Ventricular Function

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6 Ventricular Function

Wendy L. Pabich, Alina Nicoara, Madhav Swaminathan

Overview

• The pump performance of the left (LV) and right (RV) ventricles is defined by their ability to eject (systolic performance) and relax and fill (diastolic performance).
• Evaluation of cardiac function with transesophageal echocardiography (TEE) is strongly indicated in cardiac surgery and is also seeing expanded utility outside of the operating room in both the intensive care units and emergency departments.
• When evaluating ventricular function in the perioperative period, changes in preload, pacing, respirations, and performance are dynamic and are affected significantly by the physiologic changes seen in the operating room.

Left Ventricular Systolic Function

Background

Coronary Anatomy and Left Ventricular Wall Segmentation

• The left anterior descending (LAD) artery arises from the left main coronary artery and supplies the anterior wall and anterior septum.
• The left circumflex (LCX) artery arises from the left main coronary artery and supplies the lateral wall (Figure 6-1).
• The LV is divided into 17 segments for better characterization of wall motion and thickening. There are 6 segments at the basal and midpapillary levels, 4 segments each at the apex and the apical cap (Figure 6-2).
• Normal wall motion is defined as greater than 30% excursion of the endocardial border and 30% to 50% thickening (see Video 6-1 on the Expert Consult website).
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Figure 6-1 Typical distributions of the RCA, the LAD, and the LCX coronary arteries.

Modified with permission from Lang RM, Bierig M, Devereux RB, et al; Chamber Quantification Writing Group; American Society of Echocardiography’s Guidelines and Standards Committee; European Association of Echocardiography. Recommendations for chamber quantification: A report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr. 2005;18:1440-1463.

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Figure 6-2 Display, on a circumferential polar plot, of the 17 myocardial segments and the recommended nomenclature for tomographic imaging of the heart.

Modified from American Society of Nuclear Cardiology. Imaging guidelines for nuclear cardiology procedures, part 2. J Nucl Cardiol. 1999;6:G47–G84.

Left Ventricular Anatomy: Wall Thickness and Size

• Normal values for left ventricular (LV) wall thickness are 0.6 to 1.0 cm in men and 0.6 to 0.9 cm in women. Measurements are best made of the septum and inferior walls at end-diastole (Figure 6-3).
• LV size is dependent upon patient size, but typical LV diastolic diameter is 3.9 to 5.3 cm in women and 4.2 to 5.9 cm in men.
• The LV is bullet-shaped and contracts in a twisting motion with the base and apex rotating in opposite directions.
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Figure 6-3 TG mid SAX views of the LV in a patient with normal LV thickness (A) and in a patient with LVH (B). Measurements of the inferoseptal wall of the LV are shown.

Left Ventricular Ejection Fraction

• Left ventricular ejection fraction (LVEF) is a measure of contractility and can be calculated using LV systolic and diastolic volumes.
• LVEF depends upon preload and afterload.
• Normal LVEF is equal to or greater than 55%.
• LV systolic dysfunction exists when the ejection fraction (EF) is less than 55% and can be graded as mild (45-54%), moderate (30-44%), or severe (<30%) impairment.

Pathophysiology

• Wall motion and thickening are graded as normal, hypokinetic, akinetic (negligible thickening), dyskinetic (paradoxical systolic motion), or aneurysmal (diastolic deformation).
• Wall motion abnormalities (WMAs) can be either segmental or global and are most often due to decreased perfusion in the corresponding arterial distribution.
• Ventricular pacing can cause abnormal septal motion and WMAs may be difficult to assess, particularly in the perioperative period (see Videos 6-2, 6-3, and 6-4 on the Expert Consult website).
• LV function can also be affected by the long-term effects of valvular disease, particularly lesions that result in LV volume or pressure overload, such as aortic stenosis, aortic regurgitation (AR), and mitral regurgitation (MR; Figure 6-4).
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Figure 6-4 TG mid SAX view of the LV in a patient with severe aortic insufficiency and dilatation of the LV cavity. A reasonable estimate of LV cavity dimensions can be made in this view considering the depth of view (15 cm) and the 1-cm markings on the cursor to the left of the display.

Left Ventricular Hypertrophy

• Concentric hypertrophy is ventricular wall thickening as a compensatory response to chronic LV pressure overload (e.g., hypertension and aortic stenosis).

• Elevated intracavitary pressures.
• Reduced compliance.

• Eccentric hypertrophy results from chronic volume overload (e.g., aortic insufficiency).

Cardiomyopathies

• Cardiomyopathies can affect ventricular function and can result from chronic ischemic, valvular, or intrinsic myocardial disease.
• Dilated cardiomyopathy may be ischemic or nonischemic in nature (Figure 6-5).
• Tako-Tsubo cardiomyopathy is associated with specific septal ballooning.
• Peripartum cardiomyopathy.
• Hypertrophic obstructive cardiomyopathy (HOCM)

1 Familial inheritance with risk of sudden death.
2 Characterized by dynamic obstruction.
3 Worsened by hypovolemia or administration of inotropes and chronotropes.
4 Septal hypertrophy results in left ventricular outflow tract (LVOT) obstruction and elevated LVOT gradients.
5 Patients are at risk for systolic anterior motion (SAM) of the anterior leaflet of the mitral valve (MV) and MR (Figure 6-6; and see Video 6-5 on the Expert Consult website).

• Restrictive cardiomyopathy

1 Restrictive cardiomyopathy can be difficult to distinguish from constrictive pericardial disease (see “Left Ventricular Diastolic Function”).
2 Infiltrative disorders such as amyloidosis, sarcoidosis, and carcinoid disease frequently lead to restrictive cardiomyopathy.

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Figure 6-5 ME 2C view of the LV in a patient with dilatation of the LV cavity. A reasonable estimate of LV cavity dimensions can be made in this view considering the depth of view (22 cm) and the 1-cm markings on the cursor to the right of the display.

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Figure 6-6 ME LAX view of the LV shows SAM of the anterior mitral leaflet (circle) in a patient with HOCM.

Overview of Echocardiographic Approach

Table 6-1 presents an evaluation of LV systolic function.

TABLE 6-1 EVALUATION OF LEFT VENTRICULAR SYSTOLIC FUNCTION

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Anatomic Imaging

An orderly sequence of image acquisition ensures that all views will be obtained. A suggested approach is to start with the midesophageal (ME) views, progress to the transgastric (TG) views, and conclude with three-dimensional (3D) image acquisition.

Acquisition

• ME four-chamber (ME 4C) (Figure 6-7).
• ME two-chamber (ME 2C) (Figure 6-8).
• ME long axis (ME LAX) (Figure 6-9).
• TG short axis (TG SAX) at the apex, midpapillary, and basal levels (Figure 6-10).
• TG long axis (TG LAX 2C) (Figure 6-11).
• Deep TG (TG DEEP) (Figure 6-12).
• 3D ME 4C, focusing on the left side (Figure 6-13).
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Figure 6-7 ME 4C view of the LV with the multiplane scan angle at 0 degrees.

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Figure 6-8 ME 2C view of the LV with the multiplane scan angle at approximately 90 degrees.

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Figure 6-9 ME LAX view of the LV with the multiplane scan angle at approximately 120 degrees.

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Figure 6-10 TG SAX views of the LV with the multiplane scan angle at 0 degrees at the apical (A), mid (B), and basal (C) levels.

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Figure 6-11 TG 2C view of the LV with the scan angle rotated to 90 degrees.

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Figure 6-12 Deep TG LAX view of the LV with the scan angle at 0 degrees and the probe tip anteflexed.

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Figure 6-13 3D image of the LV acquired using the ME 4C view as the reference 2D image.

Analysis

Dimensions

• Chamber dimensions

• The LV chamber can be quantified by measuring the LV length (major diameter) in ME 2C and diameter (minor diameter) in ME 2C and TG LAX (Figure 6-14).

• Wall thickness

• Septal and inferior wall thicknesses are best measured in the midpapillary TG SAX view. Normal wall thickness is less than 1 cm (see Figure 6-3).

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Figure 6-14 ME 2C view of the LV demonstrates the LV length (major) and the minor diameter measurements.

Ejection Fraction Linear Measurement

• Fractional shortening (FS) (%) = [(left ventricular end-diastolic dimension [LVEDd] − left ventricular end-systolic dimension [LVESd])/LVEDd] × 100.
• LV internal dimensions at end-diastole and end-systole are measured from endocardial border to endocardial border with M-mode at a TG SAX view just above the papillary muscles (Figure 6-15).
• Superior temporal resolution of M-mode allows for more accurate identification of endocardial borders.
• FS is not accurate in patients with marked regional differences such as WMA or aneurysms.
• Normal FS is defined as 27% to 45% in women and 25% to 43% in men.
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Figure 6-15 TG mid SAX of the LV with the M-mode cursor directed perpendicularly across the image. Measurements are shown of the LVEDd and LVESd, respectively, from one endocardial border to the other.

Ejection Fraction Area Measurement

• Fractional area of change FAC (%) = [(left ventricular area in end-diastole [LVAd] − LV area in end-systole [LVAs])/LVAd] × 100
• LV cavity area is measured via manual tracing of the endocardial border to assess area at end-diastole and end-systole in the TG SAX or TG LAX views.
• The papillary muscles should be ignored when estimating the chamber area.
• FAS provides an improved estimate over linear measurements, because information regarding septal and lateral ventricular walls is taken into account.
• Normal FAC is 59% to 65% in women and 56% to 62% in men.

Ejection Fraction Volumetric Measurements

• LVEF = [(left ventricular end-diastolic volume [LVEDV] − left ventricular end-systolic volume [LVESV])/LVEDV] × 100%
• Biplane: LV systolic and diastolic volume estimation utilizing the endocardial border.

• Volume is calculated from the manually traced endocardial border in the ME 4C and ME 2C views (Figure 6-16).
• Assumes a symmetrically shaped LV.

• Simpson’s method of disks calculates diastolic and systolic volume from a summation of stacked elliptical disks.

• Measured in the ME 4C and ME 2C views (Figure 6-17).
• Endocardial border detection may be improved using automated software, enhanced tissue harmonics, or contrast-based LV opacification.

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Figure 6-16 ME 2C view of the LV with the endocardial border traced during systole (A) and diastole (B).

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Figure 6-17 ME 2C view of the LV with internal volume measured using Simpson’s method of disks during systole (A) and diastole (B).

Ejection Fraction Three-Dimensional Measurement

• Involves construction of a ventricular model based upon endocardial border detection.
• Typically a 3D data set is best obtained from an ME 4C view (Figure 6-18).
• 3D modeling may be performed using specific 3D software at the time of acquisition or off-line when the images are reviewed (Figure 6-19).
• 3D imaging accounts for regional abnormalities, yielding more accurate stroke volumes (SVs) than two-dimensional (2D) analysis (see Videos 6-6 and 6-7 on the Expert Consult website).
• Problems associated with foreshortening in 2D can be avoided with 3D imaging.
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Figure 6-18 Image of a 3D full-volume data set of the LV acquired using the ME 4C view as the reference 2D image. The default setting ensures that the 3D image displayed reflects the reference 2D image.

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Figure 6-19 Image of a 3D full-volume analysis of the LV using 3D advanced quantification software. Detailed segmental analysis is obtained for wall motion, volume, and timing of contractility.

Key Points Pitfalls

• Identification of the LV endocardial borders can be difficult, particularly with shadowing of the ventricular walls secondary to calcification, prosthetic valve artifact, air, and other factors. This can make estimates of LVEF inaccurate.
• Linear LV measurements may be inaccurate if there are regional WMAs because they evaluate only two opposing walls in one imaging plane.
• Volumetric calculations involve geometric assumptions of the shape of the LV. This may be inaccurate with regional WMAs and aneurysms.
• Foreshortening of the LV apex is common in 2D imaging, which may result in underestimations of LV dimensions, volume, and EF.
• High-quality 2D images are necessary to generate a usable 3D data set. Suboptimal 2D imaging can lead to inaccurate 3D calculations.
• Ventricular function may be more difficult to interpret in the patient with dysrhythmias that cause variability in SV, such as atrial fibrillation.
• Acquisition of full-volume 3D data sets requires minimal translational motion, electrocautery interference, or irregular rhythms. These can be difficult to avoid in the perioperative setting.

Physiologic Data

Acquisition

• ME 4C continuous wave (CW) Doppler of MR jet for dP/dT. (Figure 6-20).
• TG DEEP or TG LAX pulsed wave (PW) Doppler of the LVOT velocity time integral (VTI) for cardiac output (CO; Figure 6-21).
• ME 4C tissue Doppler imaging (TDI) PW Doppler of lateral mitral annulus peak systolic velocity (Figure 6-22).
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Figure 6-20 Top, ME 4C view with color flow Doppler across the MV shows a regurgitant jet. Bottom, CW spectral Doppler tracing across the MV shows high-velocity systolic waveforms consistent with MR.

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Figure 6-21 PW spectral Doppler across the LVOT shows a tracing (VTI) for calculating the LV SV.

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Figure 6-22 Spectral recording of tissue velocity of the lateral mitral annulus using TDI in the ME 4C view. Diastolic velocities (E′ and A′) and timings (deceleration time and slope) measurements are shown.

Analysis

Rate of Rise in Left Ventricle Pressure (dP/dT)

• The rate of rise in LV pressure is well correlated with systolic function and can be measured using the rate of rise in velocity of the MR jet (Figure 6-23).
• The MR jet is interrogated using CW Doppler and the time interval between velocities of 1 and 3 m/s is measured (Figure 6-24).
• The pressure differential can be calculated by converting the measured velocities into pressures using the simplified Bernoulli equation.

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Figure 6-23 Pressure tracing diagram.

From Pai RG, Bansal RC, Shah PM. Doppler-derived rate of left ventricular pressure rise. Its correlation with the postoperative left ventricular function in mitral regurgitation. Circulation. 1990;82:514-520.

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Figure 6-24 Spectral recording of CW Doppler interrogation of an MR jet in the ME 4C view shows the measurement of dP/dT on the MR jet waveform from 1 to 3 m/s.

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• Normal dP/dT values are greater than 1000 mm Hg/s.

Cardiac Output

• SV (in mL or cm3) can be calculated by measuring flow through a known cross-sectional area (CSA).
• Although SV can be theoretically measured anywhere, the most common site for measurement is the relatively cylindrical LVOT, just below the aortic valve (Figure 6-25).
• CSA (in cm2) is measured utilizing LVOT diameter obtained in the ME LAX view, assuming that the CSA is a circle.

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Figure 6-25 ME aortic LAX view shows the location of measurement of the LVOT.

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• Flow through the LVOT is measured using range-specific PW Doppler, obtaining a sample velocity over time. The distance traveled by blood through the cylindrical LVOT in a single beat is measured in centimeters and known as the VTI (Figure 6-26):

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Figure 6-26 Deep TG LAX view with a PW Doppler sample volume shown located in the LVOT for measurement of the VTI at the level of the LVOT.

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• CO can be calculated by multiplying the SV by the heart rate (HR).

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• Cardiac index (CI) can be calculated by factoring in the patient’s body surface area (BSA in m2). A normal cardiac index is greater than 2 L/min/m2.

Tissue Doppler Imaging of the Mitral Annulus

• Lateral mitral annular motion is measured using PW Doppler.
• Myocardial velocities are much lower than the velocities of blood flow, and adjustments to the sector width may be necessary to achieve high frame rates.
• Measurement is less dependent of loading conditions.
• Velocities are measured in the ME 4C and ME 2C views (see Figure 6-22).
• Velocities are age- and gender-dependent, but globally normal LV systolic function is associated with velocities greater than 7.5 cm/s. Velocities less than 5.5 cm/s are seen in LV impairment.

Strain/Strain Rate and Speckle Tracking

• Strain (ε) is the change of length of an object divided by its original length.
• Positive strain indicates lengthening and negative strain indicates shortening.
• Myocardial strain occurs in three dimensions: longitudinal, circumferential, and radial.
• During systole, there is negative strain in the longitudinal and circumferential dimensions and positive strain in the radial dimension.
• Strain rate is the change of strain over time (Δε/Δt).
• TDI of the mitral annulus in the ME 4C view can be used to assess strain and strain rate. Specialized software is necessary to calculate strain and strain rate.
• 2D speckle tracking can be used in place of TDI as a means of assessing strain and is not dependent upon the angle of interrogation like tissue Doppler. Specialized software is necessary for speckle tracking and may not be available on all ultrasound machines.

Key Points Pitfalls

• CO and dP/dT are load-dependent and can vary widely as a result.
• Measurements of velocities will be underestimated if the angle of Doppler interrogation is not parallel to motion/flow, giving falsely low estimations of ventricular function.
• Inaccurate 2D measurements of LVOT diameter will grossly impair the ability to calculate an accurate CO, particularly because this measurement is squared.
• dP/dT can be performed only if there is MR.
• TDI of the mitral annulus is difficult in the presence of mitral annular calcification or prosthetic valve.

Alternate Approaches—When Transesophageal Echocardiography Is Insufficient

• Visual estimation of LVEF and WMA using 2D images can be a quick method to roughly assess ventricular function. The reliability of this method may improve with observer experience, although it is still subject to interobserver variability.
• Echocardiographic assessment of LV systolic function can always be correlated with other modalities (cardiac magnetic resonance imaging [MRI], cardiac catheterization, left ventriculogram, or pulmonary artery [PA] catheterization).

Key Points

• Changes in preload and afterload can affect LVEF.
• Regional WMA must be assessed in multiple planes.
• Avoid foreshortening of the LV when assessing systolic function.
• Ventricular pacing can cause abnormal septal motion. Consequently, WMAs may be difficult to assess in the perioperative period.
• When the endocardial borders are difficult to determine in 2D, echo contrast can be used to better identify the borders and assist with volume measurements.
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