Comparison of real-time and intermittent triggered myocardial contrast echocardiography for quantification of coronary stenosis severity and transmural perfusion gradient

Acoustic Behavior of a Reactivated, Commercially Available Ultrasound Contrast Agent

BACKGROUND

Commercially available microbubbles such as Definity contain octafluoropropane encapsulated in a lipid shell. This perfluorocarbon can be compressed into liquid nanodroplets at room temperatures and activated with transthoracic diagnostic ultrasound. The aim of this study was to determine the size range and acoustic characteristics of Definity nanodroplets (DNDs) compared with Definity microbubbles (DMBs).

METHODS

An in vitro flow system was used with a diagnostic ultrasound transducer (S5-1, iE33). DMBs were prepared using package insert instructions. DNDs were prepared by cooling DMBs in a -10°C to -15°C isopropyl alcohol bath before hand-pressurizing the solution. The formed DNDs were sized, diluted to 1% solutions, and infused continuously into a phosphate-buffered saline solution running within Silastic tubing. Acoustic intensity (AI) was compared with equivalent dilutions of DMBs at different mechanical indices (MIs) ranging from 0.2 to 1.4 (n = 6 comparisons at each MI) using real-time 56-Hz and triggered 2-Hz frame rates (FRs). A 3-cm-thick tissue-mimicking phantom was used to simulate transthoracic attenuation. In vivo transthoracic studies were performed in four normal pigs infused with 10% intravenous infusions of DMBs or DNDs at real-time and triggered end-systolic FRs to compare differences in myocardial and left ventricular cavity AI.

RESULTS

DNDs were smaller than DMBs and ranged in size from 50 to 1,000 nm. In vitro studies revealed that at an MI of 0.2 and an FR of 56 Hz, DMBs had high AI (37 ± 2 dB), but AI dropped to 25 ± 2 dB at an MI of 1.0 (P < .001, analysis of variance). In comparison, DNDs had virtually no AI at MIs of 0.2 to 0.6 at both triggered and 56-Hz FRs (1 ± 0 dB), but AI increased to 34 ± 2 dB at an MI of 1.4 using an FR of 56 Hz (P < .001 vs MI of 0.2). AI also persisted longer at 56 Hz with DNDs when using higher MIs. In vivo studies demonstrated higher myocardial AI for DNDs at higher MIs when using real-time FR, most likely from microvascular nanodroplet activation.

CONCLUSION

These data indicate significant differences in acoustic responses of the commercially available DMBs when administered as an equivalent number of DNDs. The DND formulation may render them more useful for high-MI real-time imaging and other targeted transthoracic diagnostic applications.

Contrast-Enhanced Ultrasound: A Novel Noninvasive, Nonionizing Method for the Detection of Brown Adipose Tissue in Humans

BACKGROUND

Brown adipose tissue (BAT) consumes glucose when it is activated by cold exposure, allowing its detection in humans by (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) with computed tomography (CT). The investigators recently described a novel noninvasive and nonionizing imaging method to assess BAT in mice using contrast-enhanced ultrasound (CEUS). Here, they report the application of this method in healthy humans.

METHODS

Thirteen healthy volunteers were recruited. CEUS was performed before and after cold exposure in all subjects using a continuous intravenous infusion of perflutren gas-filled lipid microbubbles and triggered imaging of the supraclavicular space. The first five subjects received microbubbles at a lower infusion rate than the subsequent eight subjects and were analyzed as a separate group. Blood flow was estimated as the product of the plateau (A) and the slope (β) of microbubble replenishment curves. All underwent (18)F-FDG PET/CT after cold exposure.

RESULTS

An increase in the acoustic signal was noted in the supraclavicular adipose tissue area with increasing triggering intervals in all subjects, demonstrating the presence of blood flow. The area imaged by CEUS colocalized with BAT, as detected by ¹⁸F-FDG PET/CT. In a cohort of eight subjects with an optimized CEUS protocol, CEUS-derived BAT blood flow increased with cold exposure compared with basal BAT blood flow in warm conditions (median Aβ = 3.3 AU/s [interquartile range, 0.5-5.7 AU/s] vs 1.25 AU/s [interquartile range, 0.5-2.6 AU/s]; P = .02). Of these eight subjects, five had greater than twofold increases in blood flow after cold exposure; these responders had higher BAT activity measured by (18)F-FDG PET/CT (median maximal standardized uptake value, 2.25 [interquartile range, 1.53-4.57] vs 0.51 [interquartile range, 0.47-0.73]; P = .02).

CONCLUSIONS

The present study demonstrates the feasibility of using CEUS as a noninvasive, nonionizing imaging modality in estimating BAT blood flow in young, healthy humans. CEUS may be a useful and scalable tool in the assessment of BAT and BAT-targeted therapies.

Cocaine-induced vasoconstriction in the human coronary microcirculation: new evidence from myocardial contrast echocardiography

BACKGROUND

Cocaine is a major cause of acute coronary syndrome, especially in young adults; however, the mechanistic underpinning of cocaine-induced acute coronary syndrome remains limited. Previous studies in animals and in patients undergoing cardiac catheterization suggest that cocaine constricts coronary microvessels, yet direct evidence is lacking.

METHODS AND RESULTS

We used myocardial contrast echocardiography to test the hypothesis that cocaine causes vasoconstriction in the human coronary microcirculation. Measurements were performed at baseline and after a low, nonintoxicating dose of intranasal cocaine (2 mg/kg) in 10 healthy cocaine-naïve young men (median age, 32 years). Postdestruction time-intensity myocardial contrast echocardiography kinetic data were fit to the equation y=A(1-e(-βt)) to quantify functional capillary blood volume (A), microvascular flow velocity (β), and myocardial perfusion (A×β). Heart rate, mean arterial pressure, and left ventricular work (2-dimensional echocardiography) were measured before and 45 minutes after cocaine. Cocaine increased mean arterial pressure (by 14±2 mm Hg [mean±SE]), heart rate (by 8±3 bpm), and left ventricular work (by 50±18 mm Hg·mL(-1)·bpm(-1)). Despite the increases in these determinants of myocardial oxygen demand, myocardial perfusion decreased by 30% (103.7±9.8 to 75.9±10.8 arbitrary units [AU]/s; P<0.01) mainly as a result of decreased capillary blood volume (133.9±5.1 to 111.7±7.7 AU; P<0.05) with no significant change in microvascular flow velocity (0.8±0.1 to 0.7±0.1 AU).

CONCLUSIONS

In healthy cocaine-naïve young adults, a low-dose cocaine challenge evokes a sizeable decrease in myocardial perfusion. Moreover, the predominant effect is to decrease myocardial capillary blood volume rather than microvascular flow velocity, suggesting a specific action of cocaine to constrict terminal feed arteries.

The value of quantitative real-time myocardial contrast echocardiography for detection of angiographically significant coronary artery disease

BACKGROUND

Real-time (RT) myocardial contrast echocardiography (MCE) is a novel method for the assessment of regional myocardial perfusion. We sought to evaluate the feasibility and diagnostic accuracy of quantitative RT-MCE in predicting significant coronary stenosis, with reference to quantitative coronary angiography.

HYPOTHESIS

RT-MCE can identify anatomically significant coronary artery stenosis in selected patients. RT-MCE is probably an effective method for detection of angiographically significant coronary artery stenosis.

METHODS

Thirty-five patients (mean age, 59.94 ± 10.63 years; 25 males) scheduled for coronary angiography underwent RT-MCE at rest, and shortly afterward underwent gated single-photon emission computed tomography (gated-SPECT). Coronary angiography was performed within 1 week after RT-MCE in all patients. The observing indexes included the images of RT-MCE that were analyzed quantitatively from microbubble replenishment curves for myocardial perfusion by using the Q-Lab software. The sensitivity and specificity of RT-MCE for quantitative detection of coronary artery disease (CAD) were obtained. The receiver operator characteristic (ROC) curves were used to assess the differences of accuracy in ischemic segments with A, β and A × β respectively. The sensitivity and specificity of gated-SPECT and RT-MCE for assessment of CAD were calculated using a 4-score method.

RESULTS

A total of 513 segments among 595 segments in 35 patients were obtained. The cutoffs for A, β and A × β were 4.58, 0.64, and 2.73, and the sensitivity and specificity of quantitative RT-MCE for detection of CAD were 86.0%, 80.2%, 88.9%, and 84.1%, 64.6%, 79.9%, respectively. Meanwhile, the sensitivity and specificity of semiquantitative analysis for assessment of CAD were 66.7% and 61.8%. The ROC curve area of A and A × β was 0.91 and 0.90 in the middle segments. The ROC area of A was 0.52 in the base segments. The sensitivity and specificity of gated-SPECT for assessment of CAD were 84.8% and 82.7%, respectively. The sensitivity of multi-indexes RT-MCE increased. The sensitivity was 89.1%, 90.4%, and 96.3% by A + β, A + A × β, and β + A × β.

CONCLUSIONS

Quantitative RT-MCE is an effective method for the detection of coronary artery stenosis. Quantitative RT-MCE is segmented for assessment to ischemic myocardium. RT-MCE with multi-indexes has a valuable application for assessment of CAD surpassing SPECT.

Spatial distribution of ultrasound targeted microbubble destruction increases cardiac transgene expression but not capillary permeability

Ultrasound targeted microbubble destruction (UTMD) has evolved as a promising tool for organ specific gene and drug delivery. Using DNA-loaded microbubbles, cardiac transfection has been shown to be feasible. However, two-dimensional properties of the ultrasound beam limit cardiac transgene expression to the focal zone, thus, reducing its potential therapeutic effect. The aim of this study was to test if spatial distribution of ultrasound targeted microbubble destruction in the heart could lead to augmented transgene expression or increased capillary permeability. Lipid microbubbles containing plasmids with a luciferase transgene were used to target rat hearts. The diagnostic ultrasound probe was fixed in a mid-short axis view with a gel stand-off between the chest and probe. Ultrasound (1.3 MHz) with a mechanical index of 1.6 was intermittently applied to rats during microbubble infusion. Rats were randomized to either stay in that position or move horizontally in a cranio-caudal direction (3 mm sweep) relative to the ultrasound probe during UTMD. After 4 days, organs were harvested and analyzed for reporter gene expression. Another group of rats received Evans Blue, followed by UTMD with unloaded microbubbles. Again, rats were randomized into a static or moving group. Hearts were harvested to evaluate extravasation of Evans Blue. Moving rats in a cranio-caudal direction significantly increased transgene expression by 19-fold in the anterior heart, by sixfold in the posterior heart and by 32-fold in the apex. Interestingly, Evans Blue extravasation was not augmented in the moving group. Spatial distribution of UTMD may increase transgene expression due to sonication of larger areas in the heart. In contrast, capillary permeability does not increase, indicating less capillary damage.

Quantitative myocardial contrast echocardiography during pharmacological stress for diagnosis of coronary artery disease: a systematic review and meta-analysis of diagnostic accuracy studies

AIMS

We conducted a meta-analysis to evaluate the accuracy of quantitative stress myocardial contrast echocardiography (MCE) in coronary artery disease (CAD).

METHODS AND RESULTS

Database search was performed through January 2008. We included studies evaluating accuracy of quantitative stress MCE for detection of CAD compared with coronary angiography or single-photon emission computed tomography (SPECT) and measuring reserve parameters of A, beta, and Abeta. Data from studies were verified and supplemented by the authors of each study. Using random effects meta-analysis, we estimated weighted mean difference (WMD), likelihood ratios (LRs), diagnostic odds ratios (DORs), and summary area under curve (AUC), all with 95% confidence interval (CI). Of 1443 studies, 13 including 627 patients (age range, 38-75 years) and comparing MCE with angiography (n = 10), SPECT (n = 1), or both (n = 2) were eligible. WMD (95% CI) were significantly less in CAD group than no-CAD group: 0.12 (0.06-0.18) (P < 0.001), 1.38 (1.28-1.52) (P < 0.001), and 1.47 (1.18-1.76) (P < 0.001) for A, beta, and Abeta reserves, respectively. Pooled LRs for positive test were 1.33 (1.13-1.57), 3.76 (2.43-5.80), and 3.64 (2.87-4.78) and LRs for negative test were 0.68 (0.55-0.83), 0.30 (0.24-0.38), and 0.27 (0.22-0.34) for A, beta, and Abeta reserves, respectively. Pooled DORs were 2.09 (1.42-3.07), 15.11 (7.90-28.91), and 14.73 (9.61-22.57) and AUCs were 0.637 (0.594-0.677), 0.851 (0.828-0.872), and 0.859 (0.842-0.750) for A, beta, and Abeta reserves, respectively.

CONCLUSION

Evidence supports the use of quantitative MCE as a non-invasive test for detection of CAD. Standardizing MCE quantification analysis and adherence to reporting standards for diagnostic tests could enhance the quality of evidence in this field.

Detection of subendocardial ischemia in the left anterior descending coronary artery territory with real-time myocardial contrast echocardiography during dobutamine stress echocardiography

OBJECTIVES

The purpose of this study was to test whether the transmural delineation of myocardial perfusion during dobutamine stress imaging with real-time myocardial contrast echocardiography (RTMCE) might permit visualization of dobutamine-induced subendocardial ischemia.

BACKGROUND

Significant coronary artery disease can be present despite normal transmural wall thickening (WT) responses during dobutamine stress echocardiography (DSE). One potential reason is dobutamine-induced recruitment of epicardial WT in the presence of subendocardial ischemia.

METHODS

Myocardial perfusion and WT were examined with RTMCE during DSE with a continuous infusion of ultrasound contrast in 94 patients with normal resting WT. Fifty-five of the patients had a >50% diameter stenosis in the left anterior descending coronary artery (LAD). The WT was visually assessed by a blinded reviewer at 2 time periods: initially after a high mechanical index impulse before myocardial contrast replenishment (MCR), and again during MCR. Subendocardial %WT was measured during MCR, if a subendocardial perfusion defect was visually evident, whereas transmural WT was quantified on the pre-MCR images.

RESULTS

Fifty patients (91%) with LAD stenoses exhibited a myocardial contrast defect at peak stress, with 45 defects being subendocardial. Transmural WT pre-MCR appeared normal in 35 of the 45 patients with subendocardial perfusion defects (78%). However, a subendocardial WT abnormality was apparent during MCR in 18 of these 35 patients, even though transmural WT was not different from the 17 patients with normal subendocardial WT (33 +/- 15% vs. 36 +/- 14%). Quantitative measurements of WT within the subendocardium were significantly less in the patients with visually evident subendocardial WT abnormalities, when compared with those who seemed to have normal WT during MCR (17 +/- 8% vs. 25 +/- 10%, p < 0.01).

CONCLUSIONS

In patients with significant LAD disease, RTMCE during DSE detects subendocardial ischemia even when transmural WT appears normal. Real-time myocardial contrast echocardiography should be the preferred ultrasound imaging method when using contrast to detect coronary artery disease during DSE.

Evaluation and Optimization of Real-Time Perfusion Imaging Using Multiple Ultrasound Systems With Imagify Microspheres

Current commercially available ultrasound systems have proprietary contrast-specific imaging modes to evaluate myocardial contrast enhancement (MCE). Each of these modes uses a different pulsing scheme and has unique system terminology and a proprietary name. The aim of this study was to determine optimal system settings and MCE duration using Imagify (perflubutane polymer microspheres), a new ultrasound imaging agent undergoing development for perfusion stress echocardiography to detect coronary artery disease. Thirty-nine patients were enrolled. Four ultrasound systems with real-time, low mechanical index (nonlinear, multi-pulse) modes were evaluated. Optimal MCE settings were determined qualitatively in the apical views through systematic adjustment of multiple settings while maintaining a frame rate consistent with stress echocardiography to produce high-intensity (bright-hyperechoic), transmural myocardial enhancement. When using the clinical dose of Imagify during real-time imaging, the optimized settings for three ultrasound systems allowed prolonged, clinically useful MCE with a mean duration of 9.5 minutes.

Real Time Myocardial Contrast Echocardiography During Supine Bicycle Stress and Continuous Infusion of Contrast Agent. Cutoff Values for Myocardial Contrast Replenishment Discriminating Abnormal Myocardial Perfusion

BACKGROUND

Myocardial contrast echocardiography (MCE) is a new imaging modality for diagnosing coronary artery disease (CAD).

OBJECTIVE

The aim of our study was to evaluate feasibility of qualitative myocardial contrast replenishment (RP) assessment during supine bicycle stress MCE and find out cutoff values for such analysis, which could allow accurate detection of CAD.

METHODS

Forty-four consecutive patients, scheduled for coronary angiography (CA) underwent supine bicycle stress two-dimensional echocardiography (2DE). During the same session, MCE was performed at peak stress and post stress. Ultrasound contrast agent (SonoVue) was administered in continuous mode using an infusion pump (BR-INF 100, Bracco Research). Seventeen-segment model of left ventricle was used in analysis. MCE was assessed off-line in terms of myocardial contrast opacification and RP. RP was evaluated on the basis of the number of cardiac cycles required to refill the segment with contrast after its prior destruction with high-power frames. Determination of cutoff values for RP assessment was performed by means of reference intervals and receiver operating characteristic analysis. Quantitative CA was carried out using CAAS system.

RESULTS

MCE could be assessed in 42 patients. CA revealed CAD in 25 patients. Calculated cutoff values for RP-analysis (peak-stress RP >3 cardiac cycles and difference between peak stress and post stress RP >0 cardiac cycles) provided sensitive (88%) and accurate (88%) detection of CAD. Sensitivity and accuracy of 2DE were 76% and 79%, respectively.

CONCLUSIONS

Qualitative RP-analysis based on the number of cardiac cycles required to refill myocardium with contrast is feasible during supine bicycle stress MCE and enables accurate detection of CAD.

Three-Dimensional Echocardiographic Evaluation of Myocardial Perfusion

One of the most intriguing developments in ultrasound imaging of the heart was the use of contrast media to assess myocardial perfusion, which sparked tremendous interest and over the years generated a significant body of research. Although most published work has been based on the use of contrast for 2D perfusion imaging, there are a few recent studies aimed at exploring the idea of 3D assessment of myocardial perfusion, which has the potential to overcome many of the limitations of the 2D methodology. We provide a brief overview of the 2D work that provided the scientific basis for the emerging 3D methodology and discuss the unique features and promises as well as the challenges posed by this novel approach.

Infarct Size Assessment in Mice

Genetically modified mice are used extensively in models of ischemia reperfusion (I/R) and nonreperfused myocardial infarction (MI) to gain insights into pathways involved in these pathologies. Echocardiography is an ideal noninvasive tool to serially monitor the cardiac murine phenotype. The present review details the surgical aspects of I/R and MI models and the measurement of MI size by pathology techniques and the input of echocardiographic techniques including the extent of wall motion abnormality and of perfusion defects using myocardial contrast echocardiography in the assessment of murine area at risk and MI size.

Myocardial Contrast Echocardiography Evolving as a Clinically Feasible Technique for Accurate, Rapid, and Safe Assessment of Myocardial Perfusion

Intravenous myocardial contrast echocardiography (MCE) is a recently developed technique for assessment of myocardial perfusion. Up to now, many studies have demonstrated that the sensitivity and specificity of qualitative assessment of myocardial perfusion by MCE in patients with acute and chronic ischemic heart disease are comparable with other techniques such as cardiac scintigraphy and dobutamine stress echocardiography. Furthermore, quantitative parameters of myocardial perfusion derived from MCE correlate well with the current clinical standard for this purpose, positron emission tomography. Myocardial contrast echocardiography provides a promising and valuable tool for assessment of myocardial perfusion. Although MCE has been primarily performed for medical research, its implementation in routine clinical care is evolving. This article is intended to give an overview of the current status of MCE.

Adenosine myocardial contrast echo in intermediate severity coronary stenoses: a prospective two-center study

BACKGROUND

We sought to evaluate the role of adenosine myocardial contrast echocardiography (MCE) for the determination of functional relevance of coronary stenoses with intermediate angiographic severity and compared the results to single photon imaging (SPECT). We hypothezised that sole assessment of myocardial blood volume changes during adenosine on MCE would indicate functional stensosis relevance when accompanied by increased myocardial oxygen consumption (MVO2).

METHODS

Fifty-seven patients with >or=1 coronary stenosis underwent adenosine MCE (ultraharmonic imaging) and exercise SPECT. On MCE, myocardial blood volume was assessed and constant or increased myocardial opacification during adenosine coupled with increased MVO2 was defined as normal and decreased opacification as abnormal.

RESULTS

Rate-pressure product significantly increased during adenosine in all patients due to reflex tachycardia following mild hypotension, indicative of increased MVO2. Concordance between MCE and SPECT for the detection of reversible myocardial perfusion defects was 89% (kappa = 0.83). Comparison of regions between rest and during adenosine as opposed to comparison to remote regions of the same stage was important for accurate assessment because concordance betweenn MCE and SPECT was less on separate assessment at rest (73%, kappa = 0.40) compared to stress (91%, kappa = 0.81, P < 0.05) mainly due to territories scored normal on SPECT and abnormal on MCE.

CONCLUSIONS

Assessment of myocardial blood volume changes during adenosine using MCE can be used for the determination of the functional relevance of coronary stenoses of intermediate angiographic severity if MVO2 is increased during adenosine.

Corrected quantification method to determine myocardial blood flow using real-time myocardial contrast echocardiography

BACKGROUND

The quantitative assessment of myocardial blood flow using real-time myocardial contrast echocardiography is based on a replenishment of bubble density after bubble destruction by high-power ultrasound exposure (burst). However, all microbubbles in the myocardial vessels are not necessarily completely destroyed, which results in unreliable data of the replenishment curve analysis.

OBJECTIVE

The aim of this study was to propose a corrected equation for the replenishment curve analysis based on the hypothesis in which the initial intensity just after burst should be equivalent to the baseline intensity before contrast infusion, and to examine whether the regional difference of myocardial perfusion parameters could be minimized by the use of corrected equation of replenishment curve.

METHODS

Myocardial opacification of the left ventricular short-axis view was observed using low mechanical index during infusion of Definity in open-chest dogs. Bubble destruction was set in two ways, either high (0 dB) or low (-11 dB) power burst. The videointensity (VI) of baseline before contrast infusion (f-value) was assumed as an initial intensity after complete bubble destruction. Changes of the VI after burst were fitted to both exponential functions: y = a (1 - e(-beta t)) + c (conventional equation) and y = a (1 - e(-beta(t - d))) + f (corrected equation). The c-value was the measured VI just after burst. The d-value was the hypothetical time of onset of the replenishment curve if all bubbles were completely destroyed. The plateau VI was defined as the A-value, which was the sum of a- and c-values or a- and f-values, respectively. The maximal difference of beta-value among myocardial regions was calculated by either equation.

RESULTS

The A-value was almost identical in either equation regardless of the acoustic power of burst. The beta-value by the conventional equation was higher after the incomplete burst than that after complete burst (0.45 +/- 0.12 vs 0.54 +/- 0.16). By contrast, the beta-value calculated by the corrected equation was almost identical despite complete or incomplete bursts (0.46 +/- 0.13 vs 0.48 +/- 0.15). The maximal difference of beta-value was significantly reduced by the use of corrected equation (conventional 0.24 +/- 0.14 vs corrected 0.18 +/- 0.10).

CONCLUSIONS

Variation of beta-value because of the incomplete bubble destruction can be minimized by using the corrected equation: y = a (1 - e(-beta(t - d))) + f. Further, the corrected equation can improve the regional variation of beta-value.

Clinical utility of contrast-enhanced echocardiography

Over the past three decades, echocardiography has become a major diagnostic tool in the arsenal of clinical cardiology for real-time imaging of cardiac dynamics. More and more, cardiologists' decisions are based on images created from ultrasound wave reflections. From the time ultrasound imaging technology provided the first insight into a human heart, our diagnostic capabilities have increased exponentially as a result of our growing knowledge and developing technologies. One of the most intriguing developments that brought about a decade-long combination of expectations and disappointments was the introduction of echocardiographic contrast agents. Despite repeated waves of controversy regarding the readiness of this technology for clinical use, it has overcome multiple hurdles and currently provides useful clinical information that helps cardiologists to diagnose heart disease accurately. Since the initial reports on the use of ultrasound contrast media such as agitated saline or renografin, the major advances in the field of contrast echocardiography have included (1) the development of stable perfluorocarbon-filled microbubbles, frequently referred to as second-generation contrast agents; and (2) the development of contrast-targeted nonlinear imaging modes, such as harmonic imaging, pulse inversion, and power modulation, which allow consistent real-time visualization of these agents. These contrast agents in conjunction with the new imaging technology constitute powerful tools that improve our ability to evaluate left ventricular function and myocardial perfusion, and allow differential diagnosis of thrombi and intravascular masses. In this manuscript, we briefly review some of the literature that has provided the scientific basis for the use of echocardiographic contrast agents in the context of these important variables.

Detection of coronary artery disease using real-time myocardial contrast echocardiography: a comparison with dual-isotope resting thallium-201/stress technectium-99m sestamibi single-photon emission computed tomography

Real-time myocardial contrast echocardiography (MCE) has the potential to evaluate myocardial perfusion and wall motion (WM) simultaneously. The purposes of this study were to correlate the diagnostic value of MCE with radionuclide single-photon emission computed tomography (SPECT), and to assess the sensitivity and specificity of real-time MCE in detecting coronary artery disease (CAD). Seventy patients with clinically suspected CAD underwent MCE and SPECT at baseline and after dipyridamole infusion. Segmental perfusion with MCE using low mechanical index after 0.3-0.4-ml bolus injections of perfluorocarbon exposed sonicated dextrose albumin solution was performed. All patients had a dual-isotope (rest thallium-201, stress sestamibi) study performed both at baseline and after dipyridamole infusion, and 40 patients had subsequent quantitative coronary angiography. Abnormalities were noted in 27 patients (38.6%) by MCE, in 29 patients (41.4%) by WM analysis, and in 30 patients (42.9%) by SPECT imaging. When MCE and WM analysis were combined, the agreement with SPECT imaging improved from 75.7% (Kappa = 0.50) to 82.0% (Kappa = 0.62). In 40 patients (120 territories) who underwent coronary angiography, good perfusion concordance was achieved for the left anterior descending and left circumflex arteries, and was fair for the right coronary arteries. Compared with quantitative angiography, there was no difference in sensitivity, specificity, and accuracy in detecting significant CAD among the three modalities. The combination of MCE and WM had a better sensitivity (84%), specificity (93.3%), and accuracy (87.5%) than the MCE and WM analysis alone. However, the difference did not reach statistical significance. Real-time MCE has a good agreement with SPECT imaging for detecting CAD. The combination of MCE and WM appears to have higher sensitivity, specificity, and accuracy in detecting CAD than either technique alone.

Relationship between myocardial perfusion and dysfunction in diabetic cardiomyopathy: a study of quantitative contrast echocardiography and strain rate imaging

OBJECTIVE

To use quantitative myocardial contrast echocardiography (MCE) and strain rate imaging (SRI) to assess the role of microvascular disease in subclinical diabetic cardiomyopathy.

METHODS

Stress MCE and SRI were performed in 48 patients (22 with type II diabetes mellitus (DM) and 26 controls), all with normal left ventricular systolic function and no obstructive coronary disease by quantitative coronary angiography. Real-time MCE was acquired in three apical views at rest and after combined dipyridamole-exercise stress. Myocardial blood flow (MBF) was quantified in the 10 mid- and apical cardiac segments at rest and after stress. Resting peak systolic strain rate (SR) and peak systolic strain (epsilon) were calculated in the same 10 myocardial segments.

RESULTS

The DM and control groups were matched for age, sex and other risk factors, including hypertension. The DM group had higher body mass index and left ventricular mass index. Quantitative SRI analysis was possible in all patients and quantitative MCE in 46 (96%). The mean epsilon, SR and MBF reserve were all significantly lower in the DM group than in controls, with diabetes the only independent predictor of each parameter. No correlation was seen between MBF and SR (r = -0.01, p = 0.54) or between MBF and epsilon (r = -0.20, p = 0.20).

CONCLUSIONS

Quantitative MCE shows that patients with diabetes but no evidence of obstructive coronary artery disease have impaired MBF reserve, but abnormal transmural flow and subclinical longitudinal myocardial dysfunction are not related.

Quantitative Adenosine Real-time Myocardial Contrast Echocardiography for Detection of Angiographically Significant Coronary Artery Disease

BACKGROUND

Real-time (RT) myocardial contrast echocardiography (MCE) is a novel method for assessment of regional myocardial perfusion. We sought to evaluate the feasibility and diagnostic accuracy of quantitative adenosine RT MCE in predicting significant coronary stenoses, with reference to quantitative coronary angiography.

METHODS

Low-power RT MCE was performed in 43 patients scheduled for quantitative coronary angiography. Peak signal intensity (A), rate of signal intensity increase (beta), A x beta (myocardial blood flow), and their hyperemic reserves were estimated and compared with angiographic data.

RESULTS

The feasibility of quantitative stress RT MCE covering all coronary territories was 77% of patients with adequate baseline image quality. At rest we found no significant difference for any of the perfusion parameters between the normal and stenosed coronary territories. During hyperemia, beta and A x beta, but not A, increased significantly in normal coronary territories. In the regions subtended by significantly stenosed arteries, there were no significant increases in beta and A x beta. Receiver operating characteristic curves indicated that beta- and A x beta-reserves, but not A-reserve, could be sensitive parameters for detecting flow-limiting coronary stenosis in selected patients, particularly if significant left anterior descending coronary artery disease was involved.

CONCLUSION

Quantitative assessment of myocardial blood flow and its velocity reserve by RT MCE has the potential to detect significant coronary artery disease, but because of imaging and technical problems it is not yet robust enough for clinical use in unselected patients.

Quantification of Myocardial Perfusion Using Intravenous Myocardial Contrast Echocardiography in Healthy Volunteers: Comparison with Positron Emission Tomography

BACKGROUND

Intravenous myocardial contrast echocardiography (ivMCE) has the potential to evaluate myocardial contraction and perfusion simultaneously. The purpose of this study was to assess quantification of myocardial blood flow (MBF) using ivMCE and to compare this with MBF as measured with positron emission tomography (PET).

METHODS

A total of 16 healthy volunteers underwent ivMCE using power pulse inversion and contrast agent microbubbles at rest and during pharmacologically induced vasodilation. Microbubble destruction was achieved with a burst of high-energy ultrasound, followed by imaging of contrast replenishment with low-energy ultrasound. Regions of interest were drawn and time intensity curves were calculated that were fitted to a monoexponential function. An estimate of MBF (perfusion estime) was calculated as the product of the plateau value A and the exponential beta describing the replenishment curve. MBF was measured with PET using oxygen-15-labeled water at rest and during adenosine stress.

RESULTS

Significant correlations were found between MBF as measured with PET and perfusion estimate as measured with ivMCE in the left anterior descending coronary artery (r = 0.87, P < .01), right coronary artery (r = 0.66, P < .01), and left circumflex artery (r = 0.75, P < .01) territories. Heterogeneity, however, was significantly larger for ivMCE (coefficient of variation 32 +/- 15%) than for PET (9 +/- 6%) measurements (P < .01).

CONCLUSION

Perfusion parameters as measured with ivMCE correlated with PET-derived MBF, but associated heterogeneity was significantly larger. Currently, this heterogeneity precludes true quantification of MBF using ivMCE.

Real-time myocardial perfusion imaging for pharmacologic stress testing: added value to single photon emission computed tomography

BACKGROUND

Little is known about the incremental value of real-time myocardial contrast echocardiography (MCE) as an adjunct to pharmacologic stress testing. This study was performed to evaluate the diagnostic value of MCE to detect abnormal myocardial perfusion by technetium Tc 99m sestamibi-single photon emission computed tomography (SPECT) and anatomically significant coronary artery disease (CAD) by angiography.

METHODS

Myocardial contrast echocardiography was performed at rest and during vasodilator stress in consecutive patients (N = 120) undergoing SPECT imaging for known or suspected CAD. Myocardial opacification, wall motion, and tracer uptake were visually analyzed in 12 myocardial segments by 2 pairs of blinded observers. Concordance between the 2 methods was assessed using the kappa statistic.

RESULTS

Of 1356 segments, 1025 (76%) were interpretable by MCE, wall motion, and SPECT. Sensitivity of wall motion was 75%, specificity 83%, and accuracy 81% for detecting abnormal myocardial perfusion by SPECT (kappa = 0.53). Myocardial contrast echocardiography and wall motion together yielded significantly higher sensitivity (85% vs 74%, P < .05), specificity of 83%, and accuracy of 85% (kappa = 0.64) for the detection of abnormal myocardial perfusion. In 89 patients who underwent coronary angiography, MCE and wall motion together yielded higher sensitivity (83% vs 64%, P < .05) and accuracy (77% vs 68%, P < .05) but similar specificity (72%) compared with SPECT for the detection of high-grade, stenotic (> or = 75%) coronary lesions.

CONCLUSION

Assessment of myocardial perfusion adds value to conventional stress echocardiography by increasing its sensitivity for the detection of functionally abnormal myocardial perfusion. Myocardial contrast echocardiography and wall motion together provide higher sensitivity and accuracy for detection of CAD compared with SPECT.

Heterogeneity of Myocardial Perfusion in Distal Coronary Embolism with Different Particle Sizes

BACKGROUND

We hypothesized that altered myocardial perfusion distribution patterns could be seen with coronary distal emboli of different particle sizes using myocardial contrast echocardiography.

METHODS

In 16 open-chest anesthetized dogs, microsphere suspensions of 9 or 500 microm in diameter were injected into the left anterior descending coronary artery until the mean left anterior descending coronary artery flow rate was reduced to less than 30% of baseline flow. During baseline conditions and after maximal embolization, real-time myocardial contrast echocardiography was performed by intravenous infusion of an echocontrast agent.

RESULTS

In animals infused with 9-microm microspheres, a transmural perfusion defect was seen at the time of maximal embolization. In contrast, in animals infused with 500-microm microspheres, a subendocardial perfusion defect was observed.

CONCLUSIONS

The particle size of coronary distal emboli affects myocardial perfusion distribution.

Quantitative Analysis of Myocardial Perfusion in Rats by Contrast Echocardiography

BACKGROUND

The ability to assess myocardial perfusion in small animals is important, especially to investigate models of myocardial ischemia. Myocardial perfusion is usually assessed by postmortem techniques, eliminating the possibility of follow-up. We sought to evaluate whether contrast echocardiography was able to quantify myocardial perfusion in rats.

METHODS

Twenty-four rats divided in 3 groups (sham-operated, and 8 and 21 days after left anterior descending coronary artery stenosis) underwent myocardial contrast echocardiography using intermittent triggered imaging. Peak plateau intensity and slope of refilling were compared with myocardial blood flow achieved with fluorescent microspheres.

RESULTS

High-quality images were easily obtained for each experiment. Close correlation was found between myocardial contrast echocardiography and myocardial blood flow, especially for measurements of peak plateau intensity x slope of refilling relative to the control area (y = 1.15 x -0.14, r = 0.86).

CONCLUSION

Quantification of myocardial perfusion in rats is feasible by myocardial contrast echocardiography using intermittent triggered imaging.

Potential clinical applications of myocardial contrast echocardiography in evaluating myocardial perfusion in coronary artery disease

Myocardial contrast echocardiography (MCE) is a relatively new technique that uses microbubbles to produce myocardial opacification. Recent advances in echocardiography have resulted in improved detection of microbubbles within the myocardium allowing combined acquisition of function and perfusion data, thus making MCE suitable for bedside use. Regardless of the imaging modality chosen or the type of stress used, MCE detects changes developing in the coronary microcirculation, providing important information for the evaluation of severity of coronary artery disease and for the detection of viable myocardial tissue in acute or chronic coronary artery disease.

Comparison of specificity of quantitative myocardial contrast echocardiography for diagnosis of coronary artery disease in patients with versus without diabetes mellitus

Impaired coronary flow reserve is widely reported in diabetes mellitus (DM) but its effect on myocardial contrast echocardiography (MCE) is unclear. We sought to identify whether DM influences the accuracy of qualitative and quantitative assessment of coronary artery disease (CAD) using MCE in 83 patients who underwent coronary angiography (60 men, 27 with DM; 56 +/- 11 years;). Destruction replenishment imaging was performed at rest and after combined dipyridamole-exercise stress testing. Ischemia was identified by the development of new wall motion abnormalities, qualitative MCE (new perfusion defects apparent 1 second after flash during hyperemia), and quantitative MCE (myocardial blood flow reserve <2.0 in the anterior circulation). Qualitative and quantitative assessment of perfusion was feasible in 100% and 92% of patients, respectively. Significant left anterior descending coronary stenosis (>50% by quantitative angiography) was present in 28 patients (including 8 with DM); 55 patients had no CAD (including 19 with DM). The myocardial blood flow reserve was reduced in patients with coronary stenosis compared with those with no CAD (1.6 +/- 1.1 vs 3.8 +/- 2.5, p <0.001). Among patients with no CAD, those with DM had an impaired flow reserve compared with control patients without DM (2.4 +/- 1.0 vs 4.5 +/- 2.8, p = 0.003). In conclusion, DM significantly influenced the quantitative, but not the qualitative, assessment of MCE, with a marked reduction in specificity in patients with DM.

Quantification of resting myocardial blood flow velocity in normal humans using real-time contrast echocardiography. A feasibility study

Background

Real-time myocardial contrast echocardiography (MCE) is a novel method for assessing myocardial perfusion. The aim of this study was to evaluate the feasibility of a very low-power real-time MCE for quantification of regional resting myocardial blood flow (MBF) velocity in normal human myocardium.

Methods

Twenty study subjects with normal left ventricular (LV) wall motion and normal coronary arteries, underwent low-power real-time MCE based on color-coded pulse inversion Doppler. Standard apical LV views were acquired during constant IV. infusion of SonoVue^®. Following transient microbubble destruction, the contrast replenishment rate (β), reflecting MBF velocity, was derived by plotting signal intensity vs. time and fitting data to the exponential function; y (t) =A (1-e^-β(t-t0)) + C.

Results

Quantification was feasible in 82%, 49% and 63% of four-chamber, two-chamber and apical long-axis view segments, respectively. The LAD (left anterior descending artery) and RCA (right coronary artery) territories could potentially be evaluated in most, but contrast detection in the LCx (left circumflex artery) bed was poor. Depending on localisation and which frames to be analysed, mean values of were 0.21–0.69 s^-1, with higher values in medial than lateral, and in basal compared to apical regions of scan plane (p = 0.03 and p < 0.01). Higher β-values were obtained from end-diastole than end-systole (p < 0.001), values from all-frames analysis lying between.

Conclusion

Low-power real-time MCE did have the potential to give contrast enhancement for quantification of resting regional MBF velocity. However, the technique is difficult and subjected to several limitations. Significant variability in β suggests that this parameter is best suited for with-in patient changes, comparing values of stress studies to baseline.

Fr�hdiagnostik der funktionell relevanten koronaren Herzerkrankung

In cases of stable or to a large extent symptom-free coronary heart disease (CHD) and atypical symptomatology, the indication for diagnostic cardiac catheterization is first confirmed by noninvasive diagnostics of ischemia. This can be carried out either with ergometric stress tests or imaging procedures in combination with ergometric or pharmacological stress. Myocardial scintigraphy and stress echocardiography are established techniques and to an increasing extent stress magnetic resonance imaging (MRI). In addition to sensitivity in providing evidence for ischemia, technical improvements in computed tomography (CT) and MRI have opened up new possibilities for visualizing coronary vessels and vascular wall morphology. While CT coronary angiography with its high spatial resolution is on the threshold of clinical application for selected patients, MRI has the potential for furnishing information on wall movement analysis, perfusion, coronary flow measurement, and plaque characterization to become the future cardiovascular "all-round examination".

Adenosine triphosphate stress myocardial contrast echocardiography detects coronary artery stenosis with greater sensitivity than wall-motion abnormality measurements

BACKGROUND

Although stress myocardial contrast echocardiography (MCE) can be used to detect coronary stenosis, its efficacy relative to other methods, such as detection of wall-motion abnormalities, remains unknown. Thus, the goal of this study was to compare the sensitivity of MCE versus wall-motion abnormality detection in the assessment of coronary artery stenosis.

METHOD

Nine dogs with severe but nonflow limiting stenosis in the circumflex coronary artery underwent evaluation with real-time MCE along the short-axis view during infusion of Optison. The equation of y = a (1 - e -betat ) + c, which fits the replenishment curve of MCE, was calculated in the midseptum (normal region) and in the lateral wall (ischemic region) before and during adenosine triphosphate infusion. Wall-motion abnormalities were also evaluated by visual assessment and by measurement of wall thickening.

RESULTS

Area under the receiver operating characteristic curve in beta- and A x beta-value, and percent wall thickening, was 0.963, 0.963, and 0.889, respectively, indicating that the diagnostic accuracy for detecting the coronary artery stenosis by real-time MCE was higher than that by the wall-motion assessment.

CONCLUSION

Real-time MCE has higher sensitivity in detecting coronary stenosis during adenosine triphosphate stress test when compared with wall-motion assessment.

Detection of peripheral vascular stenosis by assessing skeletal muscle flow reserve

OBJECTIVES

We sought to determine whether the severity of peripheral arterial disease (PAD) can be assessed by measuring blood flow reserve in limb skeletal muscle with contrast-enhanced ultrasound (CEU).

BACKGROUND

Noninvasive imaging of distal limb perfusion could improve management of patients with PAD by evaluating the impact of large and small vessel disease, and collateral flow.

METHODS

In 12 dogs, blood flow in the quadriceps femoris was measured by CEU at rest and during either electrostimulated contractile exercise or adenosine infusion. Femoral artery blood flow was measured by Doppler ultrasound. Studies were performed in the absence and presence of either moderate or severe stenosis (pressure gradient of 10 to 20 mm Hg and >20 mm Hg, respectively).

RESULTS

Resting femoral artery blood flow progressively decreased with stenosis severity, while resting skeletal muscle flow was reduced only with severe stenosis (52 +/- 21% of baseline, p < 0.05), indicating the presence of collateral flow. Skeletal muscle flow reserve during contractile exercise or adenosine decreased incrementally with increasing stenosis severity (p < 0.01). The stenotic pressure gradient correlated with skeletal muscle flow reserve for exercise and adenosine (r = 0.70 for both, p < 0.01).

CONCLUSIONS

Contrast-enhanced ultrasound of limb skeletal muscle can be used to assess the severity of PAD by measuring muscle flow reserve during either contractile exercise or pharmacologic vasodilation. Unlike currently used methods, this technique may provide a measure of the physiologic effects of large- and small-vessel PAD, and the influence of collateral perfusion.

Combination of contrast with stress echocardiography: a practical guide to methods and interpretation

Contrast echocardiography has an established role for enhancement of the right heart Doppler signals, the detection of intra-cardiac shunts, and most recently for left ventricular cavity opacification (LVO). The use of intravenously administered micro-bubbles to traverse the myocardial microcirculation in order to outline myocardial viability and perfusion has been the source of research studies for a number of years. Despite the enthusiasm of investigators, myocardial contrast echocardiography (MCE) has not attained routine clinical use and LV opacification during stress has been less widely adopted than the data would support. The purpose of this review is to facilitate an understanding of the involved imaging technologies that have made this technique more feasible for clinical practice, and to guide its introduction into the practice of the non-expert user.

Instantaneous quantitative video intensity heterogeneity: evaluation with low mechanical index contrast echocardiography

BACKGROUND

Instantaneous video intensity of myocardium has been poorly characterized. Myocardial video intensity is usually displayed in the fitted curve from the exponential equation, y = a(1 - e (-bt)). However, information from the fitted curve will be as accurate as the original video intensity data from the perfusion image. Therefore, we sought to characterize the intramyocardial instantaneous video intensity from low mechanical index (MI) contrast echo imaging for variation.

METHOD

Low-MI imaging using a nonlinear cancellation technique was performed on 10 subjects with normal myocardium. Quantitative video intensity was analyzed in five segments in the epicardium and subendocardium, as well as in systole and diastole.

RESULTS

Video intensity varied between the epicardium and endocardium in each of the region that was analyzed, with the greatest variation in the inferior region (P < 0.0001). Diastolic and systolic differences were also present.

CONCLUSION

Instantaneous video intensity is heterogeneous within the myocardium. Differences can result from attenuation, myocardial fiber structure, and even isotropic effects of the contrast agent, and should be taken into account when data are fitted into an exponential function.

Real-time myocardial contrast echocardiography for pharmacologic stress testing: is quantitative estimation of myocardial blood flow reserve necessary?

BACKGROUND

Little is known about the diagnostic accuracy of quantitative real-time myocardial contrast echocardiography (MCE) as an adjunct to stress testing. This study was performed to evaluate the agreement between MCE and technetium 99m-sestamibi single photon emission computed tomography (SPECT) for detection of perfusion defects and to investigate whether quantitative assessment of myocardial perfusion can increase the diagnostic value of MCE.

METHODS

MCE was performed at rest and during peak adenosine stress in 50 unselected patients undergoing SPECT imaging. Concordance between the 2 methods was assessed using kappa statistics. MCE images were analyzed quantitatively, measuring peak intensity (A) and maximal rise of signal intensity (beta). Myocardial blood flow reserve was estimated by calculating the ratios of A(adenosine)/A(baseline) (A reserve), beta(adenosine)/beta(baseline) (beta reserve), and A x beta(adenosine)/A x beta(baseline) (A x beta reserve).

RESULTS

Visual analysis of MCE agreed well with SPECT (kappa = 0.67) with sensitivity of 64%, specificity of 97%, and overall accuracy of 87%. Quantitative analysis showed that peak signal intensity A significantly increased under adenosine stress in SPECT-normal segments (2.6 +/- 1.9 vs 3.0 +/- 1.6 dB, P <.0001), tendencially decreased in reversible (3.0 +/- 2.0 vs 2.4 +/- 1.2 dB, P =.07) and remained unchanged in fixed (0.9 +/- 0.9 vs 0.8 +/- 0.9 dB) defects. beta Increased markedly under adenosine in normal segments (0.4 +/- 0.4 vs 1.4 +/- 1.3, P <.0001) but not in segments with reversible or fixed defects. Receiver operating characteristic showed that beta reserve and A x beta reserve, but not A reserve, are sensitive parameters for detecting perfusion defects with areas under the curve of 0.84, 0.85, and 0.61, respectively. Cut-off values of 1.9 and 2.3, respectively, for beta and A x beta reserve yielded sensitivity rates of 79% and 80%, specificity rates of 75% and 78%, and overall accuracy rates of 76% and 79%, respectively.

CONCLUSION

Quantitative estimation of myocardial blood flow reserve by MCE parameters corresponds to the evaluation of myocardial perfusion by nuclear imaging and can increase the sensitivity but not the overall accuracy of contrast echocardiography.

Intravenous myocardial contrast echocardiography during angioplasty

Myocardial contrast echocardiography (MCE) using power Doppler harmonic imaging (PDHI) has been reported to document regional myocardial perfusion. Two case reports demonstrate the potential of intravenous myocardial contrast echocardiography during angioplasty.

Real-time perfusion imaging: a new echocardiographic technique for simultaneous evaluation of myocardial perfusion and contraction

Myocardial contrast echocardiography (MCE) with high acoustic energy and triggered harmonic imaging is the best established ultrasound technique to date for the assessment of myocardial perfusion. With this technique, however, the ultimate goal of MCE (noninvasive real-time simultaneous assessment of myocardial perfusion and function after an intravenous injection of microbubbles) is not met. Recently, technologic advances have enabled myocardial opacification to be visualized during low-energy real-time imaging. During real-time perfusion imaging, wall motion and myocardial perfusion may be assessed simultaneously, obviating the need of the presently time-consuming combination of different imaging modalities. When high-energy ultrasound bursts are periodically transmitted to produce bubble destruction during low-power imaging, the consecutive frames after destruction delineate the restoration of contrast intensity. Microbubble replenishment rate and peak intensity may be determined subsequently, and provide reliable quantitative parameters of regional microcirculatory flow. This review will introduce the modalities used for real-time perfusion imaging with focus on power pulse inversion imaging and quantitative analysis. Furthermore, we will describe the clinical role the technique may have in the identification of coronary artery disease, quantification of coronary stenosis severity, assessment of myocardial viability, determination of infarction size, and evaluation of reflow and no- or low-reflow after acute myocardial infarction.

Assessment of adenosine-induced coronary steal in the setting of coronary occlusion based on the extent of opacification defects by myocardial contrast echocardiography

The authors examined the ability of real-time myocardial contrast echocardiography (MCE) to assess adenosine-induced coronary steal in the setting of coronary artery occlusion. The left anterior descending (LAD) coronary artery was occluded in 8 open-chest dogs. Real-time MCE was performed during LAD occlusion, and the extent of opacification defects from MCE was measured without and with adenosine infusion. Microsphere-derived myocardial blood flow (MBF) was measured in the LAD and left circumflex (LCx) coronary artery beds, and the LAD/LCx ratio of MBF was calculated. The LAD/LCx ratio of MBF decreased in response to adenosine administration (without adenosine: 0.66, with adenosine: 0.43, p < 0.01). The extent of opacification defects from MCE increased in response to adenosine administration (without adenosine: 18%, with adenosine: 22%, p < 0.01). Thus, real-time MCE allows for the detection of adenosine-induced coronary steal as changes in the extent of opacification defects in the setting of occlusion of 1 coronary artery accompanying another normally patent coronary artery.

Assessment of right ventricular perfusion after right coronary artery occlusion by myocardial contrast echocardiography

OBJECTIVES

The purpose of this study was to examine the ability of myocardial contrast echocardiography (MCE) to assess right ventricular (RV) perfusion.

BACKGROUND

Although MCE can readily assess left ventricular perfusion abnormalities, there are no data regarding the ability to assess RV perfusion abnormalities.

METHODS

The right coronary artery (RCA) was occluded in 10 open-chest dogs. Myocardial contrast echocardiography was performed with 0.27 g/min Levovist infusion by harmonic power Doppler with electrocardiographically gated intermittent triggered imaging at pulsing intervals ranging from 1:1 to 1:20 at baseline and 90 min after RCA occlusion. Video-intensity of the RV wall was plotted against pulsing intervals and was fitted to an exponential function: y = A(1-exp(-bt)), where A is the plateau video-intensity and b is the rate of video-intensity rise. Myocardial contrast echocardiography and microsphere-derived myocardial blood flow (MBF) measurements were performed at baseline and 90 min after RCA occlusion.

RESULTS

Because the severity of RV perfusion abnormalities assessed by MBF varied during RCA occlusion, diverse grades of patchy opacification defects were observed by MCE. The RV wall thickness decreased, and the RV dimension increased, after RCA occlusion in each dog. The correlation of occlusion to baseline MBF ratios in the RV wall was closer to the ratio of b (r = 0.897, p = 0.0004) than A (r = 0.767, p = 0.0097) and was the closest to the ratio of Axb (r = 0.935, p < 0.0001).

CONCLUSIONS

The RCA occlusion is manifested by RV wall thinning and dilation as well as by perfusion abnormalities consisting of patchy opacification defects by MCE. Myocardial contrast echocardiography-derived refilling parameters can be applied to assess RV perfusion abnormalities produced by RCA occlusion.

Visualization of myocardial perfusion after percutaneous myocardial septal ablation for hypertrophic cardiomyopathy using superharmonic imaging

Harmonic imaging is used for detection of ultrasound contrast agents in myocardial perfusion studies. However, harmonic imaging has limitations because of the presence of tissue harmonics, which results in less specificity and sensitivity, thus, lower contrast-to-tissue ratio. We describe a clinical example using superharmonic imaging. This technique detects the third, fourth, and fifth harmonics. These harmonics are not created in tissue, resulting, hence, in a high contrast-to-tissue ratio. After myocardial alcohol ablation for hypertrophic cardiomyopathy areas of nontreated and treated myocardium, normal and low flow could be visualized with superharmonic imaging.

Assessment of myocardial blood flow using myocardial contrast echocardiography

Advances over the past 10 years have enabled the widespread use of myocardial contrast echocardiography (MCE) to assess myocardial perfusion. This assessment is critical in evaluating the severity of coronary artery disease and the efficacy of pharmacologic, mechanical, or surgical interventions. MCE measures myocardial blood flow (MBF) by investigating flow velocity and myocardial blood volume. Although there are potential limitations to the use of MCE for determining MBF, its use is feasible in the experimental laboratory and in the clinical environment.

Myocardial contrast echocardiography in the perfusion imaging in coronary occlusion and reperfusion

The availability of myocardial contrast echocardiography (MCE) has potential for several applications in coronary diseases. Experimental studies have demonstrated a good correlation between measurements of myocardial blood flow and regional contrast intensity, and therefore capabilities of MCE in detecting myocardial ischemia during stress. Clinical studies must then demonstrate the value of such approaches in comparison with existing techniques such as stress echo and radionuclide imaging.