The use of Gd-DTPA as a marker of myocardial viability in reperfused acute myocardial infarction.

At present, accurate assessment of the extent of myocardial viability after acute myocardial infarction is limited due to the spatial resolution of currently available imaging modalities. MR cardiac imaging, with its superior spatial resolution, would be used if viable and infarcted tissue could be separated based on signal intensity. In infarcted tissue, cell membrane breakdown allows the entry of the MR contrast agent Gd-DTPA which is normally extracellular. The increased space for Gd-DTPA distribution (partition coefficient, lambda) in this infarcted tissue results in increased Gd-DTPA concentration and hence increased signal intensity on T1-weighted MR images. In a canine model of ischemia/reperfusion injury, the partition coefficient in infarcted tissue increased as early as 1 min post reperfusion. lambda in infarcted tissue stayed increased over that in normal tissue for at least 8 weeks. The accuracy of contrast-enhanced MRI was confirmed by results of 201Tl SPECT and a cine MRI dobutamine wall motion study in a patient 1 week after an acute myocardial infarction. Thus, contrast-enhanced MRI shows great promise for the non-invasive determination of myocardial viability after acute myocardial infarction.

Low dose dobutamine echocardiography in the assessment of contractile reserve to predict the outcome of valve replacement for chronic aortic regurgitation.

BACKGROUND: When to perform surgery for aortic regurgitation is a difficult clinical decision. Occult left ventricular (LV) dysfunction may be present in patients with minimal or no symptoms, and in some patients LV dysfunction may persist after valvular replacement. OBJECTIVES: To examine the role of preoperative low dose dobutamine echocardiography (LDDE) in predicting postoperative outcome in patients who had aortic valve replacement for aortic regurgitation. PATIENTS AND METHODS: The study group comprised 16 patients (15 men, aged 48 +/- 15 years) undergoing elective surgery for aortic regurgitation. Preoperative echocardiograms were obtained in the resting state and during dobutamine infusion at 7.5 micrograms/kg/min. Complete recovery was defined by normalization of LV size and function, and the absence of symptoms at the six-month follow-up visit. Patients with complete recovery (group 1) and without complete recovery (group 2) were compared in relation to their echocardiographic parameters at rest and during LDDE. RESULTS: Of 16 patients in the study, nine were in group 1 and seven were in group 2. Age, functional class and LV end-diastolic dimensions were similar between the two groups. Group 1 patients had a smaller preoperative LV end-systolic dimension index (22.4 +/- 3.3 versus 29.9 +/- 5.9 mm/m2, P < 0.05) and a higher preoperative ejection fraction (53 +/- 8% versus 37 +/- 13%, P < 0.01). Dobutamine infusion augmented the difference in ventricular size and function between patients in group 1 and those in group 2 (LV end-systolic dimension index 18.9 +/- 3.9 mm/m2 versus 28.8 +/- 7.1 mm/m2, P < 0.01; ejection fraction 61 +/- 7% versus 41 +/- 12%, P < 0.01). CONCLUSIONS: Dobutamine accentuates differences in ventricular size and function between those with and without subsequent complete recovery following valve surgery. Because preoperative ejection fraction during LDDE is highly predictive of postoperative ejection fraction, LDDE may have a role in predicting the clinical outcome of patients following aortic valve replacement for aortic regurgitation.

Sonicated albumin in exercise echocardiography: technique and feasibility to enhance endocardial visualization.

Left ventricular cavity opacification can be produced by the intravenous injection of sonicated albumin (Albunex 422). A recent study suggested that sonicated albumin may be useful in dobutamine stress echocardiography, but its use in exercise echocardiography has not been reported. The purposes of the study were to assess the feasibility of using Albunex to enhance endocardial visualization and to evaluate the factors affecting Albunex kinetic in exercise echocardiography. Fifteen healthy volunteers underwent two exercise echocardiograms on the same day, with intravenous injection of Albunex during one of the studies. Two injections up to a maximum of 20 ml of Albunex per injection were given to enhance the four- and two-chamber views, both at rest and immediately after exercise. The degree of left ventricular enhancement and the percentages of endocardial visualization were measured in both resting and exercise images. Variables relating to the kinetics of Albunex, which included volume of contrast injected, transit time, heart rate, and cardiac output at the time of image acquisition, were also assessed. There was no difference in the image acquisition time between the two exercise echocardiograms. Albunex produced good left ventricular opacification both at rest and after exercise. More endocardial border was visualized with contrast injection than without (91.2% +/- 11.5% vs 85.8% +/- 14.2%, p = 0.007). The transit times and volumes of Albunex injected were significantly less after exercise than at rest. The parameters were inversely related to heart rate and cardiac output. In conclusion, intravenous injection of Albunex is a promising means to enhance left ventricular endocardial visualization in exercise echocardiography and can be readily incorporated without causing a significant delay in obtaining images after exercise. Whether its use can improve diagnostic accuracy of exercise echocardiography requires further studies.

Dobutamine and dipyridamole stress echocardiography in patients with a low incidence of severe coronary artery disease.

The aim of this study was to determine the relative sensitivity, specificity, accuracy, and tolerance of dobutamine and dipyridamole stress echocardiography in patients with a lower likelihood of severe coronary artery disease. Previous comparative studies, which included patients with a history of myocardial infarction or a high incidence of coronary artery disease, showed both methods to have similar and acceptable diagnostic accuracy. To assess the role of these agents in evaluating patients with a lower likelihood of significant coronary artery disease, a lower-risk group was selected by excluding patients with known coronary artery disease, myocardial infarction, unstable angina, or strongly positive stress test results. Dobutamine and dipyridamole stress echocardiographic studies were performed in random order, before coronary angiography. Of the 46 patients enrolled (31 men and 15 women), 24 had atypical chest pain or none at all. Coronary angiography revealed no significant disease in 22 (48%), single-vessel disease in 11 (24%), and multivessel disease in only 13 patients (28%). Dobutamine and dipyridamole stress echocardiography were equally well tolerated, with identical accuracy (76%) that was maintained in patients with atypical symptoms. This confirms the usefulness of both dobutamine and dipyridamole stress echocardiography in evaluating patients with suspected coronary artery disease and extends this role to a lower-risk group for severe disease who often have atypical symptoms. The choice of which agent is used should reflect an institution's experience.

Measurement of left ventricular ejection fraction by acoustic quantification and comparison with radionuclide angiography.

Left ventricular (LV) ejection fraction (EF) is an important measure of systolic function, with radionuclide angiography being the accepted standard for its determination. Echocardiography is ideal for repeated measurements of EF, but most methods are either subject to error in the presence of regional wall abnormalities or require cumbersome off-line analysis. Acoustic quantification is a recently introduced method that allows for the continuous on-line display of LV cavity dimensions, but the on-line algorithm for the measurement of EF has not been validated against an independent standard in the clinical setting. This study attempted to validate acoustic quantification in the determination of EF by comparison with off-line echocardiographic analysis and radionuclide angiography in 54 patients referred for this latter procedure. Acoustic quantification correlated well with off-line analysis in both the apical 4-chamber (r = 0.89, n = 43) and 2-chamber (r = 0.86, n = 26) views. Similarly, it also correlated well with radionuclide angiography in the 4-chamber (r = 0.81, n = 44) and 2-chamber (r = 0.83, n = 26) views. The correlation between the 2 methods was further improved when only the last 30 patients were assessed (r = 0.91, n = 25 for 4-chamber views; r = 0.86, n = 16 for 2-chamber views). The correlation was worse in patients with regional asynergy (r = 0.69, n = 17 for 4-chamber views; r = 0.76, n = 10 for 2-chamber views). Moreover, acoustic quantification tended to underestimate EF when compared with radionuclide angiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of transthoracic and transesophageal echocardiography in the diagnosis and management of infective endocarditis.

Infective endocarditis continues to be a cause of significant cardiac morbidity and mortality. To improve the prognosis of patients with this disorder, early diagnosis is crucial but difficult to establish on the basis of clinical parameters alone. Echocardiography, both transthoracic and transesophageal techniques, has a major role in the detection of vegetations that are the hallmark of endocarditis. Valvular and perivalvular complications can also be well assessed by echocardiography. With the improved resolution provided by recent technologic advances in echocardiography, vegetations can be reliably detected in most patients with endocarditis. We propose that present diagnostic criteria for endocarditis be revised to include echocardiographic findings as a major parameter in the diagnosis. Finally, a diagnostic approach incorporating transthoracic and transesophageal echocardiography in these patients will be discussed taking into consideration the different degrees of clinical suspicion for the existence of the disease.