Biomedical subjects

N B Ingels

Publications and source records attributed to N B Ingels.

At least 19 recordsLinked to original sources

PubMed2001

Pathogenesis of mitral regurgitation in tachycardia-induced cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy is often associated with mitral regurgitation (MR), or so-called functional MR, the mechanism of which continues to be debated. We studied the valvular and ventricular 3D geometric perturbations associated with MR in an ovine model of tachycardia-induced cardiomyopathy (TIC). METHODS AND RESULTS: Nine sheep underwent myocardial marker implantation in the left ventricle (LV), mitral annulus, and mitral leaflets. After 5 to 8 days, the animals were studied with biplane videofluoroscopy (baseline), and mitral competence was assessed by transesophageal echocardiography. Rapid ventricular pacing (180 to 230 bpm) was subsequently initiated for 15+/-6 days until the development of TIC and MR, whereupon biplane videofluoroscopy and transesophageal echocardiography studies were repeated. LV volume was calculated from the epicardial marker array. Valve closure time was defined as the time after end diastole when the distance between leaflet edge markers reached its minimal plateau. TIC resulted in increased LV end-diastolic volume (P=0.001) and LV end-systolic volume (P=0.0001) and greater LV sphericity (P=0.02). MR increased significantly (grade 0.2+/-0.3 versus 2.2+/-0.9, P=0.0001), as did mitral annulus area (817+/-146 versus 1100+/-161 mm(2), P=0.0001) and mitral annulus septal-lateral diameter (28.2+/-3.5 versus 35.1+/-2.6 mm, P=0.0001). Time of valve closure (70+/-18 versus 87+/-14 ms, P=0.23) and angular displacement of both the anterior (29+/-5 degrees versus 27+/-3 degrees, P=0.3) and posterior (55+/-15 degrees versus 44+/-11 degrees, P=0.13) leaflet edges relative to the mitral annulus after valve closure did not change, but leaflet edge separation after closure increased (5.2+/-0.9 versus 6.8+/-1.2 mm, P=0.019). CONCLUSIONS: MR in TIC resulted from decreased leaflet coaptation secondary to annular dilatation in the septal-lateral direction. These data support the use of annular reduction procedures, such as rigid, complete ring annuloplasty, to address functional MR in patients with dilated cardiomyopathy.

Animals↗

PubMed2001

Edge-to-edge mitral repair: tension on the approximating suture and leaflet deformation during acute ischemic mitral regurgitation in the ovine heart.

BACKGROUND: Edge-to-edge approximation of the mitral valve leaflets (Alfieri procedure) is a novel surgical treatment for patients with ischemic mitral regurgitation (IMR). Long-term durability may be limited if abnormal mitral leaflet stresses result from this procedure. The aim of the current study was to measure Alfieri stitch tension (F(A)) and to explore its geometric determinants in an ovine model of acute IMR as a reflection of the mitral leaflet stresses imposed by the procedure. METHODS AND RESULTS: Eight sheep were studied immediately after surgical placement of (1) a force transducer interposed between sutures approximating the central leaflet edges and (2) radiopaque markers around the mitral annulus and leaflet edges. Computer-aided analysis of videofluorograms was used to obtained 3D marker coordinates. Simultaneous measurements of F(A), septal-lateral annular dimension (L(S-L)), leaflet edge separation (L(SEP)), anterior (L(AL)) and posterior (L(PL)) leaflet length, and hemodynamic variables were obtained at baseline (CTL) and during acute IMR (circumflex artery occlusion). F(A) was significantly elevated throughout the cardiac cycle during IMR compared with CTL, with maximum F(A) in diastole (0.26+/-0.05 versus 0.46+/-0.08 N, CTL versus IMR; P<0.05). Multivariable analysis revealed L(S-L) as the single independent predictor of maximum F(A) (P<0.001). Positive linear correlations were shown between values of F(A) and L(AL) and L(PL) (dependent variables). CONCLUSIONS: These experimental data demonstrate higher F(A) during IMR and cyclic changes in F(A) closely paralleling changes in L(S-L), eg, being greatest in diastole when the annulus is largest. Increased F(A) during IMR is probably indicative of successful therapeutic intent, but higher diastolic leaflet stresses resulting from persistent or progressive mitral annular dilatation may adversely affect repair durability. This indirectly implies that concomitant mitral ring annuloplasty should be added to the Alfieri repair.

Acute Disease↗

PubMed2001

Influence of anterior mitral leaflet second-order chordae on leaflet dynamics and valve competence.

BACKGROUND: Chordal transposition is used in mitral valve repair, yet the effects of second-order chord transection on valve function have not been extensively studied. We evaluated leaflet coaptation, three-dimensional anterior mitral valve leaflet shape, and valve competence after cutting anterior second-order chordae. METHODS: In 8 sheep radiopaque markers were affixed to the left ventricle, mitral annulus, and leaflets. Animals were studied immediately with biplane videofluoroscopy and echocardiography before (Control) and after (Cut2) severing two anterior second-order "strut" chordae. Leaflet coaptation was assessed as separation between leaflet edge markers in the midleaflet and near each commissure (anterior commissure, posterior commissure). Anterior leaflet geometry was determined 100 milliseconds after end-diastole from three-dimensional coordinates of 13 markers. RESULTS: Anterior leaflet geometry changed only slightly after chordal transection without inducing mitral regurgitation. Leaflet coaptation times were 79+/-17 and 87+/-22 milliseconds at the anterior commissure; 72+/-21, 72+/-19 milliseconds at midleaflet, and 71+/-12 and 75+/-8 milliseconds at the posterior commissure (p = NS) for Control and Cut2, respectively. CONCLUSIONS: Cutting anterior second-order chordae did not cause delayed leaflet coaptation, alter leaflet shape, or create mitral regurgitation. These data indicate that transposition of second-order anterior chordae ("strut" chordae) is not deleterious to anterior leaflet motion per se.

Animals↗

PubMed2001

Edge-to-edge mitral repair: gradients and three-dimensional annular dynamics in vivo during inotropic stimulation.

OBJECTIVE: The edge-to-edge (Alfieri) mitral repair technique appears to be clinically promising, but the potential for functional mitral stenosis, especially with exercise, remains a concern. We used the myocardial marker method combined with Doppler echocardiography to evaluate mitral annular (MA) three-dimensional (3-D) dynamics and transvalvular gradients after leaflet approximation before and during dobutamine infusion. METHODS: Eight adult sheep underwent implantation of eight myocardial markers around the MA and nine in the left ventricle. Mitral leaflet edges were approximated at the valve center and micromanometers were placed in the left ventricle and atrium. The animals were studied with biplane videofluoroscopy to determine 3-D marker coordinates for computation of precise 3-D MA area and left ventricular (LV) volume. Epicardial Doppler echocardiography measured peak and mean diastolic mitral valve gradients at baseline and during dobutamine infusion (10 microg/kg per min). RESULTS: During dobutamine stimulation, left ventricular dP/dt increased from 1776+/-712 to 3390+/-618 mmHg/s (P=0.002), and cardiac output (CO) increased from 2.7+/-1.1 to 5.1+/-1.2 l/min (P=0.009). Mitral annular area (MAA) at end-diastole (ED) fell from 8.6+/-1.4 to 7.0+/-1.8 cm(2) (P=0.001) with inotropic stimulation, but only a modest increase was observed in mean (1.4+/-0.4 vs. 2.4+/-1.0 mmHg, P=0.046) and peak (2.7+/-0.8 vs. 4.9+/-2.5 mmHg, P=0.03) diastolic mitral valve gradients. MAA changed dynamically throughout the cardiac cycle, reflecting normal physiology, but the magnitude of MAA change was augmented during inotropic stimulation (18+/-5% and 27+/-4% for control and dobutamine, respectively; P=0.004). CONCLUSION: Dobutamine increased CO by 89% and decreased ED annular area by 19% after edge-to-edge repair, yet only a small increase in valve gradient occurred. Marker analysis showed enhanced dynamic motion of the mitral annulus. Thus, the edge-to-edge mitral valve repair was not associated with substantial transvalvular obstruction during high flow conditions and did not perturb normal MA 3-D dynamics in normal ovine hearts.

Animals↗

PubMed2001

Three-dimensional geometric comparison of partial and complete flexible mitral annuloplasty rings.

BACKGROUND: It has previously been shown in sheep that mitral annular physiologic dynamics during the cardiac cycle are abolished by complete ring annuloplasty, but recent clinical studies suggest that flexible partial ring annuloplasty preserves normal mitral annular dynamics. METHODS: Eight radiopaque markers were sutured equidistantly around the mitral anulus in 3 groups of sheep: no-ring control animals (n = 16); animals with a flexible Tailor partial ring annuloplasty (n = 6; St Jude Medical, Inc, St Paul, Minn); and animals with a flexible Duran ring annuloplasty (n = 7; Medtronic, Inc, Minneapolis, Minn). After 7 to 10 days' recovery, 3-dimensional marker coordinates were measured by biplane cinefluoroscopy. Mitral annular area and folding (defined as displacement of the mitral anulus from a least-squares plane) and mitral annular septal-lateral and commissure-commissure dimensions were calculated from the 3-dimensional marker coordinates throughout the cardiac cycle every 17 ms. RESULTS: In the no-ring control group mitral annular area varied from 8.0 +/- 0.2 to 7.2 +/- 0.2 cm(2) (10% +/- 2%), and the septal-lateral and commissure-commissure dimensions varied from 27.7 +/- 0.4 to 25.9 +/- 0.4 mm (7% +/- 1%) and from 38.2 +/- 0.8 to 36.4 +/- 0.8 mm (5% +/- 1%), respectively (mean +/- standard error of the mean, P <.001 for all comparisons). In the Duran ring annuloplasty and Tailor partial ring annuloplasty groups, the anulus was fixed in size throughout the cardiac cycle (area = 4.8 +/- 0.1 and 5.3 +/- 0.3 cm(2), septal-lateral = 21.8 +/- 0.7 and 22.0 +/- 0.8 mm, and commissure-commissure = 27.7 +/- 0.7 and 31.2 +/- 1.7 mm). Mitral annular folding did not differ significantly between the control and Tailor partial ring annuloplasty groups but was dampened in the Duran ring annuloplasty group. CONCLUSIONS: Partial Tailor flexible ring annuloplasty fixed mitral annular area and dimensions throughout the cardiac cycle in sheep; however, it preserved physiologic mitral annular folding dynamics, which might be important in terms of long-term valve function and prevention of left ventricular outflow tract obstruction.

Animals↗

PubMed2001

The role of atrial contraction in mitral valve closure.

BACKGROUND AND AIM OF THE STUDY: Ovine mitral valve closure is associated with presystolic mitral annular reduction coincident with atrial contraction, which is abolished with ventricular pacing. Whether lack of properly timed atrial contraction influences mitral valve closure or competence, however, is not known. METHODS: Eight sheep underwent myocardial marker implantation on the left ventricle, mitral annulus (MA), and mitral leaflets. After 7-10 days, the animals were studied with biplane videofluoroscopy at baseline and during ventricular or atrioventricular (AV) sequential pacing. Valve closure was timed from end-diastole (ED) and defined as minimum distance between two leaflet edge markers. ED was defined as peak of ECG R wave, end-systole as peak negative left ventricular (LV) dP/dt, and end-isovolumic contraction (EIVC) as 83.5 ms after ED. Septal-lateral (S-L) annular diameter was defined as distance between two markers at the middle of the anterior and posterior annulus. Regurgitant volume (RV) was calculated as relative volume change between ED and EIVC. RESULTS: V-pacing was associated with delayed leaflet closure (65 +/- 5 versus 29 +/- 10 ms, p = 0.008); moreover, RV (4.1 +/- 0.5 versus 1.4 +/- 0.5 ml, p = 0.02), end-diastolic S-L diameter (2.87 +/- 0.10 versus 2.67 +/- 0.09 cm, p = 0.0005), and MA area (8.12 +/- 0.37 versus 7.26 +/- 0.31 cm2, p = 0.009) all increased. RV and leaflet and annular dynamics during AV-pacing were similar to baseline. CONCLUSION: V-pacing increased S-L MA diameter by only 8 +/- 1%, but this change was associated with delayed leaflet coaptation and a 16 +/- 1% regurgitant fraction. These findings provide direct evidence that a properly timed atrial contraction is functionally important for effective mitral leaflet closure.

Animals↗

PubMed2000

Coordinate-free analysis of mitral valve dynamics in normal and ischemic hearts.

BACKGROUND: The purpose of this investigation was to study mitral valve 3D geometry and dynamics by using a coordinate-free system in normal and ischemic hearts to gain mechanistic insight into normal valve function, valve dysfunction during ischemic mitral regurgitation (IMR), and the treatment effects of ring annuloplasty. METHODS AND RESULTS: Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 on each papillary tip, 8 around the mitral annulus, and 1 on each leaflet edge midpoint. One group served as a control (n=7); all others underwent flexible Tailor partial (n=5) or Duran complete (n=6) ring annuloplasty. After an 8+/-2-day recovery, 3D marker coordinates were measured with biplane videofluoroscopy before and during posterolateral left ventricular ischemia, and MR was assessed by color Doppler echocardiography. Papillary to annular distances remained constant throughout the cardiac cycle in normal hearts, during ischemia, and after ring annuloplasty with either type of ring. Papillary to leaflet edge distances similarly remained constant throughout ejection. During ischemia, however, the absolute distances from the papillary tips to the annulus changed in a manner consistent with leaflet tethering, and IMR was observed. In contrast, during ischemia in either ring group, those distances did not change from preischemia, and no IMR was observed. CONCLUSIONS: This analysis uncovered a simple pattern of relatively constant intracardiac distances that describes the 3D geometry and dynamics of the papillary tips and leaflet edges from the dynamic mitral annulus. Ischemia perturbed the papillary-annular distances, and IMR occurred. Either type of ring annuloplasty prevented such changes, preserved papillary-annular distances, and prevented IMR.

Animals↗

PubMed2000

Ring annuloplasty prevents delayed leaflet coaptation and mitral regurgitation during acute left ventricular ischemia.

OBJECTIVE: Incomplete mitral leaflet coaptation during acute left ventricular ischemia is associated with end-diastolic mitral annular dilatation and ischemic mitral regurgitation. Annular rings were implanted in sheep to investigate whether annular reduction alone is sufficient to prevent mitral regurgitation during acute posterolateral left ventricular ischemia. METHODS: Radiopaque markers were inserted around the mitral anulus, on papillary muscle tips, and on the central meridian of both mitral leaflets in three groups of sheep: control (n = 5), Physio ring (n = 5) (Baxter Cardiovascular Div, Santa Ana, Calif), and Duran ring (n = 6) (Medtronic Heart Valve Div, Minneapolis, Minn). After 8 +/- 1 days, animals were studied with biplane videofluoroscopy before and during left ventricular ischemia. Annular area was calculated from 3-dimensional marker coordinates and coaptation defined as minimal distance between leaflet edge markers. RESULTS: Before ischemia, leaflet coaptation occurred just after end-diastole in all groups (control 17 +/- 41, Duran 33 +/- 30, Physio 33 +/- 24 ms, mean +/- SD, P >.2 by analysis of variance). During ischemia, regurgitation was detected in all control animals, and leaflet coaptation was delayed to 88 +/- 8 ms after end-diastole (P =.02 vs preischemia). This was associated with increased end-diastolic annular area (8.0 +/- 0.9 vs 6.7 +/- 0.6 cm(2), P =.004) and septal-lateral annular diameter (2.9 +/- 0.1 vs 2.5 +/- 0.1 cm, P =.02). Mitral regurgitation did not develop in Duran or Physio sheep, time to coaptation was unchanged (Duran 25 +/- 25 ms, Physio 30 +/- 48 ms [both P >.2 vs preischemia]), and annular area remained fixed. CONCLUSION: Mitral annular area reduction and fixation with an annuloplasty ring eliminated delayed leaflet coaptation and prevented mitral regurgitation during acute left ventricular ischemia after ring implantation.

Acute Disease↗

PubMed2000

Mitral annular dynamics during rapid atrial pacing.

INTRODUCTION: Ovine mitral annular area (MAA) reduction predominantly occurs before ventricular systole. We used the myocardial marker methods to investigate left atrial and MAA dynamics during rapid atrial pacing. METHODS: Seven sheep underwent implantation of 21 myocardial markers around the mitral annulus, the left ventricle and left atrium. After 7 to 10 days, animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates unpaced and during rapid atrial pacing at 140 minutes(-1). Left ventricle volume, left atrial volume (LAV), and MAA were calculated from marker coordinates. End diastole (ED) was defined at peak of the electrocardiogram R wave; times of minimum MAA and minimum LAV were expressed relative to ED (t = 0). Percent reduction in MAA and LAV were calculated from maximum and minimum values between diastole and early systole. RESULTS: The time of minimum MAA occurred earlier relative to ED during rapid pacing compared with control (-48 +/- 21 vs 19 +/- 14 msec; P <.001), as did the time of minimum LAV (-47 +/- 18 vs 4 +/- 16 msec; P <.001). Minimum MAA and LAV were significantly smaller with rapid pacing (6. 8 +/- 0.6 vs 6.5 +/- 0.5 cm(2); P <.05, respectively; and 15.4 +/- 2. 4 vs 16.5 +/- 2.3 mL; P <.01, respectively), and a relatively greater fractional reduction in MAA and LAV was observed during presystole. CONCLUSIONS: Rapid atrial pacing resulted in greater MAA and LAV reduction, both of which occurred entirely during diastole. This study supports the notion that MAA reduction is closely linked to LA dynamics.

Animals↗

PubMed2000

The effects of ring annuloplasty on mitral leaflet geometry during acute left ventricular ischemia.

BACKGROUND: The perturbed mitral leaflet geometry that leads to acute ischemic mitral regurgitation during acute left ventricular ischemia has not been quantified, nor is it known whether annuloplasty rings affect these detrimental changes in leaflet geometry. METHODS: Radiopaque markers were implanted on both mitral leaflets and around the anulus in 3 groups of sheep: one group without rings served as the control group (n = 7); the others underwent Duran (n = 6; Medtronic Heart Valve Division, Minneapolis, Minn) or Carpentier-Edwards Physio (n = 5; Baxter Cardiovascular Division, Santa Ana, Calif) ring annuloplasty. After recovery, 3-dimensional marker coordinates were obtained by means of biplane videofluoroscopy before and during acute posterolateral left ventricular ischemia. Leaflet geometry was defined by measuring distances between annular and leaflet markers and perpendicular distances to the leaflet markers from a best-fit annular plane. RESULTS: In all control animals, left ventricular ischemia was associated with acute ischemic mitral regurgitation and apical displacement (away from the annular plane) of the posterior leaflet edge and base markers by 0.6 +/- 0.4 mm (P =.01) and 0.7 +/- 0.2 mm (P <.001), respectively. The distance between the posterior leaflet markers and the mid-posterior anulus did not change significantly during ischemia. The anterior leaflet edge marker extended 1.0 +/- 0. 5 mm (P =.01) away from the mid-anterior anulus during ischemia, but compared with its nonischemic position, the anterior leaflet was not displaced apically away from the annular plane. In all animals in the Duran and Physio groups, leaflet geometry was unchanged during ischemia, and acute ischemic mitral regurgitation was not detected. CONCLUSION: Acute ischemic mitral regurgitation was associated with restricted motion of the posterior leaflet and extension of the anterior leaflet. Annuloplasty rings prevented these geometric perturbations of the mitral leaflets during acute left ventricular ischemia and preserved valvular competence.

Animals↗

PubMed1999

Deformational dynamics of the aortic root: modes and physiologic determinants.

BACKGROUND: Current surgical methods for treating aortic valve and aortic root pathology vary widely, and the basis for selecting one repair or replacement alternative over another continues to evolve. More precise knowledge of the interaction between normal aortic root dynamics and aortic valve mechanics may clarify the implications of various surgical procedures on long-term valve function and durability. METHODS AND RESULTS: To investigate the role of aortic root dynamics on valve function, we studied the deformation modes of the left, right, and noncoronary aortic root regions during isovolumic contraction, ejection, isovolumic relaxation, and diastole. Radiopaque markers were implanted at the top of the 3 commissures (sinotubular ridge) and at the annular base of the 3 sinuses in 6 adult sheep. After a 1-week recovery, ECG and left ventricular and aortic pressures were recorded in conscious, sedated animals, and the 3D marker coordinates were computed from biplane videofluorograms (60 Hz). Left ventricular preload, contractility, and afterload were independently manipulated to assess the effects of changing hemodynamics on aortic root 3D dynamic deformation. The ovine aortic root undergoes complex, asymmetric deformations during the various phases of the cardiac cycle, including aortoventricular and sinotubular junction strain and aortic root elongation, compression, shear, and torsional deformation. These deformations were not homogeneous among the left, right, and noncoronary regions. Furthermore, changes in left ventricular volume, pressure, and contractility affected the degree of deformation in a nonuniform manner in the 3 regions studied, and these effects varied during isovolumic contraction, ejection, isovolumic relaxation, and diastole. CONCLUSIONS: These complex 3D aortic root deformations probably minimize aortic cusp stresses by creating optimal cusp loading conditions and minimizing transvalvular turbulence. Aortic valve repair techniques or methods of replacement using unstented autograft, allograft, or xenograft tissue valves that best preserve this normal pattern of aortic root dynamics should translate into a lower risk of long-term cusp deterioration.

Animals↗

PubMed1999

Functional evaluation of the medtronic stentless porcine xenograft mitral valve in sheep.

BACKGROUND: Recently, renewed interest in allograft and stentless "freehand" bileaflet xenograft mitral valve replacement has arisen. The variability of human papillary tip anatomy and scarcity of donors limit allograft availability, making xenograft mitral valves an attractive alternative; however, these valves require new surgical implantation techniques, and assessment of their hemodynamics and functional geometry is lacking. METHODS: Seven sheep underwent implantation of a new stentless, glutaraldehyde-preserved porcine mitral valve (Physiological Mitral Valve [PMV], Medtronic) and were studied acutely under open-chest conditions. A new method of retrograde cardioplegia was developed. Hemodynamic valve function was assessed by epicardial Doppler echocardiography. 3D motion of miniature radiopaque markers sutured to the valve leaflets, annulus, and papillary tips was measured. Six other sheep with implanted markers served as controls. RESULTS: Both papillary muscle tips avulsed in the first animal, leaving 6 other animals. Mitral regurgitation was not observed in any xenograft valve. The peak and mean transvalvular gradients were 4.6+/-1.8 mm Hg and 2.6+/-1.5 mm Hg, respectively. The average mitral valve area was 5.7+/-1.6 cm(2). Valve closure in the xenograft group occurred later (30+/-11 ms, P<0. 015) and at higher left-ventricular pressure (61+/-9 mm Hg, P<0.001) than in the control group; furthermore, leaflet coaptation was displaced more apically (5.6+/-2.2 mm, P<0.001) and septally (5. 8+/-1.5 mm, P<0.001), and the anterolateral papillary tip underwent greater septal-lateral displacement (2.7+/-1.5 mm, P<0.001). Annular contraction during the cardiac cycle was similar in the 2 groups (xenograft 9.2+/-4.5% versus control 10.6+/-4.5% [mean+/-SD; 2-factor ANOVA model]). CONCLUSIONS: Successful freehand stentless porcine mitral valve implantation is feasible in sheep and was associated with excellent early postoperative hemodynamics. Physiological mitral valve annular contraction and functional leaflet closure mechanics were preserved. Long-term valve durability, calcification, and hemodynamic performance remain to be determined in models.

Animals↗

PubMed1999

Mitral annular dilatation and papillary muscle dislocation without mitral regurgitation in sheep.

BACKGROUND: Asymmetrical mitral annular (MA) dilatation and papillary muscle dislocation are implicated in the pathogenesis of functional mitral regurgitation (MR). METHODS AND RESULTS: To determine the mechanism by which annular and papillary muscle geometric alterations result in MR, we implanted radiopaque markers in the left ventricle, mitral annulus, anterior and posterior mitral leaflets, and papillary muscle tips and bases in 2 groups of sheep. One group served as controls (CTL, n=7); an experimental group (EXP, n=9) underwent topical phenol application to obliterate anterior annular and leaflet muscle (confirmed histologically ex vivo). After 1 week of recovery, markers were imaged with biplane videofluoroscopy, and hemodynamic data were recorded. MA area (computed from 3-dimensional marker coordinates) was 11% to 13% larger in the EXP group than in the CTL group (P<0.05 by ANOVA). This area increase resulted exclusively from intercommissural axis increase except in 1 heart with large (>1 cm) increases in both the intercommissural and septolateral annular axes. The anterior papillary muscle tip in EXP was displaced from CTL by 2.9+/-0.23 mm toward the anterolateral left ventricle and 2.5+/-0.12 mm toward the mitral annulus at end systole; the posterior papillary muscle geometry was unchanged. Transthoracic echocardiography revealed MR only in the heart exhibiting biaxial annular enlargement. CONCLUSIONS: MA dilatation in the intercommissural dimension with anterior papillary muscle tip displacement toward the annulus is insufficient to produce MR in sheep. Functional MR may require MA dilatation in the septolateral axis, as observed with proximal circumflex coronary occlusion.

Animals↗

PubMed1999

Effects of mitral valve replacement on regional left ventricular systolic strain.

BACKGROUND: Mitral valve replacement (MVR) with chordal excision impairs left ventricular (LV) systolic function, but the responsible mechanisms remain incompletely characterized. Loss of normal annular-papillary continuity also adversely affects LV torsional deformation, possibly due to changes in myocardial fiber contraction pattern. METHODS: Twenty-seven dogs underwent insertion of LV myocardial markers and a sham procedure (cardiopulmonary bypass, no MVR, n = 6), conventional MVR with chordae tendineae excision (n = 7), or chordal-sparing MVR with reattachment of the anterior leaflet chordae to the anterior annulus (n = 7) or to the posterior annulus (n = 7). In the anterior, lateral, posterior, and septal LV regions, linear chords were constructed from each region's central marker to its surrounding markers. Percent systolic shortening (regional LV strain) was calculated for each chord, and the chords were assigned to one of four angular groups: I, left-handed oblique (subepicardial fiber direction); II, circumferential (midwall); III, right-handed oblique (subendocardial); or IV, longitudinal. Regional LV strain data were compared before and after MVR. RESULTS: Sham and anterior chordal-sparing MVR had minimal effects on regional LV strain. With posterior chordal-sparing MVR: anteriorly, left-oblique (I) strain fell (31%, p<0.05), as did circumferential (II) and right-oblique (III) strains (by 49% and 51%, respectively; p<0.01). Laterally, left-oblique (I) strain fell by 36% (p<0.05), as did longitudinal (IV) strain (54% decline, p<0.01). Conventional MVR with chordal excision disrupted regional fiber shortening diffusely, affecting oblique fibers (I and III) in the anterior and septal regions and impairing longitudinal (IV) strain in all regions (45% to 68% fall, p<0.05). CONCLUSIONS: Sham and anterior chordal-sparing MVR did not substantially alter regional LV strain; however, loss of normal anatomic valvular-ventricular integrity (conventional MVR) or posterior chordal-sparing MVR resulted in pronounced alterations in LV strain, most notably in the longitudinal and oblique fiber directions. These findings demonstrate that the deleterious effects of chordal excision are associated with perturbed internal myocardial systolic deformation, which suggests that chordal disruption distorts myofiber architecture or regional systolic loading.

Animals↗

PubMed1999

Restricted posterior leaflet motion after mitral ring annuloplasty.

BACKGROUND: The effects of ring annuloplasty on mitral leaflet motion are incompletely known. The three-dimensional dynamics of the mitral valve in vivo were examined to determine how two types of annuloplasty rings affect leaflet motion during valve closure. METHODS: Miniature radiopaque markers on the mitral leaflets, annulus, and left ventricle were implanted in three groups of sheep. One group served as control (n = 7); other sheep were randomly assigned to receive either a flexible Duran (n = 6) or a semirigid Carpentier-Edwards Physio ring (n = 6). After recovery, three-dimensional marker coordinates were computed from simultaneous (60 Hz) biplane videofluoroscopic marker images. RESULTS: Both types of rings immobilized the middle scallop of the posterior leaflet without affecting anterior leaflet motion. The excursion of the anterior leaflet edge from maximally open to fully closed was not different between the groups (control, 13+/-2 mm; Duran 13+/-1 mm; Physio ring, 14+/-1 mm; p > 0.05), but posterior leaflet edge excursion was restricted (control, 7.4+/-0.4 mm; 2.3+/-0.3 mm [p < 0.001]; Physio, 2.7+/-0.2 mm [p < 0.001]) by both rings. CONCLUSIONS: Mitral annuloplasty with either ring type markedly reduced the mobility of the central posterior leaflet in normal ovine hearts such that valve closure became essentially a single (anterior) leaflet process with the frozen posterior leaflet serving only as a buttress for closing.

Animals↗

PubMed1999

Potential mechanism of left ventricular outflow tract obstruction after mitral ring annuloplasty.

OBJECTIVES: The purpose of this study was to explore whether geometric changes that predispose to left ventricular outflow tract obstruction after mitral ring annuloplasty are coupled to subvalvular apparatus disturbances. METHODS: Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 in the high interventricular septum, 1 on each papillary muscle tip, 8 around the mitral anulus, 4 on the anterior mitral leaflet, and 2 on the posterior leaflet. One group served as control (n = 5); the others were randomized to undergo annuloplasty with the Duran ring (n = 6; Medtronic, Inc, Minneapolis, Minn) or Carpentier-Edwards Physio ring (n = 6; Baxter Healthcare Corp, Irvine, Calif). After a 7- to 10-day recovery period, 3-dimensional marker coordinates were measured with biplane videofluoroscopy. RESULTS: At the beginning of ejection, (1) the anterior leaflet was displaced toward the left ventricular outflow tract; (2) the normal atrially flexed anterior anulus was flattened into the left ventricular outflow tract; (3) the posterior anulus was displaced toward the left ventricular outflow tract; (4) the anterior papillary muscle was displaced septally; and (5) the posterior papillary muscle was dislocated inwardly toward the anterior papillary muscle in the Physio ring group compared with the control group. During ejection, all these structures moved septally, encroaching further on the left ventricular outflow tract. In the Duran ring group, only the posterior anulus was displaced toward the left ventricular outflow tract; the anterior leaflet was not displaced toward the left ventricular outflow tract, and it did not move septally during ejection. CONCLUSIONS: The semirigid Physio ring was associated with perturbations in annular dynamics that caused changes in papillary muscle geometry. We propose an integrated valvular-subvalvular mechanism to explain displacement of the anterior leaflet into the left ventricular outflow tract after mitral ring annuloplasty.

Animals↗

PubMed1999

Mitral annular size and shape in sheep with annuloplasty rings.

BACKGROUND: Mitral annuloplasty is an important element of most mitral repairs, yet the effects of various types of annuloplasty rings on mitral annular dynamics are still debated. Recent studies suggest that flexible rings preserve physiologic mitral annular area change during the cardiac cycle, while rigid rings do not. METHODS: To clarify the effects of mitral ring annuloplasty on mitral annular dynamic geometry, we sutured 8 radiopaque markers equidistantly around the mitral anulus in 3 groups of sheep (n = 7 each: no ring, Carpentier-Edwards semi-rigid Physio-Ring [Baxter Healthcare Corp, Edwards Division, Santa Ana, Calif], and Duran flexible ring [Medtronic, Inc, Minneapolis, Minn]). Ring sizes were selected according to anterior leaflet area and inter-trigonal distance (Physio-Ring 28 mm, n = 7; Duran ring 31 mm, n = 5, and 29 mm, n = 2). After 8 +/- 1 days of recovery, the sheep were sedated and studied by means of biplane videofluoroscopy. Mitral annular area was calculated from 3-dimensional marker coordinates without assuming circular or planar geometry. RESULTS: In the no ring group, mitral annular area varied during the cardiac cycle by 11% +/- 2% (mean +/- SEM; maximum = 7.6 +/- 0.2, minimum = 6.8 +/- 0.2 cm2; P </=.001). Mitral annular area was fixed in the Physio-Ring group (4. 6 +/- 0.1 cm2) and, surprisingly, also static in the Duran ring group (4.8 +/- 0.1 cm2; P =.26 vs Physio-Ring). Furthermore, mitral annular 3-dimensional shape changed in the no-ring group during the cardiac cycle, but not in the Physio-Ring or Duran groups. CONCLUSIONS: Mitral annular area and shape did not change during the cardiac cycle after ring annuloplasty, regardless of ring type. Thus mitral annular area reduction, independent of intrinsic ring flexibility, is the chief mechanism responsible for the salutary effects of mitral ring annuloplasty.

Analysis of Variance↗

PubMed1998

Semirigid or flexible mitral annuloplasty rings do not affect global or basal regional left ventricular systolic function.

BACKGROUND: Previous studies have revealed that rigid mitral annuloplasty rings may be associated with left ventricular (LV) systolic dysfunction, but whether ring type affects regional systolic function at the base of the LV, in the region near the mitral annulus, is unclear. We tested the hypothesis that rigid fixation of the mitral annulus results in significant regional systolic dysfunction at the base of the LV. METHODS AND RESULTS: Twenty-six adult male sheep underwent placement of 13 miniature tantalum markers into the LV epicardium and around the mitral annulus to allow calculation of LV volume and regional epicardial area. Group I (n = 7) sheep served as controls; animals randomized to groups II (n = 11) and III (n = 8) underwent mitral annuloplasty with either a semirigid or flexible ring, respectively. After a 7- to 10-day recovery period, animals were studied in a closed-chest, sedated, autonomically blocked state. Global LV systolic function (end-systolic elastance and preload recruitable stroke work) were not significantly different among the 3 groups (P = 1.0, ANOVA). Regional systolic function at the base of the LV (fractional area shrinkage [FAS] of 4 epicardial areas) at comparable LV preload and afterload was similar in the 4 basal areas (P = 0.223, MANOVA). With the use of load-insensitive indexes (slope and area intercept of the end-systolic pressure-regional area relationship and regional stroke work-end-diastolic area relationship), regional systolic function also was not different between groups at baseline or with inotropic stimulation in any basal region (P > 0.05, MANOVA). Furthermore, neither annuloplasty ring perturbed the regional pattern of basal LV systolic function. CONCLUSIONS: Postoperative LV systolic function, both globally and in the region of the base of the LV (near the mitral annulus), was not altered with either semirigid or flexible ring fixation of the mitral annulus.

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