Surgical treatment of oligosymptomatic mitral valve incompetence?

Despite improvements of the surgical technique in NYHA (III)-(IV) mitral valve incompetence (MVI) postoperative long-term results remain poor. As long-term results reflect primarily the ventricular function rather than the quality of the surgical technique the contractile performance of isolated papillary muscles obtained from patients undergoing mitral valve replacement for MVI (n = 25) was analysed in detail.

Muscle preparations (0.4 x 5.0 mm) obtained from left ventricular papillary muscles (NYHA (I), n = 4; NYHA (II), n = 7; NYHA (III), n = 8; NYHA (IV), n = 6) were loaded for intracellular calcium measurements with FURA-2, stretched to optimal length (Lmax) and electrically stimulated with frequencies ranging from 30 to 180 beats/min (b.p.m.) (10% above threshold, 37 degrees C, Krebs-Henseleit solution). Isometric force development and diastolic intracellular calcium (measured by the 'ratio method'; excitation light: wavelengths alternating 340 and 380 nm, frequency: 250 Hz) were simultaneously recorded as a function of the stimulation frequency.

At 60 b.p.m. force development was significantly higher in NYHA (I) myocardium (21.3 +/- 2.8 mN/mm2) than in NYHA (III) myocardium (12.8 +/- 2.2 mN/mm2), (P < 0.0001). In NYHA (I) myocardium force rose with increasing stimulation frequency ('positive staircase'). In contrast the stimulation frequency associated with maximum force was shifted towards lower frequencies in NYHA (II)-(IV) myocardium ('negative staircase'). As compared with NYHA (I) myocardium diastolic intracellular calcium was significantly elevated at 150 b.p.m. in NYHA (II)-(IV) myocardium (P < 0.01).

The data show, that severe impairment of contractile function ('negative staircase phenomenon', reduced force, elevated diastolic calcium) is present in MVI classified as NYHA (III)-(IV) that may explain the poor long-term results. Most interestingly the data argue for a significant impairment of myocardial function even in NYHA (II) MVI. The results suggest an early surgical treatment of mitral valve incompetence as long as the myocardial function is normal (NYHA (I)) as (1) a reduced perioperative risk, (2) improved long-term results, and (3) a higher probability for mitral valve repair (instead of replacement) may be expected in these early stages of mitral valve disease.