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Prosthetic heart valve replacement

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									                                                                                                                       SAMT   DEEL 68   9 NOVEMBER 1985       755




 Prosthetic heart valve replacement
 Choice of prosthesis in a young, underdeveloped population group

 M. DE J. ANTUNES

                                                                                                     More information has been gathered on the Starr-Edwards
                                                                                                 valve than on any other prosthesis, because it has been used
     Summary                                                                                     most widely and for the longe t time. However, no other valve
     Despite recent advances in the perfection of cardiac                                        has undergone as many modifications of the original design,
     valve prostheses', complications still bedevil the                                          including curation of the silicone rubber poppet, the cloth
     currently available models. To a degree, valve replace-                                     covered struts, the hollow stellite ball, the composite seat and
     ment is simply exchanging one disease for another.                                          the extended cloth cover of the ring. Only a slight improvement
     Mechanical prostheses are durable but associated                                            has been produced in the thrombo-embolic rate, now reported
                                                                                                 at 2 - 9% per patient year for valves in the mitral position 5 - 7
     with a high incidence of thrombo-embolic complica-
     tions, while tissue valves are more resistant to                                            Ironically, some of these modifications introduced other
     thrombosis and thrombo-embolism but lack durability.                                        complications, such as haemolysis, thrombotic obstruction
     The choice of prosthesis must be tailored to the                                            and embolization of prosthetic material, 9 and there has been a
     individual patient's requirements, keeping in mind                                          return to the old non-cloth-covered silastic ball models 6120
     the social, economic and cultural characteristics of                                        and 1260, which are the only ones currently available.
     the population.                                                                                Transvalvular gradients of 4 - 20 mmHg are often aggravated
                                                                                                 by fibrous tissue ingrowth around the valve orifice. 10.11 Another
        Qualified support for conservative valve surgery
     (valvuloplasty) whenever reasonably possible would                                          significant problem associated with the caged-ball prosthesis is
                                                                                                 the 'third orifice' (represented by the pace for blood flow
     seem appropriate, even if it is later proved to have
     limited durability.                                                                         around the ball), which occurs most often in patients with
                                                                                                 mitral stenosis and a small or hyper3ti?ghied left ventricle, and
                                                                                                 III those WIth a narrow aortIC root. . -.   In extreme cases, the
     S Air Med J 1985; 68: 755-758.
                                                                                                 ventricular wall can impinge on the cage and impair the
                                                                                                 movements of the poppet. 14 Hence it appears appropriate to
                                                                                                 limit the use of these valves to patients with large ventricular
                                                                                                 cavities due to volume overload of pure or predominant mitral
Since the introduction of the caged-ball valve by Harken er                                      regurgitation and to those with large aortic roots."
al. I and Starr and Edwards 2 in 1960, close to a million                                           The tilting-disc prosthesis was for a long period best
prostheses have been implanted in patients throughout the                                        exemplified by the Bj6rk-Shiley valve, which has good haemo-
world. Yet despite immense strides made towards the improve-                                     dynamic properties and a more central flow pattern. 16 However,
ment of design and materials during the past 2 decades, the                                      it has a high combined rate of thrombo-embolism and
ideal prosthesis remains elusive. The characteristics of an ideal                                thrombotic obstruction, which in our experience reached 8%
valve substitute include good haemodynamics, freedom from                                        per patient year. 17 Modifications introduced include the
thrombogenicity, lifelong durability and free availability.) Other                               concave-convex diSC,18 aimed at improving flow characteristics
important but non-essential features are ease of implantation,                                   and reducing areas of stasis, and more recently the monostrut
silent function and low cost.                                                                    model. The former has had disastrous structural failures and
                                                                                                 there has as yet been insufficient clinical experience with the
                                                                                                 latter. However, the original model is still used successfully in
The available prostheses                                                                         many centres throughout the world.
                                                                                                    Recently a new generation of mechanical valves has been
The variety of prostheses available for implantation demon-                                      introduced, ostensibly with better haemodynamic and anti-
strates the inadequacies of all existing designs. 4 They can be                                  thrombotic properties: the St Jude Medical bileaflet valve and
categorized into two groups - mechanical and tissue valves.                                      the Medtronic-Hall valve. Both prostheses have negligible
                                                                                                 transvalvular gradients, even in the smaller sizes. The two
                                                                                                 leaflets of the St J ude prosthesis, opening to 80°) permit a
Mechanical valves                                                                                near-laminar flow pattern and create little obstruction. The
   Among the several types of mechanical valves, many of                                         wider opening (70 - 75°) of the occluder of the Medtronic-
which had little or no practical impact, the Starr-Edwards                                       Hall valve increases the size of the small orifice and reduces
caged-ball and the Bj6rk-Shiley tilting-disc prostheses have                                     the areas of stasis. A slightly higher degree of haemolysis ha
stood the test of time and set the 'gold standard' against which                                 been demonstrated with this valve, but it has no clinical
all other prostheses must be evaluated.                                                          significance. 19,10
                                                                                                    Although many improvements have been introduced in the
                                                                                                 manufacturing characteristics of cardiac valve prostheses, no
                                                                                                 significant advance has been made towards solving the problems
Department of Cardiothoracic Surgery, Baragwanath
                                                                                                 of anticoagulation, which is still essential with all mechanical
Hospital and University of the Witwatersrand, Johannes-
                                                                                                 prostheses. Oral anticoagulants (warfarin, coumadin, ete.) are
burg
M. DE J. ANTUNES, L.M. (LOURE~<;:O MARQUES), M.MED. (CARDIO-                                     more effective and easily administered than is systemic
THORSURG.), Principal Cardiorhoracic Surgeon                                                     heparinization. Attempts at impregnating prostheses with
                                                                                                 heparin to render them resistant to thrombosis have not yet
This work forms part of a thesis for the Ph.D. (Med.) degree, Universiry of {he Witwatersrand.   succeeded. A heparin pump which permits slow subcutaneous
 756      SAMJ   VOLUME 68    9 NOVEMBER 1985



 release of the drug is being perfected and may soon become            has been made towards the prevention of mineralization of the
 available for clinical trial. If successful, it could revolutionize   valve, this goal does not appear to be within sight. Among the
 cardiac valve replacement.                                            new valves incorPOrating most of these advances is the Xenotech
                                                                       porcine prosthesis, which may in the near future become the
                                                                       bioprosthesis of choice.
Tissue valves
    The porcine and the bovine (pericardial) xenografts are the
  most commonly used tissue valves. Homograft aortic valves            Selection of prosthesis
  are used for substitution of the aortic valve but are unsuitable
  for use in the mitral position, where they need to be stented,         With so many types of prosthesis available, the choice is
 thereby losing their favourable haemodynamic characteristics            difficult. In making his selection the surgeon and cardiologist
 and durability.21 Homografts are probably still the best aortic         should have in mind such factors as the characteristics and
  valve substitute. However, supply is usually not sufficient for        mean age of the population. A definite plan should be made
  the demands of most units, and the preparation of these valves         using a limited number of prostheses, perhaps with a basic
 is time-consuming. Hence their popularity has declined                  choice and another one or two for use in special cases or
  markedly in the past decade. Perhaps this is the right time to        groups.
  reconsider.                                                               I prefer a mechanical prosthesis for a population group with
    The tissue valves were developed as a direct response to the         a low mean age. In these circumstances we have had poor
 thrombo-embolic complications which plagued the original               experience with all types of bioprostheses, and both the St
 mechanical valves, but expectations of complete freedom from           Jude Medical and Medtronic-Hall valves have yielded the best
 thrombogenicity were not fulfilled and thrombo-embolic rates            results of all mechanical prostheses used. However, as these
 of 2 - 5% per ,~~~ient year have been reported at:ter mitral valve      were not used simultaneously or in identical circumstances,
 replacement.-- - However, these rates are still slgmficantly           comparisons may not be entirely valid. The choice of a
 lower than those associated with most mechanical prostheses,           mechanical prosthesis for children appears to be justified
 especially when it is considered that the majority of patients         further by recent reports of decreased thrombogenicity in this
 do not receive anticoagulation therapy. The major advantage            age group.36,3)
 of these valves still lies in the fact that anticoagulation is not         Compliance with anticoagulation therapy remains a major
 required.                                                              problem in underdeveloped populations. We have experienced
    Haemodynamic studies have demonstrated transvalvular                this difficulty in the past, and the poor results then obtained
 diastolic gradients of 0 - 14 mmHg, depending on the size and          led to the switch to bioprostheses, which do not require
 model utilized. 25 - 27 The most popular porcine xenografts were       anticoagulation. However, a significant improvement in follow-
 the Hancock and the Carpentier-Edwards prostheses. The                 up was achieved by the introduction of two full-time social
 several modifications introduced in the original designs resulted      workers to the programme. It is postulated that the psycho-
 in significant reductions of the transvalvular gradients, which        logical impact of someone from the hospital calling at the
 now compare bener with those observed in some of the more              patients' doorstep improved motivation to attend the clinic.
 commonly used mechanical prostheses. 28 The bovine pericardial         The surgical team cannot alienate themselves from the prevalent
 valve, initially created by Ionescu and developed in co-operation      social and geographical factors. More than half of our patients
 with the Shiley Laboratories, evolved from the quest for bener         live outside the regional boundaries of the Baragwanath
 haemodynamic performance. The popularity of the pericardial            Hospital, and a large percentage live more than 100 km away.
 valve has increased in recent years and the Edwards, Hancock           Co-operation of the local hospitals and attending physicians
 and other laboratories now produce and market their own                has been sought and obtained in most cases.
 models. Although much lower systolic gradients are observed               The question of the advisability of using bioprostheses in
 in the aortic position, the mean transvalvular diastolic gradients     the older patient is as yet unanswered. Although biodegradation
 of mitral prostheses are similar to those of the porcine xeno-         is a much slower process in this age group,24 currenily available
grafts. 29 .3o However, it appears that the characteristics of flow     models still have limited durability and it appears probable
 through the pericardial valves, with symmetrical opening of            that reoperation at a more advanced age, with increased risk,
the three cusps and abolition of areas of stasis in the sinuses,        will be required. On the other hand, bioprostheses are probably
 result in a lower incidence of thrombo-embolism. 31 One of the         indicated in all patients in whom anticoagulation is contra-
most significant disadvantages of the Ionescu-Shiley valve was         indicated or undesirable and in women of the appropriate age
its high profile, which often caused impingement of the                who want to have children, The former group includes patients
ventricular wall and/or left ventricular outflow obstruction. A        with coagulation anomalies or bleeding gastric or duodenal
lower-profile pericardial valve was introduced by the Edwards          ulcers, patients subjected to heavy trauma, mentally retarded
 Laboratory, and the concept is also used in a new Ionescu-            patients and those who live in places where adequate anti-
Shiley model.                                                          coagulation control is not possible. The risks of anticoagulation
    The major disadvantage of the tissue valves in general is          during pregnancy are well known and include fetal teratogenesis
lack of durability. Early degeneration and calcification is            in the early phase and fetal and maternal haemorrhage in the
particularly evident in children, and occurs at a rate of 5 - 20%      later stages. 38 - 39 Fetal abnormalities usually result in
per patient year. 32 - 34 The rate of failure is much lower in         spontaneous abortion, affected babies rarely being born, while
adults, but currently available evidence indicates that the            haemorrhagic complications are greatly reduced by adequate
original glutaraldehyde-preserved models last for a mean of            adjustment of the anticoagulation protocol. 40 Although the
8 - 12 years. There is as yet no proof that the pericardial valves     overall rate of complications is decreasing, the choice of a
are more durable. Recent improvements in the harvesting and            bioprosthesis for women of childbearing age still seems
fixation of the porcine xenografts have revived the hopes for          appropriate, especially for patients in the 3rd and 4th decades
increased durability of these prostheses. 35 The introduction of       of life. However, recent evidence of accelerated calcification
low (or zero) pressure fixation appears to preserve the physical       during pregnancy places a question mark over the eventual
characteristics of the collagen fibres better. On the other hand,      benefits of using bioprostheses in these patients.
modifications of the mounting process, including improvements              In summary, the choice of prosthesis should be tailored to
of the stent, have reduced the stress on the leaflets and              the patient's requirements, keeping in mind the social, economic
improved resistance to tissue fatigue. Although some progress          and cultural characteristics of the population.
                                                                                                  SAMT     DEEL 68     9 NOVEMBER 1985              757


Results                                                               of 90%. The incidence of valve-related complications such as
                                                                      thrombo-embolism and ineffective endocarditis is extremely
In our unit over 2000 valve replacements have been performed          low, but reoperation was required in approximately 10% of the
since 1976. 19 ,24,41-44 The mean age of the patients was 30 years,   patients (5,6% per patient year). The incidence of reoperation
one-third being aged 20 years or younger. The operative               was much higher in patients under 20 years of age (68% of
mortality depends largely on the functional class of the patients     reoperations), which appears to be related to persistent or
at the time of surgery. In our more recent experience, the early      recurrent rheumatic activity.
mortality was 5,6%. However, if only New York Heart Asso-
ciation class II or III patients undergoing elective operations
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surgery (35,7%). Late mortality averaged 7,5% per patient              6. Macmanus Q, Grunkemeyer GL, Lambert LE, Teply JF, Harlan BJ, Starr
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                                                                       7. Craig-Miller D, Oyer PE, Stinson EB ee al. Ten to fifteen year reassessment
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                                                                       8. Ahmad R, Manohitharah SM, Deverall PB, Watson DA. Chronic hemolysis
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degradation. Although most patients did not receive anti-                 composite-seat Starr-Edwards and frame-mount aortic homograft valves. J
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1,3% per patient year. Actuarial survival at 5 years was 65%.24           stenosis of Starr-Edwards cloth-covered prostheses. Ann Thorac Surg 1975;
Our experience confirms the poorer results of porcine xeno-               20: 249-255.
                                                                      10. Glancy DL, O'Brien K, Reis RL, Epstein SE, Morrow AG. Hemodynamic
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                                                                      11. Russel T, Kremkau EL, KIoster F, Starr A. Late hemodynamic function of
the patients were free from valve-related complications."                 cloth-covered Starr-Edwards valve prostheses. Circulaeion 1972; 45, 46:
   Late deaths of patients with mechanical prostheses were                suppl I, 8-13.
                                                                      12. Roberts WC, Morrow AG. Mechanics of acute left atrial lhrombosis after
valve-related in up to 20% of cases (2,3% per patient year),              mitral valve replacement: parhologic findings indicating obstruction    [Q   left
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                                                                      13. Seningen RP, Bulkley BH, Roberts Wc. Prosthetic aortic stenosis: a method
(systemic emboli and thrombotic obstruction) were the major               to prevent its occurrence by measurement of aortic size from preoperarive
causes of valve-related deaths (45%), followed by anticoagula-            aortogram. Circulation 1974; 49: 921-924.
tion-related bleeding and prosthetic valve endocarditis.              14. Ibarra-Perez C, Rodriguez-Trujillo F, Perez-Redondo H. Engagemem of
                                                                          ventricular myocardium by strut of mitral prosthesis: fatal complication of
Systemic thrombo-embolism occurred at a linearized rate of                use of open-eage cardiac valves.] Thorac Cardiovasc Surg 1977; 61: 403-404.
3,92% per patient year and was fatal or left neurological             IS. Bonchek LI, Starr A. Ball valve prostheses: current appraisal of late results.
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sequelae in 25% of cases (1,2% per patient year). The incidence       16. Bjork VO, Olin C. A hydrodynamic comparison between the new tilting disc
of systemic thrombo-embolism was 4 - 5 times greater in                   aortic valve prosthesis (Bjork-Shiley) and the corresponding prostheses of
                                                                          Starr-Edwards, Kay-Shiley, Smeloff-Cutter and Wada-Cutter in the pulse
patients in atrial fibrillation than in those in normal sinus             duplicator. Scalld] Thorac Cardiovasc Surg 1970; 40: 31-39.
rhythm. Thrombotic obstruction occurred at the rate of 0,65%          17. Copans H, Lakier JB, Kinsley RH, Colsen PR, Fritz VU, Barlow JB.
per patient year and half the episodes were fatal. Overall                Thrombosed Bjork-Shiley mitral prostheses. Circulaeion 1980; 61: 169-174.
                                                                      18. Bjork VO, Henze A.Ten years' experience with the Bjork-Shiley lilIing disc
actuarial survival was 77% at 5 years, but only 67% of the                valve.] Thorac Cardiovasc Surg 1979; 78: 331-342.
patients who survived the operation were free from valve-             19. Kinsley RH, Colsen PR, Antunes MJ. Medtronic-Hall valve replacemem in
                                                                          a Third World population group. Thorac Carditruasc Surg 1983; 31: suppl 11,
related complications during the same period.                             69-72.
   All the findings discussed above refer to a wide spectrum of       20. Kinsley RH, Colsen PR, Amunes MJ. St Jude Medical valve replacemem:
                                                                          an evaluation of valve performance. ] Thorac Cardiovasc Sllrg 1985 (in
population, largely of a Third-World type. The incidence of               press).
thrombo-embolic events was higher in the less developed               21. Graham AF, Schroeder JS, Daily PO, Harrison DC. Clinical and hemo-
population group, presumably owing to poorer compliance                   dynamic studies in patients with homograft mitral valve replacement. Circula-
                                                                          eion 1971; 44: 334-342.
with anticoagulation. However, evidence of hypercoagulability         22. Edmiston WA, Harrison EC, Duick GF, Parnassus W, Lau FYK. Thrombo-
has recently been demonstrated in this population.                        embolism in mitral porcine valve recipients. Am] Cardiol 1978; 41: 508-511.
                                                                      23. Oyer PE, Stinson EB, Reitz BA, Craig-Miller D, Rossiter SD, Shumway
                                                                          NE. Long term evaluation of the porcine xenograft bioprosthesis. ] Thorac
                                                                          Cardiovasc Surg 1979; 78: 343-350.
                                                                      24. Antunes MJ, Santos LP. Performance of glutaraldehyde-preserved porcine
Conclusion                                                                bioprosrhesis as a mitral valve substitute in a young population group. Ann
                                                                          Thorac Surg 1984; 37: 387-392.
These results demonstrate that valve substitution often replaces      25. Lurie AJ, Miller RR, Maxwell K, Vismara LA, Hurley EJ, Mason DT.
                                                                          Postoperarive hemodynamic assessmem of the glularaldehyde-preserved
one disease with another. Clearly every effort should be made             porcine heterograft in the aortic and mitral position (Abstract). Circulation
to preserve the patient's own valve, especially the mitral. We            1976; 53, 54: supplll, 148.
                                                                      26. Horowitz MS, Goodman DJ, Fogarty TJ, Harrison DC. Mitral valve
have adopted this policy since 1974. However, the results of              replacement with the glutaraldehyde-preserved porcine heterograft: clinical,
mitral annuloplasty were poor. 4S Rheumatic mitral valve disease          hemodynamic and pathological correlation.] Thorac Cardiovasc Surg 1974;
                                                                          67: 885-895.
is multifactorial and a simple suture plication annuloplasty          27. Johnson AD, Daily PO, Peterson KL ee al. Functional evaluation of the
cannot correct all the abnormal components of the mitral                  porcine heterograft in lhe micral posilion. Circular ion 1975; 50: suppl 11,
apparatus. A comprehensive valvuloplasty technique, following             40-48.
                                                                      28. Rossiter SJ, Miller DC, Stinson EB er al. Hemodynamic and clinical
the functional approach developed by Carpentier,46 has been               comparison of the Hancock modified orifice and standard orifice bio-
utilized in over 300 patients since January 1981. After a                 prostheses in the aortic position.] Thorac Cardiovasc Sllrg 1980; 80: 54-60.
                                                                      29. Tandon AP, Smith DR, Mary DAS, lonescu Ml. Sequential hemodynamic
striking learning curve,47 the results obtained were much                 studies in patients having aortic valve replacement with the lonescu-Shiley
improved. Current evidence indicates 4!h-year actuarial survival          pericardial xenograft. Ann Thorac Surg 1977; 24: 149-155.
 758        SAMJ     VOLUME 68       9 NOVEMBER 1985


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 31. Tandon AP, Whitaker W, lonescu MI. Multiple valve replacement with             40. Antunes M), Myers IG, Sanros LP. Thrombosis of mitral valve prosthesis
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     in porcine xenografts in children. Am] Cardiol 1980; 45: 685-689.                  heart valve replacement: an analysis of 170 patients. Ann Thorac Surg 1980;
 33. Sade RM, Ballenger JF, Hohn AR, Arrants JE, Riopel DA, Taylor AB.                  29: 415-422.
     Cardiac valve replacement in children: comparison of tissue with mechanical    42. Kinsley RH, Girdwood RW, Milner S. Surgical treatment during the acute
     prostheses.] Thorac Cardiovasc Surg 1979; 78: 123-127.                             phase of rheumatic carditis. In: Nyhus LM, ed. Surgery Annual, vol. 13.
 34. Sanders SP, Levy RH, Free MD, Norwood WI, Castaneda AR. Use of                     _few York: Appelton-Century-Crofts, 1981: 299-323.
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     46: 429-438.                                                                       cardiac prosthesis. In: DeBakey ME, ed. Advances in Cardiac Valves. New
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                                                                                        curve. Circulation 1983; 68: supp! 11, 70-75.




 Carbon dioxide laser surgery for cervical
 intra-epithelial neoplasia
 A report on 300 cases

G. L. GOLDBERG,                      B. BLOCH,              J.1. EDWARDS,                   C. A. GIE,          LORRAINE FINKELSTEIN

                                                                                    alternative effective method of treatment for Cl T Ill, which
    Summary                                                                         is acceptable and which could be used on ambulant patients,
                                                                                    resulted in the use of the CO 2 laser. The laser principle was
    The CO 2 laser was used to treat 300 patients with                              initially proposed by Schawlow and Townes 2 in 1958 and the
    cervical intra-epithelial neoplasia (GIN). The patient                          CO 2 laser was developed in 1966. It was coupled with a
    characteristics, histological features, complications                           microscope for microsurgery by Jak0 3 and first used in gynae-
    and follow-up are described and our experience is                               cological surgery by Kaplan el al. 4 in 1973.
    discussed. The G0 2 laser appears to be safe and                                   Reports on the treatment of CIN with the CO 2 laser first
                                                                                                                                                7
    efficient for outpatient treatment of GIN, with a cure                          started to appear in the literature in 1977 and 1978. 5 - The
    rate of 94%.                                                                    results of these initial series were disappointing and just about
                                                                                    comparable with those from other less expensive outpatient
    S Atr Med J 1985; 68: 758-760.                                                  techniques. Results of recent laser series are much more
                                                                                    encouraging and the first-time cure rate is now approaching
                                                                                    96%.8-10
                                                                                       In the present series of 300 patients these latter results are
There has been a definite trend in recent years towards                             matched.
conservative management of cervical intra-epithelial neoplasia
(CIN), especially CIN III or carcinoma in situ. Cervical
conization and hysterectomy have in the past been the main                          Patients and methods
treatments for carcinoma in situ of the cervix. Cryotherapy has
recently become popular for treating Cl .1 The search for an                        Benveen September 1982 and the end of December 1983, 300
                                                                                    women with CIN were treated at the Colposcopy and Laser
                                                                                    Clinics at Groote Schuur Hospital. Patients with abnormal
Colposcopy and Laser Clinics, Department of Obstetrics                              Papanicolaou smears are referred to the Colposcopy Clinic for
and Gynaecology, University of Cape Town and Groote                                 assessment and directed biopsy specimens are taken. Patients
Schuur Hospital, Cape Town                                                          with CrN lesions who were under 35 years of age and of low
G. L. GOLDBERG, .\1B. CH. B., M.R.C.O.G.                                            parity and who wished to have more children were selected for
B. BLOCH, .\I.MED. (0. & G.), F.R.C.O.G.                                            laser surgery. Exceptions were made depending on individual
J. T. EDWARDS, M.B. CH. B., M.R.C.O.G., F.R.C.S. (Present address:                  circumstances and requests.
University College Obstetric Hospital, Huntley Street, London)
                                                                                       A Sharplan CO 2 laser attached to a Zeiss colposcope was
C. A. G lE, M.B. CH. B., M.R.C.O.G., F.C.O.G. (S.A.)
LORRAINE FI KELSTEIN, RS., R.M.                                                     used. By combining a 200 mm focal length objective lens on
                                                                                    the colposcope and a 400 mm focal length lens on the laser

								
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