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Michael J. Mack, M.D.
Outcomes of aortic valve replacement (AVR) are generally good with relatively low mortality and major morbidity, especially in centers with significant valve experience. Overall operative mortality for isolated AVR from the Society of Thoracic Surgeons National Cardiac Database (STS-NCD) is 4.0%; while with AVR and coronary artery bypass (CAB) it is 6.8%. [1] There has been overall trend toward a decreased unadjusted operative mortality over the ten years from 1994 through 2004 with mortality decreasing from 4.3% to 3.4% for AVR and 8.0% to 4.6% for AVR/CAB. [2] Major complications of isolated AVR include permanent stroke (1.58%), renal failure (3.7%), prolonged ventilation (7.07%), deep sternal infection (0.5%), and reoperation for bleeding (4.12%). [1] Recently new options for aortic valve implantation have been introduced into clinical practice with the expectation of allowing patients who are too high risk to undergo conventional AVR to be treated or alternatively to potentially decrease periprocedural morbidity and mortality in very high risk surgical candidates. Those options include percutaneous and limited access transapical surgical aortic valve implantation [3,4]. One issue, therefore, is to discern how large a population of patients exists who are not currently considered surgical candidates and also to define specific subgroups of high risk patients currently undergoing surgery who may potentially benefit from a less invasive approach.
Most surgeons feel that there are very few contraindications to AVR for aortic stenosis. Patients with cirrhosis with end stage liver disease and advanced malignancy are probably the two major contraindications. However, the group from Loma Linda recently reviewed their ten year experience with all patients who had an echocardiographic diagnosis of severe aortic stenosis (AVA = 0.8cm2). [5] Only 288/740 (38%) patients diagnosed between 1993 and 2003 actually underwent AVR with 457 (62%) patients treated medically. Reasons AVR was not offered included lack of symptoms and various clinical reasons. One, five, and ten year survival rates with medical management were 60%, 32%, and 18%. Independent risk factors for the higher mortality in non-surgically treated patients included advanced age, low EF, chronic renal failure, pulmonary hypertension, and chronic renal insufficiency. It therefore appears that in there may exist a significant cohort of patients with aortic stenosis treated medically not currently being referred for surgery who could potentially be candidates for a less invasive procedure.
Regarding high risk patients currently undergoing surgical AVR, numerous series have reported on age as a risk factor. Jamieson reporting on the STS-NCD between 1986 to 1995 found an operative mortality of 2.0% in ages 30-39, 5.3% in patients in their 70s, 8.5% octogenarians, and 14.5% in nonagenarians. [6] Chiappini reported experience in 115 octogenarians with an inhospital mortality of 8.5% and one and five year survival of 86.4% and 69.4%. [7] Edwards reported from the United Kingdom Valve Registry 30-day mortality, one year and two year survivals in octogenarians (7.52%, 86.9%, 83.2%) and nonagenarians (17.14%, 74.29%, 74.29%). [8] Major morbidity was reported in 77% of patients in their 90s. Other independent risk factors for mortality with AVR reported include women with a BMI > 29kg/m2 and small patients greater than 71 years old. [9] Small body surface area and long cardiopulmonary bypass time have also ben reported as independent risk factors for early mortality in elderly patients. [10] Gardner reporting on isolated AVR from the Veterans Affairs database found that partially or totally dependent functional status preoperatively increased short term mortality (Odds Ratio 1.64). [11] Ho from the same database reported a six-month mortality of 13.2% in depressed patiented undergoing valve surgery versus 7.6% in non-depressed patients. [12]
How to define a high-risk group of patients currently being treated with AVR who may potentially benefit from a less invasive procedure and who because of age and/or significant comorbidities may have a limited life expectancy and therefore may not necessarily need a valve implanted lasting 15-20 years can be approached from a number of perspectives. Known independent risks factors for operative mortality from various sources consistently include salvage status (OR 7.12), dialysis dependent renal failure (OR 4.32), emergency status (OR 3.46), multiple operations (OR 2.27), non-dialysis dependent renal failure (OR 2.2), inotrope dependence (OR 1.47), previous stroke (OR 1.44), and others. [6]
Analysis of specific subgroups from the STS-NCD reveals the operative mortality to be higher for females (4.8% vs. 3.6%), diabetics (6.6% vs. 3.6%), dialysis patients (17.07% vs. 4.0%), previous stroke (7.55% vs. 3.9%), COPD (5.88% vs. 3.8%), immunosuppressive therapy (8.4% vs. 4.0%), urgent (6.27%), emergent (17.22%), salvage status (35.57%), or previous cardiac operation (7.64% vs. 3.55%).
So how does one collate all this information to define a specific subgroup who may be candidates for alternatives to conventional AVR? Preoperative risk algorithms have been employed in cardiac surgery and have been validated for predicting outcomes in valve patients. These include Parsonnet, EuroSCORE, and STS risk modeling. Toumpoulis divided all patients undergoing isolated AVR by quartiles of EuroSCORE (= 5, > 5 - < 8, 8 - 11, > 11). [12] Long term survival (five and ten years) was able to be predicted being 90% and 78% in the lowest risk quartile and 55% and 35% in the highest risk quartile.
We recently identified our highest risk group of 514 patients undergoing isolated AVR from 1998 to 2003 by being at or above the 90th percentile of risk by the STS risk algorithm (predicted operative mortality = 8.1%). We then computer matched these 52 patients by age and gender to patients below the 90th percentile. Operative mortality was 15.4% versus 5.8% with Kaplan-Meier survival of 50% being reached at 22 months in the high risk group.
In summary, numerous factors are well known to be independent risk predictors for early and late mortality after AVR including advanced age, renal failure, reoperation, and other comorbidities. Preoperative risk algorithms are readily available and user-friendly tools to accurately predict both early mortality and late survival for individual patients. Using these tools should help further define prospectively patients both currently not referred for surgery or are at the highest risk currently undergoing surgery who may potentially benefit from alternative treatments.
Bibliography
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2. Society of Thoracic Surgeons National Cardiac Database. http://www.sts.org/sections/stsnationaldatabase/. Accessed July 2, 2005.
3. Cribier A, Eltchaninoff H, Bash A, Borenstein N, Tron C, Bauer F, Derumeaux G, Anselme F, Laborde F, Leon MB. Percutaneous transcatheter implantation of an aortic valve prosthesis for calcific aortic stenosis: First human case description. Circulation 2002;106:3006-3008.
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11. Gardner SC, Grunwald GK, Rumsfeld JS, Cleveland JC, Schooley LM, Gao D, Grover FL, McDonald GO, Shroyer AL. Comparison of Short-Term Mortality Risk Factors for Valve Replacement Versus Coronary Artery Bypass Graft Surgery. Ann Thorac Surg 2004;77:549-56.
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13. Toumpoulis IK, Anagnostopoulos CE, Toumpoulis SK, DeRose JJ, Swistel DG. EuroSCORE Predicts Long-Term Mortality After Heart Valve Surgery. Ann Thorac Surg 2005;79:1902-8.
