Correspondence
Prosthetic Heart Valves
N Engl J Med 1997; 336:222-224January 16, 1997
- Article
To the Editor:
In their review of prosthetic heart valves, Vongpatanasin et al. (Aug. 8 issue)1 propose guidelines for anticoagulant therapy after valve implantation without citing references to support them. The authors make the surprising recommendation that patients with mechanical valves receive anticoagulant therapy “preferably within 6 to 12 hours” after valve implantation. If this recommendation refers to warfarin, how is it administered? If it refers to heparin, then the patient is at risk for bleeding during this period, given the fact that platelets are nonfunctioning after weaning from cardiopulmonary bypass. It is unclear how best to deal with the partial-thromboplastin time during this period; also unclear are the implications for the removal of chest tubes.
The authors go on to suggest that single-leaflet valves require an international normalized ratio (INR) between 3.0 and 3.9, and bileaflet-tilting-disk valves require an INR between 2.5 and 2.9, again citing no references. The current guidelines are for an INR of 2.0 for aortic valves and an INR of 2.5 to 3.0 for mitral valves.2 These recommendations are for patients at low risk for systemic embolism. I believe it is important for the authors to address these issues in order to justify their recommendations.
2 ReferencesRichard L. Weiss, M.D.
Robert Wood Johnson Medical School at Camden, Camden, NJ 081031
Vongpatanasin W ,Hillis LD ,Lange RA . Prosthetic heart valves. N Engl J Med 1996;335:407-416
Full Text | Web of Science | Medline2
Butchart EG ,Lewis PA ,Grunkemeier GL ,Kulatilake N ,Breckenridge IM . Low risk of thrombosis and serious embolic events despite low-intensity anticoagulation: experience with 1,004 Medtronic Hall valves. Circulation 1988;78:Suppl I:I-67
To the Editor:
Although Vongpatanasin et al. provide an in-depth review of standard prosthetic heart valves, they do not mention stentless bioprostheses. There has been remarkable progress recently in the implantation of stentless bioprostheses. Studies have shown the clinical benefit of stentless aortic valves, as compared with prostheses.1 Excellent hemodynamic performance and early regression of left ventricular hypertrophy have been documented by echocardiography.2
Stentless valves are now useful in routine aortic-valve replacement. Better long-term durability can be expected with such valves. They approach physiologic valves in function and preserve the dynamics of the aortic root. Along with advanced techniques to prevent calcification, stentless bioprostheses will be the heart valves of choice in the future.
2 ReferencesThomas Walther, M.D.
Volkmar Falk, M.D.
University of Leipzig, 04289 Leipzig, Germany1
David TE ,Feindel CM ,Bos J ,Sun Z ,Scully HE ,Rakowski H . Aortic valve replacement with a stentless porcine aortic valve: a six-year experience. J Thorac Cardiovasc Surg 1994;108:1030-1036
Web of Science | Medline2
Walther T ,Falk V ,Autschbach R , et al. Hemodynamic assessment of the stentless Toronto SPV bioprosthesis by echocardiography. J Heart Valve Dis 1994;3:657-665
Medline
To the Editor:
Vongpatanasin and colleagues do not mention one characteristic of prosthetic heart valves: the ability to produce gas microemboli. It is now possible to detect microemboli by Doppler examination of carotid arteries or transcranial Doppler examination with long-duration recordings.1 The embolic signals detected, called high-intensity transient signals, have been described in vitro and in vivo and have specific physical characteristics. There is a high incidence of embolic signals in patients with mechanical heart valves.
Reproducibility over time in the number of such signals, the absence of an ischemic event, and the high intensity of the signals support the hypothesis that they indicate the presence of gas microemboli. These microemboli are produced by the process of cavitation in areas of high pressure. Each model of mechanical heart valve is associated with a different number of embolic signals. Wide variations in the frequency of these signals (0 to 620 per 30-minute period) have been noted.2 In patients with bioprosthetic heart valves, microemboli are less common3 or even absent.4
4 ReferencesGilles Pettelot, M.D.
Hôpital Pasteur, 06002 Nice CEDEX 1, France1
Spencer MP. Detection of cerebral arterial emboli. In: Newell DW, Aaslid R, eds. Transcranial Doppler. New York: Raven Press, 1992:215-30.
2
Georgiadis D ,Kaps M ,Siebler M , et al. Variability of Doppler microembolic signal counts in patients with prosthetic cardiac valves. Stroke 1995;26:439-443
CrossRef | Web of Science | Medline3
Tong DC ,Bolger A ,Albers GW . Incidence of transcranial Doppler-detected cerebral microemboli in patients referred for echocardiography. Stroke 1994;25:2138-2141
CrossRef | Web of Science | Medline4
Deklunder GM ,Dauzat MM ,Aldis A ,Burte FM ,Stewart SFC ,Houdas YJ . Microbubbles cerebral emboli detected by transcranial Doppler sonography in patients with prosthetic heart valves. Circulation 1993;88:Suppl:1-223 abstract.
To the Editor:
Given the frequency of cardiac-valve replacement, most physicians at some point care for patients with prosthetic valves. Vongpatanasin and associates provide a readable review of a complex area for a general medical audience. However, they make a number of erroneous generalizations, summarized in Table 2 of their article, that would lead one to conclude that bileaflet-tilting-disk valves are superior to single-tilting-disk valves.
Although it is intuitive to classify mechanical valves according to the type of flow occluder, there are wide variations in performance characteristics because of differences in design, material, and fabrication. The authors conclude that single-tilting-disk valves are less durable, have a smaller effective orifice area, and are more thrombogenic than bileaflet valves. Although there may be a historical basis for these comments, they are not applicable to current designs. Although the Bjork–Shiley convexoconcave single-tilting-disk valve has proved to be so structurally flawed that its prophylactic removal is recommended in certain instances, structural failure of either of the other single-tilting-disk valves has never been reported, which is not true of the leading bileaflet design.1
In Table 2, the authors also provide values for the range of the effective orifice area without any reference to the diameter of the annulus. This information is of limited use, since the effective orifice area for an individual valve, or an individual patient, is determined not only by the design of the valve but also by the size of the annulus. Despite conflicting claims by the manufacturers, the effective orifice area is determined more by the angle of the opening (which is equivalent to the extent of the opening) than by the number of leaflets. For any given valve size, this value is essentially identical for the leading single-tilting-disk and bileaflet designs.
The authors' comments about thrombogenicity are equally misleading. Among currently available valves, the linearized rate for the risk of thromboembolism is lowest for the leading single-tilting-disk valve, intermediate for the bileaflet designs, and highest for the competing single-tilting-disk valve.1 The recommendations made by Cannegieter et al. for optimal anticoagulant therapy in patients with single-tilting-disk valves2 are based on a study of 1354 valves of four different designs, 1052 of which were Bjork–Shiley valves.
Cardiologists and cardiac surgeons usually decide on the specific type of valve to be implanted, yet general internists, like patients, must live with those decisions. The review by Vongpatanasin et al. gives the generalist the impression that the patient with a single-tilting-disk valve has received an inferior prosthesis. The available information indicates otherwise.
2 ReferencesThoralf M. Sundt, M.D.
Kevin D. Murray, M.D.
Washington University School of Medicine, St. Louis, MO 631101
Akins CW . Results with mechanical cardiac valvular prostheses. Ann Thorac Surg 1995;60:1836-1844
CrossRef | Web of Science | Medline2
Cannegieter SC ,Rosendaal FR ,Wintzen AR ,van der Meer FJM ,Vandenbroucke JP ,Briet E . Optimal oral anticoagulant therapy in patients with mechanical heart valves. N Engl J Med 1995;333:11-17
Full Text | Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: On the basis of studies showing that platelet-thrombus deposition occurs as soon as blood begins to flow across a mechanical prosthetic valve, Chesebro et al.1 recommended that treatment with intravenous heparin (approximately 600 to 700 units per hour to maintain an activated partial-thromboplastin time at the upper limit of the normal range) be started six hours after valve replacement and continued until the chest tubes have been removed. At that time additional heparin should be given to maintain the activated partial-thromboplastin time at a value that is one and a half to two times the upper limit of the normal range. Although warfarin therapy is initiated promptly after surgery, its effects are not evident for several days. Obviously, anticoagulant therapy should be modified if the patient has excessive bleeding or coagulopathy after valve replacement. Our recommendation for antithrombotic therapy in a patient with a single-tilting-disk mechanical valve is based on the results of the studies of Cannegieter et al.,2 who showed that the intensity of anticoagulant therapy in such a patient is optimal when the INR is 3.0 to 3.5.
As Drs. Walther and Falk note, stentless aortic heterograft bioprostheses appear to have a better hemodynamic profile than currently available stented bioprostheses. However, additional studies are required to determine whether stentless bioprostheses have favorable long-term durability, especially in younger patients, who are known to have an increased incidence of structural failure of bioprosthetic valves.3
As Drs. Sundt and Murray point out, each single-tilting-disk valve and bileaflet-tilting-disk valve has specific characteristics, but it was beyond the scope of our article to discuss the characteristics of each valve in detail, since there are more than 80 models of prosthetic valves. In general, bileaflet-tilting-disk valves have a better hemodynamic profile and a lower rate of thrombosis and thromboembolism than single-tilting-disk valves 3; however, the Medtronic–Hall single-tilting-disk valve compared favorably with bileaflet prostheses.4 The overall rate of reoperation is lower with bileaflet-tilting-disk valves than with single-tilting-disk valves.4 Although the newer prosthetic valves appear to be better than the older ones, most patients have the older models. In Table 2 of our article, we list effective orifice areas for average-size prosthetic valves in the aortic and mitral positions. Obviously, as the annular diameter of a prosthetic valve increases, the effective orifice area increases commensurately.
4 ReferencesWanpen Vongpatanasin, M.D.
L. David Hillis, M.D.
Richard A. Lange, M.D.
University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75235-90471
Chesebro JH ,Adams PC ,Fuster V . Antithrombotic therapy in patients with valvular heart disease and prosthetic heart valves. J Am Coll Cardiol 1986;8:Suppl B:41B-56B
CrossRef | Web of Science | Medline2
Cannegieter SC ,Rosendaal FR ,Wintzen AR ,van der Meer FJM ,Vandenbroucke JP ,Briet E . Optimal oral anticoagulant therapy in patients with mechanical heart valves. N Engl J Med 1995;333:11-17
Full Text | Web of Science | Medline3
Vongpatanasin W ,Hillis LD ,Lange RA . Prosthetic heart valves. N Engl J Med 1996;335:407-416
Full Text | Web of Science | Medline4
Akins CW . Results with mechanical cardiac valvular prostheses. Ann Thorac Surg 1995;60:1836-1844
CrossRef | Web of Science | Medline
- Citing Articles (1)
Citing Articles
1
Edmund Kenneth Kerut, Marie Dearstine, Patricia Dottery, Navin C. Nanda. (2008) Particulate Matter Within the Inferior Vena Cava. Echocardiography 25:7, 803-804
CrossRef
