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TORRENTS A N D BRIDGES

Stress Fracture of T u b b ' s D i la tor

Solomon Victor

Safety and efficacy of closed mitral valvotomy using a Tubb's dilator increases with experience. However, rarely when excessive force is necessary to open a densely fused valve, one or more struts of the instru- ment may bend preventing the blades from closing completely. Four such instances are reported. It is recommended that the closed procedure be aban- doned and open mitral valvotomy performed when the valve is too densely fused to be split using the usual force.

Closed mitral commissu ro tomy using the Tubb's dilator continues to be popular and is the commonest cardiac operation performed in India. It is a safe, effective, gratifying, economical and simple procedure.

Occasionally, one needs to use greater force than usual to split the fused commissures which may not yield due to dense fibrosis. In four such cases out of about 5000 procedures performed in 27 years, the use of excessive force resulted in bending or fracture of one or two of the struts supporting the blades at the working end of the Tubb's dilator (Fig la). When this happens, the proximal, angled blade related to the bent strut closes early. The straight blade on the fractured side and the blades on the opposite intact side remain open (Fig lb). In all the cases, the instrument could be withdrawn only after achieving partial closure by external pressure and somelaceration of the ventriculotomy. Pledgets were kept ready in situ, to close the ventriculotomy. There is no apparent relationship with the wear and tear

From The Heart Institute, Madras, India.

Address for correspondence: Dr. Solomon Victor, 15, East Street, Kilpauk Garden Colony, Madras 600 010, INDIA.

a b Fig 1.(a) The bent strut is seen and (b) the proximal, angled balde on the side of the bent strut has closed. The distal straight blade and the blades on the other side remain open.

on the instrument, as at least on two occasions, the fractured dilators were brand new.

Comments

Excessive use of force during closed mitral com- missurotomy may cause fracture of the strut or struts in the Tubb's dilators leading to incomplete closure of the blades. The mitral valve cusps, subvalvular apparatus or ventricular wall may be injured while withdrawing the incompletely closed instrument. The objective of obtaining an adequate commissural split may also remain unachieved on account of dense fibrosis. It is, therefore, recommended that when the fused cusps do not split fully with ordi- nary force, ideally the closed procedure should be abandoned and open valvotomy undertaken. 11~is could be done by cannulating the main pulmonary

52

vICTOR Fracture of Tubb's dilator

artery and descending or ascending aorta. After such cannulation, we have used electrical fibrillation and left atriotomy. On weaning off btpass and defibril- lation, the dynamic function of the mitral valve can be assessed easily as after closed mitral valvotomy.

The Bureau of Indian Standards has established standard dimensions for the Tubb's dilator. This should be modified to specify the strength of the struts, allowing for the occasional need to use extra force to obtain adequate commissurotomy.

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