Mohd Farid

Mohd Farid

Monday, December 30, 2013

Tissue Doppler Imaging : Cardiac Time Interval



Cardiac Time Interval

Cardiac time interval are regulated precisely by the mechanics and functions of the myocytes; hence, these intervals are good measure of cardiac function. TDI is well suited for determining the timing of myocardial events. The precise timing of these events is helpful in understanding the mechanism of myocardial relaxation and myocardial suction during early diastolic filling. In healthy heart, in which efficient myocardial relaxation is used effectively to suck blood from LA into the LV during early diastole, the time of onset of mitral inflow (E) coincides with what of myocardial early diastolic motion (relaxation) of the mitral annlus (Ea). However, in hearts with delayed myocardial relaxation and increased filling pressure, diastolic filling (onset of the E wave) depends more on the increased LA pressure and occurs earlier than the onset of the early diastolic motion of the mitral annulus. Therefore, the time interval between the onset of the mitral E velocity and that of the mitral annulus diastolic motion (Ea) increases, and this increased interval has been proposed as a new variables to assess LV filling pressure.

A limitation of measuring cardiac time intervals by pulsed wave Doppler echocardiography is nonstimultaneity because different cardiac cycles are usually needed to measure various intervals which in turn are used together. One solution is to have the capability of obtaining multiple pulsed wave Doppler recordings simultaneously. Another creative means to measure cardiac intervals from a single cardiac cycle is to use tisuue Doppler anatomic colour M-Mode from the anterior mitral leaflets. From this technique, isovolumic contraction time, isovolumic relaxation time, and LV ejection time can be measured reliably from a single cardiac cycle.

Mechanical dyssynchrony is measured by time intervals between peak ejection systolic velocities or peak strain of multiple myocardial segments.

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