• During ventricular systole, the interventricular septum (IVS) and the left ventricular posterior wall (LVPW) move towards each other.
• The amplitude of this motion is reduced in the presence of LV systolic dysfunction (Fig. 6.1).
• LV internal dimension in systole (LVESD) and end-diastole (LVEDD) are measured on the M-mode tracing in the parasternal long-axis view (PLAX), at the level of mitral valve (MV) leaflet tips.
• Measurements are taken from the endocardial lining of the septum (IVS) to that of the posterior wall (LVPW).
• LV dimensions are increased in the presence of left ventricular systolic dysfunction.
• The percentage change in LV internal dimension between systole and diastole is called fractional shortening (FS).
LVEDD – LVESD
FS = ____________________ × 100%
LVEDD
The normal range of fractional shortening is 30–45%.
• Reduced fractional shortening is an indicator of systolic dysfunction of the left ventricle.
• However, in the presence of regional wall motion abnormality, fractional shortening does not reliably reflect the overall LV systolic performance.
• The normal volume of the left ventricle during end-diastole (LVEDV) is 85±15 ml.
• A volume greater than 100 ml is indicative of LV systolic dysfunction due to myocardial disease (cardiomyopathy or myocardial infarction) or because of volume overload (mitral or aortic regurgitation).
Fig. 6.1: M-mode scan of the left ventricle showing:
A. Reduced excursion of IVS and LVPW B. Increased dimension of the LV cavity
• The LV volume is derived from the ‘Cubed equation’
V = D3 V: volume; D: diameter
• This equation is based on the assumption that the LV cavity is ellipsoid in shape and the major axis is twice the minor axis (Fig. 6.2). But this is not always true.
• The LV volume derived from the Teicholz equation gives a more realistic and accurate measurement
V = ____________ 7 × D3 2.4 + D
• Measurement of LV dimensions can be unreliable if septal motion is abnormal due to old infarction, left bundle branch block or RV volume overload.
• The percentage change in LV volume between systole and diastole is called ejection fraction (EF):
LVEDV – LVESV
EF = ___________________ × 100%
LVEDV
The normal range of ejection fraction is 50 to 75%.
Fig. 6.2: Simulation of left ventricle cavity as an ellipsoid.
Major axis (L) is twice the minor axis (D).
LV volume = D3 by the cubed equation.
• Reduced ejection fraction is an indicator of LV systolic dysfunction. However, the ejection fraction also depends upon ventricular loading (preload and afterload).
• The normal diastolic thickness of the left ventricular walls, that is interventricular septum (IVS) and left ventricular posterior wall (LVPW), is 6 to 12 mm.
• Walls thinner than 6 mm indicate to stretching due to cardiomyopathy or scarring due to myocardial infarction.
• Walls thicker than 12 mm indicate the presence of left ventricular hypertrophy.
• Normally, the walls should thicken in systole. Reduced systolic thickening of walls indicates presence of LV systolic dysfunction, either global (cardiomyopathy) or regional (myocardial infarction).
2-D Echo A4CH View
• 2-D echo can also be used to estimate LV volume in end-diastole (LVEDV) and end-systole (LVESV).
• This is done by tracing the LV endocardial borders of a systolic and a diastolic LV frame while the software of the echo machine calculates the LV volumes.
• From these volumes, the ejection fraction (EF) is calculated:
LVEDV – LVESV
EF = ____________________ × 100%
LVEDV
• The above method of calculating LV volume relies on manual tracing of the ventricular endocardial outline. Alternatively, LV volume can be calculated totally by the computer using the Simpson’s method.
• By this method, the left ventricle is divided into 20 sections of equal thickness. The computer takes multiple short-axis slices at different levels (Fig. 6.3). The volume of each slice is the area multiplied by its thickness. The sum of volumes of all slices is the volume of the left ventricle.
Area of each slice = π (D/2)2 D is diameter Thickness of slice = 1/20 × LV
LV is length Volume of each slice = Area × Thickness Left ventricle volume = Sum of all volumes
• The cardiac output can also be obtained using LV volumes by the following simple calculations:
Stroke volume (SV) = LVEDV – LVESV Cardiac output (CO) = SV × Heart rate (HR)
Fig. 6.3: Estimation of the left ventricular volume by Simpson’s method; D is LV diameter
Doppler Echo
• The cardiac output as an indicator of LV systolic function can be calculated from the peak aortic flow velocity (Vmax).
This is obtained by Doppler display of aortic outflow from the apical 5 chamber (A5CH) view (Fig. 6.4).
• Continuous wave (CW) Doppler is used to measure higher velocities and pulse wave (PW) Doppler for lower velocities.
PW Doppler provides a better spectral tracing.
• Before going into calculations of cardiac output, one must know the normal indices of ventricular ejection:
Stroke volume = 32–48 ml/beat/m2 Cardiac output = 2.8–4.2 L/min/m2 Fig. 6.4: Calculation of the cardiac output from
peak aortic flow velocity (Vmax)
FVI = flow velocity integral AT = acceleration time PEP = pre-ejection period DT = deceleration time LVET = LV ejection time
Doppler Calculations Cardiac output = SV × HR
SV : stroke volume HR : heart rate Stroke volume = CSA × FVI
CSA : cross-sectional area FVI : flow velocity integral
2 222 D 2 2
CSA r (D / 2) 0.785D
7 4
D : aortic annulus diameter (Fig. 6.5)
• The FVI is calculated by the computer software of most echo machines as the area under curve of aortic outflow velocity spectral display.
CO = 0.785 D2 × FVI × HR
• Using similar calculations, the stroke volume of the right side of heart can be obtained using the peak pulmonary flow velocity (Vmax) and diameter of the pulmonary valve.
Fig. 6.5: Measurement of aortic annulus diameter (D) to calculate aortic valve area
• Thereafter, the ratio of pulmonary flow (Qp) to systemic flow (Qs) which is the Qp: Qs ratio, can be calculated to quantify a cardiac shunt (see Congenital Diseases).