CLINICAL STUDIES
Prognostic value of the amount of dysfunctional but viable myocardium in revascularized patients with coronary artery disease and left ventricular dysfunction
Jaroslav Meluzín, MD, PhDa,
Jan  ern , MD, Prof*,
Milan Frélich, MD, PhD*,
Franti ek  t tka, MD*,
Lenka pinarová, MDa,
Jana Popelová, MD, PhD ,
Roman típal, MD, PhD on behalf of the Investigators of This Multicenter Study
a 1st Internal Department, Brno, Czech Republic
* Center of Cardiovascular and Transplant Surgery, Brno, Czech Republic
Internal Department of the Faculty Hospital Motol, Prague, Czech Republic
Internal Department of the Faculty Hospital, Ostrava, Czech Republic
Manuscript received February 25, 1998;
revised manuscript received June 5, 1998,
accepted June 12, 1998.
Address for correspondence: Dr. Jaroslav Meluzín, 1st Internal Department, St. Anna Hospital, Peka ská 53, Brno, 656 91, Czech Republic
jtoman{at}med.muni.cz
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Abstract
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Objectives. The purpose of our study was to assess the prognostic importance of the amount of dysfunctional but viable myocardium in revascularized patients with coronary artery disease (CAD) and left ventricular (LV) dysfunction.
Background. The amount of dysfunctional but viable myocardium predicts the functional improvement after revascularization and may offer more precise risk stratification of patients referred for bypass surgery or coronary angioplasty.
Methods. Two hundred and seventy-four consecutive patients with CAD and LV ejection fraction  40% underwent low-dose dobutamine echocardiography for viability assessment. One hundred and thirty-three of them were revascularized using either coronary artery bypass surgery (118 patients) or coronary angioplasty (15 patients) and entered this study. To quantify the amount of dysfunctional but viable myocardium, wall motion was scored using 16-segment model. The dysfunctional segments were defined as viable if they exhibited improvement in their thickening by at least 1 grade with dobutamine infusion. The patients were followed up for a mean period of 20 ± 12 months (range, 2 to 48) for cardiac mortality and nonfatal cardiac events including myocardial infarction, unstable angina pectoris requiring hospitalization and hospitalization for heart failure. Standard follow-up echocardiography was performed 3 to 6 months after revascularization.
Results. Twenty-nine patients exhibited a large amount of dysfunctional but viable myocardium ( 6 segments, group A), 60 patients had a small amount of dysfunctional but viable myocardium (2 to 5 segments, group B) and 44 patients were found to have dysfunctional myocardium irreversibly damaged (group C). Similar prerevascularization LV ejection fractions of 35% ± 5%, 34% ± 4%, 36% ± 4% in groups A, B and C increased to 47% ± 6% (p < 0.01 vs. baseline, p < 0.01 vs. groups B and C), to 40% ± 5% (p < 0.01 vs. baseline) and to 37% ± 6% (p = NS vs baseline), respectively, after revascularization. The greatest functional improvement after revascularization in group A patients was accompanied by a lower rate of cardiac events during follow-up (2 vs. 18 in group B, p < 0.05, and vs. 17 in group C, p < 0.01) and better cardiac event-free survival according to Kaplan–Meier survival analysis (p < 0.05 vs. groups B and C, respectively).
Conclusion. In revascularized patients with CAD and moderate or severe LV dysfunction, the presence of a large amount of dysfunctional but viable myocardium identifies patients with the best prognosis.
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Abbreviations and Acronyms
| | AP | = angina pectoris | | CAD | = coronary artery disease | | DE | = dobutamine echocardiography | | EF | = ejection fraction | | LV | = left ventricular | | MI | = myocardial infarction | | WMS | = wall motion score |
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In many patients with coronary artery disease (CAD), resting left ventricular (LV) dysfunction is a consequence of myocardial hibernation. The important attribute of hibernating myocardium is its ability to restore its function to normal or near normal after myocardial revascularization (1,2). However, such viable metabolically active but dysfunctional myocardium represents an unstable substrate which is likely to lead to ischemic events (3). Recent studies have repeatedly suggested that patients with CAD and LV dysfunction with nonrevascularized viable myocardium have a propensity to suffer later cardiac events (3–7) and that revascularization improves their survival (3,5–7). To date, there are no reports on the influence of the amount of dysfunctional but viable myocardium assessed by dobutamine echocardiography (DE) on long-term prognosis of revascularized patients with CAD and LV dysfunction. Recently, the strong correlation between the number of dysfunctional segments with contractile reserve assessed by DE and the improvement in LV ejection fraction (EF) after revascularization was found (8). Because LV systolic function is known to be the important predictor of survival in patients with CAD (9–12), one can await the prognostic impact of the quantification of the amount of dysfunctional myocardium with contractile reserve.
Thus, the purpose of our study was to assess the prognostic value of the amount of dysfunctional but viable myocardium as indicated by DE in revascularized patients with CAD and LV dysfunction.
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Methods
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Patient selection.
Patients with CAD and LV dysfunction referred for coronary angiography and potential coronary revascularization were prospectively enrolled between January 1994 and December 1997 in one center and between May 1995 and December 1997 in the other centers if they fulfilled the following criteria: 1) LV EF 40% as assessed by echocardiography; 2) luminal diameter narrowing 50% of at least one major coronary artery; 3) no myocardial infarction (MI) or unstable angina pectoris (AP) within 2 months before coronary angiography; 4) the ability to evaluate regional wall motion abnormalities of all 16 myocardial segments with echocardiography; 5) no cardiac disease except CAD; 6) no cancer or relevant liver or renal disease; 7) no need for aneurysmectomy; and 8) sinus rhythm in electrocardiography. Two hundred and seventy-four such consecutive patients underwent DE for viability evaluation within 3 days after coronary angiography. One hundred and thirty-nine of them were revascularized based on clinical criteria (stable AP and/or multivessel CAD) within the next 2 months. Six of them were excluded because of inability to revascularize all vessels supplying dysfunctional but viable myocardial segments.
Thus, 133 revascularized patients entered our study: 129 men and 4 women. The mean age of patients was 58 ± 8 years (range, 42 to 78), the mean LV EF 34% ± 5%. One hundred and twenty-three (92%) had a history of MI, 58 (44%) were treated for hypertension, 65 (49%) for hypercholesterolemia and 36 (27%) for diabetes. All patients gave their informed consent to DE and written consent to coronary angiography and coronary artery bypass grafting surgery or coronary angioplasty. The study protocol was approved by the Institutional Ethics Committee.
Coronary angiography.
Selective coronary angiography was performed in multiple views using standard techniques during 1 to 2 days after hospital admission. The severity of coronary stenoses was expressed as percent luminal diameter narrowing. Significant CAD was defined as 50% diameter stenosis of at least one major coronary artery.
Dobutamine and follow-up echocardiography.
Standard transthoracic echocardiography and DE were performed with the patients in the left lateral decubitus position. After resting images were obtained, dobutamine was administered intravenously with an infusion pump at doses 5 and 10 ug/kg/min each for 5 min. Parasternal long-axis view, parasternal short-axis views at the base, papillary muscle and apex levels and apical 2- and 4-chamber views were recorded at rest and at both doses of dobutamine on VHS videotape for subsequent off-line analysis. The electrocardiogram was monitored continuously during dobutamine infusion and blood pressure was taken at each stage. Beta-blocking agents were withdrawn 24 h before the stress. Follow-up standard echocardiography was obtained 3 to 6 months (mean 4 ± 1) after coronary revascularization.
Echocardiographic analysis.
Regional wall motion was evaluated using a 16-segment model recommended by the American Society of Echocardiography (13). Myocardial segments were scored with the following scale: 1 = normal or hyperkinetic, 2 = hypokinetic, 3 = akinetic and 4 = dyskinetic, with scoring by visual analysis of systolic wall thickening. Wall thickening was assessed at a distance of 1 cm from the adjacent segment to minimize the effect of tethering (14,15). A regional wall motion score (WMS) index was calculated as the sum of scores for each segment divided by the total number of segments. The dysfunctional segments were defined as viable if they exhibited functional improvement of at least 1 grade with any dose of dobutamine. A change from dyskinetic to akinetic was not considered to be improved wall motion. The presence of dysfunctional but viable myocardium was defined by the presence of at least two such adjacent dysfunctional but viable segments (8,16–18). The number of dysfunctional but viable myocardial segments was used to quantify the amount of dysfunctional but viable myocardium and to discriminate the patients’ groups. For the purpose of matching myocardial segments with coronary distribution in angiography, apical, anterior, anteroseptal and midseptal segments were assigned to the left anterior descending coronary artery territory, and the remaining segments either to the right coronary artery or to the left circumflex coronary artery bed (19).
End-diastolic and end-systolic frames from apical 4- and 2-chamber views were traced on a Kontron C200 (Munich, Germany) image processing computer for LV volume evaluation. Volume and EF were calculated as an average of three to five consecutive heart cycles using the biplane Simpson’s method recommended by the American Society of Echocardiography (13). Regional wall motion analysis and EF calculations were performed off-line from videotapes in one center by readers who were blinded to patients’ data. All volume calculations were done by one experienced echocardiographer (J.M.). Regional wall motion was assessed by consensus of two experienced observers (J.M., L. .). Interobserver and intraobserver variabilities of those readers have been published previously (8) and attained 93% concordance for the scoring of 800 segments and 92% concordance for identifying the presence of contractile reserve of 121 dysfunctional segments, respectively. Intraobserver variability was concordant for wall motion scoring in 769 of 800 segments (96%) and for the presence of contractile reserve in 115 of 121 segments (95%), respectively.
Coronary revascularizations.
Coronary revascularizations were performed within 2 months after coronary angiography. Of 133 patients who entered the study, 118 patients underwent coronary artery bypass grafting surgery and 15 patients underwent coronary angioplasty. There was no MI or unstable AP in the period between DE and revascularization.
Follow-up.
After coronary revascularization, 16 patients were followed up by mail and by contact with the treating physician, the others were regularly followed up by an examining echocardiographer in 3- to 6-month intervals. The patients were followed up for cardiac mortality and nonfatal cardiac events including MI, unstable AP requiring hospitalization and hospitalization for heart failure. Myocardial infarction was defined as a hospital admission for prolonged (>20 min) chest pain, electrocardiographic changes and an increase in plasma cardiac enzyme activity. Unstable AP was defined by resting anginal symptoms requiring hospitalization with parenteral nitrates and/or heparin therapy (no cardiac enzyme elevation or new Q waves on the electrocardiogram). Heart failure requiring hospitalization was identified by dyspnoe, need for intravenous inotropic and/or diuretic therapy and by symptoms associated with left (rales on lung auscultation, S3 gallop) and/or right (neck vein distension, ankle edema, hepatomegaly) heart failure. Cardiac events were analyzed as: cardiac death alone for survival; cardiac death and nonfatal MI for infarction-free survival; and cardiac death, nonfatal MI, unstable AP requiring hospitalization and hospitalization for heart failure for event-free survival. The follow-up data were available for all surviving patients. In the case of patient death or cardiac event, admitting departments or local physicians were contacted to elucidate exact reason for hospitalization or cause of death. The mean follow-up period was 20 ± 12 months (range, 2 to 48).
Statistical analysis.
To define the cutoff value for differentiating groups of patients with a large and a small amount of dysfunctional but viable myocardium, five numbers of dysfunctional but viable myocardial segments (4, 5, 6, 7 and 8) were tested to best discriminate those groups according to the risk of developing cardiac events. Using the Fisher exact test, the cutoff value of six dysfunctional but viable segments was found to have the greatest statistical power for our stratification (p = 0.02). Lower cutoff values four and five were not able to discriminate groups with increased risk of developing cardiac events (p = 0.40 and 0.30, respectively). Thus, three groups of patients were defined. Group A comprised patients with a large amount of dysfunctional but viable myocardium (six and more dysfunctional but viable myocardial segments); group B included patients with a small amount of dysfunctional but viable myocardium (two to five dysfunctional but viable segments); and group C comprised patients in whom dysfunctional myocardium was irreversibly damaged. Clinical and echocardiographic data are given as mean ± SD for continuous variables or as a number (percent) for categoric variables. Comparisons were performed for groups A, B and C, for echocardiographic parameters before and after revascularization and for patients with or without cardiac events. Differences in continuous variables were tested using Mann–Whitney or Wilcoxon tests; differences in categoric variables were evaluated using chi-square test with Yates correction or Fisher exact test, respectively. Kaplan–Meier survival curves were used to compare the survival, infarction-free survival and event-free survival in groups A, B and C. The differences between survival curves were assessed by the Mantel–Cox test. The Cox proportional hazards model was utilized to analyze the relation between cardiac event-free survival and the following variables potentially relating to the patients’ prognosis: the presence of a large amount of dysfunctional but viable myocardium, sex, age, completeness and type of revascularization (bypass grafting or angioplasty), number of revascularized arteries, prerevascularization LV EF and end-diastolic and end-systolic volume indexes. In this Cox model the stepwise elimination with the presence of a large amount of dysfunctional but viable myocardium forced in the first step was performed. The Kaplan–Meier analysis and Cox proportional hazards model were performed using the BMDP 1L and 2L programs of the BMDP statistical package for PC, version PC 90 (20). A p value <0.05 was considered significant.
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Results
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Patient characteristics.
Based on the number of dysfunctional but viable segments assessed by DE, the patients were divided into three groups. Group A comprised 29 patients with a large amount of dysfunctional but viable myocardium (six myocardial segments or more). The mean number of dysfunctional but viable segments was 7.4 ± 1.7 (range, 6 to 11). Group B comprised 60 patients with a small amount of dysfunctional but viable myocardium (two to five segments). The mean number of dysfunctional but viable segments was 3.4 ± 1.2. Group C comprised 44 patients in whom dysfunctional segments were irreversibly damaged. The baseline and postrevascularization characteristics of individual groups are shown in Tables 1 and 2,respectively. Hypercholesterolemia was defined as serum cholesterol >250 mg/dl and obesity as body mass index 30 kg/m2. The only difference between groups was the greater number of revascularized arteries in group A than in group C. Otherwise, the groups were similar with respect to gender distribution, age, frequency of stable AP or previous MI, occurrence of risk factors for CAD, number of diseased coronary arteries, completeness and type of revascularization, postrevascularization medication or any other variables potentially relating to patient prognosis. Twenty-one patients after bypass surgery and six patients after coronary angioplasty continued to have or developed mild AP after revascularization. These patients were similarly distributed in all three groups. Nine of them underwent only incomplete revascularization. Two patients (one each from groups B and C) with proven restenosis underwent repeat coronary angioplasty. There was no need for repeat bypass surgery.
Echocardiography.
Left ventricular EFs and WMS indexes at rest before revascularization were 35% ± 5%, 34% ± 5%, 35% ± 4%, and 2.13 ± 0.40, 2.17 ± 0.46, 2.06 ± 0.42, respectively (all p = NS), for groups A, B and C. Corresponding end-diastolic and end-systolic volume indexes reached 86 ± 30, 84 ± 21, 84 ± 22 and 56 ± 22, 56 ± 17, 54 ± 17, respectively (all p = NS). Follow-up echocardiography was obtained in 117 patients. It was not performed in 12 patients who died within 4 months after revascularization, in 1 patient with acute MI 2 months after bypass surgery and in 3 patients for nonmedical reasons. Table 3 represents a comparison of echocardiographic variables before and after revascularization. Left ventricular EF, WMS index and end-systolic volume index significantly improved only in groups A and B. However, improvement in LV systolic function was significantly greater in patients with a large amount of dysfunctional but viable myocardium (group A).
Cardiac events.
Of 133 patients studied, 31 (23%) suffered a cardiac event. These comprised 2 events in 2 group A patients, 18 events in 16 group B patients (1 patient had 2 episodes of unstable AP and the other suffered MI 3 days after bypass surgery and hospitalization for heart failure 15 months after bypass surgery) and 17 events in 13 group C patients (1 patient suffered 3 episodes of unstable AP and 2 patients had 2 hospitalizations for heart failure). The detailed characteristics of cardiac events are shown in Table 4. Of 11 early cardiac events (within 30 days after revascularization), 9 deaths occurred on hospital days 1, 2, 3, 4, 7, 10, 17, 28 and 30, respectively, after bypass surgery; both nonfatal MIs were diagnosed on day 3 after bypass surgery. All patients suffering cardiac events underwent bypass surgery except one group B patient who had one episode of unstable AP and one group C patient suffering MI 2 months after angioplasty. Of 9 patients who died within 30 days after bypass surgery, five suffered MI (one group A, one group C, and three group B patients) on days 1, 1, 2, 3, and 4, respectively, after operation. The cause of death of remaining patients was progressive heart failure. Of five late deaths, the reasons were progressive heart failure in two group B patients and sudden cardiac death in the remaining three. As demonstrated in Table 4, the cardiac event rate was significantly lower in patients with a large amount of dysfunctional but viable myocardium (group A) than in the remaining patients. This observation is in concordance with the Kaplan–Meier event-free survival analysis (Fig. 1) confirming significantly better event-free survival in group A than in groups B and C (both p < 0.05), respectively. There was no difference in event-free survival between groups B and C. Concerning infarction-free survival (Fig. 2) and survival (Fig. 3), there were no significant differences among groups.
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Figure 1 Kaplan–Meier curves showing survival free of cardiac events (including death, nonfatal MI, unstable AP requiring hospitalization and hospitalization for heart failure) in groups A, B and C patients. Event-free survival was significantly better in group A than in group B or group C, both being p < 0.05.
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Figure 2 Kaplan–Meier curves demonstrating infarction-free survival in groups A, B and C patients. There were no significant differences among groups.
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Figure 3 Kaplan–Meier curves showing survival in groups A, B and C patients. There were no significant differences among groups.
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Determinants of cardiac events.
Table 5 compares clinical characteristics relating to patient prognosis and prerevascularization echocardiographic variables in patients with or without cardiac events. Those suffering cardiac events were more likely to have lower LV EF and the absence of a large amount of dysfunctional but viable myocardium; otherwise, the differences were not significant. However, for late follow-up results, LV systolic function after revascularization may be more important than prerevascularization functional values. Thus, Table 6 represents the functional variables obtained 3 to 6 months after revascularization and their changes from prerevascularization values in patients without events or with late cardiac events in whom follow-up echocardiography was obtained. Patients without cardiac events exhibited significantly greater functional improvement after revascularization than those with late events, inducing greater difference in postrevascularization functional variables between these two groups. Analysis by the Cox proportional hazards model revealed two independent predictors for cardiac event-free survival: the presence of a large amount of dysfunctional but viable myocardium (relative risk = 0.257, chi-square = 5.12, p = 0.024) and LV EF before revascularization, the predictive power of which was even stronger (relative risk = 0.880, chi-square = 14.98, p < 0.001). The amount of additional information contributed by the other variables was not statistically significant.
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Table 6 Follow-up Echocardiographic Results of Patients Without Cardiac Events and Those With Late Cardiac Events
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Discussion
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This study was performed in patients with CAD and moderate-to-severe chronic LV dysfunction. Such patients have a poor prognosis which can be improved by coronary revascularization (21,22). Because of risk of bypass surgery in patients with severe LV dysfunction, stratification with respect to postoperative functional improvement—and especially prognosis—may be worthwhile. In patients with a large amount of dysfunctional but viable myocardium, there is a supposition of more pronounced functional improvement after revascularization and probably better prognosis than in those having only a small amount or no such myocardium. However, to our knowledge the prognostic significance of the amount of dysfunctional but viable myocardium assessed by DE has not been determined.
Prognostic importance of myocardial viability recognized by DE.
Dobutamine echocardiography is an established method for detecting viable myocardium in patients with CAD and LV dysfunction with very good sensitivity and specificity for predicting wall motion improvement after coronary revascularization (16–18,23–32). In addition, DE has been recently shown to provide prognostic information in patients with both acute MI (33,34) and chronic CAD with LV dysfunction (4). Sicari et al. (33) demonstrated in 778 patients with a first uncomplicated acute MI that the presence of myocardial viability assessed by low-dose DE is prognostically important and is associated with greater incidence of unstable AP during follow-up. However, the presence of viability did not significantly relate to the occurrence of hard events (death or reinfarction). On the other hand, the presence of remote ischemia with high doses of dobutamine identified patients at increased risk of cardiac-related death or nonfatal MI. In that study myocardial response to different doses of dobutamine enabled the estimate of risk of various cardiac events. Using multivariate analysis of clinical, angiographic and DE variables, Carlos et al. (34) revealed that the only independent predictors of adverse outcome after acute MI were infarction zone nonviability and ischemia/infarction at a distance. These results differ from those of Sicari et al. (33) in the importance of infarction zone nonviability for adverse outcome. The exact reason for the discrepancy is not clear, but it may be caused by the influence of infarct size (Sicari et al. included only first uncomplicated acute MI) with increased risk of adverse events in large infarcts with nonviable myocardium. Next, support for the importance of viability evaluation was provided by Bolognese et al. (35) who demonstrated progressive LV dilatation in patients after reperfused acute MI with the absence of residual infarct-zone viability.
In patients with chronic CAD and moderate or severe LV dysfunction, there is agreement of increased risk of medically treated patients with dysfunctional but viable myocardium (3–7). Using DE, Williams et al. (4) identified increase of cardiac events in patients with viable or ischemic myocardium as compared with those with scarring. This report is in keeping with results in similar studies using positron emission tomography (3,5,6) or rest-redistribution single-photon emission computed tomography (7). They concordantly proved that patients with dysfunctional but viable myocardium who are treated medically are at increased risk of cardiac events and that revascularization improves their survival (3,5–7).
Importance of quantification of the amount of dysfunctional but viable myocardium.
The main result of this study was the fact that patients with a large amount of dysfunctional but viable myocardium (group A) exhibited significantly less cardiac events and better cardiac event-free survival than those with a small amount (group B) or no dysfunctional but viable myocardium (group C). Except for the small but significant difference in the number of revascularized arteries between groups A and C, the groups were comparable in all variables listed in Tables 1 and 2 relating to the patients’ prognosis as well as in parameters of LV systolic function before revascularization (Table 3). However, they differed markedly in postrevascularization LV systolic function, being the greatest in patients with a large amount of dysfunctional but viable myocardium. This is not surprising because the linear relationship between the number of dysfunctional segments with contractile reserve and functional improvement after revascularization has been documented previously (8). These data suggest that the beneficial influence of a large amount of dysfunctional but viable myocardium on patient prognosis was mediated probably through significant functional improvement after revascularization. Recently, Pagley et al. (36) demonstrated very similar results using rest-redistribution thallium-201 scintigraphy to quantify the extent of myocardial viability. They demonstrated that patients with low EF, multivessel CAD and greater extent of viability have better short- and long-term outcomes after bypass surgery than similar patients with lesser amount of viability. In our study, patients with or without cardiac events differed only in terms of LV EF and the presence of a large amount of dysfunctional but viable myocardium (Table 5), which were both found to be predictors of cardiac event-free survival. Patients without events had mildly but significantly greater LV EF before revascularization, which is in concordance with previous reports (12,37). For long-term follow-up results, however, the values of LV systolic function after revascularization may add more valuable information than prerevascularization values. In our study, the patients without cardiac events were found to have significantly greater functional improvement after revascularization than those suffering late events, explaining greater differences in postrevascularization functional parameters between these two cohorts of patients (Table 6). The Kaplan–Meier event-free survival curves provided further support for the major impact on patient prognosis by LV systolic function after revascularization. Groups A, B and C with comparable values of prerevascularization LV EFs, WMS indexes and end-systolic volume indexes exhibited similar rates of early postoperative events. However, patients with marked postrevascularization functional improvement (group A) were found to have better event-free survival later after revascularization, and this trend increased with time of follow-up. All these data support the need for quantification of myocardial viability, because only such an approach offers information on risk of patients referred for bypass surgery and enables prediction of LV systolic function after revascularization which is a very important factor influencing patients’ long-term survival. Such stratification may add a reasonable tool for therapeutic strategy in patients with CAD and severely depressed LV function in whom both revascularization and cardiac transplantation are methods of choice.
Study limitations.
The number of patients in our study was relatively small. In addition, we do not have exact information on the extent of coronary revascularization, because follow-up coronary angiography was not performed. However, angina pectoris after revascularization was distributed in a similar frequency in all groups and its incidence was relatively low, taking into account the number of incomplete revascularizations; therefore, the different extent of revascularization is unlikely to account for the differences in patients’ survival. There are several limitations in identifying dysfunctional but viable segments inherent in DE. In some patients, one may find no postrevascularization improvement in the areas of myocardium with mix of viable tissue and fibrosis even if such myocardium may exhibit a positive response to catecholamine stimulation. On the other hand, in patients with severe stenosis of the coronary artery, even a low-dose of dobutamine may induce ischemia with no improvement in systolic thickening despite preserved myocardial viability. Moreover, echocardiographic evaluation of regional wall motion is a subjective method that may be influenced by tethering (14,15) and postoperative paradoxic septal motion (38). We attempted to minimize these potential confounding influences by assessing systolic thickening rather than motion and by performing follow-up echocardiography more than 3 months after revascularization (mean 4 ± 1 months, range 3 to 6). Recently, Afridi et al. (39) have shown that the prediction of functional recovery after revascularization with DE depends on the type of wall motion response observed during dobutamine infusion, the best being for a biphasic response (improvement in wall thickening of dysfunctional segments at low dose and worsening at high dose of dobutamine). The recommendation of this study is to administer low as well as high doses of dobutamine for the optimal prediction of postrevascularization functional recovery. In our study, which started 2 years before publishing these results, only low doses of dobutamine were applied. However, many authors using the same methodology have described very good sensitivities of 87%, 89%, 88%, 79%, 82%, and specificities of 82%, 82%, 87%, 83%, 92%, respectively, for the prediction of reversibility of wall motion after revascularization (28–32). Thus, despite the limitations mentioned, low-dose DE still represents a valuable tool for identifying dysfunctional segments that will recover after revascularization.
Conclusions.
Our data suggest that in patients with CAD and moderate or severe LV dysfunction referred for coronary revascularization, the identification and, especially, the quantification of dysfunctional but viable myocardium is of great clinical importance. Patients with a large amount of dysfunctional but viable myocardium (greater than or equal to six myocardial segments assessed by DE) exhibit greater postrevascularization improvement in LV systolic function and better prognosis as compared with those with a small amount or no dysfunctional but viable myocardium.
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Appendix
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Centers and participants: 1st Internal Department, St. Anna Hospital, Brno, Czech Republic: J. Meluzín, MD, PhD, L. pinarová, MD, L. Groch, MD. Center of Cardiovascular and Transplant Surgery, Brno, Czech Republic: J.  erný, MD, Prof, M. Frélich, MD, PhD, F. t tka, MD. Internal Department of the Faculty Hospital Motol, Prague, Czech Republic: J. Popelová, MD, PhD. Department of Cardiac Surgery of the Faculty Hospital Motol, Prague, Czech Republic: T. Honk, MD, PhD. Internal Department of the Faculty Hospital, Ostrava, Czech Republic: R. típal, MD, PhD. Cardiosurgical Department of the Faculty Hospital, Ostrava, Czech Republic: J. To ovský, MD, PhD.
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Acknowledgments
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We acknowledge J. Polach, RNDr, for his help in statistical analysis.
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Footnotes
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This work was supported in part by grant from the Ministry of Health of the Czech Republic, IGA, No. 4344-3.
 All participants and centers are mentioned in the Appendix. 
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Abstract
Methods