- Email: [email protected]
Surgical treatment of mitral stenosis
The American VOLUME x
Journal JULY
of Cardiology
1962
NUMBER
1
Editorial Surgical Treatment
of Mitral Stenosis
Open Versus Closed Technics HE EVOLUTION of the surgical approach for mitral stenosis initiated by Brunton’ in 1902, was modified during the ensuing years by Allen and Graham,2 Cutler and Levine,3 Souttar4 and others.5 The practicality of this approach, however, awaited the contributions in 1948 of Bailey,6 Harken and Brock,s who demonstrated that symptomatic relief could be had by the majority of patients with mitral stenosis by increasing the size of the valvular orifice. This instituted the era of intracardiac surgery. Later studies of operative results showed disappointingly little correlation between clinical improvement and roentgenographic, electrocardiographic, or hemodynamic improvement. Because of the lack of correlation between clinical and physiologic studies, the latter were largely discounted. However, with more experience, surgeons began to realize that with closed technics many times they had to be content with attaining a less than optimal valve opening because of subvalvular stenosis, calcification or the aggravation of regurgitation; and their results as a whole were less than desirable. This led to the development of new approaches and new instruments to improve the effectiveness of the “closed” technic. It soon became apparent that the valvular pathology was such that optimal correction could be attained in only 10 to 20 per cent of patients by means of the closed transatrial approach. Many surgeons continue to employ the closed transatrial approach, believing that at least considerable clinical improvement can be anticipated. Others, g,lo disappointed with this technic, turned to the transventricular approach for valvular dilatation, advocated by Logan,l’ with supposed greater improvement in clinical
T
results over those previously obtained. The enthusiasm of the advocates employing transventricular dilatation suggests that in their hands substantially greater benefit is afforded their patients than is possible by the transatrial method. However, little supportive hemodynamic data have been reported in behalf of this technic. MorrowI demonstrated the superiority of transventricular dilatation; only 5 of 25 patients had residual atrioventricular gradients greater than 8 mm. Hg at the time of the operative determination in contrast to a residual gradient greater than 8 mm. Hg in 24 of 50 patients in whom the transatrial approach was used. Even though this technic is obviously of greater benefit to the patient than the transatrial dilatation approach, 5 of the 25 patients, or 20 per cent, still had a persistent gradient of 8 mm. Hg or greater, which, according to Morrow, is a significant gradient. Also, the fact that 80 per cent had gradients across the mitral valve of less than 8 mm. following transventricular dilatation under basal operative conditions does not imply that a similar lack of gradient would be present if the tests were later performed with exercise or that this is indicative of maximal improvement. Past experience has shown that left atria1 pressures taken during operation under basal conditions were always considerably lower than those obtained with and without exercise at the time of postoperative evaluation. In Morrow’s series of 25 patients no significant mitral regurgitation occurred with the transventricular dilatation technic, but Bj6rk13 observed a
Editorial
2
known that the deleterious effects of even a minor valvular regurgitation may take a number of years to become clinically significant. OPEN VERSUS CLOSED TECHNICS Because of dissatisfying results obtained in the closed transatrial technics, we turned to the open approach for valvular correction employAntagonists ing extracorporeal circulation.14 of the open technic state that it is more cumbersome and associated with greater risk in contrast to the closed technics which are “simple, quick and easy.” Obviously, the open technic is more complicated, time-consuming and exacting, but if it is more beneficial to the patient, Experience other considerations are secondary. has also shown that the open technic is not associated with a higher risk nor operative mortality. To the contrary it is associated with a lower risk for comparat)le valvular lesions, in addition to enabling the surgeon to correct conditions and complications unanticipated not correctable by closed technics. In the past, successful surgical relief of mitral stenosis by closed technics has been dependent (1) the presence and degree of subupon: valvular fusion of the chordae papillary structures, (2) the degree of calcification, (3) whether or not regurgitation was present, produced or aggravated, and (4) the completeness of the correction. t\lthough Logan and Turner’s” clinical impression of the marked superiority of transventricular dilatation over the transatrial approach in a large series of patients points to the advantages of this technic, in only .28 per cent of their patients was it possible to dtvrde completely both stenosed commissures. The incidence of traumatic regurgitation occurring or increasing following transventricular dilatation as determined by the presence or character of a postoperative murmur was 19 per cent and this increased to 39 per cent when only the posterior commissure was completely divided. Reported operative mortality for the transventricular dilatation has ranged from 6.4 per cent” to By means of the open approach, 12 per cent.“’ it is routinely possible to divide both commissures and to relieve subvalvular stenosis to a far greater degree than by closed technics. Considerable amounts of calcification can be removed, and regurgitation can he corrected when present, produced or aggravated. Most past evaluations have been based on clinical appraisal of improvement after opera-
tive correction of mitral stenosis. Evaluations based upon hemodynamic improvement have either not been made or are incomplete, inconclusive, or discounted for lack of correlation with clinical improvement. In our patients operated by closed technics, those with clinical but no hemodynamic improvement were the ones who later showed signs and symptoms of valvular obstruction; no patients who showed marked hemodynamic improvement had trouble subsequently. As previously reported,14 only 22 per cent of Class III and IV patients who had complete pre- and postoperative physiologic studies had essentially normal hemodynamic findings following surgery-. INDICATIONS EOR OPEN TECHNIC Superior hemodynamic results were obtained in patients with recurrent signs and symptoms of mitral stenosis who were reoperated by the open technic using extracorporeal circulation compared to those obtained using the closed technics. As a result, the open technic was adopted 4 years ago for all patients with mitral stenosis. It is true that a certain percentage of patients have adequate benefits from the closed technics, but this group is small (10 to 20 per cent); and furthermore, it is impossible to foretell which patients will react favorably. Initially, an attempt was made to use closed technics for the “simple” case and open technics for the “complicated” valves, but it was soon evident that this preoperative differentiation was impossible. We were not satisfied with the use of closed technics as the postoperative clinical improvement did not seem to indicate that maximal benefit had been provided. Because so few closed technic operations were as successful as the majority of the open technic operations, we decided that the ideal surgical approach should I)e one that would be the most successful for the greatest number of patients. The criticism that the open technic employing the heart-lung machine subjects the patient to greater risk is not necessarily valid, in that the operative mortality with the open procedure has not been greater than that reported for the closed technics, even though the more seriously ill who could not have been helped otherwise were submitted to surgery for complicated valve conditions. Unquestionably, surgical correction by the open technic is more complicated, and the ability to recognize the anatomicopathologic landmarks of the diseased valve necessitates a completely new orientation that THE
AMERICAN
JOURNAL
OF
CARDIOLOGY
Editorial
3
TABLE 1 Postoperative Hemodynamic Studies Following Closed Technic
Case
1 2 3 4 5 6 7
Pulmonary Artery Pressure (mm. %I Exercise Rest 70/28 105/25 32/15 55/2 42,‘18 77/5 63/40
45/25 95/55 62/30 98/40 80/44
Following Open Technic PC* (mm. Hg)
32/21
Pulmonary Artery Pressure (mm. Hg) Rest Exercise 40/18 68/28 19/17 35/12 21/6 25/9 42/22
30/12 42/19 31/15 34/19 55/24
/
PC*
( mm. Ha)
I 1 I I/ ~
21/18 22/18 (9) 12/6 9/7
* Pulmonary capillary wedge pressure. Figures in parentheses = mean pressure. requires time, patience and considerable study for proper correction. But if the surgeon is willing to employ this more exacting technic, greater correction can be accomplished. RESULTS OF OPEN TECHNIC REPAIR One hundred and six patients with mitral stenosis have been operated upon by the open approach. Fifty-seven patients (54 per cent) had suhualvular stenosis from chordae papillary fusion to the extent that, in the opinion of the surgeon, separation could not have been accomplished as effectively “blindly,” regardless of the type of closed dilatation employed. Twenty-eight patients (26 per cent) had associated regurgitation in whom the maximal opening of the stenosed valve could not have been made without unduly increasing the degree of regurgitation. This was of no concern in the open technic, for it was then possible to correct the factors producing the regurgitation. In 19 patients (18 per cent) with severe calc$ication, greater valvular mobility not possible by the closed method was accomplished by the removal of considerable calcification. There was an operative mortality of 8 per cent in the 106 patients operated upon by means of the open technic. This has been reduced to 5 per cent in the last 40 patients. This compares to the closed technic operative mortality of 4 per cent in 200 patients. Of the 9 patients dying following the open correction, 7 patients had either completely clotted auricles or extensive calcific destruction of the mitral valves which in four instances required valvular replacement with artificial valves. Closed operation would not have been possible in these JULY1962
patients. Myocardial infarction from coronary artery disease caused the seventh patient’s death, and myocardial failure the eighth death of a patient who had been operated upon previously. POSTOPERATIVEEVALUATION Of equal importance is the de
Editorial is greater then that provided I)y the closed technic (31 per cent). Evidence and impressions based on hemodynamic findings obtained by cardiac catheterization obviouslv do not present the entire clinical picture Ijut’should at least be more accurate than analysis I)ascd on clinical impressions alone. Factors Influencing Operative Results: Success in the surgical relief of mitral stenosis depends on (1) the status of the myocardium affected l)y rheumatic fever and by chronic strain from valvular obstruction ; (2) the status of the stenosed valve--whether it is fibrotic but pliable; heavily scarred with subvalvular stenosis from matting together of the leaflets, chordae tenor heavily dineae, and papillary muscles; calcified; and (3) the status of the pulmonary vasculature. Other lesser factors are the age of the patient, the chronicity of the obstruction and the presence of atria1 fibrillation. Factors 1 and 3 are somewhat under the control of the physician who has followed the patient’s course over a number of years. Surgical intervention prior to irreversible pulmonary hypertension and chronic myocardial strain undoubtedly will improve the results. Greater effectiveness of the open technic will bring further benefits and, in the future, will probatjly entail the greater use of partial and complete artificial valves. SUhM4RY
With accumulated experience, it became increasingly apparent that maximal valvular correction by the closed technic was not possible or entirely successful because of subvalvular stenosis, calcification or aggravation of regurgitation. One hundred and six patients have now had valvular correction I,y means of the open approach employing extracorporeal circulation with far greater improvement than previously provided by the closed approach. Postoperative physiologic studies demon-
strated marked hemodynamic improvement and greater valvular correction by the open technic in twice as many patients with mitral stenosis as the closed technic. EARLE B. KAY, M.D., F.A.C.C. HENRY A.~IMMERMAN, M.D.,F.A.C.C. St. Vincent Charity Hospital
Cleveland,
Ohio
REFERENCES 1. BRUNTON,L. Preliminary note on the possibility of treating mitral stenosis by surgical methods. Lancet, 1: 352, 1902. 2. ALLEN, D. S. and GRAHAM,E. A. Intracardiac snrgery-a new method. J.A.M.A., 79: 1028, 1922. 3. CUTLER, E. C. and LEVINE, S. A. Cardiotomy and valvulotomy for mitral stenosis. Boston Med. B Surg. J., 188: 1023, 1923. 4. SOUTTAR, P. W. The surgical treatment of mitral stenosis. Brit. M. J., 2: 603, 1925. 5. BOURNE, G. The surgical treatment of mitral stenosis. St. Barth. Hosp. J., 35: 22, 1927. 6. BAILEY, C. P. Surgical treatment of mitral stenosis (mitral commissurotomy). Dis. Chest., 15: 377, 1949. 7. HARKEN, D. E., ELLIS, L. B., WARE, P. F. and NORMAL, L. R. Surgical treatment of mitral stenosis. 1. Valvulonlastv. New Eneland J. Med., 239: 801, 1948. ’ 8. BAKER, C., BROCK, R. C. and CAMPBELL, M. Valvulotomy for mitral stenosis: Report of six successful cases. Brit. M. J., 1: 1283, 1950. 9. COOLEY, D. A. and STONEBURNER,J. M. Transventricular mitral valvotomy. Surgery, 46 : 414, 1959. 10. GERBODE, F. Transventricular mitral valvotomy. Circulation, 21 : 563, 1960. 11. I,OGAN, A. and TURNER, R. Surgical treatment of mitral stenosis. Lancet, 2: 874, 1959. 12. MORROW, A. G. and BRAUNWALD, N. S. Transventricular mitral commissurotomy. J. T/ioracic GY Cardiouas. Surg., 41 : 225, 1961. 13. BJ~RK, V. O., HOLMDAHL,M. and LBF, B. Transventricular mitral valvulotomy under controlled hypotension. J. Thoracic @ Cardiovas. Surg., 41: 236, 1961. 14. KAY, E. B., NOQUEIRA, C. and ZIMMERMAN, H. A. Surgical treatment of mitral stenosis by open technic. .J.rl.M.~-l., 173: 1644, 1960.
THE AMERICANJOURNALOF
CARDIOLOGY
Journal JULY
of Cardiology
1962
NUMBER
1
Editorial Surgical Treatment
of Mitral Stenosis
Open Versus Closed Technics HE EVOLUTION of the surgical approach for mitral stenosis initiated by Brunton’ in 1902, was modified during the ensuing years by Allen and Graham,2 Cutler and Levine,3 Souttar4 and others.5 The practicality of this approach, however, awaited the contributions in 1948 of Bailey,6 Harken and Brock,s who demonstrated that symptomatic relief could be had by the majority of patients with mitral stenosis by increasing the size of the valvular orifice. This instituted the era of intracardiac surgery. Later studies of operative results showed disappointingly little correlation between clinical improvement and roentgenographic, electrocardiographic, or hemodynamic improvement. Because of the lack of correlation between clinical and physiologic studies, the latter were largely discounted. However, with more experience, surgeons began to realize that with closed technics many times they had to be content with attaining a less than optimal valve opening because of subvalvular stenosis, calcification or the aggravation of regurgitation; and their results as a whole were less than desirable. This led to the development of new approaches and new instruments to improve the effectiveness of the “closed” technic. It soon became apparent that the valvular pathology was such that optimal correction could be attained in only 10 to 20 per cent of patients by means of the closed transatrial approach. Many surgeons continue to employ the closed transatrial approach, believing that at least considerable clinical improvement can be anticipated. Others, g,lo disappointed with this technic, turned to the transventricular approach for valvular dilatation, advocated by Logan,l’ with supposed greater improvement in clinical
T
results over those previously obtained. The enthusiasm of the advocates employing transventricular dilatation suggests that in their hands substantially greater benefit is afforded their patients than is possible by the transatrial method. However, little supportive hemodynamic data have been reported in behalf of this technic. MorrowI demonstrated the superiority of transventricular dilatation; only 5 of 25 patients had residual atrioventricular gradients greater than 8 mm. Hg at the time of the operative determination in contrast to a residual gradient greater than 8 mm. Hg in 24 of 50 patients in whom the transatrial approach was used. Even though this technic is obviously of greater benefit to the patient than the transatrial dilatation approach, 5 of the 25 patients, or 20 per cent, still had a persistent gradient of 8 mm. Hg or greater, which, according to Morrow, is a significant gradient. Also, the fact that 80 per cent had gradients across the mitral valve of less than 8 mm. following transventricular dilatation under basal operative conditions does not imply that a similar lack of gradient would be present if the tests were later performed with exercise or that this is indicative of maximal improvement. Past experience has shown that left atria1 pressures taken during operation under basal conditions were always considerably lower than those obtained with and without exercise at the time of postoperative evaluation. In Morrow’s series of 25 patients no significant mitral regurgitation occurred with the transventricular dilatation technic, but Bj6rk13 observed a
Editorial
2
known that the deleterious effects of even a minor valvular regurgitation may take a number of years to become clinically significant. OPEN VERSUS CLOSED TECHNICS Because of dissatisfying results obtained in the closed transatrial technics, we turned to the open approach for valvular correction employAntagonists ing extracorporeal circulation.14 of the open technic state that it is more cumbersome and associated with greater risk in contrast to the closed technics which are “simple, quick and easy.” Obviously, the open technic is more complicated, time-consuming and exacting, but if it is more beneficial to the patient, Experience other considerations are secondary. has also shown that the open technic is not associated with a higher risk nor operative mortality. To the contrary it is associated with a lower risk for comparat)le valvular lesions, in addition to enabling the surgeon to correct conditions and complications unanticipated not correctable by closed technics. In the past, successful surgical relief of mitral stenosis by closed technics has been dependent (1) the presence and degree of subupon: valvular fusion of the chordae papillary structures, (2) the degree of calcification, (3) whether or not regurgitation was present, produced or aggravated, and (4) the completeness of the correction. t\lthough Logan and Turner’s” clinical impression of the marked superiority of transventricular dilatation over the transatrial approach in a large series of patients points to the advantages of this technic, in only .28 per cent of their patients was it possible to dtvrde completely both stenosed commissures. The incidence of traumatic regurgitation occurring or increasing following transventricular dilatation as determined by the presence or character of a postoperative murmur was 19 per cent and this increased to 39 per cent when only the posterior commissure was completely divided. Reported operative mortality for the transventricular dilatation has ranged from 6.4 per cent” to By means of the open approach, 12 per cent.“’ it is routinely possible to divide both commissures and to relieve subvalvular stenosis to a far greater degree than by closed technics. Considerable amounts of calcification can be removed, and regurgitation can he corrected when present, produced or aggravated. Most past evaluations have been based on clinical appraisal of improvement after opera-
tive correction of mitral stenosis. Evaluations based upon hemodynamic improvement have either not been made or are incomplete, inconclusive, or discounted for lack of correlation with clinical improvement. In our patients operated by closed technics, those with clinical but no hemodynamic improvement were the ones who later showed signs and symptoms of valvular obstruction; no patients who showed marked hemodynamic improvement had trouble subsequently. As previously reported,14 only 22 per cent of Class III and IV patients who had complete pre- and postoperative physiologic studies had essentially normal hemodynamic findings following surgery-. INDICATIONS EOR OPEN TECHNIC Superior hemodynamic results were obtained in patients with recurrent signs and symptoms of mitral stenosis who were reoperated by the open technic using extracorporeal circulation compared to those obtained using the closed technics. As a result, the open technic was adopted 4 years ago for all patients with mitral stenosis. It is true that a certain percentage of patients have adequate benefits from the closed technics, but this group is small (10 to 20 per cent); and furthermore, it is impossible to foretell which patients will react favorably. Initially, an attempt was made to use closed technics for the “simple” case and open technics for the “complicated” valves, but it was soon evident that this preoperative differentiation was impossible. We were not satisfied with the use of closed technics as the postoperative clinical improvement did not seem to indicate that maximal benefit had been provided. Because so few closed technic operations were as successful as the majority of the open technic operations, we decided that the ideal surgical approach should I)e one that would be the most successful for the greatest number of patients. The criticism that the open technic employing the heart-lung machine subjects the patient to greater risk is not necessarily valid, in that the operative mortality with the open procedure has not been greater than that reported for the closed technics, even though the more seriously ill who could not have been helped otherwise were submitted to surgery for complicated valve conditions. Unquestionably, surgical correction by the open technic is more complicated, and the ability to recognize the anatomicopathologic landmarks of the diseased valve necessitates a completely new orientation that THE
AMERICAN
JOURNAL
OF
CARDIOLOGY
Editorial
3
TABLE 1 Postoperative Hemodynamic Studies Following Closed Technic
Case
1 2 3 4 5 6 7
Pulmonary Artery Pressure (mm. %I Exercise Rest 70/28 105/25 32/15 55/2 42,‘18 77/5 63/40
45/25 95/55 62/30 98/40 80/44
Following Open Technic PC* (mm. Hg)
32/21
Pulmonary Artery Pressure (mm. Hg) Rest Exercise 40/18 68/28 19/17 35/12 21/6 25/9 42/22
30/12 42/19 31/15 34/19 55/24
/
PC*
( mm. Ha)
I 1 I I/ ~
21/18 22/18 (9) 12/6 9/7
* Pulmonary capillary wedge pressure. Figures in parentheses = mean pressure. requires time, patience and considerable study for proper correction. But if the surgeon is willing to employ this more exacting technic, greater correction can be accomplished. RESULTS OF OPEN TECHNIC REPAIR One hundred and six patients with mitral stenosis have been operated upon by the open approach. Fifty-seven patients (54 per cent) had suhualvular stenosis from chordae papillary fusion to the extent that, in the opinion of the surgeon, separation could not have been accomplished as effectively “blindly,” regardless of the type of closed dilatation employed. Twenty-eight patients (26 per cent) had associated regurgitation in whom the maximal opening of the stenosed valve could not have been made without unduly increasing the degree of regurgitation. This was of no concern in the open technic, for it was then possible to correct the factors producing the regurgitation. In 19 patients (18 per cent) with severe calc$ication, greater valvular mobility not possible by the closed method was accomplished by the removal of considerable calcification. There was an operative mortality of 8 per cent in the 106 patients operated upon by means of the open technic. This has been reduced to 5 per cent in the last 40 patients. This compares to the closed technic operative mortality of 4 per cent in 200 patients. Of the 9 patients dying following the open correction, 7 patients had either completely clotted auricles or extensive calcific destruction of the mitral valves which in four instances required valvular replacement with artificial valves. Closed operation would not have been possible in these JULY1962
patients. Myocardial infarction from coronary artery disease caused the seventh patient’s death, and myocardial failure the eighth death of a patient who had been operated upon previously. POSTOPERATIVEEVALUATION Of equal importance is the de
Editorial is greater then that provided I)y the closed technic (31 per cent). Evidence and impressions based on hemodynamic findings obtained by cardiac catheterization obviouslv do not present the entire clinical picture Ijut’should at least be more accurate than analysis I)ascd on clinical impressions alone. Factors Influencing Operative Results: Success in the surgical relief of mitral stenosis depends on (1) the status of the myocardium affected l)y rheumatic fever and by chronic strain from valvular obstruction ; (2) the status of the stenosed valve--whether it is fibrotic but pliable; heavily scarred with subvalvular stenosis from matting together of the leaflets, chordae tenor heavily dineae, and papillary muscles; calcified; and (3) the status of the pulmonary vasculature. Other lesser factors are the age of the patient, the chronicity of the obstruction and the presence of atria1 fibrillation. Factors 1 and 3 are somewhat under the control of the physician who has followed the patient’s course over a number of years. Surgical intervention prior to irreversible pulmonary hypertension and chronic myocardial strain undoubtedly will improve the results. Greater effectiveness of the open technic will bring further benefits and, in the future, will probatjly entail the greater use of partial and complete artificial valves. SUhM4RY
With accumulated experience, it became increasingly apparent that maximal valvular correction by the closed technic was not possible or entirely successful because of subvalvular stenosis, calcification or aggravation of regurgitation. One hundred and six patients have now had valvular correction I,y means of the open approach employing extracorporeal circulation with far greater improvement than previously provided by the closed approach. Postoperative physiologic studies demon-
strated marked hemodynamic improvement and greater valvular correction by the open technic in twice as many patients with mitral stenosis as the closed technic. EARLE B. KAY, M.D., F.A.C.C. HENRY A.~IMMERMAN, M.D.,F.A.C.C. St. Vincent Charity Hospital
Cleveland,
Ohio
REFERENCES 1. BRUNTON,L. Preliminary note on the possibility of treating mitral stenosis by surgical methods. Lancet, 1: 352, 1902. 2. ALLEN, D. S. and GRAHAM,E. A. Intracardiac snrgery-a new method. J.A.M.A., 79: 1028, 1922. 3. CUTLER, E. C. and LEVINE, S. A. Cardiotomy and valvulotomy for mitral stenosis. Boston Med. B Surg. J., 188: 1023, 1923. 4. SOUTTAR, P. W. The surgical treatment of mitral stenosis. Brit. M. J., 2: 603, 1925. 5. BOURNE, G. The surgical treatment of mitral stenosis. St. Barth. Hosp. J., 35: 22, 1927. 6. BAILEY, C. P. Surgical treatment of mitral stenosis (mitral commissurotomy). Dis. Chest., 15: 377, 1949. 7. HARKEN, D. E., ELLIS, L. B., WARE, P. F. and NORMAL, L. R. Surgical treatment of mitral stenosis. 1. Valvulonlastv. New Eneland J. Med., 239: 801, 1948. ’ 8. BAKER, C., BROCK, R. C. and CAMPBELL, M. Valvulotomy for mitral stenosis: Report of six successful cases. Brit. M. J., 1: 1283, 1950. 9. COOLEY, D. A. and STONEBURNER,J. M. Transventricular mitral valvotomy. Surgery, 46 : 414, 1959. 10. GERBODE, F. Transventricular mitral valvotomy. Circulation, 21 : 563, 1960. 11. I,OGAN, A. and TURNER, R. Surgical treatment of mitral stenosis. Lancet, 2: 874, 1959. 12. MORROW, A. G. and BRAUNWALD, N. S. Transventricular mitral commissurotomy. J. T/ioracic GY Cardiouas. Surg., 41 : 225, 1961. 13. BJ~RK, V. O., HOLMDAHL,M. and LBF, B. Transventricular mitral valvulotomy under controlled hypotension. J. Thoracic @ Cardiovas. Surg., 41: 236, 1961. 14. KAY, E. B., NOQUEIRA, C. and ZIMMERMAN, H. A. Surgical treatment of mitral stenosis by open technic. .J.rl.M.~-l., 173: 1644, 1960.
THE AMERICANJOURNALOF
CARDIOLOGY