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Ann Thorac Surg 1995;59:403-407
© 1995 The Society of Thoracic Surgeons
Department of Surgery III, Nara Medical College, Nara, Japan
Accepted for publication September 27, 1994.
| Abstract |
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| Introduction |
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| Material and Methods |
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Cardiac Catheterization Studies
In all patients, cardiac catheterization and coronary and left ventricular angiography were performed before and 1 to 2 months after operation to measure hemodynamic parameters. The left ventricular end-diastolic pressure and mean pulmonary artery pressure were measured. Cardiac output also was measured by the thermodilution method. The left ventricular end-diastolic volume index (LVEDVI) was calculated by dividing the angiographic stroke volume by the ejection fraction obtained from radioisotopic angiography [6] as described below. Using preoperative left ventriculograms in the right anterior oblique position, the contractile sectional ejection fraction was calculated by Watson and associates' method [7] and the ratio of the circumferential length of the aneurysm to that of the left ventricle was determined. The preoperative contractile sectional ejection fraction was 0.46 ± 0.16 and the ratio of the circumferential length of the aneurysm to that of the left ventricle was 48% ± 17.8% in these patients.
Radioisotopic-Angiographic Evaluation
An equilibrium cardiac pool image using labeled erythrocytes with 740MBq 99mTc was obtained in the 45-degree left anterior oblique position. The ejection fraction was obtained from the cumulative radioactivity counts. The count curve was subjected to a linear differential to obtain the one-third filling fraction and the peak filling rate [8]. Radioisotopic angiography was performed 1 to 2 months before and after operation. An incremental ergometer exercise test was employed in 15 patients with the patient in the supine position with submaximal loads.
Doppler Ultrasonography Measurements
Cardiac ultrasonography was performed 1 month before and on several occasions after operation, ranging from postoperative day 3 to 16 months and up to 24 months (mean, 19 ± 3.6 months) after the operation. The ratio of the peak flow velocity during the atrial kick phase to the peak flow velocity in the rapid filling phase at the level of the mitral valve (A/R ratio) [9] was calculated. The sampling point was identified at the center of the mitral orifice using an apical four-chamber view. The A/R ratio was calculated by averaging the values obtained over five cardiac cycles.
Statistical Analysis
The data are expressed as the mean ± standard deviation. Data were statistically analyzed using paired or nonpaired Student's t test for heart rate and ejection fraction, paired or nonpaired Wilcoxon test for other variables, and analysis of variance. Standard linear regressions were calculated using the least squares method.
| Results |
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Hemodynamic Variables
There were no significant differences between preoperative and postoperative resting or exercise heart rates (Table 2
). The ejection fractions at rest and during exercise increased significantly from 0.28 ± 0.12 to 0.39 ± 0.12 (p = 0.007) and 0.32 ± 0.14 to 0.41 ± 0.10 (p = 0.008) after operation. The mean pulmonary artery pressure decreased from 17 ± 5.6 to 13 ± 2.1 mm Hg after operation. However, this difference was not statistically significant. The LVEDVI also decreased significantly from 178 ± 116 to 92 ± 21 mL/m2 (p = 0.016) after operation, as did the left ventricular end-diastolic pressure, from 14 ± 7.0 to 8 ± 3.2 mm Hg (p = 0.032). The one-third filling fraction remained higher after operation. The peak filling rate increased significantly from 1.2 ± 0.47 to 1.8 ± 0.6/s (p = 0.048) after operation.
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Relationship Between A/R Ratio and Left Ventricular End-diastolic Volume Index
The ratio of postoperative A/R ratio to preoperative A/R ratio reveals a positive correlation (r = +0.823; p = 0.014) in relation to the ratio of the postoperative to preoperative LVEDVI (Fig 1
). The postoperative reduction in the A/R ratio was greater in patients with a large left ventricular aneurysm.
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| Comment |
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We analyzed the one-third filling fraction and peak filling rate calculated from radioisotopic angiograms and assessed the A/R ratio by Doppler ultrasonography in patients undergoing patch reconstruction. In the present study, the A/R ratio, one-third filling fraction, and peak filling rate were selected as indices of diastolic function. The A/R ratio seems to be the most useful diastolic index in assessing the time course of cardiac function [9]. However, for this parameter to be valid in comparing diastolic function between different groups, it is necessary for the patient to be in normal sinus rhythm, free from mitral valve disease, and to have a left ventricular end-diastolic pressure less than or equal to 18 mm Hg. The subjects in the present study satisfied all of these requirements. Changes in the A/R ratio from the preoperative to postoperative periods had a significantly positive correlation with changes in LVEDVI (r = +0.823; p = 0.014) (see Fig 1
). Furthermore, this ratio greatly improved in the early postoperative period, suggesting that the postoperative reduction in the A/R ratio was a direct effect of aneurysmectomy resulting in a reduction in the LVEDVI. A comparison between 9 patients with concomitant CABG and 7 patients without it revealed that concomitant CABG had no direct effects on reducing the A/R ratio.
Changes in One-third Filling Fraction and Peak Filling Rate
Radioisotopic studies are very useful for evaluating left ventricular aneurysms because geometric changes of the left ventricular cavity occur after operation and conventional angiographic studies are limited by applying the assumption of an ellipsoid shape. In patients with a left ventricular aneurysm, the preoperative one-third filling fraction and peak filling rate are low, similar to the preoperative levels reported for patients with ischemic heart disease [8]. After operation, both variables improved but remained lower than the normal range. These results suggest that an akinetic area, formed by the patch and residual myocardial fibrosis, probably limits the improvements in these variables, as has been previously reported in patients after myocardial infarction [8].
Patch Size Used for Left Ventricular Reconstruction
It is unknown what patch size is the most appropriate to reconstruct the left ventricle following aneurysmectomy. If the size of patch is maximally reduced, it will essentially represent a conventional direct closure, and may deform the left ventricular contour. If the size is kept large enough to maintain the original end-diastolic contour of the contractile portion of the left ventricle, it will remain a large akinetic patch area. According to the hemispheric model by Watson and colleagues [7], and left ventricular geometric analysis with an akinetic area by Kitamura and associates [15], we divided the left ventricular silhouette into aneurysmal and contractile portions (Fig 2
). Each portion is assumed to be a hemisphere with a radius r and a cylindrical portion with a width h. The surface area of the aneurysmal portion and the maximal patch area can be expressed as
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![]() | (1) |
Therefore, to resect the aneurysmal portion without changing the volume of the contractile portion at diastole, the area of a patch to be applied should theoretically be less than 50% of the surface area of the aneurysmal region (S/2 -
rh). This figure of 50% includes the overlapped suture line of the patch and myocardial scar. Based on this model analysis, although very simplified, we tried prospectively to estimate the patch size to be less than 50% of the resected scar and prepared so using a large Dacron vessel graft. However, in small aneurysms, it was difficult to use the patch that was less than 50% of the resected area. In large aneurysms, it was easy to reduce the area of a patch to less than 50% of the resected area. As a result, the patch actually used in the present series varied from 38% to 76% (mean, 57% ± 19%) of the surface area of the resected scar, including the area to be used for suturing, depending upon sizes of the resectable free wall scar and the unresected but excluded septal scar. Thus, the actual size of the patch (without the sewing cuff) forming a part of the left ventricular wall was considered to be less than 50% of the resected area. Although this still may be too large in some cases, postoperative systolic and diastolic ventricular functions improved significantly early after the operation and remained so for an extended period after operation.
| Footnotes |
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| References |
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