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.