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Biomedical subjects

David Liang

Publications and source records attributed to David Liang.

At least 37 records · Page 2Linked to original sources
PubMed2004

Mitral annular size predicts Alfieri stitch tension in mitral edge-to-edge repair.

BACKGROUND AND AIM OF THE STUDY: Whilst increased 'Alfieri stitch' tension may reduce the durability of 'edge-to-edge' mitral repair, the factors affecting suture tension are unknown. In order to study hemodynamics and left ventricular (LV) and annular dynamics that determine suture tension, the central edge of the mitral leaflets was approximated with a miniature force transducer to measure leaflet tension (T) at the leaflet approximation point. METHODS: Eight sheep were studied under open-chest conditions immediately after surgical placement of a force transducer and implantation of radiopaque markers on the left ventricle and mitral annulus (MA). Hemodynamic variables were altered by two caval occlusion steps (deltaV1 and deltaV2) and dobutamine infusion. Three-dimensional marker coordinates were obtained by simultaneous biplane videofluoroscopy to measure LV volume, MA area (MAA) and septal-lateral (SL) annular dimension throughout the cardiac cycle. RESULTS: At baseline, peak Alfieri stitch tension (0.30 +/- 0.18 N) was observed 96 +/- 61 ms prior to end-diastole coincident with peak annular SL diameter (98 +/- 58 ms before end-diastole). Dobutamine infusion decreased suture tension (from 0.30 +/- 0.18 N to 0.20 +/- 0.12 N, p = 0.01), although peak systolic pressure increased significantly (138 +/- 19 versus 115 +/- 14 mmHg; p = 0.03). A regression model was fitted with the goal of interpreting the hemodynamic and geometric predictors of tension as their influence varied with time: Tt (N) = 0.1916 + 0.2115 x SL (cm) - 0.1996 x MAA/SL (cm2/cm) + ft x LVP (mmHg), where Tt is tension at any time during the cardiac cycle and ft is the time-varying coefficient of LVP. CONCLUSION: Tension on the leaflets in the edge-to-edge repair is determined primarily by MA SL size, and paradoxically is lower when the contractile state is enhanced. This indicates that annular and/or LV dilatation increase stitch tension and may adversely affect durability of the repair if concomitant ring annuloplasty is not performed.

Animals↗
PubMed2004

Mitral suture annuloplasty corrects both annular and subvalvular geometry in acute ischemic mitral regurgitation.

BACKGROUND AND AIM OF THE STUDY: Papillary muscle displacement is an important element in the pathogenesis of ischemic mitral regurgitation (IMR). The effects of standard ring annuloplasty on subvalvular geometry are incompletely understood. The hypothesis was tested that annular reduction with a Panethtype suture annuloplasty would correct both annular and papillary muscle geometric abnormalities during acute left ventricular (LV) ischemia. METHODS: Eight adult sheep underwent insertion of an adjustable, double-suture Paneth-type mitral annuloplasty and radiopaque markers on the left ventricle, mitral annulus, leaflet edges, and anterior (APM) and posterior (PPM) papillary muscle tips. Immediately after surgey, 3-D marker coordinates were determined during Control conditions and during proximal left circumflex occlusion before and after tightening the annuloplasty suture. RESULTS: Acute IMR (MR grade 0.3 +/- 0.3 to 2.1 +/- 0.4, Control versus Ischemia) was associated with end-systolic LV dilatation (+27 +/- 16 ml, change relative to Control), greater septal-lateral (+4.6 +/- 3.1 cm) and commissure-commissure (+3.3 +/- 1.6 cm) mitral annular diameters, longer anterior (+1.5 +/- 0.9 cm) and posterior (+0.6 +/- 0.9 cm) papillary muscle tethering distances, greater distance from the APM to the anterior commissure (+0.9 +/- 0.8 cm), and shorter distance from the PPM to the poslerior commissure (-1.3 +/- 1.5 cm). Suture annuloplasty corrected the annular and subvalvular changes, and IMR returned to Control levels (0.5 +/- 0.5); only LV end-systolic volume (ESV) was different from Control (+25 +/- 18 ml) (mean +/- SD, p < 0.05 versus Control by RMANOVA and Dunnett's test). CONCLUSION: Suture annuloplasty corrected ischemia-induced end-systolic distortions of the entire valvular-ventricular complex (i.e. inter-leaflet separation, mitral annular dilatation in both axes, and papillary muscle displacements), and abolished acute IMR, independent of any change in ESV. A better understanding of the effects of annular reduction on papillary muscle geometry may lead to improved subvalvular mitral repair techniques.

Animals↗
PubMed2004

Increases in mitral leaflet radii of curvature with chronic ischemic mitral regurgitation.

BACKGROUND AND AIM OF THE STUDY: Leaflet curvature is a primary determinant of leaflet stress, but no quantitative in-vivo leaflet curvature data exist. Chronic ischemic mitral regurgitation (CIMR) is associated with remodeling of the valvular-ventricular complex. It was hypothesized that leaflet radii of curvature (ROC) would change with such remodeling. METHODS: Twelve sheep had placement of radiopaque markers on the anterior (APM) and posterior (PPM) papillary muscles, mitral annulus, and anterior (AL) and posterior leaflet (PL) midlines. After 8 +/- 2 days, videofluoroscopy provided baseline 3-D marker data prior to creating inferior myocardial infarction (MI) by snare occlusion of the obtuse marginal coronary arteries. After 7 +/- 1 weeks, the animals were re-studied; 3-D marker coordinates were used to determine end-systolic leaflet ROC, leaflet length, annular septal-lateral diameter, and the distance of each papillary muscle to the mid-septal annulus and each commissure. RESULTS: Before and after CIMR, the AL had compound curvature, and CIMR increased ROC of both curves (proximal ROC 1.27 +/- 0.59 to 1.38 +/- 0.60 cm (p <0.05); distal ROC 1.41 +/- 0.61 to 2.60 +/- 1.52 cm (p < 0.05)). The PL ROC also increased with CIMR (from 2.01 +/- 1.40 to 3.46 +/- 3.93) (p <0.05). Multiple regression analysis determined that annular septal-lateral diameter (proximal AL and distal AL), distance from the APM to anterior commissure (distal AL), and PPM to mid-septal annulus (PL) were independent predictors of leaflet ROC. CONCLUSION: CIMR increased ROC of both the AL and PL. Leaflet extension may be a compensatory mechanism to minimize the regurgitant orifice, but the attendant increase in ROC will tend to augment leaflet stress. Annular and subvalvular geometry both affect leaflet curvature, and should be considered during mitral repair. These novel quantitative in-vivo data are now available for modification of finite element models, and for comparison to finite element model output.

Animals↗
PubMed2003

Geometric distortions of the mitral valvular-ventricular complex in chronic ischemic mitral regurgitation.

BACKGROUND: Better understanding of the precise 3-dimensional geometric changes of the mitral valvular-ventricular complex in chronic ischemic mitral regurgitation (CIMR) is needed in order to devise better surgical repair techniques. We hypothesized that changes after inferior myocardial infarction would be different in hearts that developed CIMR compared with those that did not. METHODS AND RESULTS: Twenty-four sheep underwent coronary snare and marker placement (annulus, papillary muscles, and anterior and posterior leaflets). After 8 days, cinefluoroscopy provided 3-dimensional marker data, and snare occlusion of obtuse marginal branches created inferior myocardial infarction, including the posterior papillary muscle. After 7 weeks, the 16 surviving animals were studied again and grouped by mitral regurgitation grade (>or= 2+, n=10 versus <or= 1+, n=6). End-systolic mitral annulus dimensions, components of papillary muscle and leaflet displacement, were calculated. After inferior myocardial infarction, total displacement of the posterior papillary muscle from the midseptal annulus ("saddle horn") was greater in CIMR(+) animals: 6.5+/-3.2 versus 3.1+/-2.7 (P=0.02), with the posterior papillary muscle moving more laterally (6.8+/-3.4 versus 2.5+/-3.5 mm, P=0.01). Increase in mitral annular septal-lateral diameter was greater in animals with CIMR (4.9+/-2.7 versus 2.3+/-2.0, P=0.02), and apical displacement of the posterior leaflet (PL) margin was also greater in the CIMR(+) group (1.7+/-1.0 versus 0.3+/-0.5, P=0.01). CONCLUSIONS: The CIMR(+) group had greater septal-lateral annular dilatation, lateral posterior papillary muscle displacement, and apical PL restriction, indicating that these associated geometric alterations may be important in the pathogenesis of CIMR. Treatment of CIMR should address both annular septal-lateral dilatation and lateral displacement of the posterior papillary muscle.

Animals↗
PubMed2003

Paneth suture annuloplasty abolishes acute ischemic mitral regurgitation but preserves annular and leaflet dynamics.

BACKGROUND: Ring annuloplasty, the standard treatment for ischemic mitral regurgitation (IMR), abolishes normal annular dynamics and freezes the posterior leaflet. We examined the impact of Paneth suture annuloplasty during acute IMR on motion of the mitral annulus and leaflets in an ovine model. METHODS AND RESULTS: Eight sheep had radiopaque markers placed on the left ventricle, anterior mitral leaflet, posterior mitral leaflet, and mitral annulus. A Paneth suture annuloplasty that could be reversibly tightened was anchored to each fibrous trigone and externalized through the mid-lateral mitral annulus. Acute IMR was induced by proximal circumflex artery occlusion. Transesophageal echocardiography assessed the degree of IMR, and biplane cinefluoroscopy measured 3-dimensional marker coordinates before and during circumflex ischemia, and tightening of the Paneth suture. Paneth suture annuloplasty eliminated acute IMR, and reduced septal-lateral and commissure-commissure mitral annular dimensions. Tightening of the annuloplasty sutures, even beyond the degree necessary to eliminate mitral regurgitation (MR), did not reduce septal-lateral or commissure-commissure annular shortening, shortening of the muscular annular perimeter, annular flexion, or angular excursion of the anterior or posterior leaflets relative to ischemic conditions. CONCLUSIONS: In contrast to ring annuloplasty, annular reduction sufficient to restore mitral competence during acute IMR can be achieved with a Paneth suture annuloplasty while simultaneously maintaining normal annular and leaflet dynamic motion. These findings should prompt additional investigation and design of repair methods that preserve the mobility of the mitral apparatus.

Acute Disease↗
PubMed2003

Edge-to-edge mitral valve repair without ring annuloplasty for acute ischemic mitral regurgitation.

BACKGROUND: Alfieri edge-to-edge mitral repair has been used clinically with ring annuloplasty to correct ischemic mitral regurgitation (IMR), but its efficacy without concomitant ring annuloplasty has not been described in this setting. METHODS: Seventeen sheep underwent implantation of 9 radiopaque markers on the left ventricle, 8 on the mitral annulus (MA), 1 on each papillary muscle (PM) tip, and 1 on the anterior and posterior leaflet edges near the anterior and posterior commissures. Alfieri repair was performed in 7 animals, and 10 were controls. Biplane videofluoroscopy and transesophageal echocardiography (TEE) were performed (open chest) before and continuously during left circumflex coronary artery occlusion to induce acute IMR. MA area (MAA), anterior (APM), and posterior (PPM) papillary muscle tip distances to midseptal MA ("saddle horn"), and distance of each leaflet marker to the mitral annular plane were calculated from 3-dimensional marker coordinates at end-systole (ES). RESULTS: Severity of IMR was not different between groups (+1.9+/-0.7 versus +1.4+/-0.5 for Control and Alfieri, respectively; P=not significant [NS]). Mitral annular area (MAA; 21+/-15 versus 19+/-9%; P =NS) and septal-lateral (SL) annular diameter (12+/-6 versus 12+/-11%; P =NS) increased similarly during ischemia. While PPM-saddle horn distance increased in both groups (1.5+/-1.3 and 1.6+/-1.4 mm for Control and Alfieri, respectively; P<0.05 versus preischemia), APM-saddle horn distance increased in Control (1.0+/-1.2 mm; P=0.03) but not in the Alfieri animals (0.8+/-08 mm; P=0.07). Leaflet edge displacements from the annular plane during ischemia were similar in both groups. CONCLUSIONS: Alfieri repair did not prevent acute IMR nor alter ischemic valvular or subvalvular geometric perturbations. Adjunct surgical procedures, such as ring annuloplasty, are also necessary.

Acute Disease↗
PubMed2003

Annular remodeling in chronic ischemic mitral regurgitation: ring selection implications.

BACKGROUND: More precise understanding of annular remodeling in the evolution of chronic ischemic mitral regurgitation is needed to provide a more rational basis for optimal annuloplasty ring sizing and selection as well as the design of new reparative techniques. Three-dimensional in vivo data describing these geometric perturbations however are lacking. Using an ovine model of chronic myocardial infarction we determined the three-dimensional distortions of the mitral annulus associated with the development of chronic ischemic mitral regurgitation. METHODS: Ten sheep underwent placement of radiopaque markers on the left ventricle and mitral annulus as well as placement of snares around the second and third obtuse marginal coronary arteries. After 8 days biplane cinefluoroscopy provided three-dimensional marker data and snare occlusion created an inferior infarction. After 7 more weeks the animals were studied again. RESULTS: Severity of mitral regurgitation increased (0.6 +/- 0.5 to 2.5 +/- 0.7). Septal-lateral (2.99 +/- 0.20 cm to 3.64 +/- 0.35 cm, maximum dimension) and commissure-commissure (3.71 +/- 0.32 cm to 4.40 +/- 0.30 cm) mitral annular diameters and the lengths of the muscular (7.77 +/- 0.39 cm to 9.51 +/- 0.72 cm) and fibrous annular perimeters (3.36 +/- 0.37 cm to 3.85 +/- 0.39 cm, p < 0.0001 for all) increased while the height of the annular "saddle horn" above a best-fit plane fell (0.73 +/- 0.52 cm to 0.57 +/- 0.42 cm, minimum dimension, p = 0.01). CONCLUSIONS: These three-dimensional in vivo data reflect annular remodeling in chronic ischemic mitral regurgitation and suggest that mitral repair in this context should be aimed at preventing further lengthening of the intertrigonal distance, reducing the septal-lateral annular diameter to reestablish adequate leaflet coaptation, and restoring the saddle shape of the annulus.

Animals↗
PubMed2003

Aorto-mitral annular dynamics.

BACKGROUND: The aortic and mitral valves are coupled through fibrous aorto-mitral continuity, but their synchronous dynamic physiology has not been completely characterized. METHODS: Seven sheep underwent implantation of five radiopaque markers on the left ventricle, 10 on the mitral annulus, and 3 on the aortic annulus. One of the mitral annulus markers was placed at the center of aorto-mitral continuity (mitral annulus "saddle horn"). Animals were studied with bi-plane videofluoroscopy 7 to 10 days postoperatively. Total circumference and lengths of mitral fibrous annulus, mitral muscular annulus, aortic fibrous annulus, and aortic muscular annulus were calculated throughout the cardiac cycle from three dimensional marker coordinates as was mitral annular area and aortic annular area. Aorto-mitral angle was determined as the angle between the centroid of the aortic annulus markers, the saddle horn, and the centroid of the mitral annulus markers. Aortic annulus and mitral annulus flexion was expressed as the difference between maximum and minimum values of the aortic and mitral annulus angles during the cardiac cycle. RESULTS: Mitral and aortic annular areas changed in roughly a reciprocal fashion during late diastole and early systole with an overall 32 +/- 8% change in aortic annular area and a 13 +/- 13% change in mitral annular area. Aortic fibrous annulus changed much less than aortic muscular annulus (6 +/- 2% vs 18 +/- 4%; p = 0.0003) as did mitral fibrous annulus relative to mitral muscular annulus (4 +/- 1% vs 8 +/- 2%; p = 0.004). Aortic annulus and mitral annulus flexion was 8 +/- 2 degrees and increased to 11 +/- 2 degrees (p = 0.009) with inotropic stimulation. CONCLUSIONS: Dynamic aortic and mitral annular area changes were not mediated through the anatomic fibrous continuity. Aorto-mitral flexion, which increased with enhanced contractility, may facilitate left ventricle ejection. The effect of valvular surgical interventions on aorto-mitral flexion needs further investigation.

Animals↗
PubMed2003

Accuracy of hand-carried ultrasound.

Hand-carried ultrasound introduces a new group of devices, operators and usage patterns to echocardiography. This may have significant impact on the accuracy of the findings obtained with hand-carried ultrasound. Although reasonable agreement can be obtained with standard echocardiography in certain circumstances, limitations in imaging modes, device image quality, operator experience, and study completeness may significantly limit the diagnostic accuracy of hand carried ultrasound. Despite this, hand-carried ultrasound has the potential to improve significantly upon the data obtained by physical examination.

Echocardiography↗
PubMed2003

Ischemia in three left ventricular regions: Insights into the pathogenesis of acute ischemic mitral regurgitation.

BACKGROUND: Acute posterolateral left ventricular ischemia in sheep results in ischemic mitral regurgitation, but the effects of ischemia in other left ventricular regions on ischemic mitral regurgitation is unknown. METHODS: Six adult sheep had radiopaque markers placed on the left ventricle, mitral annulus, and anterior and posterior mitral leaflets at the valve center and near the anterior and posterior commissures. After 6 to 8 days, animals were studied with biplane videofluoroscopy and transesophageal echocardiography before and during sequential balloon occlusion of the left anterior descending, distal left circumflex, and proximal left circumflex coronary arteries. Time of valve closure was defined as the time when the distance between leaflet edge markers reached its minimum plateau, and systolic leaflet edge separation distance was calculated on the basis of left ventricular ejection. RESULTS: Only proximal left circumflex coronary artery occlusion resulted in ischemic mitral regurgitation, which was central and holosystolic. Delayed valve closure (anterior commissure, 58 +/- 29 vs 92 +/- 24 ms; valve center, 52 +/- 26 vs 92 +/- 23 ms; posterior commissure, 60 +/- 30 vs 94 +/- 14 ms; all P <.05) and increased leaflet edge separation distance during ejection (mean increase, 2.2 +/- 1.5 mm, 2.1 +/- 1.9 mm, and 2.1 +/- 1.5 mm at the anterior commissure, valve center, and posterior commissure, respectively; P <.05 for all) was seen during proximal left circumflex coronary artery occlusion but not during left anterior descending or distal left circumflex coronary artery occlusion. Ischemic mitral regurgitation was associated with a 19% +/- 10% increase in mitral annular area, and displacement of both papillary muscle tips away from the septal annulus at end systole. CONCLUSIONS: Acute ischemic mitral regurgitation in sheep occurred only after proximal left circumflex coronary artery occlusion along with delayed valve closure in early systole and increased leaflet edge separation throughout ejection in all 3 leaflet coaptation sites. The degree of left ventricular systolic dysfunction induced did not correlate with ischemic mitral regurgitation, but both altered valvular and subvalvular 3-dimensional geometry were necessary to produce ischemic mitral regurgitation during acute left ventricular ischemia.

Acute Disease↗
PubMed2003

Tachycardia-induced cardiomyopathy in the ovine heart: mitral annular dynamic three-dimensional geometry.

BACKGROUND: Ring annuloplasty has been used to correct annular dilatation and mitral regurgitation in dilated cardiomyopathy, but little is known about the dynamic precise 3-dimensional geometry of the mitral annulus in this condition. METHODS: Nine sheep had radiopaque markers sewn to the mitral annulus, creating 8 distinct segments beginning at the posterior commissure (segments 1-4, septal mitral annulus; segments 5-8, lateral mitral annulus). Biplane videofluoroscopy and transesophageal echocardiography were performed before and after rapid pacing (180-230 min(-1) for 15 +/- 6 days) sufficient to develop tachycardia-induced cardiomyopathy and mitral regurgitation. Mitral annular segment contraction was defined as the percentage difference between maximum and minimum lengths. Mitral annular area and mitral annular septal-lateral and commissure-commissure diameters and 3-dimensional shape were determined from marker coordinates. RESULTS: With tachycardia-induced cardiomyopathy, end-diastolic mitral annular area, septal-lateral diameter, and commissure-commissure diameter increased by 36% +/- 14%, 25% +/- 12%, and 9% +/- 5%, respectively (P <.01), whereas mitral regurgitation increased from 0.3 +/- 0.2 to 2.2 +/- 0.9 (P <.0001). All annular segments dilated at end-diastole with tachycardia-induced cardiomyopathy, except the segment between the midseptal annulus and the left fibrous trigone. Annular segment contraction was significantly decreased with tachycardia-induced cardiomyopathy in the lateral, but not in the septal, regions. Three-dimensional reconstruction of annular shape revealed a saddle shape of the annulus at baseline; this shape was also measured with tachycardia-induced cardiomyopathy, but there was some flattening of the septal annulus. CONCLUSIONS: With tachycardia-induced cardiomyopathy, the mitral annulus dilated substantially, being more in the septal-lateral than in the commissure-commissure dimension. Greater annular segmental dilatation and decreased contraction occurred in the lateral annulus. The saddle shape of the annulus was retained but flattened.

Animals↗
PubMed2003

Genetic diversity in yeast assessed with whole-genome oligonucleotide arrays.

The availability of a complete genome sequence allows the detailed study of intraspecies variability. Here we use high-density oligonucleotide arrays to discover 11,115 single-feature polymorphisms (SFPs) existing in one or more of 14 different yeast strains. We use these SFPs to define regions of genetic identity between common laboratory strains of yeast. We assess the genome-wide distribution of genetic variation on the basis of this yeast population. We find that genome variability is biased toward the ends of chromosomes and is more likely to be found in genes with roles in fermentation or in transport. This subtelomeric bias may arise through recombination between nonhomologous sequences because full-gene deletions are more common in these regions than in more central regions of the chromosome.

Chromosome Mapping↗
PubMed2003

Large-scale identification of single-feature polymorphisms in complex genomes.

We have developed a high-throughput genotyping platform by hybridizing genomic DNA from Arabidopsis thaliana accessions to an RNA expression GeneChip (AtGenome1). Using newly developed analytical tools, a large number of single-feature polymorphisms (SFPs) were identified. A comparison of two accessions, the reference strain Columbia (Col) and the strain Landsberg erecta (Ler), identified nearly 4000 SFPs, which could be reliably scored at a 5% error rate. Ler sequence was used to confirm 117 of 121 SFPs and to determine the sensitivity of array hybridization. Features containing sequence repeats, as well as those from high copy genes, showed greater polymorphism rates. A linear clustering algorithm was developed to identify clusters of SFPs representing potential deletions in 111 genes at a 5% false discovery rate (FDR). Among the potential deletions were transposons, disease resistance genes, and genes involved in secondary metabolism. The applicability of this technique was demonstrated by genotyping a recombinant inbred line. Recombination break points could be clearly defined, and in one case delimited to an interval of 29 kb. We further demonstrate that array hybridization can be combined with bulk segregant analysis to quickly map mutations. The extension of these tools to organisms with complex genomes, such as Arabidopsis, will greatly increase our ability to map and clone quantitative trait loci (QTL).

Arabidopsis↗
PubMed2003

Ablation of mitral annular and leaflet muscle: effects on annular and leaflet dynamics.

Mitral annular (MA) and leaflet three-dimensional (3-D) dynamics were examined after circumferential phenol ablation of the MA and anterior mitral leaflet (AML) muscle. Radiopaque markers were sutured to the left ventricle, MA, and both mitral leaflets in 18 sheep. In 10 sheep, phenol was applied circumferentially to the atrial surface of the mitral annulus and the hinge region of the AML, whereas 8 sheep served as controls. Animals were studied with biplane video fluoroscopy for computation of 3-D mitral annular area (MAA) and leaflet shape. MAA contraction (MAACont) was determined from maximum to minimum value. Presystolic MAA (PS-MAACont) reduction was calculated as the percentage of total reduction occurring before end diastole. Phenol ablation decreased PS-MAACont (72 +/- 6 vs. 47 +/- 31%, P = 0.04) and delayed valve closure (31 +/- 11 vs. 57 +/- 25 ms, P = 0.017). In control, the AML had a compound sigmoid shape; after phenol, this shape was entirely concave to the atrium during valve closure. These data indicate that myocardial fibers on the atrial side of the valve influence the 3-D dynamic geometry and shape of the MA and AML.

Animals↗
PubMed2003

Alterations in left ventricular curvature and principal strains in dilated cardiomyopathy with functional mitral regurgitation.

BACKGROUND AND AIM OF THE STUDY: Functional mitral regurgitation (FMR) is increasingly recognized as a left ventricular (LV) disease. Dilated cardiomyopathy (DCM) is commonly accompanied by FMR and reduction of LV torsion. Therapeutic targets for DCM include LV size reduction, altered LV shape, elimination of MR, and increasing LV torsion. It was hypothesized that, in addition to increasing LV size, DCM with FMR would alter normal LV shape and reduce and alter the direction of principal strains across the LV wall. This hypothesis was tested by measuring changes in epicardial and endocardial 2-D principal strains and regional radii of curvature accompanying tachycardia-induced cardiomyopathy in ovine hearts. METHODS: Radio-opaque marker arrays were implanted into the left ventricle of eight sheep, including one subepicardial triangle and one subendocardial triangle in the anterior wall of the left ventricle. At one week postoperatively, biplane videofluoroscopy was used to determine marker dynamics. Rapid ventricular pacing was then instituted until FMR and signs of heart failure developed, and fluoroscopy was repeated. Circumferential LV radii of curvature were determined from marker triplets. RESULTS: DCM changed the normal epicardial oval LV cross-section to a more circular configuration. The endocardium maintained its normal circular shape as the left ventricle dilated. Deformations of the triangles from end-diastole to end-systole were determined, and the magnitude and direction of 2-D principal strains calculated. DCM was associated with decreased magnitude of both epicardial (-0.095 +/- 0.055 versus -0.040 +/- 0.032, p = 0.006) and endocardial (-0.117 +/- 0.047 versus -0.073 +/- 0.037, p = 0.023) principal strains. DCM reduced the angle of epicardial but not endocardial principal strain. CONCLUSION: DCM with FMR is associated with LV dilation, circularization of the normally oval equatorial circumferential LV epicardium, transmural reduction in principal strain, and decrease in angle of principal epicardial strain. These changes contribute to a reduction in the net torsional moment and may guide the development of reverse remodeling procedures for the dilated, failing ventricle with FMR.

Animals↗
PubMed2002

Annular versus subvalvular approaches to acute ischemic mitral regurgitation.

BACKGROUND: Ischemic mitral regurgitation (IMR) has been attributed to annular dilatation, papillary muscle (PM) displacement ("apical leaflet tenting"), or both. We compared the efficacy of reducing annular or subvalvular dimensions to gain more mechanistic insight into acute IMR. METHODS: Eight adult sheep underwent implantation of radiopaque markers on the LV, mitral annulus (MA), each leaflet edge, and each PM tip. Trans-annular septal-lateral (SL) and inter-PM tip sutures were placed and externalized. Biplane videofluoroscopy and transesophageal echocardiography were performed before and continuously during LCx occlusion-induced IMR with SL annular (SLAC) or inter-PM (PAPS) suture tightening (4 to 5 mm of cinching for 5 seconds during ischemia). MA SL dimension, inter-papillary distance (APM-PPM), and the distances between the anterior (APM) and posterior (PPM) PM tips and the mid-septal annulus ("saddle horn") were calculated from 3-D marker coordinates at end-systole. RESULTS: SLAC reduced IMR (grade=2.1+/-0.6 versus 0.7+/-0.5, P.001), SL annular diameter (4.9+/-2.5 mm smaller versus pre-cinching; P.001), and PM-"saddle horn" distances (0.9+/-0.7 and 1.0+/-0.8 mm reduction for APM and PPM, respectively; P.005). PAPS reduced APM-PPM distance (3.7+/-1.8 mm reduction versus precinching; P.001), only slightly decreased the PPM-"saddle horn" distance (0.3+/-0.3 mm reduction; P.03), and had no effect on IMR. CONCLUSIONS: Acute IMR was abolished by annular SL reduction, which also repositioned both PM tips closer to the mid-septal annulus and paradoxically increased leaflet "apical tenting"; reducing inter-papillary dimension was not effective, even though it displaced the leaflets toward the annular plane (less "apical tenting").

Acute Disease↗
PubMed2002

Will a partial posterior annuloplasty ring prevent acute ischemic mitral regurgitation?

BACKGROUND: Acute posterolateral ischemia in sheep results in ischemic mitral regurgitation (IMR). While complete ring annuloplasty prevents acute IMR, partial annuloplasty rings may offer a more physiologic repair, but are untested in animal models of IMR. METHODS: Radiopaque markers were placed on the LV, mitral annulus (MA), and leaflets in 13 sheep. Seven sheep served as controls, and 6 had a St. Jude Tailor partial flexible ring implanted (29 mm in 5, 31 mm in 1). After 8+/-1 day, the animals were studied with biplane videofluoroscopy and echocardiography before and during acute posterolateral LV ischemia (balloon occlusion of circumflex artery). Mitral annular area (MAA), septal-lateral annular diameter (SL), annular perimeters, and leaflet edge separation were calculated from 3-D marker coordinates. RESULTS: The average degree of mitral regurgitation increased from 0.0+/-0.0 to 2.1+/-0.7 (P=0.0006) in the control group during acute ischemia but remained unchanged in the Tailor group (0.1+/-0.2 for both conditions). The change in MAA throughout the cardiac cycle before ischemia was 17+/-4% in control animals, but only 5+/-2% (P=0.0002) in the Tailor ring group. Unlike the control animals, there was no increase in MAA (5.4+/-0.8 and 5.5+/-0.7 cm(2), respectively; p=NS) nor dilatation of the muscular annulus (6.2+/-0.3 and 6.2+/-0.4, respectively; p=NS) during ischemia with the Tailor ring. Mitral SL dimension increased slightly with ischemia (2.3+/-0.2 versus 2.2+/-0.2 cm, P=0.03). Although posterior leaflet motion was limited, as observed with complete rings, normal annular flexion was maintained with the Tailor ring before and during acute ischemia. CONCLUSIONS: The Tailor partial annuloplasty ring prevented acute IMR probably by limiting SL diameter dilatation during acute ischemia. In this animal model of acute IMR, a partial, flexible posterior annuloplasty ring is as effective as a complete ring.

Acute Disease↗