Simultaneous real-time echocardiographic imaging of myocardial perfusion and regional function using color-encoded, contrast-enhanced power modulation

Quantification of left ventricular size and function using contrast-enhanced real-time 3D imaging with power modulation: comparison with cardiac MRI

In patients with optimal images, real-time 3-D echocardiography (RT3DE) allows accurate evaluation of left ventricular (LV) volumes and ejection fraction (EF). However, in patients with poor acoustic windows, lower correlations were reported despite the use of contrast. We hypothesized that power modulation (PM) RT3DE imaging that uses low mechanical indices and provides uniform LV opacification could overcome this problem. Accordingly, we sought to: (i) Test the feasibility of quantification of LV volumes and EF from contrast-enhanced (CE) PM RT3DE images, (ii) validate this technique against cardiac magnetic resonance (CMR) reference and (iii) test its clinical value by quantifying the improvement in accuracy and reproducibility. We studied 20 patients who underwent CMR, harmonic nonenhanced RT3DE and CE PM RT3DE imaging on the same day. All images were analyzed to obtain end-systolic and end-diastolic LV volumes (EDV, ESV) and calculate EF. To determine the reproducibility of each RT3DE technique, imaging was repeated in the same setting by a second sonographer. In addition, patients were divided according to the quality of their RT3DE images into two groups, for which agreement with CMR and reproducibility were calculated separately. CE PM RT3DE imaging improved the accuracy of EDV, ESV and EF measurements in patients with poor acoustic windows without significantly affecting those in patients with optimal images. In addition, CE PM RT3DE imaging improved the reproducibility of the measurements, as reflected by a twofold decrease in intermeasurement variability. Importantly, the variability in CE PM RT3DE-derived volumes and EF was under 10%, irrespective of image quality. This methodology may become the new standard for LV size and function, which will be particularly important in patients with poor acoustic windows or contraindications to CMR.

Diagnostic value of parametric imaging of left ventricular wall motion from contrast-enhanced echocardiograms in patients with poor acoustic windows

BACKGROUND

Analysis of left ventricular (LV) regional wall motion (RWM) is subjective and may be challenging in patients with suboptimal images, even with contrast enhancement. It was hypothesized that the amplitude and timing of RWM obtained from contrast-enhanced echocardiograms can be accurately represented in still-frame parametric images. This study was designed to (1) test this hypothesis, (2) establish the diagnostic value of these images as an aid for inexperienced readers, and (3) test the feasibility of automated quantitative analysis of RWM.

METHODS

Contrast-enhanced apical 4-chamber, 2-chamber, and 3-chamber LV views were acquired in 45 patients with poor acoustic windows. The interpretation of dynamic images by an experienced reader who classified RWM as normal or abnormal was used as a reference for comparisons against (1) visual interpretation of parametric images, (2) interpretation of dynamic images by two inexperienced readers (American Society of Echocardiography level I) without and subsequently with parametric images, and (3) automated quantification of RWM.

RESULTS

Expert readers detected abnormal RWM in 30 patients (437 of 945 segments). Visual interpretation of parametric images showed good agreement with the reference (sensitivity, 85%; specificity, 82%; accuracy, 84%). The interpretations by inexperienced readers improved with the addition of parametric images, with increases in specificity (from 58% to 79%) and accuracy (from 74% to 84%), despite a slight decrease in sensitivity (from 92% to 91%). Automated classification was feasible and accurate (sensitivity, 82%; specificity, 78%; accuracy, 80%).

CONCLUSION

Parametric images derived from contrast-enhanced echocardiograms of patients with poor acoustic windows accurately depicted RWM, improved the diagnostic accuracy of inexperienced readers, and allowed the objective detection of RWM abnormalities.

Imaging and Quantification of Myocardial Perfusion Using Real-Time Three-Dimensional Echocardiography

OBJECTIVES

We tested the feasibility of real-time three-dimensional echocardiographic (RT3DE) perfusion imaging and developed and validated an algorithm for volumetric analysis of myocardial contrast inflow. The study included three protocols wherein perfusion was measured: 1) in an ex-vivo model of controlled global coronary flow, 2) in an in-vivo model during regional perfusion variations, and 3) in humans during pharmacologically induced hyperemia.

BACKGROUND

The RT3DE technology offers an opportunity for myocardial perfusion imaging without multi-slice reconstruction and repeated contrast maneuvers.

METHODS

Electrocardiographically triggered harmonic RT3DE datasets were acquired (Philips 7500) while infusion of Definity was initiated and reached a steady state. Protocol 1 was performed in nine isolated rabbit hearts and included three coronary flow levels. In protocol 2, changes in regional perfusion caused by partial left anterior descending artery occlusion were measured in five pigs. In protocol 3, adenosine-induced changes in perfusion were measured in eight normal volunteers. Myocardial video-intensity (MVI) was measured over time in three-dimensional (3D) slices to calculate peak contrast inflow rate (PCIR). In pigs, PCIR was measured on a regional basis and validated against microspheres.

RESULTS

The RT3DE imaging allowed selection of slices for perfusion analysis in rabbit hearts, pigs, and humans. Administration of contrast resulted in clearly visible and quantifiable changes in MVI. In rabbits, The PCIR progressively decreased with coronary flow (p < 0.0001). In pigs, coronary occlusion caused a 59 +/- 26% decrease in PCIR exclusively in the left anterior descending artery territory (p < 0.05) in agreement with microspheres. In humans, adenosine increased PCIR to 198 +/- 57% of baseline (p < 0.05).

CONCLUSIONS

Contrast-enhanced RT3DE imaging provides the basis for volumetric imaging and quantification of myocardial perfusion.

Cardiac imaging techniques in systemic autoimmune diseases

Systemic autoimmune disorders are frequently associated to cardiac involvement and to a high prevalence of ischemic coronary events, often occurring at a younger age than in the normal population. Large increase in mortality is related to premature atherosclerosis with coronary artery disease and stroke in patients with connective tissue diseases. Coronary heart disease is responsible for 40-50% of the deaths of patients with rheumatoid arthritis. Transesophageal or transthoracic echocardiography are the most useful and noninvasive techniques able to detect not only valvular abnormalities, embolic sources or pulmonary hypertension, but also left ventricular systolic or diastolic dysfunction. Furthermore, the introduction of new indexes, contrast agents and software increased the accuracy of this technique. It is possible now to evaluate coronary flow reserve by transthoracic echocardiography in patients with systemic autoimmune disease in order to detect microvasculature disorder. However, an ischemic response in a symptomatic patient requires, in most cases, further evaluation with cardiac catheterization. Coronary artery imaging allows confirmation of the presence, extent and position of atheromatous lesions. More recently, other imaging modalities including magnetic resonance and computerized tomography angiography have been developed to allow imaging of the coronary arteries.

Quantitative Echocardiographic Evaluation of Myocardial Perfusion Using Interrupted Contrast Infusion Technique: In Vivo Validation Studies and Feasibility in Human Beings

BACKGROUND

We recently developed a new approach for contrast echocardiographic quantification of myocardial perfusion, based on brief interruptions of contrast infusion, which was designed to overcome the limitations of existing techniques. In this study, our technique was initially validated in a series of animal experiments designed to detect regional perfusion variations in vivo. Subsequently, clinical feasibility of perfusion measurements was tested.

METHODS

Regional perfusion was measured transthoracically in 6 anesthetized pigs during baseline, partial left anterior descending coronary artery occlusion, and reperfusion, and validated with fluorescent microspheres. Adenosine-induced changes in perfusion were measured in 8 healthy volunteers. In both protocols, imaging was optimized during contrast infusion (Definity). Infusion was interrupted to allow contrast clearance and images were acquired during subsequent contrast inflow. Myocardial videointensity was measured over time and peak contrast inflow rate was calculated.

RESULTS

In pigs, partial coronary occlusion resulted in a 47 +/- 23% decrease in peak contrast inflow rate in the left anterior descending coronary artery perfusion territory (P < .05), which was reversed during reperfusion, without concomitant decrease in other perfusion territories. These changes were in agreement with microspheres. In human beings, adenosine increased peak contrast inflow rate to 278 +/- 123% of baseline (P < .05).

CONCLUSION

The interruption of contrast infusion technique is a sensitive tool for accurate quantification of myocardial perfusion, which may constitute an alternative to currently used techniques.

Angiogenic growth factors and/or cellular therapy for myocardial regeneration: A comparative study

BACKGROUND

Locally delivered angiogenic growth factors and cell implantation have been proposed for patients with myocardial infarcts without a possibility of percutaneous or surgical revascularization. The goal of this study was to compare the effects of these techniques in an experimental model of myocardial infarct.

METHODS

Left ventricular myocardial infarction was created in 27 sheep by ligation of 2 coronary arteries. Three weeks after creation of the infarct, animals were randomized into 4 groups. In group 1, sheep received a culture medium injection to the infarct area (control group); group 2 underwent autologous myoblast implantation; group 3 received vascular endothelial growth factor; and group 4 received injection of both vascular endothelial growth factor and myoblasts. Evaluation included serum troponin IC levels, echocardiography (2-dimensional and color kinesis), and immunohistologic studies for quantitative analysis of capillaries (3 months after surgery).

RESULTS

Four animals died of refractory ventricular fibrillation during myocardial infarction; 2 died after surgery because of stroke and 2 because of infections. Serum troponin increased to 45.6 +/- 4.7 ng/mL at postinfarction day 2. Echocardiography at 3 months showed a significant limitation of left ventricular dilation in the cell group (57 +/- 11.1 mL) and in the cell plus vascular endothelial growth factor group (58.6 +/- 6.6 mL: control group, 74.4 +/- 11.2 mL; vascular endothelial growth factor group, 68.1 +/- 3.4 mL). Color kinesis echography showed important improvements of regional fractional area change in the cell group (from 13.6% +/- 0.8% to 21.1% +/- 1.5%) and in the cell plus vascular endothelial growth factor group (from 12.8% +/- 0.9% to 18.7% +/- 2.3%). The number of capillaries increased in the peri-infarct region of the vascular endothelial growth factor group (1036 +/- 75: control group, 785 +/- 31; cell group, 830 +/- 75; cell plus vascular endothelial growth factor group, 831 +/- 83).

CONCLUSIONS

In the cell therapy groups, regional ventricular contractility improved and heart dilatation was limited compared with either vascular endothelial growth factor or control; thus, postischemic remodeling was reduced. Angiogenesis was demonstrated in the vascular endothelial growth factor group, without improvement of ventricular function and remodeling. To improve local conditions for cell survival, further studies are warranted on prevascularization of myocardial scars with angiogenic therapy.

Assessment of left ventricular function with contrast echocardiography

Echocardiography continues to be the primary noninvasive imaging modality for the assessment of cardiac structure and function because of significant advances in ultrasound imaging technology over the last two decades, yet quantification of the LV function has remained an elusive goal. The introduction of contrast agents has represented a major advance in clinicians' ability to visualize the endocardium and to assess LV function accurately, particularly in patients who have poor acoustic windows. Ongoing and future refinements in imaging technology used with contrast enhancement have placed automated quantification of LV function on the brink of widespread clinical use.