Discussion
Prosthetic valve thrombosis (PVT) is one of the major causes of primary
valve failure with an incidence of 0.5%–8% in mechanical valves in
the aortic position (1). The clinical presentation of prosthetic aortic
valve thrombosis (PAVT) is variable, with symptoms including dyspnea,
decreased exercise capacity, palpitation, chest pain, vertigo,
cerebrovascular accident. On physical examination, stenotic or
regurgitant murmurs may be revealed. Hemodynamic stability may depend on
the number of leaflets involved with better hemodynamic conditions
seeing if a single leaflet is involved as opposed to two leaflets (2).
In patients with prosthetic valve presenting with symptoms and signs
suggestive of valve dysfunction, echocardiography examination should be
urgently performed especially if there is suspicion for PVT.
Transthoracic echocardiography (TTE) and transesophageal
echocardiography (TEE) are the standard techniques for the evaluation of
prosthetic valve function (3). Cinefluoroscopic is however, considered
the gold standard as TTE and TEE do not always allow for quantitative
evaluation of leaflet motion. Cinefluoroscopic has the advantages of
being low cost, fast and easily repeatable so it can be used for
evaluation of valve motion during thrombolytic treatment (4). It is
however not useful in assessing the etiology of prosthetic valve failure
(4). Multi detector computed tomography (MDCT) diagnostic yield is in
the identification of the etiology of prosthetic valve failure (5).
Determining the cause of valvular dysfunction is important to guide
therapy as surgery is the only option for pannus, PVT may require
non-surgical approaches.
The optimal management of PAVT is controversial in part due to the lack
of clinical trials. Treatment options include surgery, thrombolytic
therapy, and anticoagulation therapy, the latest being inferior to the
first two (6). In a systematic review and meta-analysis of observational
studies, urgent surgery was found not superior to thrombolytic therapy
at restoring valve function, but substantially reduced the occurrence of
thrombo-embolic events, major bleeding, and recurrent PVT (7). The
authors recommended that in experienced centers, urgent surgery be
preferred over thrombolytic therapy for treating left-sided PVT, pending
the results of randomized controlled trials (8).
In a multicenter observational prospective study of thrombolytic therapy
involving 158 patients with PVT, the authors recommended a low-dose and
slow/ultraslow infusion of t-PA as a viable treatment in patients with
obstructive PVT. The patients in the study received slow (6 hours)
and/or ultraslow (25 hours) infusion of low-dose tissue plasminogen
activator (t-PA) (25 mg) mostly in repeated sessions (7). This study
found that a low-dose and slow/ultraslow infusion of t-PA were
associated with low complications and mortality and high success rates
(7). Furthermore, the TROIA trial also showed that slow infusion of 25
mg t-PA without a bolus appears to be the safest thrombolytic regimen
with lower complication and mortality rates for PVT compared with higher
doses or rapid infusions (8). Recently, Özkan and his colleague also
demonstrated that Ultraslow (25hours) infusion of low-dose (25mg) t-PA
without bolus appears to be associated with quite low nonfatal
complications and mortality for PVT patients without loss of
effectiveness, when compared with higher doses or faster infusions of
t-PA (9). This Ultraslow thrombolytic infusion approach could be used
with repetition without increasing adverse events including major
bleeding and intracranial bleeding. (9,10)
In the era of cardiac multimodality imaging, evaluation and management
of prosthetic valve thrombosis should not be done only based on clinical
findings, or indirect imaging modalities. Rather, MDCT should be
incorporated into the decision-making process, as it’s diagnostic
yielding in identifying the etiology of PVT is invaluable.