Utility of stress echocardiography for postinfarct prognosis

[Risk stratification after acute myocardial infarction]

In recent years, the characteristics of patients who suffer acute myocardial infarction without complications during hospitalization have changed. In addition, the range of non-invasive studies available for evaluating left ventricular systolic function, residual myocardial ischemia, and myocardial viability in these patients has improved. Left ventricular systolic function and residual ischemia should be evaluated in all patients before release. The non-invasive technique used (exercise test, echocardiography, nuclear cardiology, magnetic resonance imaging) depends on availability, experience, and results at each institution. Coronary arteriography should be performed in patients with significant ischemia or severe left ventricular systolic dysfunction in non-invasive studies. In these cases coronary angiography must be performed to determine if coronary arteries are suitable for revascularization before performing a test of myocardial viability.

How does computer-assisted digital wall motion analysis influence observer agreement and diagnostic accuracy during stress echocardiography?

This study assessed interobserver and intraobserver variation and diagnostic accuracy during 25 dipyridamole stress echocardiography tests interpreted with different analysis systems: a) computer display of high frame rate digital cineloops (47 frames/s); b) computer display of lower frame rate digital cineloops (24 frames/s); and c) videotape recordings. The majority of the patients (84%) had documented coronary artery disease with baseline wall motion abnormalities due to previous myocardial infarctions and/or coronary bypass surgery, thus comprising a population with difficult interpretation of stress echocardiography. Diagnostic accuracy was assessed using coronary angiography as reference method. Interobserver and intraobserver agreement was highest when analysis was performed from computer-displayed cineloops, 96 and 92%, respectively, compared to 84 and 80% respectively, using videotape recordings. Sensitivity for identification of coronary artery stenosis was similar using digital cineloops with high frame rate or videotape recordings (67% to 80% for both systems), and tended to be lower using cineloops with lower frame rate for analysis (53%). Inter- and intraobserver differences for wall motion score index were not significantly influenced by the analysis system. We conclude that computer assisted analysis with high frame rate of the displayed cineloops provides optimal observer agreement and diagnostic accuracy in the same range as videotape analysis in patients undergoing stress echocardiography.

Interobserver and intraobserver variation for analysis of left ventricular wall motion at baseline and during low- and high-dose dobutamine stress echocardiography in patients with high prevalence of wall motion abnormalities at rest

Interobserver and intraobserver variation for analysis of left ventricular regional wall motion during dobutamine stress echocardiography was assessed. Computer-displayed cineloops from 33 patients, 25 with baseline wall motion abnormalities, were analyzed by two observers blinded for patient data. Assessment included (1) baseline wall motion abnormalities, (2) evidence of myocardial viability at 10 micrograms/kg/min dobutamine, and (3) evidence of myocardial ischemia at 30 to 40 micrograms/kg/min. Wall motion score index was calculated at each stage. Interobserver and intraobserver agreement for baseline wall motion abnormalities was 100%. Interobserver agreement for viability and ischemia was 84% and 82%, respectively; intraobserver agreement was 92% and 85%, respectively. Mean interobserver differences in wall motion score index ranged from 0.06 +/- 0.14 at baseline to 0.09 +/- 0.20 at high doses (p < 0.05 at all levels); mean intraobserver differences ranged from 0.001 +/- 0.14 to 0.01 +/- 0.15 (difference not significant at all levels).

Strategies for prognostic assessment of uncomplicated first myocardial infarction: 5-year follow-up study

OBJECTIVES

Our aim was to use noninvasive studies early after infarction to assess medium-term prognosis in patients with a first uncomplicated myocardial infarction.

BACKGROUND

Although the use of early postinfarction assessment to gauge short-term prognosis in myocardial infarction is well established, there have been few comprehensive evaluations of noninvasive methods for assessing medium- and long-term prognosis.

METHODS

We prospectively studied 115 consecutive patients < 65 years old with a first acute uncomplicated myocardial infarction to evaluate the prognostic role of predischarge cardiac studies. These included submaximal exercise testing, thallium-201 scintigraphy, radionuclide exercise ventriculography, two-dimensional echocardiography, ambulatory electrocardiographic (Holter) monitoring and cardiac catheterization. All patients without complications were followed up > or = 5 years.

RESULTS

During the follow-up period, 78 patients (68%) developed complications, which were severe in 37 (32%). Exercise thallium-201 scintigraphy yielded the highest percentage (77%) for correctly classified patients. It also had the highest predictive value for complications (97%) and severe complications (92%) when it was used in association with exercise testing and radionuclide ventriculography. The addition of cardiac catheterization did not improve on the predictive power of noninvasive studies. Four decision trees (exercise testing + echocardiography, exercise testing + radionuclide ventriculography, thallium-201 + echocardiography, thallium-201 + radionuclide ventriculography) allowed stratification of all patients in a high, intermediate or low risk category. The combination of thallium-201 scintigraphy and radionuclide ventriculography yielded the best results (90% predictive value for complications if the outcome of both tests was positive), but there were no significant differences with the other models.

CONCLUSIONS

Any combination of a test detecting residual ischemia or functional capacity, or both (exercise testing or thallium-201 scintigraphy), and a test assessing ventricular function (echocardiography or radionuclide ventriculography) results in useful prognostic information in patients with an uncomplicated first acute myocardial infarction.

Distinctive subtypes of bovine phospholipase C that have preferential expression in the retina and high homology to the norpA gene product of Drosophila

The Drosophila norpA gene encodes a phospholipase C involved in phototransduction. However, phospholipase C apparently is not directly involved in phototransduction in vertebrate photoreceptors, although light-activated phospholipase C activity has been reported in vertebrate rod outer segments. Conserved regions of norpA cDNA were used to isolate bovine cDNAs that would encode four alternative forms of phospholipase C of the beta class that are highly homologous to the norpA protein and expressed preferentially in the retina. Two of the variants are highly unusual in that they lack much of the N-terminal region present in all other known phospholipases C. The sequence conservation between these proteins and the norpA protein is higher than that between any other known phospholipases C. GTPase sequence motifs found in proteins of the GTPase superfamily are found conserved in all four variants of the bovine retinal protein as well as the norpA protein but not in other phospholipases C. Results suggest that these proteins together with the norpA protein constitute a distinctive subfamily of phospholipases C that are closely related in structure, function, and tissue distribution. Mutations in the norpA gene, in addition to blocking phototransduction, cause light-dependent degeneration of photoreceptors. In view of the strong similarity in structure and tissue distribution, a defect in these proteins may have similar consequences in the mammalian retina.