Handbook of Contrast Echocardiography: Left ventricular function and myocardial perfusion
Contents:
Throughout the past few years, it has been demonstrated that contrast echocardiography using intravenous injection of microbubbles is an useful technique for the assessment of patients with suboptimal imaging as it enables a better evaluation of the cardiac anatomy. Microbubbles act as blood flow tracer, remaining within the intravascular space, and their distribution in the myocardium indicate the integrity of coronary microcirculation. MCE has proven to be safe and efficient to assess myocardial perfusion, and has incremental value over the analysis of wall motion for the wide spectrum of patients with acute and chronic coronary disease.
Becker H, Burns P. J Am Soc Echocardiogr. Detection of myocardial perfusion abnormalities during dobutamine and adenosine stress echocardiography with transient myocardial contrast imaging after minute quantities of intravenous perfluorocarbon-exposed sonicated dextrose albumin. Transient myocardial contrast after initial exposure to diagnostic ultrasound pressures with minute doses of intravenously injected microbubbles: Diagnostic accuracy and prognostic value of dobutamine stress myocardial contrast echocardiography in patients with suspected acute coronary syndromes.
Noninvasive diagnosis of coronary artery disease in patients with diabetes by dobutamine stress real-time myocardial contrast perfusion imaging.
JACC: Cardiovascular Imaging
Detection of myocardial perfusion in multiple echocardiographic windows with one intravenous injection of microbubbles using transient response second harmonic imaging. J Am Coll Cardiol. Contrast echocardiography can save nondiagnostic exams in mechanically ventilated patients. Potential utility of left heart contrast agents in diagnosis of myocardial rupture by 2-dimensional echocardiography. Left ventricular free wall impeding rupture in post-myocardial infarction period diagnosed by myocardial contrast echocardiography: Improved endocardial border resolution during dobutamine stress echocardiography with intravenous sonicated dextrose albumin.
Intravenous albunex during dobutamine stress echocardiography: Endocardial border delineation during dobutamine infusion using contrast echocardiography. Detection of coronary artery disease with myocardial contrast echocardiography: Real-time perfusion imaging with low mechanical index pulse inversion Doppler imaging. Real-time assessment of myocardial perfusion and wall motion during bicycle and treadmill exercise echocardiography: Safety of dobutamine stress real-time myocardial contrast echocardiography.
Quantification of myocardial blood flow with ultrasound-induced destruction of microbubbles administered as a constant venous infusion. Incremental value of quantitative analysis of myocardial perfusion in dobutamine and adenosine stress real-time perfusion echocardiography. Assessment of risk area during coronary occlusion and infarct size after reperfusion with myocardial contrast echocardiography using left and right atrial injections of contrast. Noninvasive prediction of ultimate infarct size at the time of acute coronary occlusion based on the extent and magnitude of collateral-derived myocardial blood flow.
The "no-reflow" phenomenon after temporary coronary occlusion in the dog. Lack of myocardial perfusion immediately after successful thrombolysis: Myocardial perfusion patterns related to thrombolysis in myocardial infarction perfusion grades after coronary angioplasty in patients with acute anterior wall myocardial infarction. Functional significance of collateral blood flow in patients with recent acute myocardial infarction: Detection of functional recovery using low-dose dobutamine and myocardial contrast echocardiography after acute myocardial infarction treated with successful thrombolytic therapy.
Senior R, Swinburn JM. Incremental value of myocardial contrast echocardiography for the prediction of recovery of function in dobutamine nonresponsive myocardium early after acute myocardial infarction. Value of myocardial contrast echocardiography for predicting left ventricular remodeling and segmental functional recovery after anterior wall acute myocardial infarction.
Myocardial viability during dobutamine echocardiography predicts survival in patients with coronary artery disease and severe left ventricular systolic dysfunction. Identification of hibernating myocardium with quantitative intravenous myocardial contrast echocardiography: Manuscript received June 15, ; revised received September 24, ; accepted October 5, All the contents of this journal, except where otherwise noted, is licensed under a Creative Commons Attribution License.
Although real-time MCE may be useful for ruling in or ruling out significant CAD in these patients, it has yet to be determined in published clinical studies. An example of a patient with left bundle branch block who exhibited normal perfusion with myocardial contrast echocardiography but abnormal perfusion in the septum during radionuclide single-photon emission computed tomography despite no significant coronary artery disease.
See text for details. Reprinted, with permission, from Hayat et al. One must be able to differentiate potential artifacts that create the appearance of perfusion defects. The most common source of artifacts is attenuation. This typically occurs in basal segments and is differentiated from true defects by its location. Attenuation typically masks not only the myocardium, but adjacent epicardial and endocardial borders as well.
Attenuation is usually present both at rest and during stress, whereas inducible defects are present only during stress and typically involve just the subendocardium. Other potential artifacts are lung shadows, which will often mask an entire region e. A second location where artifacts tend to occur is in the apical region.
If the near-field gains time gain compensation are set too low, the apex will appear hypoperfused. Unlike true defects, this can be corrected by increasing the near-field potentiometer settings. Near-field destruction of microbubbles can also cause the false appearance of perfusion defects in the apex. This can be corrected by moving the focus to the near field, which decreases the scan-line density in this region and reduces destruction. MCE is a bedside imaging technique that has very high resolution and can be performed without the need of ionizing radiation.
The use of intravenous microbubbles for perfusion imaging is now a reality. Food and Drug Administration still has not approved the use of ultrasound contrast for myocardial perfusion imaging. Nonetheless, the real-time methods used to achieve optimal left ventricular opacification the approved U. Food and Drug Administration indication often result in myocardial opacification, which permits the simultaneous analysis of perfusion.
Consensus documents from both the U.
CONTRAST AGENTS FOR ULTRASOUND
Clinical studies have demonstrated the potential for this technique in the emergency department, during stress echocardiography, and in the detection of viability, and prospective studies are underway to examine the prognostic value of real-time perfusion imaging during stress echocardiography as compared with conventional echocardiographic imaging. Thank you for your interest in spreading the word about JACC: We request your email address only as a reference for the recipient. We do not save email addresses. Skip to main content. American College of Cardiology Foundation.
Abstract This report reviews the development and clinical application of myocardial perfusion imaging with myocardial contrast echocardiography MCE. Perfusion Imaging Techniques With Myocardial Contrast Echocardiography Microbubbles in an ultrasonic field are strong scatterers, sending compression and rarefaction waves back to the scanner.
Figure 1 An Example of the Excellent Background Subtraction The images are achieved with low—mechanical index pulse sequence schemes designed to assess myocardial perfusion. Qualitative and quantitative methods of myocardial perfusion analysis Regardless of the route of microbubble injection, an accurate definition of microbubble concentration in the myocardium requires that the relationship between concentration and signal intensity be linear. Clinical Application of Ultrasonographic Contrast for Perfusion Imaging With Vasodilator Stress Perfusion Imaging Detection of coronary artery disease Radionuclide scintigraphy is still considered by the majority of cardiologists as the diagnostic tool to assess myocardial perfusion during stress testing.
Figure 3 An Example of a Subendocardial Perfusion Defect The defect is evident in the anteroseptal and apical segments of the left ventricle during the replenishment phase of contrast after a high—mechanical index impulse during adenosine stress imaging. Figure 4 Proposed Protocols for Dipyridamole or Adenosine Stress Infusions The images shown are not intended for analysis of perfusion, but to serve as reminders when to examine myocardial contrast echocardiography.
View inline View popup. During Dobutamine Stress Echocardiography Animal studies have shown that perfusion defects appear before wall-thickening abnormalities during dobutamine infusion and better delineate the area at risk Real-time MCE during exercise stress echocardiography There are greater challenges when attempting to use real-time perfusion imaging during treadmill or bicycle exercise stress echocardiography. Figure 6 An Example of an Inferior Wall Perfusion Defect The defect was confined to the subendocardium after treadmill exercise stress, where a subendocardial wall-thickening abnormality was also observed blue arrows.
Assessment of myocardial viability in the acute and chronic setting MCE has proven useful in evaluating patients after interventional or thrombolytic treatment in acute myocardial infarction. Real-time MCE to detect CAD in clinical scenarios where radionuclide imaging and wall motion are limited Patients with left bundle branch block LBBB or pacemaker-dependent patients represent clinical scenarios where both the assessment of wall thickening and conventional myocardial perfusion imaging with radionuclide SPECT are not helpful in the detection of CAD Figure 8 An Example of a Patient With Left Bundle Branch Block An example of a patient with left bundle branch block who exhibited normal perfusion with myocardial contrast echocardiography but abnormal perfusion in the septum during radionuclide single-photon emission computed tomography despite no significant coronary artery disease.
Artifacts in myocardial perfusion assessments One must be able to differentiate potential artifacts that create the appearance of perfusion defects. Conclusions MCE is a bedside imaging technique that has very high resolution and can be performed without the need of ionizing radiation. Am Heart J J Am Coll Cardiol Kluwer Academic Publishers , Dordrecht, the Netherlands , 2nd edition , p J Am Soc Echocard Eur J Echocardiogr Comparison with technetiumm sestamibi single-photon emission computed tomography and quantitative coronary angiography.
Am J Cardiol J Am Soc Echocardiogr Ultrasound Med Biol Cutoff values for myocardial contrast replenishment discriminating abnormal myocardial perfusion. Comparison of myocardial contrast echocardiography and 99mTc MiBI single photon emission computed tomography. Int J Cardiol Eur J Echocardiogr 9: J Am Coll Cardiol Img 1: Cardiovascular Imaging web site. Porter , Feng Xie. Figures in Article Figures.
CONTRAST ECHOCARDIOGRAPHY
Although initially developed as an aid to contrast echo, tissue also generates harmonics and the ability to enhance conventional grey scale imaging was rapidly appreciated. Harmonic imaging is now a standard feature on most ultrasound machines marketed today. By imaging contrast agent and not tissue, tissue perfusion can potentially be identified. The harmonic response is dependent upon the physical characteristics of the agent both size and mechanical properties , the incident pressure of the ultrasound field, and the frequency.
Thus, optimal contrast imaging must be set up for the agent and equipment in use. Pulse inversion and power modulation imaging have been developed to improve the differentiation of contrast from tissue still further. These methods are so sensitive to contrast that weaker echoes from bubbles insonated at very low intensity can be readily imaged, resulting in oscillation without bubble destruction, prolonging the contrast effect and enabling real time myocardial perfusion imaging.
Apical four chamber view, end diastolic A and end systolic B frames, in a patient with recent myocardial infarction referred for assessment of left ventricular systolic function. Images acquired utilising tissue harmonic imaging at frequency of 3. Lateral wall endocardium was not clearly defined making accurate measurement of left ventricular volumes difficult. Apical four chamber view, end diastolic C and end systolic D frames, imaged after intravenous bolus injection of 0. The mechanical index has been reduced to 0. The entire endocardial border is now clearly defined and systolic thickening of entire lateral wall appreciated.
Contrast imaging requires ultrasound machine settings to be optimised for the modality used. Generally, this requires variation in the system power output, indicated on clinical systems as the mechanical index MI. This is an estimate of the peak negative pressure within insonated tissue defined as the peak negative pressure divided by the square root of the ultrasound frequency. This is clearly dependent on both ultrasound beam properties and tissue characteristics but the latter is assumed to be standard across all patients.
Display of the MI was made mandatory in the USA as a safety measure, to enable an estimate of the tissue effects of ultrasound exposure to be made. As this also reflects the mechanical effect of ultrasound on a contrast bubble, this has proved useful in developing machine settings for contrast ultrasound. It is relatively imprecise and not directly comparable from machine to machine, but is nonetheless one of the most important parameters to set correctly in a contrast echo study.
Standard clinical echocardiography imaging utilises an MI of around 1. To achieve myocardial perfusion imaging the extremes of power output are utilised: Initially contrast echocardiography utilised free air in solution but these large, unstable bubbles were not capable of crossing the pulmonary vascular capillary bed, allowing right heart contrast effects only. The first agents capable of left heart contrast after intravenous injection first generation agents were air bubbles stabilised by encapsulation Albunex or by adherence to microparticles Levovist.
Replacing air with a low solubility fluorocarbon gas stabilises bubbles still further second generation agents—for example, Optison, SonoVue , greatly increasing the duration of the contrast effect. Bubbles in contrast agents are delicate and prone to destruction by physical pressure. Performing a contrast study requires meticulous attention to the preparation and administration of the contrast agent to optimise the desired effect.
The agent should be prepared immediately before injection and vents used when withdrawing the agent into the syringe. Bubbles tend to float towards the surface and the contrast vial or syringe should be gently agitated each time fresh contrast administration is required. Injection through a small lumen catheter increases bubble destruction—a 20 G or greater cannula should be used.
This is best done using a three way tap, with contrast injected along the direct path to minimise bubble destruction, and saline flush injected into the right angle bend. For myocardial perfusion work, infusion produces more reproducible results with the potential for quantification 6 but brings its own problems. Bubbles in agents currently available are buoyant and will tend to rise to the surface of the syringe.
Purpose designed infusion pumps which agitate contrast continuously are in development but not yet widely available. Conventional contrast echocardiography is performed predominantly with agitated saline. This is most readily achieved by hand agitation of saline between two 10 ml syringes connected to a three way tap. Approximately 5 ml of saline and 0.
The maximum velocity recorded was 2. This technique, developed by Philips Andover, Massachusetts , is also a multipulse cancellation technique; however, with power modulation, the power of each pulse is varied. Harmonic imaging is now a standard feature on most ultrasound machines marketed today. Then, it was discovered that the typical ultrasound imaging techniques at a high mechanical index MI were destroying these microbubbles as they transited through the myocardial microcirculation. It is during this time period that there is a linear relationship between concentration and signal intensity. Several transpulmonary contrast agents have been developed, capable of crossing the pulmonary vascular bed and hence achieving left heart opacification following intravenous injection.
Contrast should be injected immediately after preparation. Air bubbles produced by hand agitation are too large to cross the pulmonary vascular bed and so predominantly aid visualisation of the right heart. Thus, any significant contrast effect in the left heart is likely to be the result of an intracardiac shunt.
By far the most common indication in adult cardiology is the detection of patent foramen ovale PFO in patients in whom paradoxical embolism is suspected. Use of harmonic imaging and a relatively low MI will enhance the contrast effect of agitated saline, with the result that most clinically important intracardiac shunts and PFO can be detected during transthoracic echocardiography, with sensitivity greater than that of a transoesophageal examination. An initial study should be performed during normal respiration, when the normal reversal of atrial pressure gradient in early systole may be sufficient to allow shunting if a large defect is present.
If successfully performed, the atrial septum can be seen to bow transiently from right to left. Assessment of left ventricular LV systolic function is the most common indication for echocardiography. Accurate assessment and quantification is dependent on visualising the entire endocardium in cross section. These problems are amplified still further when performing stress echocardiography, where recognition of regional wall motion defects is crucial but frequently hampered by reduced image quality resulting from rapid heart rate, increased cardiac translocation, and respiratory interference.
Most centres performing stress echocardiography will now routinely use contrast in the majority of studies. Contrast echocardiography has been shown to be particularly useful in the assessment of LV function in patients ventilated in intensive care, reducing the time required to obtain diagnostic information and obviating the need for transoesophageal echocardiography.
Contrast will not enable visualisation of the left ventricle when baseline images are totally inadequate.
It is of most use when between a quarter and a half of endocardial segments are not well visualised. While apical imaging is greatly enhanced, parasternal views may deteriorate, at least initially, with contrast in the right ventricle attenuating visualisation of the left. For this reason, apical views should routinely be obtained first in any contrast study. LV opacification is also used to delineate LV anatomy, particularly apically, confirming pseudoaneurysm, apical hypertrophy or ventricular non-compaction and demonstrating filling defects, typically apical thrombus.
LV opacification studies should routinely utilise harmonic B mode imaging with the MI set to approximately 0. Compression is optimally set in the medium to high range and focus should be set at the level of the mitral valve or below. Intravenous bolus injection is the simplest method of contrast administration but infusion may be utilised, particularly during stress studies.
- Clinical use of contrast echocardiography with microbubble-based.
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- Myocardial Perfusion Imaging With Contrast Ultrasound | JACC: Cardiovascular Imaging;
- Hobsons Choice.
If the MI is too high or focus wrongly set, excessive destruction of contrast in the near field will result in apical swirling. If too much contrast is used, visualisation of basal segments may be attenuated. As bubble destruction occurs during imaging, this will spontaneously resolve, but a lower dose should be used for subsequent imaging.
In some studies, lateral wall dropout caused by rib artefact can prevent imaging of entire endocardium. This can usually be overcome by repositioning the image with the lateral wall more central.