Ann Thorac Surg 1997;64:1728-1734
© 1997 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Myocardial Revascularization in Patients With Ischemic Cardiomyopathy: Functional Observations
Maurizio Salati, MD,
Massimo Lemma, MD,
Daniel G. Di Mattia, MD,
Paolo Danna, MD,
Alessandro Cialfi, MD,
Antonino Salvaggio, MD,
Carmine Santoli, MD
Department of Thoracic and Cardiovascular Surgery, Luigi Sacco Hospital, Milan, Italy
Accepted for publication June 16, 1997.
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Abstract
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Objective. A prospective angiographic study was undertaken to investigate, with an objective analysis, the global and regional wall response to myocardial revascularization.
Methods. Thirty-one patients (30 men and 1 woman, mean age, 61 years) with a left ventricular ejection fraction of less than 0.30 were admitted to our institution between 1992 and 1995 for two- or three-vessel coronary artery disease requiring myocardial revascularization. All patients underwent isolated coronary artery bypass grafting and were studied 3 months later with angiography. Preoperative and postoperative wall motion were analyzed using special software that computed a segmental left ventricular ejection fraction, generating a segmental score. Computerized analysis allowed us to distinguish patients with diffuse hypokinesis and a symmetric contraction pattern from patients with akinesis involving at least two segments and an asymmetric contraction pattern.
Results. There were no operative deaths and no patient required intraaortic balloon counterpulsation. One patient had postoperative enzymatic evidence of myocardial infarction. Postoperative angiography showed a graft patency rate of 84%. Global analysis showed a small but significant rise in the left ventricular ejection fraction (0.25 ± 0.51 to 0.31 ± 0.70, p < 0.001) and a fall in the left ventricular end-diastolic pressure (23.7 ± 10 to 16.5 ± 9 mm Hg, p < 0.01). Mean scores always have been lower after the operation than before it, with the best results obtained for the apex and the worst for the anterobasal segment. The group with a symmetric contraction pattern showed a trend toward a better hemodynamic response than the group with an asymmetric contraction pattern. Regression analysis revealed two important predictors of segmental functional improvement: (1) the absence of an echocardiographic scar, and (2) the presence of a collateral circulation.
Conclusions. Coronary artery bypass grafting produced a small but substantial improvement in patients with ischemic cardiomyopathy. The greater benefit occurred in patients with a symmetric contraction pattern. The absence of an echocardiographic scar and the presence of a collateral circulation predicted segmental functional improvement.
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Introduction
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There is uncertainty about the mechanism of clinical benefit of myocardial revascularization in patients with ischemic cardiomyopathy [1–3]. This benefit may be mediated by hemodynamic improvement or by simple protection from ischemic events. In this setting, several investigators have pointed out the potential for regional improvement of left ventricular function after coronary artery bypass grafting. Unfortunately, most of their studies were supported by "ghost images" on thallium scintigraphy or echocardiography that preclude an assessment of the effective coronary artery flow [1–3]. This prospective study was undertaken to investigate, with an objective angiographic analytic method, the global and regional response of a poorly contractile left ventricle to coronary artery bypass grafting.
Clarification of this issue is important from both a theoretic and a clinical standpoint, because it has the potential to change the current indications for coronary artery bypass grafting. If the clinical benefit of the procedure derives from hemodynamic improvement, the focus of the preoperative evaluation should be shifted toward the biologic properties ("viability") of ischemic myocardium.
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Material and Methods
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We studied 31 patients who were admitted to our department of thoracic surgery between October 1992 and January 1995 for coronary artery disease requiring myocardial revascularization. The criteria adopted for inclusion in the study were as follows: (1) an ejection fraction of less than 0.30, (2) two- or three-vessel disease, (3) no evidence of recent or ongoing myocardial infarction or unstable angina, and (4) informed consent of the patient for the procedure, including repeated angiography 8 to 12 weeks after the operation. Two patients refused postoperative coronary angiography for extracardiac causes and were excluded from the study. Thirty of the patients were men and 1 was a woman. Their mean age was 61 years (range, 48 to 78 years). Fourteen patients presented with clinical symptoms of congestive heart failure, whereas the others presented with chronic angina. Previous myocardial infarction had occurred in all patients, affecting the anterior wall in 11 patients, the inferior wall in 13 patients, and the lateral wall in 7 patients.
All patients underwent a routine echocardiographic examination. A diagnosis of important fibrosis was made when two of the three following criteria were met: (1) an end-diastolic thickness of less than 9 mm, (2) absence of systolic thickening, and (3) increased echogenicity. No patient had severe mitral regurgitation; 10 patients had mild or moderate regurgitation.
Coronary arteriograms and left ventriculograms were obtained using a standard protocol. Left ventriculography was performed in the 30-degree right anterior oblique projection and was filmed at 50 frames per second. Collateral circulation was defined as heterocoronaric retrograde filling of the poststenotic segment. Postoperative evaluation of the bypass conduits was performed in all patients; any stenosis of greater than 75% was considered significant. Revascularization was declared incomplete when a coronary artery was not bypassed or a stenosed or occluded bypass graft occurred.
Left Ventricular Function Analysis
Left ventricular silhouettes were outlined manually by the same observer (P.D.) and analyzed by a computer software program [4]. End-diastolic and end-systolic silhouettes were divided by the computer into five segments, and each segment was divided further into four subsegments. Thus, 20 areas (5 segments x 4 subsegments) were obtained using the long axis as a reference system. The percentage of the systolic reduction of each area (subsegmental ejection fraction) was obtained to display a contraction curve. This curve was compared with a reference contraction curve obtained from a healthy population. The software program generated a score for each subsegment. The area under the normal contraction curve between the mean - 2 standard deviations and 5% was divided into three equal portions: mild hypokinesis (1 point), moderate hypokinesis (2 points), and severe hypokinesis (3 points). The area between 5% and 0% represented akinesis (4 points), and the area below 0% represented dyskinesis (5 points). Thus, a normally contractile wall segment received a score of 0, whereas a fully dyskinetic segment received a score of 20 (5 points x 4 segments). The global score was computed as the sum of all segmental scores. The morphology of the contraction curve then was observed: when the curve resembled the reference contraction curve, it was considered symmetric (Fig 1
); when the curve presented alternative segmental motion, it was considered asymmetric (Fig 2) [5].
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Fig 1. . Individual contraction curve and left ventricular silhouettes of a patient with a symmetric contraction pattern (diffuse hypokinesis). The shape of the contraction curve is similar to that of a healthy population (dotted lines). (anbas = anterobasal; anlat = anterolateral; diaph = diaphragmatic; pobas = posterobasal.)
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Fig 2. . Individual contraction curve and left ventricular silhouettes of a patient with an asymmetric contraction pattern. There is a gross deformation of the contraction curve. (anbas = anterobasal; anlat = anterolateral; diaph = diaphragmatic; pobas = posterobasal.)
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All patients underwent operation within 2 months of coronary angiography. All patients were pretreated with allopurinol. Myocardial protection was achieved with anterograde crystalloid (St. Thomas) cardioplegic solution. The left ventricle was inspected and the presence of epicardial fibrosis or wall thinning was recorded. Fourteen patients had a double bypass graft, 14 had a triple bypass graft, and 2 had a quadruple bypass graft. All patients but 1 underwent grafting of the left internal thoracic artery. The saphenous vein was used to perform the remaining grafts. No patient had a mitral valve procedure or left ventriculotomy.
Statistical Analysis
Where not otherwise specified, the data are presented as means ± standard deviation. Interindividual comparisons were performed using a paired Student's t test. Comparisons between the two groups were performed by unpaired Student's t test or 
2 test. The postintervention score expected for each subject i and each segment j, yij, may include only the values between 0 and 20. Therefore, yij, and its stochastic fluctuations, have been considered according to a precalculated model in which yij was constrained between 0 and 20, and the variance was considered proportional to 1/[(yij/20) • {1-(yij/20)}] [6, 7]. The expected value of yij, E(yij, was modeled with reference to a dependence on the preintervention score sij, which was transformed according to an empiric logic function: zij = log{(sij + 0.5/1 - sij + 0.5)}. In addition, the differences between segments in which the bypass closed or remained open were taken into consideration. Finally, we examined the possible explanatory contribution offered by some other variables: the presence of fibrosis, the presence of myocardial infarction, and the presence of diffuse contractile dysfunction. Therefore, for each subject and each segment, the nonlinear regression model adopted was as follows:
 | (1) |
 | (2) |
where 
was a coefficient accounting for the relation between the preoperative and postoperative scores (logic transformed), y0 was the constant coefficient of the regression model, and 
1 and m were the coefficients accounting for the dependence of the postoperative score on different variables 1 and m. Preoperative to postoperative changes in the three anterior scores were substantially unrelated (nonparametric Spearman correlation coefficients ranged between -0.086 and 0.303; all p values were >0.10). Further, the changes relative to the three anterior scores did not show a substantial connection with those of the two posterior scores (Spearman correlation coefficients ranged between -0.189 and -0.070; all p values were >0.10). A weak but significant correlation was observed only between the changes in the posterior scores (Spearman correlation coefficient, 0.534; p < 0.01). Thus, the regression model was fitted at a segment level (significant results were confirmed by fitting a regression model in which only one weighted mean of the scores was considered for each individual).
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Results
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No operative death occurred and no patient required intraaortic balloon counterpulsation. All patients required mild or moderate inotropic support to stabilize their postoperative hemodynamics. All patients except 1 had no electrocardiographic or enzymatic evidence of postoperative myocardial infarction. The patient with a postoperative myocardial infarction had enzyme release after operation without electrocardiographic changes and was included in the study. One patient had a cerebral embolism. During the operation, epicardial fibrosis was detected in 16 patients (52%) (anterior, 10; posterior, 5; lateral, 1). No patient had an area of wall thinning larger than 2 x 2 cm. At postoperative angiography, the graft patency rate was 84%. One of 29 grafts on the left anterior descending artery (3.4%), 6 of 25 grafts on the right coronary artery (24%), and 5 of 21 grafts (23.8%) on the circumflex artery were occluded or critically stenosed.
Hemodynamic Results
Globally, the ejection fraction rose from 0.25 ± 0.05 to 0.31 ± 0.07 (p < 0.001) as the left ventricular end-diastolic pressure (LVEDP) fell from 23.7 ± 10.0 to 16.5 ± 9.0 mm Hg (p < 0.01). Patients without congestive heart failure showed improvement in ejection fraction from 0.25 ± 0.05 to 0.33 ± 0.07 (p < 0.01) and in LVEDP from 23.1 ± 8.8 to 12.3 ± 5.6 mm Hg (p < 0.01). Patients with congestive heart failure showed improvement in ejection fraction from 0.24 ± 0.33 to 0.03 ± 0.07 (p < 0.01), but not in LVEDP, which decreased from 22.3 ± 10.8 to 20.7 ± 10.4 mm Hg (p = not significant). The presence of anterior fibrosis did not impair the increase in ejection fraction from 0.23 ± 0.03 to 0.30 ± 0.08 (p < 0.05).
Asymmetric or Symmetric Contraction Pattern
The preoperative characteristics of the two groups are shown in Table 1. The group with a symmetric contraction pattern had a significant improvement in ejection fraction from 0.25 ± 0.04 to 0.30 ± 0.05 (p < 0.001), in LVEDP from 26.2 ± 8.9 to 17.2 ± 10.5 mm Hg (p < 0.01), and in global score from 45.8 ± 6.9 to 37.6 ± 8.0 points (p < 0.01). In contrast, the group with an asymmetric contraction pattern showed a slight but not significant rise in ejection fraction from 0.27 ± 0.10 to 0.33 ± 0.08 (p = not significant) and a similar fall in LVEDP from 19.8 ± 9.7 to 16.4 ± 9.2 mm Hg (p = not significant). In this group, the fall in global score from 46.5 ± 7.2 to 40.0 ± 12.7 points (p < 0.05) was significant. The mean differences between preoperative and postoperative findings in the two groups did not vary significantly.
Complete or Incomplete Revascularization
The group with complete revascularization (14 patients) exhibited satisfactory improvement in global myocardial function, with an increase in ejection fraction from 0.23 ± 0.04 to 0.32 ± 0.06 (p < 0.001), an increase in LVEDP from 25 ± 11 to 17 ± 11 mm Hg (p = 0.05), and an increase in hypokinesis score from 47.6 ± 6.9 to 38.3 ± 12.6 points (p < 0.01). The group with incomplete revascularization (15 patients) did not show significant changes in ejection fraction, which rose from 0.28 ± 0.08 to 0.31 ± 0.07 (p = not significant), or LVEDP, which rose from 21.7 ± 8.8 to 16.5 ± 8.5 mm Hg (p = not significant), but they did demonstrate a fall in global score from 44.9 ± 7 to 39.1 ± 8.7 points (p < 0.05). The mean differences between the preoperative and postoperative findings of the two groups did not vary significantly.
Regional Wall Response
Table 2 shows some summary statistics relative to the scores recorded before and after the operation. Mean postoperative scores were consistently lower than preoperative scores, with the best results obtained for the apex and the worst for the anterobasal segment. Table 3 shows the results of the nonlinear regression analysis as applied to all segments and as applied separately to the anterior and posterior segments. The bypass status was not significant. A significant correlation was observed between the postoperative score and the bypass status, and between the presence of fibrosis (at echocardiography, positive relation) and a collateral circulation (negative relation). Considering anterior and posterior segments separately, the presence of fibrosis was important only in connection with the score of the anterior segments. Detecting fibrosis by echocardiography seems to be preferable to detecting it during operation (which is not significantly related to the score determined by analyzing the anterior segments). In contrast, the presence of a collateral circulation was an important determinant of the score of the posterior segments. In Figures 3 and 4, we show the relation between the preoperative score, bypass graft patency, and the presence of fibrosis or a collateral circulation when anterior and posterior segments are analyzed separately. Because scores relative to the anterior and posterior segments showed a positive correlation, we confirmed the significant relation between postoperative scores, fibrosis, and a collateral circulation by analyzing a weighted mean of the anterior and posterior scores. Our previous results were confirmed substantially for both fibrosis (all segments, t = 2.23, p = 0.03; anterior segments only, t = 2.84, p = 0.001) and a collateral circulation (all segments, t = -1.64, p = 0.108; posterior segments only, t = 3.2, p = 0.006).
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Table 3. . Regression Coefficients for the Nonlinear Models Relating the Postoperative Score to the Logit (log P/[1 - P], where P represents the portion) of the Preoperative Score, the Bypass Status, and Other Explanatory Variables
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Fig 3. . Relation between the preoperative (PRE-OP.) and postoperative (POST-OP.) scores and the presence of fibrosis in the anterior segments only. (0 = normokinesis; 20 = dyskinesis.)
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Fig 4. . Relation between the preoperative (PRE-OP.) and postoperative (POST-OP.) scores and the presence of a collateral circulation (d.d.). (0 = normokinesis; 20 = dyskinesis.)
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Comment
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Many reports have evaluated the clinical effects of myocardial revascularization in patients with severely depressed left ventricular function, focusing mostly on operative mortality and long-term survival. Recent improvements in surgical technique have produced more satisfactory operative results [8–10]. Our experience confirms that myocardial revascularization can be accomplished safely in these patients, with a low operative risk when the operation is scheduled electively. In our series, the postoperative course was surprisingly smooth and, in spite of some incidence of early venous graft occlusion, there were no perioperative myocardial infarctions.
We found a small but significant overall hemodynamic improvement, with a 25% rise in ejection fraction and a fall in LVEDP toward the upper range of normal. Despite the fact that our patients remained in the setting of low ejection fractions and high filling pressures, the hemodynamic changes we observed cannot be attributed to biologic variability [11]. Moreover, the patients who underwent complete revascularization exhibited a better hemodynamic response than those who underwent incomplete revascularization. Notably, the patients with preoperative congestive heart failure had improved ejection phase indexes, but their filling pressures remained unchanged, suggesting the persistence of diastolic dysfunction after revascularization.
Computerized analysis of regional wall function has gained wide acceptance and enables us to divide patients with ischemic cardiomyopathy into two subgroups: (1) a subgroup with a contraction pattern similar to the aneurysmic model (asymmetric pattern) and (2) a subgroup with a contraction pattern that resembles dilated cardiomyopathy (symmetric pattern). The two groups had the same clinical and hemodynamic characteristics; they differed only in their incidence of fibrosis. In our experience, better functional results were obtained in the second subgroup of patients even when the operation did not induce any dramatic change in the contraction pattern (ie, from an asymmetric to a symmetric pattern). It seems that the presence of a symmetric contraction pattern, irrespective of absolute ejection fraction or LVEDP, may be considered a predictor of a satisfactory hemodynamic result.
Regional wall motion response analysis showed that the best results in terms of functional improvement were obtained in the apical segment. In many patients, the rise in ejection fraction could be attributed to apical improvement alone. There is no clear explanation for this "apex effect." The left ventricular apex may be thought of as a "no-man's-land" in which a collateral circulation is well represented, a premise for myocardial viability. On the other hand, the hypothesis of recruitment of the viable muscle (hibernating myocardium) does not comply with the finding of greater vulnerability of the apical region to infarct expansion [12, 13] and the incidence of apical fibrosis in our patients (34%). It is clear that these results are in conflict with the existence of a simple relation between viable muscle and its function. In contrast, the changes in apical motion could be read as global improvement in ventricular ergonomics. Some investigators [4, 14] have pointed out that the apical wall obliterates the cavity in end-systole and that segmental ejection fraction is greater in the apical segment. Thus, the dysfunctional left ventricle tries to resume the global systolic function of the heart after surgical revascularization. This improvement could be mediated by resynchronization of the systolic motion between the different regions.
Regression analysis (Table 3
) emphasized three important points: (1) The patency of the graft had no significant relevance. This fact can be explained by the low rate of occlusion of the left anterior descending artery graft (3.4%), which weakened statistical analysis on this point. Interestingly, occlusion of the right coronary artery graft did not influence the functional response of the inferior segments to operation. This could be related to the importance of a collateral circulation in these regions, or to the beneficial effect of internal mammary artery secretion on left ventricular function. (2) The presence of fibrosis detected during echocardiography exerts a negative effect on anteroapical segmental function. Echocardiographic diagnosis of fibrosis is a better predictor than macroscopic detection of fibrosis, probably because the septum is not visible to the surgeon. The amount of fibrosis has been related to the severity of asynergy, but different amounts of fibrosis also were found in akinetic segments [15–17]. Positron emission tomography seems to differentiate viable myocardium with acceptable predictive values [18, 19]. Recently, metabolic activity was found in regions with reduced end-diastolic wall thickness and absent wall thickening [20]. In our experience, more than half the patients had numerous small patches of fibrosis scattered throughout the wall. In this situation, metabolic activity can be recorded in the presence of significant fibrosis, even without reaching a critical mass, to permit substantial improvement; metabolic or stress-echo studies thus may overestimate the chances of motion improvement after revascularization, especially in the anterior segment. (3) The presence of a collateral circulation had a positive effect on postoperative function. This factor played a role only in the diaphragmatic and posterobasal segments. This fact was corroborated by the finding of better functional improvement after percutaneous transluminal coronary angioplasty in patients with inferior myocardial infarction and adequate collateral flow [21]. In another study [22], the viability of anterior segments after myocardial infarction was not influenced by a collateral circulation.
In this way, a provisional model for postoperative segmental function can be constructed separately for the anterior (see Fig 3) and inferior (see Fig 4) segments. These models could be a valid aid in establishing the operative strategy (need for ventricular remodeling or coronary endarterectomy) in doubtful cases.
We conclude that myocardial revascularization induces a small but significant improvement in overall systolic function in patients with ischemic cardiomyopathy. The hemodynamic benefit is substantial only in patients who have a symmetric contraction pattern, resembling dilated cardiomyopathy. Gross preoperative deformities of the systolic contour were not reversible. The greater regional improvement occurred in the apical segment, configuring a real apex effect. There was a significant association between segmental improvement and the presence of a collateral circulation or the absence of echocardiographically detected fibrosis. Our results may be used to modify the operative plan without any need for costly, time-consuming, and largely unavailable studies, which in turn may overestimate myocardial viability.
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Footnotes
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Address reprint requests to Dr Di Mattia, Dipartimento di Chirurgia Toracica e Cardiovascolare, Ospedale Luigi Sacco, Via G.B. Grassi, 74, 20157, Milano, Italy.
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Top
Abstract
Introduction
