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Mitral valve replacement: What should be the standard technique?
EDITORIALS
Mitral Valve Replacement: What Should Be the Standard Technique? G. F. 0. Tyers, MD, FRCS(C) Division of Cardiovascular and Thoracic Surgery, Department of Surgery, The University of British Columbia and the Vancouver General Hospital, Vancouver, British Columbia, Canada
0
perative mortality reported with mitral valve replacement (MVR) is usually higher than that for aortic valve or coronary bypass procedures. Physiological and chronological age, type of valvar lesion, chronicity, and left ventricular functional deterioration play a role in determining operative and late risks but are immutable at the time of surgical referral. Correction of mitral regurgitation by leaflet and chordal excision and MVR results in decreased total stroke volume because of elimination of low-resistance ventricular decompression into the left atrium. Other pathophysiological features of MVR include substitution of a rigid prosthetic ring for the flexible natural annulus and the potential for myocardial damage during cardiopulmonary bypass and aortic crossclamping. Increased MVR operative mortality has been noted in patients with mitral regurgitation especially when associated with reduced ventricular function and in patients with mitral stenosis related to the development of posterior transverse left ventricular disruption. Perivalvar leak and low cardiac output states after cardiopulmonary bypass are also associated with increased risk. Preservation of the continuity of one or both papillary muscles and chordae tendineae with the atrioventricular ring (mitral loop) was originally reported by Lillehei and
See also page 866. co-authors [l] to improve cardiac output and reduce operative mortality after MVR. These findings have been generally substantiated [2-51 including in the highest risk patients with acute ischemic mitral regurgitation and markedly reduced ejection fractions (EFs). Shortening of the left ventricular longitudinal axis and circumferential expansion, the response to volume loading, the endsystolic volume index, and the EF at rest and in response to exercise are best maintained or improved when the mitral loop is preserved. Further, few functional differences are demonstrable between patients undergoing repair versus patients undergoing replacement for mitral regurgitation when annular-chordal continuity is maintained [3]. Preservation of the posterior or mural mitral leaflet also appears to largely eliminate posterior transverse left ventricular disruption [6] and may reduce the incidence of perivalvar leak by buttressing the naturally occurring posterior defect in the fibrous mitral annulus. The study of Harpole and co-workers [7], which fails to confirm that partial preservation of the mitral loop helps Address reprint requests to Dr Tyers, Suite 314, 700 W 10th Ave, Vancouver, BC V5Z 1L9 Canada. 0 1990 by The Society of Thoracic Surgeons
to maintain ventricular function after MVR, raises several concerns. It is small, involving 12 patients, only 8 of whom have mitral regurgitation in which the relevance of chordal preservation to ventricular function is most critical. Even the 8 patients with mitral regurgitation were not treated homogenously, as 1 patient underwent total mitral valve excision and 7 patients had posterior leaflets preserved. Compared with preoperative values, heart rate averaged 8 to 10 beats/min faster during the early and subsequent postoperative studies. Could the potential inotropic effect of increased heart rate have partially masked the effect of mitral loop division? This variable could have been controlled by preoperative and postoperative atrial pacing or by ventricular pacing in patients with atrial fibrillation. Harpole and co-workers define standard MVR as complete excision of the anterior leaflet and preservation of the mural leaflet when convenient; however, they totally excised both the anterior and mural leaflets and chordae in 42% (5112) of their patients. Thus, posterior leaflet preservation can hardly be defined as standard in their practice, and a review of the recent literature confirms that leaflet and subvalvar apparatus excision preparatory to MVR is still most commonly practiced, especially when a mechanical valve is to be used. Harpole and co-workers' measures of left ventricular function are independent of numerous physiological variables, but are they of more clinical relevance than studies of left ventricular peak volume elastance and EF indicating that the mitral loop may contribute as much as 40% of maximal left ventricular performance? Although left ventricular wall volume and the relationship of stroke work to end-diastolic volume did not deteriorate after MVR for mitral regurgitation in the present study, several potential clinically relevant variables changed. Both the peak left ventricular pressure and end-systolic wall stress increased while left ventricular EF decreased. Ejection fraction as an index of myocardial function has been questioned because it may be affected by preload, afterload, heart rate, and contractility. However, the clinical relevance of EF is supported by the limited potential for functional recovery and survival after MVR in patients with marked preoperative reductions and/or lack of appropriate response to exercise [8]. As in the present study, low-risk patients with normal preoperative EF may tolerate the acute increase in left ventricular afterload and the reduced total stroke volume and fractional shortening after MVR for mitral regurgitation relatively well. The overall effect is still beneficial, ie, improved ventricular efficiency and forward stroke volume even though EF is reduced. But Ann Thorac Surg 1990;49:861-2
0003-4975/90/$3.50
862
EDITORIAL TYERS MITRAL VALVE REPLACEMENT
are these data reassuring with regard to management of patients with decreased preoperative EF and acute or chronic mitral regurgitation? This latter group of individuals, who have an increased operative risk and a markedly reduced 5-year survival with standard MVR (by which I mean associated with leaflet and subvalvar excision), will provide a more fertile area for investigation of the potential benefits of mitral loop preservation. Studies of the type conducted by Harpole and coworkers need to be repeated with a larger number of patients and with a clear-cut separation of treatment subgroups into (1) total valvar excision, (2) total valvar preservation, and (3) posterior apparatus preservation. In each treatment group, patients with mitral stenosis and mitral regurgitation and patients with normal and subnormal ventricular function should be analyzed separately. However, would a study of planned excision of the posterior leaflet be ethical considering all of the data showing a significant reduction in operative risk from posterior transverse left ventricular disruption when the mural leaflet is retained? Because of Lillehei's original report, I have routinely preserved the posterior leaflet since I began practice 20 years ago and coincidentally have never had a patient with posterior transverse left ventricular disruption. Further, essentially all of the publications on left ventricular rupture complicating MVR that detail operative technique report posterior leaflet excision. A more appropriate question may relate to selective preservation of the anterior leaflet support apparatus. The potential complication of left ventricular outflow tract obstruction is easily avoided by subannular prosthetic positioning and/or rolling up the anterior leaflet like a Roman shade. However, I use interrupted sutures rather than Lillehei's reefing stitch [l],which has a tendency to pursestring the annulus. Partially excising the anterior leaflet [l, 3, 41, also originally described by Lillehei, extends the number of patients in whom the anterior subvalvar apparatus can be preserved. With appropriate
Ann Thorac Surg 1990;49:861-2
valvar sizing and excision of all loose tissues, continued use of mitral loop-preserving techniques with prosthetic mitral valves is supported by my own experience, personal communications, and the literature [l,4, 51. Based on the available data, it is probable that many technical and functional problems associated with increased MVR mortality can be ameliorated by preservation of as much of the mitral valve annular and subvalvar apparatus as technically feasible at the time of operation.
References 1. Lillehei CW, Levy MJ, Bonnabeau RC. Mitral valve replacement with preservation of papillary muscles and chordae tendineae. J Thorac Cardiovasc Surg 1964;47:532-43. 2. Spence PA, Paniston CM, David TE, et al. Toward a better understanding of the etiology of left ventricular dysfunction after mitral valve replacement: an experimental study with possible clinical implications. Ann Thorac Surg 1986;41: 363-71. 3. Angel1 WW, Oury JH, Shah P. A comparison of replacement and reconstruction in patients with mitral regurgitation. J Thorac Cardiovasc Surg 1987;93:665-74. 4. Miki S, Kusuhara K, Ueda Y, Komeda M, Ohkita Y, Tahata T. Mitral valve replacement with preservation of chordae tendineae and papillary muscles. Ann Thorac Surg 1988;45:28-34. 5. Goor DA, Mohr R, Lavee J, Serraf A, Smolinsky A. Preservation of the posterior leaflet during mechanical valve replacement for ischemic mitral regurgitation and complete myocardial revascularization. J Thorac Cardiovasc Surg 1988;96: 253-60. 6. Craver JM, Jones EL, Guyton RA, Cobbs BW, Hatcher CR. Avoidance of transverse mid-ventricular disruption following mitral valve replacement. Ann Thorac Surg 1985;40:163-71. 7. Harpole DH Jr, Rankin JS, Wolfe WG, et al. Effects of standard mitral valve replacement on left ventricular function. Ann Thorac Surg 1990;49:866-74. 8. Phillips HR, Levine FH, Carter JE, et al. Mitral valve replacement for isolated mitral regurgitation: analysis of clinical course and late postoperative left ventricular ejection fraction. Am J Cardiol 1981;48:647-54.
Mitral Valve Replacement: What Should Be the Standard Technique? G. F. 0. Tyers, MD, FRCS(C) Division of Cardiovascular and Thoracic Surgery, Department of Surgery, The University of British Columbia and the Vancouver General Hospital, Vancouver, British Columbia, Canada
0
perative mortality reported with mitral valve replacement (MVR) is usually higher than that for aortic valve or coronary bypass procedures. Physiological and chronological age, type of valvar lesion, chronicity, and left ventricular functional deterioration play a role in determining operative and late risks but are immutable at the time of surgical referral. Correction of mitral regurgitation by leaflet and chordal excision and MVR results in decreased total stroke volume because of elimination of low-resistance ventricular decompression into the left atrium. Other pathophysiological features of MVR include substitution of a rigid prosthetic ring for the flexible natural annulus and the potential for myocardial damage during cardiopulmonary bypass and aortic crossclamping. Increased MVR operative mortality has been noted in patients with mitral regurgitation especially when associated with reduced ventricular function and in patients with mitral stenosis related to the development of posterior transverse left ventricular disruption. Perivalvar leak and low cardiac output states after cardiopulmonary bypass are also associated with increased risk. Preservation of the continuity of one or both papillary muscles and chordae tendineae with the atrioventricular ring (mitral loop) was originally reported by Lillehei and
See also page 866. co-authors [l] to improve cardiac output and reduce operative mortality after MVR. These findings have been generally substantiated [2-51 including in the highest risk patients with acute ischemic mitral regurgitation and markedly reduced ejection fractions (EFs). Shortening of the left ventricular longitudinal axis and circumferential expansion, the response to volume loading, the endsystolic volume index, and the EF at rest and in response to exercise are best maintained or improved when the mitral loop is preserved. Further, few functional differences are demonstrable between patients undergoing repair versus patients undergoing replacement for mitral regurgitation when annular-chordal continuity is maintained [3]. Preservation of the posterior or mural mitral leaflet also appears to largely eliminate posterior transverse left ventricular disruption [6] and may reduce the incidence of perivalvar leak by buttressing the naturally occurring posterior defect in the fibrous mitral annulus. The study of Harpole and co-workers [7], which fails to confirm that partial preservation of the mitral loop helps Address reprint requests to Dr Tyers, Suite 314, 700 W 10th Ave, Vancouver, BC V5Z 1L9 Canada. 0 1990 by The Society of Thoracic Surgeons
to maintain ventricular function after MVR, raises several concerns. It is small, involving 12 patients, only 8 of whom have mitral regurgitation in which the relevance of chordal preservation to ventricular function is most critical. Even the 8 patients with mitral regurgitation were not treated homogenously, as 1 patient underwent total mitral valve excision and 7 patients had posterior leaflets preserved. Compared with preoperative values, heart rate averaged 8 to 10 beats/min faster during the early and subsequent postoperative studies. Could the potential inotropic effect of increased heart rate have partially masked the effect of mitral loop division? This variable could have been controlled by preoperative and postoperative atrial pacing or by ventricular pacing in patients with atrial fibrillation. Harpole and co-workers define standard MVR as complete excision of the anterior leaflet and preservation of the mural leaflet when convenient; however, they totally excised both the anterior and mural leaflets and chordae in 42% (5112) of their patients. Thus, posterior leaflet preservation can hardly be defined as standard in their practice, and a review of the recent literature confirms that leaflet and subvalvar apparatus excision preparatory to MVR is still most commonly practiced, especially when a mechanical valve is to be used. Harpole and co-workers' measures of left ventricular function are independent of numerous physiological variables, but are they of more clinical relevance than studies of left ventricular peak volume elastance and EF indicating that the mitral loop may contribute as much as 40% of maximal left ventricular performance? Although left ventricular wall volume and the relationship of stroke work to end-diastolic volume did not deteriorate after MVR for mitral regurgitation in the present study, several potential clinically relevant variables changed. Both the peak left ventricular pressure and end-systolic wall stress increased while left ventricular EF decreased. Ejection fraction as an index of myocardial function has been questioned because it may be affected by preload, afterload, heart rate, and contractility. However, the clinical relevance of EF is supported by the limited potential for functional recovery and survival after MVR in patients with marked preoperative reductions and/or lack of appropriate response to exercise [8]. As in the present study, low-risk patients with normal preoperative EF may tolerate the acute increase in left ventricular afterload and the reduced total stroke volume and fractional shortening after MVR for mitral regurgitation relatively well. The overall effect is still beneficial, ie, improved ventricular efficiency and forward stroke volume even though EF is reduced. But Ann Thorac Surg 1990;49:861-2
0003-4975/90/$3.50
862
EDITORIAL TYERS MITRAL VALVE REPLACEMENT
are these data reassuring with regard to management of patients with decreased preoperative EF and acute or chronic mitral regurgitation? This latter group of individuals, who have an increased operative risk and a markedly reduced 5-year survival with standard MVR (by which I mean associated with leaflet and subvalvar excision), will provide a more fertile area for investigation of the potential benefits of mitral loop preservation. Studies of the type conducted by Harpole and coworkers need to be repeated with a larger number of patients and with a clear-cut separation of treatment subgroups into (1) total valvar excision, (2) total valvar preservation, and (3) posterior apparatus preservation. In each treatment group, patients with mitral stenosis and mitral regurgitation and patients with normal and subnormal ventricular function should be analyzed separately. However, would a study of planned excision of the posterior leaflet be ethical considering all of the data showing a significant reduction in operative risk from posterior transverse left ventricular disruption when the mural leaflet is retained? Because of Lillehei's original report, I have routinely preserved the posterior leaflet since I began practice 20 years ago and coincidentally have never had a patient with posterior transverse left ventricular disruption. Further, essentially all of the publications on left ventricular rupture complicating MVR that detail operative technique report posterior leaflet excision. A more appropriate question may relate to selective preservation of the anterior leaflet support apparatus. The potential complication of left ventricular outflow tract obstruction is easily avoided by subannular prosthetic positioning and/or rolling up the anterior leaflet like a Roman shade. However, I use interrupted sutures rather than Lillehei's reefing stitch [l],which has a tendency to pursestring the annulus. Partially excising the anterior leaflet [l, 3, 41, also originally described by Lillehei, extends the number of patients in whom the anterior subvalvar apparatus can be preserved. With appropriate
Ann Thorac Surg 1990;49:861-2
valvar sizing and excision of all loose tissues, continued use of mitral loop-preserving techniques with prosthetic mitral valves is supported by my own experience, personal communications, and the literature [l,4, 51. Based on the available data, it is probable that many technical and functional problems associated with increased MVR mortality can be ameliorated by preservation of as much of the mitral valve annular and subvalvar apparatus as technically feasible at the time of operation.
References 1. Lillehei CW, Levy MJ, Bonnabeau RC. Mitral valve replacement with preservation of papillary muscles and chordae tendineae. J Thorac Cardiovasc Surg 1964;47:532-43. 2. Spence PA, Paniston CM, David TE, et al. Toward a better understanding of the etiology of left ventricular dysfunction after mitral valve replacement: an experimental study with possible clinical implications. Ann Thorac Surg 1986;41: 363-71. 3. Angel1 WW, Oury JH, Shah P. A comparison of replacement and reconstruction in patients with mitral regurgitation. J Thorac Cardiovasc Surg 1987;93:665-74. 4. Miki S, Kusuhara K, Ueda Y, Komeda M, Ohkita Y, Tahata T. Mitral valve replacement with preservation of chordae tendineae and papillary muscles. Ann Thorac Surg 1988;45:28-34. 5. Goor DA, Mohr R, Lavee J, Serraf A, Smolinsky A. Preservation of the posterior leaflet during mechanical valve replacement for ischemic mitral regurgitation and complete myocardial revascularization. J Thorac Cardiovasc Surg 1988;96: 253-60. 6. Craver JM, Jones EL, Guyton RA, Cobbs BW, Hatcher CR. Avoidance of transverse mid-ventricular disruption following mitral valve replacement. Ann Thorac Surg 1985;40:163-71. 7. Harpole DH Jr, Rankin JS, Wolfe WG, et al. Effects of standard mitral valve replacement on left ventricular function. Ann Thorac Surg 1990;49:866-74. 8. Phillips HR, Levine FH, Carter JE, et al. Mitral valve replacement for isolated mitral regurgitation: analysis of clinical course and late postoperative left ventricular ejection fraction. Am J Cardiol 1981;48:647-54.