Proceed with caution: Standard protocol exercise stress tests fail to replicate the diagnostic utility of supine-stand tests for long QT syndrome.

BACKGROUND: Long QT syndrome (LQTS) is a sudden death predisposing condition characterized by ECG-derived prolongation of the QT interval. Previous studies have demonstrated that the supine-stand test may aid in the diagnosis of LQTS as patients fail to shorten their QT interval in response to standing up. The aim of this study was to evaluate the diagnostic accuracy of ECG data derived from standard protocol, clinically performed treadmill exercise stress tests (TESTs) in their ability to mimic the formal supine-stand test. METHODS: We performed a retrospective review of 478 TESTs from patients evaluated for LQTS. Patients referred for evaluation of LQTS but who were dismissed as normal served as controls. Heart rate & QT values were obtained from standard protocol TESTs. RESULTS: Overall, 243 patients with LQTS (125 LQT1, 63 LQT2, 55 LQT3; 146 [60%] female, mean age at TEST 30 ± 17 years) and 235 controls (142 [60%] female, mean age 24 ± 15 years) were included. The paired ΔQTc (QTcStand -QTcSupine ) was similar between LQTS (-5 ± 26) and controls (-2 ± 25; p = .2). During position change, the QT interval shortened by ≥20 ms in 33% of LQTS patients, remained unchanged in 62%, and increased in 5% of LQTS patients which was similar to controls (shortened in 40%, unchanged in 54%, and increased in 6% of controls; p = .2). Receiver-operator curve analysis to test the diagnostic ability of supine-stand ΔQT performed poorly in differentiating LQTS from controls with an of AUC 0.52 (p = .4). CONCLUSION: TESTs should be used with caution when trying to interpret supine-stand changes for diagnosis of LQTS.

Sodium channel ß1 subunits are post-translationally modified by tyrosine phosphorylation, S-palmitoylation, and regulated intramembrane proteolysis.

Voltage-gated sodium channel (VGSC) ß1 subunits are multifunctional proteins that modulate the biophysical properties and cell-surface localization of VGSC α subunits and participate in cell-cell and cell-matrix adhesion, all with important implications for intracellular signal transduction, cell migration, and differentiation. Human loss-of-function variants in SCN1B, the gene encoding the VGSC ß1 subunits, are linked to severe diseases with high risk for sudden death, including epileptic encephalopathy and cardiac arrhythmia. We showed previously that ß1 subunits are post-translationally modified by tyrosine phosphorylation. We also showed that ß1 subunits undergo regulated intramembrane proteolysis via the activity of ß-secretase 1 and γ-secretase, resulting in the generation of a soluble intracellular domain, ß1-ICD, which modulates transcription. Here, we report that ß1 subunits are phosphorylated by FYN kinase. Moreover, we show that ß1 subunits are S-palmitoylated. Substitution of a single residue in ß1, Cys-162, to alanine prevented palmitoylation, reduced the level of ß1 polypeptides at the plasma membrane, and reduced the extent of ß1-regulated intramembrane proteolysis, suggesting that the plasma membrane is the site of ß1 proteolytic processing. Treatment with the clathrin-mediated endocytosis inhibitor, Dyngo-4a, re-stored the plasma membrane association of ß1-p.C162A to WT levels. Despite these observations, palmitoylation-null ß1-p.C162A modulated sodium current and sorted to detergent-resistant membrane fractions normally. This is the first demonstration of S-palmitoylation of a VGSC ß subunit, establishing precedence for this post-translational modification as a regulatory mechanism in this protein family.

Utility of a Telephone Triage Hotline in Response to the COVID-19 Pandemic: Longitudinal Observational Study.

BACKGROUND: During the initial months of the COVID-19 pandemic, rapidly rising disease prevalence in the United States created a demand for patient-facing information exchanges that addressed questions and concerns about the disease. One approach to managing increased patient volumes during a pandemic involves the implementation of telephone-based triage systems. During a pandemic, telephone triage hotlines can be employed in innovative ways to conserve medical resources and offer useful population-level data about disease symptomatology and risk factor profiles. OBJECTIVE: The aim of this study is to describe and evaluate the COVID-19 telephone triage hotline used by a large academic medical center in the midwestern United States. METHODS: Michigan Medicine established a telephone hotline to triage inbound patient calls related to COVID-19. For calls received between March 24, 2020, and May 5, 2020, we described total call volume, data reported by callers including COVID-19 risk factors and symptomatology, and distribution of callers to triage algorithm endpoints. We also described symptomatology reported by callers who were directed to the institutional patient portal (online medical visit questionnaire). RESULTS: A total of 3929 calls (average 91 calls per day) were received by the call center during the study period. The maximum total number of daily calls peaked at 211 on March 24, 2020. Call volumes were the highest from 6 AM to 11 AM and during evening hours. Callers were most often directed to the online patient portal (1654/3929, 42%), nursing hotlines (1338/3929, 34%), or employee health services (709/3929, 18%). Cough (126/370 of callers, 34%), shortness of breath (101/370, 27%), upper respiratory infection (28/111, 25%), and fever (89/370, 24%) were the most commonly reported symptoms. Immunocompromised state (23/370, 6%) and age >65 years (18/370, 5%) were the most commonly reported risk factors. CONCLUSIONS: The triage algorithm successfully diverted low-risk patients to suitable algorithm endpoints, while directing high-risk patients onward for immediate assessment. Data collected from hotline calls also enhanced knowledge of symptoms and risk factors that typified community members, demonstrating that pandemic hotlines can aid in the clinical characterization of novel diseases.

Injectable contraceptive Depo-Provera induces erratic beating patterns in patient-specific induced pluripotent stem cell-derived cardiomyocytes with long QT syndrome type 2.

BACKGROUND: Long QT syndrome type 2 (LQT2) is caused by pathogenic variants in KCNH2. LQT2 may manifest as QT prolongation on an electrocardiogram and present with arrhythmic syncope/seizures and sudden cardiac arrest/death. Progestin-based oral contraceptives may increase the risk of LQT2-triggered cardiac events in women. We previously reported on a woman with LQT2 and recurrent cardiac events temporally related and attributed to the progestin-based contraceptive medroxyprogesterone acetate ("Depo-Provera" [Depo] MilliporeSigma, Catalog# 1378001, St. Louis, MO). OBJECTIVE: The purpose of this study was to evaluate the arrhythmic risk of Depo in a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model of LQT2. METHODS: An iPSC-CM line was generated from a 40-year-old woman with p.G1006Afs∗49-KCNH2. A CRISPR/Cas9 gene-edited/variant-corrected isogenic control iPSC-CM line was generated. FluoVolt (Invitrogen, F10488, Waltham, MA) was used to measure the action potential duration after treatment with 10 µM Depo. Erratic beating patterns characterized as alternating spike amplitudes, alternans, or early afterdepolarization-like phenomena were assessed using multielectrode array (MEA) after 10 µM Depo, 1 µM isoproterenol (ISO), or combined Depo + ISO treatment. RESULTS: Depo treatment shortened the action potential duration at 90% repolarization of G1006Afs∗49 iPSC-CMs from 394 ± 10 to 303 ± 10 ms (P < .0001). Combined Depo + ISO treatment increased the percentage of electrodes displaying erratic beating in G1006Afs∗49 iPSC-CMs (baseline: 18% ± 5% vs Depo + ISO: 54% ± 5%; P < .0001) but not in isogenic control iPSC-CMs (baseline: 0% ± 0% vs Depo + ISO: 10% ± 3%; P = .9659). CONCLUSION: This cell study provides a potential mechanism for the patient's clinically documented Depo-associated episodes of recurrent ventricular fibrillation. This in vitro data should prompt a large-scale clinical assessment of Depo's potential proarrhythmic effect in women with LQT2.

Sodium channel ß1 subunits participate in regulated intramembrane proteolysis-excitation coupling.

Loss-of-function (LOF) variants in SCN1B, encoding voltage-gated sodium channel ß1 subunits, are linked to human diseases with high risk of sudden death, including developmental and epileptic encephalopathy and cardiac arrhythmia. ß1 Subunits modulate the cell-surface localization, gating, and kinetics of sodium channel pore-forming α subunits. They also participate in cell-cell and cell-matrix adhesion, resulting in intracellular signal transduction, promotion of cell migration, calcium handling, and regulation of cell morphology. Here, we investigated regulated intramembrane proteolysis (RIP) of ß1 by BACE1 and γ-secretase and show that ß1 subunits are substrates for sequential RIP by BACE1 and γ-secretase, resulting in the generation of a soluble intracellular domain (ICD) that is translocated to the nucleus. Using RNA sequencing, we identified a subset of genes that are downregulated by ß1-ICD overexpression in heterologous cells but upregulated in Scn1b-null cardiac tissue, which lacks ß1-ICD signaling, suggesting that the ß1-ICD may normally function as a molecular brake on gene transcription in vivo. We propose that human disease variants resulting in SCN1B LOF cause transcriptional dysregulation that contributes to altered excitability. Moreover, these results provide important insights into the mechanism of SCN1B-linked channelopathies, adding RIP-excitation coupling to the multifunctionality of sodium channel ß1 subunits.

CT-measured Cortical Volume Ratio Is an Accurate Alternative to Nuclear Medicine Split Scan Ratio Among Living Kidney Donors.

BACKGROUND: The 125I-iothalamate clearance and 99mTc diethylenetriamine-pentaacetic acid (99mTc-DTPA) split scan nuclear medicine studies are used among living kidney donor candidates to determine measured glomerular filtration rate (mGFR) and split scan ratio (SSR). The computerized tomography-derived cortical volume ratio (CVR) is a novel measurement of split kidney function and can be combined with predonation estimated GFR (eGFR) or mGFR to predict postdonation kidney function. Whether predonation SSR predicts postdonation kidney function better than predonation CVR and whether predonation mGFR provides additional information beyond predonation eGFR are unknown. METHODS: We performed a single-center retrospective analysis of 204 patients who underwent kidney donation between June 2015 and March 2019. The primary outcome was 1-y postdonation eGFR. Model bases were created from a measure of predonation kidney function (mGFR or eGFR) multiplied by the proportion that each nondonated kidney contributed to predonation kidney function (SSR or CVR). Multivariable elastic net regression with 1000 repetitions was used to determine the mean and 95% confidence interval of R2, root mean square error (RMSE), and proportion overprediction ≥15 mL/min/1.73 m2 between models. RESULTS: In validation cohorts, eGFR-CVR models performed best (R2, 0.547; RMSE, 9.2 mL/min/1.73 m2, proportion overprediction 3.1%), whereas mGFR-SSR models performed worst (R2, 0.360; RMSE, 10.9 mL/min/1.73 m2, proportion overprediction 7.2%) (P < 0.001 for all comparisons). CONCLUSIONS: These findings suggest that predonation CVR may serve as an acceptable alternative to SSR during donor evaluation and furthermore, that a model based on CVR and predonation eGFR may be superior to other methods.