Tissue Doppler Imaging High Output Heart Failure

BSA, body suface area; PLAX, parasternal long-axis ; LVIDd, left ventricular internal diameter at end diastole; LVIDs, left ventricular internal diameter at end systole; PSAX, parasternal short-axis; A4C, apical four chamber.

M-mode or 2D, essentially subtract ventricular cavity volume from the total ventricular volume to obtain the "shell" or myocardial volume (Fig. 15). This value

Echocardiography
Fig. 13. Geometric models to estimate left ventricle (LV) volumes by two-dimensional echocardiography use short-axis area multiplied by long-axis length. Comparison of volumes at end-systole and end-diastole can be a measure of LV systolic function.

multiplied by the density of the myocardium gives the LV mass.

Left ventricular mass (MassLV) = 0.8 x [1.04 (IVS + PWT + LVIDd)3 - LVIDd3] + 0.6 g Accurate measures are crucial, as errors will be cubed.

3D Echocardiography

3D echocardiography will likely replace current echocardiographic methods of calculating ventricular mass and volumes in the near future (Figs. 16A-D; please see companion DVD for corresponding video). The limitations and assumptions of 2D and M-mode echocardiography are overcome by both real-time and off-line reconstructive 3D echocardiography. Modern 3D equipment uses planar array transducer technology to obtain a pyramidal "volume" of data. This makes 3D echocardiography less dependent on the sonographer imaging the correct plane.

assessment of myocardial viability

Dobutamine echocardiography can provide additional information on the LV contractile reserve. This has value in predicting recovery of function following coronary revascularization procedures. Assessment of myocardial viability is also important in heart failure patients.

The important clinical question that frequently confronts the cardiology team is whether coronary revascu-larization procedures will benefit a particular patient with LV dysfunction. To answer this, we need to help predict the probability of improvement following the proposed revascularization procedure. Nuclear techniques assess myocardial perfusion, but not contractile reserve. A biphasic response on dobutamine stress echocardiography, however, can be a good predictor of improvement in patients scheduled to undergo coronary revascularization procedures (Fig. 17; see companion DVD for corresponding video; see also Chapter 8).

Echo Simpson Biplane

Fig. 14. (A,B) Modified Simpson's method. The American Society of Echocardiography recommends the modified Simpson's method (biplane method of discs) for calculating left ventricular volumes and ejection fraction. Manual tracing of ventricular endocardium at end-systole and end-diastole from two orthogonal planes, and summation of the volumes of discs derived, serve as the basis of this calculation.

Fig. 14. (A,B) Modified Simpson's method. The American Society of Echocardiography recommends the modified Simpson's method (biplane method of discs) for calculating left ventricular volumes and ejection fraction. Manual tracing of ventricular endocardium at end-systole and end-diastole from two orthogonal planes, and summation of the volumes of discs derived, serve as the basis of this calculation.

doppler assessment of ventricular systolic function

Doppler assessment provides complementary and alternative indices of ventricular systolic function (Table 7). Traditional Doppler indices are used to calculate SV and CO. SV is calculated from the equation: volume = area x velocity time integral; where area is the cross-sectional area of ventricular outflow or inflow tract of interest; velocity time integral corresponds to the velocity time integral across the same. CO is then calculated according to the equation:

Cardiac index calculated by dividing CO by body surface area.

Doppler indices have the advantage in being independent of geometric assumptions used in M-mode and 2D-based calculation of volumes. The most accurate and reproducible Doppler method for calculating SVs uses the left LV outflow tract (LVOT) diameter and the velocity

Area Mid-papillary level PSAX

endocardium

Length

Left Ventricular Mass

Area x Length Method

Left Ventricular Mass

Area x Length Method

cylinder hemi-ellipsoid

Volume = 5/g Area x Length cylinder hemi-ellipsoid

LV Mass (AL) 1.05{[5/6Ai (a+ d+t)] - [5/6A2<a+d)]}

Fig. 15. Left ventricular mass. The area-length method for using a cylinder hemi-ellipsoid of the left ventricle (LV) is the recommended equation for measuring LV mass. It is a simple formula with easily obtainable measurements. End-diastolic measurements using parasternal short-axis (PSAX) and apical four-chamber at the mid- or high-papillary muscle levels are made and inserted into the equation as shown. The sum of a + d is the end-diastolic LV cavity length; b = minor axis radius; t = wall thickness; Aj= total planimetered PSAX area at the mid- or high-papillary muscle level; A2 = LV cavity planimetered PSAX area.

time integral across the LVOT by pulsed Doppler examination (Fig.18A; see also "Continuity Equation" in Chapter 11) LVOT geometry most closely approximates a circle compared with the ellipsoid mitral annulus (Fig. 18B), and is logistically easier to measure than the pulmonary artery diameter (Figs. 18C). Tricuspid annular geometry is complex, and is almost never used to calculate SVs.

Continuous-wave Doppler of the mitral regurgitant jet can reveal clues about LV performance by assessing changes in LV pressure over time (dP/dT). The pressure is measured at two points (at ~1 m/s and 3 m/s after the onset of the mitral regurgitation) and the Bernoulli equation (dP = 4v2) applied. Normal dP/dT is greater than 1200 mmHg/s.

other doppler measures of ventricular systolic function

Tissue Doppler imaging is a useful tool in ventricular diastolic function assessment, but also shows promise in assessing systolic function (Fig. 19). Doppler interrogation of the mitral annulus can provide a measurable index of annular movement and velocity, and the information derived can be extrapolated to assess ventricular function. A good relationship exists between tissue Doppler assessment of myocardial contraction velocity and LVEF.

Tissue velocity imaging employs color codes to reflect ventricular longitudinal shortening using the scheme: red—for movement toward the transducer, and blue—movement away from transducer (Fig. 20; please see companion DVD for corresponding video). It is based on the rationale that most of the cardiac muscle fibers are oriented longitudinally. A direct relationship exists between pulsed-wave tissue velocity imaging and ventricular systolic function.

EF is not a load-independent measure of contractility. Load is important when considering contractility and this is not normally accounted for in traditional measures. Newer less load-dependent methods, e.g., Doppler strain imaging, are being investigated. Strain—a dimensionless quantity, measures deformation produced by the application of stress. It represents the percentage change in myocardial fiber length from its original or unstressed dimension (Fig. 21A-C). Comparisons of Doppler velocities at interrogation points along the myocardium are used to measure LV strain.

Strain Echocardiography
Fig. 16. (Continued)
Strain Echocardiography

Fig. 16. Left ventricle (LV) quantification by three-dimensional (3D) echo. (A) Apical full-volume cropped 3D image. (B) Semiautomatic border detection with multiplanar reconstruction (MPR) in 3D echocardiography. (C) A 17-segment 3D volumetric data for left ventricular segmental analysis. 3D echocardiography overcomes several limitations of 2D echocardiography in quantification of systolic function including: endocardial border definition, foreshortening, off-axis views, and translational motion. It is slated to supercede 2D echocardiography in the assessment of LV function, mass, and volumetric assessments. 3D echo is especially valuable in right ventricular assessment and quantification, with utility comparable to that of cardiac magnetic resonance imaging. (D) LV systolic frame with diastolic reference mesh. (E) Systolic frame in patient with cardiomyopathy and asynchrony. (Please see companion DVD for corresponding video.)

Fig. 16. Left ventricle (LV) quantification by three-dimensional (3D) echo. (A) Apical full-volume cropped 3D image. (B) Semiautomatic border detection with multiplanar reconstruction (MPR) in 3D echocardiography. (C) A 17-segment 3D volumetric data for left ventricular segmental analysis. 3D echocardiography overcomes several limitations of 2D echocardiography in quantification of systolic function including: endocardial border definition, foreshortening, off-axis views, and translational motion. It is slated to supercede 2D echocardiography in the assessment of LV function, mass, and volumetric assessments. 3D echo is especially valuable in right ventricular assessment and quantification, with utility comparable to that of cardiac magnetic resonance imaging. (D) LV systolic frame with diastolic reference mesh. (E) Systolic frame in patient with cardiomyopathy and asynchrony. (Please see companion DVD for corresponding video.)

Stress Echocardiogram

Fig. 17. Dobutamine stress echocardiogram: biphasic response. A biphasic response on dobutamine stress echocardiography may be a candidate for coronary artery revascularization procedures. This patient shows augmentation of a previously poorly functioning region on low dose dobutamine (10 |g), but demonstrates ischemia (decreased contractility) at higher doses. At baseline, this region of the heart (arrows) are hypokinetic—contractility improves at the 5 |ig infusion rate, is maintained at 10 |ig, worsens at 40 |ig. This represents an ischemic region that augmented at low doses that can benefit from revascularization. (Please see companion DVD for corresponding video.)

Fig. 17. Dobutamine stress echocardiogram: biphasic response. A biphasic response on dobutamine stress echocardiography may be a candidate for coronary artery revascularization procedures. This patient shows augmentation of a previously poorly functioning region on low dose dobutamine (10 |g), but demonstrates ischemia (decreased contractility) at higher doses. At baseline, this region of the heart (arrows) are hypokinetic—contractility improves at the 5 |ig infusion rate, is maintained at 10 |ig, worsens at 40 |ig. This represents an ischemic region that augmented at low doses that can benefit from revascularization. (Please see companion DVD for corresponding video.)

Table 7

Doppler Indices of Left Ventricular Systolic Function

Traditional Doppler indices

Newer Doppler indices

SV = VTI x CSA = VTI x nr2 = VTI x nD2/4 = 0.785 D2 x VTI

Measurement sites: LVOT

Left ventricular inflow (mitral valve) Pulmonary artery CO = SV x HR CI = CO/body surface area CW Doppler in mitral regurgitation: dP/dt = 32/time (mmHg/s)

Velocity/acceleration times, e.g., aortic flow/velocity acceleration, aortic ejection time

TDI/DTI

TVI for left ventricular dyssynchrony

Doppler strain imaging: strain and strain rate

Left ventricular torsion by TDI

SV, stroke volume; VTI, velocity time integral; CSA, cross-sectional area; D, diameter; TDI, tissue Doppler imaging; DTI, Doppler tissue imaging; LVOT, left ventricular outflow; CO, cardiac output; HR, heart rate; CI, cardiac index; TVI, tissue velocity imaging; CW, continuous wave; dP/dT, rate of ventricular pressure rise.

Myocardial Performance Index Finding
Fig. 18. (A) Stroke volume by Doppler (LVOT). (B) Stroke volume by Doppler (mitral inflow). (C) Stroke volume by Doppler (pulmonary artery).

myocardial performance index (tei index)

The myocardial performance index (MPI) is a Doppler-derived integrated measure of ventricular systolic and diastolic function.

It has been the subject of much interest since its inception in 1995, and has been well received for its ability to assess both LV and RV function in a variety of patients—heart failure, cardiomyopathy, coronary heart disease, heart transplantation, and in prospective clinical trials. It is reproducible, easy to measure and can predict morbidity and mortality in patients with cardiomyopathy and heart failure.

When applied to the LV, it is the sum of the isovolumic contraction and relaxation times (ICT + IRT) divided by

Doppler Tissue Imaging TheHow Measure Tie Index Tissue Doppler

Fig. 19. Tissue Doppler imaging (TDI). Tissue Doppler assesses myocardial velocities during the cardiac cycle. Doppler shift measured at the lateral (A) and septal annulus (B) are shown. Systolic shifts (Sm) are upward (positive). Shifts away from the transducer (Em and Am), reflecting early and late diastolic velocities, are downward (negative).

Color Tissue Doppler Imaging

Fig. 20. Tissue velocity imaging (TVI). Differential tissue velocities by color Doppler can detect differential contractility of left ventricle (LV) segments—and color coded as shown. This reflects LV dyssynchrony and impaired LV systolic function. (Please see companion DVD for corresponding video.)

Fig. 20. Tissue velocity imaging (TVI). Differential tissue velocities by color Doppler can detect differential contractility of left ventricle (LV) segments—and color coded as shown. This reflects LV dyssynchrony and impaired LV systolic function. (Please see companion DVD for corresponding video.)

the ejection time. These measurements are obtained by Doppler assessment of both LV inflow and outflow and using the formula (Fig. 22):

Left Ventricular MPI =

The MPI has its limitations. It is not a load-independent measure, and one of its components, the IRT, is less discriminatory in patients with worsening diastolic dysfunction. Therefore, despite its utility, it should complement (not substitute) established measures of LV function, e.g., ventricular volumes and EF.

assessment of rv function in heart failure and postmyocardial infarction

In patients with heart failure, RV dysfunction is associated with increased mortality. RV dysfunction is an important predictor of risk and heart failure following myocardial infarction.

morphological considerations

The RV exhibits a far more complex geometry than that of the LV. It is thin walled (<0.5 cm) and assumes

Reduced Strain Rate Echocardiography
Fig. 21. Doppler strain imaging. Doppler strain imaging showing normal synchronous tissue Doppler tracings of three interrogated myocardial segments are shown.

a flattened pear-shaped appearance folded over the LV (Fig. 23). Such geometry makes it especially difficult to assess by 2D techniques. Most volumetric methods of RV assessment are complex and not well validated, especially in diseased states—when RV geometry is becomes even more complex (Chapter 18).

rv chamber dimensions

Like the LV, the RV should be assessed using multiple windows. The subcostal window provides the best visualization of the RV free wall. RV size, wall thickness, and systolic function should be recorded, and systolic function described as normal or reduced to varying degrees. RV enlargement can be estimated using the "rule of thirds" in the parasternal long-axis view, or by comparing its size relative to that of the LV in the apical four-chamber view. The RV diameter does not normally exceed one-third the total ventricular width in the apical four-chamber view (Fig. 24; Tables 8 and 9).

Attempts to quantify RV volumes and systolic function by echocardiography include indices like tri-cuspid annular motion, tricuspid fractional shortening, and RV fractional area change (RVFAC). Tricuspid annular motion refers to the distance the tricuspid annulus moves in the antero-posterior direction. Tricuspid fractional shortening is an assessment

Function Assessment
Fig. 22. Myocardial infarction (Tei) index.

of the difference between the maximal and minimal distance between the tricuspid annuli during the cardiac cycle. RVFAC is assessed by measuring RV areas in the apical four-chamber view and comparing the relative change between diastolic and systole. When all three approaches are compared to cardiac magnetic resonance imaging (MRI), the best correlation is seen with RVFAC measurements. RV MPI has also proven a useful measure of RV function. Standards for RV volumetric assessment, however, are yet to be established.

High Output Heart Failure
Fig. 23. Right ventricular morphology.
High Output Heart Failure
Fig. 24. Right ventricle dimensions (cm). (Please see companion DVD for corresponding video.)

dilated LV with reduced systolic function. Pressure overload conditions, such as aortic stenosis, severe hypertension, or coarctation, usually lead to hypertrophy, although ventricular dilatation and dysfunction can occur late in the course of disease. Various forms of congenital heart disease can lead to systolic dysfunction and can usually be identified on echocardiography. Infiltrative diseases such as amyloidosis can cause severe LV dysfunction and can usually be identified by pathognomonic echocardiographic features. In the case of amyloid, severe LV hypertrophy, "speckled" appearing myocardium, atrial dilatation, nonspecific valve thickening and pericardial effusions are common. Occasionally, hypertrophic cardiomyopathy can ultimately lead to ventricular dilatation and dysfunction (so-called "burnt-out" hypertrophic cardiomyopathy).

echocardiography to determine etiology of systolic dysfunction

Echocardiography can be of use in determining the etiology of systolic dysfunction (Table 1). Patients with ischemic heart disease almost always have discrete regional wall motion abnormalities—most often secondary to prior myocardial infarction. In contrast, global systolic dysfunction, without regional variation, is more suggestive of nonischemic cardiomyopathy. Severe regurgitant valvular heart disease, such as mitral and aortic regurgitation, can lead to a use of contrast agents in echocardiography

As early as the late 1960s, it was noted that intravascular injection of almost any solution resulted in a contrast effect detectable by echocardiography. Contrast microbubbles are used nowadays to complement the imaging process in ultrasound. The advances in imaging modalities in the modern ultrasound systems in tandem with the development of newer agents has made contrast imaging more effective and applicable in daily clinical practice.

Table 8

Reference Limits and Partition Values of Right Ventricular Size

Reference range Mildly abnormal Moderately abnormal Severely abnormal

RV Dimensions

Basal right ventricular 2.0-2.8 2.9-3.3 3.4-3.8 >3.9

diameter (RVD1) (cm)

Mid right ventricular 2.7-3.3 3.4-3.7 3.8-4.1 >4.2

diameter (RVD2) (cm)

Base-to-apex length 7.1-7.9 8.0-8.5 8.6-9.1 >9.2

Table modified from Recommendations for Chamber Quantification. American Society of Echocardiography (ASE), 2005.

Table 9

Reference Limits and Partition Values of Right Ventricular Size and Function as Measured in the Apical Four-Chamber View

Reference range Mildly abnormal Moderately abnormal Severely abnormal

Right ventricular diastolic area (cm2) 11-28 29-32 33-37 >38

Right ventricular systolic area (cm2) 7.5-16 17-19 20-22 >23

Right ventricular fractional area 32-60 25-31 18-24 <17

Table modified from Recommendations for Chamber Quantification. American Society of Echocardiography (ASE), 2005.

Contrast Agents

Contrast agents are encapsulated bubbles of gas smaller than the red blood cells and, therefore, capable of circulating freely within the body. The use of contrast dates back to 1968 when Gramiak and Shah first used injected saline to enhance the signals from the blood pool. This was followed years later by encapsulated air bubbles, and more recently by the use of encapsulated low solubility gas bubbles (such as perfluorocarbons). These newer agents are capable of passing through the pulmonary circulation without destruction.

Contrast agents approved for use in the United States to improve LV opacification (LVO) in technically difficult echocardiograms include Optison®, an octafluoro-propane within albumin microspheres, Definity™, an octafluoropropane in a phospholipid shell, and Imavist®, a perfluorohexane and other perfluorocarbon gases encapsulated within a surfactant shell. In Europe, SonovueTM, which contains sulfur hexafluoride in a phospholipid shell, is widely used.

The ideal contrast agent should be a nontoxic, easily injectable intravenously (as a bolus or infusion) and should remain stable during cardiac and pulmonary passage for the duration of the ultrasound examination.

The agent should have strong echogenic interaction in response to incident ultrasound waves.

Preparation and Administration of the Contrast Agent

The ASE recommends that cardiac sonographers take the appropriate steps to become trained in the preparation and administration of contrast agents. The sono-grapher is often the first person to recognize the need for contrast, but the physician is ultimately responsible for prescribing its use, which should be done on a case-by-case basis.

Venous access and appropriate instrument settings should be performed prior to preparation of the contrast agent. Each agent has a different method of preparation and administration. Each manufacturer's separate instructions should therefore be followed. The choice between bolus vs continuous infusion depends on the indication for the study and the type of information required. Bolus administration is easier to perform and is sufficient for LVO and Doppler enhancement. However, continuous infusion may be required for myocardial perfusion studies and quantitative analysis. A registered nurse or physician usually administers the injection or infusion of the contrast agent while the sonographer acquires the images.

Ultrasound and Contrast

The mechanical index (MI) represents the normalized energy to which a target (such a bubble) is exposed in an ultrasound field. It gives an estimate of the peak negative pressure to which tissue is exposed. In simple terms, the MI is the intensity of the transmitted ultrasound beam. It varies with the depth in the image. In most of the ultrasound systems, the MI ranges from 0.1 to 2.0. In the absence of attenuation, the MI is maximal at the focus of the ultrasound beam.

Gas bubbles are very effective scatterers of ultrasound waves within the diagnostic frequency range compared to solids. The degree of scattering increases as the MI is increased. Echo signals from microbub-bles contain harmonics, which can be detected. Bubble destruction at high MI emits a strong harmonic echo.

There are three main patterns of scattering produced by microbubbles, depending on the peak pressure of the incident sound field. At a peak pressure of less than 100 kPa (MI < 0.1), bubbles produce "linear" oscillations resulting in backscatter enhancement. During this low MI imaging, bubbles act as simple, but powerful, echo enhancers. This is the principle utilized for enhancing spectral Doppler such as in pulmonary venous flow signals. At a peak pressure of 100 kPa to 1 MPa (MI 0.1-1.0), there is "nonlinear" oscillation resulting in harmonic backscatter. This principle is utilized in harmonic B-mode LVO and real-time perfusion imaging. At a peak pressure of more than 1 MPa (MI > 1.0), there is bubble disruption resulting in transient harmonic echoes. This is the principle utilized in power Doppler imaging.

Contrast Imaging Modes

Conventional grayscale imaging results in linear backscatter, and, hence, is useful for enhancement of the LV cavity, providing better endocardial definition (see Fig. 7B). The concept of "harmonic imaging" emerged from the observation that "nonlinear" oscillations of the microbubbles results in the generation of "second harmonics." Therefore, imaging can be improved by preferential detection of these "second harmonics" that emanate directly from the microbubbles themselves rather than the tissue. In harmonic B mode imaging, the transmitted frequency typically lies between 1.5 and 3 MHz and the received frequency between 3 and 6 MHz to enable detection of these bubble harmonics.

"Contrast-Specific" Imaging Modalities

Although harmonic imaging improves visualization of bubble harmonics, it imposes some fundamental limitations in bandwidth and hence fails to completely suppress the tissue harmonics. Detection of bubbles in myocardial capillaries (i.e., perfusion), therefore, would require tedious off-line background subtraction to suppress the echoes produced by the tissue. To overcome this, "contrast specific" methods are required for assessment of myocardial perfusion by enhancing contrast harmonics while suppressing tissue harmonics.

Examples of such modalities are:

1. Pulse inversion: high MI technique. By sending two pulses (one inverted) in rapid succession toward the tissue, summation occurs and results in a strong harmonic signal that is exclusively from the microbub-bles. However, wall motion artifacts could still attenuate image quality.

2. Harmonic power Doppler: intermittent imaging (high MI technique). The strong, transient echoes produced by bubble destruction provide a highly sensitive method of imaging the microbubbles. The disadvantage is that wall motion (which produces a Doppler shift), is also detected and this potentially interferes with image quality.

3. Low power "real-time" contrast imaging (power pulse inversion/power modulation/coherent imaging): this is a nondestructive, continuous real-time imaging (low MI) technique. In this mode, sequences of more than two pulses are transmitted in alternating phase. Although the sensitivity may be slightly lower than the high power technique, this method allows wall motion information to be available without the need for bubble disruption. This method is much easier to use and avoids many artifacts that occur with high power harmonic imaging. The echoes from the bubbles are well separated from those of tissues, thereby providing better characterization of "realtime" myocardial perfusion.

Clinical Uses of Contrast Echocardiography LV Opacification

One of the most common clinical indications for echocardiography is in the assessment of regional and global LV function. This should be accurate and reproducible. A pre-requisite for reliable assessment of LV function is accurate visualization of the endocardium. In up to 20% of resting studies, endocardial border definition is suboptimal—defined as the inability to visualize at least two myocardial segments of the LV. The advent of tissue harmonic imaging has significantly improved endocardial definition compared to fundamental imaging.

Contrast Echocardiography

Fig. 25. Frame (i) is immediately following a high power ultrasound flash that destroys the microbubbles within the myocardium. Frames (ii) to (iv) show replenishment of microbubbles in the septum and lateral walls within two heartbeats. A clear apical perfusion defect (A) that persists is demonstrated. (Reproduced with permission from R Janardhanan, et al. Myocardial contrast echocardiography: a new tool for assessment of myocardial perfusion. Ind Heart J 2005;57:210-216.)

Fig. 25. Frame (i) is immediately following a high power ultrasound flash that destroys the microbubbles within the myocardium. Frames (ii) to (iv) show replenishment of microbubbles in the septum and lateral walls within two heartbeats. A clear apical perfusion defect (A) that persists is demonstrated. (Reproduced with permission from R Janardhanan, et al. Myocardial contrast echocardiography: a new tool for assessment of myocardial perfusion. Ind Heart J 2005;57:210-216.)

Nevertheless, 5-10% of studies employing tissue harmonics imaging are still suboptimal.

The primary clinical use of contrast echocardiography is for LVO (Chapter 5, Fig. 7B; Chapter 8, Figs. 8 and 10). By injecting microbubbles that traverse the pulmonary circulation, the LV can be opacified and endocardial definition significantly improved. Studies using contrast-enhanced LVO have shown excellent correlation with MRI in the determination of LV volumes and EF. Currently, this use is the only Food and Drug Administration-approved indication for echocardiography contrast agents.

Many studies have shown the incremental value of using contrast agents to improve image quality, the percentage of wall segments visualized, and the confidence of interpretation of resting and stress echocardiography images (Chapter 8, Figs. 8 and 10). Contrast agents in stress echocardiography should be used whenever resting image quality is suboptimal.

Contrast agents can assist in the identification of LV thrombi. Approximately 15-45% of echocardiography studies may fail to identify a LV thrombus. Fundamental imaging from the apical windows may fail to detect apical LV thrombi owing to near-field artifacts. The use of contrast agents permits almost 90% of initially nondiagnostic images to become diagnostic.

Enhancement of Doppler Flow Signals

The accuracy of spectral Doppler velocity measurements depends on obtaining a clear envelope of the Doppler signal. The quality of Doppler recordings, e.g., tricuspid regurgitation velocity, pulmonary venous signals, and so on, can be augmented by using contrast agents. Contrast agents may also be useful in the detection of suspected intracardiac and intrapulmonary shunts.

Echocardiography Contrast Agents vs Saline Contrast. Echocardiography contrast agents that traverse the pulmonary circulation differ from agitated saline contrast used for detecting intracardiac shunts. Saline bubbles do not traverse the pulmonary circulation, except when an arterio-venous malformation is present. Because they do not traverse the pulmonary circulation, agitated saline contrast provide no LVO under normal conditions. Echocardiographic contrast agents that traverse the pulmonary circulation should not be used to diagnose intracardiac shunts.

Myocardial Perfusion Imaging

Myocardial contrast echocardiography (MCE) can accurately assess both myocardial blood volume and microbubble velocity (both of which determine myocardial blood flow). Although not yet licensed for this indication, MCE shows great potential as a clinical tool to evaluate myocardial perfusion.

MCE may be superior to techniques like sestamibi SPECT in the detection of myocardial perfusion. This is most likely explained by the superior temporal and spatial resolution of MCE over SPECT. Furthermore, MCE can be performed at the bedside and does not involve ionizing radiations.

MCE detects contrast bubbles at the capillary level within the myocardium and hence, is marker of capillary integrity. This is the principle behind the use of MCE in patients post-MI in the detection of myocardial viability (Fig. 25).

Safety Considerations. Current contrast agents have an excellent safety profile, and complications are rare. Allergic reactions have been occasionally reported. However, in patients with intracardiac or intrapulmonary right-to-left shunts, the potential for adverse events are slightly greater. There are conflicting reports of increased frequency of premature ventricular complexes especially with high MI-triggered imaging. However, this has not been shown in larger studies.

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Responses

  • cynthia
    Where to measure Pulmonary Regurge ED velocity echo?
    6 years ago
  • Aaliyah
    How to measure cardiac ejection fraction WITH DOPPLER?
    5 years ago
  • AATIFA TEWELDE
    What is vti ans icrt in echocardiography?
    5 years ago
  • Philipp
    How to measure lv diastolic volume?
    5 years ago
  • elen
    How to calculate ejection fraction by by plan Simpson methods?
    2 years ago
  • romeo
    How does an echocardiogram measure ejection fraction?
    11 months ago

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