Influence of reperfusion induced by thrombolytic treatment on natural history of left ventricular regional wall motion abnormality in acute myocardial infarction

Detection of residual tissue viability within the infarct zone in patients with acute myocardial infarction: ultrasonic integrated backscatter analysis versus dobutamine stress echocardiography

OBJECTIVES

The goals of this study were to analyze temporal changes in cardiac cyclic variation of integrated backscatter (CVIB) in acute myocardial infarction (AMI) and to investigate the predictive value of CVIB normalization compared with that of dobutamine stress echocardiography (DSE) in the assessment of functional recovery after revascularization.

BACKGROUND

The normal CVIB is blunted by ischemia and recovers early after reperfusion, faster than wall motion improvement. Analysis of CVIB has been widely investigated for its potential to detect viable myocardium in the early stage of infarction. No studies have compared CVIB analysis with other techniques for viability assessment in patients with acute ischemic.

METHODS AND RESULTS

Integrated backscatter images were obtained in 12 patients with AMI on days 1, 3, and 7 after admission and 1 month after revascularization. On day 7, DSE was performed in all patients. On admission, 22 of 144 segments were dyssynergic. On day 1, CVIB was abnormal in all 22 infarcted segments, on day 3, in 16, and on day 7, in only 10 infarcted segments. Eight of 10 segments nonviable by CVIB (CVIB-nonviable) were also nonrespondent by DSE; whereas 12 of 14 segments viable by DSE (DSE-viable) were also CVIB-viable. At follow-up, 10 CVIB-viable segments and 1 CVIB-nonviable segment showed functional recovery; whereas 10 of 14 DSE-viable segments showed functional recovery. Thus the positive predictive value of CVIB and DSE was 83% and 72%, respectively, with a diagnostic agreement between techniques in 77% of segments.

CONCLUSIONS

Our data suggest that the normalization in CVIB in the first week after AMI accurately predicts residual tissue viability within the infarct zone. We also observed that the initial pattern of cyclic variation may be predictive of functional recovery. Finally, we found a good correlation between the recovery of a normal CVIB in segments that were still dysfunctional and a more validated method to assess tissue viability, such as the dobutamine test.

Clinical impact of echocardiography in prognostic stratification after acute myocardial infarction

Risk stratification is mandatory in the management of the postinfarction period. The identification of high-risk patients, on the basis of clinical data (recurrent angina, overt heart failure, etc.), is quite easy, whereas stratification of uncomplicated subjects needs an accurate noninvasive strategy. In the last 20 years, echocardiography has been gaining an increasing role, allowing increasingly precise evaluation of infarct size. This detection of the extent of infarct size has a definite prognostic value. Since 1980, we have observed that a dysfunctioning left ventricular myocardium >40% marked patients with a poor prognosis. These observations are most important in asymptomatic infarct patients, in whom clinical features may not reflect the amount of left ventricular dysfunction. Our recent results on a large series of patients with acute myocardial infarction (MI) without overt heart failure have shown that the extension of wall motion abnormalities at 2-dimensional (2D) echocardiography was highly predictive of cardiac death or new coronary events in a 3-year follow-up (univariate analysis; p <0.0005). Echocardiography also plays an important role in detecting postinfarct ischemia, as seen by its wide use during stress tests. In our experience, the response to exercise echocardiographic testing has a high prognostic value. In fact, in our series, univariate analysis (Kaplan-Meier) showed that the best predictors of coronary events were the number of markers of ischemia during exercise (p <0.00001), the work load (p <0.00001), a positive exercise echo (p <0.0005), and the echo score at rest (p <0.0005). Multivariate analysis (Cox) confirmed these data: number of markers of ischemia: odds ratio (OR) 4.45, 95% confidence interval (CI) 1.5-13.1; work load: OR 2.46, CI 1.3-4.5; positive exercise echo OR 1.88, CI 1.1-3.2. Thus, serial echocardiography together with predischarge stress echocardiography is recommended for risk stratification after acute MI. In particular, in thrombolytic-treated patients, echo examinations allow the detection of functional recovery of viable reperfused myocardium whereas stress echo may show exercise-induced worsening in the region supplied by the infarct-related vessel, a predictor of a higher rate of coronary events.

Echocardiography in the coronary care unit: diagnostic and prognostic impact in comparison with clinical and other indicators

The clinical arena in which we must consider the role of echocardiography is characterized by 2 fundamental findings: (1) most patients with chest pain and suspected acute myocardial infarction (MI) do not present diagnostic electrocardiograms; and (2) an early and correct diagnosis is necessary to match the patient with the most adequate treatment. Echocardiography may be very useful in the coronary care unit, allowing a correct diagnosis of ischemic heart disease when electrocardiography is unclear, even before the rise of cardiac enzymes is detected. It may also play a role in decision-making for thrombolytic therapy. In addition, echocardiography provides useful information for early risk stratification. In fact, although high-risk patients are well identified by simple clinical or instrumental variables (i.e., Killip classification, enzymatic data, blood-gas analysis, electrocardiogram, etc.), most patients (>60%) are identified as low risk, and several subjects classified into the low-risk groups have a poor prognosis and are not detected using a single variable. In our experience, 2-dimensional echocardiography was able to further stratify between patients of low-risk classes. Therefore, echocardiography plays an important role in the early stratification of acute MI patients, especially in those without signs or symptoms of heart failure.

Dissociation between changes in intramyocardial function and left ventricular volumes in the eight weeks after first anterior myocardial infarction

OBJECTIVES

We sought to examine the relation between regional changes in intramyocardial function and global left ventricular (LV) remodeling in the first 8 weeks after reperfused first anterior myocardial infarction (MI).

BACKGROUND

Because of limitations in imaging methods used to date, this relation has not been thoroughly evaluated.

METHODS

We studied 26 patients (21 men, 5 women; mean age 51 years) by magnetic resonance imaging (MRI) on day 5 +/- 2 (mean +/- SD) and week 8 +/- 1 after their first anterior MI. All patients had single-vessel left anterior descending coronary artery disease and although they had received reperfusion therapy, all had regional LV dysfunction and an initial ejection fraction (EF) < or = 50%. Short-axis magnetic resonance tagging was performed spanning the LV. Percent intramyocardial circumferential shortening (%S) on a topographic basis, LV mass index, LV end-diastolic volume index (LVEDVI), LV end-systolic volume index and LV ejection fraction (LVEF) were measured.

RESULTS

Left ventricular mass index tended to decrease, whereas the LVEDVI increased from 82 +/- 24 to 96 +/- 27 ml/m2 (p = 0.002). Left ventricular end-systolic volume index remained unchanged, whereas LVEF increased from 39 +/- 12% to 45 +/- 14% (p = 0.002). Apical %S improved from 9 +/- 6% to 13 +/- 5% (p < 0.0001), as it did in the midanterior (6 +/- 6% to 10 +/- 7%, p < 0.02) and midseptal regions (8 +/- 7% to 12 +/- 6%, p < 0.02). Early dysfunction in remote midinferior and basal lateral regions resolved by 8 weeks. By multivariate analysis, the only significant predictor of an increase in LVEDVI over the study period was peak creatine kinase (p = 0.04).

CONCLUSIONS

In the first 8 weeks after a large, reperfused anterior MI, %S improved in the apex, midanterior and midseptal regions and normalized in remote noninfarct-related regions, but LV end-diastolic volumes also increased. This increased LVEDVI correlated with infarct size by peak creatine kinase and was not related to changes in global and regional LV function.

Contractile versus microvascular reserve for the determination of the extent of myocardial salvage after reperfusion. The effect of residual coronary stenosis

BACKGROUND

We hypothesized that microvascular reserve is a better indicator of the extent of viable myocardium postinfarction than contractile reserve, especially in the presence of a residual stenosis of the infarct-related artery.

METHODS AND RESULTS

Fifteen dogs with various infarct sizes were studied after reperfusion. Contractile reserve, studied by use of dobutamine echocardiography, and microvascular reserve, studied by use of myocardial contrast echocardiography, were measured both before and after creation of a stenosis. In the absence of a stenosis, the relation between infarct size, expressed as percent of risk area, and wall thickening improved with increasing doses of dobutamine (r = .41, .71, and .90 for 5, 10, and 15 micrograms.kg-1.min-1, respectively; P < .01 for dobutamine 15 micrograms.kg-1.min-1). In the presence of a stenosis, however, the relation was poor for all doses of dobutamine (r = .22, .57, and .32 for 5, 10, and 15 micrograms.kg-1.min-1, respectively; P < .01 for 15 micrograms.kg-1.min-1 dobutamine in the absence of a stenosis). There was a fair correlation between infarct size and perfusion defect size on myocardial contrast echocardiography after reperfusion (r = .82), with the defect size underestimating infarct size by approximately 20%. This relationship improved (P < .01) during infusions of both adenosine (r = .99) and dobutamine (r = .94) in the absence of a stenosis. The correlations between infarct size and perfusion defect on myocardial contrast echocardiography also remained good in the presence of a stenosis (r = .95 and .81 for adenosine and dobutamine, respectively; P = NS compared with stenosis).

CONCLUSIONS

Microvascular reserve is superior to contractile reserve for definition of the spatial topography of necrosis and hence the extent of viable myocardium within the infarct bed after reperfusion, particularly when a residual stenosis is present in the infarct-related artery.

Stunned myocardium after thrombolytic treatment. Identification by dobutamine echocardiography and role of the residual stenosis in the infarction artery

The aim of this study was to identify post-thrombolysis stunned myocardium using low dose (10 micrograms/kg/min) dobutamine echocardiography, and to elucidate the role of the residual stenosis in the infarction artery in wall motion recovery. Forty-seven consecutive patients treated with thrombolytic agents for a first non-complicated myocardial infarction were included. An early dobutamine echocardiogram was performed 7 +/- 2 days after thrombolysis to calculate a wall motion score index at baseline and with dobutamine. A late resting echocardiogram 36 +/- 7 days and a coronariography 41 +/- 8 days after thrombolysis were also performed. In 12 patients no baseline regional dysfunction was observed in the early echocardiogram (Group I), whereas 35 patients (Group II) presented regional dysfunction which improved with dobutamine in 11 cases (Group IIA), but not in 24 (Group IIB). Maximum creatine kinase peak was smaller in Group I (458 +/- 162, P < or = 0.01) and in Group IIA (931 +/- 593, P < or = 0.05) than in Group IIB (1547 +/- 886). Late resting echocardiogram was performed in 44 patients: all 12 from Group I, 10 from Group IIA and 22 from Group IIB; all patients from Group I persisted with normal wall motion, while the baseline score index improved in seven patients (70%) from Group IIA vs. three patients (14%) from Group IIB (P < or = 0.01). Quantitative angiographic parameters in the infarction artery failed to differentiate the subgroup of patients in whom wall motion improved in the late echocardiogram. By simple regression, smaller creatine kinase peak (P < or = 0.05) and a positive response to dobutamine in the early echocardiogram (P < or = 0.001) correlated with wall motion recovery, but the minimum lumen diameter in the infarction artery did not correlate; by multiple logistic regression, only a positive response to dobutamine in the early echocardiogram independently predicted late wall motion improvement (P < or = 0.001).

CONCLUSIONS

(1) Low dose dobutamine echocardiography early after thrombolytic treatment identifies dysfunctional myocardium with potential late spontaneous improvement (stunned myocardium). (2) Myocardial stunning tends to occur in small infarctions. (3) Late wall motion improvement can occur despite severe residual stenosis in the infarction artery.

Improved posterobasal segment function after thrombolysis is associated with decreased incidence of significant mitral regurgitation in a first inferior myocardial infarction

OBJECTIVES

This study was designed to investigate the association between wall motion abnormalities and the occurrence of ischemic mitral regurgitation in patients with a first inferior or posterior myocardial infarction and to reassess the role of thrombolytic treatment in these patients.

BACKGROUND

We previously demonstrated that thrombolytic therapy reduces the incidence of significant mitral regurgitation in patients with a first inferior myocardial infarction, but the mechanisms responsible for this decrease were not clear.

METHODS

Wall motion score on two-dimensional echocardiography (16 segments) and mitral regurgitation grade (0 to 3) on Doppler color flow imaging were assessed in 95 patients (in 47 after thrombolysis) at 24 h, 7 to 10 days and 1 month after myocardial infarction. Significant mitral regurgitation was defined as moderate or severe (grade 2 or 3).

RESULTS

Multivariate analysis revealed that the presence of an advanced wall motion abnormality of the posterobasal segment of the left ventricle was the most significant independent variable associated with significant mitral regurgitation: odds ratio (OR) 15.0, 90% confidence interval (CI) 1.4 to 165.6 at 24 h; OR 2.8, CI 0.9 to 9.3 at 7 to 10 days; OR 4.2, CI 1.2 to 11.4 at 1 month. Thrombolysis reduced the prevalence of advanced wall motion abnormalities in the posterobasal segment at 24 h (55% vs. 75%, OR 0.5, CI 0.2 to 0.99), 7 to 10 days (44% vs. 73%, OR 0.3, CI 0.1 to 0.7) and 1 month (36% vs. 56%, OR 0.4, CI 0.2 to 0.9).

CONCLUSIONS

There is a strong association between advanced wall motion abnormalities in the posterobasal segment and significant mitral regurgitation. In this study group, thrombolysis reduced the prevalence of advanced wall motion abnormalities in the posterobasal segment and thereby reduced the incidence of significant mitral regurgitation.

Influence of residual perfusion within the infarct zone on the natural history of left ventricular dysfunction after acute myocardial infarction: a myocardial contrast echocardiographic study

OBJECTIVES

This study used myocardial contrast echocardiography to investigate the extent of residual perfusion within the infarct zone in a select group of patients with recently reperfused myocardial infarction and evaluated its influence on the ultimate infarct size.

BACKGROUND

Limited information is available on the status of myocardial perfusion within postischemic dysfunctional segments at predischarge and on its influence on late regional and global functional recovery.

METHODS

Twenty patients with acute myocardial infarction were selected for the study. Patients met the following inclusion criteria: 1) single-vessel coronary artery disease; 2) patency of infarct-related artery with persistent postischemic dysfunctional segments at predischarge; 3) stable clinical condition up to 6 months after hospital discharge. All selected patients underwent coronary angiography and myocardial contrast echocardiography before hospital discharge and repeated the echocardiographic examination 6 months later. Patients were grouped according to the pattern of contrast enhancement in predischarge dysfunctional segments.

RESULTS

In nine patients (group I), the length of segments showing abnormal contraction coincided with that of the contrast defect segments. In the remaining 11 patients (group II), postischemic dysfunctional segments were partly or completely reperfused. There was no difference between the two groups in asynergic segment length at predischarge (7.3 +/- 2.5 vs. 7.2 +/- 4.3 cm, p = NS). At follow-up study, asynergic segment length was significantly reduced in group II patients, whereas no changes were observed in group I patients (from 7.2 +/- 4.3 to 4.7 +/- 3.7 cm, p < 0.005; and from 7.3 +/- 2.5 to 7.5 +/- 2.9 cm, p = NS, respectively).

CONCLUSIONS

Among patients with a predischarge patent infarct-related artery, further improvement in regional and global function may be expected during follow-up when residual perfusion in the infarct zone is present.