401
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Cairns JA. Which Oral Anticoagulant for Which Atrial Fibrillation Patient: Recent Clinical Trials and Evidence-Based Choices. Can J Cardiol 2013; 29:1165-72. [DOI: 10.1016/j.cjca.2013.05.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 05/21/2013] [Accepted: 05/22/2013] [Indexed: 11/25/2022] Open
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402
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Capodanno D, Tamburino C. Antithrombotic Strategies in Valvular and Structural Heart Disease Interventions: Current Status and Future Directions. Interv Cardiol Clin 2013; 2:635-642. [PMID: 28582190 DOI: 10.1016/j.iccl.2013.05.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Antithrombotic prophylaxis is the cornerstone of adjunctive pharmacologic therapy in patients undergoing transcatheter intervention for valvular and structural heart disease. However, drugs and doses of antiplatelet and anticoagulant agents are mostly empiric for these indications and typically administered at the operator's discretion. This article describes the rationale for antithrombotic management of patients undergoing transcatheter aortic valve implantation, percutaneous mitral valve repair with the Mitraclip system, patent foramen ovale, and atrial septal defect closure, as well as common strategies for managing antiplatelet and anticoagulant therapy in patients with valvular and structural heart disease undergoing transcatheter procedures.
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Affiliation(s)
- Davide Capodanno
- Cardiovascular Department, Ferrarotto Hospital, University of Catania, Via Citelli 6, Catania 95124, Italy; Excellence Through Newest Advances (ETNA) Foundation, Via Citelli 6, Catania 95124, Italy.
| | - Corrado Tamburino
- Cardiovascular Department, Ferrarotto Hospital, University of Catania, Via Citelli 6, Catania 95124, Italy; Excellence Through Newest Advances (ETNA) Foundation, Via Citelli 6, Catania 95124, Italy
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403
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Kaatz S, Gage BF. Top practice-changing articles over the last two years. J Thromb Thrombolysis 2013; 35:325-32. [PMID: 23456774 DOI: 10.1007/s11239-013-0896-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The field of thromboembolic disease and anticoagulation has had critical advances since the Anticoagulation Forum last met (May of 2011). We summarize our "top ten list" of papers that are likely to change the care of the anticoagulated population and improve their outcomes: (1) Patient self-management of their vitamin K antagonist and self monitoring can decrease thromboembolic events; (2) restarting warfarin after gastrointestinal bleeding may decrease mortality; (3) rivaroxaban is effective in the treatment of pulmonary embolism; either (4) apixaban or (5) low-dose aspirin prevented recurrent venous thromboembolic disease after a standard course of therapy; (6) warfarin prevents thrombotic complications up to at least 90 days after bioprosthetic aortic valve replacement; (7) the relative risk reduction of apixaban compared to warfarin is similar across CHADS2 scores, but the absolute risk reduction is higher in high-risk patients; (8) adherence to a warfarin dose-adjustment algorithm improved time in the therapeutic range and thromboembolic outcomes in the RE-LY trial; (9) warfarin had little benefit (if any) over aspirin in patients with decreased ejection fraction and sinus rhythm; (10) adding clopidogrel to aspirin in patients with lacunar infarcts did not reduce the risk of recurrent stroke and increased bleeding.
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Affiliation(s)
- Scott Kaatz
- Hurley Medical Center, One Hurley Plaza, Flint, MI 48503, USA.
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404
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Colli A, Verhoye JP, Heijmen R, Antunes M. Low-dose acetyl salicylic acid versus oral anticoagulation after bioprosthetic aortic valve replacement. Final report of the ACTION registry. Int J Cardiol 2013; 168:1229-36. [DOI: 10.1016/j.ijcard.2012.11.056] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Revised: 09/24/2012] [Accepted: 11/11/2012] [Indexed: 11/27/2022]
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405
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Liew A, Eikelboom JW, O'Donnell M, Hart RG. Assessment of anticoagulation intensity and management of bleeding with old and new oral anticoagulants. Can J Cardiol 2013; 29:S34-44. [PMID: 23790596 DOI: 10.1016/j.cjca.2013.04.013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Revised: 04/16/2013] [Accepted: 04/16/2013] [Indexed: 11/17/2022] Open
Abstract
Warfarin is effective for the prevention and treatment of thromboembolism but produces variable anticoagulant effects and requires routine monitoring of the international normalized ratio (INR) to optimize the balance between efficacy and safety. The new oral anticoagulants (NOACs) have a more predictable anticoagulant effect and were recently demonstrated to be at least as efficacious and safe as warfarin despite being administered in fixed doses without routine coagulation monitoring. Specific laboratory tests have been developed to measure the anticoagulant effect of the NOACs but are not yet widely available, and the relation between drug levels and both coagulation test results and outcomes is uncertain. It remains to be demonstrated whether adjustment of the dose of NOACs, according to the results of laboratory testing, may lead to even greater efficacy and safety. The principles of bleeding management in patients treated with NOACs compared with patients receiving warfarin are similar. Most patients can be safely managed by interrupting drug treatment, performing local measures to stem the bleeding, and providing transfusion support as required. In patients with major or life-threatening bleeding and those requiring surgery, the anticoagulant effects of warfarin can be reversed using oral or intravenous vitamin K, fresh frozen plasma (FFP), and prothrombin complex concentrates (PCCs). Specific antidotes are under development for the NOACs but are not yet approved for clinical use. PCCs and recombinant factor VIIa may improve hemostasis in patients in whom bleeding develops during treatment with a NOAC, but their efficacy is unproven.
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Affiliation(s)
- Aaron Liew
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
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406
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Saikrishnan N, Gupta S, Yoganathan AP. Hemodynamics of the Boston Scientific Lotus™ Valve: An In Vitro Study. Cardiovasc Eng Technol 2013. [DOI: 10.1007/s13239-013-0163-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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407
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Casais P, Rolandi F. Prosthetic valve thrombosis in pregnancy: a promising treatment for a rare and mostly preventable complication. Circulation 2013; 128:481-2. [PMID: 23812181 DOI: 10.1161/circulationaha.113.004259] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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408
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Abstract
Anticoagulation is an effective therapeutic means of reducing thrombotic risk in patients with various conditions, including atrial fibrillation, mechanical heart valves, and major surgery. By its nature, anticoagulation increases the risk of bleeding; this risk is particularly high during transitions of care. Established anticoagulants are not ideal, due to requirements for parenteral administration, narrow therapeutic indices, and/or a need for frequent therapeutic monitoring. The development of effective oral anticoagulants that are administered as a fixed dose, have low potential for drug-drug and drug-food interactions, do not require regular anticoagulation monitoring, and are suitable for both inpatient and outpatient use is to be welcomed. Three new oral anticoagulants, the direct thrombin inhibitor, dabigatran etexilate, and the factor Xa inhibitors, rivaroxaban and apixaban, have been approved in the US for reducing the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation; rivaroxaban is also approved for prophylaxis and treatment of deep vein thrombosis, which may lead to pulmonary embolism in patients undergoing knee or hip replacement surgery. This review examines current options for anticoagulant therapy, with a focus on maintaining efficacy and safety during transitions of care. The characteristics of dabigatran etexilate, rivaroxaban, and apixaban are discussed in the context of traditional anticoagulant therapy.
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Affiliation(s)
- Franklin Michota
- Department of Hospital Medicine, Cleveland Clinic, Cleveland, OH, USA
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409
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Suri RM, Thourani VH, He X, Brennan JM, O'Brien SM, Rankin JS, Schaff HV, Gammie JS. Variation in Warfarin Thromboprophylaxis After Mitral Valve Repair: Does Equipoise Exist and Is a Randomized Trial Warranted? Ann Thorac Surg 2013; 95:1991-8; discussion 1998-9. [DOI: 10.1016/j.athoracsur.2013.03.024] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Revised: 03/05/2013] [Accepted: 03/07/2013] [Indexed: 10/26/2022]
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410
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Tran HA, Chunilal SD, Harper PL, Tran H, Wood EM, Gallus AS. An update of consensus guidelines for warfarin reversal. Med J Aust 2013; 198:198-9. [PMID: 23451962 DOI: 10.5694/mja12.10614] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Accepted: 01/13/2013] [Indexed: 12/19/2022]
Abstract
• Despite the associated bleeding risk, warfarin is the most commonly prescribed anticoagulant in Australia and New Zealand. Warfarin use will likely continue for anticoagulation indications for which novel agents have not been evaluated and among patients who are already stabilised on it or have severe renal impairment. • Strategies to manage over-warfarinisation and warfarin during invasive procedures can reduce the risk of haemorrhage. • For most warfarin indications, the target international normalised ratio (INR) is 2.0-3.0 (venous thromboembolism and single mechanical heart valve excluding mitral). For mechanical mitral valve or combined mitral and aortic valves, the target INR is 2.5-3.5. • Risk factors for bleeding with warfarin use include increasing age, history of bleeding and specific comorbidities. • For patients with elevated INR (4.5-10.0), no bleeding and no high risk of bleeding, withholding warfarin with careful subsequent monitoring seems safe. • Vitamin K1 can be given to reverse the anticoagulant effect of warfarin. When oral vitamin K1 is used for this purpose, the injectable formulation, which can be given orally or intravenously, is preferred. • For immediate reversal, prothrombin complex concentrates (PCC) are preferred over fresh frozen plasma (FFP). Prothrombinex-VF is the only PCC routinely used for warfarin reversal in Australia and New Zealand. It contains factors II, IX, X and low levels of factor VII. FFP is not routinely needed in combination with Prothrombinex-VF. FFP can be used when Prothrombinex-VF is unavailable. Vitamin K1 is essential for sustaining the reversal achieved by PCC or FFP. • Surgery can be conducted with minimal increased risk of bleeding if INR ≤ 1.5. For minor procedures where bleeding risk is low, warfarin may not need to be interrupted. If necessary, warfarin can be withheld for 5 days before surgery, or intravenous vitamin K₁ can be given the night before surgery. Prothrombinex-VF use for warfarin reversal should be restricted to emergency settings. Perioperative management of anticoagulant therapy requires an evaluation of the risk of thrombosis if warfarin is temporarily stopped, relative to the risk of bleeding if it is continued or modified.
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Affiliation(s)
- Huyen A Tran
- Clinical Haematology, The Alfred Hospital, Melbourne, VIC.
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411
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Whitlock R, Danter M. Response. Chest 2013; 143:1514. [PMID: 23648925 DOI: 10.1378/chest.13-0557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Affiliation(s)
- Richard Whitlock
- Division of Cardiac Surgery, McMaster University, Hamilton, ON, Canada.
| | - Matthew Danter
- Division of Cardiac Surgery, McMaster University, Hamilton, ON, Canada
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412
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413
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Fu B, Chen H, Dong L. Antithrombotic and Thrombolytic Therapy for Valvular Disease. Chest 2013; 143:1513-1514. [DOI: 10.1378/chest.12-3077] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
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414
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Tiong IS, Williams MJ, Perez DJ. Nonbacterial Thrombotic Endocarditis with ST-elevation Myocardial Infarction Treated with Percutaneous Coronary Aspiration Thrombectomy. Heart Lung Circ 2013; 22:386-9. [DOI: 10.1016/j.hlc.2012.10.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 10/23/2012] [Accepted: 10/24/2012] [Indexed: 11/28/2022]
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415
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Petsche Connell J, Camci-Unal G, Khademhosseini A, Jacot JG. Amniotic fluid-derived stem cells for cardiovascular tissue engineering applications. TISSUE ENGINEERING PART B-REVIEWS 2013; 19:368-79. [PMID: 23350771 DOI: 10.1089/ten.teb.2012.0561] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Recent research has demonstrated that a population of stem cells can be isolated from amniotic fluid removed by amniocentesis that are broadly multipotent and nontumorogenic. These amniotic fluid-derived stem cells (AFSC) could potentially provide an autologous cell source for treatment of congenital defects identified during gestation, particularly cardiovascular defects. In this review, the various methods of isolating, sorting, and culturing AFSC are compared, along with techniques for inducing differentiation into cardiac myocytes and endothelial cells. Although research has not demonstrated complete and high-yield cardiac differentiation, AFSC have been shown to effectively differentiate into endothelial cells and can effectively support cardiac tissue. Additionally, several tissue engineering and regenerative therapeutic approaches for the use of these cells in heart patches, injection after myocardial infarction, heart valves, vascularized scaffolds, and blood vessels are summarized. These applications show great promise in the treatment of congenital cardiovascular defects, and further studies of isolation, culture, and differentiation of AFSC will help to develop their use for tissue engineering, regenerative medicine, and cardiovascular therapies.
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416
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Wong PYH, Schulman S, Woodworth S, Holbrook A. Supplemental patient education for patients taking oral anticoagulants: systematic review and meta-analysis. J Thromb Haemost 2013; 11:491-502. [PMID: 23279062 DOI: 10.1111/jth.12107] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 12/06/2012] [Indexed: 11/28/2022]
Abstract
OBJECTIVE Lack of patient knowledge has been associated with poor anticoagulation control, but the effect of patient education on clinical outcomes is unclear. We systematically reviewed the effect of supplemental patient education vs. usual care on hemorrhage, thromboembolic events (TEEs), time in therapeutic range (TTR) and knowledge test scores for all oral anticoagulants. DATA SOURCES The data sources were electronic databases, including MEDLINE, EMBASE, CENTRAL, CINAHL and IPA, to February 2012 examining any oral anticoagulant. We reviewed references for additional potentially relevant studies. METHODS Only randomized controlled trials (RCTs) were considered. Data extraction and quality assessment were conducted with GRADE. Pooled relative risks (RRs) were calculated, and heterogeneity was determined by use of χ(2) and I(2) statistics. RESULTS Seven RCTs (n = 1209) were included in the systematic review, and five RCTs (n = 847) in the meta-analysis. All included studies examined vitamin K antagonists. No significant difference was found for hemorrhage (RR 0.92, 95% confidence interval [CI] 0.04-20.56), TEE (RR 0.66, 95% CI 0.10-4.39), a composite outcome of hemorrhage or TEE (RR 0.48, 95% CI 0.23-1.01), or TTR (mean absolute difference of 2.02%, 95% CI - 2.81 to 6.84). Evidence was conflicting on the impact of supplemental education on test scores. All trials had at least one substantial methodologic limitation. CONCLUSION Current evidence does not support supplemental patient education as a means to improve patient outcomes, but the quality of this evidence is poor. Larger randomized trials are needed with longer follow-up, recruitment of patients initiating anticoagulation in primary care settings, and clearly defined education interventions.
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Affiliation(s)
- P Y H Wong
- Department of Family Medicine, McMaster University, Hamilton, Ontario, Canada
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417
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Lynch DR, Dantzler D, Robbins M, Zhao D. Considerations in antithrombotic therapy among patients undergoing transcatheter aortic valve implantation. J Thromb Thrombolysis 2013; 35:476-82. [DOI: 10.1007/s11239-013-0886-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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418
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Karthikeyan G, Senguttuvan NB, Joseph J, Devasenapathy N, Bahl VK, Airan B. Urgent surgery compared with fibrinolytic therapy for the treatment of left-sided prosthetic heart valve thrombosis: a systematic review and meta-analysis of observational studies. Eur Heart J 2013; 34:1557-66. [DOI: 10.1093/eurheartj/ehs486] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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419
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Managing patients with an indication for anticoagulant therapy after transcatheter aortic valve implantation. Am J Cardiol 2013; 111:237-42. [PMID: 23111140 DOI: 10.1016/j.amjcard.2012.09.023] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Revised: 09/25/2012] [Accepted: 09/25/2012] [Indexed: 11/22/2022]
Abstract
Patients who undergo transcatheter aortic valve implantation are generally discharged on dual-antiplatelet therapy. However, many of these patients also have indications for anticoagulant therapy, and it is unclear what the best antithrombotic strategy is in these cases. Data from 360 patients who underwent transcatheter aortic valve implantation were retrospectively analyzed, of whom 60 (16.7%) had indications for anticoagulant treatment, mainly because of atrial fibrillation. The antithrombotic regimen was decided according to clinical evaluation of thrombotic and hemorrhagic risk; most of these patients (n = 43) were discharged with warfarin plus a single antiplatelet drug. Their outcomes were compared to those in a group with no indications for anticoagulation (n = 300) treated with dual-antiplatelet therapy. During the follow-up period (median 11 months), 53 patients (15%) died; mortality was not associated with antithrombotic regimen. The incidence of cerebral events or intracranial hemorrhage (4.6% and 1.1%, respectively) was low in the study population, and no significant differences were detected between groups; the bleeding rate was also unaffected by antithrombotic therapy. In conclusion, when anticoagulation is indicated after transcatheter aortic valve implantation, many variables must be taken into account. The most frequent scenario in this study was patients in atrial fibrillation, most of whom were discharged with warfarin plus a single antiplatelet medication. When bleeding was a concern, especially in the absence of coronary disease, warfarin alone was prescribed. These results suggest that this approach is safe, but data from larger, randomized studies are needed.
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420
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Wang JG, Kuai XC, Ren BQ, Gong GF, Zhou XM. Reduced leaflet stress in the stentless quadrileaflet mitral valve: a finite element model. PLoS One 2013; 8:e67683. [PMID: 23844060 PMCID: PMC3699618 DOI: 10.1371/journal.pone.0067683] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 05/20/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Failure of bioprosthetics is usually caused by calcification of the leaflets as a consequence of high tensile stresses. The stentless valve resembles native mitral valve anatomy, has a flexible leaflet attachment and a suspension at the papillary muscles, and preserves annuloventricular continuity. In this study, the effects of the stentless valve design on leaflet stress were investigated with a finite element model. METHODS Finite element models of the stentless quadrileaflet mitral valve were created in the close and open configurations. The geometry of the stented trileaflet mitral valve was also analyzed for comparative purposes. Under the designated pressures, the regional stresses were evaluated, and the distributions of stresses were assessed. RESULTS Regardless of whether the valve is in the open or close configuration, the maximum first principal stress was significantly lower in the stentless valve than in the stented valve. For the stentless valves, limited stress concentration was discretely distributed in the papillary flaps under both close and open conditions. In contrast, in the stented valve, increased stress concentration was evident at the central belly under the open condition and at the commissural attachment under close condition. In either configuration, the maximum second principal stress was markedly lower in the stentless valve than in the stented valve. CONCLUSIONS The stentless valve was associated with a significant reduction in leaflet stress and a more homogeneous stress distribution compared to the stented valve. These findings are consistent with recent reports of the clinical effectiveness of the stentless quadrileaflet mitral valve.
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Affiliation(s)
- Jian-Gang Wang
- Department of Cardiac Surgery, Beijing Anzhen Hospital, Capital Medical University, Beijing, China.
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421
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Mahtani KR, Heneghan CJ, Nunan D, Bankhead C, Keeling D, Ward AM, Harrison SE, Roberts NW, Hobbs FDR, Perera R. Optimal loading dose of warfarin for the initiation of oral anticoagulation. Cochrane Database Syst Rev 2012; 12:CD008685. [PMID: 23235665 PMCID: PMC8454262 DOI: 10.1002/14651858.cd008685.pub2] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
BACKGROUND Warfarin is used as an oral anticoagulant. However, there is wide variation in patient response to warfarin dose. This variation, as well as the necessity of keeping within a narrow therapeutic range, means that selection of the correct warfarin dose at the outset of treatment is not straightforward. OBJECTIVES To assess the effectiveness of different initiation doses of warfarin in terms of time in-range, time to INR in-range and effect on serious adverse events. SEARCH METHODS We searched CENTRAL, DARE and the NHS Health economics database on The Cochrane Library (2012, Issue 4); MEDLINE (1950 to April 2012) and EMBASE (1974 to April 2012). SELECTION CRITERIA All randomised controlled trials which compared different initiation regimens of warfarin. DATA COLLECTION AND ANALYSIS Review authors independently assessed studies for inclusion. Authors also assessed the risk of bias and extracted data from the included studies. MAIN RESULTS We identified 12 studies of patients commencing warfarin for inclusion in the review. The overall risk of bias was found to be variable, with most studies reporting adequate methods for randomisation but only two studies reporting adequate data on allocation concealment. Four studies (355 patients) compared 5 mg versus 10 mg loading doses. All four studies reported INR in-range by day five. Although there was notable heterogeneity, pooling of these four studies showed no overall difference between 5 mg versus 10 mg loading doses (RR 1.17, 95% CI 0.77 to 1.77, P = 0.46, I(2) = 83%). Two of these studies used two consecutive INRs in-range as the outcome and showed no difference between a 5 mg and 10 mg dose by day five (RR 0.86, 95% CI 0.62 to 1.19, P = 0.37, I(2 )= 22%); two other studies used a single INR in-range as the outcome and showed a benefit for the 10 mg initiation dose by day 5 (RR 1.49, 95% CI 1.01 to 2.21, P = 0.05, I(2 )= 72%). Two studies compared a 5 mg dose to other doses: a 2.5 mg initiation dose took longer to achieve the therapeutic range (2.7 versus 2.0 days; P < 0.0001), but those receiving a calculated initiation dose achieved a target range quicker (4.2 days versus 5 days, P = 0.007). Two studies compared age adjusted doses to 10 mg initiation doses. More elderly patients receiving an age adjusted dose achieved a stable INR compared to those receiving a 10 mg initial dose (and Fennerty regimen). Four studies used genotype guided dosing in one arm of each trial. Three studies reported no overall differences; the fourth study, which reported that the genotype group spent significantly more time in-range (P < 0.001), had a control group whose INRs were significantly lower than expected. No clear impacts from adverse events were found in either arm to make an overall conclusion. AUTHORS' CONCLUSIONS The studies in this review compared loading doses in several different situations. There is still considerable uncertainty between the use of a 5 mg and a 10 mg loading dose for the initiation of warfarin. In the elderly, there is some evidence that lower initiation doses or age adjusted doses are more appropriate, leading to fewer high INRs. However, there is insufficient evidence to warrant genotype guided initiation.
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Affiliation(s)
- Kamal R Mahtani
- Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
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422
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Di Legge S, Koch G, Diomedi M, Stanzione P, Sallustio F. Stroke prevention: managing modifiable risk factors. Stroke Res Treat 2012; 2012:391538. [PMID: 23213626 PMCID: PMC3504482 DOI: 10.1155/2012/391538] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Accepted: 10/08/2012] [Indexed: 12/12/2022] Open
Abstract
Prevention plays a crucial role in counteracting morbidity and mortality related to ischemic stroke. It has been estimated that 50% of stroke are preventable through control of modifiable risk factors and lifestyle changes. Antihypertensive treatment is recommended for both prevention of recurrent stroke and other vascular events. The use of antiplatelets and statins has been shown to reduce the risk of recurrent stroke and other vascular events. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) are indicated in stroke prevention because they also promote vascular health. Effective secondary-prevention strategies for selected patients include carotid revascularization for high-grade carotid stenosis and vitamin K antagonist treatment for atrial fibrillation. The results of recent clinical trials investigating new anticoagulants (factor Xa inhibitors and direct thrombin inhibitors) clearly indicate alternative strategies in stroke prevention for patients with atrial fibrillation. This paper describes the current landscape and developments in stroke prevention with special reference to medical treatment in secondary prevention of ischemic stroke.
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Affiliation(s)
- Silvia Di Legge
- Stroke Unit, Department of Neuroscience, University of Tor Vergata, Viale Oxford 81, 00133 Rome, Italy
| | - Giacomo Koch
- Stroke Unit, Department of Neuroscience, University of Tor Vergata, Viale Oxford 81, 00133 Rome, Italy
- Santa Lucia Foundation, IRCCS, Viale Ardeatina 306, 00134 Rome, Italy
| | - Marina Diomedi
- Stroke Unit, Department of Neuroscience, University of Tor Vergata, Viale Oxford 81, 00133 Rome, Italy
| | - Paolo Stanzione
- Stroke Unit, Department of Neuroscience, University of Tor Vergata, Viale Oxford 81, 00133 Rome, Italy
- Santa Lucia Foundation, IRCCS, Viale Ardeatina 306, 00134 Rome, Italy
| | - Fabrizio Sallustio
- Stroke Unit, Department of Neuroscience, University of Tor Vergata, Viale Oxford 81, 00133 Rome, Italy
- Santa Lucia Foundation, IRCCS, Viale Ardeatina 306, 00134 Rome, Italy
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423
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Whitlock RP, Eikelboom JW. Prevention of Thromboembolic Events After Bioprosthetic Aortic Valve Replacement. J Am Coll Cardiol 2012; 60:978-80. [DOI: 10.1016/j.jacc.2012.06.014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 06/12/2012] [Indexed: 11/27/2022]
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424
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You JJ, Singer DE, Howard PA, Lane DA, Eckman MH, Fang MC, Hylek EM, Schulman S, Go AS, Hughes M, Spencer FA, Manning WJ, Halperin JL, Lip GYH. Antithrombotic therapy for atrial fibrillation: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:e531S-e575S. [PMID: 22315271 DOI: 10.1378/chest.11-2304] [Citation(s) in RCA: 686] [Impact Index Per Article: 57.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND The risk of stroke varies considerably across different groups of patients with atrial fibrillation (AF). Antithrombotic prophylaxis for stroke is associated with an increased risk of bleeding. We provide recommendations for antithrombotic treatment based on net clinical benefit for patients with AF at varying levels of stroke risk and in a number of common clinical scenarios. METHODS We used the methods described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines article of this supplement. RESULTS For patients with nonrheumatic AF, including those with paroxysmal AF, who are (1) at low risk of stroke (eg, CHADS(2) [congestive heart failure, hypertension, age ≥ 75 years, diabetes mellitus, prior stroke or transient ischemic attack] score of 0), we suggest no therapy rather than antithrombotic therapy, and for patients choosing antithrombotic therapy, we suggest aspirin rather than oral anticoagulation or combination therapy with aspirin and clopidogrel; (2) at intermediate risk of stroke (eg, CHADS(2) score of 1), we recommend oral anticoagulation rather than no therapy, and we suggest oral anticoagulation rather than aspirin or combination therapy with aspirin and clopidogrel; and (3) at high risk of stroke (eg, CHADS(2) score of ≥ 2), we recommend oral anticoagulation rather than no therapy, aspirin, or combination therapy with aspirin and clopidogrel. Where we recommend or suggest in favor of oral anticoagulation, we suggest dabigatran 150 mg bid rather than adjusted-dose vitamin K antagonist therapy. CONCLUSIONS Oral anticoagulation is the optimal choice of antithrombotic therapy for patients with AF at high risk of stroke (CHADS(2) score of ≥ 2). At lower levels of stroke risk, antithrombotic treatment decisions will require a more individualized approach.
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Affiliation(s)
- John J You
- Department of Medicine, McMaster University, Hamilton, ON, Canada; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada
| | - Daniel E Singer
- Department of Medicine, General Medicine Division, Massachusetts General Hospital, Boston, MA; Harvard Medical School, and Clinical Epidemiology Unit, General Medicine Division, Massachusetts General Hospital, Boston, MA
| | - Patricia A Howard
- School of Pharmacy, University of Kansas Medical Center, Kansas City, KS
| | - Deirdre A Lane
- University of Birmingham Centre for Cardiovascular Sciences, City Hospital, Birmingham, England
| | - Mark H Eckman
- Department of Clinical Medicine, Division of General Internal Medicine and Center for Clinical Effectiveness, University of Cincinnati, Cincinnati, OH
| | - Margaret C Fang
- Department of Medicine, Division of Hospital Medicine, University of California, San Francisco, San Francisco, CA
| | - Elaine M Hylek
- Boston University Medical Center Research Unit, Section of General Internal Medicine, Boston, MA
| | - Sam Schulman
- Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Alan S Go
- Comprehensive Clinical Research Unit, Division of Research, Kaiser Permanente Northern California, Oakland, CA
| | | | | | - Warren J Manning
- Section of Non-invasive Cardiac Imaging, Beth Israel Deaconess Medical Center, Boston, MA
| | | | - Gregory Y H Lip
- University of Birmingham Centre for Cardiovascular Sciences, City Hospital, Birmingham, England.
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425
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Holbrook A, Schulman S, Witt DM, Vandvik PO, Fish J, Kovacs MJ, Svensson PJ, Veenstra DL, Crowther M, Guyatt GH. Evidence-based management of anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:e152S-e184S. [PMID: 22315259 DOI: 10.1378/chest.11-2295] [Citation(s) in RCA: 887] [Impact Index Per Article: 73.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND High-quality anticoagulation management is required to keep these narrow therapeutic index medications as effective and safe as possible. This article focuses on the common important management questions for which, at a minimum, low-quality published evidence is available to guide best practices. METHODS The methods of this guideline follow those described in Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement. RESULTS Most practical clinical questions regarding the management of anticoagulation, both oral and parenteral, have not been adequately addressed by randomized trials. We found sufficient evidence for summaries of recommendations for 23 questions, of which only two are strong rather than weak recommendations. Strong recommendations include targeting an international normalized ratio of 2.0 to 3.0 for patients on vitamin K antagonist therapy (Grade 1B) and not routinely using pharmacogenetic testing for guiding doses of vitamin K antagonist (Grade 1B). Weak recommendations deal with such issues as loading doses, initiation overlap, monitoring frequency, vitamin K supplementation, patient self-management, weight and renal function adjustment of doses, dosing decision support, drug interactions to avoid, and prevention and management of bleeding complications. We also address anticoagulation management services and intensive patient education. CONCLUSIONS We offer guidance for many common anticoagulation-related management problems. Most anticoagulation management questions have not been adequately studied.
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Affiliation(s)
- Anne Holbrook
- Division of Clinical Pharmacology and Therapeutics, McMaster University, Hamilton, ON, Canada; Department of Medicine, McMaster University, Hamilton, ON, Canada; Department of Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada.
| | - Sam Schulman
- Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Daniel M Witt
- Department of Pharmacy, Kaiser Permanente Colorado, Denver, CO
| | - Per Olav Vandvik
- Department of Medicine, Innlandet Hospital Trust, Gjøvik, Norway
| | - Jason Fish
- Department of Internal Medicine, University of California Los Angeles, Los Angeles, CA
| | - Michael J Kovacs
- Department of Medicine, University of Western Ontario, London, ON, Canada
| | - Peter J Svensson
- Department for Coagulation Disorders, University of Lund, University Hospital, Malmö, Sweden
| | | | - Mark Crowther
- Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Gordon H Guyatt
- Department of Medicine, McMaster University, Hamilton, ON, Canada; Department of Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada
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426
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Guyatt GH, Akl EA, Crowther M, Gutterman DD, Schuünemann HJ. Executive summary: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:7S-47S. [PMID: 22315257 DOI: 10.1378/chest.1412s3] [Citation(s) in RCA: 1148] [Impact Index Per Article: 95.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Gordon H Guyatt
- Department of Clinical Epidemiology and Biostatistics, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada; Department of Medicine, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada.
| | - Elie A Akl
- Department of Clinical Epidemiology and Biostatistics, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada; Department of Medicine and Family Medicine, State University of New York, Buffalo, NY
| | - Mark Crowther
- Department of Medicine, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada
| | - David D Gutterman
- Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee, WI
| | - Holger J Schuünemann
- Department of Clinical Epidemiology and Biostatistics, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada; Department of Medicine, McMaster University Faculty of Health Sciences, Hamilton, ON, Canada
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427
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Monagle P, Chan AKC, Goldenberg NA, Ichord RN, Journeycake JM, Nowak-Göttl U, Vesely SK. Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:e737S-e801S. [PMID: 22315277 DOI: 10.1378/chest.11-2308] [Citation(s) in RCA: 964] [Impact Index Per Article: 80.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
BACKGROUND Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children. METHODS The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. RESULTS We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C). CONCLUSIONS The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.
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Affiliation(s)
- Paul Monagle
- Haematology Department, The Royal Children's Hospital, Department of Paediatrics, The University of Melbourne, Murdoch Children's Research Institute, Melbourne, VIC, Australia
| | - Anthony K C Chan
- Department of Pediatrics, McMaster University, Hamilton, ON, Canada
| | - Neil A Goldenberg
- Department of Pediatrics, Section of Hematology/Oncology/Bone Marrow Transplantation and Mountain States Regional Hemophilia and Thrombosis Center, University of Colorado, Aurora, CO
| | - Rebecca N Ichord
- Department of Neurology, Children's Hospital of Philadelphia, Philadelphia, PA
| | - Janna M Journeycake
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, TX
| | - Ulrike Nowak-Göttl
- Thrombosis and Hemostasis Unit, Institute of Clinical Chemistry, University Hospital Kiel, Kiel, Germany
| | - Sara K Vesely
- Department of Biostatistics and Epidemiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK.
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428
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Bates SM, Greer IA, Middeldorp S, Veenstra DL, Prabulos AM, Vandvik PO. VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:e691S-e736S. [PMID: 22315276 PMCID: PMC3278054 DOI: 10.1378/chest.11-2300] [Citation(s) in RCA: 843] [Impact Index Per Article: 70.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2011] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The use of anticoagulant therapy during pregnancy is challenging because of the potential for both fetal and maternal complications. This guideline focuses on the management of VTE and thrombophilia as well as the use of antithrombotic agents during pregnancy. METHODS The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement. RESULTS We recommend low-molecular-weight heparin for the prevention and treatment of VTE in pregnant women instead of unfractionated heparin (Grade 1B). For pregnant women with acute VTE, we suggest that anticoagulants be continued for at least 6 weeks postpartum (for a minimum duration of therapy of 3 months) compared with shorter durations of treatment (Grade 2C). For women who fulfill the laboratory criteria for antiphospholipid antibody (APLA) syndrome and meet the clinical APLA criteria based on a history of three or more pregnancy losses, we recommend antepartum administration of prophylactic or intermediate-dose unfractionated heparin or prophylactic low-molecular-weight heparin combined with low-dose aspirin (75-100 mg/d) over no treatment (Grade 1B). For women with inherited thrombophilia and a history of pregnancy complications, we suggest not to use antithrombotic prophylaxis (Grade 2C). For women with two or more miscarriages but without APLA or thrombophilia, we recommend against antithrombotic prophylaxis (Grade 1B). CONCLUSIONS Most recommendations in this guideline are based on observational studies and extrapolation from other populations. There is an urgent need for appropriately designed studies in this population.
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Affiliation(s)
- Shannon M Bates
- Department of Medicine, McMaster University and Thrombosis and Atherosclerosis Research Institute, Hamilton, ON, Canada.
| | - Ian A Greer
- Faculty of Health and Life Sciences, University of Liverpool, Liverpool, England
| | - Saskia Middeldorp
- Department of Vascular Medicine, Academic Medical Center, Amsterdam, The Netherlands
| | | | - Anne-Marie Prabulos
- Department of Obstetrics and Gynecology, University of Connecticut School of Medicine, Farmington, CT
| | - Per Olav Vandvik
- Medical Department, Innlandet Hospital Trust and Norwegian Knowledge Centre for the Health Services, Gjøvik, Norway
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429
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Lansberg MG, O'Donnell MJ, Khatri P, Lang ES, Nguyen-Huynh MN, Schwartz NE, Sonnenberg FA, Schulman S, Vandvik PO, Spencer FA, Alonso-Coello P, Guyatt GH, Akl EA. Antithrombotic and thrombolytic therapy for ischemic stroke: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest 2012; 141:e601S-e636S. [PMID: 22315273 PMCID: PMC3278065 DOI: 10.1378/chest.11-2302] [Citation(s) in RCA: 307] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2011] [Indexed: 12/13/2022] Open
Abstract
OBJECTIVES This article provides recommendations on the use of antithrombotic therapy in patients with stroke or transient ischemic attack (TIA). METHODS We generated treatment recommendations (Grade 1) and suggestions (Grade 2) based on high (A), moderate (B), and low (C) quality evidence. RESULTS In patients with acute ischemic stroke, we recommend IV recombinant tissue plasminogen activator (r-tPA) if treatment can be initiated within 3 h (Grade 1A) or 4.5 h (Grade 2C) of symptom onset; we suggest intraarterial r-tPA in patients ineligible for IV tPA if treatment can be initiated within 6 h (Grade 2C); we suggest against the use of mechanical thrombectomy (Grade 2C) although carefully selected patients may choose this intervention; and we recommend early aspirin therapy at a dose of 160 to 325 mg (Grade 1A). In patients with acute stroke and restricted mobility, we suggest the use of prophylactic-dose heparin or intermittent pneumatic compression devices (Grade 2B) and suggest against the use of elastic compression stockings (Grade 2B). In patients with a history of noncardioembolic ischemic stroke or TIA, we recommend long-term treatment with aspirin (75-100 mg once daily), clopidogrel (75 mg once daily), aspirin/extended release dipyridamole (25 mg/200 mg bid), or cilostazol (100 mg bid) over no antiplatelet therapy (Grade 1A), oral anticoagulants (Grade 1B), the combination of clopidogrel plus aspirin (Grade 1B), or triflusal (Grade 2B). Of the recommended antiplatelet regimens, we suggest clopidogrel or aspirin/extended-release dipyridamole over aspirin (Grade 2B) or cilostazol (Grade 2C). In patients with a history of stroke or TIA and atrial fibrillation we recommend oral anticoagulation over no antithrombotic therapy, aspirin, and combination therapy with aspirin and clopidogrel (Grade 1B). CONCLUSIONS These recommendations can help clinicians make evidence-based treatment decisions with their patients who have had strokes.
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Affiliation(s)
- Maarten G Lansberg
- Stanford Stroke Center, Department of Neurology and Neurological Sciences, Stanford University, Palo Alto, CA
| | - Martin J O'Donnell
- HRB-Clinical Research Faculty, National University of Ireland Galway, Galway, Ireland
| | - Pooja Khatri
- Department of Neurology, University of Cincinnati, Cincinnati, OH
| | | | | | - Neil E Schwartz
- Stanford Stroke Center, Department of Neurology and Neurological Sciences, Stanford University, Palo Alto, CA
| | - Frank A Sonnenberg
- Division of General Internal Medicine, UMDNJ/Robert Wood Johnson Medical School, New Brunswick, NJ
| | - Sam Schulman
- Department of Medicine, McMaster University, ON, Canada
| | - Per Olav Vandvik
- Norwegian Knowledge Centre for the Health Services, Oslo, Norway
| | | | | | - Gordon H Guyatt
- Department of Medicine, McMaster University, ON, Canada; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada
| | - Elie A Akl
- State University of New York at Buffalo, Buffalo, NY; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada.
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430
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Dimitrova NA, Dimitrov GV, Bonow RO, Carabello BA, Erwin JP, Guyton RA, O’Gara PT, Ruiz CE, Skubas NJ, Sorajja P, Sundt TM, Thomas JD. Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres. J Am Coll Cardiol 1988; 63:e57-185. [PMID: 2460319 DOI: 10.1016/j.jacc.2014.02.536] [Citation(s) in RCA: 1837] [Impact Index Per Article: 51.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Intracellular action potentials (IAPs) produced by short fibres in response to their electrical stimulation were analysed. IAPs were calculated on the basis of the Hodgkin-Huxley (1952) model by the method described by Joyner et al. (1978). Principal differences were found in processes of activation of short (semilength L less than 5 lambda) and long fibres under near-threshold stimulation. The shorter the fibre, the lower was the threshold value (Ithr). Dependence of the latency on the stimulus strength (Ist) was substantially non-linear and was affected by the fibre length. Both fibre length and stimulus strength influenced the IAP amplitude, the instantaneous propagation velocity (IPV) and the site of the first origin of the IAP (and, consequently, excitability of the short fibre membrane). With L less than or equal to 2 lambda and Ithr less than or equal to Ist less than or equal to 1.1Ithr, IPV could reach either very high values (so that all the fibre membrane fired practically simultaneously) or even negative values. The latter corresponded to the first origin of the propagated IAP, not at the site of stimulation but at the fibre termination or at a midpoint. The characters of all the above dependencies were unchanged irrespective of the manner of approaching threshold (variation of stimulus duration or its strength). Reasons for differences in processes of activation of short and long fibres are discussed in terms of electrical load and latency. Applications of the results to explain an increased jitter, velocity recovery function and velocity-diameter relationship are also discussed.
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Affiliation(s)
- N A Dimitrova
- CLBA, Centre of Biology, Bulgarian Academy of Sciences, Sofia
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