Diastolic "locking" of the mitral valve: the importance of atrial systole and intraventricular volume.

Abstract

SUMMARY Diastolic mitral valve "locking," defined as sustained diastolic closure of the mitral valve after atrial systole, was investigated by simultaneous hemodynamic and echocardiographic recordings during a protocol of programmed pacing in six dogs with surgically induced atrioventricular block. Atrial extrasystoles were introduced at progressively increasing coupling intervals during programmed prolonged pauses in ventricular pacing. As the coupling interval of the atrial extrasystole was increased, both the mitral reopening time (MRT) and the calculated left ventricular volume (LVV) at the end of the MRT increased proportionally. These interrelations could be best expressed by a general logarithmic function of the form y = a + b In (x), where x = the coupling interval of the atrial extrasystole and y = the MRTor the LVV. Correlations between the measured data and the predicted data were excellent (r ¢ 0.95). In each dog, a specific LVV had to be attained to allow a diastolic "locking" of the mitral valve. Atrial standstill and atrial fibrillation were also induced in each dog to study the relative role of atrial systole in locking of the mitral valve. During either atrial standstill or atrial fibrillation, the mitral valve closed transiently, but did not lock, despite the accumulation of a LVV larger than the LVV necessary to lock the valve during sinus rhythm. Thus, diastolic locking of the mitral valve has several determinants, including the presence of active atrial systole and the accumulation of a sufficient intraventricular volume.THE MECHANISMS of mitral valve closure have been studied, but not completely elucidated. In 1843, Baumgarten' postulated that atrial contraction was an important element in the presystolic closure of the mitral leaflets. Others have shown that the abrupt cessation of rapid forward flow through the mitral valve at the end of atrial systole and the vortex formation or eddy currents behind the mitral leaflets may be important in the initiation of mitral valve closure.`4 Evidence for these hypotheses has been obtained in both experimental and human studies.2-19 However, Dean6 observed that in the absence of a subsequent, properly timed ventricular systole, the mitral valve, previously closed by atrial systole, tended to reopen and assume a "midstream" position. It was apparent, therefore, that the contribution of atrial systole to mitral valve motion could only initiate a closing motion of the mitral valve, but was insufficient to "lock" the valve in the closed position for the duration of diastole. The mechanisms that sustain diastolic mitral valve "locking" have never been demonstrated. In this study, we correlated echocardiographic and hemodynamic data obtained during various patterns of atrioventricular (AV) pacing in an experimental canine model. Material and MethodsThe study was performed in six healthy mongrel

Evidence of Atrial Functional Mitral Regurgitation Due to Atrial Fibrillation

“…The function of the LA likely plays a role. Well-timed atrial contraction is important for appropriate mitral valve closing (12), and the strength and timing of atrial contraction may contribute to normal mitral valve function as well (13). Significance of atrial functional MR.…”

Left ventricular synchronization and systolic function estimated by speckle tracking echocardiography pre-and post-radiofrequency ablation in patients with atrial fibrillation

“…AF may lead to MR and the mediating pathophysiologic process appears to be LA dilatation [21,22]. Left atrium dilatation presumably leads to MR by altering mitral valve geometry which remains controversial [23,24]. Well-timed atrial contraction is important for appropriate mitral valve closing [25], and the strength and timing of atrial contraction may contribute to normal mitral valve function as well [26].…”

Invited Commentary

“…Our own focus during repair is restoration of the relationships of all the elements whose interrelated structures and dynamic behavior are necessary for normal mitral valve function, starting with normal mitral diastolic locking [4][5][6].…”