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.