Antonio F. Amico

Superiority of visual versus computerized echocardiographic estimation of radionuclide left ventricular ejection fraction

An optimal method for determining left ventricular ejection fraction (LVEF) by echocardiography should be rapid, reliable, and widely applicable in order to be utilized routinely in a busy clinical laboratory. Most methods reported in the literature are reliable in selected, high-quality echocardiograms. Most require off-line computer analysis and are time-consuming and poorly suited to the routine of a busy laboratory. We compared in a blinded manner several echocardiographic methods of LVEF determination with the ejection fraction obtained by equilibrium radionuclide angiography (ERNA) in 44 patients unselected for image quality. Echocardiographic methods included: [1] cubed M-mode formula; [2] Teichholz M-mode formula; [3] subjective estimation of LVEF from two-dimensional echocardiographic videotape; [4] area-length method in one four-chamber view; [5] average of area-length method in three four-chamber views; [6] average of area-length method in four-chamber and two-chamber views (one beat each); [7] subjective estimation from stored videoloop of four-chamber and two-chamber view. In 30 cases M-mode tracings were available for analysis. In only 23 of the 44 patients were the apical views suitable for quantitative analysis. The ERNA ejection fraction was 44 +/- 17% (mean +/- 1 SD). The best echocardiographic correlation with ERNA ejection fraction in each patient subgroup studied was obtained by method 3. We concluded that subjective analysis of the videotaped study by an experienced cardiologist/echocardiographer provided the best estimation of ERNA ejection fraction. More time-consuming and costly computer techniques yielded a worse estimate.

Myocardial perfusion imaging by contrast echocardiography with use of intracoronary sonicated albumin in humans.

Sonicated albumin has been proposed as a near ideal echocardiographic contrast agent with little myocardial toxicity or hemodynamic effect. Its use has not yet been reported in humans, partly because of difficulties in preparation. With use of the newly modified sonication method, 10 ml of 5% albumin was sonicated for 75 s with a 5.0 ml slow infusion of air. This resulted in microbubbles with a mean diameter (+/- SD) of 5 +/- microns). Fourteen patients undergoing routine coronary angiography were studied. One patient had normal coronary arteries; the other 13 had significant coronary artery disease. In a subgroup of nine patients, sonicated albumin and sonicated diatrizoate meglumine sodium (microbubble diameter 9 +/- 3 microns) were injected several minutes apart, using the same technique. Videodensity-time curves were obtained from a region of interest in the myocardium. Corrected peak contrast intensity (baseline contrast intensity subtracted from peak contrast intensity, gray scale U/pixel) for sonicated albumin and for sonicated diatrizoate meglumine sodium was 51 +/- 26 and 52 +/- 19, respectively (p = 0.89). Washout half-time (T1/2) for the two agents was 5.5 +/- 4.5 and 16.0 +/- 12.2 s, respectively (p = 0.01). One patient with unstable angina experienced transient chest pain after repeated albumin injections. No electrocardiographic changes, blood pressure changes or wall motion abnormalities were observed. Administered by intracoronary injection, sonicated 5% albumin is a safe and effective echocardiographic contrast agent for myocardial perfusion imaging, yielding excellent myocardial contrast with physiologic washout time.

Quantitative assessment of the immediate results of coronary angioplasty by myocardial contrast echocardiography.

A low pressure gradient across the residual lesion and a minimal percent residual stenosis are markers of a successful coronary angioplasty. A more physiologic method of assessing the results of coronary angioplasty would involve assessment of myocardial perfusion in the affected coronary bed. Contrast two-dimensional echocardiography provides information about regional myocardial perfusion. To assess the correlation between pre- to postcoronary angioplasty changes in gradient or percent stenosis and the increase in peak contrast intensity, 23 consecutive patients were studied during coronary angioplasty. In 19 of the 23 patients, the coronary angioplasty was successful and in 15 (79%) of the 19, an adequate echocardiographic study was obtained. Mild and transient side effects of echo contrast were observed in 3 of the 15 patients. The gradient across the residual lesions decreased from 52 +/- 12 to 11 +/- 4 mm Hg (mean +/- SD), the diameter of the stenotic lesion decreased from 89 +/- 10 to 25 +/- 16% and corrected peak contrast intensity (peak contrast - baseline contrast in gray level U/pixel) increased from 15 +/- 16 to 50 +/- 26. All these differences were significant at the p less than 0.001 level. Corrected peak contrast intensity correlated exponentially with the decrease in pressure gradient (r = 0.82, p less than 0.001). The correlation curve had a greater increase in peak contrast intensity at gradient decreases greater than 45 mm Hg. Corrected peak contrast intensity did not correlate with decrease in diameter of the stenotic lesion (r = 0.19).

Reproducibility of quantitative myocardial contrast echocardiography

To determine whether myocardial contrast echocardiography is quantitatively reproducible, repeated intracoronary injections of sonicated albumin (5%) were performed in eight open chest dogs. Paired injections were performed at baseline, during ischemia produced by ligation of a coronary artery, and during hyperemia induced by intravenous infusion of 0.75 mg/kg body weight of dipyridamole. Contrast washout curves were generated for the left anterior descending coronary artery territory (ischemic area) and left circumflex coronary artery territory (nonischemic area) by beat per beat analysis of frozen end-diastolic frames of left ventricular short-axis views. Peak contrast intensity, contrast washout half-time and area under the curve were derived from these curves. A total of 75 contrast washout curves were analyzed for the study of interinjection, intraobserver and interobserver reproducibility. The correlation coefficients between measurements obtained from paired injections of the echocardiographic contrast agent (interinjection reproducibility) ranged from 0.78 for peak contrast intensity to 0.87 for area under the curve. Percent error varied between 14.7% and 24.7%. The intraobserver variability in measurements was less than the interinjection variability, with a cumulative mean percent error of 17.8% and correlation coefficients of 0.72 (peak contrast intensity), 0.95 (area under the curve) and 0.96 (washout half-time). Interobserver correlation for all indexes was high (r = 0.92 to 0.96). It is concluded that peak contrast intensity, contrast washout half-time and the area under the curve derived from myocardial contrast washout curves can be measured reproducibly from videotapes. In addition, the variability between two injections attempted under identical conditions is greater than reader variability from videotapes.

Diagnosis of pericardial abnormalities by 2D-echo: a pathology-echocardiography correlation in 85 patients.

A blinded pericardial echocardiography-pathology correlation was performed using 85 pericardiectomy or autopsy patients. All patients had two-dimensional (2D)-echocardiography performed within 6 months of autopsy or surgery. 2D-echocardiography was able to detect pericardial abnormalities in 35% of patients with a pathologic pericardium. Obliterative processes, such as fibrosis after open-heart surgery, were particularly not well detected echocardiographically. A specificity of 90% to detect pericardial abnormalities is reported. Acute fibrin strands, malignancies, and chronic fibrous connective tissue involving the pericardium were recognized as abnormal. Interobserver variability does exist, but overall reporting was similar. Specific 2D-echocardiographic signs of pericardial disease require prospective validation including direct pathologic correlation.

Contrast agents for myocardial perfusion studies

Twenty years after Gramiak and Shah at the University of Rochester reported the echocardiographic contrast effect [1], the uses and applications of contrast echocardiography are still growing. The need for new and more standardized contrast agents with superior reproducibility and capillary transmission capability has been felt for years [2]. Meltzer et al. [3] and Armstrong et al. [4] reported on commercially prepared contrast agents in the early 1980s. Feinstein et al. [5] introduced the use of ultrasonic energy (sonication) to create smaller microbubbles. Current knowledge and future prospects about mechanisms of the ultrasound contrast effect and the new contrast agents are summarized in this chapter.

Coronary anatomy and myocardial perfusion: Role of contrast echocardiography

Coronary stenoses reduce coronary flow and, consequently, myocardial perfusion. This is the main cause of clinical symptoms of coronary artery disease. Though coronary arteriography is the most important diagnostic examination for evaluating this disease, it does have several limitations. It cannot, for example, estimate the actual ‘haemodynamic’ severity of the coronary stenoses and, therefore, its real significance in limiting myocardial perfusion. Interpretation of coronary angiograms is also affected by an intra- and inter-observer variability which cannot be overlooked [1, 2]. Furthermore, coronary arteriography as performed in most institutions gives only qualitative information on the distribution and characteristics of coronary stenoses. Myocardial perfusion is further influenced by many other factors which cannot be evaluated by coronary angiography (the microcirculation, heart muscle conditions, interstitial characteristics, wall stress, collateral circulation etc.).

Quantitative analysis of wall motion abnormalities

Two-dimensional echocardiography has emerged as being an ideal noninvasive technique for studying the mechanical consequences of acute and chronic ischemia: because of its high spatial resolution, its sampling frequency and its safety, wall motion abnormalities can be identified within seconds of the onset of the ischemia and be monitored sequentially [1]. The clinical significance of the capability of the technique is demonstrated by the close relationship between the extent of the mechanical impairment as evaluated by echocardiography and the prognosis for the patients in whom spontaneous or induced ischemia is present [2–4].

Stress echocardiography for identifying patients at risk after myocardial infarction

Several factors contribute to the prognosis of patients surviving acute myocardial infarction [1–3]. Among these, the presence of additional myocardium at jeopardy is felt to be one of the most important. Consequently, many stress tests have been developed and proposed over the last few years for evaluating patients with recent myocardial infarction [1–9]. These tests are based on the combined use of a stress capable of inducing ischemia and a diagnostic technique capable of detecting the direct or indirect signs of acute myocardial ischemia. Among the stress tests used so far for prognostically stratifying patients with recent myocardial infarction, exercise echocardiography (treadmill or bicycle) is certainly the most common.

Echocardiography during transesophageal atrial pacing

Echocardiographically detected wall motion abnormalities are a sensitive marker of coronary artery disease. However, even patients with severe coronary stenoses may have a normal ventricular wall motion at rest. Any stress which is able to induce myocardial ischemia may also induce mechanical alterations (i.e. wall motion abnormalities) whose onset is known to be an even earlier ischemic marker than electrical alterations and angina. Therefore, one can reasonably expect that by combining a suitable stress with an imaging technique such as echocardiography one has an efficient diagnostic means for coronary artery disease.