left atrium of some individuals. Awareness of this structure may avoid misinterpretation of the electrogram during left AP ablation and may be useful in future therapies of atypical atrial flutter and fibrillation.

Cardioprotection: emerging pharmacotherapy

By the year 2020, it is predicted that acute coronary occlusion will be the major cause of death in the world. Recent advances in reperfusion therapy have substantially improved survival of patients with acute coronary syndromes. While early reperfusion reduces mortality, a time limitation exists with regard to myocardial salvage. In fact, the major limiting factor in further improving survival of patients with myocardial ischaemia is the susceptibility of the cardiomyocyte to ischaemic insult and lethal cell injury. Over the last decade substantial progress has been made in our understanding of the fundamental mechanisms of ischaemia/reperfusion injury. From this work novel means which limit or delay myocyte death have emerged and are currently under development as therapeutic candidates for the management of acute coronary syndromes. This report examines cardioprotective mechanisms and reviews clinical evidence for myocardial protective therapies.

Long-term survival after ablation of the atrioventricular node and implantation of a permanent pacemaker in patients with atrial fibrillation

BACKGROUND

In patients with atrial fibrillation that is refractory to drug therapy, radio-frequency ablation of the atrioventricular node and implantation of a permanent pacemaker are an alternative therapeutic approach. The effect of this procedure on long-term survival is unknown.

METHOD

We studied all patients who underwent ablation of the atrioventricular node and implantation of a permanent pacemaker at the Mayo Clinic between 1990 and 1998. Observed survival was compared with the survival rates in two control populations: age- and sex-matched members of the Minnesota population between 1970 and 1990 and consecutive patients with atrial fibrillation who received drug therapy in 1993.

RESULTS

A total of 350 patients (mean [+/-SD] age, 68+/-11 years) were studied. During a mean of 36+/-26 months of follow-up, 78 patients died. The observed survival rate was significantly lower than the expected survival rate based on the general Minnesota population (P<0.001). Previous myocardial infarction (P<0.001), a history of congestive heart failure (P=0.02), and treatment with cardiac drugs after ablation (P=0.03) were independent predictors of death. Observed survival among patients without these three risk factors was similar to expected survival (P=0.43). None of the 26 patients with lone atrial fibrillation died during follow-up (37+/-27 months). The observed survival rate among patients who underwent ablation was similar to that among 229 controls with atrial fibrillation (mean age, 67+/-12 years) who received drug therapy (P=0.44).

CONCLUSIONS

In the absence of underlying heart disease, survival among patients with atrial fibrillation after ablation of the atrioventricular node is similar to expected survival in the general population. Long-term survival is similar for patients with atrial fibrillation, whether they receive ablation or drug therapy. Control of the ventricular rate by ablation of the atrioventricular node and permanent pacing does not adversely affect long-term survival.

Restoration of Ca2+-inhibited oxidative phosphorylation in cardiac mitochondria by mitochondrial Ca2+ unloading

Mitochondria, the major source of cellular ATP, display high vulnerability to metabolic stress, in particular to excessive Ca2+ loading. Here, we show that Ca2+-inhibited mitochondrial ATP generation could be restored through stimulated Ca2+ discharge from mitochondrial matrix. This was demonstrated using a Ca2+ ionophore or through Na+/Ca2+ exchange-mediated decrease of mitochondrial Ca2+ load. Furthermore, diazoxide, a mitochondrial potassium channel opener, which maintained mitochondrial Ca2+ homeostasis, also restored Ca2+-inhibited ATP synthesis and preserved the structural integrity of Ca2+-challenged mitochondria. Thus, under conditions of excessive mitochondrial Ca2+ overload targeting mitochondrial Ca2+ transport pathways restores oxidative phosphorylation required for vital cellular processes. This study, therefore, identifies an effective strategy capable to rescue Ca2+-disrupted mitochondrial energetics.

Is sinus node modification appropriate for inappropriate sinus tachycardia with features of postural orthostatic tachycardia syndrome?

Inappropriate sinus tachycardia and postural orthostatic tachycardia are ill-defined syndromes with overlapping features. Although sinus node modification has been reported to effectively slow the sinus rate, long-term clinical response has not been adequately assessed. Furthermore, whether patients with postural orthostatic tachycardia would benefit from sinus node modification is unknown. The study prospectively assessed the short- and long-term clinical outcomes of seven consecutive female patients with postural orthostatic tachycardia syndrome and inappropriate sinus tachycardia who were treated with sinus node modification. The study was conducted in a tertiary care center. The electrophysiological and clinical responses were prospectively assessed as defined by autonomic function testing, including Valsalva maneuver, deep breathing, tilt table testing, and quantitative sudomotor axonal reflex testing. Among the study population (mean age was 41+/-6 years), 5 (71%) patients had successful sinus node modification. At baseline, heart rates were 101+/-12 beats/min before modification and 77+/-9 beats/min after modification (P = 0.001). With isoproterenol, heart rates were 136+/-9 and 105+/-12 beats/min (P = 0.002) before and after modification, respectively. The mean heart rate during 24-hour Holter monitoring was also significantly reduced: 96+/-9 and 72+/-6 beats/min (P = 0.005) before and after modification, respectively. Despite the significant reduction in heart rate, autonomic symptom score index (based on ten categories of clinical symptoms) was unchanged before (15.6+/-4.1) and after (14.6+/-3.6) sinus node modification (P = 0.38). Sinus rate can be effectively slowed by sinus node modification. Clinical symptoms are not significantly improved after sinus node modification in patients with inappropriate sinus tachycardia and postural orthostatic tachycardia. A primary subtle autonomic disregulation is frequently present in this population. Sinus node modification is not recommended in this patient population.

Diazoxide protects mitochondria from anoxic injury: implications for myopreservation

BACKGROUND

Heart muscle primarily relies on adenosine triphosphate produced by oxidative phosphorylation and is highly vulnerable to anoxic insult. Although a number of strategies aimed at improving myopreservation are available, no effective means of preserving mitochondrial energetics under conditions of anoxic injury have been developed. Openers of mitochondrial adenosine triphosphate-sensitive potassium channels have emerged as powerful cardioprotective agents presumably capable of maintaining mitochondrial function under metabolic stress. Here, we evaluated the ability of a prototype mitochondrial adenosine triphosphate-sensitive potassium channel opener, diazoxide, to preserve oxidative phosphorylation in mitochondria subjected to anoxia and reoxygenation.

METHODS

Mitochondria were isolated from rat hearts and subjected to 20 minutes of anoxia, followed by reoxygenation. Mitochondrial respiration and oxidative phosphorylation, as well as mitochondrial integrity, were assessed by means of ion-selective minielectrodes, high-performance liquid chromatography, fluorometry, and electron microscopy.

RESULTS

Anoxia-reoxygenation decreased the rate of adenosine diphosphate-stimulated oxygen consumption, inhibited adenosine triphosphate production, and disrupted mitochondrial integrity. On average, anoxic stress reduced adenosine diphosphate-stimulated respiration from 291 +/- 14 to 141 +/- 15 ng-atoms O(2). min(-1). mg(-1) protein and decreased the rate of adenosine triphosphate production from 752 +/- 14 to 414 +/- 34 nmol adenosine triphosphate. min(-1). mg(-1) protein. After anoxia, the majority (88%) of mitochondria was damaged or swollen and released adenylate kinase, a marker of mitochondrial integrity. Diazoxide (100 micromol/L), present throughout anoxia, preserved adenosine diphosphate-stimulated respiration at 255 +/- 7 ng-atoms O(2). min(-1). mg(-1) protein and adenosine triphosphate production at 640 +/- 39 nmol adenosine triphosphate. min(-1). mg(-1) protein. Diazoxide also protected mitochondrial structure from anoxia-mediated damage, so that after anoxic stress, 67% of mitochondria remained intact and adenylate kinase was confined to the mitochondria.

CONCLUSIONS

The present study demonstrates that diazoxide diminishes anoxia-induced functional and structural deterioration of cardiac mitochondria. By protecting mitochondria and preserving myocardial energetics, diazoxide may be useful under conditions of reduced oxygen availability, including global surgical ischemia or storage of donor heart.

Electrophysiologic characteristics of diverse accessory pathway locations of antidromic reciprocating tachycardia

This study assessed antidromic reciprocating tachycardia (ART) in patients with paraseptal accessory pathways (APs). Previous clinical experience suggests that paraseptal APs are unable to serve as the anterograde limb during ART. Based on the reentry wavelength concept, we hypothesized that anatomic location of a paraseptal AP may not preclude occurrence of ART. If wavelength criteria were met due to prolonged conduction time retrogradely in the atrioventricular node or anterogradely in the AP, ART may be sustained. All patients who had ART in the electrophysiologic laboratory at our institution (1991 to 1998) were studied. Based on fluoroscopically guided electrophysiologic mapping and radiofrequency ablation, AP location was classified as paraseptal, posterior, or lateral. Conduction time and refractoriness measurements were made for all components of the ART circuit. Of 24 patients with ART, 5 (21%) had ART utilizing a paraseptal AP. Anterograde conduction time through the AP and retrograde atrioventricular nodal conduction time were significantly longer in patients with paraseptal versus lateral pathways. Isoproterenol was required for ART induction in 38% of patients with a posterior AP, 36% with lateral AP location, but not in patients with a paraseptal AP. There were no significant differences in tachycardia cycle length or refractoriness of anterograde and/or retrograde components of the macroreentry circuit between the 3 pathway locations. Thus, ART can occur in patients with a paraseptal AP. Slower anterograde pathway conduction, or retrograde atrioventricular nodal conduction renders the wavelength critical for completion of the antidromic re-entrant circuit.

Global right atrial mapping of human atrial flutter: the presence of posteromedial (sinus venosa region) functional block and double potentials : a study in biplane fluoroscopy and intracardiac echocardiography

BACKGROUND

Previous studies of atrial flutter have found linear block at the crista terminalis; this was thought to predispose the patient to the arrhythmia. More recent observations, however, have demonstrated crista conduction. We sought to characterize the posterior boundary of atrial flutter.

METHODS AND RESULTS

Patients with counterclockwise flutter (n=20), clockwise flutter (n=3), or both (n=5) were studied using two 20-pole catheters. Biplane fluoroscopy determined catheter positions. During counterclockwise flutter, craniocaudal activation occurred along the entire lateral and posterior right atrial walls. Septal activation proceeded caudocranially. In all patients, a line of block was seen in the posteromedial (sinus venosa) right atrium; this was manifested by the presence of double potentials where the upward and downward activations collided. Anatomic location was confirmed by intracardiac echocardiography in 9 patients. In patients with clockwise flutter, the line of block and double potentials were seen in the same location during counterclockwise flutter, but the activation sequence around the line of block was reversed. Pacing near the site of double potentials during sinus rhythm excluded a fixed line of block, and premature atrial complexes demonstrated functional block with manifest double potentials. In 2 patients, posterior ectopy organized to subsequently initiate isthmus-dependent atrial flutter.

CONCLUSIONS

(1) A functional line of block is seen at the posteromedial (sinus venosa region) right atrium during counterclockwise and clockwise atrial flutter. (2) All lateral wall right atrial activation can be uniform during flutter, without linear block or double potentials in the region of the crista terminalis. (3) Activation at the site of posteromedial right atrial functional block can organize to subsequently initiate isthmus-dependent atrial flutter.

Channelopathies of inwardly rectifying potassium channels

Mutations in genes encoding ion channels have increasingly been identified to cause disease conditions collectively termed channelopathies. Recognizing the molecular basis of an ion channel disease has provided new opportunities for screening, early diagnosis, and therapy of such conditions. This synopsis provides an overview of progress in the identification of molecular defects in inwardly rectifying potassium (Kir) channels. Structurally and functionally distinct from other channel families, Kir channels are ubiquitously expressed and serve functions as diverse as regulation of resting membrane potential, maintenance of K(+) homeostasis, control of heart rate, and hormone secretion. In humans, persistent hyperinsulinemic hypoglycemia of infancy, a disorder affecting the function of pancreatic beta cells, and Bartter's syndrome, characterized by hypokalemic alkalosis, hypercalciuria, increased serum aldosterone, and plasma renin activity, are the two major diseases linked so far to mutations in a Kir channel or associated protein. In addition, the weaver phenotype, a neurological disorder in mice, has also been associated with mutations in a Kir channel subtype. Further genetic linkage analysis and full understanding of the consequence that a defect in a Kir channel would have on disease pathogenesis are among the priorities in this emerging field of molecular medicine.

Relation between mode of pacing and long-term survival in the very elderly

OBJECTIVES

This study analyzes the relationship between pacing mode and long-term survival in a large group of very elderly patients (> or = 80 years old).

BACKGROUND

The relationship between pacing mode and long-term survival is not clear. Because the number of very elderly who are candidates for pacing is increasing, issues related to pacemaker (PM) use in the elderly have important clinical and economic implications.

METHODS

We retrospectively reviewed 432 patients (mean age, 84.5+/-3.9 years) who received their initial PM (ventricular in 310 and dual chamber in 122) between 1980 and 1992. Follow-up was complete (3.5+/-2.6 years). Observed survival was estimated by the Kaplan-Meier method. Age- and gender-matched cohorts from the Minnesota population were used for expected survival. Log-rank test and Cox regression hazard model were used for univariate and multivariate analyses.

RESULTS

Patients with ventricular PMs appeared to have poor overall survival compared with those with dual-chamber PMs. Observed survival after PM implantation in high grade atrioventricular block (AVB) patients was significantly worse than expected survival of the age- and gender-matched population (p < 0.0001), whereas observed survival of patients with sinus node dysfunction was not significantly different from expected survival of the matched population (p = 0.413). By univariate analysis, ventricular pacing in patients with AVB appeared to be associated with poor survival compared with dual-chamber pacing (hazard ratio [HR] 2.08; 95% confidence interval [CI] 1.33 to 3.33). After multivariate analysis, this difference was no longer significant (HR 1.41; 95% CI 0.88 to 2.27). Independent predictors of all-cause mortality were number of comorbid illnesses, New York Heart Association functional class, left ventricular depression and older age at implant. Pacing mode was not an independent predictor of overall survival. Older age at implantation, diabetes mellitus, dementia, history of paroxysmal atrial fibrillation and earlier year of implantation were independent predictors of ventricular pacemaker selection.

CONCLUSIONS

After PM implantation, long-term survival among very elderly patients was not affected by pacing mode after correction of baseline differences. Selection bias was present in pacing mode in the very elderly, with ventricular pacing selected for sicker and older patients, perhaps partly explaining the apparent "beneficial impact on survival" observed with dual-chamber pacing.

Utility of a single-stage isoproterenol tilt table test in adults: a randomized comparison with passive head-up tilt

OBJECTIVES

This study was conducted to develop a time-efficient tilt table test.

BACKGROUND

Current protocols of tilt table testing are quite time-consuming. This study was designed to assess the diagnostic value, tolerance and procedural time of a single-stage isoproterenol tilt table protocol.

METHODS

A single-stage isoproterenol tilt table test was compared with the passive tilt table test. The study was prospectively designed in a randomized and crossover fashion.

RESULTS

The study population consisted of 111 patients with a history of syncope (mean age 55 +/- 20 years). Of the total, 62 patients (56%; 95% confidence interval, 46% to 65%) had a positive vasovagal response during isoproterenol tilt table testing and 35 (32%; 23% to 41%) during passive tilt table testing (p = 0.002). The mean procedural times of the study population were 11.7 +/- 3.6 min and 36.9 +/- 13.3 min for isoproterenol and passive tilt table testing, respectively (p < 0.001). All patients tolerated single-stage isoproterenol testing. In the 23 control subjects (mean age 34 +/- 11 years), the apparent specificities were 91% (72% to 99%) and 83% (61% to 99%) for passive and single-stage tilt table testing, respectively.

CONCLUSIONS

The single-stage isoproterenol tilt table test was more effective in inducing a positive vasovagal response in an adult population than the standard passive tilt table test, and it significantly reduced the procedural time. The increase in positive yield was associated with a moderate decrease in apparent specificity. These observations support the conclusion that single-stage tilt table testing could be a reasonable diagnostic option in patients undergoing syncope evaluation.

Fatal pancarditis associated with human granulocytic Ehrlichiosis in a 44-year-old man

Human cases of infection with a granulocytotropic Ehrlichia species closely related to Ehrlichia equi are now being described with increasing frequency in the United States, especially in areas where Lyme disease is already endemic. We describe a case of fatal pancarditis during the course of human granulocytic ehrlichiosis (HGE) in a 44-year-old outdoor worker who was previously treated for presumptive Lyme disease. Serological and molecular diagnostic tests for Borrelia burgdorferi and Babesia microti infections were negative. Postmortem serum specimens were seroreactive for HGE, and molecular evidence of infection with the HGE agent was obtained. These findings suggest that carditis may be a manifestation of HGE, further complicating the differential diagnosis of tick-borne illness.

Potassium channel openers prevent potassium-induced calcium loading of cardiac cells: possible implications in cardioplegia

Hyperkalemic solutions that are used as cardioplegic agents, while effective in inducing electromechanical arrest, are only partially cardioprotective, and ventricular dysfunction has been observed. The underlying pathophysiology of cardioplegia-associated ventricular dysfunction is complex and not fully understood, but it could be related, in part, to intracellular Ca2+ loading induced by high K+ concentrations present in cardioplegic solutions. Yet no effective cytoprotective means against possible intracellular Ca2+ loading, under these conditions, has been described. Recently, potassium channel openers, which open adenosine triphosphate-sensitive K+ channels, have been reported to possess cardioprotective properties under global ischemic conditions. However, it is not known whether these novel agents could prevent intracellular Ca2+ loading that could occur during cardioplegia. Intracellular Ca2+ was monitored in ventricular myocytes, loaded with the Ca(2+)-sensitive fluorescent probe Fluo-3AM, using epifluorescent digital imaging and laser confocal microscopy. Exposure of a myocyte to a 16 mmol/L concentration of K+, a concentration of K+ commonly used in cardioplegic solutions, induced a nonhomogeneous increase in intracellular Ca2+. Potassium channel opening drugs, such as aprikalim or nicorandil, effectively prevented these solutions from increasing intracellular Ca2+. The preventive effect of potassium channel opening drugs was antagonized by glyburide, a selective blocker of adenosine triphosphate-sensitive K+ channels. This study demonstrates, at the single cardiac cell level, that solutions containing a 16 mmol/L concentration of K+ promote intracellular Ca2+ loading, which can be prevented by potassium channel opening drugs. Therefore, potassium channel opening drugs should be considered to prevent intracellular Ca2+ loading associated with the use of cardioplegic solutions.

Cardiac ATP-sensitive K+ channels: regulation by intracellular nucleotides and K+ channel-opening drugs

ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells where they regulate cardiac function during cellular metabolic impairment. KATP channels have been implicated in the shortening of the action potential duration and the cellular loss of K+ that occurs during metabolic inhibition. KATP channels have been associated with the cardioprotective mechanism of ischemia-related preconditioning. Intracellular ATP (ATPi) is the main regulator of KATP channels. ATPi has two functions: 1) to close the channel (ligand function) and 2) in the presence of Mg2+, to maintain the activity of KATP channels (presumably through an enzymatic reaction). KATP channel activity is modulated by intracellular nucleoside diphosphates that antagonize the ATPi-induced inhibition of channel opening or induce KATP channels to open. How nucleotides will affect KATP channels depends on the state of the channel. K+ channel-opening drugs are pharmacological agents that enhance KATP channel activity through different mechanisms and have great potential in the management of cardiovascular conditions. KATP channel activity is also modulated by neurohormones. Adenosine, through the activation of a GTP-binding protein, antagonizes the ATPi-induced channel closure. Understanding the molecular mechanisms that underlie KATP channel regulation should prove essential to further define the function of KATP channels and to elucidate the pharmacological regulation of this channel protein. Since the molecular structure of the KATP channel has now become available, it is anticipated that major progress in the KATP channel field will be achieved.

Molecular cloning and functional expression of cDNA encoding a second class of inward rectifier potassium channels in the mouse brain

We have cloned a second class of inward rectifier potassium channels, designated MB-IRK2, from a mouse brain cDNA library. The amino acid sequence of this clone shares 70% identity with the mouse IRK1. Xenopus oocytes injected with cRNA derived from MB-IRK2 expressed a K+ current, which showed inward rectifying channel characteristics similar to the MB-IRK1 current. In contrast to the MB-IRK1 current, however, the MB-IRK2 current exhibited significant inactivation during hyperpolarizing pulses. In patch clamp experiments with 140 mM K+ in the pipette, the single channel conductance of MB-IRK2 was 34.2 +/- 2.1 picosiemens (n = 5), a value significantly larger than that of MB-IRK1 (22.2 +/- 3.0 picosiemens, n = 5). Consistent with the whole cell current, the steady-state open probability (Po) of the MB-IRK2 channel decreased with hyperpolarization, whereas that of the MB-IRK1 remained constant. Northern blot analysis revealed the mRNA for MB-IRK2 to be expressed in forebrain, cerebellum, heart, kidney, and skeletal muscle. In the brain, the abundance of mRNA for MB-IRK2 was much higher in cerebellum than in forebrain and vice versa in the case of MB-IRK1. These results demonstrate that the IRK family is composed of multiple genes, which may play heterogenous functional roles in various organs, including the central nervous system.

Molecular cloning and functional expression of a novel brain-specific inward rectifier potassium channel

We have cloned a novel brain-specific inward rectifier K+ channel from a mouse brain cDNA library and designated it MB-IRK3. The mouse brain cDNA library was screened using a fragment of the mouse macrophage inward rectifier K+ channel (IRK1) cDNA as a probe. The amino acid sequence of MB-IRK3 shares 61% and 64% identity to MB-IRK1 and RB-IRK2, respectively. Xenopus oocytes injected with cRNA derived from this clone expressed a potassium current which showed inward-rectifying channel characteristics similar to MB-IRK1 and RB-IRK2 currents, but distinct from ROMK1 or GIRK1 current. However, the single channel conductance of MB-IRK3 was approximately 10 pS with 140 mM extracellular K+, which was distinct from that of MB-IRK1 (20 pS). MB-IRK3 mRNA expressed specifically in the forebrain, which clearly differed from MB-IRK1 and RB-IRK2 mRNAs. These results indicate that members of the IRK family with distinct electrophysiological properties express differentially and may play heterogenous functional roles in brain functions.

Intracellular acidification and ADP enhance nicorandil induction of ATP sensitive potassium channel current in cardiomyocytes

OBJECTIVE

Potassium channel openers target ATP sensitive potassium (KATP) channels, and might be beneficial in the treatment of ischaemic cardiac conditions. Ischaemia is associated with an increase in the concentrations of intracellular nucleoside diphosphates and protons, two regulators of KATP channels. Since it is largely unknown whether these factors modulate the action of potassium channel openers, the aim of this study was to define the effects of ADP and intracellular acidification on KATP channel activation by nicorandil, a potassium channel opener currently in clinical use.

METHODS

To measure ionic currents, the whole cell patch clamp technique was employed in guinea pig single ventricular myocytes. Induction of KATP channel current by pinacidil, a potassium channel opener chemically unrelated to nicorandil, was used for comparison.

RESULTS

Nicorandil (300 microM) and pinacidil (100 microM) induced a time independent K+ current, which was inhibited by glibenclamide (6 microM), a selective blocker of KATP channels. ADP in the pipette solution was required for the nicorandil induced activation of KATP channels when the pH of the pipette solution was 7.2. In the absence of ADP, lowering the pH of the pipette solution to 6.5 was necessary for nicorandil to induce KATP channel current. For pinacidil to induce KATP channel current neither the addition of intracellular ADP nor acidification was required.

CONCLUSIONS

Nicorandil may activate KATP channel current more effectively in conditions associated with a change in intracellular proton and ADP concentrations such as cardiac ischaemia.

HOE-234, a second generation K+ channel opener, antagonizes the ATP-dependent gating of cardiac ATP-sensitive K+ channels

Effects of (3S,4R)-3-hydroxy-2,2-dimethyl-4-(2-oxo-1-pyrrolidinyl)-6- phenylsulfonylchroman hemihydrate (HOE-234), a novel dilator of bronchial and vascular smooth muscles, were examined on whole-cell and single channel currents in guinea pig cardiomyocytes. Under the whole-cell voltage-clamp condition, HOE-234 (0.6-100 microM) induced a time-independent K(+)-dominant current in atrial and ventricular myocytes. This current was inhibited by glyburide, a selective blocker of ATP-sensitive K+ (KATP) channels, suggesting that HOE-234 activates KATP channels. Neither intracellular acidification nor the absence of intracellular ADP inhibited the ability of HOE-234 to induce the current. In inside-out membrane patches in the presence of 200 microM ATP, HOE-234 (0.3-10 microM) increased concentration dependently (EC50 approximately 1 microM) the KATP channel activity. In the absence of HOE-234, half-inhibition of spontaneously operative KATP channels occurred at 25 microM of intracellular ATP (ATPi), whereas in the presence of HOE-234 (10 microM), 316 microM of ATPi was required for half-inhibition. In ATP-free internal solution, KATP channels appeared and then ran down. In the absence of ATPi, HOE-234 did not increase channel activity when channels were in a fully open or in the partially or completely run-down state. After run-down, the nucleoside diphosphate, UDP, restored KATP channel activity which was not further augmented by HOE-234. However, HOE-234 relieved at ATP- or ATP gamma S-mediated inhibition of the UDP-induced KATP channel activity.(ABSTRACT TRUNCATED AT 250 WORDS)

YM934, a novel K+ channel opener, activates ATP-sensitive K+ channels in cardiac myocytes

2-(3,4-Dihydro-2,2-dimethyl-6-nitro-2H-1,4-benzoxazin-4-yl)pyridin e N-oxide (YM934) is a newly synthesized benzoxazin. The effects of YM934 on ATP-sensitive K+ (KATP) channels in guinea pig cardiac ventricular myocytes and in an insulin-secreting cell line, HIT T15 beta-cells, were examined using the gigaohm-seal patch-clamp techniques. Under the whole-cell clamp condition, YM934 induced in ventricular myocytes a time-independent, glibenclamide-sensitive K+ current in a concentration-dependent fashion (EC50 = approximately 3 microM). On formation of inside-out patches in ATP-free solution, the KATP channel current abruptly appeared and then ran down. YM934 was applied to inside-out patches before, during and after channel "run-down." Because nucleoside diphosphates, such as uridine diphosphate (UDP), can induce channel openings after complete run-down, the effects of YM934 on the UDP-induced channel openings were also examined. Before run-down, YM934 enhanced KATP channel activity by decreasing the sensitivity of channels to intracellular ATP. YM934 also enhanced the partially run-down channel, even in the absence of ATP. After run-down, YM934 had no effect but could enhance the UDP-induced KATP channel openings. These effects of YM934 on cardiac KATP channels were similar to those of pinacidil and lemakalim. In HIT T15 beta-cells, 100 microM YM934 was ineffective in both cell-attached and inside-out patch configurations, suggesting the tissue-specific nature of the action of this novel K+ channel opener.

GK* and brain G beta gamma activate muscarinic K+ channel through the same mechanism

A pertussis toxin-sensitive G protein (GK) links muscarinic cholinergic and A1-purinergic receptors with an inwardly rectifying K+ (KACh) channel in cardiac atrial cell membranes. Although the beta gamma subunits of pertussis toxin-sensitive G proteins (G beta gamma) have been reported to fully activate this channel, it is not known whether exogenously applied G beta gamma interacts with the KACh channel through the same mechanism as the active subunit of endogenous GK (GK*). We examined in inside-out patches the relationship between the concentration of GTP and KACh channel activity with or without preactivation of the channels by either GTP gamma S (guanosine 5'-3-O-(thio)triphosphate) or G beta gamma purified from bovine brain. In the control, KACh channels were activated by intracellular GTP (with acetylcholine in the pipette) in a positive cooperative manner (Hill coefficient approximately 2.5). As the channels were preactivated by GTP gamma S to progressively higher levels, the GTP channel activity relationship shifted more to the left, but the Hill coefficients of the curves remained the same. The same changes were observed when KACh channels were preactivated with brain G beta gamma. These results indicate that endogenous GK* and exogenous G beta gamma share a common molecular mechanism to activate the KACh channel.

Digital embolization from plaque-related thrombus in the thoracic aorta: identification with transesophageal echocardiography and resolution with warfarin therapy

A 71-year-old man had painful blue toes after an episode of protracted vomiting. Abdominal, cardiac, and transesophageal ultrasound studies were performed before angiography was considered. A large mobile mass in the proximal descending thoracic aorta, which suggested thrombus, was identified by transesophageal echocardiography. With no further evaluation, anticoagulant therapy with heparin and warfarin was initiated. Three months later, repeated transesophageal echocardiography demonstrated only a tiny vestige of the plaque-related mass. The pain and discoloration of the toes resolved completely. The advantages and disadvantages of the various diagnostic and therapeutic approaches to peripheral embolization are discussed.