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Eur J Cardiothorac Surg 2004;25:352-357
© 2004 Elsevier Science NL

Changes in mitral annular and left ventricular dimensions and left ventricular pressure–volume relations after off-pump treatment of mitral regurgitation with the Coapsys device

Kiyotaka Fukamachia*, Zoran B. Popovicb, Masahiro Inouea, Kazuyoshi Doia, Soren Schenka, Yoshio Ootakia, Michael W. Kopcak, Jr.a, Patrick M. McCarthya,c

a Department of Biomedical Engineering/ND 20, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
b Department of Cardiovascular Medicine, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
c Department of Thoracic and Cardiovascular Surgery, Kaufman Center for Heart Failure, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA

Received 14 October 2003; accepted 3 December 2003.

* Corresponding author. Tel.: +1-216-445-9344; fax: +1-216-444-9198
e-mail: fukamach{at}bme.ri.ccf.org


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
Objective: The objective of this study was to evaluate the changes in mitral annular and left ventricular dimensions and left ventricular pressure–volume relations produced by the Myocor Coapsys device that has been developed to treat functional mitral regurgitation (MR) off-pump. Methods: The Coapsys device, which consists of anterior and posterior epicardial pads connected by a sub-valvular chord, was implanted in seven dogs with functional MR resulting from pacing induced cardiomyopathy. The Coapsys device was then sized by drawing the posterior leaflet and annulus toward the anterior leaflet. During sizing, MR grade was assessed using color flow Doppler echocardiography. Final device size was selected when MR was eliminated or minimized. Following implantation, heart failure was maintained by continued pacing for a period of 8 weeks. Mitral annular and left ventricular dimensions and left ventricular pressure–volume relations were evaluated by two-dimensional echocardiography and a conductance catheter, respectively, at pre-sizing, post-sizing, and after 8 weeks. Results: All implants were performed on beating hearts without cardiopulmonary bypass. Mean MR grade was reduced from 2.9±0.7 at pre-sizing to 0.7±0.8 at post-sizing (P<0.001), and was maintained at 0.8±0.8 after 8 weeks (P<0.01). The septal–lateral dimensions were significantly reduced at both mitral annular level [2.4±0.2 cm at pre-sizing, 1.5±0.3 cm at post-sizing (P<0.001), and 1.8±0.3 cm after 8 weeks (P<0.05)] and mid-papillary level [4.1±0.4 cm at pre-sizing, 2.4±0.2 cm at post-sizing (P<0.001), and 3.3±0.4 cm after 8 weeks (P<0.001)]. The end-systolic pressure–volume relation shifted leftward at post-sizing with a significantly steeper slope (P=0.03). There was a significant (P=0.03) leftward shift of the end-diastolic pressure–volume relation at post-sizing. After 8 weeks, these changes in pressure–volume relations tended to return to pre-sizing relations. Conclusions: The Coapsys device significantly reduced MR by treating both the mitral annular dilatation and the papillary muscle displacement. Despite these significant dimensional changes, the Coapsys device did not negatively affect the left ventricular pressure–volume relations.

Key Words: Beating heart • Heart valves • Mitral valve repair • Off-pump


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
Functional mitral regurgitation (MR) results from dilatation of the mitral valve (MV) annulus and/or papillary muscle displacement with chordal tethering in dysfunctional left ventricles (LV) and is commonly considered to be one of the initiators of heart failure, as well as an ongoing impetus of the progression of the disease. Annuloplasty is a widely used means for MV repair. However, it does not treat papillary muscle displacement, and the surgical procedure requires the patient to be placed on cardiopulmonary bypass (CPB).

The Coapsys device (Myocor, Inc., Maple Grove, MN), which was designed to treat both the mitral annular dilatation and the papillary muscle displacement, has the advantage of being placed on a beating heart without CPB, and can be adjusted under echo guidance. We have demonstrated that the Coapsys device significantly reduced or eliminated MR off-pump in a canine model of functional MR [1,2]. The objective of this study was to evaluate the mitral annular and LV dimensional changes. We also evaluated LV pressure–volume relations produced by the Coapsys device to assess the changes in LV contractility and compliance, as the geometric changes may affect LV performance.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 Appendix A. Conference...
 References
 
2.1. The Coapsys design
The Coapsys device was developed to treat patients with clinically significant MR and LV dysfunction. The treatment is intended to be at least as effective as currently available treatments for MR reduction, with the following added benefits: (1) ability to affect both the mitral annulus and the papillary muscle, (2) off-pump implantation, (3) simple implantation procedure, (4) intraoperatively assessable, tunable, and reversible implantation, and (5) potential for a more stable repair which does not impede annular dynamics.

The Coapsys device consists of an epicardial posterior pad, an epicardial anterior pad, and an expanded polytetrafluoroethylene (ePTFE) coated, braided polyethylene sub-valvular chord [1,2]. The two pads are located on the surface of the heart with the load bearing sub-valvular chord passing through the ventricle. The posterior pad has two heads, configured such that the annular head and papillary head create shape change at the mitral annuls level and papillary muscle level, respectively, when the anterior and posterior pads are drawn together. This configuration also allows the device to pass between the papillary muscles and below the valve leaflets, ensuring that the device does not interact negatively with these structures. The polyester-covered anterior pad is adjustable and utilizes a deployable pin mechanism to fix the opposing end after sizing the device.

2.2. In vivo study preparation
This study was approved by the Cleveland Clinic's Institutional Animal Care and Use Committee, and all animals received humane care in compliance with the European Convention on Animal Care. Among several potential MR models, chronic rapid ventricular pacing was chosen in this study because the hemodynamic and echocardiographic changes are very similar to those found in human functional MR [3]. Also, rapid ventricular pacing produces heart failure [3–5], which is a common co-morbidity among this patient group.

Seven adult mongrel dogs (body weight, 25.0±1.1 kg) were paced via a right ventricular (RV) transvenous lead using rapid asynchronous ventricular pacing at 230 beats/min for an average of 31±4 days to induce functional MR with LV dysfunction. No medications for heart failure, including diuretics, were given during the induction phase.

On the day of the Coapsys implantation, the pacing rate was reduced to 30 beats/min in demand mode so that the animal would resume normal sinus rhythm. The animal was anesthetized with thiopental (15 mg/kg) and intubated, and the anesthesia was maintained with isoflurane (0.5–2.5%). A conductance catheter with two Millar pressure sensors (model SPC-562; Millar Instruments, Inc., Houston, TX) was placed via the carotid artery to record aortic (AoP) and LV (LVP) pressures and LV volume. Transthoracic two-dimensional (2D) echocardiograms were obtained to evaluate MR (grades 0–4) by color Doppler imaging. The mitral annular septal–lateral (S–LMA) dimension was measured using the long axis view and the mitral annular commissure–commissure (C–CMA) dimension was measured using the two-chamber view at end-diastole. The LV cross-sectional dimensions in septal–lateral (S–LLV) and commissure–commissure (C–CLV) planes were also measured at mid-papillary muscle level. These data were recorded as the ‘baseline closed chest’ data point.

2.3. Coapsys implant surgery
The Coapsys device was surgically implanted as previously reported [1,2]. The appropriate sites for Coapsys device placement were identified through a combination of external landmarks and 2D echocardiogram visualization of internal structures. The placement avoided papillary muscle interference, the mitral apparatus, and main coronary artery branches. The posterior position was approximately 2.5 cm from the atrio-ventricular groove and midway between the papillary muscles with the annular head of the pad directly opposed to the valve annulus. The anterior position was at the base of the RV outflow tract, approximately 2 cm RV side of the left anterior descending artery. Following site identification, the Coapsys device was placed using a specially designed delivery instrument.

The 2D echocardiographic measurements were repeated as the ‘pre-sizing’ data point. Epicardial three-dimensional (3D) echocardiogram was also recorded (Volumetrics Medical Imaging, Inc., Durham, NC) to measure LV volume for conductance volume calibration purpose. The LV pressure and volume were recorded during preload reduction by transiently occluding the superior and inferior vena cava (bicaval occlusion). The data were acquired digitally at a sample rate of 200 Hz using the PowerLab (AD Instruments Inc., Mountain View, CA) data acquisition system and stored on a hard disk for subsequent complete analysis. The resistivity ({rho}) of the blood was measured and adjusted in the Leycom system (Model SIGMA 5/DF, CardioDynamics BV, Zoetermeer, The Netherlands) at each data point.

The Coapsys device was then sized by drawing the posterior leaflet and annulus toward the anterior leaflet using a specially designed, sizing instrument. Final device size was selected when MR was minimized or eliminated as assessed by Color Doppler images. Echocardiographic and hemodynamic measurements were repeated at steady state and during bicaval occlusion as the ‘post-sizing’ data point. The chest was then closed in the standard fashion.

Rapid pacing at a reduced rate of 190 beats/min was started 3 days after surgery and maintained for 8 weeks until the terminal study to avoid the natural recovery of the LV and MV performance after cessation of pacing [4]. Furosemide (40 mg/day) was given to all dogs during the post-operative period. One dog showed severe heart failure symptoms, and pacing was discontinued for 1 week (data from this animal were included in all data points). Another dog died on post-operative day 14 due to an ascending aortic rupture, which was induced by the chronically implanted aortic flow probe (data from this animal were included in baseline closed chest, pre-sizing, and post-sizing data points).

2.4. Study after 8 weeks
Eight weeks after the Coapsys implantation, the animals were again anesthetized and echocardiographic and hemodynamic measurements were repeated at steady state and during bicaval occlusion as the ‘after 8 weeks’ data point. All animals were sacrificed and complete autopsies were performed. The hearts were excised, and the device's relationship to the coronary vessels and intraventricular structures was examined.

2.5. Data analysis for pressure–volume relations
Total LV conductance, G(t), is calculated as the sum of five segmental conductances. Instantaneous total LV volume is calculated as V(t)=(1/{alpha})({rho}L2)(G(t)-Gp), where {alpha} is the slope factor, {rho} is the specific resistivity of the blood sample measured using a special cuvette, L is the electrode spacing, and Gp is the parallel conductance.

At first, {alpha} was determined in each steady state data point by 3D echocardiography using a two-point calibration based on matching end-diastolic (Ved) and end-systolic (Ves) volumes as shown in the following equation:

where Ved(cath) is the Ved measured by the conductance catheter, Ves(cath) is the Ves measured by the conductance catheter, Ved(3D) is the Ved measured by 3D echocardiography, and Ves(3D) is the Ves measured by 3D echocardiography. The average value of the {alpha} from all animals was 0.433. To avoid introducing errors in the method that estimate {alpha} in individual animals, we used a single mean slope factor ({alpha}=0.433) in this study. The calibration offset (Gp) was corrected by matching Ved(cath) and Ved(3D) [6,7].

The LV pressure–volume loops under various preloads were obtained by bicaval occlusion. By connecting the upper left corners of the pressure–volume loops using an iterative linear regression method, the Ees (the slope of the end-systolic pressure–volume relation, ESPVR) was determined as

where Pes is the end-diastolic pressure and V0 is the volume axis intercept [8]. We arbitrarily entered Pes values of 50, 60, 70, 80, and 90 mmHg in this equation and calculated corresponding Ves. These Ves were averaged and used to reconstruct the ESPVR at each data point.

LV compliance, or diastolic property, was assessed by the end-diastolic pressure–volume relationship (EDPVR) during bicaval occlusion. LV end-diastolic pressure (Ped) and Ved data were fitted to the following exponential equation [7]:

where a1 and b1 are the constants. Interpolated pressures from the fitted curves were used to generate average EDPVR for each data point.

2.6. Statistical analysis
Data were expressed as mean±standard deviation. A paired t-test was used for each paired data. In all analyses, a P-value of <0.05 was considered statistically significant.


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 Appendix A. Conference...
 References
 
All Coapsys device implantations were performed off-pump. MR decreased from 2.9±0.7 at pre-sizing to 0.7±0.8 at post-sizing (P<0.001), and from 2.5±0.8 at baseline closed chest to 0.8±0.8 after 8 weeks (P<0.01).

Geometric change produced by the device in a representative dog is shown in Fig. 1 . The S–LMA dimension decreased significantly at post-sizing and after 8 weeks (Fig. 2) . The C–CMA dimension was unchanged (Fig. 2). Similar to the results of S–LMA dimension, the S–LLV dimension decreased significantly at post-sizing. Although S–LLV significantly increased after 8 weeks, it was still significantly smaller than that at baseline closed chest. Although the C–CLV dimension at post-sizing increased slightly but significantly, the C–CLV dimension after 8 weeks was not significantly different from the baseline closed chest value.



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  		Fig. 1. Short axis views by 2D echocardiogram in a representative dog, demonstrating geometric change in the shape of the left ventricle produced by the device (A, pre-sizing; B, post-sizing).

 


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  		Fig. 2. Dimensional changes by the Coapsys device. S–LMA, the mitral annular septal–lateral dimension; C–CMA, the mitral annular commissure–commissure dimension; S–LLV, the left ventricular cross-sectional dimension at mid-papillary level in septal–lateral plane; C–CLV, the left ventricular cross-sectional dimension at mid-papillary level in the same plane of the commissure–commissure direction of the mitral annulus.

 
Acute changes in LV pressure–volume relations in a representative dog are shown in Fig. 3 . The pressure–volume loops shifted to the left at post-sizing. Fig. 4 shows the averages of the ESPVR and EDPVR at each data point. The ESPVR shifted to the left at post-sizing with a significantly steeper slope (Ees=2.0±0.9 mmHg/ml at pre-sizing and 2.8±0.9 mmHg/ml at post-sizing, P<0.05). There was a significant (P<0.05) leftward shift of the EDPVR at post-sizing. After 8 weeks, both ESPVR and EDPVR remained shifted to the left but with a slope closer to the pre-sizing level.



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  		Fig. 3. Left ventricular pressure–volume loops obtained during bicaval occlusion at pre-sizing and post-sizing. LV, left ventricular.

 


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  		Fig. 4. The averages of the ESPVR and EDPVR at each data point. The standard deviation bars for the data after 8 weeks are not shown. ESPVR, end-systolic pressure–volume relation; EDVPR, end-diastolic pressure–volume relation; LV, left ventricular.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
Appendix A. Conference...
 References
 
The Coapsys device significantly reduced MR by significantly reducing the septal–lateral dimensions chronically at mitral annular level as well as at mid-papillary levels. These data indicated that the Coapsys device treated both of the two important factors that contribute to the development of functional MR: annular dilatation and displacement of the papillary muscles [9,10]. Treating the annular dilatation, especially the reduction in septal–lateral dimension, has been reported to be the most important surgical goal when repairing the MV [11,12]. Timek and associates [11] eliminated MR by septal–lateral annular cinching that decreased the septal–lateral diameter by 22±10% in their acute ischemic MR model in sheep. At the same time, there have been several reports that emphasized the importance of treating the displacement of the papillary muscles [9,13,14]. Tibayan and associates [9] demonstrated geometric distortions of mitral valvular–ventricular complex in a chronic ischemic MR model and concluded that treatment of chronic ischemic regurgitation should address both the annular septal–lateral dilatation and the lateral displacement of the posterior papillary muscle. For this reason, the Coapsys device was designed in such a way that its posterior pad has two heads. The annular head imparts shape change to the mitral annulus, while the papillary head located between the papillary muscles, repositions the papillary muscles. This arrangement enabled the Coapsys device to reduce MV annular area and reposition the papillary muscles. Although annuloplasty is a widely used means of MV repair, it only addresses one of the components of MR. Therefore, surgeons attempt to overcorrect the mitral annulus to compensate for the ventricular dilatation that displaced the papillary muscles and restricted the leaflet motion [15].

The advantages of the MV repair on beating hearts without CPB are obvious. The possible complications associated with the use of CPB can be avoided. Furthermore, immediate evaluation is possible as the device is being sized. The outcome of the annuloplasty ring placement cannot be adequately assessed until the patient is weaned from CPB. The complications associated with an inadequate repair result in added procedural and anesthetic times, and are among the reasons for increased morbidity/mortality rates in annuloplasty-treated patients. The increased morbidity/mortality profile leads directly to non-treatment of MR in the earlier stage heart failure patient. If the patients are treated while remaining largely asymptomatic, these patients are more likely to possess sufficient contractile reserve to adapt to the sudden increase in the effective afterload when the competence of the valve is restored. Restoration of the valve's function would thereby assist in halting the initiation/progression of heart failure, and may even reverse its effects. Therefore, a device intended to address these issues by correcting valve dysfunction earlier without requiring the use of CPB or an open-heart access method would provide significant clinical benefit. There are a few such devices reported in the literatures [13,16,17].

In this study, we evaluated LV pressure–volume relations to assess LV contractility and compliance, as the changes in MV or LV geometry may affect LV performance. The ESPVR shifted to the left acutely with a significantly steeper slope, which suggested an increase in contractility. The EDPVR also shifted to the left, which suggested a change in compliance. These changes are thought to be due to LV geometry change produced by the Coapsys device. After 8 weeks, the pressure–volume relations remained shifted to the left with a slope closer to the pre-sizing level. This fact may indicate that the heart failure still progresses in this prolonged pacing protocol. Despite the significant dimensional changes, the Coapsys device did not negatively affect the LV performance. As we previously reported, the hemodynamics were maintained after the Coapsys implantation [1,2].

A study limitation is that the geometrical measurements are limited to the S–L and C–C dimensions at mitral annular and mid-papillary levels, which provides only indirect evidence of repositioning of the papillary muscles.

In conclusion, the Coapsys device significantly reduced MR by treating both the mitral annular dilatation and the papillary muscle displacement. The Coapsys device did not negatively affect the LV pressure–volume relations.


   Acknowledgments
 
This study was financially supported by Myocor Inc. (Maple Grove, MN). Dr Patrick M. McCarthy is a consultant to Myocor. We appreciate the superb technical assistance provided by Maureen Martin-Miklovic and Raymond Dessoffy, AA. We also than James D. Thomas, MD for his laboratory's support.


   Footnotes
 
Presented at the joint 17th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 11th Annual Meeting of the European Society of Thoracic Surgeons, Vienna, Austria, October 12–15, 2003.


   Appendix A. Conference discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
References
 
Mr D. Wheatley (Glasgow, UK): The Myocor device that I am more familiar with was marketed as a means of decreasing left ventricular dimensions and it didn't, to my recollection, mention changing the papillary muscle. Is there a difference in concept? Is this different from the other device?

Dr Fukamachi: The concept is totally different but the device is very similar. It uses the same intraventricular chord and a very similar pad. But the other device, called Myosplint, is used to reduce the effective radius to actually reduce the wall stress to improve cardiac function. Through these studies we tried a lot of different locations of the Myosplint, and we noticed that in some positions this device actually worsened mitral regurgitation or improved mitral regurgitation. In the Myosplint studies, we focused on improving cardiac function. Through those studies, we know that at a certain position, this device eliminates mitral regurgitation. So the concept is totally different but the device is similar.

Dr G. Lutter (Kiel, Germany): I have one question referring to your dog model. You showed us that you have brought together the anterior and the posterior wall of the left ventricle because of symmetric dilatation of the left ventricle in your fibrillation model you have demonstrated us. Could you imagine having an ischemic model with dilatation of the lateral wall where you re-position the lateral ischemic wall to receive a normal ejection fraction and bring together also the anterior and posterior wall? Did you think of this ischemic asymmetric possibility, too?

Dr Fukamachi: Actually we don't have data of an ischemic mitral regurgitation model to test this device, however, all the clinical studies currently ongoing are for patients with ischemic MR. So usually the surgery involved off-pump CABG plus off-pump Coapsys implantation. The results I am hearing about are very similar to our experimental results using dilated cardiomyopathy, which shows MR decreased from 3+ down to less than 1+. So I think this device works for ischemic MR also.

Dr Lutter: Could you also imagine to change the positioning of your Coapsys device? In case you observe in your echocardiographic control that the device doesn't function very well and you can't decrease the regurgitation, can you change the position after deploying the Coapsys device?

Dr Fukamachi: Yes, we can easily remove it and reimplant it.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 Appendix A. Conference...
 References
 

  1. Fukamachi K., Inoue M., Popovic Z.B., Doi K., Schenk S., Nemeh H., Ootaki Y., Kopcak M.W., Jr., Dessoffy R., Thomas J.D., Bianco R.W., Berry J.M., McCarthy P.M. Off-pump mitral valve repair using the Coapsys device; a pilot study in a pacing induced mitral regurgitation model. Ann Thorac Surg 2003.
  2. Inoue M., McCarthy P.M., Popovic Z.B., Doi K., Schenk S., Nemeh H., Ootaki Y., Kopcak M.W., Jr., Dessoffy R., Thomas J.D., Bianco R.W., Berry J.M., Fukamachi K. The Coapsys device to treat functional mitral regurgitation: in vivo chronic canine study and ex vivo study on excised recipients' hearts. J Thorac Cardiovasc Surg 2003.
  3. Takagaki M., McCarthy P.M., Goormastic M., Ochiai Y., Doi K., Kopcak M.W., Jr, Tabata T., Cardon L.A., Thomas J.D., Fukamachi K. Determinants of the development of mitral regurgitation in pacing-induced heart failure. Circ J 2003;67:78-82.[CrossRef][Medline]
  4. Takagaki M., McCarthy P.M., Tabata T., Dessoffy R., Cardon L.A., Connor J., Ochiai Y., Thomas J.D., Francis G.S., Young J.B., Fukamachi K. Induction and maintenance of an experimental model of severe cardiomyopathy with a novel protocol of rapid ventricular pacing. J Thorac Cardiovasc Surg 2002;123:544-549.[Abstract/Free Full Text]
  5. Howard R.J., Moe G.W., Armstrong P.W. Sequential echocardiographic-Doppler assessment of left ventricular remodelling and mitral regurgitation during evolving experimental heart failure. Cardiovasc Res 1991;25:468-474.[Abstract/Free Full Text]
  6. Feldman M.D., Pak P.H., Wu C.C., Haber H.L., Heesch C.M., Bergin J.D., Powers E.R., Cowart T.D., Johnson W., Feldman A.M., Kass D.A. Acute cardiovascular effects of OPC-18790 in patients with congestive heart failure. Time- and dose-dependence analysis based on pressure–volume relations. Circulation 1996;93:474-483.[Abstract/Free Full Text]
  7. Ratcliffe M.B., Wallace A.W., Salahieh A., Hong J., Ruch S., Hall T.S. Ventricular volume, chamber stiffness, and function after anteroapical aneurysm plication in the sheep. J Thorac Cardiovasc Surg 2000;119:115-124.[Abstract/Free Full Text]
  8. Suga H., Sagawa K., Shoukas A.A. Load independence of the instantaneous pressure–volume ratio of the canine left ventricle and effects of epinephrine and heart rate on the ratio. Circ Res 1973;32:314-322.[Abstract/Free Full Text]
  9. Tibayan F.A., Rodriguez F., Zasio M.K., Bailey L., Liang D., Daughters G.T., Langer F., Ingels N.B., Jr., Miller D.C. Geometric distortions of the mitral valvular–ventricular complex in chronic ischemic mitral regurgitation. Circulation 2003;108(Suppl 1):II116-II121.
  10. Kumanohoso T., Otsuji Y., Yoshifuku S., Matsukida K., Koriyama C., Kisanuki A., Minagoe S., Levine R.A., Tei C. Mechanism of higher incidence of ischemic mitral regurgitation in patients with inferior myocardial infarction: quantitative analysis of left ventricular and mitral valve geometry in 103 patients with prior myocardial infarction. J Thorac Cardiovasc Surg 2003;125:135-143.[Abstract/Free Full Text]
  11. Timek T.A., Lai D.T., Tibayan F., Liang D., Daughters G.T., Dagum P., Ingels N.B., Jr, Miller D.C. Septal-lateral annular cinching abolishes acute ischemic mitral regurgitation. J Thorac Cardiovasc Surg 2002;123:881-888.[Abstract/Free Full Text]
  12. Miller D.C. Ischemic mitral regurgitation redux—to repair or to replace?. J Thorac Cardiovasc Surg 2001;122:1059-1062.[Free Full Text]
  13. Hung J., Guerrero J.L., Handschumacher M.D., Supple G., Sullivan S., Levine R.A. Reverse ventricular remodeling reduces ischemic mitral regurgitation: echo-guided device application in the beating heart. Circulation 2002;106:2594-2600.[Abstract/Free Full Text]
  14. Hvass U., Tapia M., Baron F., Pouzet B., Shafy A. Papillary muscle sling: a new functional approach to mitral repair in patients with ischemic left ventricular dysfunction and functional mitral regurgitation. Ann Thorac Surg 2003;75:809-811.[Abstract/Free Full Text]
  15. McCarthy P.M. Does the intertrigonal distance dilate? Never say never. J Thorac Cardiovasc Surg 2002;124:1078-1079.[Free Full Text]
  16. Kaye D.M., Byrne M., Alferness C., Power J. Feasibility and short-term efficacy of percutaneous mitral annular reduction for the therapy of heart failure-induced mitral regurgitation. Circulation 2003;108:1795-1797.[Abstract/Free Full Text]
  17. St Goar F.G., Fann J.I., Komtebedde J., Foster E., Oz M.C., Fogarty T.J., Feldman T., Block P.C. Endovascular edge-to-edge mitral valve repair: short-term results in a porcine model. Circulation 2003;108:1990-1993.[Abstract/Free Full Text]



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ANN THORAC SURG ASIAN CARDIOVASC THORAC ANN EUR J CARDIOTHORAC SURG
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