FROM THE JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY
Recent findings on the incidence and pathophysiology of bioprosthetic valve thrombosis require revisiting existing guidelines against routine echocardiography in the first 5 years after bioprosthetic valve replacement and a longer course of anticoagulation therapy than the current standard of 3 months, investigators from the Mayo Clinic said in an expert opinion article in the October issue of the Journal of Thoracic and Cardiovascular Surgery ( 2016;152;975-8 ).
In the expert commentary, Alexander C. Egbe, MBBS , of the departments of cardiovascular diseases and cardiovascular surgery at Mayo Clinic in Rochester, Minn., and coauthors explored the implications of their previous research, published in the Journal of the American College of Cardiology, that reported that bioprosthetic valve thrombosis (BPVT) is “not an uncommon cause of prosthetic valve dysfunction.” They identified BPVT in 46 of 397 (11%) bioprosthetic valves explanted at Mayo Clinic, and estimated the incidence of BPVT at 1% ( J Am Coll Cardiol. 2015;66:2285-94 ), although Dr. Egbe and colleagues acknowledged the true incidence of BPVT is unknown, as is the time to occurrence. They noted that a different study design would be needed to determine that, along with the incidence of BPVT.
“The occurrence of BPVT is not restricted to surgically implanted bioprosthetic valves, but has also been observed after transcatheter aortic valve replacement (TAVR),” Dr. Egbe and colleagues said. They noted an association between BPVT and a lack of anticoagulation therapy in two earlier reports ( N Engl J Med. 2015;373:2015-24 ; J Am Coll Cardiol. 2016;67:644-55 ). In their own study, 14 of 15 patients (93%) with diagnosed BPVT responded to anticoagulation therapy and avoided reoperation.
Dr. Egbe and coauthors did somewhat define the extent of the problem of misdiagnosis of BPVT. The diagnosis was considered in only 6 of 45 patients (13%) who had transesophageal echocardiography. “A significant proportion of the patients with BPVT were misdiagnosed as having structural failure and referred for reoperation,” Dr. Egbe and coauthors said. “This attests to the low level of awareness of the existence of BPVT and the lack of well-defined diagnostic criteria.”
They proposed a diagnostic model based on the echocardiography characteristics of three findings: a 50% increase in gradient within 5 years of implantation; increased cusp thickness; and abnormal cusp mobility. “The presence of all three echocardiographic features reliably diagnosed BPVT with a sensitivity of 72% and a specificity of 90%,” they said.
Their finding that 85% of BPVT cases occurred within 5 years of implantation flies in the face of clinical guidelines that state routine annual echocardiography is not recommended in that time frame ( J Am So Echocardiogr. 2009;22;975-1014 ). But abnormal physical examination findings as a prerequisite for echocardiography may not be an effective method to diagnose BPVT. “In addition to transthoracic and transesophageal echocardiography, the use of other complementary imaging modalities, such as computed tomography, could be very effective in identifying subtle BPVT,” Dr. Egbe and colleagues said,
But preventing BPVT is more complicated. Clinical guidelines recommend anticoagulation of bioprosthetic valves for 3 months after implantation, but adhering to that guideline showed no protective effect against BPVT in their study, Dr. Egbe and coauthors said. Nor did antiplatelet therapy prove effective in preventing BPVT. However, a Danish study showed stopping anticoagulation within 6 months of surgical aortic valve replacement increased risk of thromboembolic complications and cardiovascular death ( JAMA. 2012;308:2118-25 ). And the role of prosthesis type in BPVT “remains unclear.”
Dr. Egbe and coauthors acknowledged a number of questions persist with regard to BPVT in bioprosthetic valve dysfunction, including the true incidence, best screening method, risk factors, and the duration of anticoagulation, as well as the role of novel oral anticoagulants. “Answers to these questions will come from population-based prospective studies,” Dr. Egbe and colleagues said.
Dr. Egbe and his coauthors had no relationships to disclose.
