Biomedical subjects

David Liang

Publications and source records attributed to David Liang.

45 records · Page 3Linked to original sources

PubMed2002

Mechanistic insights into posterior mitral leaflet inter-scallop malcoaptation during acute ischemic mitral regurgitation.

BACKGROUND: Three-dimensional dynamics of the 3 individual scallops within the posterior mitral leaflet during acute ischemic mitral regurgitations have not been previously measured. METHODS: Radiopaque markers were sutured to the mitral annulus, papillary muscle tips, and leaflet edges in 13 sheep. Immediately postoperatively, under open-chest conditions, 3-D marker coordinates were obtained using high-speed biplane videofluoroscopy before and during echocardiographically verified acute ischemic mitral regurgitation produced by occlusion of the left circumflex coronary artery. RESULTS: During acute ischemic mitral regurgitation, at end systole, the anterolateral edge of the central scallop was displaced 0.8+/-0.9 mm laterally and 0.9+/-0.6 mm apically away from the anterolateral scallop; such displacement correlated with lateral displacement of the lateral annulus (R(2)=0.7, SEE=0.7 mm, P<0.001) and movement of the right lateral annulus away from the nonischemic anterior papillary tip (R(2)=0.6, SEE=0.8 mm, P=0.002), respectively. End-systolic displacement of the posteromedial edge of the central scallop was 1.4+/-0.9 mm anteriorly and 0.9+/-0.6 mm laterally away from the posteromedial scallop, corresponding to anterior displacement of the mid-lateral annulus (R(2)=0.5, SEE=1.0 mm, P<0.001). CONCLUSIONS: Malcoaptation of the scallops within the posterior leaflet during acute left ventricular ischemia is a novel observation. The primary geometric mechanism underlying scallop malcoaptation in acute ischemic mitral regurgitation was annular dilatation, which hindered leaflet coaptation by drawing the individual scallops apart. These findings support the use of annular reduction in the repair of ischemic mitral regurgitation and also suture closure of prominent subcommissures between posterior leaflet scallops.

Acute Disease↗

PubMed2002

The effects of mitral annuloplasty rings on mitral valve complex 3-D geometry during acute left ventricular ischemia.

OBJECTIVE: Annuloplasty rings are used to treat ischemic mitral regurgitation (IMR), but their exact effects on 3-D geometry of the overall mitral valve complex during acute left ventricular (LV) ischemia remain unknown. METHODS: Radiopaque markers were sutured to the mitral leaflet edges, annulus, papillary muscle tips, and ventricle in three groups of sheep. One group served as control (n = 5), and the others underwent Duran (n = 6) or Physio (n = 5) ring annuloplasty. One week later, 3-D marker coordinates at end-systole were obtained before and during balloon occlusion of the circumflex artery. RESULTS: In all control animals, acute LV ischemia was associated with: (i) septal-lateral separation of the leaflet edges, which was predicted by lateral displacement of the lateral annulus during septal-lateral mitral annular dilatation; (ii) apical restriction of the posterior leaflet edge, which was predicted by displacement of the lateral annulus away from the non-ischemic anterior papillary muscle; (iii) displacement of the posterior papillary muscle, which was not predictive of either septal-lateral leaflet separation or leaflet restriction; and (iv) mitral regurgitation. In the Duran group during ischemia, the posterior leaflet edge shifted posteriorly due to posterior movement of the lateral annulus, but no IMR occurred. In the Physio group during ischemia, neither the posterior leaflet edge nor the lateral annulus changed positions, and there was no IMR. In both the Duran and Physio groups, displacement of the posterior papillary muscle did not lead to IMR. CONCLUSIONS: Either annuloplasty ring prevented the perturbations of mitral leaflet and annular--but not papillary muscle tip--3-D geometry during acute LV ischemia. By fixing the septal-lateral annular dimension and preventing lateral displacement of the lateral annulus, annuloplasty rings prevented systolic septal-lateral leaflet separation and posterior leaflet restriction, and no acute IMR occurred. The flexible ring allowed posterior displacement of the posterior leaflet edge and the lateral annulus, which was not observed with a semi-rigid ring.

Acute Disease↗

PubMed2002

Reversal of Phen-Fen associated valvular regurgitation documented by serial echocardiography.

We report a case of anorexigen-associated moderate to severe aortic and mitral regurgitation in which the regression of lesions was marked and well documented over more than 2 years. The stability of our patient, as well as the degree of regression of regurgitation documented in our patient, and others, suggests it is prudent both to observe such patients and to avoid operation until such observation has been carried out.

Appetite Depressants↗

PubMed2002

Alterations in left ventricular torsion in tachycardia-induced dilated cardiomyopathy.

OBJECTIVE: Left ventricular torsion reduces transmural systolic gradients of fiber strain, and torsional recoil in early diastole is thought to enhance left ventricular filling. Left ventricular remodeling in dilated cardiomyopathy may result in changes in torsion dynamics, but these effects are not yet characterized. Tachycardia-induced cardiomyopathy is accompanied by systolic and diastolic heart failure and left ventricular remodeling. We hypothesized that cardiomyopathy would alter systolic and diastolic left ventricular torsion mechanics, and this hypothesis was tested by studying sheep before and after the development of tachycardia-induced cardiomyopathy. METHODS: Implanted miniature radiopaque markers were used in 8 sheep to measure left ventricular geometry and function, maximal torsional deformation, and early diastolic recoil before and after rapid ventricular pacing was used to create tachycardia-induced cardiomyopathy. RESULTS: All animals had significant heart failure with ventricular dilatation and remodeling. With tachycardia-induced cardiomyopathy, maximum torsion relative to control conditions decreased (1.69 degrees +/- 0.61 degrees vs 4.25 degrees +/- 2.33 degrees ), and early diastolic recoil was completely abolished (0.53 degrees +/- 1.19 degrees vs -1.17 degrees +/- 0.94 degrees ). CONCLUSIONS: Cardiomyopathy is accompanied by decreased and delayed systolic left ventricular torsional deformation and loss of early diastolic recoil, which may contribute to left ventricular dysfunction by increasing systolic transmural strain gradients and impairing diastolic filling. Analysis of left ventricular torsion with radiofrequency-tagging magnetic resonance imaging should be explored to elucidate the role of torsion in patients with cardiomyopathy.

Animals↗

PubMed2002

Septal-lateral annular cinching abolishes acute ischemic mitral regurgitation.

OBJECTIVE: Ring annuloplasty prevents acute ischemic mitral regurgitation in sheep, but it also abolishes normal mitral annular and posterior leaflet dynamics. We investigated a novel surgical approach of simple septal-lateral annular cinching with sutures to treat acute ischemic mitral regurgitation. METHODS: Nine adult sheep underwent implantation of multiple radiopaque markers on the left ventricle, mitral anulus, and mitral leaflets. A septal-lateral transannular suture was anchored to the midseptal mitral anulus and externalized to a tourniquet through the midlateral mitral anulus and left ventricular wall. Open-chest animals were studied immediately postoperatively. Acute ischemic mitral regurgitation was induced by means of proximal left circumflex artery snare occlusion, and 3 progressive steps of septal-lateral annular cinching (each 2-3 mm suture tightening for 5 seconds) were performed with the transannular suture. Biplane videofluoroscopy for 3-dimensional marker coordinates and transesophageal echocardiography were performed continuously before and during left circumflex ischemia and septal-lateral annular cinching. RESULTS: Acute left circumflex ischemia caused ischemic mitral regurgitation (+0.5 +/- 0.4 [baseline] vs +2.0 +/- 0.7 [ischemia]; P =.005; scale, +0-4), which decreased progressively with each step of septal-lateral annular cinching and was eliminated during the third step (ischemic mitral regurgitation, +0.6 +/- 0.5; P = not significant vs baseline). The third step of septal-lateral annular cinching decreased the septal-lateral diameter by 6.0 +/- 2.6 mm (P =.005); however, mitral anulus area reduction (8.5% +/- 1.0% and 6.9% +/- 1.9% for ischemic mitral regurgitation and septal-lateral annular cinching step 3, respectively; P =.006) and posterior leaflet excursion (50 degrees +/- 9 degrees and 44 degrees +/- 11 degrees for regurgitation and annular cinching step 3, respectively; P =.002) throughout the cardiac cycle were affected only mildly. Normal mitral annular 3-dimensional shape was maintained with septal-lateral annular cinching. CONCLUSIONS: Isolated 22% +/- 10% reduction in mitral annular septal-lateral dimension abolished acute ischemic mitral regurgitation in normal sheep hearts while allowing near-normal mitral annular and posterior leaflet dynamic motion. Septal-lateral annular cinching may represent a simple method for the surgical treatment of ischemic mitral regurgitation, either as an adjunctive technique or alone, which helps preserve physiologic annular and leaflet function.

Acute Disease↗

PubMed2002

Hemodynamic performance of an unstented xenograft mitral valve substitute.

OBJECTIVE: Stentless mitral xenografts offer potential clinical benefits because they mimic the normal bileaflet mitral valve. How best to implant them and their hemodynamic performance and durability, however, remain unknown. METHODS: A stentless porcine mitral xenograft valve (Medtronic physiologic mitral valve) was implanted in 7 sheep with papillary muscle sewing tubes attached with transmural left ventricular sutures. Radiopaque markers were inserted on the leaflets, annular cuff, papillary tips, and left ventricle. After 10 +/- 5 days, the animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates at baseline and during dobutamine infusion. Transesophageal echocardiography assessed mitral regurgitation and valvular gradients. Mitral annular area was calculated from the annular markers. Physiologic mitral valve leaflet and annular dynamics were compared with 8 native sheep valves. RESULTS: Average mitral regurgitation grade at baseline was 1.2 +/- 1.0 (range, 0-4), and the mean transvalvular pressure gradients were 3.6 +/- 1.3 and 6.2 +/- 2.2 mm Hg during baseline and dobutamine infusion, respectively. Xenograft mitral annular area contraction throughout the cardiac cycle was reduced (6% +/- 6% vs 13% +/- 4% for physiologic mitral valve and control valve, respectively; P =.03). Physiologic mitral valve leaflet geometry during closure differed from the native valve, with the anterior leaflet being convex to the atrium and with little motion of the posterior leaflet. Three animals survived more than 3 months; good healing of the annular cuff and papillary muscle tubes was demonstrated. CONCLUSION: This stentless xenograft mitral valve substitute had low gradients at baseline and during stress conditions early postoperatively, with mild mitral regurgitation. Preliminary analysis of healing characteristics appeared favorable at 3 months. Additional studies are needed to determine long-term xenograft mitral valve performance and resistance to calcification.

Animals↗

PubMed2002

Atrial contraction and mitral annular dynamics during acute left atrial and ventricular ischemia in sheep.

In six sheep, radiopaque markers were placed on the left ventricle (LV), the mitral annulus, the left atrium (LA), and the central edge of both mitral leaflets to investigate the effects of acute LV ischemia on atrial contraction, mitral annular area (MAA), and mitral regurgitation (MR). Animals were studied with biplane videofluoroscopy and transesophageal echocardiography before and during balloon occlusion of the left anterior descending (LAD), distal circumflex (dLCX), and proximal circumflex (pLCX) coronary arteries. MAA and LA area were calculated from the corresponding markers. LAD occlusion did not alter LA area reduction or presystolic MAA reduction, whereas dLCX occlusion resulted in a mild decrease in the former with no change in the latter. Neither occlusion resulted in MR. pLCX occlusion, however, significantly decreased LA area and presystolic MAA reduction and resulted in increased end-diastolic MAA, delayed valve closure from end diastole, and MR. Decreased atrial contractile function, as observed during acute posterolateral ischemia, is linked to diminished presystolic mitral annular reduction, a larger mitral annular size at end diastole, and MR.

Acute Disease↗

PubMed2002

Septal-lateral annular cinching ('SLAC) reduces mitral annular size without perturbing normal annular dynamics.

BACKGROUND AND AIM OF THE STUDY: Septal-lateral (S-L) mitral annular diameter reduction is thought to be central to the efficacy of ring annuloplasty in correcting functional mitral regurgitation (MR), but rings perturb mitral annulus (MA) dynamic motion and limit posterior leaflet excursion. The effects of S-L annular cinching ('SLAC'), a novel method for mitral annular reduction, were investigated. METHODS: Eight adult sheep had multiple radioopaque markers placed on the left ventricle, leaflet edges, and around the MA. The S-L trans-annular suture was anchored to the mid-septal MA and externalized through the mid-lateral MA and left ventricular wall. Animals were studied immediately postoperatively with biplane videofluoroscopy before and after suture cinching to reduce annular size. MA area (MAA) and S-L dimension were calculated throughout the cardiac cycle from the annular marker coordinates. MAA contraction (AMAA) was expressed as percentage decrease from maximum to minimum MAA. Anterior (AML) and posterior (PML) leaflet angular excursion were calculated as the change in angle between each leaflet edge marker and the S-L annular dimension during the cardiac cycle. MA folding was calculated as the change in distance during systole of the mid-septal annular marker from a plane fitted to the lateral MA markers. RESULTS: SLAC reduced end-diastolic (ED) S-L diameter (21.6+/-2.8 versus 17.1+/-2.6 mm; p = 0.0005) and ED MAA (618+/-126 versus 525+/-114 mm2; p = 0.0004), but did not perturb normal AMAA (15.8+/-4.1 versus 15.1+/-4.8%; p = 0.4), annular flexion (2.0+/-0.7 versus 1.8+/-0.7 mm; p = 0.3) or AML excursion (55+/-7 versus 53+/-7 degrees; p = 0.1). PML excursion was decreased only slightly (52+/-11 versus 44+/-12 degrees; p = 0.002). CONCLUSION: SLAC substantially reduced S-L annular size, but without perturbing normal MA contraction dynamics, MA flexion, or anterior leaflet excursion. This novel surgical method might represent an alternative to mitral annuloplasty for patients with certain types of mitral pathology.

Animals↗

PubMed2002

Ischemia-induced malcoaptation of scallops within the posterior mitral leaflet.

BACKGROUND AND AIMS OF THE STUDY: The posterior mitral leaflet is divided into a variable number of scallops, and little is known about the role of scallopmalcoaptation in ischemic mitral regurgitation. The study aim was to assess whether acute ischemia in the posterolateral wall of the left ventricle would induce scallop separation that would contribute to mitral regurgitation. METHODS: Radio-opaque markers were surgically placed in the left ventricle, around the mitral annulus, and at three sites along the posterior mitral leaflet edge in eight sheep. Three-dimensional marker coordinates were obtained by biplane videofluoroscopy at 60 Hz and 0.1 mm resolution before and during echocardiographically verified acute ischemic mitral regurgitation produced by balloon occlusion of the circumflex coronary artery. RESULTS: During systole, the mean (+/-SD) distance between the central and anterolateral markers, both placed on the central scallop of the posterior mitral leaflet, was unaffected by ischemia (7.4+/-2.4 versus 7.4+/-2.5 mm; n = 8; p = NS). In contrast, the systolic distance between the central scallop marker and the posteromedial marker increased by 2.3+/-0.2 mm (p = 0.008) in three hearts with the posteromedial marker on the posteromedial scallop, compared with no separation (0.2+/-0.5 mm; p = NS) in five hearts with both the central and posteromedial markers on the central scallop itself. This result shows systolic separation of the central and posteromedial scallops during acute ischemic mitral regurgitation. CONCLUSION: During acute left ventricular ischemia, the central and posteromedial scallops of the posterior mitral leaflet can fail to coapt during systole, potentially contributing to the mitral regurgitation observed.

Animals↗