Effect of intracoronary injections of sonicated microbubbles on left ventricular contractility

Interleukin 8 targeted contrast echocardiography is effective to evaluate myocardial ischemia-reperfusion injury in the rabbits

Interleukin 8 (IL-8) is an important pro-inflammatory cytokine that recruits neutrophil to the areas of inflammation and has been implicated in myocardial ischemia reperfusion injury (MIRI). This study aimed to apply IL-8 targeted myocardial contrast echocardiography (MCE) to evaluate MIRI in rabbits. MCE imaging with IL-8 targeted microbubbles (MB_IL-8) and control microbubbles (MB_c) was performed in 40 Japanese white rabbits after brief proximal left anterior descending (LAD) partial occlusion for 30 min and subsequent reperfusion for 30 min, 60 min, 120 min and 180 min. Electrocardiogram and regional wall motion were assessed during occlusion and reperfusion. MCE demonstrated that IL-8 level rapidly increased in reperfused myocardial tissue and reached the peak after 120 min of reperfusion and lasted to 180 min of reperfusion. ELISA showed that the tendency of MCE data to change with reperfusion time was the same as that of IL-8 content. Taken together, these results suggest that targeted MCE with IL-8 antibody provides a new approach to noninvasive evaluation of MIRI using ultrasound imaging techniques.

Contrast echocardiography

Myocardial contrast echocardiography (MCE) is a noninvasive imaging technique that relies on the ultrasound detection of microbubble contrast agents. These agents are confined to the intravascular space thereby producing signal enhancement from the blood pool. This review encompasses many of the key concepts regarding the clinical application of MCE. The first section focuses on the composition, safety, and biokinetics of ultrasound contrast agents. Then we discuss new ultrasound imaging methodology that has been developed to enhance detection of contrast agent and to assess perfusion at the tissue level. Next, the clinical applications of contrast ultrasound are reviewed. These include enhancement of the cardiac chambers for better assessment of cardiac function and masses, myocardial perfusion imaging for the detection of coronary artery disease, and the assessment of myocardial viability and microvascular reflow. Finally, we discuss some of the future applications for MCE, which include molecular imaging of disease and drug/gene delivery. The overall aim of the review is to update the clinician on state-of-the-art MCE and how it can be applied in patients with cardiovascular disease.

3D perfusion mapping in post-infarct mice using myocardial contrast echocardiography

Myocardial contrast echocardiography (MCE) was used to construct three-dimensional maps of perfusion defects in closed-chest mice, with and without myocardial infarction (MI) induced by permanent coronary ligation. Contiguous, short-axis MCE cine images spanning the heart from apex to base were acquired at 1 mm elevations in each mouse. MCE images at each elevation were color-coded to indicate relative perfusion and were compared with postmortem histology. A strong correlation (R > 0.93) in the size of perfused areas was observed between in vivo measurements and the results of conventional ex vivo tissue staining. 3D multislice and 3D surface renderings of perfusion distribution were created and these perfusion maps also matched well with postmortem histology. These methods provide for the noninvasive determination of the total ischemic region placed at risk by coronary occlusion: this is a critical variable in assessing the potential of novel therapeutic agents to reduce MI size in murine models of ischemia/reperfusion injury.

Fetal atrial tachycardia diagnosed by magnetocardiography and direct fetal electrocardiography. A case report of treatment with propranolol hydrochloride

At 26 weeks of gestation, fetal tachyarrhythmias (about 250 bpm) and ascites were detected by ultrasonography, and oral treatment with propranolol (30 mg/day) was commenced. Within 10 h, the fetal heart rate changed to approximately 85 bpm. The averaged fetal magnetocardiogram triggered by R peaks showed P wave and QRS complexes and an extra P wave. In addition, many extra nonconducted P-waves were detected in a fetal direct electrocardiogram. At 27 weeks of gestation, fetal tachycardia occurred again, and arrhythmia was diagnosed as the result of a blocked premature atrial contraction (PAC) with intermittent atrial tachycardia by fetal electrocardiogram. Administration of transplacental propranolol (90 mg/day) resolved the fetal tachyarrhythmias and ascites. Further studies are required to evaluate the efficacy and adverse effects of propranolol for fetal atrial tachycardia.

Myocardial contrast echocardiography: basic principles

Myocardial contrast echocardiography (MCE) is a new technique that can be used to examine the myocardial microcirculation. It uses gas-filled microbubbles that behave similarly to red blood cells in the microcirculation. This report describes the parts of the coronary microcirculation visualized by MCE. It also describes the types of microbubbles currently available for research. The properties of microbubbles and their interaction with ultrasound are also described as well as different imaging techniques. This information is necessary to understand the basics of MCE.

Combined assessment of reflow and collateral blood flow by myocardial contrast echocardiography after acute reperfused myocardial infarction

OBJECTIVE

To evaluate the combined assessment of reflow and collateral blood flow by myocardial contrast echocardiography after myocardial infarction.

DESIGN

Myocardial contrast echocardiography was performed in patients with acute myocardial infarction shortly after successful coronary reperfusion (TIMI 3 patency) by direct angioplasty. Collateral flow was assessed before coronary angioplasty, and contrast reflow was evaluated 15 minutes after reperfusion. The presence of contractile reserve was assessed by low dose dobutamine echocardiography (5 to 15 micrograms/kg/min) at (mean (SD)) 3 (2) days after myocardial infarction. Recovery of segmental function (myocardial viability) was evaluated by resting echocardiography at a two month follow up. The study was prospective.

PATIENTS

35 consecutive patients referred for acute transmural myocardial infarction.

RESULTS

Contrast reflow was observed in 20 patients (57%) and collateral flow in 14 (40%). Contrast reflow and collateral contrast flow were both correlated with reversible dysfunction on initial dobutamine echocardiography and at follow up (p < 0.05). The presence of reflow or collateral flow on myocardial contrast echocardiography was a highly sensitive (100%) but weakly specific (60%) indicator of segmental dysfunction recovery. Simultaneous presence of contrast reflow and collateral flow was more specific of reversible dysfunction than reflow alone (90% v 60%).

CONCLUSIONS

Combined assessment of reflow and collateral blood flow enhanced the sensitivity of myocardial contrast echocardiography in predicting myocardial viability after acute, reperfused myocardial infarction. The simultaneous presence of reflow and collateral blood flow was highly specific of recovery of segmental dysfunction.

Echocardiographic contrast agents and left ventricular contractility: evaluation using an isolated rabbit heart model

The effects of Albunex (Molecular Biosystems, Inc., San Diego, Calif.) and a second generation contrast agent, FS069, on left ventricular (LV) contractility were evaluated using an isolated rabbit heart model under constant loading conditions and heart rate. Contrast injections (2 ml total volume) were performed in two separate protocols (N1 = 6, N2 = 6). In protocol 1, various doses of Albunex (0.1 to 2.0 ml in saline solution) were used, and paired control injections of a matched dose of 5% solution of human albumin in saline solution were administered. In protocol 2, LV contractility was assessed during injections of the following solutions: (1) 1:250 suspension of FS069 in saline solution, which caused optimal myocardial contrast enhancement; (2) a 1:25 suspension of FS069; (3) a 1:25 suspension of FS069 prefiltered using an 8 microns pore filter; and (4) 2 ml saline solution as a control. Instantaneous LV pressure was analyzed for variations in peak systolic pressure (peak P) and maximum pressure derivative (peak P'), both indices of LV contractility under conditions of fixed heart rate and chamber volume. Albumin alone caused a transient, dose-dependent depression of LV contractility, reflected by decreases in both peak P and peak P' values. These decreases presumably were caused by the decreasing availability of ionized calcium as a result of calcium binding. No further decrease in contractility was noted when Albunex microspheres were present in the solution. Saline injections caused a transient minor increase in LV contractility, reflected by increases of 4.5% +/- 1.1% and 10.6% +/- 3.8% in peak P and peak P' values, respectively. These levels returned to baseline levels within 2 minutes. A similar response was observed when a 1:250 suspension of FS069 was used. The 1:25 suspension of FS069 caused a bimodal response, with initial rises in peak P and peak P' levels (5.2% +/- 3.6% and 12.8% +/- 6.5%, respectively), followed by minor reductions in contractility (2.0% +/- 2.4% and 1.7% +/- 2.1%, respectively). The latter decrease in contractility caused by the 1:25 suspension of FS069 was eliminated by filtering. The isolated rabbit heart model is a highly sensitive tool that allows accurate and direct assessment of possible adverse effects of intravascular contrast agents on LV contractility. Using this model, we showed that neither Albunex microspheres nor FS069 microspheres impaired myocardial contractility.

Clinical applications of myocardial contrast echocardiography

Myocardial contrast echocardiography is a new technique that uses microbubbles of air in conjunction with simultaneously performed 2-dimensional echocardiographic imaging. Currently, it can be used to determine myocardial perfusion in the cardiac catheterization laboratory and the operating room. For myocardial contrast echocardiography to find a broader clinical application for the assessment of myocardial perfusion, it will be necessary to opacify the myocardium from venous injection of contrast in humans. In this regard, enhancement in bubble engineering, optimization of echocardiographic systems (greater sensitivity and dynamic range), and availability of digital image enhancement techniques will be required for myocardial contrast echocardiography to realize its full clinical potential by the year 2000.

Contrast echocardiographic mapping of collateralized myocardium in humans before and after coronary angioplasty

Conventional coronary arteriography is able to demonstrate the presence of coronary collateral vessels but cannot delineate the specific region of myocardium to which they supply blood. To test the hypothesis that contrast echocardiography can specifically identify collateralized myocardium, contrast echocardiographic perfusion "maps" were compared in patients with (n = 12) and without (n = 12) angiographic evidence of coronary collateral flow, both before and after coronary angioplasty. Contrast echocardiographic images of the mid-left ventricle in the short-axis view at end-diastole were obtained after separate injections of a sonicated contrast agent into both the right and the left coronary arteries. A computer-based contouring system was used to determine the individual areas of myocardium perfused by each of the two coronary arteries and then to superimpose the images of the two perfusion beds. The resulting area of overlapping perfusion represented myocardium receiving blood flow from both coronary systems and was defined as collateralized myocardium. To normalize for heart size, overlap area was expressed as a percent of total myocardial area, which was the area between endocardium and epicardium in the short-axis view. To adjust for differences in vascular distribution, overlap area was expressed as a percent of the perfusion area of the recipient vessel. In patients with angiographic collateral flow, the recipient vessel was that vessel receiving the collateral flow. In patients without angiographic collateral flow, the right coronary artery was considered the recipient vessel. Overlap area was 1.3 +/- 0.4% of total myocardial area and 6.6 +/- 1.7% of recipient vessel area in patients without angiographic evidence of collateral flow compared with 30.6 +/- 2.5% and 89.2 +/- 6.4%, respectively, in patients with angiographic collateral flow (p less than 0.001 for both). In four patients in whom angiographic collateral flow was abolished by angioplasty, overlap area decreased from 30.3 +/- 5.3% to 6.8 +/- 2.7% of total myocardial area and from 100% to 18.5 +/- 5.4% of recipient vessel area (p less than 0.05 for both). Thus, contrast echocardiography is able to map the specific myocardial territory perfused by coronary collateral flow and document an immediate reduction in perfusion in this territory when collateral flow is abolished by angioplasty.

Intraoperative assessment of myocardial perfusion using contrast echocardiography

Myocardial contrast echocardiography is a new technique capable of assessing regional myocardial perfusion in vivo in real time. This article reviews the background, principles, experimental validation, and clinical uses of intraoperative myocardial contrast echocardiography. Data can be derived both for online visual and computer analyses. The technique can be useful in determining the sequence of bypass graft placement and the success of graft anastamoses. Anastamoses can be revised immediately if needed. It is hoped that this technique will improve intraoperative myocardial preservation and will diminish the rate of perioperative myocardial infarction.

Myocardial perfusion studies by contrast echocardiography

Determination of regional myocardial blood flow may provide clinically valuable information about ischemia, risk area, and the effect of angioplastic, surgical, and pharmacologic interventions. Contrast echocardiography, with use of prepared microbubbles of 4 to 8 microns size, graphically demonstrates perfusion characteristics in the catheterization laboratory. Analysis and interpretation of this data and the creation of contrast materials that will demonstrate myocardial perfusion after intravenous injection are some of the next challenges in these techniques.

Assessment of myocardial perfusion with contrast two-dimensional echocardiography

Myocardial contrast echocardiography (MCE) is a new technique capable of assessing regional myocardial perfusion in vivo in real time. At present, this technique involves the intraaortic or intracoronary injection of microbubbles of air. As these microbubbles traverse the myocardium, they produce opacification of the myocardium in concomitantly performed echocardiographic images. In animal models, MCE has been demonstrated to assess accurately the in vivo risk area (region of the myocardium at risk for necrosis after acute coronary occlusion). It has also been shown to provide quantitative information on regional myocardial blood flow (both antegrade and collateral). This technique has been demonstrated to be safe in humans. In clinical studies it has been shown to be a useful adjunct to cardiac catheterization, particularly in the assessment of coronary blood flow reserve and collateral blood flow. MCE is also used in the operating room to assess regional myocardial perfusion before and after bypass graft operations. The microbubbles used for MCE were shown to opacify the left ventricular cavity after their injection into a peripheral vein. If myocardial opacification after venous injection can be achieved, MCE will have the potential for the simultaneous noninvasive in vivo assessment of regional myocardial perfusion and function in humans.

Echocardiographic contrast in two-dimensional echocardiography: new applications for an old technique?

Although Gramiak and Shah first introduced the technique of using contrast enhanced two-dimensional echocardiography in 1968, it has seen a resurgence of new and varied applications. Three of the areas of interest are in the use of microbubble enhanced contrast agents to evaluate: (1) regional myocardial blood flow; (2) regional myocardial function; and (3) myocardial ischemic areas and infarct size. Whether these new approaches will have applications and value in the clinical laboratory is still a matter of conjecture. The objective of this review is to briefly summarize the potential uses and the advantages and disadvantages of each application.

Assessment of regional myocardial blood flow with myocardial contrast two-dimensional echocardiography

It was hypothesized that regional myocardial blood flow could be measured using myocardial contrast echocardiography. Accordingly, arterial blood was perfused into the coronary circulation in 16 dogs. In Group 1 dogs (n = 8), blood flow to the cannulated left circumflex artery was controlled with use of a roller pump, whereas in Group 2 dogs (n = 8) blood flow to the left anterior descending coronary artery was controlled by a hydraulic occluder placed around it. Sonicated microbubbles (mean size 4 microns) were used as the contrast agent. In Group 1 dogs the microbubbles were injected subselectively into the left circumflex artery, whereas in Group 2 dogs they were injected selectively into the left main coronary artery and two-dimensional echocardiographic images were recorded. Computer-generated time-intensity curves were derived from these images and variables of these curves correlated with transmural blood flow measured with radiolabeled microspheres. A gamma-variate function (y = Ate-alpha t) best described the curves, and alpha (a variable of curve width) correlated well with transmural blood flow at different flow rates in all Group 1 and Group 2 dogs (mean r = 0.81 and 0.97, respectively). Other variables of the curve width also correlated well with myocardial blood flow, but peak intensity had a poor correlation with myocardial blood flow in both groups of dogs (r = 0.39 and r = 0.63, respectively). When data from all dogs were pooled, Group 1 dogs still showed good correlation between variables of curve width and myocardial blood flow (r = 0.81); Group 2 dogs did not (r = 0.45). The difference between the two sets of dogs was related to the site of contrast agent injection. It is concluded that measurement of the transit time of microbubbles through the myocardium with two-dimensional echocardiography accurately reflects regional myocardial blood flow. Although injection of contrast agent selectively into the left main coronary artery only allows measurement of relative flow, it may be feasible to measure absolute flow by injecting contrast agent subselectively into a coronary artery. Myocardial contrast echocardiography may, therefore, offer the unique opportunity of simultaneously assessing regional myocardial perfusion and function in vivo.

Myocardial contrast two-dimensional echocardiography: dose-myocardial effect relations of intracoronary microbubbles

It is controversial whether echocardiographic contrast agents prepared by sonication cause transient myocardial depression beyond that known to occur with contrast agents alone. In nine open chest dogs, contrast injections were made into the left anterior descending coronary artery during two-dimensional echocardiography. One hundred forty-four recordings were analyzed subsequently, by an observer who was unaware of other data, for percent depression of systolic wall thickening, duration of regional wall motion abnormalities, peak contrast enhancement and contrast washout. Two microbubble sizes were obtained by sonicating Renografin-76 (meglumine sodium diatrizoate): mean diameter 12 +/- 3 (SEE) and 20 +/- 6 micron. Four doses (range 0.5 to 3 ml) of each of four agents (12 and 20 micron bubbles in Renografin, nonsonicated Renografin and saline solution) were injected in random order. Significant relations were found between percent depression of systolic wall thickening, duration of regional wall motion abnormalities and contrast washout time versus microbubble size (p less than 0.001) and microbubble dose (p less than 0.01). Little increased contrast effect was found at larger doses or with larger microbubbles compared with the smaller doses and size studied. Injections of nonsonicated Renografin caused less depression of systolic wall thickening (p less than 0.05), faster resolution of wall motion abnormalities (p less than 0.05), less contrast (p less than 0.001) and more rapid contrast washout (p less than 0.001) than did 12 micron bubbles in Renografin. A significant correlation was found between the duration of regional wall motion abnormalities and contrast washout time (r = 0.93, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)