M-mode echocardiography in evaluating left ventricular function and surgical risk in patients with coronary artery disease

Overview of stress echocardiography: uses, advantages, and limitations

Responses of the heart to changes in our environment are probably even more important than how the heart functions at rest. Accordingly, stress testing with noninvasive imaging has become important for diagnosis, prognosis, and monitoring the effects of therapy. Echocardiography at rest and with stress permits characterization of global and segmental left ventricular function as well as valvular structure and function. Moreover, echocardiography can be performed during or after a number of different physical or even mental stressors. Advantages of stress echocardiography include its ready availability, relatively low capital cost, and incremental value in that it allows characterization of cardiac anatomy as well as the myocardial response to a potentially ischemic stimulus. Moreover, echocardiography has the potential to image myocardial perfusion along with wall motion and wall thickening. Substantial literature has now been accumulated on the value of stress echocardiography for the diagnosis of ischemic disease, preoperative risk assessment, and assessment of myocardial viability. Echocardiography has compared generally well with nuclear imaging techniques for the detection of angiographic coronary artery disease. Overall sensitivity, however, has been slightly less, particularly for the detection of single-vessel coronary disease, although specificity has been on average somewhat higher than nuclear cardiology techniques. Because of the potential for variability in study acquisition as well as interpretation, careful safeguards need to be employed. Specifically, meticulous technique needs to be applied to obtain high-quality images and to assure that those images are obtained promptly after treadmill exercise stress. Only readers with specific interest and expertise should interpret stress echocardiography studies. Continuing efforts need to be made to assess and minimize variability and to assure continuing quality improvement. Advances in instrumentation, including evolving technology for real-time 3-dimensional imaging, and echocardiography contrast assessment of myocardial perfusion will likely improve the sensitivity of echocardiography and further extend its usefulness.

Analysis of left ventricular systolic function

Images

Prospective study comparing different echocardiographic measurements of pulmonary capillary wedge pressure in patients with organic heart disease other than mitral stenosis

In 25 patients with cardiac disease, but free of left ventricular inflow obstruction, the electrocardiogram and M-mode echocardiogram of the aortic root, left atrium and both the mitral and the aortic valves were obtained simultaneously with the pulmonary artery wedge pressure (PAWP) during right heart catheterization. The echocardiographic measurements of the left atrial size, PR-AC interval, left atrial emptying index and the ratio between the electrocardiographic Q wave to mitral valve closure (Q-MVC) and between aortic valve closure to the mitral E point (AVC-E) were correlated to the pulmonary artery wedge pressure by means of linear regression analysis. A formula in which PAWP = 36.6 (Q-MVC/AVC-E)-- 2 was prospectively used to study the measured pressure in the current group of patients. The pulmonary artery wedge pressure derived from these latter measurements correlated well with the invasive measurement of this pressure (r = 0.91). The pulmonary artery wedge pressure calculated by echocardiography differed from the pulmonary artery wedge pressure measured by catheterization by 3 mm Hg or less in 19 of the 25 patients, by 4 mm Hg or less in 22 patients and by 6 mm Hg or less in 24 patients. Although the correlation between the (Q-MVC/AVC-E) ratio and measured pulmonary artery wedge pressure was highly significant (r = 0.91, probability [p] less than 0.001, n = 25), the left atrial emptying index, PR-AC and left atrial size revealed poor correlation coefficients (r = 0.45, r = 0.45 and r = 0.56 [p less than 0.05]), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of M-mode echographic estimates of left ventricle function: relationship of selected ultrasonic and hemodynamic parameters

We examined the relationship between echocardiographic and hemodynamic parameters in 48 patients with left ventricular ejection fractions less than 50% without primary valvular disease. Pulmonary wedge pressure (PWP) correlated with the PR-AC interval (r = -0.62) and with left atrial dimension (r = 0.64) but not with left ventricular diastolic dimension. A PR-AC interval less than or equal to 60 msec was observed in 26 of 29 (90%) patients with a PWP greater than or equal to 14 mm Hg versus 1 of 10 (10%) patients with a PWP less than 14 mm Hg. The correlation between PWP and the PR-AC interval was substantially better in patients with a PR interval less than or equal to 200 msec (r = -0.79) than in patients with a PR interval greater than 200 msec (r = -0.55). The PR-AC interval also correlated with the ejection fraction (r = 0.47). A left atrial dimension greater than or equal to 4.0 cm was observed in 29 of 35 (83%) patients with a PWP greater than or equal to 14 mm Hg versus 0 of 9 (0%) patients with a PWP less than 14 mm Hg. Stroke volume (SV) correlated with aortic root excursion (r = 0.71) and with SV calculated from formulas based on mitral valve motion (r = 0.76) or aortic valve motion (r = 0.62). However, no echo formula provided valid estimates of cardiac output. We conclude that M-mode echocardiography provides a relatively useful noninvasive method of assessing left ventricular filling pressure in patients with reduced ejection fraction and no valvular disease.

Echocardiography: pericardial tickening and constrictive pericarditis

To evaluate the relation between mitral valve motion and left ventricular end-diastolic pressure, the PR-AC interval, an index derived from the electrocardiogram and mitral echogram, and the left ventricular endodiastolic pressure were determined simultaneously in 22 patients undergoing diagnostic cardiac catheterization. Intravenous infusion of dextran or administration of nitroglycerin was used to alter left ventricular end-diastolic pressure to determine if there was a predictive relation between this pressure and the PR-AC interval during acute hemodynamic manipulations. There was a weak negative correlation (r = -0.33, P less than 0.01) between this pressure and the PR-AC interval. At rest a PR-AC interval greater than 0.06 second correctly predicted a left ventricular end-diastolic pressure of less than 20 mm Hg in 15 of 16 subjects. However, in four of six subjects with a PR-AC interval of 0.06 second or less, the end-diastolic pressure was less than 20 mm Hg. After interventions that varied left ventricular end-diastolic pressure by a factor of 2, the PR-AC interval changed slightly or not at all. These data suggest that the PR-AC interval is of limited value in predicting abnormal values or serial changes in left ventricular end-diastolic pressure.

Echocardiography in ischemic heart disease

Echocardiographic findings in patients with ischemic heart disease are described; their correlations with clinical, hemodynamic and angiographic data are presented and discussed. Regional abnormalities of left ventricular wall motion and/or thickening during systole are detected in 84 per cent of patients with acute myocardial infarction and in a high percentage of patients with larger than or equal to 75 per cent narrowing of a major coronary artery. These abnormalities may occur with stress and may be reversible. Left ventricular wall thinning during systole indicates acute ischemia or infarction and thin, dense myocardial echoes indicate scar. Echocardiographic evidence of left ventricular dysfunction is useful in predicting heart failure and mortality in patients with acute myocardial infarction and in predicting surgical mortality for patients undergoing aneurysmectomy and/or coronary artery bypass surgery. Echocardiography has not proved useful in determining graft patency following coronary artery bypass surgery. Technical difficulties and limitations of echocardiography in patients with coronary artery disease are discussed.