Antithrombotic Therapy in Valvular Heart Disease—Native and Prosthetic

Embolic and bleeding events after modified Bentall procedure in selected patients

AIM

As valve-sparing procedures gain increasing popularity, the long-term results of the total aortic root replacement (TARR) were evaluated using mechanical valve grafts in selected patients.

METHODS AND RESULTS

From January 1993 to December 2003, 100 patients (87 men), aged >65 years (mean 51 (SD 10.4 years), presenting with isolated aortic root dilatation with or without aortic valve insufficiency, undergoing elective root replacement using a mechanical valve graft were reviewed. The aetiology of aortic root disease was degenerative in 69 patients and related to the bicuspid aortic valve in 31 patients. In 11 patients, concomitant coronary artery bypass graft was performed. Hospital mortality was 4%. Overall survival was 93.9% (2.4%), 89.1% (3.5%) and 83.2% (5.2%) at 1, 5 and 7 years, respectively. 14 patients experienced 45 embolic events (3.21 (2.64) events/patient; range: 1-10 events). Thus, the linearised rate of embolic events was 10.3 per 100 patient-years (95% confidence interval (CI) 7.29 to 13.31). The actuarial embolism-free survival was 96.6% (1.9%), 77.1% (6%) and 74.3% (6.4%) at 1, 5 and 7 years, respectively. The linearised rate of bleeding events was 2.2 per 100 patient-years (95% CI 0.87 to 3.71). Actuarial bleeding free survival was 95.6% (2.1%), 93.2% (2.6%) and 87.7% (5.8%) at 1, 5 and 7 years. respectively. None of the patients required reoperation and no cases of structural or non-structural valve dysfunction were observed.

CONCLUSIONS

TARR using mechanical valve grafts yields excellent survival results in selected patients. However, a high rate of minor thromboembolic events was recorded. Aspirin in combination with oral anticoagulants might be of potential interest in these patients.

Antithrombotic therapy in cardiac surgery

PURPOSE

To review the perioperative management of antithrombotic therapy in cardiac surgery, including the management of cardiopulmonary bypass (CPB) and off-pump surgery.

METHODS

A review of the relevant English literature over the period 1975-2005 was undertaken, in addition to a review of international practices in antithrombotic therapy in cardiac surgery.

PRINCIPAL FINDINGS

Cardiopulmonary bypass is required in most procedures and makes anticoagulation mandatory. Anticoagulation is, usually, achieved with unfractionnated heparin (UFH). Unfractionated heparin is monitored by point-of-care (POC) testing, such as the activated clotting time or the determination of heparin concentration. The target values of both tests remain empirical, with no clearly validated thresholds. The target value needs to be adjusted according to the POC test, given significant variations between devices and activators. After CABG, the need for antiplatelet therapy is well demonstrated, in order to limit the risk of postoperative death or ischemic events, and improve venous graft patency. Immediately after valvular surgery, antithrombotic therapy should take into account the specific risk carried by each patient and by each prosthetic device. The risk of venous thromboembolism, though poorly defined, is also present in the postoperative period and may require additional attention. Given the frequent exposure to UFH, occurrence of heparin-induced thrombocytopenia is not infrequent in these patients and requires careful individual management.

CONCLUSIONS

Antithrombotic therapy is an essential component of cardiac surgery. Yet, with the exception of antiplatelet agents in CABG patients, antithrombotic therapy is often based on the clinical experience of medical teams more than on an evidence-based assessment of the literature.

Yield of transesophageal echocardiography for nonbacterial thrombotic endocarditis and other cardiac sources of embolism in cancer patients with cerebral ischemia

Cerebrovascular events occur frequently in patients who succumb to cancer, and nonbacterial thrombotic endocarditis (NBTE) is a frequent postmortem finding in these patients. Despite the excellent diagnostic accuracy of transesophageal echocardiography (TEE) for cardiac sources of cerebral embolism, however, the prevalence of NBTE and other cardioembolic sources in patients with cancer and cerebral ischemia has not been investigated using this modality. This study examined the frequency of cardioembolic findings in consecutive patients with cancer referred to our institution for TEE evaluation of cerebrovascular events. The study cohort comprised 51 patients, of whom 18% had marantic vegetations, and 47% and 55% of whom had definite and definite or probable cardiac sources of embolism, respectively. The present study documents, for the first time, a high frequency of marantic endocarditis and other cardioembolic sources in patients with cancer and cerebrovascular events selected for TEE. This finding has important implications for evaluation and management in this patient population.

Adherence to American College of Cardiology/American Heart Association guidelines for the management of anticoagulation in patients with mechanical valves undergoing elective outpatient procedures

This study sought to establish the practice patterns of a diverse group of academic physicians, in the management of periprocedural anticoagulation for patients with mechanical heart valves, to study adherence to American College of Cardiology/American Heart Association (ACC/AHA) guidelines. Physicians (n = 140) were surveyed to assess strategies for the periprocedural anticoagulation of patients with bileaflet mechanical heart valves undergoing 2 common outpatient procedures. Six patient scenarios with graded risk profiles were presented for each valve location (mitral and aortic). In >90% of high-risk patient scenarios, for which the ACC/AHA guidelines recommend periprocedural anticoagulation, anticoagulation was recommended, with minimal differences between physician specialties. However, periprocedural anticoagulation was also recommended in >70% of non-high-risk scenarios, for which the ACC/AHA guidelines recommend no periprocedural anticoagulation. Noncardiologists recommended anticoagulation more often in non-high-risk patients (p <0.01), especially for patients with aortic valve prostheses. Thus, academic physicians appropriately recommend periprocedural anticoagulation for high-risk patients with mechanical heart valves who undergo elective procedures. However, these data specifically suggest variability in practice for non-high-risk patients that are discordant with current ACC/AHA guidelines, with differences by treating specialty especially notable in this risk subset.

Heart valve replacement: which valve for which patient?

The ideal heart valve substitute would show no deterioration or thrombogenicity, offer no resistance to blood flow, and be easy to implant. However, such a valve does not exist and we must accept compromises in some of these qualities based on our patients' needs. In selection of cardiac valve prosthesis, valve-related factors such as durability, thrombogenicity, and fluid dynamics should be carefully matched to patient-related factors such as age, size, life expectancy, comorbidities, plans for pregnancy, and lifestyle. In addition, surgeon- or operation-related factors should be considered. Technical aspects of implantation, ease of reoperation, and operative mortalities may tip the risk and benefit balance in a particular direction. We review currently available heart valve prostheses and the clinical factors that are involved in selection of a heart valve substitute.

Grading strength of recommendations and quality of evidence in clinical guidelines: report from an american college of chest physicians task force

While grading the strength of recommendations and the quality of underlying evidence enhances the usefulness of clinical guidelines, the profusion of guideline grading systems undermines the value of the grading exercise. An American College of Chest Physicians (ACCP) task force formulated the criteria for a grading system to be utilized in all ACCP guidelines that included simplicity and transparency, explicitness of methodology, and consistency with current methodological approaches to the grading process. The working group examined currently available systems, and ultimately modified an approach formulated by the international GRADE group. The grading scheme classifies recommendations as strong (grade 1) or weak (grade 2), according to the balance among benefits, risks, burdens, and possibly cost, and the degree of confidence in estimates of benefits, risks, and burdens. The system classifies quality of evidence as high (grade A), moderate (grade B), or low (grade C) according to factors that include the study design, the consistency of the results, and the directness of the evidence. For all future ACCP guidelines, The College has adopted a simple, transparent approach to grading recommendations that is consistent with current developments in the field. The trend toward uniformity of approaches to grading will enhance the usefulness of practice guidelines for clinicians.

Perioperative Management of Oral Anticoagulation

Based on an individual assessment of risk factors for arterial or venous thrombosis and the risk of postoperative bleeding, this article outlines the preoperative and postoperative approach to anticoagulant management. Preceding this is a brief description of the therapies most commonly used in the perioperative period. The prevention of arterial thromboembolism is considered separately from the prevention of venous thrombosis.

The management of patients who require temporary reversal of vitamin K antagonists for surgery: a practical guide for clinicians

The management of patients who require temporary interruption of vitamin K antagonists is a common clinical problem, affecting an estimated 400 000 patients per year in Europe and North America. Managing such patients is challenging because of the lack of randomized trials assessing different perioperative anticoagulation management strategies and inconsistent recommendations from consensus groups. Recent non-randomized trials have helped to estimate the risks for arterial thromboembolism and bleeding with bridging anticoagulation involving low-molecular-weight heparin. The objectives of this review are to describe bridging anticoagulation and how it may be used with a short-acting heparin, such as unfractionated heparin or low-molecular-weight heparin, to discuss preoperative patient management, focusing on risk stratification for thromboembolic events and interruption of vitamin K antagonist therapy, and to discuss postoperative patient management, focusing on surgery-related bleeding risk and the resumption of bridging anticoagulation and vitamin K antagonist therapy.

New Anti-thrombotic Agents: Emphasis on Hemorrhagic Complications and Their Management

Our advanced knowledge of coagulation has led to the synthesis of novel procoagulant substances, such as recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark). Similarly, in-depth understanding of the interaction between anticoagulant proteins and their natural inhibitors has led to the synthesis of various novel anticoagulants. Novel anticoagulants are characterized by highly specific coagulation-inhibiting activities and, frequently, a complete lack of effective antidotes. This lack of antidotes is particularly important in the case of novel inhibitors with extended half-lives; for example, idraparinux may produce effective anticoagulation for as long as one week after subcutaneous administration. As novel anticoagulants complete licensing evaluations and are used in clinical practice, the likelihood of anticoagulant-associated hemorrhage will increase. This will require physicians to have an understanding of the mechanism of action of these anticoagulants, and to have an advanced degree of knowledge of the potential specific and nonspecific inhibitors of these anticoagulant agents. This paper will briefly review the biochemistry of coagulation, focusing on the complexes inhibited by currently available and novel anticoagulants. Specific and nonspecific prohemostatic agents will be reviewed and discussed. The ability of nonspecific procoagulant agents (particularly rFVIIa) to reverse the effects of novel anticoagulants will also be reviewed.

Search for Predictors of Nontherapeutic INR Results with Warfarin Therapy

BACKGROUND

The effectiveness and safety of warfarin require maintaining an international normalized ratio (INR) within the therapeutic range.

OBJECTIVE

To identify predictors of nontherapeutic INR results in patients receiving warfarin.

METHODS

A retrospective study was conducted using 350 ambulatory care patients from a broad geographic region, all receiving long-term warfarin therapy and followed in a tertiary-care cardiology clinic. Possible predictors of nontherapeutic INR results (gender, age, body weight, body mass index, height, race, tobacco use, alcohol use, warfarin dose, therapeutic indication, regimen intensity, INR monitoring frequency/category, interacting medications, adverse events) were assessed with logistic regression models. Subset analysis involved 146 patients concurrently monitored with capillary whole blood INR (CoaguChek).

RESULTS

As measured on venous specimens, 52% (182/350) of the patients had subtherapeutic INR results and 13% (44/350) had supratherapeutic INR results despite frequent (≤4 wk) monitoring in 75% of the patients. Due to the small sample size, supratherapeutic INR results could not be further analyzed. Of 19 predictors tested, only daily warfarin dose (p < 0.02) and regimen intensity (p < 0.03) were significant independent and additive predictors of subtherapeutic results. Patients on the high-intensity regimen (INR 2.5–3.5) and receiving warfarin ≤6 mg/day had >50% risk of having subtherapeutic INR results. Subtherapeutic CoaguChek results were independent predictors of subtherapeutic venipuncture INR results in the subset (p = 0.001).

CONCLUSIONS

In the absence of readily identifiable predictors, only higher warfarin dosing and/or more frequent monitoring (possibly with point-of-care/home monitoring devices) may minimize the time that INRs are subtherapeutic, especially in patients receiving low-dose and/or high-intensity anticoagulation therapy.

Thrombosis and Coagulation: Operative Management of the Anticoagulated Patient

The surgical management of the anticoagulated patient requires an understanding of the fundamentals of blood thrombosis, the mechanisms that enable anticoagulants to work, and the indications for anticoagulation. As percutaneous cardiac and peripheral procedures become increasingly sophisticated, we can expect to encounter more patients on aspirin and clopidogrel. Management strategies will require continued appraisal of available literature for evidence-based surgical practice. This article summarizes how coagulation takes place and explains the role of certain agents that alter coagulation, such as aspirin, clopidogrel, warfarin, heparin and low-molecular-weight heparin. The article also discusses thrombosis risks involving patients with nonvalvular atrial fibrillation, patients with mechanical heart valves and patients with a history of deep vein thrombosis.

Safety of outpatient dalteparin therapy in veterans with mechanical heart valves

STUDY OBJECTIVES

To determine the rate of bleeding and thromboembolic events within 1 month of outpatient dalteparin therapy in veterans with mechanical heart valves, to evaluate potential risk factors associated with these events, and to examine the prescribing patterns of dalteparin in this patient population.

DESIGN

Single-center retrospective electronic chart review.

SETTING

Large, academically affiliated Veterans Affairs hospital.

SUBJECTS

Thirty-eight men with mechanical heart valves who received outpatient prescriptions for dalteparin from October 1, 1998-June 30, 2003.

MEASUREMENTS AND MAIN RESULTS

Charts were reviewed for thromboembolic and bleeding events. Demographic, clinical, and drug utilization variables were assessed. The associations of adverse events with potential risk factors, indication for dalteparin therapy, and prescribing clinic were analyzed. Sixty-four dalteparin regimens were evaluated. No thromboembolic events were reported in any case within 1 month after receiving dalteparin for thromboembolic prophylaxis during warfarin interruption for periprocedural anticoagulation or for anticoagulation during an unintentional subtherapeutic international normalized ratio. Bleeding events occurred in 15 (23%) of the 64 regimens. Most bleeding events resolved spontaneously and without intervention. No potential risk factors for bleeding were identified.

CONCLUSION

Dalteparin appeared to be a safe, effective means of short-term thromboembolic prophylaxis in this population of ambulatory male veterans with mechanical heart valves. Large, randomized, controlled, prospective trials are warranted.

Recommendations for the management of patients after heart valve surgery

Approximately 50,000 valve replacement operations take place in Europe annually and almost as many valve repair procedures. Previous European guidelines on management of patients after valve surgery were last published in 1995 and were limited to recommendations about antithrombotic prophylaxis. American guidelines covering the broader topic of the investigation and treatment of patients with valve disease were published in 1998 but devoted relatively little space to post-surgical management. This document represents the consensus view of a committee drawn from three European Society of Cardiology (ESC) Working Groups (WG): the WG on Valvular Heart Disease, the WG on Thrombosis, and the WG on Rehabilitation and Exercise Physiology. In almost all areas of patient management after valve surgery, randomized trials and meta-analyses do not exist. Such randomized trials as do exist are very few in number, are narrowly focused with small numbers, have limited general applicability, and do not lend themselves to meta-analysis because of widely divergent methodologies and different patient characteristics. Recommendations are therefore almost entirely based on non-randomized studies and relevant basic science.

Drug Insight: an overview of current anticoagulation therapy after heart valve replacement

Vitamin K antagonists, such as warfarin, are the gold standard approach for the long-term anticoagulant therapy of patients with mechanical heart valves. Management decisions are, however, based predominantly on expert consensus and on data from nonrandomized, follow-up studies, which have inherent limitations in their methods. Low-intensity anticoagulation therapy provides protection against thromboembolic complications in patients with most types of modern prosthetic heart valve. The addition of low-dose aspirin is safe if international normalized ratio values below 3.5 are maintained. A combined regimen should be considered in high-risk patients and those with coexistent coronary artery or cerebrovascular disease, and in patients who have suffered a thromboembolic event despite a therapeutic international normalized ratio. Thromboprophylaxis with unfractionated or low-molecular-weight heparins is restricted to specific situations, such as when a patient is intolerant to vitamin K antagonists, when surgical procedures require discontinuation of oral anticoagulation, or when the patient is pregnant. A lack of uniformity across practice guidelines make it difficult to reach treatment decisions. Each patient's preference, expressed after counseling about the risks and benefits of each treatment strategy, and an individual assessment of the patient's risk factors, should guide treatment decisions. At present, new anticoagulant agents such as factor Xa inhibitors do not represent a treatment option for heart valve recipients.

The clinical challenge of bridging anticoagulation with low-molecular-weight heparin in patients with mechanical prosthetic heart valves: an evidence-based comparative review focusing on anticoagulation options in pregnant and nonpregnant patients

BACKGROUND

Recent labeling changes for enoxaparin, a low-molecular-weight heparin (LMWH), have prompted a reexamination of its role in patients with mechanical prosthetic heart valves (MPHVs). Healthcare providers are faced with the challenge of weighing favorable trial results with LMWHs and balancing their clinical experiences with these agents as a bridge to oral anticoagulation in patients with prosthetic heart valves. This review will provide evidence-based guidance on issues surrounding the use of LMWH that require bridging anticoagulant therapy in the setting of cardiac surgery (MPHVs), cardiovascular disease, and during temporary interruption of oral anticoagulants in patients requiring periprocedural bridging therapy.

METHODS

A Medline search was conducted of articles appearing in the medical literature published in English between 1992 and 2004. Approximately 120 clinical trials, case reports, editorials, and/or guideline statements were retrieved and reviewed by the authors as to their relevance for the subject under review, ie, bridging anticoagulation in patients with MPHVs. Approximately 80 of these publications were selected for detailed review, analysis, and discussion in a consensus format.

RESULTS

This review addresses the controversy surrounding the divergence between the new labeling recommending against the use of LMWH in patients with MPHVs as well as the ongoing clinical experience and evidence in the medical literature. The clinical challenges in the use of LMWH and unfractioned heparin (UFH) in pregnant patients with MPHVs are presented; the evidence for LMWHs in nonpregnant patients with prosthetic valves is described; and the role of LMWH for bridging immediately after mechanical valve surgery and its periprocedural and perioperative uses are discussed. Based on an expert consensus panel, clinical algorithms for the use of LMWH in pregnant and nonpregnant patients with MPHVs are also illustrated.

CONCLUSIONS

Based on the available data sets, clinical trials, reviews, and registry data, the evidence suggests that LMWH compared to UFH may be a safe and effective agent in patients with MPHVs. Future large-scale, randomized trials are warranted.

Thromboembolic and Bleeding Complications Following St. Jude Medical Valve Replacement

STUDY OBJECTIVES

Due to their inherent thrombogenicity, mechanical cardiac valves necessitate lifelong oral anticoagulation. Less intensive oral anticoagulation than recommended earlier might result in a lower incidence of bleeding complications without increasing the embolic hazard significantly.

DESIGN

Comparison of three different intensities of oral anticoagulation in a prospective, randomized multicenter design. Three months after valve replacement, patients were randomly assigned to stratum A, international normalized ratio (INR) 3.0 to 4.5; stratum B, INR 2.5 to 4.0; or stratum C, INR 2.0 to 3.5.

PATIENTS

Data from 2,735 patients following aortic valve replacement (AVR; n = 2,024), mitral valve replacement (MVR; n = 553), and combined AVR and MVR (n = 158) with the St. Jude Medical (SJM) valve (St. Jude Medical; St. Paul, MN) between July 1993 and May 1999 were analyzed, covering a total follow-up period of 6,801 patient-years. All complications were registered prospectively.

MEASUREMENTS AND RESULTS

Fifty-one thromboembolic events (TEs) were documented, resulting in a linearized incidence of 0.75 TEs per 100 patient-years, 22 of which were minor (0.32% per patient-year), 10 were moderate (0.15% per patient-year), and 19 were severe (0.28% per patient-year). Thromboembolism following AVR was significantly lower than after MVR (0.53% per patient-year vs 1.64% per patient-year). Patients reported 1,687 bleeding complications (24.8% per patient-year). The vast majority of bleeding complications (n = 1,509; 22.2% per patient-year) were classified as minor, 140 were classified as moderate (2.06% per patient-year), and 38 were classified as severe (0.56% per patient-year). The clinically relevant incidences of moderate and severe TEs and bleeding complications were not significantly different between the three prespecified INR strata.

CONCLUSIONS

The intention-to-treat analysis of the results of the German Experience With Low Intensity Anticoagulation study leads to the unexpected result that despite a sophisticated reporting system, the incidence of moderate and severe TE and bleeding complications was comparably low in all INR strata and more or less within the so-called background incidence reported for an age-related "normal" population. This study supports reexamination of the intensity of anticoagulation in patients with the SJM valve.

Perioperative Anticoagulation for Patients with Mechanical Heart Valves: A Survey of Current Practice

BACKGROUND

Patients with mechanical heart valves (MHV) require temporary interruption of warfarin when undergoing invasive procedures. Current guidelines addressing this subject are discordant because there is no high quality evidence to support any single management strategy. We tested the hypothesis that there is significant practice variation amongst clinicians caring for patients with MHV who require temporary cessation of their warfarin therapy.

METHODS

A survey describing 4 hypothetical patients with mechanical heart valves was distributed to all clinicians attending an anticoagulation specialty meeting. For each scenario, the attendee was given several choices for preoperative and postoperative anticoagulation management. Information about each respondent's profession, specialty and the frequency with which they make perioperative anticoagulation recommendations was also collected.

RESULTS

Three hundred twenty-four of 650 surveys were returned. In each of the case scenarios, a majority of respondents selected subcutaneous low molecular weight heparin (LMWH) or subcutaneous unfractionated heparin (UH) as the preferred pre- and postoperative anticoagulant. Significant variation in practice was noted: for none of the questions was a single strategy selected by greater than 80% of respondents.

CONCLUSION

Expert clinicians differ in their perioperative management strategies for patients with MHV who require interruption of warfarin. Although subcutaneous LMWH/UH was the treatment of choice in all scenarios, the lack of consensus found in our survey highlights the need for randomized controlled clinical trials of peri-procedural anticoagulant therapy. This survey of anticoagulation experts reveals that there is significant practice variation in scenarios where temporary interruption of warfarin is necessary in patients with mechanical heart valves. Despite discordant guidelines and a lack of high-quality data to support any strategy, a majority of the respondents surveyed would use low molecular weight heparin (or subcutaneous unfractionated heparin) to anticoagulate patients with mechanical heart valves during the peri-operative period.