Strut fracture in the new Bjørk-Shiley mitral valve prosthesis

In vivo accuracy of two radiographic systems in the detection of Björk-Shiley convexo-concave heart valve outlet strut single leg separations

OBJECTIVE

Modified cineradiographic systems have been used clinically to detect partially broken outlet struts in normally functioning Björk-Shiley convexo-concave heart valves. Almost all such valves were explanted, presuming that full failure would likely follow. Inasmuch as the clinical setting only rarely permits examination of normally rated valves, the accuracy of radiographic detection cannot be clinically defined. This study uses the clinical radiographic technique in sheep implanted with known-status convexo-concave valves, comparing its accuracy and that of a newly developed, geometric image magnification radiography system.

METHODS

Twenty-one sheep with mitral convexo-concave valves were studied on both systems. Five were used for extensive training. When operators were expert with both systems, images of four intact valves and 12 valves with outlet strut single leg separations, along with a seventeenth single leg separation valve used for calibration, were integrated into 112 image sets organized into a balanced incomplete block design for evaluation by eight trained, blinded reviewers.

RESULTS

Cineradiography sensitivity was 24% versus 31% for direct image magnification. The odds ratio for detection of single leg separation by direct image magnification versus cineradiography was 2.0 (95% confidence interval, 0.76 to 5.9; p = 0.13). Cineradiography specificity was 93% versus 90% for direct image magnification. Sensitivity and specificity varied markedly by reviewer, with sensitivity ranging from 8% to 55% and specificity from 51% to 100% for the combined technologies.

CONCLUSIONS

The data support the need for more intensive training for convexo-concave valve imaging and further investigation of unconventional radiographic technologies. Clinical cineradiography of convexo-concave valves may detect as little as 25% of valves having a single leg separation, underestimating the prevalence of single leg separations and thereby implying more rapid progression to full fracture than is actually the case.

Discrimination in vitro between the acoustic emissions from Bjork-Shiley convexo-concave valves with and without a broken minor strut

A statistical pattern recognition technique is used to learn and recognise the frequency spectra of the closing sounds emitted by Bjork-Shiley convexo-concave heart valves, with and without fractured minor struts, when operating in vitro. The sounds are generated with test valves operating under a variety of conditions in a model left ventricle. It is found in the learning stage that the discriminant functions generated correctly classified almost all of the cases within the learning set. When applied to cases outside the learning set, including a recording of a clinically implanted valve, the functions correctly classify the valves. These preliminary results, for a limited number of valves, lead us to believe that the discriminant analysis of heart valve sounds is a promising noninvasive method for screening patients with implanted Bjork-Shiley convexo-concave valves.

Digital acoustical analysis of normal and bimodal Björk-Shiley 60 degrees convexo-concave heart valves

Fracture of the outlet strut of the Björk-Shiley 60 degrees convexo-concave (BS60CC) valve has been attributed to a bimodal closing pattern in certain valves in which the closing disk rotates about the inlet strut, causing upward displacement of the outlet strut and its eventual fracture. This article reports the in vivo studies of the normal BS60CC valve and the in vitro studies of the normal and bimodal BS60CC valves, using a digital acoustical signal processing technique, in which the individual collisions (impact history) of the occluder disk with the components of the valve body are revealed during each closing cycle. In vitro analysis of the closing acoustical signals of normal BS60CC valves showed impact history cluster width (IHCW) means of 2.07 +/- 0.85 ms (standard error), not significantly different from those of 1.86 +/- 0.58 ms (standard error) observed in 38 clinically normal patients with BS60CC valves (p greater than 0.1). The bimodal valves showed IHCW of 6.14 +/- 0.98 ms (standard error), in vitro, which was significantly greater than those observed in the normal in vitro valve group and in the normal patient population (p less than 0.0001).

Outlet strut fracture of the Björk-Shiley 60 degrees Convexo-Concave valve: current information and recommendations for patient care

Mechanical failure of artificial heart valves can be a catastrophic event. The problem of outlet strut fracture of the Björk-Shiley 60 degrees Convexo-Concave tilting disc prosthesis has received much attention in the medical literature and generated both concern and confusion among patients and physicians. Analysis of current data from the manufacturer, as well as a review of the medical literature, suggests that the overall risk of outlet strut fracture is low and that elective explantation of a well functioning Björk-Shiley 60 degrees Convexo-Concave valve prosthesis is not warranted. Diagnostic features of outlet strut fracture can be seen with overpenetrated chest X-ray films so that diagnosis can be established promptly. Early operation to replace the fractured prosthesis is essential for patient survival.

Metallurgical analysis of failed Björk-Shiley cardiac valve prostheses

An investigation into the mechanisms of failure of current Björk-Shiley cardiac valve prostheses is reported. Two failed valves, one apparently unfailed but defective valve, and one unused valve, were examined by scanning electron microscopy and metallographic section. In the first two valves (removed 12 and 23 months after implantation) fracture was associated with the welds joining the short strut to the valve ring. The fracture surfaces in all cases were heavily faceted and showed branching cracks. Extensive wear had occurred on one fracture surface in the first case, suggesting that one leg of the short strut had failed before the other, though this had been clinically undetectable. The third valve was removed owing to failure of the suturing (24 months after implantation) but one leg of the short strut was found to be completely fractured. The other leg showed extensive cracking and porosity in the weld region. A metallographic section taken through the weld region of the fourth (unused) valve illustrated several sizable defects directly attributable to the welding process. It is suggested that the valves failed by fatigue and that these problems could be overcome if the complete valve cage were machined as a single piece.

Strut fracture and disc embolization in Björk-Shiley mitral valve prostheses: diagnosis and management

Mechanical failure of the Björk-Shiley tilting disc prosthesis is a rare but catastrophic complication of the valve. Several previously reported cases of major strut fracture with disc embolization led to improvements in the structure of the prosthesis. A case of minor strut fracture in the improved convexoconcave model of the Björk-Shiley mitral valve prosthesis is described. The literature on mechanical failures in the Björk-Shiley mitral valve prosthesis is reviewed, and recommendations for recognition and management of this problem are made.

Metallurgic and design development in response to mechanical dysfunction of Björk-Shiley heart valves

In 16 years' experience with the Björk-Shiley tilting disc valve, the failures encountered have been disc-related. A. Obstruction of the disc movement in the aortic area has been due to faulty implantation technique, i.e. a suture cut too long and caught between the disc and the valve ring. Immediate reexploration, with cutting of the suture, has restored function. Disc obstruction in the mitral area has also been attributable to technique--leaving chordae tendineae too long. The author utilizes the universal sewing ring, which prevents the suture from encroaching on the disc. B. Disc escape by strut dislocation or strut fracture is a risk which can be reduced by care during valve implantation, always using only the valve holder to orient the valve. Forceful use of forceps, or use of the disc itself as a handle, may produce a crack in the weld which can propagate a strut fracture in the course of a year. When a patient's condition suddenly deteriorates, with dyspnea and tachycardia, immediate referral to the heart surgeon can be life-saving. Stethoscopy and chest X-ray suffice to reveal disc location and/or outflow strut fracture. Other investigations waste crucial time, as only reoperation with ex-change of the valve can save the patient. To strengthen the valve and avoid a weld, a mono-outflow strut has now been used for three years at the Karolinska Hospital, with no mechanical dysfunction and with excellent hemodynamic results.

Late strut fracture in a Björk-Shiley valve prosthesis (current series)

Fracture of the short strut of the latest series of Björk-Shiley mitral valve prostheses occurred 12 months after implantation. The patient died despite emergency surgery to excise and replace the prosthesis. Björk-Shiley 29-33 mm valves with a 60 degree opening angle manufactured between February 1981 and March 1982 have a predicted strut fracture rate of 0.3% (three times greater than that of valves produced outside these dates). Unimplanted valves from this batch have now been recalled by the manufacturers.

A case of strut fracture of the new Björk-Shiley mitral valve prosthesis

We treated a 61-year-old Japanese man with a strut fracture of the new Björk-Shiley mitral valve. This fracture occurred about two months after mitral valve replacement. Emergency reoperation was performed as soon as the chest X-ray showed the fracture, despite the presence of cardiopulmonary shock. He died on the 3rd postoperative day. Similar reported cases of literature are reviewed.