The objective of the study is to obtain the clinical data from patients who received a biological prosthesis in aortic or mitral position, in order to evaluate the occurrence of peri-operative thrombocytopenia.

The aim of the study is to analyze the eventual clinical impact of the phenomenon (re-operation for bleeding, blood transfusion) and the mortality rate.

This is a multicentre retrospective, observentional clinical study. This study will enroll up to 5000 patients since 2000 to date.

Cardiac surgery is commonly associated with a transient post-operative decrease in the platelet count. Thrombocytopenia after cardiopulmonary bypass can be explained by hemodilution, exposure to artificial surfaces with platelet activation and adhesion, hypothermia, blood loss and mechanical sequestration. It usually occurs between the second and third postoperative days, resulting in a reduction of platelet counts by 40-50% from baseline values. Moreover, when a foreign body as a valve prosthesis is literally placed into the blood flow, blood cells are constantly exposed to its surface and eventually inflammatory and, perhaps, autoimmune reactions could start. The interactions biomaterial-blood induce changes in platelet shape, metabolism as well as receptor-mediated dysfunction and lysis. Then, any significant decline in the circulating platelet count raises concerns about coagulation disorders and bleeding.

Despite the advanced hemodynamic performance, recently thrombocytopenia (defined as nadir platelet count < 150.000 x 1000/uL) has been associated to new aortic biological prostheses, either rapid deployment or trans-catheter valves. Although several studies have been carried on, the drop in the platelet count after aortic valve replacement with certain tissue valves remains unexplained yet. The decrease after the valve implantation, however, is not exclusively limited to the surgical prostheses. Trans-catheter aortic valves, in fact, were found to be associated to post-procedure thrombocytopenia. Thrombocytopenia following transcatheter aortic valve implantation (TAVI) procedures is related to the increased adverse events rate such as death, stroke, acute kidney injury, bleeding and vascular complications. Furthermore, thrombocytopenia seems to occur most likely associated after balloon-expandable valves implantation.The literature, however, is confounding.

Despite several studies, little is known about the mechanism involved. Variations in biocompatibility of valve tissue as like a strong immune/inflammatory response could be some explanations. However, there is still uncertainty about the mechanism conditioning post-operative platelet drop. To address this uncertain the underlying process should be evaluated in a large multicentre trial.

The aims of the study are the following:

• to analyze the occurrence of thrombocytopenia after isolated aortic valve replacement/implantation and after isolated mitral valve replacement;
• to evaluate the clinical impact of thrombocytopenia (length of stay, bleeding, re-operation for bleeding, blood transfusion, mortality).

The study is multicentre, retrospective, observational and will enroll up to 5000 since 2000 to date.

Inclusion Criteria:

• Patients undergoing isolated aortic valve replacement/implantation or isolated mitral valve replacement with a biological prosthesis.

Exclusion Criteria:

• Pre-existent thrombocytopenia;
• Oncologic diseases;
• Pre-existent infections/inflammations;
• Use of drugs inducing thrombocytopenia (<3months);
• Combined cardiac surgery operations;
• Recent percutaneous cardiac intervention (<1month).

The population is composed by adult patients submitted to isolated aortic valve replacement, percutaneous trans-catheter aortic valve implantation, and mitral valve replacement with a bio-prosthesis.