Lawrence Lazar and James Thomas
There are two major classes of prosthetic valves, mechanical and bioprosthetic (Fig. 36.1). Each specific valve within these groups has unique features that provide differences in hemodynamics, durability, and thromboembolic risk.
FIGURE 36.1 A:Ball-in-cage valve. B:Bioprosthetic valve. C:Bileaflet mechanical valve.
MECHANICAL VALVES
The three main types of mechanical valves available are bileaflet, tilting disc, and ball-in-cage. Bileaflet tilting disc valves include the St. Jude’s Medical (see Fig. 36.1A), Carbomedics, and On-X valves. The symmetric flow across the bileaflet system provides excellent hemodynamics, with lower transvalvular pressure gradients at any outer diameter or cardiac output than the tilting disc valves or ball-in-cage types. Along with lower rates of mechanical failure or thromboembolism, bileaflet valves are currently the most commonly used mechanical prostheses worldwide.
Single tilting disc valves such as the Bjork–Shiley (see Fig. 36.1B) or Medtronic Hall valves consist of a metallic sewing ring attached to a tilting disc that rotates about an off-centered pivot axis. Some models of the convexoconcave Bjork–Shiley valve demonstrated a high degree of strut fracture (2% per year) and embolization of the disc, resulting in withdrawal of these valves from the market, and prophylactic valve replacement in those whose risk of embolization exceeded the risk of reoperation. Valves at particular risk for this are larger valves in the mitral position implanted in younger patients. Since no Bjork–Shiley valve has been implanted in more than 20 years, the at-risk population is getting quite small. The earlier tilting disc valves also have greater thrombosis risk than newer Medtronic-Hall valves, in which a small orifice in the center permits regurgitant flow to “wash” potentially thrombogenic material from the disc.
The Starr–Edwards valve (see Fig. 36.1C) is the prototypical ball-in-cage valve. Ball-in-cage valves demonstrate a less favorable hemodynamic profile and a higher incidence of thromboembolic complications. Despite these limitations, however, some Starr–Edwards valves have performed for over 40 years.
BIOPROSTHETIC VALVES
Bioprosthetic valves fall into one of two categories: heterografts, such as Carpentier–Edwards (CE, see Fig. 36.1D), which are non–human tissue valves, and homografts, which are cadaveric human aortic valves within a small portion of the donor’s aortic root for support. Compared to mechanical valves, bioprosthetic valves require less anticoagulation, but they are less durable. Stented heterografts are manufactured from porcine valvular tissue (e.g., Medtronic Mosaic valve) or bovine pericardium (e.g., CE Perimount valve). With improvements in design and preseration techniques, currently produced bovine and porcine valves are expected to have comparable durability. Aortic homografts are harvested from cadaveric hearts and cryopreserved. They may be implanted as isolated valves in the subcoronary position or, more commonly, with a short segment of the donor’s aortic root, in which the recipient’s coronary arteries are reimplanted. Although the durability of homograft prostheses may be slightly higher, they are less frequently used due to the complexity of reoperation (calcification of the root and need for reimplantation of the coronary arteries). Homografts have a reduced rate of early reinfection and are the valve of choice in aortic valve endocarditis (Fig. 36.2).
FIGURE 36.2 Although mechanical and bioprosthetic valves have similar external diameters, the figure demonstrates that the stented bioprosthetic valves have a smaller internal diameter and thus a more unfavorable hemodynamic profile.
SELECTION OF VALVE TYPE
Valve repair is preferred over replacement, when feasible. Mitral valves are much more frequently repaired, with repair offering advantages of preserving left ventricular (LV) function via conservation of the subvalvular apparatus, lower operative mortality, higher long-term survival rate, and freedom from anticoagulation. Aortic valve repair is less frequent, although possible in cases with predominant regurgitation due to prolapse or redundancy without severe stenosis or calcification.
Multiple factors need to be considered in selecting a prosthetic valve, including the age of the patient, the probability of future pregnancy, life expectancy, occupation, and lifestyle. Mechanical valves are more durable than bioprosthetic valves, but they require a commitment to chronic anticoagulation. Age recommendations differ with valve position, as bioprosthetic mitral valves deteriorate more rapidly than aortic valves. Mechanical aortic and mitral valves are generally recommended for patients younger than 60 and 65 years of age, respectively, who have no contraindications to anticoagulation and are expected to be medically compliant. The minimum age for a bioprosthesis is later for mitral than for aortic valves due to the more rapid deterioration of bioprostheses in the mitral position. The most recent valve guidelines, however, emphasize patient choice, particularly lifestyle, in valve implantation. With reduction in the risk of redo valve surgery, many patients 50 years of age or younger are opting for bioprosthetic valves.
The development of transcatheter aortic valve replacement (TAVR) is encouraging a further move toward bioprosthetic valves for younger patients: one may choose the benefits of less anticoagulation now in spite of the decreased valve durability, banking on the hope that future TAVR will carry a lower procedural risk should future valve replacement be required.
ANTICOAGULATION
Anticoagulation is a frequent topic of cardiology consultation and board testing. We review here the essentials including general guidelines for mechanical and bioprosthetic valves, therapy adjustment after thromboembolic events, perioperative management, and management in pregnancy.
1. Anticoagulation for mechanical prosthetic valves (Table 36.1). For board review purposes, recommendations are simplified here to just the Class I recommendations, except where indicated. Aortic position bileaflet and Medtronic-Hall tilting disc valves, without risk factors, may be anticoagulated to an international normalizing ratio (INR) of 2.0 to 3.0. All other aortic mechanical valves and all mitral mechanical valves should be anticoagulated to an INR of 2.5 to 3.5. Furthermore, patients with even low-risk aortic mechanical valves and any thromboembolic risk factors, such as atrial fibrillation, previous thromboembolism, hypercoagulable state, or severe systolic dysfunction (left ventricular ejection fraction [LVEF] <30%) should also be anticoagulated to 2.5 to 3.5. All patients with prosthetic valves should be on aspirin (81 mg daily).
Rates of thromboembolism are highest with Starr–Edwards valves, followed by single tilting disc valves. Bileaflet tilting disc valves have the lowest reported rates of thromboembolism, because the built-in regurgitation acts to “clean” debris off the valve. Regardless of the type of valve, at appropriate levels of anticoagulation, the incidence of thromboembolism is <1% in those maintained on therapeutic anticoagulation. The majority of patients who experience thromboembolic complications have subtherapeutic INR at the time of the event. Currently, there is no approved use of dabigatran in anticoagulation of prosthetic heart valves (PHVs), though future trials may lead to expansion of the indication to include this.
TABLE
36.1 Recommended Anticoagulation Therapy for Patients with Prosthetic Valves
INR, international normalizing ratio; AVR, aortic valve replacement; MVR, mitral valve replacement; BL, bileaflet; MH, Medtronic-Hall; BS, Bjork–Shiley; SE, Starr–Edwards.
aHigh Risk defined as atrial fibrillation, prior thromboembolism, hypercoagulable state, or severe left ventricular dysfunction (EF < 30%). From Bonow RO, Carabello BA, Chatterjee K, et al. 2008 Focused update incorporated into the ACC/AHA 2006 Guidelines for the management of patients with valvular heart disease. J Am Coll Cardiol. 2008;52:e1-e142, with permission from Elsevier.
2. Anticoagulation for bioprosthetic valves. Patients with bioprosthetic aortic or mitral valves and no risk factors may be maintained on aspirin alone. Patients with risk factors should be anticoagulated to an INR of 2 to 3. As with mechanical valves, risk factors are atrial fibrillation, prior thromboembolic event, hypercoagulable state, or severe LV dysfunction (EF < 30%).
Early postoperative anticoagulation: In the early postoperative period, the approach to anticoagulation for bioprostheses varies widely. American College of Cardiology/American Heart Association (ACC/AHA) guidelines give a class Ila recommendation to warfarin starting 2 to 4 days following surgery, after epicardial wires are removed. Bioprosthetic valve recipients without risk factors may discontinue warfarin after 3 months and continue aspirin alone. In many center, however, low-risk patients are managed entirely without warfarin.
3. Adjustment of anticoagulation after a thromboembolic event. Patients who have an embolic event while therapeutically anticoagulated should have their therapy increased as follows:
On Warfarin, not taking aspirin: add aspirin 81 mg daily
INR 2 to 3 and aspirin: Increase INR to 2.5 to 3.5.
INR 2.5 to 3.5 and aspirin: Increase INR to 3.5 to 4.5.
Aspirin alone: Add Warfarin to target INR 2 to 3. Guidelines also give options to increase dose to 325 mg daily or add clopidogrel 75 mg daily.
4. Perioperative anticoagulation for noncardiac surgery. For patients with mechanical valves who require major surgery with anticipated substantial blood loss, warfarin should be stopped 2 to 3 days prior to the procedure, to achieve an INR level of 1.5 or less, and restarted 24 hours after the surgery. For low-risk patients with bileaflet aortic valve (i.e., baseline target INR of 2 to 3), the short-term risk is so low that routine heparinization is not recommended. For all patients with a target INR of 2.5 to 3.5 (any mitral mechanical valve, aortic mechanical valves excluding bileaflet or Medtronic-Hall, or any risk factors—see Table 36.1), hospital admission is recommended with initiation of heparin when INR falls below 2.0. Postoperatively, heparin should be restarted as soon as it is considered safe and continued until therapeutic anticoagulation is achieved with warfarin. For minor procedures, in which blood loss is minimal, anticoagulation can be continued. High-dose vitamin K should not be given routinely (class III recommendation), as this may create a hypercoagulable state. Use of fresh frozen plasma is preferable in emergency situations.
5. Pregnancy. Warfarin is teratogenic between 6 and 12 weeks of gestation. Women requiring warfarin therapy who are attempting to become pregnant should have frequent pregnancy tests and cease warfarin when pregnancy is achieved. They should then use dose-adjusted subcutaneous unfractionated heparin (UFH), continuous IV UFH, or low molecular weight heparin (LMWH) for the remainder of the first trimester. Subcutaneous heparin, dosed 17,500 to 20,000 units twice daily, should be adjusted to a target activated partial thromboplastin time (aPTT) of at least twice the control, checked 6 hours after injection. LMWH is dosed twice daily, adjusted to maintain an anti-Xa level between 0.7 and 1.2 units per mL, checked 4 hours after administration. LMWH should only be used if anti-Xa levels are appropriately monitored.
Patients may resume warfarin therapy for the second and third trimesters. As pregnancy is a hypercoagulable state, all pregnant women with mechanical valves on warfarin should be treated to a target INR of 2.5 to 3.5. In those patients who resume warfarin, it should again be discontinued 2 to 3 weeks before term and continuous UFH initiated. Low-dose aspirin can be used in conjunction with anticoagulation therapy in the second and third trimesters. Nursing mothers can safely use both heparin and warfarin, which do not appear to be secreted into breast milk.
COMPLICATIONS OF VALVE PROSTHESES
Monitoring By Echocardiography
A postoperative transthoracic echocardiogram (TTE) should be obtained either prior to discharge or within 4 weeks of discharge. Asymptomatic uncomplicated patients should follow-up annually, although routine TTEs are not indicated in the absence of a change in clinical status. In asymptomatic patients with mechanical valves, no further follow-up echocardiography is required, in the absence of other indications. In patients with bioprosthetic valves, annual TTEs may be considered after the first 5 years. Of course, a TTE is indicated in any patient with a prosthetic valve whenever there is a change in clinical status, new murmur, question of valve function, or concerns of ventricular function. Of note, cardiac magnetic resonance imaging (MRI) is safe for all available prosthetic valves, though artifact induced by metal in the valve will obscure adjacent structures.
Normally functioning mechanical and bioprosthetic valves all have gradients across them, with mean gradients up to 14 mm Hg in the aortic position (except Starr–Edwards, up to 24 mm Hg) and up to 7 mm Hg in the mitral position. Conditions with increased cardiac output such as anemia, tachycardia, pregnancy, hyperthyroidism, or severe prosthetic, leak can lead to higher-than-normal gradients and give the false impression of prosthetic stenosis. Occasionally, a high gradient across an aortic valve demonstrates a prosthesis–patient mismatch, which is defined as <0.6 cm2/m2. The recently published prosthetic valve guidelines from the American Society of Echocardiography provide comprehensive normal values for all prosthetic valves in common use.
Pressure recovery can complicate measurements across bileaflet mechanical prostheses (Fig. 36.3). In this situation, flow deceleration through the gently flaring central orifice may cause Doppler to overestimate the true pressure gradient by up to one-third. This phenomenon may be particularly problematic with small mechanical bileaflet prostheses in the aortic position. Given the need to follow transvalvular gradients to exclude pannus, thrombus, or stenosis secondary to increasing calcification, it is critical to obtain a baseline echocardiogram early postoperatively for future reference.
FIGURE 36.3 Demonstration of pressure recovery. The higher pressure gradient recorded through a prosthesis by Doppler overestimates the true pressure gradient as a result of flow acceleration through a narrowed orifice. Pressure recovers distally, at the position of the catheter recording. This occurs primarily with small mechanical bileaflet prostheses in the aortic position.
Mechanical valves have physiologic regurgitation from multiple jets to help clean off debris, but it should be no more than mild and should not be paravalvular in origin. Regurgitation from mechanical valves in the mitral position is often underestimated by transthoracic echocardiography because of acoustic shielding. Indirect evidence of increased flow across the valve can be obtained in the presence of severe regurgitation if peak gradients are elevated with relatively low mean gradients. Transesophageal echocardiography (TEE) remains the best way to detect and quantify prosthetic mitral regurgitation.
The diagnosis of structural valve degeneration relies primarily on echocardiographic findings, but physical exam findings can sometimes provide clues to complications (Fig. 36.4). Prosthetic valve degeneration occurs more commonly with bioprosthetic valves. The leaflets gradually become thickened and calcified, resulting in both stenosis and regurgitation. Elevated gradients across the valve support the diagnosis and define the severity. Replacement is usually deferred until symptoms appear. Prosthetic deterioration can be more rapid for mechanical prostheses, resulting from thrombosis, encroachment by pannus, infection, or abrasion of a silastic ball occluder (Fig. 36.5). Abrupt failure can be fatal, although rare, occurring as a result of strut fracture or disc dislodgement.
FIGURE 36.4 Acoustic characteristics of various mechanical and bioprosthetic valves. (From Vongpatanasin W, Hillis LD, Lange RA. Prosthetic heart valves. N Engl J Med 1996;335:410, with permission from the Massachusetts Medical Society.)
FIGURE 36.5 Starr–Edwards valve showing degeneration of silicone ball and pannus invasion of the suture ring.
The annual incidence of prosthetic valve thrombosis is approximately 0.5% to 1.5%. The highest incidence is at the tricuspid position, followed by the mitral and then the aortic position. Thrombus is suspected in patients with acute onset of symptoms, embolic event, or inadequate anticoagulation. TEE is a useful diagnostic technique, particularly for mitral prostheses, although cinefluoroscopy and CT scanning are the tests of choice to document restriction in disk or occluder mobility. Heparin should be initiated early, and may be adequate for small (<5 mm) nonobstructive thrombi. Any evidence of valve obstruction should be met with emergent surgical consultation, and fibrinolytic therapy should be considered if surgery is not available.
Approximately 3% to 6% of patients with PVEs will experience endocarditis. PVE is typically associated with large vegetations because microorganisms are sheltered from the host defense mechanisms. Early PVE (<2 months following implantation) is typically caused by Staphylococcus epidermidis. The clinical course is often fulminating, with mortality as high as 50% to 70%. Surgery is almost universally required for effective treatment. Late PVE occurs most commonly in patients with multiple prostheses, especially involving the aortic position. Its clinical course resembles that of native-valve endocarditis, and the most common infectious agents are Staphylococcus aureusand streptococci, followed by S. epidermidis, enterococci, gram-negative bacteria, and fungal agents. The general therapy for patients with PVE is surgery, although a few patients can be treated successfully with medical therapy alone. Patients with PVE should also continue to receive anticoagulation. PVE is associated with a 50% incidence of stroke in the absence of anticoagulation, as opposed to a 10% incidence with anticoagulation, and there is no compelling evidence of increased hemorrhage with warfarin in patients with PVE. Surgery is clearly indicated in patients with persistent bacteremia despite IV antibiotics, tissue invasion or fistula formation, recurrent embolization, fungal infection, prosthetic valve dehiscence or obstruction, new or worsening heart block, or medically refractory congestive heart failure (Fig. 36.6). As discussed, the cure rates with medical therapy in PVE are considerably lower, and repeat surgery should be a consideration for all appropriate candidates who fail a trial of antibiotics. The use of antibiotic prophylaxis is recommended for all patients with prosthetic valves.
FIGURE 36.6 Prosthetic aortic valve demonstrating large vegetation and surrounding abscess. RA, right atrium; LA, left atrium.
Subclinical hemolysis is present in many patients with mechanical valves but rarely results in significant anemia. Clinical hemolysis occurs in approximately 10% of patients with ball/disc-and-cage valves but is uncommon with normal bioprostheses or tilting disc valves. Clinical hemolysis is associated with multiple prosthetic valves, small prostheses, periprosthetic leaks, and PVE. Mechanisms involved in the generation of hemolysis include high shear stress or turbulence across the prosthesis. Diagnosis is made by various laboratory tests (elevated LDH, reticulocyte count, unconjugated bilirubin, decreased haptoglobin, and the presence of schistocytes on blood smear) and echo imaging showing abnormal rocking of the prosthesis or regurgitant jets of high shear stress such as periprosthetic regurgitant jets or those impacting on a solid surface such as the left atrial appendage. Mild anemia from hemolysis can be managed with iron, folic acid, and occasional blood transfusions. Beta-blockade and blood-pressure control may reduce the severity of hemolysis. Surgical therapy or percutaneous occlusion is recommended for those with periprosthetic leaks in patients with severe anemia requiring repeated transfusions or those with congestive heart failure.
Dehiscence of the sewing ring from the annulus may occur in the early postoperative period because of poor surgical techniques, excessive annular calcification, chronic steroid use, fragility of the valvular tissue (particularly following prior valve operations), or infections. Late dehiscence occurs mainly by infectious endocarditis. Abnormal rocking of the prosthesis on echo or cinefluoroscopy is an indication for urgent surgery, but some rocking may occur with preservation of the mitral valve apparatus.
ACKNOWLEDGMENTS
The authors acknowledge the efforts of Dr. Daniel Sauri and Dr. Mario Garcia in writing the first edition of this chapter.
SUGGESTED READINGS
Bloomfield P, Wheatley DJ. Twelve-year comparison of a Bjork-Shiley mechanical heart valve with porcine bioprostheses. N Engl J Med. 1991;324(9):573–579.
Bonow RO, Carabello BA, et al. 2008 Focused Update Incorporated Into the ACC/AHA 2006 Guidelines for the Management of Patients With Valvular Heart Disease: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 1998 Guidelines for the Management of Patients With Valvular Heart Disease) Endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2008;52(13):e1–e142.
Davis EA, Greene PS, et al. Bioprosthetic versus mechanical prosthesis for aortic valve replacement in the elderly. Circulation. 1996;94:II-121–II-125.
Garcia MJ. Prosthetic heart valves. In: Topol EJ, eds. Textbook of Cardiovascular Medicine. 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2008:389–401.
O’Gara PT, Bonow RO, Otto CM. Prosthetic Heart Valves. In: Otto CM, Bonow RO, eds. Valvular Heart Disease. Philadelphia: Saunders Elsevire; 2009:383–99.
Hammermeister KE, Seithi GK, et al. A comparison of outcomes in men 11 years after heart-valve replacement with a mechanical valve or bioprosthesis. Veterans Affairs Cooperative Study on Valvular Heart Disease. N Engl J Med. 1993;328(18):1289–1296.
Vongpatanasin W, Hillis LD, Lange RA. Prosthetic heart valves. N Engl J Med. 1996;335:407–416.
Zoghbi, WA, et al. Recommendations for evaluation of prosthetic valves with echocardiography and Doppler ultrasound. J Am Soc Echocardiogr. 2009;22:975–1014.
QUESTIONS AND ANSWERS
Questions
1. Assuming no other thromboembolic risk factors, what is the recommended anticoagulation therapy for a St. Jude mitral valve?
a. International normalizing ratio (INR) of 2 to 3 for life of valve
b. INR of 2.5 to 3.5 for life of valve
c. Anticoagulation therapy with INR of 2.5 to 3.5 for first 3 months, then aspirin therapy thereafter
d. INR of 3.5 to 4.5 for life of valve
e. INR of 3 to 4 for life of valve
2. A homograft is the preferred valve choice in which of the following clinical situations?
a. A 45-year-old man with aortic valve endocarditis and aortic root abscess in the presence of a bicuspid aortic valve
b. A 30-year-old man with a nonrepairable aortic bicuspid valve in the setting of severe symptomatic aortic insufficiency
c. A 68-year-old woman with chronic lymphocytic leukemia, who has rheumatic mitral stenosis that is not amenable to valvuloplasty
d. A 70-year-old woman with a nonrepairable aortic bicuspid valve in the setting of severe symptomatic aortic insufficiency
3. Which of the following statements regarding prosthetic valve thrombosis (PVT) is true?
a. The annual incidence of PVT is approximately 0.5% to 1.5%.
b. Incidence is highest for the mitral position and then the aortic position followed by the tricuspid position.
c. Fibrinolysis is generally performed rather than surgery for left-sided prosthetic valve thrombosis.
d. Surgery is generally considered the treatment of choice for right-sided PVT.
e. Cinefluoroscopy is not usually reliable to determine restriction in occluder mobility at a mechanical prosthesis.
4. When assessing transvalvular gradients across a prosthetic valve, all of the following can lead to a false assessment of prosthetic valve stenosis except:
a. Patient–prosthesis mismatch
b. Anemia
c. Sepsis
d. Regurgitation
e. Pressure recovery phenomenon
5. A 55-year-old man has a #19 mechanical tilting disc prosthesis placed 6 months ago for aortic stenosis. Initially, postoperatively, the peak and mean gradients across the prosthesis were 60/35 mm Hg (peak/mean), respectively. He now feels short of breath on minimal exertion and a repeat transthoracic echocardiogram shows normal apparent valve function, normal LV function, and a peak and mean gradient of 70/45 mm Hg. A transesophageal echocardiography (TEE) is performed. There is no abnormal regurgitation at the valve. Valve motion appears full and no abnormal masses are seen at the valve. He is not anemic and his LDH is mildly elevated. His INR has been in the therapeutic range throughout. What is the most likely cause of his symptoms?
a. Hemolysis at the valve.
b. Pannus at the valve causing obstruction and leading to prosthetic stenosis
c. Patient–prosthesis mismatch due to inadequate sized valve for patients needs
d. Pressure recovery at the valve giving an overestimate of the true pressure gradient across the left ventricular outflow tract
e. Occult valve thrombosis
6. A 45-year-old healthy man with a mechanical double tilting disc aortic prosthesis is seen in clinic with a recent episode of transient dysphasia. He has otherwise been well and afebrile. His INRs have been therapeutic in the 2.5 to 3.0 range and coumadin is his only medication. A TTE shows normal gradients and a TEE shows normal valve motion and function. The most appropriate management now is to:
a. Increase coumadin to maintain an INR of 3.0 to 4.0.
b. Refer for surgical evaluation for bioprosthetic insertion.
c. Get blood cultures and start antibiotics intravenously.
d. Start aspirin 81 mg in addition to coumadin.
e. Consider a trial of dabigatran given the failure of therapeutic coumadin therapy.
7. A 55-year-old man has had increasing fatigue over the last several months. He has a mechanical valve at the mitral position for the last several years. His prosthetic click sounds fine and no murmur is appreciated. He has had adequate INR levels. A routine blood count shows normocytic anemia of 10 g and no leucocytosis and normal platelet count. An LDH level is 1,100 IU. A TTE shows a peak gradient of 25 and mean gradient of 10 mm Hg across the valve (previously 10/5 peak/mean mm Hg). There is considerable shielding of the left atrium but no mitral regurgitation is detected. The most appropriate test now to determine a course of action would be to
a. Perform cinefluoroscopy to exclude valve thrombosis.
b. Perform TEE to exclude a paravalvular leak.
c. Perform GI workup to determine source of GI bleeding.
d. Stop coumadin until anemia resolves.
e. Check blood cultures to exclude endocarditis.
8. An 80-year-old woman has a mitral bioprosthesis that is 16 years old. You saw her 6 months ago and a transthoracic echocardiogram revealed mildly increased gradients across the prosthesis. There is some calcium on the leaflets and mild regurgitation. Her LV function is normal. Her family practitioner calls you urgently to say that she has gone into pulmonary edema unexpectedly without any fever or other illness or recent symptomatic deterioration. The most likely cause of her sudden deterioration is:
a. Atypical endocarditis
b. Acute valve thrombosis
c. Acute coronary embolism from degenerative valve
d. Patient–prosthetic mismatch
e. Flail prosthetic valve leaflet with severe acute mitral regurgitation
9. You are called to the operating room by the anesthetist who has performed a postoperative TEE on a 50-year-old man who has had a mitral bileaflet tilting disc valve placed for severe calcific mitral stenosis. The anesthetist has noted multiple small low-velocity jets emanating from the valve edges that are systolic in timing and that are relatively short in duration (see figure). The motion of the valve leaflets is normal and the patient is off bypass. Protamine has been given to reverse heparin but the jets are still present. The pressure gradients across the prosthesis are not increased. The most likely cause of these jets is:
a. Paravalvular leaks at the site of the sewing ring due to calcium impingement
b. Normal regurgitation from the valve that is of no concern
c. Prosthetic occluder impingement from a severed chord
d. Valve thrombosis
e. Pulmonary vein stenosis with high-velocity jet in left atrium
Intraoperative TEE of mitral valve prosthesis. LA: left atrium
a. Which of the following is the most likely finding in patient with severe paravalvular regurgitation at a mitral bioprosthesis and previously normal LV function?
b. Reduced LV ejection fraction
c. Increased cardiac output
d. Normal pulmonary pressure
e. Elevated peak transvalvular gradient across the bioprosthesis
f. Normal LDH levels
Answers
1. Answer B: Embolic event rates are higher for mitral valves than for aortic valves and therefore generally require higher anticoagulation therapy. Caged ball and single tilting valves also carry greater embolic risk than double tilting mechanical valves. Bioprosthetic valves generally carry the lowest risk of embolization, yet according to AMA guidelines, anticoagulation is still recommend in the first 3 months after placement, although this varies according to institution.
2. Answer A: In the setting of infection and, in particular, aortic root abscess, an aortic homograft is generally considered the best choice to prevent subsequent immediate reinfection. The durability of homografts was once thought to be superior to that of bioprosthetics, but recent experience has demonstrated this not to be the case. Furthermore, the difficulty of reoperation in such a patient (coronary reimplantation and subsequent extensive calcification) should be taken into account. A mechanical aortic valve with the lowest thromboembolic risk, such as a St. Jude or Carbomedics, is preferred in a young person, given its durability and potential to prevent future reoperation. The risk of anticoagulation for the patient must also be taken into consideration. Given the comorbidity of chronic lymphocytic leukemia, which carries a decreased life expectancy yet not imminent death, a bioprosthetic valve is probably a good option. Of course, there are surgical considerations to the placement of a bioprosthetic valve, such as the larger profile of the valve secondary to its struts. If possible, however, the risk of anticoagulation should be avoided, given the low potential for reoperation in this patient. Recent data with bovine pericardial bioprosthetic valves demonstrate a higher-than-expected durability of approximately 85% at 15 years, which may have shifted the threshold for bioprosthetic valves to many patients in their 50s and 60s. The 70-year-old woman would probably be best served by a bioprosthesis given its durability and higher risk of anticoagulation in this age group.
3. Answer A: Thrombus formation is most common at the tricuspid valve and least common at the aortic valve. Fibrinolytic therapy is considered the treatment of choice for right-sided PVT because the consequences of distal embolization are less severe than in a left-sided prosthesis. Streptokinase and urokinase are the most common agents, and the success rate is approximately 82%, with a 12% rate of thromboembolism and 5% incidence of major bleeding for right-sided PVT. Leftsided PVT is generally considered for surgery unless the thrombus is small or the surgical risk is prohibitive as the consequences of embolization at a left-sided valve during thrombolysis may be catastrophic. Cinefluoroscopy is an excellent way to evaluate occluder motion.
4. Answer A: Patient–prosthesis mismatch implies a true physiologic stenosis that is a result of the placement of a relatively small prosthesis, typically in the aortic position, that leads to a reduction in cardiac output. All prosthetic valves have an inherent relative stenosis, but when an inappropriately small prosthesis is placed, a patient can be left with a true gradient that is similar to that prior to the operation. Anything that increases cardiac output, such as anemia, as in the postoperative period, or sepsis, will increase flow through the prosthesis and produce higher-than-normal transvalvular gradients. Similarly, increased regurgitation, such as mitral regurgitation, which is often shielded on surface echo by prosthetic valves, will increase flow across the valve and produce a picture of pseudostenosis. Pressure recovery phenomenon describes a false elevation in gradients that is obtained by echocardiography, typically as a result of high-velocity flow through the central orifice of a bileaflet mechanical valve, which dissipates in the ascending aorta.
5. Answer C: The patient has persistently high gradients across the valve since surgery and has a small prosthesis (#19) implanted. Initially, the gradients might be attributed to anemia postoperatively but have actually got higher postresolution of this. There may be an element of pressure recovery leading to high gradients at this mechanical valve but this would not account for his symptoms. No thrombus or pannus was evident at TEE and it would be unusual to have pannus ingrowth this early postoperatively. This patient may require reoperation with placement of a larger valve. The aortic annulus may have to be enlarged at the same time to fit a bigger valve. Another option may be the insertion of a stentless valve such as a homograft that has a larger orifice size for its diameter.
6. Answer D: The most appropriate treatment is to add aspirin or clopidogrel in the absence of structural abnormality at the valve and absence of other embolic source. Dabigatran is not approved for mechanical valve anticoagulation. Occasionally, surgical exploration and bioprosthetic insertion are necessary for recurrent embolization despite adequate and even supertherapeutic anticoagulation. Blood cultures are indicated if infection is suspected but not otherwise.
7. Answer B: The patient has high gradients and high LDH even for a mechanical valve. This suggests a hemolytic anemia related to the valve. The most likely cause of this is a paravalvular leak that may be hard to detect because of shielding especially if it is posteriorly directed. This will render it inaudible also. There tends to be a disproportionate increase in the peak rather than the mean gradient with concomitant regurgitation at a prosthetic valve. Hemolysis normally occurs at mechanical prostheses even in the absence of a paravalvular leak but rarely cause anemia and LDH levels are in the 300 IU range.
8. Answer E: The patient has a degenerated bioprosthesis. Valve failure at bioprostheses is rarely catastrophic but when it occurs is generally due to a flail valve leaflet leading to regurgitation. Patient–prosthetic mismatch is the presence of a valve of inadequate size to meet the hemodynamic needs of the patient. This is associated with high valve gradients that are usually present from the time of surgery. Thrombosis and embolism from bioprostheses are very rare but can occur.
9. Answer B: These jets are what is expected normally at a double tilting disc mitral valve prosthesis. The jets emanate peripherally, are of low velocity, and frequently may not persist throughout systole. They are a design feature of the valve. Paravalvular leaks are generally larger. Valve thrombosis usually causes central regurgitation because the leaflets neither open nor close fully as does occluder impingement from a severed chord.
10. Answer D: Mitral regurgitation at a prosthesis will usually give rise to increased gradients across the valve and especially of the peak gradients because of the increased flow through the valve. Severe mitral regurgitation will usually lead to increased ejection fraction at least initially though contractile function may not have changed as the ventricle is ejecting a lot of its output back into to the low-pressure left atrium. Forward cardiac output is not usually increased though the flow through the regurgitant valve is. Paravalvular leak will typically cause some increase in LDH levels. These are not usually elevated in bioprosthetic valves, unlike in mechanical valves where they are elevated mildly normally. Pulmonary hypertension is usually present when there is significant mitral regurgitation. With severe paravalvular leak, it is often severe.