Microembolic Signals in Patients with Prosthetic Valves: Relationship with the Degree of Anticoagulation

Microembolic signals (MES), detectable by transcranial Doppler, are usually observed in patients with prosthetic valves. The clinical relevance of this finding is still unsettled. We evaluated the presence and number of MES and the degree of anticoagulation in 47 patients submitted to aortic or mitral valve replacement with mechanical prostheses at least 6 months before, with normal cardiac function and no other possible cardiac or carotid sources of cerebral embolism. Each patient was submitted to transcranial Doppler of both middle cerebral arteries for 45 minutes. Detection of MES was based on the double presence of the high intensity signal at two different depths with temporal delay, using a dedicated software with visual and acoustic confirmation. MES were observed in 18 patients (38.3%). Among them, 9 (19.1%) had 1–2 MES, and 9 (19.1%) had 3 or more MES. Twenty patients had an International Normalized Ratio (INR) ? 2.0, patients with the highest number of MES having the lowest INR (ANOVA: F = 4.21, p <0.01). No differences in MES number were observed between patients with either mitral or aortic valve replacement. The finding of a relationship between the number of MES and the degree of anticoagulation raises the possibility that, in patients with prosthetic valves, MES may have a greater clinical relevance than previously thought.     

Anticoagulation for Mechanical Heart Valves in Patients with and without Atrial Fibrillation

Surgical replacement of a native valve with a biological or mechanical prosthesis is the definitive treatment for many forms of advanced valvular heart disease. Mechanical heart valves are less prone to structural deterioration compared with bioprostheses, but require chronic oral anticoagulation to prevent thromboembolic events. Thromboembolic risk varies based on patient-related risk factors, including atrial fibrillation, advanced age, low ejection fraction, and hypercoagulability. Other important correlates of high thromboembolic risk include valve design, valve position, anticoagulation variability, and time from surgery. Clinical management is further complicated when antithrombotics may need to be interrupted or altered during surgery or pregnancy. At present, vitamin K antagonists are the only approved agents for thromboprophylaxis but are limited because of a narrow therapeutic window and requirement for frequent monitoring. Novel anticoagulants, including inhibitors of factor IIa and Xa, are currently being evaluated and may emerge as alternatives to vitamin K antagonists.     

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 respondents 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.Abbreviated Abstract 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.This revised version was published online in May 2005 with a corrected cover date.     

Cavitation versus Degassing: In Vitro Study of the Microbubble Phenomenon Observed During Echocardiography in Patients with Mechanical Prosthetic Cardiac Valves

Background: With the advent of second harmonic imaging in echocardiography, microbubbles have been observed during opening and closure of mechanical prosthetic valves. The single phenomenon of cavitation, an extremely short event described in the literature, cannot explain the persistence of microbubbles during several hundred milliseconds. Therefore, in vitro we reproduced two distinct phenomena created by a local depression occurring during the closure and/or opening of prosthetic valves: Cavitation and degassing. Methods: We used a water circuit system enriched with CO₂ that passes through a Venturi tube in order to create variable pressure gradients. Three types of observations were performed: (1) the dimensions of the bubbles as a function of pressure, (2) calibration of the echocardiograph, and (3) comparison and illustrations of the difference between bubble formation by cavitation (vaporization) and degassing (liberation of CO₂). Results: According to the different pressures exerted, the dimensions of the bubbles only vary by several microns, not measurable in practice. Second, the calibration of the echocardiograph reveals that the dimensions of the bubbles measured by ultrasound are greater by a factor of 1.75. Finally, the observed cavitation is a short phenomenon (several milliseconds) and happens under a great local pressure gradient. The degassing produces microbubbles lasting up to as long as > 1 second under much lower pressure. Conclusion: This in vitro study suggests that microbubbles observed during several hundred milliseconds after the opening of prosthetic cardiac valves are the result of degassing of CO₂ in blood rather than a cavitation phenomenon as suggested in the literature.     

Management of Anticoagulant Therapy for Patients with Prosthetic Heart Valves or Atrial Fibrillation

There is a wide array of recommendations for the management of anticoagulant therapy in patients with mechanical heart valves. Especially the optimal intensity of vitamin K antagonists (VKA) is a ongoing matter of debate. On the basis of several studies, recommendations for daily clinical practice can be made. In this review, we discussed the studies and the different guidelines. Guidelines for the prevention of thromboembolic complications in patients with atrial fibrillation are more stringent. VKA with a target INR between 2.0 and 3.0 is more effective in the prevention of stroke than aspirin, especially in the presence of riskfactors for thromboembolism (age above 65, previous thromboembolism, history of hypertension and diabetes, enlarged left atrial diameter and left ventricular dysfunction). In the absence of clinical or echocardiographical riskfactors for thromboembolism, patients may be safely treated with aspirin.     

Improved Assessment of Pathological Regurgitation in Patients with Prosthetic Heart Valves by Multiplane Transesophageal Echocardiography

The aim of this study was to evaluate the diagnostic increment of individually optimized axes in the assessment of pathological prosthetic valve regurgitation. Forty-two patients with pathologically regurgitant prostheses in the aortic (n = 21), mitral (n = 15), and tricuspid (n = 6) positions were examined by multiplane transesophageal echocardiography. The investigation was performed utilizing the transverse axis first, the longitudinal axis second, and the intermediate axes afterwards. The presence of regurgitation, the differentiation between trans- and perivalvular origin, and the localization of perivalvular leakages at the sewing ring were evaluated. Findings in the biplane and intermediate axes were compared to surgery or autopsy in all patients. There was slightly higher detection rate for aortic prosthetic regurgitation using the intermediate axes than the biplane axes. The intermediate axes revealed significantly fewer differences to the morphological control than the biplane axes with regard to the differentiation of peri- and transprosthetic aortic regurgitation and to the localization of a periprosthetic aortic regurgitant origin. The intermediate axes provided significantly better agreement to surgery/autopsy than the biplane axes regarding the localization of the origin of mitral periprosthetic regurgitation. Morphological visualization of the perivalvular gap adds important information on the precise localization of the regurgitant origin. The pathological gap was visualized significantly more often using the intermediate than the biplane axes in all types of prostheses. The data in this study therefore suggest that multiplane transesophageal echocardiography is superior to biplane transesophageal echocardiography in the assessment of pathologic prosthetic regurgitation.     

Role of Novel Anticoagulants for Patients with Mechanical Heart Valves

The introduction of the target-specific oral anticoagulants (TSOACs) has led to a major shift in the management of patients at risk for thrombosis. The landscape continues to evolve as the evidence regarding their efficacy and safety in various clinical situations emerges. Antithrombotic therapy for thromboprophylaxis in patients with mechanical heart valves is challenging. To date, the RE-ALIGN trial comparing dabigatran etexilate to warfarin is the only randomized controlled study in this patient population. The higher risk of thromboembolic and bleeding events in the group of patients who received dabigatran compared with warfarin reinforced current guidelines recommending against the use of TSOACs in patients with mechanical heart valves. However, additional studies are needed to find suitable alternatives to vitamin K antagonists in this unique patient population.     

Echocardiographic Assessment of Prosthetic Heart Valves

Valvular heart disease is a global health problem. It is estimated that more than 280,000 prosthetic heart valves are implanted worldwide each year. As the world's population is aging, the incidence of prosthetic heart valve implantation and the prevalence of prosthetic heart valves continue to increase. Assessing heart valve prosthesis function remains challenging, as prosthesis malfunction is unpredictable but not uncommon.     

心脏瓣膜置换术后抗凝观察

目的分析心脏瓣膜置换术后华法令抗凝治疗的影响因素、给药方法和国际标准比值（INR）的关系。方法我院2008年6月—2011年6月323例行心脏机械瓣膜置换术后患者进行随访研究。术后使用华法令抗凝,出院后定期复查随访。记录年龄、性别、华法令剂量和INR值等,观察出血、栓塞、死亡等不良事件发生情况。结果在患者术后抗凝达到稳定状态后,总体INR值为1.5～2.5,术后413例无不良事件的发生,10例出现抗凝相关并发症,其中血栓栓塞3例,抗凝有关出血7例。出院随访因抗凝出现不良事件的发生率与国外文献报道相近。结论心脏机械瓣膜置换术后根据INR给予个体化剂量华法令,控制INR值在1.5～2.5可以达到相对安全的抗凝效果。