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Circulation. 2000;102:IV-24-IV-33

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(Circulation. 2000;102:IV-24.)
© 2000 American Heart Association, Inc.

Special Anniversary Issue

Valvular Heart Disease

Shahbudin H. Rahimtoola, MB, FRCP; Robert L. Frye, MD

From the Griffith Center, Division of Cardiology, Department of Medicine, Los Angeles County and University of Southern California Medical Center, Keck School of Medicine of the University of Southern California; and the Division of Cardiology, Department of Internal Medicine, Mayo Clinic and Foundation, Mayo Medical School, Rochester, Minn.

Science is about the systematic collection of data and the interpretation of that data. Dr Stanley B. Prusiner 1997 Nobel Laureate in Physiology/Medicine

Era Before 1950

In 1950, rheumatic valvular heart disease (VHD) was the most common cause of VHD. The link between streptococcal infection and rheumatic fever was established, and a successful trial of penicillin prophylaxis against rheumatic fever was reported.1 In 1944, Jones published a seminal article on diagnosis of rheumatic fever.2 The American Heart Association (AHA) and Circulation played an important role in communicating the importance of (1) penicillin prophylaxis, which resulted in a dramatic reduction of rheumatic fever and rheumatic VHD, and (2) diagnosis of rheumatic fever, by revising the Jones criteria in 1956, 1965, 1984, and most recently in 1992.3

It was well recognized that the mitral valve was the valve most commonly affected in rheumatic heart disease. As a consequence, closed-chest mitral commissurotomy for mitral stenosis (MS) was the most common early and successful cardiac surgical intervention. 1950 was the first year of Circulation, and one of the articles published that year described the surgical experience in 8 patients.4

The etiology of mitral regurgitation (MR) in 1950 was rheumatic carditis; mitral valve prolapse (MVP) was not even recognized. As late as 1958, the following quote reflects the lack of recognition of MVP: "mid- and late systolic clicks are commonly produced by the tensing of pleuropericardial adhesions"; thus, MVP was considered to be of extracardiac origin.5

Circulation in 1950 had a smaller number of articles regarding VHD than one might expect. Some of the articles are of interest: (1) There were several articles on subacute bacterial endocarditis. One of these included the Lewis Conner Lecture by Bloomfield, "The Present Status of Treatment of SBE."6 (2) Levinson et al7 discussed the "Increasing Bacterial Resistance to the Antibiotics ... ," a recurring theme in today’s literature.7 (3) The absence of noninvasive diagnostic imaging and hemodynamic assessment of VHD is striking. Also, the limitations in surgical therapy of congenital VHD before the development of open-heart surgery are obvious. An example of these 1950 realities is provided by Engle and Taussig’s article,8 which includes the early use of cardiac catheterization and angiocardiography to differentiate between tetralogy of Fallot and valvular pulmonary stenosis in other settings. This represented a critical distinction in those days before open-heart surgery. The former was treated with a Blalock-Taussig anastomosis, and the latter was treated with closed pulmonary valvotomy. (4) There were several articles on cardiac catheterization and other efforts to enhance diagnosis of VHD. These included one of the first articles on left heart catheterization via the retrograde crossing of the aortic valve.9 (5) There was a study of the electrokymograph in analysis of aortic and pulmonary valve regurgitation.

A common cause of isolated severe aortic regurgitation (AR) in 1950 was tertiary syphilis.10

In summary, the state of knowledge in 1950 included (1) detailed and remarkably accurate bedside clinical descriptions and increasing understanding of the natural history of VHD; (2) an understanding of the pathogenesis of rheumatic fever, its diagnosis, and effective prophylaxis of rheumatic heart disease; and (3) recognition of the need to improve diagnostic precision in anticipation of the future development of open-heart surgery. In fact, it is the successful implementation of open-heart surgery that forced improvements and refinements in all aspects of cardiovascular medicine and surgery.

Era 1950 to 2000

Julius Comroe Jr emphasized that breakthroughs in medicine are a culmination of advances in many different areas (Figure 1Down).11 Thus, it is our goal to "walk through" succinctly how we have arrived in 2000 at a very advanced state in treatment of VHD.



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  		Figure 1. Figure 1Up. Left, Did the cardiac surgeon make one giant leap to the pinnacle? Or (right) did he climb the steps up the back of the mountain? From Reference 11.

Prophylaxis for Recurrences of Rheumatic Fever
A randomized trial of 405 children was started in 1954 in Irvington House12 ; the final 6-year data are shown in Table 1Down. The recommendations of the AHA for prophylaxis of recurrences of rheumatic fever are the standard of practice in the United States (Table 2Down).13 The AHA has also contributed in a major way by continuously providing updated educational materials and also by continued revisions of the recommendations for prophylaxis against bacterial endocarditis.14


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  		Table 1. Recurrence of Rheumatic Fever


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  		Table 2. American Heart Association Recommendations for Prophylaxis of Recurrence of Rheumatic Fever

Invasive Studies
In a seminal article, Gorlin and Gorlin15 used information derived from hydraulic systems to derive the following equations:

where AVA is aortic valve area (AVA) (cm2), CO is cardiac output (L/min), HR is heart rate (bpm), SEP is systolic ejection period (seconds), 44.3 is a constant, and gradient is mean systolic aortic gradient (mm Hg).

The MVA equation was revised by Gorlin16 :

where MVA is in cm2 and gradient is mean diastolic mitral gradient (mm Hg).

These equations have stood the test of time and are the standard for assessment of severity of valve stenosis.

This led to a series of attempts to measure left atrial and left ventricular (LV) pressures directly. The transseptal technique developed by Ross17 (subsequently an editor in chief of Circulation, 1988 to 1992) is still in use, particularly in patients with MS undergoing catheter balloon commissurotomy (CBC) and in selected patients with aortic stenosis (AS) and mitral/aortic prosthetic valves. The use of a systemic arterial site for retrograde entry into the LV, accelerated by percutaneous entry into a systemic artery (Seldinger technique),18 facilitated the performance of aortic and LV angiography, which was essential for assessment of AR/MR and calculation of LV volumes and ejection fraction (EF).19 The percutaneous technique later led to the development of the Judkins technique20 for coronary arteriography, which largely replaced the pioneering Sones technique,21 which had used the cut-down technique for arterial entry.

These diagnostic invasive techniques are still the bedrock for assessment of severity of VHD in many patients and assessment of extent and severity of associated coronary artery disease.

Valve Surgery
In 1951, Bailey reported closed transventricular aortic valve commissurotomy for AS.22 This produced significant AR and was abandoned altogether after heart valve replacement (VR) was developed.

After Bailey’s and Harken’s efforts at closed mitral commissurotomy in the late 1940s, transatrial and transventricular dilation in the 1950s improved the results that were obtained.

In 1954, John Gibbon, Jr described the use of total cardiopulmonary bypass for intracardiac surgery23 (Figure 2Down), which had an enormous impact on and completely changed the performance of valve surgery.



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  		Figure 2. Figure 2Up. The Gibbon pump. A, Front view showing recording and control instruments and lung suspended above cabinet on left. B, Oblique rear view showing rotary blood pumps and battery-type screen lung suspended above cabinet on right side. From Reference 23.

In 1956, Lillehei performed successful open mitral commissurotomy. With experienced and skilled operators, the long-term results of closed and open mitral commissurotomy in appropriate patients are similar when the baseline patient characteristics are the same.24

Also in 1956, Lillehei and associates performed open annuloplasty for severe MR.25 However, largely because of the report of Carpentier in 1971,26 mitral valve repair revolutionized the surgical management of many patients with severe MR.

1960 was the start of heart VR. Two major classes of valves for heart VR are (1) mechanical prosthetic valves and (2) biological (tissue) valves, which include autograft, homograft (allograft), and bioprosthesis (xenograft). Mechanical heart valves were first used in 1960 by Harken et al27 and Starr and Edwards (Figure 3Down).28 The use of homografts was first described by Ross29 and by Barratt-Boyes30 in 1962 and 1964, respectively. Heterografts (xenografts) were first used by Carpentier in 196531 ; in 1971, Carpentier used the term bioprosthesis for heterografts (Figure 4Down).32 Ross described the use of autografts in 1967.33



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  		Figure 3. Figure 3Up. The Starr-Edwards valve, which is virtually unchanged since 1965. From: Valvular heart disease. In: Rahimtoola SH, ed. Atlas of Heart Disease. St Louis, Mo: CV Mosby; 1997.



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  		Figure 4. Figure 4Up. Bioprostheses. A, Hancock porcine valve. B, Carpentier-Edwards pericardial valve. From: Valvular heart disease. In: Rahimtoola SH, ed. Atlas of Heart Disease. St Louis, Mo: CV Mosby; 1997.

It was Starr’s initial results that changed the scene.28 Of his first 8 patients (all were in NYHA functional class IV), 6 survived and left the hospital, and several returned shortly thereafter to an active life. The longest known survival of these 8 patients is 31 years. In the 1950s, Starr thought that he would have no chance of obtaining research funds from national agencies and organizations because he was young and without a track record and because the feasibility of his proposed techniques being successful was unproven. Therefore, he turned to the Oregon Affiliate of the AHA for funding of his initial research.34 Of Starr’s series, the known maximal follow-up for aortic valve replacement (AVR) is 35 years and for mitral valve replacement (MVR) is 34 years (Table 3Down).


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  		Table 3. Actuarially Determined Complication Rates of Mechanical Valves, %

By the mid-1970s, it was recognized that the major clinical problem with mechanical valves was thromboembolism and that with bioprostheses was limited durability because of valve degeneration. To evaluate differences in patient outcome between these 2 types of prosthetic heart valves, the VA Randomized Trial was initiated. The principal long-term findings (average follow-up 15 years) of this randomized trial35 are as follows. (1) Use of a mechanical valve resulted in a lower mortality rate (66% versus 79%, P=0.02) and a lower reoperation rate after AVR (Figure 5Down). (2) The mortality rate after MVR was similar with use of 2 prosthetic-valve types. (3) There were virtually no primary valve failures with use of a mechanical valve. (4) Primary valve failure after AVR and MVR occurred more frequently in patients with a bioprosthetic valve, especially in patients <65 years old (AVR 26% versus 0%, P<0.001, and MVR 44% versus 4%, P=0.0001). (5) The primary valve failure rate between bioprosthesis and mechanical valve for AVR was not significantly different in those >=65 years old (Table 4Down). (6) Use of a bioprosthetic valve resulted in a lower bleeding rate. (7) There were no significant differences between the 2 valve types with regard to other valve-related complications, including thromboembolism, and all complications.



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  		Figure 5. Figure 5Up. DVA randomized trial: 15-year survival after AVR is better with a mechanical valve than with a bioprosthetic porcine valve. From Reference 35.


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  		Table 4. Primary Valve Failure Rate at 15 Years After AVR, %: VA Randomized Trial

Future studies will need to delineate (1) the optimal timing of valve surgery in asymptomatic and minimally symptomatic patients, (2) improvements in valve repair and VR devices, (3) optimal matching of an appropriate valve surgery procedure/device to an individual patient, (4) the ideal minimally invasive surgery, (5) percutaneous implantation of prosthetic valves, and (6) the proper role of robotic surgery.

Echocardiography: Doppler
The use of high-frequency ultrasound to assess cardiac structure and function is one of the great advances in the past 50 years; it has greatly enhanced our ability to safely and accurately make cardiac diagnoses noninvasively. Edler and Hertz36 first recorded movements of cardiac structures with ultrasound. M-mode studies had particular success in diagnosing the presence and severity of MS. Early efforts by Joyner37 and Feigenbaum38 led to the rapid development of echocardiography in clinical cardiology in the United States. These initial recordings of ultrasound reflections from cardiac structures provided only an "ice-pick" view of the heart. The development of 2D sector scanning allowed real-time tomographic images of cardiac morphology and function (Figures 6Down, 7Down).39 In the late 1970s, the addition of Doppler echocardiography allowed noninvasive hemodynamic assessment of VHD (Figure 8Down) and reduced the need for cardiac catheterization to obtain the hemodynamics of VHD, particularly in patients with mild to moderate valve lesions. Intracardiac pressure gradients, when obtained with meticulous care with Doppler (initially pioneered by Hatle40 ), were demonstrated to be reasonably accurate on the basis of careful comparison with simultaneously measured gradients at the time of cardiac catheterization.41 Widespread application of these techniques now allows assessment not only of VHD but also of LV systolic and diastolic function. Transesophageal echocardiography represents a further enhancement of echocardiographic study, which now has wide application, including intraoperative imaging, which has contributed importantly to enhancing surgical repair of valvular regurgitation42 and in diagnosis of infective endocarditis involving both native and prosthetic valves. Future important research includes improving methods for quantification of valvular regurgitation and simplification of technology to allow easy bedside application of ultrasound imaging of the heart and role 3D echocardiography. The major accomplishments since 1950 are summarized in Table 5Down.



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  		Figure 6. Figure 6Up. Postmortem specimen demonstrating anatomy of myxomatous mitral valve with prolapse and partial flail segment of posterior leaflet secondary to rupture of chordae. Specimen has been sectioned in a plane simulating a left parasternal long-axis view with 2D echocardiography.



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  		Figure 7. Figure 7Up. Echocardiogram demonstrating severe prolapse with partial flail segment of posterior leaflet of mitral valve (arrows). LA indicates left atrium; RV, right ventricle.



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  		Figure 8. Figure 8Up. 2D echo color flow imaging demonstrating a large, medially directed jet of severe mitral regurgitation. Abbreviations as in Figure 7Up.


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  		Table 5. Valvular Heart Disease: Major Accomplishments Since 1950

Aortic Stenosis
Calcific AS in the older patient is now the most common cause for VR, which will continue to increase because of the marked increase of life span of the population. Major advances have occurred:

  1. Severe AS is defined as AVA <=1.0 cm2 (<=0.60 cm2/m2).13 43
  2. Symptomatic patients with severe AS were shown to have a very high mortality without VR.44 45 46
  3. AVR was shown to improve survival, symptomatic state, and impaired LV function (Figures 9Down and 10Down).45 46 47
  4. Severe AS in older people has several distinctive features:
    A. The initial lesion may be an atherosclerotic plaque, which then by autoimmune reaction leads to calcification and stenosis.48
    B. Women have a much higher incidence of excessive LVH leading to a supernormal LVEF.49
    C. Heart failure is not an uncommon presentation.50 Such patients frequently have normal LV systolic function.
    D. A subset of patients who have severe AS with a low mean AV gradient and severe LV dysfunction (LVEF<0.35) have good results when treated with AVR.51



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  		Figure 9. Figure 9Up. Survival is better after AVR than with medical therapy in patients with severe AS. A, From Reference 46. B, From Reference 45.



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  		Figure 10. Figure 10Up. LVEF improves and even normalizes after AVR in patients with severe AS and clinical heart failure. From Reference 47.

All patients with severe AS have been shown to benefit from AVR unless they have a very serious noncardiac condition that severely restricts their life span.

Vasodilator Therapy in VHD
In 1953, Kelley, a Research Fellow of the Washington, DC, affiliate of the AHA, used intravenous (IV) hexamethonium in 2 patients with VHD out of a total of 14 patients with heart failure.52 In 1956, IV hydralazine produced marked improvements in cardiac hemodynamics and renal function.53 In 1973, Chatterjee and coworkers54 documented the marked beneficial effects in hemodynamics and cardiac function in patients with acute valve regurgitation treated with IV nitroprusside (Figure 11Down).



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  		Figure 11. Figure 11Up. IV nitroprusside in a patient with acute MR rapidly normalizes pulmonary arterial wedge pressure. From Reference 54.

Subsequent studies showed beneficial effects of oral hydralazine both at rest and on exercise in symptomatic patients with severe AR55 ; the mechanism is arteriolar dilatation, which increases forward flow and reduces regurgitant flow.56 However, results of long-term use of hydralazine were disappointing.57

Subsequently, a randomized trial58 in asymptomatic patients with severe AR and normal LVEF showed that at the end of 6 years, of patients assigned to long-acting nifedipine, 15% needed AVR, compared with 34% in those assigned to digoxin (Figure 12Down). All patients in the nifedipine group needed AVR because of LV dysfunction; 85% of patients in the digoxin group needed AVR because of development of LV dysfunction. Digitalis has never been shown to produce LV dysfunction. Moreover, after AVR, all patients on nifedipine normalized LVEF, but 25% of those in the digoxin group did not do so. This observation is compatible with the hypothesis that digoxin therapy masked early LV dysfunction that, when detected, had already progressed to beyond the stage of afterload mismatch, so that after AVR, recovery of LV function was incomplete. This trial shows that all asymptomatic patients with chronic severe AR and normal LV systolic function (1) should be treated with long-acting nifedipine unless there is a contraindication to its use and (2) should not be given digitalis therapy.



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  		Figure 12. Figure 12Up. Long-acting nifedipine results in a lower incidence of the need for AVR in asymptomatic patients with chronic AR and normal LVEF. From Reference 58.

Natural History of Chronic Severe Aortic Regurgitation
Up until the early 1980s, it was claimed that asymptomatic patients with severe AR and normal LV systolic function frequently developed LV systolic dysfunction while they were still asymptomatic. The seminal natural history study by Bonow et al59 from the NHLBI showed that in younger patients (average age 36 years), the event rate was low (Figure 13Down). Dujardin and coworkers60 have shown that in older asymptomatic patients (56±19 years old) with LVEF >=55%, the annual mortality was 2% per year (Figure 14Down). This was not significantly different (P=0.81) from that of age- and sex-matched people, suggesting that the mortality is related to older age and/or associated comorbid conditions. These studies have played an important role in the decision not to recommend premature AVR in such patients.



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  		Figure 13. Figure 13Up. Low incidence of development of symptoms or LV dysfunction in younger patients with chronic severe AR. From Reference 59.



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  		Figure 14. Figure 14Up. Survival in older asymptomatic patients with severe chronic AR and normal LV function. From Reference 60.

Mitral Stenosis
In a seminal article in 1954, Wood61 described the clinical features and pathophysiology of MS; in another seminal article, Heath and Edwards described the 6 grades of structural changes in the pulmonary arteries in patients with pulmonary hypertension.62

Roy and Gopinath’s study63 from India showed that in comparable patients, surgical commissurotomy was associated with a better survival than medical therapy in patients with class II symptoms as well as in those with class III and IV symptoms (Figure 15Down). In less developed countries, excellent results have been reported in a very high percentage of young patients for up to 25 years.64



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  		Figure 15. Figure 15Up. Closed mitral commissurotomy is associated with better survival than with medical therapy in patients with severe MS who were mildly symptomatic (A) and severely symptomatic (B). From Reference 63.

CBC for MS was first used by Inoue in Japan.65 Al Zaibag in Saudi Arabia developed the double-balloon technique for CBC.66 The immediate and 30-day hemodynamic and clinical results of CBC are comparable to those obtained by surgical commissurotomy.13 67 The mitral valve area increases from a mean of 1.0 to 2.0 cm2.67 The reductions of left atrial and pulmonary arterial pressures at rest are more marked on exercise,68 and there is an increase of exercise capacity.68 The immediate results of CBC are greatly influenced by the characteristics of the valve and its supporting apparatus, which are best determined by 2D echocardiography (transthoracic and/or transesophageal).69 Echocardiographic scores of <=8 or of 0 to 1 determined by the 2 different methods provide a clue to the best early results. After CBC, the long-term outcome was best predicted by the post-CBC mitral valve area (>=1.5 cm2) and mean pulmonary arterial wedge pressure (<=18 mm Hg); the 7-year event-free survival was 90±6% (Figure 16Down).70 In the appropriate patient and in centers with skilled and experienced staff, CBC is the procedure of first choice for relief of severe MS.



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  		Figure 16. Figure 16Up. The 7-year event-free survival is 95% in patients with severe MS who after CBC had MVA >1.5 cm2 and mean pulmonary arterial wedge pressure <=18 mm Hg. From Reference 70.

Mitral Valve Prolapse/Mitral Regurgitation
Recognition of MVP as the cause of midsystolic clicks followed by a late systolic murmur is credited to Barlow,71 who made his initial observations at autopsy. MVP is now the most common valve disorder in developed countries. Criley and colleagues72 defined the clinical and angiographic features of MVP in the mid-1960s, and a voluminous literature has evolved over the subsequent years. Some have suggested a genetic basis for MVP,73 and there is a wide range of abnormalities of mitral valve function, ranging from minor prolapse to severe thickening and redundancy of the valve74 and finally flail leaflets.75 The importance of recognition of MVP relates to planning subacute bacterial endocarditis prophylaxis and maintaining surveillance in those with MR. There is growing evidence from observational studies that early repair of mitral valves with severe MR associated with prolapse or flail leaflets may help preserve LV function. The importance of recognition of MVP and myxomatous degeneration of the mitral valve is reflected in the fact that this spectrum of pathology is now the most common basis of MR, at least in those areas of the world in which rheumatic fever has been controlled. The observational data supporting early intervention in repair of severe MR need confirmation in properly controlled clinical trials, and this represents an important area of future research. In 1997, Connolly and coworkers described the occurrence of VHD in patients taking anorectic drugs.76 The precise prevalence and progression of valve disease with use of these drugs and regression after discontinuation of these drugs is being evaluated.

Footnotes

Reprint requests to Shahbudin H. Rahimtoola, MD, Distinguished Professor, Keck School of Medicine of the University of Southern California, 2025 Zonal Ave, Los Angeles, CA 90033.

References

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