Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Heart failure wikipedia , lookup
History of invasive and interventional cardiology wikipedia , lookup
Electrocardiography wikipedia , lookup
Hypertrophic cardiomyopathy wikipedia , lookup
Jatene procedure wikipedia , lookup
Quantium Medical Cardiac Output wikipedia , lookup
Coronary artery disease wikipedia , lookup
Management of acute coronary syndrome wikipedia , lookup
Ventricular fibrillation wikipedia , lookup
Arrhythmogenic right ventricular dysplasia wikipedia , lookup
Am J Physiol Heart Circ Physiol 287: H2697–H2704, 2004. First published August 19, 2004; doi:10.1152/ajpheart.00160.2004. Remodeling in myocardium adjacent to an infarction in the pig left ventricle Scott D. Zimmerman, John Criscione, and James W. Covell School of Medicine, University of California, San Diego, La Jolla, California 92093 Submitted 23 February 2004; accepted in final form 16 August 2004 the present study, we have defined the condition of the initial end diastolic configuration of the tissue with a transmural array of gold beads before coronary occlusion and calculated the deformation of the tissue occurring at 4 wk (deformed configuration). The resulting deformation represents a remodeling strain. With this approach it is possible to estimate not only tissue loss but also rearrangement of the components of the myocardium (e.g., myofiber orientation or arrangement into radial laminae). Although data exist regarding regional changes in uniaxial dimensions after MI (29), it is not possible to relate these measurements to components of the wall (e.g., myofiber direction). Therefore, the purpose of the present study was to examine the hypotheses that changes in the adjacent tissue are related not only to known myocyte elongation but also to myofiber rearrangement and changes in the extracellular matrix in the adjacent tissue. We tested these hypotheses by determining the structure of the remodeled wall and threedimensional remodeling deformation during the 3 wk after acute coronary occlusion in the pig. METHODS AFTER MYOCARDIAL INFARCTION (MI), cardiac remodeling is characterized by wall thinning, chamber dilation, and increased ventricular sphericity. Early chamber dilation after coronary occlusion results both from changes in the infarcted myocardium (9, 29) as well as changes in the normally perfused myocardium. Remodeling of the noninfarcted ventricular wall post-MI occurs, in part, because of structural changes in myocytes (14) and in part due to rearrangement of myofibrils and changes in the cardiac interstitium. Myocyte responses to MI may include cellular hypertrophy and reexpression of a fetal phenotype (34). Myocytes in noninfarcted myocardium elongate, which is perhaps structurally more important. Myocyte length increases after MI and is greater in tissue adjacent to the infarct than more remote myocardium (14). Changes in the structure of the “normal” ventricular wall adjacent to the infarcted area involve all three components of the myocardium (myocytes, fibroblasts and the extracellular matrix, and the coronary vasculature) and their three-dimensional structural relationship. Because it is not possible to assess the structure of the tissue before the infarct, assessing changes in these components of the tissue requires tracking material markers in the remodeling tissue over long periods of time with a three-dimensional approach as well as a detailed histological evaluation of the remodeled structure. In Surgical preparation. All experiments were conducted in accordance with American Association for Accreditation of Laboratory Animal Care guidelines for the use of animals in research and were approved by the University of California San Diego Institutional Animal Care and Use Committee. The surgical protocol and bead implantation technique have been described in detail previously (35). Eleven Hampshire farm-raised pigs weighing 23.3 ⫾ 3.2 kg were sedated with 24 mg/kg ketamine and pretreated with 0.03 mg/kg atropine. Anesthesia was induced with 4 –5% isofluorane with the use of a mask. All animals were then intubated, ventilated, and maintained with a mixture of isofluorane (1%), nitrous oxide, and oxygen. The heart was exposed via a fifth interspace thoracotomy. During the procedure, arterial pressure was monitored via a catheter inserted into the right femoral artery via a cutdown. Cardiac support (0.33 g 䡠 kg⫺1 䡠 min⫺1 dobutamine-HCl) and antiarrhythmics (0.04 ml/kg, single bolus lidocaine-HCl, 2%) were administered as necessary during the procedure to maintain femoral artery pressure at ⬎65 mmHg (dobutamine) and to prevent prolonged episodes of ventricular tachycardia (lidocaine). Inotropic support and lidocaine were discontinued as soon as the chest was closed, and no animals received postoperative support. A 40-cm-long fluid-filled catheter (model S-54-HL, Tygon) was inserted through the apex into the left ventricular (LV) chamber and tunneled to the back of the neck, allowing for chronic measurement of LV pressure. The larger of the first or the second marginal branch of the left circumflex coronary artery (Fig. 1) was dissected free and temporarily constricted (⬃5–10 s) to visualize the ischemic border. In the pig with little collateral circulation, the ischemic area appears blanched with a bluish tinge. Three columns of three radio-opaque gold beads (0.8 – 0.9 mm diameter) were implanted transmurally within the LV wall. The nearest column was placed ⬃1 cm from the Address for reprint requests and other correspondence: S. Zimmerman, Dept. of Biomedical Sciences, Southwest Missouri State Univ., 901 S. National Ave., Springfield, MO 65804-0027 (E-mail: [email protected]). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. myofiber rearrangement; finite deformation; remodeling strains http://www.ajpheart.org 0363-6135/04 $5.00 Copyright © 2004 the American Physiological Society H2697 Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 Zimmerman, Scott D., John Criscione, and James W. Covell. Remodeling in myocardium adjacent to an infarction in the pig left ventricle. Am J Physiol Heart Circ Physiol 287: H2697–H2704, 2004. First published August 19, 2004; doi:10.1152/ajpheart.00160.2004.— Changes in the structure of the “normal” ventricular wall adjacent to an infarcted area involve all components of the myocardium (myocytes, fibroblasts and the extracellular matrix, and the coronary vasculature) and their three-dimensional structural relationship. Assessing changes in these components requires tracking material markers in the remodeling tissue over long periods of time with a three-dimensional approach as well as a detailed histological evaluation of the remodeled structure. The purpose of the present study was to examine the hypotheses that changes in the tissue adjacent to an infarct are related to myocyte elongation, myofiber rearrangement, and changes in the laminar architecture of the adjacent tissue. Three weeks after myocardial infarction, noninfarcted tissue adjacent to the infarct remodeled by expansion along the direction of the fibers and in the cross fiber direction. These changes are consistent with myocyte elongation and myofiber rearrangement (slippage), as well as a change in cell shape to a more elliptical cross section with the major axis in the epicardial tangent plane, and indicate that reorientation of fibers either via “cell slippage” or changes in orientation of the laminar structure of the ventricular wall are quantitatively important aspects of the remodeling of the normally perfused myocardium. H2698 REMODELING POSTMYOCARDIAL INFARCTION Fig. 1. Schematic representation of surgical preparation, bead placement, and coronary artery ligation site. LCx, left circumflex coronary artery; LAD, left anterior descending coronary artery. x1–x3, cicumferential, longitudinal, and radial axes, respectively. AJP-Heart Circ Physiol • VOL Strain calculations. After each biplane X-ray experiment, a calibration phantom with beads embedded in known locations was imaged and used for perspective calibration (30). In particular, digitizing the two views of the phantom allowed calculation of a calibration transformation matrix from the known phantom bead positions and the pixel-based coordinates of the images of the calibration phantom. The resolution of this technique has been calculated at 0.2 mm (30). A least-squares finite-element method was used to calculate nonhomogeneous distributions of three-dimensional finite strain, as described elsewhere (17). Briefly, LV pressure tracings and ECG synchronized with a frame grabber (model DT2651, Data Translation) were used to define end-diastolic frames. At least two frames were averaged to obtain each end-diastolic view and the three-dimensional coordinates of each bead were computed from the calibration transformation matrix. The coordinates were then converted to cardiac coordinates defined by the apex and base beads. Three normal strains (E11, E22, and E33) quantified stretch or shortening along local circumferential (X1), longitudinal (X2), or radial (X3) axes. Three shear strains (E12, E13, and E23) quantified changes in angle between pairs of initially orthogonal axes. Remodeling strains were calculated as the bead set deformed between the control diastolic and the 3 wk postinfarct diastolic configurations (22, 28, 31). The myofiber and sheet orientations were measured in the remodeled configuration, and to estimate their orientations back to the initial configuration we followed the method outlined in the appendix of Takayama et al. (28). Briefly, it is assumed that circumferential segments in the initial configuration remain circumferential and that planes parallel to the epicardium in the initial configuration remain parallel to the epicardium. These two conditions allow the strain alone to specify the mapping of material segments from the initial configuration to the final configuration. Moreover, this mapping is one-toone for all of the remodeling strain fields that were measured in this study. Hence, the solution was obtained once we correctly guessed (in an iterative computational manner) an initial myofiber orientation ␣0 that (when strained as measured) gave rise to the measured orientation ␣1. The same approach was used for finding the initial sheet orientation 0 from the measured strain field and measured orientation 1. Changes in LV chamber size were estimated from a calculation of the distance from the apex-base axis (linear distance from the apex bead to the base bead) to the epicardial centroid of the bead set. Tissue processing. At the time of death, animals were again sedated with ketamine (24 mg/kg) and pretreated with atropine (0.03 mg/kg). Anesthesia was induced with isofluorane (4 –5%) with the use of a mask. All animals were then intubated, ventilated, and maintained with a mixture of isofluorane (1%), nitrous oxide, and oxygen. The heart was exposed via a medial sternotomy. Once the heart was exposed and any noncardiac tissue dissected away, an overdose of pentobarbital was administered. Hearts were arrested via infusion of a hyperkalemic-cardiopelegic solution, dissected free, trimmed of the 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 ischemic border and in red contracting myocardium. Bead columns were implanted perpendicular to the epicardium by temporarily suturing a platform onto the epicardium above the desired location. A trocar was used to insert each bead to a predetermined depth. This was repeated until three to four beads were in the myocardium in each column and three columns of beads were completed. After the platform was removed, a larger gold bead (1 mm diameter) was sutured on the epicardium to mark each transmural column. Beads were also sutured to the LV apex and the bifurcation of the left coronary artery to define an apex-base cardiac coordinate system for the transmural bead set (Fig. 1). Data are reported on 6 of the 11 animals. Two animals did not survive the initial surgery. Both had arrhythmias after coronary ligation and did not survive the first 24 h. The remaining three animals were excluded because the marker set was not adequate (not transmural or had overlapping markers precluding visualization with the biplane system). No animals developed clinical evidence of heart failure. The deepest bead in three columns in each of the six animals averaged 75% of the distance from epicardium to endocardium (32%96%). Data for strains referenced to the sheet-fiber axis system are presented in five animals. The average depth of the deepest bead for the five animals was 83% (53%-96%) of the distance from epicardium to endocardium. For presentation of strain data results are averaged for the inner (n ⫽ 5) and outer (n ⫽ 6) halves of the wall for each animal. Transmural data is presented at six binned depths [0%-2.5% (6); 5%-12% (6); 24%-28% (6); 36%-37% (5); 66%-78% (5); and 84%-94% (4), where the number in parenthesis indicates the number of animals contributing to each bin]. Control studies. Saline infusion was occasionally used to elevate left ventricular end diastolic pressure ⬎10 mmHg so that data could be captured at the same end-diastolic pressure at control and 3 wk after coronary occlusion. With respiration suspended during expiration, three-dimensional control locations of each bead were assessed by biplane cineradiography for three to four cardiac cycles (⬃3.3 s). The dissected artery was then ligated. Ischemia was verified visually by tissue blanching and akinesis. The infarct region was covered with a patch of pericardium, which was not reapproximated, and the chest was closed. Air was evacuated from the chest, anesthesia was discontinued, and animals were allowed to recover. All pigs received 400 mg Sulfamethoxazole/80 mg Trimethoprim in oral suspension for 5 days after surgery. The catheter in the left ventricle was flushed and filled with heparin every other day. Conscious animal studies. Before surgery, all animals were habituated to a canvas sling and the laboratory over the course of 1–2 wk. Three weeks after coronary ligation animals, they were placed in the sling and biplane X-ray images of the cardiac beads were taken. The animals were given 0 –1.0 mg/kg iv diazepam as necessary for mild sedation. LV pressure and heart rate were monitored throughout the procedure. REMODELING POSTMYOCARDIAL INFARCTION great vessels and atria, and weighed. The right and left coronary arteries were cannulated via their respective ostia and hearts were fixed by perfusion at 120 mmHg with 10% buffered formalin (Fisher Scientific) while suspended in saline (zero distending pressure). The entire isolation and fixation process lasted ⬍40 min. The right ventricular wall was removed, and a plastic rod was inserted through the apex, which extended beyond the base along the apex-base axis. The LV chamber was filled with silicone, which was allowed to set for 48 h. Hearts were placed in a cutting apparatus, supported by the rod. The apparatus allowed cuts to be made in the LV wall perpendicular to the apex-base axis. Tissue blocks containing bead sets were removed, dehydrated, embedded in paraffin, and sectioned to 10 m in the epicardial tangent plane. Sections were mounted and stained for collagen with picrosirius red. Each tissue section was oriented with the cardiac circumferential axis horizontal on the image and acquired at ⫻20 total magnification with the use of a color video camera (Sony CCD/RGB) mounted on a microscope and connected to a Macintosh computer (Quadra 900 with NIH Image version 1.61 software). Images were analyzed for collagen area fraction and muscle fiber orientation relative to the circumferential axis of the heart. Mean angle for each tissue depth was determined by averaging 10 measurements within 2 nonadjacent fields in the tissue section. In this way, we could generate a progression of muscle fiber angles transmurally through the noninfarcted wall. Methods for identifying sheet orientation. It was possible to determine sheet angle in a block of tissue adjacent to the block of tissue, which contained the bead set in five of the six animals. Because this initial block was used to histologically determine the myocyte angles, an adjacent region of tissue was used. A through-wall block of fixed tissue was excised with dimensions (in mm) 3 ⫻ 3 ⫻ n, where n is the ventricular wall thickness (rounded down to the mm). Two cuts (3 mm apart) were in the circumferential plane whereas the other two cuts (3 mm apart) were in the apex-base plane. After the apex side was marked, a custom made sledge-type slicer was used to cut the block in cross-section at 1-mm intervals parallel to the epicardial surface to yield n blocks with dimensions (in mm) 3 ⫻ 3 ⫻ 1. The order of the 1-mm slices from epicardium to endocardium was preserved by gluing them with cyanoacrylic adhesive, to a piece of paper with the epicardial side facing up and with the marked apex side toward the bottom of the paper. The slices were infiltrated for 1 wk and embedded with JB-4 plastic embedding media (Polysciences) according to the product instructions for infiltration and embedding. The embedded tissue is translucent and the myofiber direction can be seen on transillumination with a dissecting microscope. After the plastic was allowed to soften by exposing the sample to air for 2 h, 2 parallel, cross-fiber cuts (1 mm apart) were made with a utility knife. This cut sample was mounted so it could be sectioned with the microtome blade in a plane transverse to the myofiber. Figure 2 displays such a section. , the sheet orientation angle, is the angle subtended by the sheet gap and the radial direction, and  is positive if the sheet gap points toward the positive cross-fiber direction (see Fig. 3 for explanation of fiber and sheet coordinates). For the sample in Fig. 2,  ⫽ ⫺44° on average. Statistics. Cardiac strain, muscle fiber angle, and fiber strain data were each analyzed for an effect of ventricular wall depth by one-way ANOVA with repeated measures (SPSS; Chicago, IL). Each strain data point was assessed for a significant difference from zero by one-sample t-test with a Bonferroni correction for repeated tests. For graphical and statistical comparisons, the absolute value of the change in sheet and fiber angle was averaged at all sites in each animal and was assessed for a significant difference from zero by one-sample t-test with a Bonferroni correction for repeated tests. RESULTS End-diastolic remodeling strains. Remodeling strains were calculated by comparing the end-diastolic configuration of the transmural gold bead set in control (preinfarction) and 3-wk post-MI configuration. There was no significant difference in end diastolic pressure (control, mean ⫽ 11.3, range 3.0 –7.0 mmHg; 3 wk, mean ⫽ 13.2, range 2.0 –20.3 mmHg) at the two points in time. End-diastolic remodeling strains referred to cardiac coordinates. Remodeling strains averaged for the inner and outer halves of the wall are shown in Fig. 4. Circumferential strain was positive at all depths and significantly different from zero with the greatest strain magnitude occurring from the midwall to the endocardium. Radial remodeling strains were not significantly different from zero in the outer third of the wall becoming negative and significantly different from zero at Fig. 3. Nomenclature of the fiber (A) and sheet (B) coordinate systems. Once the fiber and sheet angles were identified, the cardiac coordinate system from Fig. 1 was rotated into the respective angles. The in-fiber axis (F) was defined by the long axis of the myocytes. The in-sheet axis (F) was the same as the in-fiber axis. The sheet thickness axis (N) was defined by the orientation of the sheet. Strains were then recalculated to reflect this new coordinate system and reveal the resulting changes in the tissues due to changes in sheet orientation. ECC, cross fiber remodeling strain; EFF, fiber remodeling strain; ENN, strain normal to the sheet; ERR, radial strain; ESS, sheet strain remodeling. AJP-Heart Circ Physiol • VOL 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 Fig. 2. Thick section (15 m) of myocardial block that was mounted in the microtome so that the blade cuts perpendicular to the myofiber. The sample is 1 mm in minor dimension, and the paper that is seen below the tissue was glued to the endocardial side before being embedded. The radial direction points up, the cross-fiber direction points to the left, and the myofiber direction is directly into the page. The myofibers are arranged in sheets that are about four cells thick, and the gaps between the sheets are the lines evident in the image. H2699 H2700 REMODELING POSTMYOCARDIAL INFARCTION DISCUSSION Fig. 4. Normal remodeling strains in cardiac coordinates averaged for the inner (N ⫽ 5) and outer (N ⫽ 6) half of the spared myocardium ventricular wall. Bars indicate one SD. A: E11, E22, and E33, normal stretch or shortening strains. B: E12, E13, and E23, in-plane shear, circumferential-transverse shear, and longitudinal-transverse shear, respectively. depths below the midwall. Shear in the plane of the ventricular wall (in-plane shear, E12) and circumferential-transverse shear (E13) were not different from zero at any depth. Longitudinaltransverse shear strains (E23) were positive and significantly different from zero at the endocardium. Changes in tissue volume and chamber radius. Changes in tissue volume were calculated from the product of the three principal remodeling stretch ratios. The average 3-wk volume ratio was 1.10 ⫾ 0.11 (means ⫾ SE) suggesting that during the 3 wk after coronary occlusion, noninfarcted myocardium encompassing the gold beads increased 10% in volume on average. The increase in volume was most prominent in the epicardial and endocardial regions with a less prominent volume change at the midwall. Changes in LV radius were estimated from a calculation of the distance from the apex-base axis (linear distance from the apex bead to the base bead) to the epicardial centroid of the bead set. Chamber radius increased 2.12 ⫾ 0.83 mm (means ⫾ SD). Changes in fiber and sheet angle. Myocyte fiber angle was ⫺65.4 ⫾ 7.5° at the epicardium and linearly progressed to 50.3 ⫾ 7.2° at the endocardium. Subepicardial, midwall and subendocardial collagen area fractions were similar (9.7 ⫾ 3.6%, 8.8 ⫾ 2.3%, and 8.2 ⫾ 3.4%, respectively). Because myofiber and sheet orientation were determined only in the remodeled configuration, it was necessary to estimate the original fiber and sheet orientation to use as a reference for calculating strain components. This was done as described earlier from the measured strains. Figure 5 shows the AJP-Heart Circ Physiol • VOL Three weeks after MI, noninfarcted tissue adjacent to the infarct remodeled by expansion along the direction of the fibers and in the cross-fiber direction. The laminar structure of the wall is remodeled as well. Myocardial sheets thicken substantially and shorten modestly. These changes are consistent with myocyte elongation and myofiber rearrangement (slippage) and/or a change in myocyte cross sectional shape. Although this is the first study to clearly demonstrate cross-fiber remodeling, these data are qualitatively consistent with a wealth of previous data showing increased ventricular dimensions (18, 25), changes in myocyte shape (13, 14), and myocyte rearrangement (33) after infarction. Moreover, these data indicate that reorientation of fibers either via cell slippage (33) or rearrangement within laminae (5, 16) are the major changes in early tissue remodeling after infarction in the pig. Fig. 5. Absolute value of the change in fiber and sheet angle from control to 3 wk after coronary occlusion. Bars indicate one SD. The change in both fiber and sheet angle is significantly different from zero (P ⬎ 0.05). 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 estimated changes in muscle fiber and sheet orientation at all sites across the wall in five animals. There was a small change in muscle fiber angle in the spared myocardium adjacent to an infarction [average 4.1 ⫾ 2.4°: absolute value of (control ⫺ 3 wk)], whereas the average change in sheet angle was approximately twofold greater (9.4 ⫾ 8.2°). Remodeling strains in fiber coordinates. Figure 6 summarizes the remodeling deformation expressed in fiber sheet coordinates. Transmural average fiber remodeling strain was positive and significantly different from zero. The changes were maximal near the endocardium (0.23 ⫾ 0.19). Cross-fiber remodeling strain was also positive and at the inner half of the wall significantly different from zero. Radial remodeling strain was different from zero only at the endocardium (negative values indicate modest endocardial wall thinning). Shearing deformation tended to be small and with only positive values of cross-fiber radial strain achieving significance at the endocardium. Remodeling strains in fiber sheet coordinate system. Strains in the fiber sheet coordinate system reflected again the positive fiber strain across the wall, which was accompanied by a significant and large sheet thickening deformation (Fig. 7). On average, there were no significant shearing deformations when strains were expressed in the fiber sheet reference system and there was minor sheet shortening at the endocardium. H2701 REMODELING POSTMYOCARDIAL INFARCTION After infarction, global remodeling of the infarcted ventricle occurs rapidly. Initial enlargement of the infarcted ventricle may occur as a direct result of lost contractile tissue and a subsequent decrease in stroke volume that causes increased end diastolic volume (24). Remodeling of the post-MI ventricle is characterized by chamber dilation in mouse (23), rat (4, 19, 32) and large animal models (10). Fifty days post-MI, the transverse LV dimension increased 22% in the rat and 35% in the dog (10). Interestingly, there seems to be some interspecies variability in chamber remodeling. Whereas the two species had similar infarct sizes, the relative increase in ventricular globularity postinfarction was greater in the rat than the dog (10). LV dilation after infarction also occurs in humans. Two weeks after a patient’s first MI, end-diastolic volume increased 27.6%, as measured by MRI (18). The hearts in the present study also increased in size, as reflected by an increase in chamber dimension of ⬎2 mm at the same end diastolic pressure 3 wk after infarction. In the present study, changes in chamber dimensions were also accompanied by changes in the structure of the ventricular wall. Three weeks postinfarction, there was a 10% increase in tissue volume in spared myocardium adjacent to the infarct. This increase in tissue volume was uniform across the wall, and qualitatively agrees with the volume change observed in myocytes isolated from rat hearts 3 to 4 wk postinfarction. Within 72 h of surgically induced infarction, rat myocytes exhibit a 14% increase in length and a 28% increase in volume AJP-Heart Circ Physiol • VOL (1). Eight-weeks post-MI, ovine myocytes in noninfarcted tissue adjacent to the MI exhibited an 18% increase in length and a 36% increase in volume (14). Changes in myocyte diameter are less consistent. In rats, the increased volume and length were accompanied by a 6% increase in diameter (1). However, ovine myocytes showed no change in cell crosssectional area or myocyte width (14). Our data suggest a 13.3–23.8% strain in the direction of the myocytes (see Fig. 5), which is in close agreement with the increase in length from isolated myocytes (14% to 22%). Thus myocyte length changes may contribute significantly to ventricular remodeling postMI. Although we did not measure myocyte cross-sectional area, the small increase in tissue volume in this study (⬃10%) is substantially less than the 28 –36% increase seen in individual myocytes (1, 14) implying either fewer cells across the wall or a change in myocyte density. The latter seems unlikely based on the data of Weisman et al. (33). Apoptosis may be a contributing factor in the decrease in myocytes across the remodeling ventricular wall (21). Our remodeling data directly show for the fist time substantial cross-fiber remodeling in the “normal” tissue adjacent to an infarct. In our data, both cross-fiber remodeling deformation and radial cross-fiber shear were positive and significantly different from zero in the inner half of the ventricular wall. These data provide strong support for the concept of cell slippage, which has been inferred from measurements of myocyte density (unchanged) and the number of myocytes across 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 Fig. 6. Average transmural remodeling strains in the fiber coordinate reference system 3 wk after coronary artery ligation in the pig. EFC, fiber crossfiber strain; EFR, radial strain; ECR, cross-fiber radial strain. Values are means ⫾ SD. H2702 REMODELING POSTMYOCARDIAL INFARCTION the wall (decreased) in several experimental studies after MI (20, 32). However, these and previous results cannot exclude several other potential mechanisms that may explain crossfiber remodeling. Kramer et al. (14) and Gerdes et al. (7) have mentioned changes in cell shape in the failing myocardium as a possibility and have presented preliminary data supporting this contention. These data provide evidence that the type of hypertrophy is reflected in differential myocyte shape change. In the present study, myocytes with larger in-plane dimension would explain the large positive cross-fiber strains and very large positive sheet normal strains. However, there is no direct evidence for this shape change in our post-infarct spared myocardium. Changes in the interstial space would also explain these changes. However, no changes in myocyte density have been reported. Collagen content in the present study, as reflected by picrosirus red staining, averaged 8.9 ⫾ 3.05% and was not different from values determined with the same technique (12) in pigs. Thus changes in the interstitial volume seem unlikely. However, significant changes in the structure of the wall of the ventricle as observed in this study imply that the organization of the matrix is also altered. Indeed, other recent studies (26), which indicate that collagenase activity is essential for ventricular remodeling, imply that these changes may allow the remodeling to occur. Myocyte dropout due to apoptosis has been shown to be present postinfarction but would not explain the positive cross-fiber strains. The significant positive cross-fiber radial remodeling strains in the present study could be explained by the following: a rotation of myocytes as proposed by Weisman and others (20, AJP-Heart Circ Physiol • VOL 32); by changes in cell shape; or by alterations in the orientation laminar architecture () (5, 16). However, because there were no significant changes in sheet normal shear, the latter possibility seems unlikely. In the present study, the inner half of the ventricular wall adjacent to a MI thinned substantially. In rats, noninfarcted myocardium may thin (32), remain un- Fig. 8. Schematic representation of potential mechanisms of cross-fiber remodeling. 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 Fig. 7. Average transmural remodeling strains in the fiber-sheet reference system 3 wk after coronary artery ligation in the pig. EFS, fiber sheet strain; EFN, fiber normal strain. Values are means ⫾ SD. REMODELING POSTMYOCARDIAL INFARCTION AJP-Heart Circ Physiol • VOL diastolic pressure where bead configuration was measured (11 mmHg). In summary, 3 wk after MI, noninfarcted tissue adjacent to the infarct remodeled by expansion along the direction of the fibers and in the cross-fiber direction. These changes are consistent with myocyte elongation and myofiber rearrangement (slippage) as well as a change in cell shape to a more elliptical cross section with the major axis in the epicardial tangent plane. Although this is the first study to clearly demonstrate cross-fiber remodeling, these data are qualitatively consistent with a wealth of previous data showing increased ventricular dimensions (18, 25), changes in myocyte shape (13, 15), and myocyte rearrangement (33) after MI. Moreover, these data indicate that reorientation of fibers either via cell slippage (32) or changes in orientation of the laminar structure (5, 16) of the ventricular wall are quantitatively important aspects of the remodeling of the adjacent normally perfused myocardium. GRANTS This research was supported by National Heart, Lung, and Blood Institute Grant HL-43617 and by Training Grant HL-7444 (to S. Zimmerman). REFERENCES 1. Anversa P, Loud AV, Levicky V, and Guideri G. Left ventricular failure induced by myocardial infarction. I. Myocyte hypertrophy. Am J Physiol Heart Circ Physiol 248: H876 –H882, 1985. 2. Anversa P, Olivetti G, and Capasso JM. Cellular basis of ventricular remodeling after myocardial infarction. Am J Cardiol 68: 7D–16D, 1991. 3. Bogaert J, Bosmans H, Maes A, Suetens P, Marchal G, and Rademakers FE. Remote myocardial dysfunction after acute anterior myocardial infarction: impact of left ventricular shape on regional function: a magnetic resonance myocardial tagging study. J Am Coll Cardiol 35: 1525–1534, 2000. 4. Capasso JM, Li P, Zhang X, and Anversa P. Heterogeneity of ventricular remodeling after acute myocardial infarction in rats. Am J Physiol Heart Circ Physiol 262: H486 –H495, 1992. 5. Costa KD, Hunter PJ, Wayne JS, Waldman LK, Guccione JM, and McCulloch AD. A three-dimensional finite element method for large elastic deformations of ventricular myocardium. II: prolate spheroidal coordinates. J Biomech Eng 118: 464 – 472, 1996. 6. Costa KD, Takayama Y, McCulloch AD, and Covell JW. Laminar fiber architecture and three-dimensional systolic mechanics in canine ventricular myocardium. Am J Physiol Heart Circ Physiol 276: H595–H607, 1999. 7. Gerdes AM, Kellerman SE, Malec KB, and Schocken DD. Transverse shape characteristics of cardiac myocytes from rats and humans. Cardioscience 5: 31–36, 1994. 8. Gosselin LE, Adams C, Cotter TA, McCormick RJ, and Thomas DP. Effect of exercise training on passive stiffness in locomotor skeletal muscle: role of extracellular matrix. J Appl Physiol 85: 1011–1016, 1998. 9. Holmes JW, Yamashita H, Waldman LK, and Covell JW. Scar remodeling and transmural deformation after infarction in the pig. Circulation 90: 411–20, 1994. 10. Jugdutt BI, Joljart MJ, and Khan MI. Rate of collagen deposition during healing and ventricular remodeling after myocardial infarction in rat and dog models. Circulation 94: 94 –101, 1996. 11. Kajstura J, Liu Y, Baldini A, Li B, Olivetti G, Leri A, and Anversa P. Coronary artery constriction in rats: necrotic and apoptotic myocyte death. Am J Cardiol 82: 30K-41K, 1998. 12. Kato S, Spinale FG, Tanaka R, Johnson W, Cooper TG, and Zile MR. Inhibition of collagen cross-linking: effects on fibrillar collagen and ventricular diastolic function. Am J Physiol Heart Circ Physiol 269: H863–H868, 1995. 13. Kozlovskis PL, Gerdes AM, Smets M, Moore JA, Bassett AL, and Myerburg RJ. Regional increase in isolated myocyte volume in chronic myocardial infarction in cats. J Mol Cell Cardiol 23: 1459 –1466, 1991. 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 changed (8), or hypertrophy (10). In larger animals and patients, noninfarcted myocardium distal to an infarct either thickens (3) or does not change (10). Fewer data exist for remodeling in tissue adjacent to an infarct. A reexamination of data from Kramer et al. (14) reveals significant thinning of myocardium they referred to as “adjacent” at 8 wk after surgically induced infarction (P ⫽ 0.001) and the magnitude of the thinning (⬃8%) was similar to that measured in the current work. In the present study, the average cross-fiber radial shear, calculated in the inner half of the wall, was 0.15. This is equivalent to a 15° angle change (31). Figure 8 shows a schematic diagram of potential mechanisms of wall thinning remodeling that have been proposed by several authors. Cell slippage has been investigated by a change in the number of cells across the wall. Several researchers have shown an ⬃40% reduction in transmural myocyte number (2, 19, 20, 33). A relative rotation of myocytes around the cellular long axis of ⬃20° can explain the 40% wall thinning. This calculated 20° change is in relative agreement with our measured 15° crossfiber radial sheer strain and the large positive strain normal to sheet remodeling strains. However, it is not possible to eliminate two other likely possibilities. A change in myocyte shape to a cell flatter in the epicardial tangent plane also could explain the decrease in radial strain. There is no information on the absolute loss of myocytes across the wall. A 10% decrease in wall thickness would require a 10% cell loss, which seems unlikely considering the short period of time and the relatively low apoptosis rates seen in the rat infarct model (11). Limitations of present study. Previous studies of tissue remodeling either used a uniaxial approach to determine dimension changes or sampled the myocardium at discrete points in time in different animals. Because this study documents changes in the position of material markers in the myocardium over time and employs a three-dimensional finite strain approach, we were not limited to determining the deformation in only one direction or to sampling tissue in different animals at discrete time points. However, the approach does have significant limitations. First, the markers are ⬃8 mm apart in the in epicardial tangent plane direction, and thus we are averaging strains over a relatively large sample of myocardium. Moreover, the resolution of the radiographic system is ⬃0.2 mm and the absolute measurements of cardiac dimensions are of this magnitude, which adds substantial difficulty in resolving small changes. We also assume that the markers (gold beads) remain coupled to the same tissue and do not independently migrate. In support of this assumption, none of our previous studies with this technique, which observed the markers repeated over time, showed rapid discontinuous movement of the markers (9). It was not possible to examine sheet and fiber architecture at the same site. In the present study sample blocks may have been as much as 5– 8 mm apart, and this could clearly add to the variability in the fiber-sheet data. Moreover, the hearts were fixed at zero distending pressure and we did not have hemodynamic and marker data at that pressure. This should not affect the fiber data greatly because the fiber direction does not change appreciably with distending pressure (6, 27, 28). However, our present data indicate that sheet angle changes with distending pressure. Thus the sheet angle changes here may well include a component due to the difference between zero distending pressure where the hearts were fixed and the end- H2703 H2704 REMODELING POSTMYOCARDIAL INFARCTION AJP-Heart Circ Physiol • VOL 24. Pfeffer JM, Fischer TA, and Pfeffer MA. Angiotensin-converting enzyme inhibition and ventricular remodeling after myocardial infarction. Annu Rev Physiol 57: 805– 826, 1995. 25. Pfeffer MA. Left ventricular remodeling after acute myocardial infarction. Annu Rev Med 46: 455– 466, 1995. 26. Spinale FG, Coker ML, Bond BR, and Zellner JL. Myocardial matrix degradation and metalloproteinase activation in the failing heart: a potential therapeutic target. Cardiovasc Res 46: 225–238, 2000. 27. Streeter DD Jr, Spotnitz HM, Patel DP, Ross J Jr, and Sonnenblick EH. Fiber orientation in the canine left ventricle during diastole and systole. Circ Res 24: 339 –347, 1969. 28. Takayama Y, Costa KD, and Covell JW. Contribution of laminar myofiber architecture to load-dependent changes in mechanics of LV myocardium. Am J Physiol Heart Circ Physiol 282: H1510 –H1520, 2002. 29. Theroux P, Ross J Jr, Franklin D, Covell JW, Bloor CM, and Sasayama S. Regional myocardial function and dimensions early and late after myocardial infarction in the unanesthetized dog. Circ Res 40: 158 –165, 1977. 30. Waldman LK, Fung YC, and Covell JW. Transmural myocardial deformation in the canine left ventricle. Normal in vivo three-dimensional finite strains. Circ Res 57: 152–163, 1985. 31. Waldman LK, Nosan D, Villarreal F, and Covell JW. Relation between transmural deformation and local myofiber direction in canine left ventricle. Circ Res 63: 550 – 662, 1988. 32. Weisman HF, Bush DE, Mannisi JA, and Bulkley BH. Global cardiac remodeling after acute myocardial infarction: a study in the rat model. J Am Coll Cardiol 5: 1355–1362, 1985. 33. Weisman HF, Bush DE, Mannisi JA, Weisfeldt ML, and Healy B. Cellular mechanisms of myocardial infarct expansion. Circulation 78: 186 –201, 1988. 34. Yue P, Long CS, Austin R, Chang KC, Simpson PC, and Massie BM. Post-infarction heart failure in the rat is associated with distinct alterations in cardiac myocyte molecular phenotype. J Mol Cell Cardiol 30: 1615– 1630, 1998. 35. Zimmerman SD, Karlon WJ, Holmes JW, Omens JH, and Covell JW. Structural and mechanical factors influencing infarct scar collagen organization. Am J Physiol Heart Circ Physiol 278: H194 –H200, 2000. 287 • DECEMBER 2004 • www.ajpheart.org Downloaded from http://ajpheart.physiology.org/ by 10.220.33.6 on May 8, 2017 14. Kramer CM, Lima JA, Reichek N, Ferrari VA, Llaneras MR, Palmon LC, Yeh IT, Tallant B, and Axel L. Regional differences in function within noninfarcted myocardium during left ventricular remodeling. Circulation 88: 1279 –1288, 1993. 15. Kramer CM, Rogers WJ, Park CS, Seibel PS, Shaffer A, Theobald TM, Reichek N, Onodera T, and Gerdes AM. Regional myocyte hypertrophy parallels regional myocardial dysfunction during post-infarct remodeling. J Mol Cell Cardiol 30: 1773–1778, 1998. 16. LeGrice IJ, Smaill BH, Chai LZ, Edgar SG, Gavin JB, and Hunter PJ. Laminar structure of the heart: ventricular myocyte arrangement and connective tissue architecture in the dog. Am J Physiol Heart Circ Physiol 269: H571–H582, 1995. 17. May-Newman K, Omens JH, Pavelec RS, and McCulloch AD. Threedimensional transmural mechanical interaction between the coronary vasculature and passive myocardium in the dog. Circ Res 74: 1166 –1178, 1994. 18. McKay RG, Pfeffer MA, Pasternak RC, Markis JE, Come PC, Nakao S, Alderman JD, Ferguson JJ, Safian RD, and Grossman W. Left ventricular remodeling after myocardial infarction: a corollary to infarct expansion. Circulation 74: 693–702, 1986. 19. Olivetti G, Capasso JM, Meggs LG, Sonnenblick EH, and Anversa P. Cellular basis of chronic ventricular remodeling after myocardial infarction in rats. Circ Res 68: 856 – 869, 1991. 20. Olivetti G, Capasso JM, Sonnenblick EH, and Anversa P. Side-to-side slippage of myocytes participates in ventricular wall remodeling acutely after myocardial infarction in rats. Circ Res 67: 23–34, 1990. 21. Olivetti G, Quaini F, Sala R, Lagrasta C, Corradi D, Bonacina E, Gambert SR, Cigola E, and Anversa P. Acute myocardial infarction in humans is associated with activation of programmed myocyte cell death in the surviving portion of the heart. J Mol Cell Cardiol 28: 2005–2016, 1996. 22. Omens JH, May KD, and McCulloch AD. Transmural distribution of three-dimensional strain in the isolated arrested canine left ventricle. Am J Physiol Heart Circ Physiol 261: H918 –H928, 1991. 23. Patten RD, Aronovitz MJ, Deras-Mejia L, Pandian NG, Hanak GG, Smith JJ, Mendelsohn ME, and Konstam MA. Ventricular remodeling in a mouse model of myocardial infarction. Am J Physiol Heart Circ Physiol 274: H1812–H1820, 1998.