Browsing by Subject "Arrhythmias, Cardiac"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Cardiac sodium channel palmitoylation regulates channel availability and myocyte excitability with implications for arrhythmia generation
    (Nature Publishing Group, 2016-06-23) Pei, Zifan; Xiao, Yucheng; Meng, Jingwei; Hudmon, Andy; Cummins, Theodore R.; Department of Pharmacology and Toxicology, IU School of Medicine
    Cardiac voltage-gated sodium channels (Nav1.5) play an essential role in regulating cardiac electric activity by initiating and propagating action potentials in the heart. Altered Nav1.5 function is associated with multiple cardiac diseases including long-QT3 and Brugada syndrome. Here, we show that Nav1.5 is subject to palmitoylation, a reversible post-translational lipid modification. Palmitoylation increases channel availability and late sodium current activity, leading to enhanced cardiac excitability and prolonged action potential duration. In contrast, blocking palmitoylation increases closed-state channel inactivation and reduces myocyte excitability. We identify four cysteines as possible Nav1.5 palmitoylation substrates. A mutation of one of these is associated with cardiac arrhythmia (C981F), induces a significant enhancement of channel closed-state inactivation and ablates sensitivity to depalmitoylation. Our data indicate that alterations in palmitoylation can substantially control Nav1.5 function and cardiac excitability and this form of post-translational modification is likely an important contributor to acquired and congenital arrhythmias.
  • Thumbnail Image
    Item
    Drug-induced atrial fibrillation
    (Springer Nature, 2012-08-20) Kaakeh, Yaman; Overholser, Brian R.; Lopshire, John C.; Tisdale, James E.; Medicine, School of Medicine
    Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with severe consequences, including symptoms, haemodynamic instability, increased cardiovascular mortality and stroke. While other arrhythmias such as torsades de pointes and sinus bradycardia are more typically thought of as drug induced, AF may also be precipitated by drug therapy, although ascribing causality to drug-associated AF is more difficult than with other drug-induced arrhythmias. Drug-induced AF is more likely to occur in patients with risk factors and co-morbidities that commonly co-exist with AF, such as advanced age, alcohol consumption, family history of AF, hypertension, thyroid dysfunction, sleep apnoea and heart disease. New-onset AF has been associated with cardiovascular drugs such as adenosine, dobutamine and milrinone. In addition, medications such as corticosteroids, ondansetron and antineoplastic agents such as paclitaxel, mitoxantrone and doxorubicin have been reported to induce AF. Whether bisphosphonate drugs are associated with new-onset AF remains controversial and requires further study. The potential contribution of specific drug therapy should be considered when patients present with new-onset AF.
  • Thumbnail Image
    Item
    Pathogenesis of Arrhythmias in a Model of CKD
    (American Society of Nephrology (ASN), 2014-12-01) Hsueh, Chia-Hsiang; Chen, Neal X.; Lin, Shien-Fong; Chen, Peng-Sheng; Gattone, Vincent H.; Allen, Matthew R.; Fishbein, Michael C.; Moe, Sharon M.; Department of Medicine, IU School of Medicine
    Patients with CKD have an increased risk of cardiovascular mortality from arrhythmias and sudden cardiac death. We used a rat model of CKD (Cy/+) to study potential mechanisms of increased ventricular arrhythmias. Rats with CKD showed normal ejection fraction but hypertrophic myocardium. Premature ventricular complexes occurred more frequently in CKD rats than normal rats (42% versus 11%, P=0.18). By optical mapping techniques, action potential duration (APD) at 80% of repolarization was longer in CKD rats (78±4ms) than normal rats (63±3 ms, P<0.05) at a 200-ms pacing cycle length. Calcium transient (CaT) duration was comparable. Pacing cycle length thresholds to induce CaT alternans or APD alternans were longer in CKD rats than normal rats (100±7 versus 80±3 ms and 93±6 versus 76±4 ms for CaT and APD alternans, respectively, P<0.05), suggesting increased vulnerability to ventricular arrhythmia. Ventricular fibrillation was induced in 9 of 12 CKD rats and 2 of 9 normal rats (P<0.05); early afterdepolarization occurred in two CKD rats but not normal rats. The mRNA levels of TGF-β, microRNA-21, and sodium calcium-exchanger type 1 were upregulated, whereas the levels of microRNA-29, L-type calcium channel, sarco/endoplasmic reticulum calcium–ATPase type 2a, Kv1.4, and Kv4.3 were downregulated in CKD rats. Cardiac fibrosis was mild and not different between groups. We conclude that cardiac ion channel and calcium handling are abnormal in CKD rats, leading to increased vulnerability to early afterdepolarization, triggered activity, and ventricular arrhythmias.
  • Thumbnail Image
    Item
    Utilization Rates of Implantable Cardioverter-Defibrillators for Primary Prevention of Sudden Cardiac Death: A 2012 Calculation for a Midwestern Health Referral Region
    (Elsevier, 2014-05) Hoang, Allen; Shen, Changyu; Zheng, James; Taylor, Stanley; Groh, William J; Rosenman, Marc; Buxton, Alfred E.; Chen, Peng-Sheng; Department of Medicine, IU School of Medicine
    Background Utilization rates (URs) for implantable cardioverter-defibrillators (ICDs) for primary prevention of sudden cardiac death (PPSCD) are lacking in the community. Objective To establish the ICD UR in central Indiana. Methods A query run on two hospitals in a health information exchange database in Indianapolis identified patients between 2011 and 2012 with left ventricular ejection fraction (EF) ≤0.35. ICD-eligibility and utilization were determined from chart review. Results We identified 1,863 patients with at least one low-EF study. Two cohorts were analyzed: 1,672 patients without, and 191 patients with, ICD-9-CM procedure code 37.94 for ICD placement. We manually reviewed a stratified (by hospital) random sample of 300 patients from the no-ICD procedure code cohort and found that 48 (16%) had no ICD but had class I indications for ICD. Eight of 300 (2.7%) actually had ICD implantation for PPSCD. Review of all 191 patients in the ICD procedure code cohort identified 70 with ICD implantation for PPSCD. The ICD UR (ratio between patients with ICD for PPSCD and all with indication) was 38% overall (95% CI 28–49%). URs were 48% for males (95% CI 34–61%), 21% for females (95% CI 16–26%, p=0.0002 vs males), 40% for whites (95% CI 27–53%), and 37% for blacks (95% CI 28–46%, p=0.66 vs whites). Conclusions The ICD UR is 38% among patients meeting Class I indications, suggesting further opportunities to improve guideline compliance. Furthermore, this study illustrates limitations in calculating ICD UR using large electronic repositories without hands-on chart review.