Variation in Warfarin Thromboprophylaxis After Mitral Valve Repair: Does Equipoise Exist and Is a Randomized Trial Warranted?

Oral Anticoagulation Versus Antiplatelet Treatment After Mitral Valve Repair: A Systematic Review and Meta-Analysis

Oral anticoagulation with vitamin K antagonists is currently advised for a period of 3 months after surgical mitral valve repair, regardless of the rhythm status. The evidence supporting this recommendation is weak and recent studies have challenged the safety and efficacy of this recommendation. A systematic review of literature was conducted by searching PubMed, Embase, Web of Science, Emcare, and Cochrane Library databases for original publications comparing the efficacy and safety of oral anticoagulation with vitamin K antagonists to antiplatelet treatment early after mitral valve surgery in patients with no atrial fibrillation. Study end points included thromboembolic complications, bleeding complications and survival. A total of 5 studies, including 5,093 patients, met the inclusion criteria; 2,824 patients were included in the oral anticoagulation and 2,269 in the antiplatelet treatment group. Pooled analyses demonstrated no beneficial effect of oral anticoagulation on the incidence of thromboembolic complications (risk ratio 1.14, 95% confidence interval 0.76 to 1.70, p = 0.53, I2 = 8%). Moreover, oral anticoagulation did not result in a significantly increased risk of bleeding complications (risk ratio 0.89, 95% confidence interval 0.32 to 2.44, p = 0.81, I2 = 87%). When combining the efficacy and safety end points, no difference was observed between groups (risk ratio 1.01, 95% confidence interval 0.51 to 1.97, p = 0.99 I2 = 85%). Likewise, mortality did not differ between groups (risk ratio 0.89, 95% confidence interval 0.15 to 5.23, p = 0.90 I2 = 71%). Our results confirmed the safety but failed to confirm the efficacy of oral anticoagulation in patients who underwent mitral valve surgery. A randomized controlled trial would provide the evidence needed to support treatment recommendations.

Long-term Outcomes and Anticoagulation in Mitral Valve Surgery-A Report From The Society of Thoracic Surgeons Database

BACKGROUND

Anticoagulation after bioprosthetic mitral valve (MV) replacement (BMVR) and repair (MVrep) is controversial. We explore outcomes among BMVR and MVrep patients in The Society of Thoracic Surgeons Adult Cardiac Surgery Database based on discharge anticoagulation status.

METHODS

BMVR and MVrep patients aged ≥65 years in The Society of Thoracic Surgeons Adult Cardiac Surgery Database were linked to the Centers for Medicare and Medicaid Services claims database. Long-term mortality, ischemic stroke, bleeding, and a composite of the primary end points were compared as a function of anticoagulation. Hazard ratios (HRs) were calculated using multivariable Cox regression.

RESULTS

A total of 26,199 BMVR and MVrep patients were linked to the Centers for Medicare and Medicaid Services database; of these, 44%, 4%, and 52% were discharged on warfarin, non-vitamin K-dependent anticoagulant (NOAC), and no anticoagulation (no-AC; reference), respectively. Warfarin was associated with increased bleeding in the overall study cohort (HR, 1.38; 95% CI 1.26-1.52) and in the BMVR (HR, 1.32; 95% CI, 1.13-1.55) and MVrep subcohorts (HR, 1.42; 95% CI, 1.26-1.60). Warfarin was associated with decreased mortality only among BMVR patients (HR, 0.87; 95% CI, 0.79-0.96). Stroke and the composite outcome did not differ across cohorts with warfarin. NOAC use was associated with increased mortality (HR, 1.33; 95% CI 1.11-1.59), bleeding (HR, 1.37; 95% CI, 1.07-1.74), and the composite outcome (HR, 1.26; 95% CI, 1.08-1.47).

CONCLUSIONS

Anticoagulation was used in fewer than half of mitral valve operations. In MVrep patients, warfarin was associated with increased bleeding and was not protective against stroke or mortality. In BMVR patients, warfarin was associated with a modest survival benefit, increased bleeding, and equivalent stroke risk. NOAC was associated with increased adverse outcomes.

Risk of Stroke and Major Bleeding With Vitamin K Antagonist Use After Mitral Valve Repair

BACKGROUND

Guidelines are discordant on the use of a vitamin K antagonist (VKA) after mitral valve repair (MVr) to reduce the risk of cerebral embolic events. We performed an observational study among patients who underwent a MVr, without perioperative atrial fibrillation, to determine the risk of cerebral ischemic and major bleeding events with or without VKA.

METHODS

From 2004 to 2016, we included patients who underwent MVr, using a national administrative claims database. Those with preoperative atrial fibrillation and anticoagulant use were excluded. Patients were stratified based on the presence of a VKA. Inverse probability weighting with a Cox proportional hazard model was used.

RESULTS

After MVr, 754 patients were discharged on VKA and 1462 on no-VKA. We found no difference in the cumulative incidence for embolic stroke at 180 days (VKA: 2.21% vs no-VKA: 1.50%; hazard ratio, 1.35; P = .38). However, VKA patients had a significantly increased risk for any-cause major bleeding events at 180 days (VKA: 8.58% vs no-VKA: 4.21%; hazard ratio, 2.09; P < .001). VKA patients also had increased need for a pericardiocentesis/pericardial window at 30 days after discharge (VKA: 1.13% vs no-VKA: 0.37%; hazard ratio, 3.88; P = .025).

CONCLUSIONS

Our study suggests that VKA after MVr does not reduce the risk of cerebral embolic events but is associated with an increased risk of major bleeding events.

Anticoagulation After Isolated Mitral Valve Repair: A Systematic Review and Meta-Analysis of Clinical Outcomes

Recommendations from international guidelines on optimal thromboprophylaxis after mitral repair are controversial and based on underpowered observational studies. This study aimed to evaluate the prophylactic use of warfarin after isolated mitral valve repair (MVr). A PubMed, EMBASE and Scopus search for studies in English on postoperative thromboprophylaxis for isolated MVr published to February 2020 was performed. The analysis excluded all studies with combined operations, mitral valve replacement and preoperative or postoperative atrial fibrillation. Clinical endpoints that were studied were thromboembolic events, bleeding complications and mortality. Random effects meta-analyses of the effect of postoperative warfarin use as compared with no warfarin use across all clinical endpoints was conducted. Warfarin use did not confer benefit in terms of thromboembolic prophylaxis after isolated MVr in patients without atrial fibrillation (OR, 0.97; 95% CI, 0.72-1.31). At the same time, it did not increase the risk of bleeding complications (OR, 1.10; 95% CI, 0.53-2.30) or affect overall survival during the follow-up period of the included studies (OR, 1.06; 95% CI, 0.28-4.05). To conclude, warfarin use is not necessary for patients after isolated MVr who remain in sinus rhythm. Recommendations from international guidelines may need to be revisited for this group of patients.

Anticoagulation following mitral valve repair

BACKGROUND AND AIM

Anticoagulation after mitral valve repair is controversial and guidelines are not well-established. This study evaluated the association between postoperative warfarin use and complications after mitral valve repair, including bleeding and thromboembolic incidents, readmission, and mortality.

METHODS

This retrospective study investigated 1097 patients who underwent elective mitral valve repair between April 2003 and March 2017, and was naïve to atrial fibrillation or prior cardiac surgery. This cohort had no other indication for or against anticoagulation. About 775 patients were placed on warfarin with international normalized ratio goal 2.5 and 322 patients were not anticoagulated. The association between anticoagulation and complications was assessed with univariate comparisons between groups and multiple logistic regression.

RESULTS

Postoperative warfarin use was associated with a reduced composite of bleeding and thromboembolic complications (pulmonary embolism, TIA, stroke, pericardial effusion or cardiac tamponade, gastrointestinal bleeding, and reoperation for bleeding) with an odds ratio of 0.29 (95% confidence interval, 0.13-0.64, P = .003). There was no difference in 30-day or 6-month mortality or readmission rate between groups. Long-term survival estimates were superior in the warfarin group (10-year: 92% vs 85%; log-rank P < .001).

CONCLUSIONS

Our analysis showed that postoperative warfarin use was associated with an overall reduced composite of bleeding and thromboembolic incidents and superior long-term survival. These findings suggest that anticoagulation with warfarin following mitral valve repair may be a safe and effective means for avoiding postoperative complications and that a large prospective randomized clinical trial is warranted.

Antithrombotic therapy after mitral valve repair: VKA or aspirin?

The optimal antithrombotic therapy following mitral valve repair (MVr) is still a matter of debate. Therefore, we evaluated the rate of thromboembolic and bleeding complications of two antithrombotic prevention strategies: vitamin K antagonists (VKA) versus aspirin. Consecutive patients who underwent MVr between 2004 and 2016 at three Dutch hospitals were evaluated for thromboembolic and bleeding complications during three postoperative months. The primary endpoint was the combined incidence of thromboembolic and bleeding complications to determine the net clinical benefit of VKA strategy as compared with aspirin. Secondary objectives were to evaluate both thromboembolic and bleeding rates separately and to identify predictors for both complications. A total of 469 patients were analyzed, of whom 325 patients (69%) in the VKA group and 144 patients (31%) in the aspirin group. Three months postoperatively, the cumulative incidence of the combined end point of the study was 9.2% (95%CI 6.1-12) in the VKA group and 11% (95%CI 6.0-17) in the aspirin group [adjusted hazard ratio (HR) 1.6, 95%CI 0.83-3.1]. Moreover, no significant differences were observed in thromboembolic rates (adjusted HR 0.82, 95%CI 0.16-4.2) as well as in major bleeding rates (adjusted HR 1.89, 95%CI 0.90-3.9). VKA and aspirin therapy showed a similar event rate of 10% during 3 months after MVr in patients without prior history of AF. In both treatment groups thromboembolic event rate was low and major bleeding rates were comparable. Future prospective, randomized trials are warranted to corroborate our findings.

Variation in Warfarin Use at Hospital Discharge After Isolated Bioprosthetic Mitral Valve Replacement: An Analysis of the Society of Thoracic Surgeons Adult Cardiac Surgery Database

BACKGROUND

Anticoagulation with warfarin following bioprosthetic mitral valve replacement (BMVR) is recommended by multiple practice guidelines. We assessed practice variability and patient characteristics associated with warfarin prescription following BMVR.

METHODS

We analyzed 7,637 patients in the Society of Thoracic Surgeons Database (January 1, 2008 to June 30, 2011) who were discharged following isolated primary nonemergent BMVR. Patients requiring preoperative warfarin, those with preoperative atrial fibrillation, or those with a contraindication to warfarin were excluded. The association between patient, hospital, and surgeon characteristics and warfarin prescription were evaluated.

RESULTS

Fifty-eight percent of this cohort (median age, 66 years; female sex, 58.7%) was prescribed warfarin. Patients receiving warfarin were older (67 vs 65 years; P < .0001), were less likely to have had preoperative stroke (9.3% vs 12.1%; P < .001), CHF (51.4% vs 54.1%; P < .02), or dialysis (4.9% vs 9.0%; P < 0.001), and had a longer postoperative length of stay (8.0 vs 7.0 days; P < 0.01). Warfarin was prescribed less often for patients with postoperative GI events (44.4% vs 55.6%; P < .001) but more often for patients with postoperative myocardial infarction (75.8% vs 24.2%; P < .001) or new atrial fibrillation (68% vs 32%; P < .001) and those requiring blood transfusions intraoperatively (55.7% vs 44.3%; P < .001) or postoperatively (57% vs 43%; P < .03). Similar rates of warfarin prescription were observed in patients requiring reoperation for bleeding (54.9% vs 45.1%; P = .20) and those with postoperative stroke (53.6 % vs 46.4 %; P = .30). After adjusting for patient characteristics, significant surgeon and hospital variation in warfarin prescription at hospitals was observed.

CONCLUSIONS

Although patient characteristics and postoperative events may be associated with the prescription of warfarin following BMVR, substantial surgeon and hospital variability remains. This variability largely ignores the established practice guidelines and warrants further study to define the optimal anticoagulation strategy in patients undergoing BMVR.

Effect of electrical stimulus parameters on the development and propagation of action potentials in short excitable fibres

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.