Electromechanical reciprocity and arrhythmogenesis in long-QT syndrome and beyond.

An abundance of literature describes physiological and pathological determinants of cardiac performance, building on the principles of excitation-contraction coupling. However, the mutual influencing of excitation-contraction and mechano-electrical feedback in the beating heart, here designated 'electromechanical reciprocity', remains poorly recognized clinically, despite the awareness that external and cardiac-internal mechanical stimuli can trigger electrical responses and arrhythmia. This review focuses on electromechanical reciprocity in the long-QT syndrome (LQTS), historically considered a purely electrical disease, but now appreciated as paradigmatic for the understanding of mechano-electrical contributions to arrhythmogenesis in this and other cardiac conditions. Electromechanical dispersion in LQTS is characterized by heterogeneously prolonged ventricular repolarization, besides altered contraction duration and relaxation. Mechanical alterations may deviate from what would be expected from global and regional repolarization abnormalities. Pathological repolarization prolongation outlasts mechanical systole in patients with LQTS, yielding a negative electromechanical window (EMW), which is most pronounced in symptomatic patients. The electromechanical window is a superior and independent arrhythmia-risk predictor compared with the heart rate-corrected QT. A negative EMW implies that the ventricle is deformed-by volume loading during the rapid filling phase-when repolarization is still ongoing. This creates a 'sensitized' electromechanical substrate, in which inadvertent electrical or mechanical stimuli such as local after-depolarizations, after-contractions, or dyssynchrony can trigger abnormal impulses. Increased sympathetic-nerve activity and pause-dependent potentiation further exaggerate electromechanical heterogeneities, promoting arrhythmogenesis. Unraveling electromechanical reciprocity advances the understanding of arrhythmia formation in various conditions. Real-time image integration of cardiac electrophysiology and mechanics offers new opportunities to address challenges in arrhythmia management

Barriers and Facilitators Associated With App-Based Treatment for Female Urinary Incontinence:Mixed Methods Evaluation

BACKGROUND: App-based treatment for urinary incontinence is a proven effective and cost-effective alternative to care as usual, but successful implementation requires that we identify and address the barriers and facilitators associated with app use. OBJECTIVE: The goal of the research was to explore the factors influencing app-based treatment for urinary incontinence and identify which barriers or facilitators are associated with treatment success or failure. METHODS: We used a sequential explanatory mixed methods design to connect the results of a randomized controlled trial with data from semistructured interviews. This previous RCT had shown the noninferiority of app-based treatment compared with care as usual for urinary incontinence over 4 months. Participants who reported success or failure with app-based treatment, as measured by the change in International Consultation on Incontinence Modular Questionnaire Urinary Incontinence Short Form symptom score, were selected for telephone interview by purposive sampling (n=17). This study reports mainly on the qualitative component of our mixed methods study. Qualitative analyses were conducted in two ways. First, we analyzed the qualitative data of all interviewed participants and discussed the relationships between the main themes. Second, the experiences between the success (n=9) and failure group (n=8) were compared and contrasted to explore factors that were positively or negatively associated with the quantitative effect of app-based treatment. These factors were then interpreted as barriers to and facilitators of successful app-based treatment. RESULTS: Four interrelated themes were identified as affecting the app based treatment effect: adherence, personal factors, app factors, and awareness. Qualitative analyses of the relationships between the themes showed that adherence-related factors directly influenced treatment effect in both a positive and negative matter. In turn, adherence was also positively and negatively influenced by the other 3 themes. Additionally, awareness was positively influenced by the treatment effect. Within these themes, several factors were identified that acted as barriers (eg, unrealistic expectation of time investment and interfering personal circumstances), facilitators (eg, strict integration of exercises and prior pelvic floor muscle therapy), or both (eg, personality traits and increased awareness of symptoms). CONCLUSIONS: This study shows that the effect of app-based treatment for urinary incontinence is mainly influenced by adherence, which in turn is affected by personal factors, app-based factors, and awareness. The identified factors could function as both facilitators and barriers depending on the user and interaction with other themes. Insight into these facilitators and barriers could lead to improved implementation and increased treatment effectiveness by targeting women most likely to benefit and through further development of the app. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): RR2-10.1002/nau.2350

Interventricular Differences in β‐Adrenergic Responses in the Canine Heart: Role of Phosphodiesterases

Background RV and LV have different embryologic, structural, metabolic, and electrophysiologic characteristics, but whether interventricular differences exist in β‐adrenergic (β‐AR) responsiveness is unknown. In this study, we examine whether β‐AR response and signaling differ in right (RV) versus left (LV) ventricles. Methods and Results Sarcomere shortening, Ca2+ transients, ICa,L and IKs currents were recorded in isolated dog LV and RV midmyocytes. Intracellular [cAMP] and PKA activity were measured by live cell imaging using FRET‐based sensors. Isoproterenol increased sarcomere shortening ≈10‐fold and Ca2+‐transient amplitude ≈2‐fold in LV midmyocytes (LVMs) versus ≈25‐fold and ≈3‐fold in RVMs. FRET imaging using targeted Epac2camps sensors revealed no change in subsarcolemmal [cAMP], but a 2‐fold higher β‐AR stimulation of cytoplasmic [cAMP] in RVMs versus LVMs. Accordingly, β‐AR regulation of ICa,L and IKs were similar between LVMs and RVMs, whereas cytoplasmic PKA activity was increased in RVMs. Both PDE3 and PDE4 contributed to the β‐AR regulation of cytoplasmic [cAMP], and the difference between LVMs and RVMs was abolished by PDE3 inhibition and attenuated by PDE4 inhibition. Finally LV and RV intracavitary pressures were recorded in anesthetized beagle dogs. A bolus injection of isoproterenol increased RV dP/dtmax≈5‐fold versus 3‐fold in LV. Conclusion Canine RV and LV differ in their β‐AR response due to intrinsic differences in myocyte β‐AR downstream signaling. Enhanced β‐AR responsiveness of the RV results from higher cAMP elevation in the cytoplasm, due to a decreased degradation by PDE3 and PDE4 in the RV compared to the LV

The cardiac electromechanical window & arrhythmogenesis:Veni-Vidi-Vivo

During the development of medicines, people try to minimize the risk of unwanted side effects. In particular, the “torsades de pointes” side effect (TdP; a chamber rhythm disorder) is feared. Patients with the hereditary long QT syndrome are particularly sensitive. They may unexpectedly faint or sometimes suddenly die. In this research, a unique model was developed to study the development of TdP in detail. The studies were done in narcotized dogs so that the animals did not experience any pain or stress. We identified a groundbreaking new parameter, the electromechanical window (EMW). This parameter has the potential to more adequately determine the risk of TdP during drug development. Currently EMW measurements are successfully evaluated by means of computer models and safety studies in cells by the pharmaceutical industry and in clinical studies with different patient populations by academic specialists worldwide

The Potential Mechanisms behind Loperamide-Induced Cardiac Arrhythmias Associated with Human Abuse and Extreme Overdose

Loperamide has been a safe and effective treatment for diarrhea for many years. However, many cases of cardiotoxicity with intentional abuse of loperamide ingestion have recently been reported. We evaluated loperamide in in vitro and in vivo cardiac safety models to understand the mechanisms for this cardiotoxicity. Loperamide slowed conduction (QRS-duration) starting at 0.3 µM [~1200-fold (×) its human Free Therapeutic Plasma Concentration; FTPC] and reduced the QT-interval and caused cardiac arrhythmias starting at 3 µM (~12,000× FTPC) in an isolated rabbit ventricular-wedge model. Loperamide also slowed conduction and elicited Type II/III A-V block in anesthetized guinea pigs at overdose exposures of 879× and 3802× FTPC. In ion-channel studies, loperamide inhibited hERG (IKr), INa, and ICa currents with IC50 values of 0.390 µM, 0.526 µM, and 4.091 µM, respectively (i.e., >1560× FTPC). Additionally, in silico trials in human ventricular action potential models based on these IC50s confirmed that loperamide has large safety margins at therapeutic exposures (≤600× FTPC) and confirmed repolarization abnormalities in the case of extreme doses of loperamide. The studies confirmed the large safety margin for the therapeutic use of loperamide but revealed that at the extreme exposure levels observed in human overdose, loperamide can cause a combination of conduction slowing and alterations in repolarization time, resulting in cardiac proarrhythmia. Loperamide’s inhibition of the INa channel and hERG-mediated IKr are the most likely basis for this cardiac electrophysiological toxicity at overdose exposures. The cardiac toxic effects of loperamide at the overdoses could be aggravated by co-medication with other drug(s) causing ion channel inhibition

Diastolic Spontaneous Calcium Release From the Sarcoplasmic Reticulum Increases Beat-to-Beat Variability of Repolarization in Canine Ventricular Myocytes After β-Adrenergic Stimulation

Rationale: Spontaneous Ca2+ release (SCR) from the sarcoplasmic reticulum can cause delayed afterdepolarizations and triggered activity, contributing to arrhythmogenesis during β-adrenergic stimulation. Excessive beat-to-beat variability of repolarization duration (BVR) is a proarrhythmic marker. Previous research has shown that BVR is increased during intense β-adrenergic stimulation, leading to SCR. Objective:We aimed to determine ionic mechanisms controlling BVR under these conditions. Methods and Results:Membrane potentials and cell shortening or Ca2+ transients were recorded from isolated canine left ventricular myocytes in the presence of isoproterenol. Action-potential (AP) durations after delayed afterdepolarizations were significantly prolonged. Addition of slowly activating delayed rectifier K+ current (IKs) blockade led to further AP prolongation after SCR, and this strongly correlated with exaggerated BVR. Suppressing SCR via inhibition of ryanodine receptors, Ca2+/calmodulin-dependent protein kinase II inhibition, or by using Mg2+ or flecainide eliminated delayed afterdepolarizations and decreased BVR independent of effects on AP duration. Computational analyses and voltage-clamp experiments measuring L-type Ca2+ current (ICaL) with and without previous SCR indicated that ICaL was increased during Ca2+-induced Ca2+ release after SCR, and this contributes to AP prolongation. Prolongation of QT, Tpeak-Tend intervals, and left ventricular monophasic AP duration of beats after aftercontractions occurred before torsades de pointes in an in vivo dog model of drug-induced long-QT1 syndrome. Conclusions:SCR contributes to increased BVR by interspersed prolongation of AP duration, which is exacerbated during IKs blockade. Attenuation of Ca2+-induced Ca2+ release by SCR underlies AP prolongation via increased ICaL. These data provide novel insights into arrhythmogenic mechanisms during β-adrenergic stimulation besides triggered activity and illustrate the importance of IKs function in preventing excessive BVR

Metoclopramide, Dexamethasone, or Palonosetron for Prevention of Delayed Chemotherapy-Induced Nausea and Vomiting After Moderately Emetogenic Chemotherapy (MEDEA): A Randomized, Phase III, Noninferiority Trial

BACKGROUND: For the prevention of chemotherapy-induced nausea and vomiting (CINV) during the delayed phase (24-120 hours) after moderately emetogenic chemotherapy (MEC), the use of 3-day dexamethasone (DEX) is often recommended. This study compared the efficacy and safety of two DEX-sparing regimens with 3-day DEX, focusing on delayed nausea. PATIENTS AND METHODS: This open-label, randomized, phase III study was designed to demonstrate noninferiority of two DEX-sparing regimens: ondansetron + DEX on day 1 + metoclopramide on days 2-3 (MCP arm), and palonosetron + DEX on day 1 (PAL arm) versus ondansetron on day 1 + DEX on days 1-3 (DEX arm) in chemotherapy-naïve patients receiving MEC. Primary efficacy endpoint was total control (TC; no emetic episodes, no use of rescue medication, no nausea) in the delayed phase. Noninferiority was defined as a lower 95% CI greater than the noninferiority margin set at -20%. Secondary endpoints included no vomiting, no rescue medication, no (significant) nausea, impact of CINV on quality of life, and antiemetics-associated side effects. RESULTS: Treatment arms were comparable for 189 patients analyzed: predominantly male (55.7%), median age 65.0 years, colorectal cancer (85.7%), and oxaliplatin-based chemotherapy (81.5%). MCP demonstrated noninferiority to DEX for delayed TC (MCP 56.1% vs. DEX 50.0%; 95% CI, -11.3%, 23.5%). PAL also demonstrated noninferiority to DEX (PAL 55.6% vs. DEX 50.0%; 95% CI, -12.0%, 23.2%). There were no statistically significant differences for all secondary endpoints between treatment arms. CONCLUSION: This study showed that DEX-sparing regimens are noninferior to multiple-day DEX in terms of delayed TC rate in patients undergoing MEC. ClinicalTrials.gov identifier. NCT02135510. IMPLICATIONS FOR PRACTICE: Chemotherapy-induced nausea and vomiting (CINV) in the delayed phase (24-120 hours after chemotherapy) remains one of the most troublesome adverse effects associated with cancer treatment. In particular, delayed nausea is often poorly controlled. The role of dexamethasone (DEX) in the prevention of delayed nausea after moderately emetogenic chemotherapy (MEC) is controversial. This study is the first to include nausea assessment as a part of the primary study outcome to better gauge the effectiveness of CINV control and patients' experience. Results show that a DEX-sparing strategy does not result in any significant loss of overall antiemetic control: DEX-sparing strategies incorporating palonosetron or multiple-day metoclopramide are safe and at least as effective as standard treatment with a 3-day DEX regimen with ondansetron in controlling delayed CINV-and nausea in particular-following MEC

The Rasnik 3-point optical alignment system

The Rasnik alignment system was developed initially in 1983 for the monitoring of the alignment of the muon chambers of the L3 Muon Spectrometer at CERN. Since then, the development has continued as new opto-electronic components become available. Rasnik systems are 3-point optical displacement monitors and their precision ranges from below nanometers to several micrometers, depending on the design and requirements of the systems. A result, expressed in the range/precision ratio of 2 × 106, is presented. According to the calculations of the Cram&aposer-Rao limit, and by means of MonteCarlo simulations, a typical Rasnik image should have enough information to reach deep sub-nanometer precision. This paper is an overview of the technological developments and achievements since Rasnik was applied in high energy physics experiments