Middiastole

Middiastole, also known as mid-diastole or diastasis, is a phase of the cardiac diastolic period. It is the interval between the end of rapid passive ventricular filling and the onset of atrial systole. During middiastole the mitral valve remains open, but ventricular filling proceeds slowly as left atrial and left ventricular pressures approach equality. The extent of filling during this interval is small relative to the early diastolic filling that precedes it and is influenced by heart rate and ventricular compliance. At slower heart rates middiastole is longer, whereas tachycardia shortens or can eliminate this phase.

Clinically, middiastole is not usually singled out in examination; it is described in detail in hemodynamic studies and Doppler echocardiography as part of diastolic filling patterns. In Doppler studies the early filling phase (E) and atrial contraction phase (A) largely define diastolic function; the diastasis interval corresponds to the relatively quiet period between these flows as the E wave decelerates toward the A wave.

In diastolic dysfunction, changes in ventricular compliance or filling pressures alter the duration and role of middiastole, but the terminology is less commonly used in contemporary practice. Diastolic dysfunction is typically described using indices such as the E/A ratio, deceleration time, isovolumic relaxation time, and tissue Doppler measurements.

Etymology: the term derives from diastole with the prefix mid- indicating the middle portion. The term middiastole is largely synonymous with diastasis.