Acute postoperative block of mechanical prostheses: incidence and treatment

Acute intermittent postoperative block of mechanical prostheses is a rare and life-threatening complication; its incidence and treatment are not well defined. Between January 1975 and June 1991, 2839 mechanical prostheses were implanted using the same technique: mattress suture for mitral valve replacement and simple suture for aortic valve replacement. Prosthetic block occurred in eight patients: four following mitral valve replacement and four after aortic valve replacement. The blocked prosthesis was always a tilting disc valve (five Sorin, two Björk-Shiley and one Medtronic). The event occurred over a time interval of 6-48 h (mean(s.d.) 17.3 (15.6)h). All patients having mitral valve replacement needed emergency prosthetic replacement. In aortic valve replacement, reoperation was necessary in two patients; the disc block disappeared in the others. All patients are alive with a follow-up ranging between 3 and 168 (mean 32.5) months. No structural failure was found in explanted prostheses leading to a diagnosis of extrinsic block. The overall incidence of this complication was 0.28% (eight of 2839); 0.24% (four of 1645) for mitral valve replacement and 0.33% (four of 1194) for aortic valve replacement respectively (n.s.). It was exclusively related to tilting disc valves (0.44%; eight of 1830) versus ball and bileaflets valve (0 of 1009). In mitral valve replacement reoperation on patients is mandatory; in aortic valve replacement patients the left ventricular pressure itself can overcome the prosthetic block. Attention should be paid to valve excision and suture techniques as tilting disc prostheses are more vulnerable to extrinsic block. Furthermore, their use is contraindicated in redo operations and mitral valve replacement with total or partial preservation of mitral apparatus.