New Mitral Valve Annuloplasty Concept: Optimizing Annular Dynamics and Force Distribution.

BACKGROUND: Temporal three-dimensional (3D) analysis of the mitral valve biomechanics has prompted a re-evaluation of surgical approaches and repair device designs to accommodate the natural dynamics of the valve. Such new designs strive to obtain lower annulus restraining forces, resulting in more natural leaflet and chordal stresses. A new annuloplasty system was evaluated using 3D motion and out-of-plane force analysis. It was hypothesized that this system would not impact the valve with adverse motion restrictions or high systolic annular forces compared to conventional flat rigid ring designs. METHODS: In an acute porcine set-up, six 80 kg pigs were monitored before and after implantation of the new annuloplasty system consisting of two half-rings with a saddle-shaped outline. Valvular 3D dynamic geometry was obtained using sonomicrometry before and after annuloplasty system implantation. Strain gauges mounted on the commissural segments provided the annular restraining force distribution perpendicular to the annular plane. RESULTS: The change in annular height to commissural width ratio from diastole to systole did not alter following implantation (p >0.05). Out-of-plane systolic restraining forces were 0.2 ± 0.1 N and 0.8 ± 0.3 N (mean ± SEM) in the posterior and anterior commissural segments, respectively, without any difference in-between (p >0.1). Forces in both commissural segments were significantly lowered compared to previous measurements with a flat and stiff mitral annuloplasty ring (p <0.01). Mitral annular septal-lateral distance, area, and circumference in the commissural segments were decreased after implantation (p <0.05). The cross-annular distance between the commissural segments and the lengths of the anterior and posterior annular segments did not change following implantation (p >0.05). CONCLUSIONS: The new annuloplasty system design maintained annular 3D dynamics and provided a minimized out-of-plane restraining force distribution compared to earlier studies on flat rigid rings. This may have important implications in the selection of annuloplasty devices in order to increase repair durability.

Shed-blood-separation and cell-saver: an integral Part of MiECC? Shed-blood-separation and its influence on the perioperative inflammatory response during coronary revascularization with minimal invasive extracorporeal circulation systems - a randomized controlled trial.

OBJECTIVE: The postoperative systemic inflammatory response after cardiopulmonary bypass (CPB) is still an undesirable side-effect after cardiac surgery. It is most likely caused by blood contact with foreign surfaces and by the surgical trauma itself. However, the recirculation of activated shed mediastinal blood is another main cause of blood cell activation and cytokine release. Minimal invasive extracorporeal circulation (MiECC) comprises a completely closed circuit, coated surfaces and the separation of suction blood. We hypothesized that MiECC, with separated cell saved blood, would induce less of a systemic inflammatory response than MiECC with no cell-saver. The aim of this study was, therefore, to investigate the impact of cell washing shed blood from the operating field versus direct return to the ECC on the biomarkers for systemic inflammation. MATERIAL AND METHODS: In the study, patients with MiECC and cell-saver were compared with the control group, patients with MiECC and direct re-transfusion of the drawn blood shed from the surgical field. RESULTS: High amounts of TNF-α (+ 120% compared to serum blood) were found in the shed blood itself, but a significant reduction was demonstrated with the use of a cell-saver (TNF-α ng/l post-ECC 10 min: 9.5±3.5 vs. 19.7±14.5, p<0.0001). The values for procalcitonin were not significantly increased in the control group (6h: 1.07±3.4 vs. 2.15±9.55, p=0.19) and lower for C-reactive protein (CRP) (24h: 147.1±64.0 vs.134.4±52.4 p=0.28). CONCLUSION: The use of a cell-saver and the processing of shed blood as an integral part of MiECC significantly reduces the systemic cytokine load. We, therefore, recommend the integration of cell-saving devices in MiECC to reduce the perioperative inflammatory response.

Remodeling Mitral Annuloplasty Ring Concept with Preserved Dynamics of Annular Height.

BACKGROUND AND AIM OF THE STUDY: The configuration of the native annulus changes from nearly flat in the diastolic phase to saddle-shaped in the systolic phase. The present study was conducted to test a novel remodeling annuloplasty ring with built-in septal-lateral fixation and commissural axial flexibility so as to maintain the change in annular saddle shape. The study aim was to evaluate the in-vivo biomechanical performance of the novel annuloplasty ring, compared with the native valve and a semi-rigid and rigid annuloplasty ring. METHODS: All measurements were performed in vivo using a porcine model. A total of 28 pigs (bodyweight ca. 80 kg) were randomized to four groups: (i) with no ring; (ii) with a novel remodeling ring; (iii) with a semi-rigid ring (Physio I Ring, Edwards Lifesciences); and (iv) with a rigid ring (Classic Annuloplasty Ring, Edwards Lifesciences). Force measurements were performed using a dedicated transducer to determine remodeling capacity of the annuloplasty rings. Geometric parameters were measured by implanting sonomicrometry crystals along the mitral annulus. RESULTS: All ring groups significantly restricted the cyclic change of the mitral annulus compared with the 'no-ring' group. The change and maximum value of the annular height were maintained for the novel ring but were significantly decreased for the rigid and semi-rigid rings compared with the 'no-ring' group. Mitral annular force measurements confirmed that the overall remodeling capacity of the novel ring was comparable with the conventional ring groups, and significantly higher in the septal-lateral direction compared to the semi-rigid ring. CONCLUSIONS: In-vivo geometry and force measurements indicated that the intended design features of the new device were successfully provided. The novel ring concept with remodeling properties, combined with the advantages of a flexible annuloplasty ring, is unique. The maintenance of annular saddle shape and cyclic change in annular height may be an important step towards improved mitral valve repair.

The thick left ventricular wall of the giraffe heart normalises wall tension, but limits stroke volume and cardiac output.

Giraffes--the tallest extant animals on Earth--are renowned for their high central arterial blood pressure, which is necessary to secure brain perfusion. Arterial pressure may exceed 300 mmHg and has historically been attributed to an exceptionally large heart. Recently, this has been refuted by several studies demonstrating that the mass of giraffe heart is similar to that of other mammals when expressed relative to body mass. It thus remains unexplained how the normal-sized giraffe heart generates such massive arterial pressures. We hypothesized that giraffe hearts have a small intraventricular cavity and a relatively thick ventricular wall, allowing for generation of high arterial pressures at normal left ventricular wall tension. In nine anaesthetized giraffes (495±38 kg), we determined in vivo ventricular dimensions using echocardiography along with intraventricular and aortic pressures to calculate left ventricular wall stress. Cardiac output was also determined by inert gas rebreathing to provide an additional and independent estimate of stroke volume. Echocardiography and inert gas-rebreathing yielded similar cardiac outputs of 16.1±2.5 and 16.4±1.4 l min(-1), respectively. End-diastolic and end-systolic volumes were 521±61 ml and 228±42 ml, respectively, yielding an ejection fraction of 56±4% and a stroke volume of 0.59 ml kg(-1). Left ventricular circumferential wall stress was 7.83±1.76 kPa. We conclude that, relative to body mass, a small left ventricular cavity and a low stroke volume characterizes the giraffe heart. The adaptations result in typical mammalian left ventricular wall tensions, but produce a lowered cardiac output.

Subcoronary Stentless Aortic Valves are Not Superior to Supra-Annular Stented Valves Regarding Turbulent Stress.

BACKGROUND: Regions of turbulence downstream of bioprosthetic heart valves may cause damage to blood components, vessel walls, and also to aortic valve leaflets. Stentless aortic heart valves are known to possess several hemodynamic benefits such as a larger effective orifice area and a lower aortic transvalvular pressure difference compared to their stented counterparts. To date, turbulence analysis downstream of a stentless valve prosthesis has been investigated exclusively indirectly, using magnetic resonance imaging or in animal settings only. The study aim was to investigate turbulence using direct Doppler ultrasonography measurements in subcoronary stentless and stented valves in human subjects. METHODS: Either stented pericardial valve prostheses (Mitroflow) or stentless valve prostheses (Solo) were implanted in 15 patients in a randomized fashion. Following surgery, blood velocity was measured in the cross-sectional area downstream of the valves using 10 MHz ultrasonic probes connected to dedicated pulsed Doppler equipment. As a measure of turbulence, Reynolds normal stress (RNS) values were calculated, as well as two-dimensional maps of the turbulence distribution. Preoperative and perioperative data were collected prospectively, and postoperative data retrospectively, from hospital records. RESULTS: The median follow up was 1,624 days. No differences were found in perioperative or postoperative clinical data. Implantation of the Mitroflow valve was significantly faster than that of the Solo valve (p <0.05). Neither was any difference found in the mean or max RNS between the two valve groups. However, the turbulence profiles showed a large variation in the Solo valve compared to the more uniform profiles of the Mitroflow valve. CONCLUSIONS: Comparable turbulent flow values were found between the two valve types, although the Solo group exhibited a large variation in turbulence profiles. As no clear clinical advantages were shown to exist for stentless valves, a normal stented valve should be the first choice in most cases.

Mitral valve mechanics following posterior leaflet patch augmentation.

BACKGROUND AND AIM OF THE STUDY: Attention towards the optimization of mitral valve repair methods is increasing. Patch augmentation is one strategy used to treat functional ischemic mitral regurgitation (FIMR). The study aim was to investigate the force balance changes in specific chordae tendineae emanating from the posterior papillary muscle in a FIMR-simulated valve, following posterior leaflet patch augmentation. METHODS: Mitral valves were obtained from 12 pigs (body weight 80 kg). An in vitro test set-up simulating the left ventricle was used to hold the valves. The left ventricular pressure was regulated with water to simulate different static pressures during valve closure. A standardized oval pericardial patch (17 x 29 mm) was introduced into the posterior leaflet from mid P2 to the end of the P3 scallop. Dedicated miniature transducers were used to record the forces exerted on the chordae tendineae. Data were acquired before and after 12 mm posterior and 5 mm apical posterior papillary muscle displacement to simulate the effect from one of the main contributors of FIMR, before and after patch augmentation. RESULTS: The effect of displacing the posterior papillary muscle induced tethering on the intermediate chordae tendineae to the posterior leaflet, and resulted in a 39.8% force increase (p = 0.014). Posterior leaflet patch augmentation of the FIMR valve induced a 31.1% force decrease (p = 0.007). There was no difference in force between the healthy and the repaired valve simulations (p = 0.773). CONCLUSION: Posterior leaflet patch augmentation significantly reduced the forces exerted on the intermediate chordae tendineae from the posterior papillary muscle following FIMR simulation. As changes in chordal tension lead to a redistribution of the total stress exerted on the valve, patch augmentation may have an adverse long-term influence on mitral valve function and remodeling.

Aortic root distensibility after subcoronary stentless valve implantation.

BACKGROUND AND AIM OF THE STUDY: The preservation of aortic root dynamics is considered important for the durability of aortic valve bioprostheses. Stentless heart valves are believed to support physiologic biomechanics. To date, dynamic analysis has been limited to the full root prosthesis, and exclusively in the radial direction. The study aim was to investigate and compare the radial and longitudinal aortic root distensibilities of subcoronary stentless valves, and of stented and native pig valves. METHODS: Stented pericardial (Mitroflow) or stentless (Solo, Toronto SPV) valve prostheses, or native porcine valves, were investigated in 32 pigs. Postoperatively, 12 sonomicrometry crystals were placed on the aortic root in order to measure aortic root distensibility, in both radial and longitudinal directions. RESULTS: Sonomicrometry data were obtained from 23 pigs (72%). At the annular level, the native and Solo valves were significantly more distensible in a radial direction than the Mitroflow valve (p = 0.04). However, at the level of the sinotubular junction (STJ), commissures and aorta, the native valve was significantly more distensible than all of the artificial valves (p = 0.006, p = 0.006, and p = 0.02, respectively). The Solo valve exhibited less longitudinal distensibility than the Toronto SPV and Mitroflow valves. The Toronto SPV initiated a radial expansion at the STJ significantly later in the cardiac cycle than did both the Solo and native valves (p = 0.03), but showed no difference compared to the Mitroflow valve. Longitudinal expansion between the annulus and the STJ started significantly earlier for the Solo valve than for both the Toronto SPV (p = 0.03) and Mitroflow (p = 0.02) valves. CONCLUSION: The Solo valve proved to be superior in maintaining annular distensibility immediately following implantation when compared to the Mitroflow valve. The Solo valve did not, however, preserve longitudinal distensibility as well as the other investigated valves. Finally, the Solo valve appeared to provide a more physiologic aortic root expansion pattern than its prosthetic counterparts.

Leaflet opening and closing dynamics of stentless bioprostheses.

BACKGROUND AND AIM OF THE STUDY: Stiffening of the aortic root may entail asynchronous aortic leaflet movement, and result in enhanced flexion-stress in specific areas of the cusps. As stentless prostheses are more flexible than their stented counterparts, they are more likely to exhibit physiologic leaflet movements. The study aim was to compare leaflet movement dynamics in stented versus non-stented aortic valves implanted in pigs. METHODS: Aortic bioprostheses were implanted surgically into adult pigs as follows: stented Mitroflow (n = 6), stentless Solo (n = 5), and stentless Toronto SPV (n = 4). In five control animals, the native aortic valve leaflets were untouched. Postoperatively, the aortic valve was displayed by epicardial echocardiography. M-mode display of the non-coronary leaflet was applied to assess rapid valve-opening velocity (V(open)) and rapid valve-closing velocity (V(close)). RESULTS: The mean V(open) values were 29.2, 25.5, 37.8, and 31.9 cm/s, respectively, for the native, Toronto SPV, Solo, and Mitroflow valves. The mean V(close) values were 23.2, 21.9, 34.1, and 34.3 cm/s, respectively. A comparison of V(open) values showed no statistically significant difference between the valves. The Mitroflow and Solo valves yielded significantly higher V(close) values than the native and Toronto SPV valves. The Toronto SPV exhibited marked systolic leaflet folding. CONCLUSION: The stent of a bioprosthetic valve does not appear to affect leaflet velocities when compared to the stentless bioprosthetic valve. The Solo and Mitroflow valves closed more abruptly than the porcine native aortic valve; however, the Toronto SPV valve displayed diverging systolic leaflet movement patterns.

In-vivo blood velocity and velocity gradient profiles downstream of stented and stentless aortic heart valves.

BACKGROUND AND AIM OF THE STUDY: Abnormal flow conditions across aortic bioprosthetic valves may result in degenerative processes. Thus, it is important to implant biological valve prostheses with velocity profiles similar to those of native valves. The study aim was to compare blood velocity and velocity gradient profiles downstream of stented and stentless aortic valves implanted in pigs, and in native porcine valves. METHODS: Stented valve prostheses (Mitroflow, n = 7) or stentless valve prostheses (Solo, n = 5 or Toronto SPV, n = 7) were implanted into pigs; the native valve was retained in eight animals. After weaning the animals from cardiopulmonary bypass, cardiac magnetic resonance imaging was performed to determine the blood velocities and velocity gradient profiles. RESULTS: The native valves had a significantly lower peak velocity (92 +/- 26 cm/s) than the artificial valves (Solo: 247 +/- 107 cm/s; Toronto: 252 +/- 41 cm/s; Mitroflow: 229 +/- 18 cm/s). The native valves exhibited a flat velocity profile during systole, whereas the Solo valve, and especially the Toronto SPV valve, displayed more parabola-shaped velocity profiles; velocity profiles downstream of the Mitroflow valve exhibited a flat shape. The native valves had a lower mean velocity gradient at peak systole (p < 0.0001). The velocity gradient percentage above mean was lowest for the native valve (0.14 +/- 0.11; p < 0.0001), while the Mitroflow valve had a percentage of 0.57 +/- 0.09, which was lower than the Solo valve (0.69 +/- 0.12; p = 0.074), and significantly lower than the Toronto valve (0.70 +/- 0.08; p = 0.015). All valves displayed high velocity gradients adjacent to the aortic wall; in particular, the Toronto SPV which also had high velocity gradients at the center of the vessel. CONCLUSION: All of the artificial valves tested had a significantly higher mean velocity gradient and peak velocity than the native valves. However, the Mitroflow had a mean velocity and a velocity gradient percentage lower than the two stentless valves. The Solo and Mitroflow valves displayed velocity profiles most like native valves, while the Toronto valve had a more irregular asymmetric velocity profile.

An automated in vitro model for the evaluation of ultrasound modalities measuring myocardial deformation.

BACKGROUND: Echocardiography is the method of choice when one wishes to examine myocardial function. Qualitative assessment of the 2D grey scale images obtained is subjective, and objective methods are required. Speckle Tracking Ultrasound is an emerging technology, offering an objective mean of quantifying left ventricular wall motion. However, before a new ultrasound technology can be adopted in the clinic, accuracy and reproducibility needs to be investigated. AIM: It was hypothesized that the collection of ultrasound sample data from an in vitro model could be automated. The aim was to optimize an in vitro model to allow for efficient collection of sample data. MATERIAL & METHODS: A tissue-mimicking phantom was made from water, gelatin powder, psyllium fibers and a preservative. Sonomicrometry crystals were molded into the phantom. The solid phantom was mounted in a stable stand and cyclically compressed. Peak strain was then measured by Speckle Tracking Ultrasound and sonomicrometry. RESULTS: We succeeded in automating the acquisition and analysis of sample data. Sample data was collected at a rate of 200 measurement pairs in 30 minutes. We found good agreement between Speckle Tracking Ultrasound and sonomicrometry in the in vitro model. Best agreement was 0.83 ± 0.70%. Worst agreement was -1.13 ± 6.46%. CONCLUSIONS: It has been shown possible to automate a model that can be used for evaluating the in vitro accuracy and precision of ultrasound modalities measuring deformation. Sonomicrometry and Speckle Tracking Ultrasound had acceptable agreement.

Saddle-shaped mitral valve annuloplasty rings experience lower forces compared with flat rings.

BACKGROUND: New insight into the 3D dynamic behavior of the mitral valve has prompted a reevaluation of annuloplasty ring designs. Force balance analysis indicates correlation between annulus forces and stresses in leaflets and chords. Improving this stress distribution can intuitively enhance the durability of mitral valve repair. We tested the hypothesis that saddle-shaped annuloplasty rings have superior uniform systolic force distribution compared with a nonuniform force distribution in flat annuloplasty rings. METHODS AND RESULTS: Sixteen 80-kg pigs had a flat (n=8) or saddle-shaped (n=8) mitral annuloplasty ring implanted. Mitral annulus 3D dynamic geometry was obtained with sonomicrometry before ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat and saddle-shaped annuloplasty rings provided the intraoperative force distribution perpendicular to the annular plane. Average systolic annular height to commissural width ratio before ring implantation was 14.0%+/-1.6%. After flat and saddle shaped ring implantation, the annulus was fixed in the diastolic (9.0%+/-1.0%) and systolic (14.3%+/-1.3%) configuration, respectively (P<0.01). Force accumulation was seen from the anterior (0.72N+/-0.14N) and commissural annular segments (average 1.38N+/-0.27N) of the flat rings. In these segments, the difference between the 2 types of rings was statistically significant (P<0.05). The saddle-shaped annuloplasty rings did not experience forces statistically significantly larger than zero in any annular segments. CONCLUSIONS: Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings and appear to represent a configuration that minimizes out-of-plane forces that could potentially be transmitted to leaflets and chords. This may have important implications for annuloplasty ring selections.

Biomechanical characterization and comparison of different aortic root surgical techniques.

OBJECTIVES: Understanding the biomechanical impact of aortic valve-sparing techniques is important in an era in which surgical techniques are developing and are increasingly being used based on biomechanical understanding that is essential in the refining of existing techniques. The objective of this study was to describe how the valve-sparing remodelling (Yacoub) and reimplantation (David Type-1) techniques affect the biomechanics of the native aortic root in terms of force distribution and geometrical changes. METHODS: Two force transducers were implanted into 22 pigs, randomized to 1 of 3 groups (David = 7, native = 7 and Yacoub = 8) along with 11 sonomicrometry crystals and 2 pressure catheters. Force and geometry data were combined to obtain the local structural stiffness in different segments of the aortic root. RESULTS: The radial structural stiffness was not different between groups (P = 0.064) at the annular level; however, the David technique seemed to stabilize the aortic annulus more than the Yacoub technique. In the sinotubular junction, the native group was more compliant (P = 0.036) with the right-left coronary segment than the intervention groups. Overall, the native aortic root appeared to be more dynamic at both the annular level and the sinotubular junction than both intervention groups. CONCLUSIONS: In conclusion, the David procedure may stabilize the aortic annulus more than the Yacoub procedure, whereas the leaflet opening area was larger in the latter (P = 0.030). No difference (P = 0.309) was found in valve-opening delay between groups. The 2 interventions show similar characteristics at the sinotubular junction, whereas the David technique seemed more restrictive at the annular level than the Yacoub technique.

Are sounds from mechanical heart valves equal for different valve types?

BACKGROUND AND AIM OF THE STUDY: The closing 'click' sounds from mechanical heart valve prostheses are often clearly audible for patients and their relatives. These sounds have been recognized as a disturbing factor causing sleeping disturbances or social embarrassment, which patients must endure for the rest of their lives. The study aim was to determine whether the intensity of the transmitted sounds varies according to the type of valve implanted. METHODS: Closing sounds were measured from 15 patients with ATS valves, 29 with Medtronic-Hall valves, and 40 with St. Jude Medical (SJM) valve prostheses; all prostheses were implanted in the aortic position. The sounds were recorded by a microphone placed 5 cm above the chest of the patient when placed in a supine position in a bioacoustical laboratory. The mean sound pressure levels (SPLs) from the valves were measured in dB(A). RESULTS: The mean SPL values were 43 +/- 5 dB(A) for ATS valves, 41 +/- 4 dB(A) for Medtronic-Hall valves and 40 +/- 4 dB(A) for SJM valves (p < 0.05, ATS versus SJM). CONCLUSION: The study results showed a statistically significant difference in SPLs among the three investigated mechanical heart valve prostheses. The highest levels were in the ATS valves, and the lowest in the SJM valves. These objectively measured SPLs must be correlated with the sound as perceived by the patient in order to determine the annoyance that they cause.

What forces act on a flat rigid mitral annuloplasty ring?

BACKGROUND AND AIM OF THE STUDY: Increasing mitral valve repair durability requires successful restoration and support with annuloplasty rings. The stress distribution in these devices indirectly determines the success of the repair. It is hypothesized that changes in annular geometry throughout the cardiac cycle result in adverse strain distribution in stiff, flat annuloplasty rings, and hence non-physiological loading of the myocardium. The study aim was to identify the three-dimensional (3-D) force distribution in mitral annuloplasty rings. METHODS: Eight animals were included in an acute porcine study. The mitral annulus 3-D dynamic geometry was assessed with sonomicrometry prior to ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat annuloplasty rings enabled dynamic force measurements to be made perpendicular to the annulus plane. RESULTS: The average systolic annular height to commissural width ratio before ring implantation was 13.7 +/- 1.4%. Following ring implantation, the annulus was fixed in the diastolic flat configuration (p <0.01). Force accumulation was seen from the anterior (0.7 +/- 0.4 N) and commissural (1.4 +/- 1.0 N) annular segments; both forces were acting in opposite directions and were statistically significantly larger than zero (p <0.01; n = 8). CONCLUSION: These data demonstrate highest strains at the anterior and commissural areas of flat mitral annuloplasty rings, and support the hypothesis that the mitral valve annulus and its attached valvular and subvalvular structures apply systolic torque onto the flat annuloplasty ring in an attempt to conform it into the saddle-shaped configuration.

Semi-rigid mitral annuloplasty rings improve myocardial stress adaptation compared to rigid rings: insights from in vitro and in vivo experimental evaluation.

OBJECTIVES: Investigate myocardial stress adaptation and remodelling capacity of a rigid and semi-rigid mitral annuloplasty ring. METHODS: The annuloplasty rings were characterized in vitro in a mechanical setup with tensile and compressive forces from 0 to 3 N. The rings were tested with and without fixation of the ring to imitate the effect of annular implantation. In vivo measurements were performed with 21 porcine animals randomized into: A no ring group, a rigid ring group (Classic Annuloplasty Ring TM , Edwards Lifesciences) and a semi-rigid ring group (Physio I Annuloplasty Ring, Edwards Lifesciences). The rings were implanted together with a force transducer and sonomicrometry was used for geometry measurements. RESULTS: The flexibility range of the semi-rigid ring was 7.6 and 2.4 mm in the septal-lateral and commissural direction, respectively. With fixation the flexibility was reduced to 1.0 and 0.6 mm, similar to the rigid ring without fixation. In vivo measurements indicated that the rigid and semi-rigid rings equally restrict the annular movement. Septal-lateral flexibility of the semi-rigid ring was not observed. Both rings induced force absorption in the ring and sutures due to the annular fixation. The absorbed forces were significantly lower for the semi-rigid ring in the posterior segment and septal-lateral direction. CONCLUSIONS: This study demonstrates the importance of correct fixation when characterizing annuloplasty rings. The annular movement of the semi-rigid ring was similar to the rigid ring when implanted at the mitral annulus as confirmed in vitro . Despite this the semi-rigid ring demonstrated a favourable stress adaptation which could potentially decrease the risk of ring dehiscence.

The effect of different mitral annuloplasty rings on valve geometry and annular stress distribution†.

OBJECTIVES: To characterize the remodelling effects and deformational forces of normosized rigid, semirigid and flexible mitral annuloplasty rings after implantation in healthy pigs. METHODS: Measurements were performed in vivo with 80-kg porcine animals. Twenty-eight animals were randomized into a no ring group, a flexible ring group (Duran AnCore Ring, Medtronic, Minneapolis, MN, USA), a rigid ring group (Carpentier-Edwards Classic annuloplasty ring, Edwards Lifesciences, Irvine, CA, USA) and a semirigid ring group (Carpentier-Edwards Physio I annuloplasty ring, Edwards Lifesciences). Sonomicrometry crystals were implanted together with an annuloplasty ring and a dedicated mitral annular force transducer. The mitral annuloplasty rings were compared with respect to annular geometry and mitral annular forces. RESULTS: Cyclic changes in the mitral annulus (MA) circumference were significantly lower for all ring groups (flexible: 7 ± 3 mm, semirigid: 4 ± 2 mm and rigid: 2 ± 1 mm) compared to the no ring group (11 ± 5 mm), implying the remodelling capacity of all annuloplasty rings. The cyclic change of the MA area and the septa-lateral and inter-commissural distances were equal in the semirigid and rigid ring groups and significantly lower compared to the no ring and flexible ring groups, suggesting a stronger and equal remodelling effect in the semirigid and rigid ring groups. Forces measured in the transducer reflected the remodelling capacity of the annuloplasty rings and were in general lower for the semirigid and rigid ring groups compared to the no ring and flexible ring groups. Especially the forces in the inter-commissural direction were significantly reduced for the semirigid and rigid ring groups (semi-rigid: 1.4 ± 0.8 N, rigid: 1.2 ± 0.8 N) compared to the no ring and flexible ring groups (no ring: 3.0 ± 1.1 N, flexible: 3.4 ± 1.6 N). CONCLUSIONS: This study is the first to describe different remodelling effects and deformational forces of normosized mitral annuloplasty rings in vivo . Insights into the relationship between the remodelling effects and the accumulated forces of different mitral annuloplasty rings may have implications for ring selections in an aetiology-based mitral valve repair strategy. We propose the application of such a biomechanical approach for quantitative comparison of mitral annuloplasty rings and for future innovations on a rational basis.

Turbulent stress measurements downstream of three bileaflet heart valve designs in pigs.

OBJECTIVE: Mechanical heart valves can cause thromboembolic complications, possibly due to abnormal flow patterns that produce turbulence downstream of the valve. The objective of this study was to investigate whether three different bileaflet valve designs would exhibit clinically relevant differences in downstream turbulent stresses. METHODS: Three bileaflet mechanical heart valves (Medtronic Advantage), CarboMedics Orbis Universal and St. Jude Medical Standard) were implanted into 19 female 90 kg pigs. Blood velocity was measured during open chest conditions in the cross sectional area downstream of the valves with 10 MHz ultrasonic probes connected to a modified Alfred Pulsed Doppler equipment. As a measure of turbulence, Reynolds normal stress (RNS) was calculated at three different cardiac output ranges (3-4, 4.5-5.5, 6-7 L/min). RESULTS: Data from 12 animals were obtained. RNS correlated with increasing cardiac outputs. The highest instantaneous RNS observed in these experiments was 47 N/m2, and the mean RNS taken spatially over the cross sectional area of the aorta during systole was between 3 N/m2 and 15 N/m2. In none of the cardiac output ranges RNS values exceeded the lower critical limit for erythrocyte or thrombocyte damage for any of the valve designs. CONCLUSIONS: Reynolds normal stress values were below 100 N/m2 for all three valve designs and the difference in design was not reflected in generation of turbulence. Hence, it is unlikely that any of the valve designs causes flow induced damage to platelets or erythrocytes.

New mitral annular force transducer optimized to distinguish annular segments and multi-plane forces.

Limited knowledge exists about the forces acting on mitral valve annuloplasty repair devices. The aim of this study was to develop a new mitral annular force transducer to measure the forces acting on clinically used mitral valve annuloplasty devices. The design of an X-shaped transducer in the present study was optimized for simultaneous in- and out-of-plane force measurements. Each arm was mounted with strain gauges on four circumferential elements to measure out-of-plane forces, and the central parts of the X-arms were mounted with two strain gauges to measure in-plane forces. A dedicated calibration setup was developed to calibrate isolated forces with tension and compression for in- and out-of-plane measurements. With this setup, it was possible with linear equations to isolate and distinguish measured forces between the two planes and minimize transducer arm crosstalk. An in-vitro test was performed to verify the crosstalk elimination method and the assumptions behind it. The force transducer was implanted and evaluated in an 80kg porcine in-vivo model. Following crosstalk elimination, in-plane systolic force accumulation was found to be in average 4.0±0.1N and the out-of-plane annular segments experienced an average force of 1.4±0.4N. Directions of the systolic out-of-plane forces indicated movements towards a saddle shaped annulus, and the transducer was able to measure independent directional forces in individual annular segments. Further measurements with the new transducer coupled with clinical annuloplasty rings will provide a detailed insight into the biomechanical dynamics of these devices.

The effect of the aortic valve orientation on cavitation.

When implanting a mechanical aortic valve the annulus orientation is important with respect to turbulence. However, the effect on cavitation has not yet been investigated. The aim of this study was to investigate how cavitation is influenced hereof in vivo. Three pigs were included in the study. An Omnicarbon 21mm valve equipped with a rotating mechanism enabling controlled rotation of the valve was implanted in aortic position. Under stable hemodynamic conditions, measurements were performed using a hydrophone positioned at the aortic root. The valve was rotated from 0-360° in increments of 30°. From the pressure fluctuations recorded by the hydrophone the root mean square of the 50 kHz high pass filtered signal as well as the non-deterministic signal energy was calculated as indirect measures of cavitation. Various degrees of cavitation were measured but no relationship was found between either of the two cavitation measures and the valve orientation. Hemodynamics varied during the experiments for all pigs (3.9-5.7 l/min; 5.0-7.2 l/min; 3.1-7.5 l/min). Changes in cavitation quantities seemed to be caused by changes in hemodynamics rather than valve angular position. In conclusion, these results do not favor any position over another in terms of cavitation potential.

Imbalanced chordal force distribution causes acute ischemic mitral regurgitation: mechanistic insights from chordae tendineae force measurements in pigs.

BACKGROUND: Ischemic mitral regurgitation is caused by an imbalance of the entire mitral-ventricular complex. This interaction is mediated through the chordae tendineae force distribution, which may perturb several elements of the mitral valve apparatus. Our objective was to investigate the association between the mitral valvular 3-dimensional geometric perturbations and chordae tendineae force redistribution in a porcine model of acute ischemic mitral regurgitation. METHODS: In 9 pigs, acute ischemic mitral regurgitation was induced by repeated microembolization of the left circumflex coronary artery. Mitral leaflet coaptation geometry was determined by 2-dimensional echocardiography and reconstructed 3-dimensionally. Leading edge chordal forces were measured by dedicated miniature force transducers at control and during ischemic mitral regurgitation. RESULTS: During acute ischemic mitral regurgitation, there was a decreased tension of the primary chorda from the ischemic posterior left ventricular wall to the anterior leaflet (0.295 +/- 0.063 N vs 0.336 +/- 0.071 N [control]; P < .05). The tension of the chorda from the nonischemic anterior left ventricular wall to the anterior leaflet increased (0.375 +/- 0.066 N vs 0.333 +/- 0.071 N [control]; P < .05). In accordance, relative leaflet prolapse was observed at the ischemic commissural side, whereas there was an increase in the leaflet surface area at the nonischemic commissural side, indicating localized leaflet tethering. CONCLUSIONS: Acute ischemic mitral regurgitation due to posterior left ventricular wall ischemia was associated with focal chordal and leaflet tethering at the nonischemic commissural portion of the mitral valve and a paradoxical decrease of the chordal forces and relative prolapse at the ischemic site of the anterior mitral valve leaflet.