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Eur J Cardiothorac Surg 2006;30:584-591
© 2006 Elsevier Science NL

Mitral valve motion assessed by high-speed video camera in isolated swine heart

Shunei Saito*, Yoshimori Araki, Akihiko Usui, Toshiaki Akita, Hideki Oshima, Jun Yokote, Yuichi Ueda

Department of Cardiothoracic Surgery, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan

Received 4 March 2006; received in revised form 22 July 2006; accepted 25 July 2006.

* Corresponding author. Tel.: +81 52 744 2375; fax: +81 52 744 2383. (Email: shunei{at}med.nagoya-u.ac.jp).


   Abstract
Top
 Abstract
1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
 References
 
Objective: We have recently reported our isolated and working swine heart model that examines the valve motion precisely by a high-speed digital video camera system. Using this modality, the present study aimed (1) to delineate the motion of the mitral leaflets, chords and annulus throughout the cardiac cycle, and (2) to elucidate the influence of alterations in loading conditions on leaflet excursion. Methods: The valve motion of five isolated and working swine hearts was observed by an endoscope recording the images at 250 frames per second. Modified Krebs–Ringer solution was used as the sole perfusate. The images were obtained in hearts 30 min after reperfusion, changing the left atrial pressure as 4, 8, and 12 mmHg. Results: The motion of the mitral valve in the vicinity of diastole was considered to be well understood by dividing the entire sequence into five stages: ‘decoaptation,’ ‘E excursion,’ ‘diastasis,’ ‘A excursion,’ and ‘coaptation.’ Initial separation occurred at both sides of the central tips of the leaflets. The leading edges always followed the mid-portion of the rough zone during opening and closing. The ‘strut’ second-order chords retained their tension throughout the cardiac cycle and played the role as rotary shafts of the other branching chords. The first-order chords lost their tension during opening, suggesting they mainly are involved in valve competence. Annular constriction occurred coincident with atrial contraction. An increase in preload made the isovolumic relaxation and contraction times shorter. The leaflets opened faster in the rapid-filling phase, whereas they required more time for opening and closing in the atrial-filling phase. Conclusions: The present study revealed the integrated movement of the mitral leaflets, chords and annulus, as well as the impact of altered preload.

Key Words: Mitral valve • Imaging • Physiology • Diastole • Animal model


   1. Introduction
Top
 Abstract
 1. Introduction
2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
 References
 
The motion of the mitral valve has been studied using various modalities including cineangiography, cinefluoroscopy with radiopaque marker implantation, and two-dimensional echocardiography [1–5]. In recent years, accurate measurements of the mitral leaflet and annular motion by use of three-dimensional analysis of implanted markers are vigorously reported [6–10]. Aside from this, some efforts were made to visualize the mitral valve directly, using an endoscope to capture video images [11–16]. These studies have revealed changes in annular shape following annuloplasty, the anatomy inside the beating heart, and the different functions of first-order and second-order chords. However, none has focused on the integrated motion of the mitral valve throughout the entire cardiac cycle.

Many researchers have investigated the mechanism of mitral leaflet excursion and left ventricular filling since the 1980s. In their studies, measurement of transmitral flow, by use of either electromagnetic probe or Doppler echocardiography, played an important role [17–24]. Through these works, several factors, such as preload, PQ interval, left ventricular contractility and relaxation had been shown to influence the transmitral flow pattern. It is quite natural to consider that these factors have an impact on mitral valve motion likewise. Out of them, altered preload will affect the leaflet excursion most directly, because pressure gradient between the left atrium (LA) and left ventricle (LV) is the driving force of mitral valve opening.

We have recently reported our isolated and working swine heart model that examines the valve motion precisely by a high-speed digital video camera system recording the images at 250 frames per second (fps) [25]. By use of this modality, the present study aimed (1) to delineate the motion of the mitral leaflets, chords and annulus throughout the cardiac cycle, and (2) to elucidate the influence of alterations in loading conditions on leaflet excursion.


   2. Material and methods
Top
 Abstract
 1. Introduction
 2. Material and methods
3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
 References
 
The research protocol was approved by the Nagoya University Laboratory Research Animal Care and Ethics Committee. The investigation conforms to the Principles of Laboratory Animal Care formulated by the National Society for Medical Research and the Guide for the Care and Use of Laboratory Animals published by National Institute of Health, as revised in 1996.

2.1 Animal preparation
Five Landrace and Yorkshire swines weighing 34–43 kg were used for this study. The animals were anesthetized with intramuscular ketamine (7.5 mg/kg) and atropine (0.5 mg), intubated with a 5.5 mm tube and mechanically ventilated. Blood gas was obtained and the respiratory rate and volume were adjusted to maintain pH in the physiological range. Anesthesia was maintained by inhalation of 0.02–0.04% Halothane. The physiological temperature of the animal was maintained through the use of a circulating-water heating pad (38 °C). The heart was exposed by median sternotomy, and in vivo hemodynamic data were collected. Following cross-clamp of the descending aorta, 500 ml of cold St. Thomas No. 2 solution (Miotecter, Kobayashi Pharmaceutical Co., Ltd., Osaka, Japan) was infused via the right carotid artery to the coronary arteries. After complete cardiac arrest was confirmed, the heart and lungs were extracted.

2.2 Instrumentation and measurements
2.2.1 Isolated heart apparatus
The details of our isolated heart apparatus have recently been described [25]. In summary, the apparatus was designed to perfuse the isolated heart either in Langendorff mode or in working heart mode (Fig. 1 ). Modified Krebs–Ringer solution (NaCl 120.0 mmol/l, KCl 4.0 mmol/l, MgSO4 1.3 mmol/l, NaH2PO4 1.2 mmol/l, CaCl2 1.2 mmol/l, glucose 11.0 mmol/l) was used as the sole perfusate, which was oxygenated by a mixed-gas bubbling system with 10 l/min oxygen and 0.5 l/min carbon dioxide. The fluid temperature of the main reservoir was maintained at 38 °C. The settled level of the preload column could be changed to regulate inflow to the left atrium. The afterload column was placed 100 cm higher than the heart, and the ejected perfusate was allowed to spill out in order to maintain a constant afterload. A bifurcated tube, one branch used for Langendorff perfusion and the other for providing afterload, was connected to the aorta. A 24 Fr tube was inserted to the left upper pulmonary vein for perfusate delivery to the LA. An additional 18 Fr tube was introduced into the appendage of the LA for venting and deairing. It has been shown that the left ventricular function can be maintained for 3 h in working heart mode.


Figure 1
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  		Fig. 1. Isolated heart apparatus. Modified Krebs–Ringer solution was used as the sole perfusate. Rigid endoscope connected with high-speed digital video camera system is introduced via the apex. LD, Langendorff mode; WH, working heart mode; AF, aortic flow; CF, coronary flow.

 
2.2.2 Hemodynamic measurements
For both in vivo and ex vivo pressure studies, one 5 Fr micromanometer-tipped catheter (MPC-500, Millar Instruments, Houston, TX, USA) was introduced to the mid-position of the LV via the apex, and the other to the LA via the appendage. Epicardial electrodes were applied to obtain electrocardiograms. The data were recorded online on our multiple- acquisition system (Leg-1000, Nihon Kohden Corp., Tokyo, Japan, and Dipp-Motion 2D, Ditect Co., Ltd., Tokyo, Japan). Dipp-Motion 2D software enabled these data to synchronize with simultaneously obtained video images.

2.2.3 High-speed video camera system
A high-speed video camera (Fastcam-PCI, Photron, Inc., Tokyo, Japan) was connected to a 10 mm diameter rigid endoscope (Olympus Corp., Tokyo, Japan). The endoscope was introduced to the LV through the apex, and intraventricular movements were visualized. The images were recorded at 250 fps (4 ms increment) with 512 x 480 resolution, and were directly stored on the computer hard disk.

2.3 Experimental protocol
In vivo hemodynamics and electrocardiograms were recorded with the pericardium opened but keeping the heart inside the pericardial sac. Following complete cardiac arrest, the heart and lungs were extracted and connected to the isolated heart apparatus. Perfusion was immediately resumed in Langendorff mode within 15 min after cardiac arrest. All catheters and cannulas were placed. Twenty minutes after reperfusion, and following confirmation of a stable heartbeat, an endoscope was introduced into the LV via the apex. After the perfusion was changed to the working heart mode, simultaneous video images and hemodynamic data acquisition were performed while changing the preload. The loading condition was determined by mean left atrial pressure (LAP) as 4, 8, and 12 mmHg. The data was recorded within 30 s at each LAP level, and the perfusion was set back to Langendorff mode. Three minutes later, perfusion was again switched to working heart mode with the LAP changed, and data collection was completed.

2.4 Data analysis
Time-synchronized video images, pressures and electrocardiograms were analyzed using Dipp-Motion 2D software at every 4 ms. Timing of intracardiac events was counted along the time axis during five consecutive cardiac cycles, and the average was adopted as the representative value of each run. To eliminate subjectivity, the images were always assessed by two researchers simultaneously and the time points were determined. Paired t-test or repeated-measures analysis of variance (ANOVA) was used for statistics. A p-value less than 0.05 was considered statistically significant. Spearman rank test was used to examine the correlation between RR intervals and every time point or time interval.


   3. Results
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
 References
 
3.1 In vivo and ex vivo hemodynamics
Hemodynamic data for all hearts in vivo and ex vivo (LAP 8 mmHg) are summarized in Table 1 . Peak negative dP/dt significantly decreased in ex vivo hearts. No statistical differences were recognized in other items.


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  		Table 1. Hemodynamic data of in vivo and ex vivo hearts
 
3.2 Representative mitral valve motion throughout cardiac cycle
Through intracardiac observation, the motion of the mitral valve in the vicinity of diastole was considered to be well understood by dividing the entire sequence into five stages, as shown in Fig. 2 . The representative valve motion is described below. See online for confirmation.


Figure 2
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  		Fig. 2. Diagram showing time points, time intervals, distance between mitral leaflets and stages of valve motion. Electrocardiogram and intracardiac pressure curve are also shown above. LVP, left ventricular pressure; LAP, left atrial pressure; AVC, aortic valve closure; BAVO, beginning of aortic valve opening; BDC, beginning of decoaptation; BEO, beginning of E opening; MEO, maximum E opening; MDC, mid-diastolic closure; BAO, beginning of A opening; MAO, maximum A opening; MLA, mitral leaflet approximation; CC, completion of coaptation; DAVO, duration of aortic valve opening; DAVC, duration of aortic valve closure; DDF, duration of diastolic filling; IRT, isovolumic relaxation time; EOT, E opening time; ECT, E closing time; AOT, A opening time; ACT, A closing time; ICT, isovolumic contraction time; DDC, duration of decoaptation; DEE, duration of E excursion; DD, duration of diastasis; DAE, duration of A excursion; DC, duration of coaptation; ILD, interleaflet distance.

 
3.2.1 Decoaptation
Almost simultaneously with aortic valve closure, the mitral leaflets descended toward the LV. Snugly coapted leaflets began to separate gradually and progressively. The annulus also began to dilate at that time. We denoted this motion as ‘decoaptation.’

3.2.2 E excursion
This is the stage corresponding to the rapid-filling phase or the E wave of transmitral flow measurement. As the motion observed was not a ‘wave,’ we designated this sequence in which the leaflets opened and then reached their semi-closed position as ‘E excursion.’

After a small space arose between the leaflets, the valve opened with increasing acceleration. The site where separation was first recognized was both sides near the tips of the central portion of the leaflets (A2-P2) in four animals. In the other animal, separation was between the medial scallop of the posterior leaflet and the corresponding anterior leaflet (A3-P3). Separation of both tips was uniformly last and was 4–16 ms later than the initial separation of the leaflets. Initial separation occurred –15 to +25 ms later than the pressure crossover (PCO) of left ventricular pressure (LVP) and LAP. During opening, the mid-portion of the rough zone preceded the remainder of the leaflet and the leading edge bent toward the LA.

Among the second-order chords, which attach to the rough zone of the anterior leaflet, the two largest are called ‘strut’ chords. They stand mostly laterally and insert into the junction of the rough and smooth zones. During opening, the strut chords moved toward the annulus with their tension retained. Other second-order chords, mainly branching from the strut chords and inserting into the mid-portion of the rough zone, deviated toward the LV and the annulus, retaining their tension. First-order chords, which attach to the leading edge, deviated toward the LV and annulus following the second-order chords but with their tension clearly diminished (Fig. 3A). The strut chords played a role as rotary shafts of the first-order as well as second-order chords.


Figure 3
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  		Fig. 3. Intracardiac images. (A) Diminished tension of first-order chords is visible during opening. (B) At maximum open position, the anterior leaflet shows a ‘hammock-like’ shape between two strut chords. (C) First-order chords converge and maintain competence of valve during systole. White arrows indicate ‘strut’ chords, whereas black arrows indicate first-order chords.

 
When the leaflets reached their maximum open position, the leading edges bent outward, and their atrial surface became visible. The first-order chords recovered their tension only at this instant. The degree of maximum opening of the anterior leaflet was limited by the second-order chords branching from the strut chords. The anterior leaflet showed a ‘hammock-like’ form suspended by all chords branching from the strut chords at maximum opening (Fig. 3B). Similarly, the maximum open position of the posterior leaflet was defined by large second-order chords.

The leaflets stayed at the maximum open position for 8–12 ms and then began to close. During opening, the mid-portion of the rough zone preceded the remainder of the leaflets. Meanwhile, the phenomenon that the LA wall moved closer toward the LV, reflecting a decrease in atrial volume due to ventricular filling, was recognized through the opened valve orifice.

3.2.3 Diastasis
This stage corresponds to the slow-filling phase in which both leaflets stay at their semi-closed positions. Interleaflet distance varied between animals. In two animals, the valve almost completely closed once. In 11 runs among all 15 runs observed, the anterior leaflet preceded the posterior leaflet for 4–36 ms to reach the semi-closed position. First-order chords restored their tension at this position.

3.2.4 A excursion
This is the stage corresponding to the atrial-filling phase or the A wave. The same as for the E excursion, we denominated this stage as ‘A excursion.’ Owing to atrial contraction, leaflets reached their fully opened position with increasing acceleration. The fashion of leaflets and chords was the same as recognized in E excursion. In two animals, the posterior leaflet preceded the anterior leaflet to reach the maximum open position for 4–8 ms. The leaflets stayed here for 8–12 ms and then began to close. The mid-portion of the rough zone took the lead and the free edge followed. Atrial contraction and subsequent relaxation was clearly observed thorough the mitral orifice. Annular constriction was simultaneously recognized.

3.2.5 Coaptation
Both leaflets contacted each other at their atrial surfaces, and the orifice was closed. However, the degree of coaptation was somewhat shallow. Until the beginning of ventricular contraction, this degree did not change. Simultaneous with the aortic valve opening, the coaptation became deeper. The annulus constricted further, and first-order as well as second-order chords converged to close the valve snugly (Fig. 3C). This sequence was defined as ‘coaptation.’ Throughout the ventricular systole, the mitral valve kept this configuration, until decoaptation began.

3.3 Impact of alteration in preload on mitral valve motion
The influence of changing preload on valve motion was assessed. The time points measured and time intervals calculated are described in Fig. 2. In particular, several time points were defined as follows: beginning of decoaptation (BDC), the point when the movements of both leaflets toward the annulus were first recognized; beginning of E opening (BEO), when an obvious space was recognized between the leaflets; mid-diastolic closure (MDC), when the anterior leaflet reached its semi-closed position; maximum A opening (MAO), when the anterior leaflet reached its fully opened position in A excursion; completion of coaptation (CC), when the movements of both leaflets toward the center of the orifice finished. The preceding R wave was defined as reference zero of every time point. Fig. 4 shows the change in time points among three LAP levels. Table 2 shows the change in time intervals. Also see online .


Figure 4
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  		Fig. 4. Diagram showing time points of leaflet excursion. Aortic valve closure delayed as preload increased. Beginning of E opening, maximum E opening, mid-diastolic closure, occurred earlier. Isovolumic relaxation and contraction times became shorter. Leaflets opened more rapidly in E excursion, whereas they required more time for opening and closing in A excursion. Abbreviations are the same as given in Fig. 2. Values are mean ± SD (ms) except LAP (mmHg). * p < 0.05 between different LAP groups; tested by repeated-measures ANOVA.

 

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  		Table 2. Influence of alteration in preload on time intervals of valve motion
 
As a small variation was recognized between mean values of RR intervals, Spearman rank test was performed to examine the correlation between RR intervals and each time point or time interval. No significant correlation was observed.

Aortic valve closure (AVC) delayed as preload increased. Beginning of E opening (BEO), maximum E opening (MEO), mid-diastolic closure (MDC), beginning of A opening (BAO), and beginning of aortic valve opening (BAVO) occurred earlier, though the last was not significant. Regarding time intervals when preload was increased, duration of aortic valve opening (DAVO) lengthened, whereas duration of aortic valve closure (DAVC) shortened. In spite of the decrease in DAVC, duration of diastolic filling (DDF) increased. Therefore, isovolumic relaxation time (IRT) as well as isovolumic contraction time (ICT) decreased. E opening time (EOT) decreased, indicating that the leaflets reached their maximum open position earlier in E excursion. In contrast, A opening time (AOT) increased. A closing time (ACT) likewise increased, resulting in an increase in duration of A excursion (DAE).

In LAP 8 and 12 mmHg, the leaflets approached their maximum open position in E excursion as well as in A excursion. In LAP 4 mmHg, however, the leaflets did not fully open in A excursion, indicating that E excursion was dominant at low preload.

3.4 Videos
Videos are available for review as a supplement in the online version of the Journal. shows the mitral valve motion at LAP 12 mmHg (run at 5 fps, x0.02 speed). shows the different degree of mitral valve opening during A excursion at LAP 4 and 8 mmHg (run at 15 fps, x0.06 speed).


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
5. Study limitations
 6. Conclusions
 Appendix A
 References
 
Endoscopic observations of the cardiac cavity filling with crystalloid perfusate had been reported by van Rijk-Zwikker, Obadia and the Minnesota Group (Chinchoy and Hill) [11–16]. The advantage of intracardiac observation by an endoscope is that the mitral leaflets, chords and annulus can be assessed simultaneously in the same image plane. In particular, the motion of the chords cannot be visualized by any other modality. What is novel in the present study is the introduction of a high-speed video camera system recording the images at 250 fps (4 ms increment). The movement of the chords at maximum leaflet opening is of interest. However, the leaflets stay fully open only for 8–12 ms. Likewise, though the E opening time (EOT) differed significantly between LAP 4 and 8 mmHg, the difference was only 8 ms. These findings could not have been elucidated without the use of a high-speed video camera.

The concept of the present study was to observe mitral valve motion close to nature wherever possible. Therefore, we avoided any interventions which needed left atriotomy, such as marker implantation into the annulus or leaflets. Though heart rate might be controlled by excising the sinus node and providing atrial pacing, we did not adopt this strategy in fear that this may result in a disturbance of atrioventricular or atrioatrial conduction. The mean RR intervals in the ex vivo hearts at three LAP levels were very close at 736–740 ms, and no significant correlation between RR intervals and any time point or time interval was recognized by use of the Spearman rank test. Thus, this small variance in RR intervals was considered to be acceptable to compare the timing of every event in valve motion.

4.1 Leaflet separation
Some speculations had been made on the site where leaflet separation first occurs [2,4,6]. This has been clearly elucidated through the present study. Initial separation was recognized at both sides near the central tips of the leaflets (A2-P2) in four animals, and between the medial scallop of the posterior leaflet and the corresponding site of the anterior leaflet (A3-P3) in one animal. As the flow from the cannula may have some effect on leaflet motion in the latter case, it is reasonable to consider that initial separation essentially begins at both sides of the leaflet tips (A2-P2). Separation of the central tips was uniformly last, and followed the initial separation by 4–16 ms. During this period, the leaflet edges near the commissures (A1-P1, A3-P3) were likely to have separated, and filling of the LV may have already begun.

4.2 Time lag between anterior and posterior leaflets
The time lag between the motion of anterior and posterior leaflets has also been revealed. The anterior leaflet reached its semi-closed position 4–36 ms earlier in 11 among 15 runs. Vortex formation had been cited as one of the closing mechanisms of the leaflets [17], and the anterior leaflet may be more susceptible to this during E excursion. Annular constriction may facilitate valve closure at end-diastole [8], and this may be the reason why no delay was observed in leaflet approximation following A excursion.

4.3 Preceding portion during excursion
Pohost et al. [2] indicated through cineangiographic study with contrast medium injection that the leading edge preceded the remainder of the leaflet during valve opening. In contrast, Karlsson et al. [6] mentioned that the leading edge followed the other part of the leaflet. Our observations clearly supported this. During opening as well as closing, the mid-portion of the rough zone always took the lead and the free edge always followed.

4.4 Chords
The maximum open position of the anterior leaflet was determined by the chords branching from the strut chords, which acted as rotary shafts of the other chords during leaflet excursion. Though the second-order chords kept their tension during both opening and closing, first-order chords lost tension completely during opening but retrieved tension just at the moment when the delaying free edge fully opened, limited its further outward motion, and then relaxed again only 4 ms later like a stretched and released rubber band. The first-order chords regained tension when the leaflets approximated, and then converged firmly toward the center of the orifice. In short, first-order chords did not play an important role during opening. Their main function must be to maintain valve competence, as Obadia et al. [13] indicated.

Anterior leaflet prolapse has been repaired by transposing the ‘strut’ chords to the leading edge of the leaflet. However, as the strut chords give rise to many first-order and second-order chords, we are concerned about the contortion of the entire mitral valve which may be caused by this procedure. From this point of view, we consider artificial chordae implantation is a more natural procedure.

4.5 Annulus
Annular constriction coincident with atrial and ventricular contraction can be recognized by appreciating the video carefully. This presystolic annular size reduction is consistent with the reports by Glasson et al. [7] and Timek et al. [8,10]. Atriogenic annular constriction facilitates valve closure. Leaflet coaptation becomes deeper by ventriculogenic annular constriction as well as rapid increase in LVP. On the condition that the first-order chords are intact, complete closure of the valve is then accomplished.

4.6 LA–LV pressure gradient and leaflet excursion
The driving force of the valve opening is the LA–LV pressure gradient. The first intersection point between LVP and LAP is usually referred to as the pressure crossover (PCO). Beginning of E opening (BEO) is reported to occur slightly before or simultaneously with PCO [2,4], as was also observed in the present study (BEO occurred –15 to +25 ms later than PCO).

As preload increased, E excursion as well as A excursion occurred earlier. Regarding time intervals, E opening time (EOT) shortened. This is presumably attributed to the augmented LA–LV pressure gradient, which made leaflet opening more rapid. In contrast, A opening time (AOT) lengthened. The leaflet may react to atrial contraction more sensitively due to the increased atrial volume. Likewise, because of the increased transmitral flow volume, it may take longer before valve closure during A excursion. The prolonged duration of A excursion (DAE) presumably has the same origin with the prolonged duration of aortic valve opening (DAVO). Isovolumic relaxation time (IRT) and isovolumic contraction time (ICT) both shortened. The former is attributable to the delay in aortic valve closure, as well as the early occurrence of PCO. The latter is accountable by the prolongation of duration of diastolic filling (DDF) and the early occurrence of aortic valve opening.

We consider that the mitral valve motion is closely related to the transmitral flow volume. In another words, the change in the transmitral flow volume is reflected in the mitral valve motion. We are quite sure that the flow volume has increased with increasing preload. It is a future task to assess the valve motion simultaneously with the volume across the valve.


   5. Study limitations
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
6. Conclusions
 Appendix A
 References
 
Our model does not fully resemble the heart in vivo. (1) Though complete crystalloid perfusion enabled us to observe intracardiac movements clearly, oxygen delivery to the myocardium decreased approximately by half compared to in vivo [25]. (2) Volume loading was accomplished directly from the left atrium. This circulation skipping of the pulmonary vasculature was not physiological. (3) Though we placed the heart so as to mimic its in vivo position, its geometry may be changed. (4) Having a rigid endoscope in the apex might influence the left ventricular function. However, the impact was considered to be minimal because the rotatory and reciprocating movements of the LV were preserved. (5) Afterload was not physiological and might affect the timing of aortic valve closure.


   6. Conclusions
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
Appendix A
 References
 
The motion of the mitral valve in the vicinity of diastole was considered to be well understood by dividing the entire sequence into five stages: ‘decoaptation,’ ‘E excursion,’ ‘diastasis,’ ‘A excursion,’ and ‘coaptation.’ The leading edges always followed the mid-portion of the rough zone during opening and closing. The strut chords retained their tension throughout the cardiac cycle and played the role as rotary shafts of the other branching chords. First-order chords lost their tension during opening, suggesting they mainly are involved in valve competence. Annular constriction occurred coincident with atrial contraction. The increase in preload made the isovolumic relaxation and contraction time shorter. The opening began earlier in both E and A excursions. The leaflets opened more rapidly in E excursion, whereas they required more time for opening and closing in A excursion.

Important facts had been elucidated through the previous endoscopic observations of the cardiac cavity. In the present study, we provided the readers with more accurate images by use of a high-speed video camera. We consider it is of great value that the mitral valve motion was reproduced under physiologically low LAP with crystalloid perfusion and that the effect of altered preload was clarified. These findings should serve as the basis when surgical procedures for the mitral valve will be assessed using this animal model in the near future.


   Appendix A
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
References
 
Supplementary data

Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ejcts.2006.07.021.


   Acknowledgments
 
The authors gratefully acknowledge Professor Hideaki Toyoshima of Nagoya University Graduate School of Medicine for his valuable advice on statistical analysis.


   References
Top
 Abstract
 1. Introduction
 2. Material and methods
 3. Results
 4. Discussion
 5. Study limitations
 6. Conclusions
 Appendix A
 References
 

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