Discussion:
The true incidence of BPVT remains uncertain; estimates range from less than 0.5% to over 6% of BPV recipients depending on the mode of diagnosis (pathology vs imaging) and length of follow up1. BPV dysfunction due to thrombosis is commonly mistaken with ‘valve degeneration’, leading to underreporting. Though rare, BPVT is a clinically important entity and can occur in all four valve locations. BPVT is distinguished from BPV degeneration based on various echocardiographic criteria. BPVT presents with increased cusp thickness, reduced cusp mobility, and less severe regurgitation, whereas BPV degeneration is associated with calcified cusps, reduced mobility, and significant regurgitation.
The mechanisms underlying BPVT are incompletely understood, but involve blood flow perturbation resulting in high wall shear stress and increased blood stasis, plasma protein adsorption leading to activation of hemostatic factors, and patient related factors including hypercoagulable states, anemia, renal insufficiency, obesity, diabetes mellitus, smoking, low cardiac output and periprocedural trauma. Suboptimal anticoagulation in patients taking oral anticoagulation (OAC) and pAF are additional risk factors for BPVT 1.
BPVT presentation may vary from incidental imaging findings without symptoms to syncope, dyspnea, heart failure, or cardiogenic shock from valve obstruction. Diagnosis is typically made by echocardiography. A model consisting of three echocardiographic predictors increased the sensitivity and specificity of diagnosing BPVT in the setting of concordant clinical features: 1) 50% increase in transvalvular gradients compared with baseline within five years of surgery, in the absence of a high cardiac output state; 2) increased cusp thickness (>2 mm), especially on the downstream aspect of the valve; and 3) abnormal cusp mobility 2. Although TTE is helpful, performing TEE is strongly recommended when clinical suspicion is high to facilitate expeditious diagnosis.
Although current 2017 ACC/AHA and ESC guidelines recommend oral anticoagulation for only the first three months following surgical BPV replacement in the absence of risk factors34, our case highlights the fact that risk of BPVT is not limited to first three months after implantation. Several studies have reported that BPVT may occur late after initial implantation and should be suspected in the appropriate clinical scenario. Among 149 patients who underwent mitral BPV implantation at a single center, a retrospective review of TEE’s identified 9 patients (6%) with BPVT and median time from implantation to diagnosis was 12 months 5. Another study identified 46 cases (11.6%) of histologically proven BPVT among 397 patients who underwent BPV explantation. The median time to explantation was 24 months, with 15% of cases occurring more than 5 years after valve placement 2.
Anticoagulation is the mainstay treatment for BPVT in hemodynamically stable patients. Early diagnosis of BPVT is crucial as most patients respond to anticoagulation and BPVT resolves completely, thus avoiding need for repeat valvular intervention. Several studies have reported successful resolution of BPVT when treated with VKA (vitamin K antagonist) 5678. A prospective evaluation of warfarin showed that anticoagulation was effective in 83% of patients with suspected BPVT, and most responded within 3 months 7. A recent study by Petrescu et al. reported long term outcomes of anticoagulation in 83 patients treated with warfarin for suspected BPVT. Echocardiographic parameters normalized in 75% of patients within three months. However, warfarin-treated patients had significant higher rates of major bleeding compared with matched controls. Additionally, BPVT recurred in 23% of warfarin responders after a median of 23 months, and all but one patient with recurrent BPVT responded to anticoagulation. Thus, longer term or even indefinite anticoagulation with warfarin could be considered after an initial BPVT episode while balancing bleeding risks 8. In retrospect, we believe that our patient’s presentation of BPV stenosis two years prior to the current presentation was likely BPVT. At that time, an extended trial of anticoagulation may have obviated the need for redo MVR.
While current 2017 ACC/AHA guidelines do not recommend routine surveillance with TTE until after 10 years of bioprosthetic valve implantation in the absence of symptoms, our case highlights that early diagnosis and management of BPVT is critical. Thus, consideration should be given to regular TTE monitoring for the development of BPVT in high risk cohorts. Determining the optimal frequency of TTE monitoring for BPV recipients requires further investigation.