In the previous chapter, methods of estimation of cardiac output and organ blood flow indices were discussed. These are essential components of the echocardiographic assessment of adequacy of cardiovascular function. The current chapter focuses upon the noninvasive assessment of systolic and diastolic cardiac function.
Assessment of systolic function is a basic component of functional echocardiography. Shortening fraction (SF), also known as fractional shortening, is the most commonly used index of left ventricular systolic function in children. This index reflects the degree of myocardial fiber shortening during systole. As the loading condition affects the initial myocardial fiber length (preload effect) and the degree of shortening (afterload effect), this index of cardiac systolic function is considered to be load-dependent. Therefore, changes in loading condition impact the myocardial contractility as assessed by SF without necessarily a change in the inherent myocardial function. In addition, the most commonly used method to measure SF has significant limitations (see below). Nevertheless, SF provides the clinician with a simple and quick way to assess myocardial systolic function. Assessment of SF is generally performed with M-mode echocardiography (see also Chapter 5).
The normal value of SF for all gestational and postnatal ages is considered to be in range between 27% and 42%. In hemodynamically stable preterm infants ≤30 weeks’ gestation, average SF was 34%±5% (range 23–48%) in the first 3 postnatal days and 38%±6% (range 25–51%) from 4–14 days after birth.1
The patient should be placed in a supine position.
For better resolution, a high-frequency (10–12 MHz) probe is preferable.
Optimal visualization of the left ventricle (LV) can be achieved using standard parasternal short- or long-axis views. In neonates it is preferable to use a parasternal short-axis view.
Using the parasternal short-axis view, obtain a cross section of the LV at the level of the papillary muscles or the tip of mitral valve leaflet (Figure 8-1). The latter is preferred in neonates. Care should be taken to obtain a two-dimensional (2D) image of the cross section of the LV in such a way as to have mitral valve closure as a horizontal line. Next, place the M-mode line to be perpendicular to the septum, the above-mentioned horizontal line, and the posterior wall, with about equal distance between the two papillary muscles. Initiating the M-mode setting on the ultrasound machine will yield the motion of the various structures along the M-mode line.
A schematic drawing of the short-axis view of the heart at the level of mitral valve tip. The dotted line on the drawing ...