Detection of regional perfusion abnormalities during adenosine stress echocardiography with intravenous perfluorocarbon-exposed sonicated dextrose albumin

Current role of contrast echocardiography in the diagnosis of cardiovascular diseases

The use of contrast echocardiography (CE) in cardiovascular medicine has grown significantly over the last 15 years. Depending on the site of injection, contrast enhancement of the right- or left-sided cardiac chambers or myocardium now can be achieved. Contrast echocardiography can improve the evaluation of patients with valvular heart disease by enhancing the Doppler signal; CE also improves detection of intracardiac or intrapulmonary shunts. In patients with coronary artery disease, enhancement of the endocardial blood-tissue boundary allows for improved visualization of endocardial wall motion, assessment of wall thickening, and calculation of ejection fraction. Contrast echocardiography promises to delineate myocardial perfusion and has the potential for quantitating coronary flow and assessing myocardial viability. These applications may add important physiologic information to the anatomic information readily available from noncontrast echocardiography. Because it can be rapidly performed at the bedside, CE may be a valuable tool for use with inpatients with acute myocardial ischemia. When CE has been used after recanalization of occluded coronary arteries, the assessment of myocardial salvage conveys information concerning reflow, stunning, and prognosis, and in the case of an angioplasty it provides immediate information regarding the success of the procedure. Contrast echocardiography can also assess myocardial areas at risk of irreversible damage and the presence or absence of collateral flow. When performed with transesophageal or epicardial echocardiography in the operating room, CE is emerging as a valuable tool in the assessment of cardioplegia distribution and graft patency as well as in the delineation of the regional supply of each graft. With the continued development of newer contrast agents and refinement of ultrasound imaging equipment, the applications of CE will continue to grow.

A head-to-head comparison of infusion and bolus doses of adenosine for stress myocardial contrast echocardiography

BACKGROUND

This study was a head-to-head, intraindividual comparison of the diagnostic accuracy and side effect profile of bolus and infusion administration of adenosine for stress myocardial contrast echocardiography (MCE).

METHODS

Adenosine MCE was performed in 64 subjects, referred for stress thallium-201 single-photon emission computed tomography (SPECT) for known or suspected CAD. Each patient received adenosine by multiple boluses (6-12 mg/bolus) and infusion (140 mug/kg per min for 6 min) forms in random order, given at least 20 minutes apart.

RESULTS

No prolonged or serious adverse events occurred during either adenosine bolus or infusion. Compared to SPECT imaging, the sensitivity, specificity, and concordance for the diagnosis of CAD were 77%, 87%, and 82% for adenosine infusion MCE and 81%, 90%, and 86% for adenosine bolus MCE, respectively.

CONCLUSIONS

Both adenosine infusion and adenosine bolus protocols are safe for MCE in humans and can be used for the diagnosis of CAD.

Bioeffects of albumin-encapsulated microbubbles and real-time myocardial contrast echocardiography in an experimental canine model

Myocardial contrast echocardiography has been used for assessing myocardial perfusion. Some concerns regarding its safety still remain, mainly regarding the induction of microvascular alterations. We sought to determine the bioeffects of microbubbles and real-time myocardial contrast echocardiography (RTMCE) in a closed-chest canine model. Eighteen mongrel dogs were randomly assigned to two groups. Nine were submitted to continuous intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin (PESDA) plus continuous imaging using power pulse inversion RTMCE for 180 min, associated with manually deflagrated high-mechanical index impulses. The control group consisted of 3 dogs submitted to continuous imaging using RTMCE without PESDA, 3 dogs received PESDA alone, and 3 dogs were sham-operated. Hemodynamics and cardiac rhythm were monitored continuously. Histological analysis was performed on cardiac and pulmonary tissues. No hemodynamic changes or cardiac arrhythmias were observed in any group. Normal left ventricular ejection fraction and myocardial perfusion were maintained throughout the protocol. Frequency of mild and focal microhemorrhage areas in myocardial and pulmonary tissue was similar in PESDA plus RTMCE and control groups. The percentages of positive microscopical fields in the myocardium were 0.4 and 0.7% (P = NS) in the PESDA plus RTMCE and control groups, respectively, and in the lungs they were 2.1 and 1.1%, respectively (P = NS). In this canine model, myocardial perfusion imaging obtained with PESDA and RTMCE was safe, with no alteration in cardiac rhythm or left ventricular function. Mild and focal myocardial and pulmonary microhemorrhages were observed in both groups, and may be attributed to surgical tissue manipulation.

Usefulness of power Doppler contrast echocardiography to identify reperfusion after acute myocardial infarction

Microvascular integrity, as seen by myocardial contrast echocardiography (MCE), assesses whether myocardium has been successfully reperfused after an acute myocardial infarction. Until now this has been demonstrated only with intracoronary injection of an ultrasound contrast agent. Power Doppler imaging is a recently developed myocardial contrast echocardiographic method that counts the contrast microbubbles destroyed by ultrasounds and displays this number in color. This study sought to evaluate whether power Doppler MCE is able to visualize myocardial reperfusion during intravenous contrast injection. Thirty patients were evaluated 2 days after their first myocardial infarction during intravenous infusion of perfluorocarbon-exposed sonicated dextrose albumin (PESDA). Coronary artery angiography and single-photon emission computed tomography (SPECT) were used as reference techniques. A 16-segment left ventricular model was used to relate perfusion to coronary artery territories. Sensitivity and specificity of power Doppler MCE for segments supplied by infarct-related arteries were 82% and 95%, respectively. Accuracy of power Doppler MCE and SPECT were similar (90% vs 92% on segmental basis and 98% vs 98% on coronary artery territory basis). Two-dimensional echocardiography was repeated after 6 weeks. Segments recovering wall motion after 6 weeks were defined as stunning myocardium. Dysfunctional but perfused myocardium at day 2 after the infarction showed a better late recovery of wall motion compared with dysfunctional but nonperfused myocardium (p <0.001). In conclusion, harmonic power Doppler imaging is a sensitive and specific method for the identification of myocardial reperfusion early after myocardial infarction. It yields prognostic information for late recovery of ventricular function differentiating stunning (dysfunctional but perfused) from necrotic myocardium (dysfunctional and nonperfused).

Assessment of myocardial perfusion by harmonic power Doppler imaging at rest and during adenosine stress: comparison with (99m)Tc-sestamibi SPECT imaging

BACKGROUND

Harmonic power Doppler imaging (HPDI) is a novel technique for assessing myocardial perfusion by contrast echocardiography in humans. The purpose of this study was to compare myocardial perfusion by HPDI with that obtained by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) during rest and pharmacological stress.

METHODS AND RESULTS

HPDI was performed on 123 patients who were referred for SPECT imaging for known or suspected coronary artery disease. Images were obtained at baseline and during adenosine infusion (0.14 mg. kg(-)(1). min(-)(1)x6 minutes) in 3 apical views. Myocardial perfusion by HPDI was graded for each coronary territory as absent, patchy, or full. The persistence of absent or patchy myocardial perfusion by HPDI between rest and adenosine was interpreted as a fixed defect, whereas any decrease in perfusion grade was interpreted as a reversible defect. Overall concordance between HPDI and SPECT was 83 (81%) of 103 for normal versus abnormal perfusion. Agreement between the 2 methods for each of the 3 coronary territories was 81% (kappa=0.57) for the left anterior descending artery, 76% (kappa=0.52) for the right coronary artery, and 72% (kappa=0.40) for the left circumflex artery. Discrepancies between the 2 techniques were most notable in the circumflex territory, where fixed defects were observed in 33% by HPDI but in only 14% by SPECT (chi(2)=15.8, P=0.0001).

CONCLUSIONS

This study demonstrates that HPDI can reliably detect myocardial perfusion during pharmacological stress, although there was a significantly higher number of falsely abnormal results in the circumflex territory.

Contrast harmonic color Doppler left ventriculography: machine-interpreted left ventricular ejection fraction compared with equilibrium-gated radionuclide ventriculography

BACKGROUND

Multi-gated acquisition (equilibrium-gated radionuclide ventriculography) (MUGA) is considered the gold standard for measuring left ventricular ejection fraction (LVEF) because it is accurate, machine interpreted, and reproducible. Echocardiographic LVEF measurements are subject to variability in image acquisition and interpretation and to the limitations of 2-dimensional (2D) versus 3-dimensional imaging.

GOAL

The shortcomings of traditional echocardiography may be addressed by combining multiplane 2D harmonic imaging, echocardiographic contrast, color Doppler ultrasonography, and digital image processing to create a new imaging modality: contrast harmonic color Doppler left ventriculography.

METHODS

We compared the accuracy of a new method for measuring LVEF that allows for machine interpretation and uses contrast-enhanced intermittent harmonic color Doppler ultrasonography (CHCD). Quantitative LVEF measurements by hand-traced harmonic 2D echocardiography, contrast-enhanced harmonic 2D echocardiography, CHCD, and machine-interpreted CHCD were compared with MUGA in 35 patients.

RESULTS

Contrast-enhanced intermittent harmonic color Doppler provided images with vivid endocardial definition in all patients, but hand-traced harmonic 2D echocardiography and contrast-enhanced harmonic 2D echocardiography had inadequate images in 9% of patients. The MUGA LVEF range was 0. 09 to 0.70. All echocardiographic methods showed excellent correlation with the MUGA LVEF (R (2) > 0.96), but the CHCD method had the best limits of agreement.

CONCLUSIONS

Contrast-enhanced intermittent harmonic color Doppler LVEF correlates with MUGA at least as well as traditional noncontrasted echocardiography, but it provides diagnostic images in a greater proportion of patients. The CHCD images have vivid endocardial delineation and can be machine interpreted.

Assessment of Left Ventricular Area at Risk by Myocardial Contrast Two-Dimensional Echocardiography: An Evaluation of a New Animal Model

BACKGROUND: New echocardiographic contrast agents are commonly tested in the dog model. However, this species has a number of drawbacks, including difficulties in experimentation, cost, and ethical considerations. The rabbit has a number of advantages due to its relative simple coronary circulation. The present study was designed to evaluate the rabbit model for determination of areas of risk (ARs) by contrast echocardiography. METHODS: Eight rabbits were intubated and mechanically ventilated after occlusion of the left coronary artery with a ligature. The transducer (operating at 7.5 MHz) was positioned on the right ventricle through a right thoracotomy. The images were obtained after intra-aortic injection of 1 ml of Albunex, followed by 3 ml of dye (Blue Uniperse) for histological analysis postmortem. The ARs were obtained after circumscription of the various echocardiographic and histological images. RESULTS: Excellent echocardiographic images were obtained, largely due to the hemodynamic stability of the rabbit to ischemia. Echocardiographic ventricular areas, absolute AR, and relative AR correlated closely with postmortem data (r = 0.86, 0.94, and 0.94, respectively). The measurements were highly reproducible with low variability. CONCLUSIONS: The rabbit model shows promise for study by contrast echocardiography of myocardium subjected to ischemia. This method for determination of ARs was validated against postmortem findings. The method also should be of value in the evaluation of reperfusion.