Exercise hemodynamics of aortic prostheses: comparison between stentless bioprostheses and mechanical valves

To fly as a pilot after cardiac surgery

Aircrew are responsible for safe and reliable aircraft operations. Cardiovascular disease accounts for 50% of all pilot licences declined or withdrawn for medical reasons in Western Europe and is the most common cases of sudden incapacitation in flight. Aircrew retirement age is increasing (up to age 65) in a growing number of airlines and the burden of subclinical, but potentially significant, coronary atherosclerosis is unknown in qualified pilots above age 40. Safety considerations are paramount in aviation medicine, and the most dreaded cardiovascular complications are thromboembolic events and rhythm disturbances due to their potential for sudden incapacitation. In aviation, the current consensus risk threshold for an acceptable level of controlled risk of acute incapacitation is 1% (for dual pilot commercial operations), a percentage calculated using engineering principles to ensure the incidence of a fatal air accident is no greater than 1 per 107 h of flying. This is known as the '1% safety rule'. To fly as a pilot after cardiac surgery is possible; however, special attention to perioperative planning is mandatory. Choice of procedure is crucial for license renewal. Licensing restrictions are likely to apply and the postoperative follow-up requires a tight scheduling. The cardiac surgeon should always liaise and communicate with the pilot's aviation medicine examiner prior to and following cardiac surgery.

Non-coronary cardiac surgery and percutaneous cardiology procedures in aircrew

This manuscript focuses on the broad aviation medicine considerations that are required to optimally manage aircrew following non-coronary surgery or percutaneous cardiology interventions (both pilots and non-pilot aviation professionals). Aircrew may have pathology identified earlier than non-aircrew due to occupational cardiovascular screening and while aircrew should be treated using international guidelines, if several interventional approaches exist, surgeons/interventional cardiologists should consider which alternative is most appropriate for the aircrew role being undertaken; liaison with the aircrew medical examiner is strongly recommended prior to intervention to fully understand this. This is especially important in aircrew of high-performance aircraft or in aircrew who undertake aerobatics. Many postoperative aircrew can return to restricted flying duties, although aircrew should normally not return to flying for a minimum period of 6 months to allow for appropriate postoperative recuperation and assessment of cardiac function and electrophysiology.

Hemodynamic assessment of Perceval sutureless bioprosthesis by dobutamine stress echocardiography

OBJECTIVES

The aim of this study was to evaluate the hemodynamic performance of a sutureless bioprosthesis under high workload at mid-term follow-up.

METHODS

Thirty-two patients who underwent isolated aortic valve replacement with a Perceval sutureless bioprosthesis with a minimum follow-up of 1 year were enrolled in this study. S size prosthesis was deployed in 10 patients (31.3%), M size in 9 (28.1%), L size in 8 (25%) and XL size in 5 (15.6%). Effective orifice area (EOA), EOA index (EOAi), and transvalvular gradients were assessed at rest and during dobutamine stress echocardiography (DSE) a median of 19.5 months after surgery.

RESULTS

Dobutamine stress echocardiography (DSE) significantly increased heart rate, stroke volume, ejection fraction, and transvalvular gradients (peak gradient, 24.0 ± 7.6 vs 38.7 ± 13.6 mm Hg, P < .001; mean gradient, 12.6 ± 4.2 vs 19.8 ± 8.3, P < .001). When compared to baseline, estimated valve areas significantly increased at follow-up (EOA, 1.48 ± 0.46 vs 2.06 ± 0.67, P < .001; EOAi, 0.84 ± 0.26 vs 1.17 ± 0.37, P < .001). Mean percentage increase in EOAi was 40.3% ± 28.0%. S size prostheses had the highest increase in EOA1, but the difference was not significant (S 46.0% ± 27.5% vs M 45.4% ± 34.5% vs L 32.7% ± 26.4% vs XL 32.1% ± 20.5%, P = .66). Severe patient-prosthesis mismatch (EOAi ≤ 0.65 cm² /m² ) was present at rest in 8 patients (25%), but only in one patient (3.1%) during DSE.

CONCLUSIONS

The Perceval sutureless bioprosthesis demonstrated good hemodynamics at rest and under high workload. The significant increase in EOAi during DSE suggests the potential advantages of Perceval sutureless bioprostheses in case of small aortic annulus or when patient-prosthesis mismatch is anticipated.

Current indications for stentless aortic bioprostheses

The best aortic prostheses have been debated for decades. The introduction of stentless aortic bioprostheses was aimed at improving hemodynamics and potentially the durability of aortic bioprostheses. Despite the good short- and long-term outcomes after implantation of stentless aortic bioprostheses, their use remains limited owing to the technically demanding implantation techniques. Nevertheless, stentless aortic bioprostheses might be of special benefit in certain indications, where they could be a valuable addition to the surgical armamentarium.

The Effect of Pulmonary Valve Replacement (PVR) Surgery on Hemodynamics of Patients Who Underwent Repair of Tetralogy of Fallot (TOF)

Introduction: Pulmonary insufficiency (PI) frequently develops in patients who underwent repair of tetralogy of fallot (TOF). The aim of present study was to assess the effect of pulmonary valve replacement (PVR) on hemodynamics of patients who underwent repair of TOF.

Methods: This retrospective cohort carried out between July 2010 and October 2012 among consecutive PVRs of 19 patients who underwent TOF surgery. The PVRs was performed using bioprosthetic (n=17) and mechanical (n=2) valves. Our data was collected during follow up visits within 6 to 12 month after PVR.

Results: Our results show that PVR significantly decreased right ventricular end-diastolic volume (180.89±13.78 vs. 107.21±12.02 ml/m², P < .01), right ventricular end-systolic volume (105.42±15.98 vs. 58.15±11.67 ml/m², P < .01), RV mass (47.78±6.20 vs. 30.68±8.95 g/m², P < .01), and PI (48.21±1.43% vs. 12.68±5.60%, P < .01). Moreover, left ventricular end-diastolic volume significantly increased (78.05±17.21 vs. 90.78±14.82 ml/m², P < .01) after PVR. The other hemodynamics indexes did not change, significantly.

Conclusion: Despite the controversies about efficacy of PVR after repair of TOF, the remarkable improvement of hemodynamic is a supportive rationale for performing PVR surgery in TOF patients.

Systemic Semilunar Valve Replacement in Pediatric Patients Using a Porcine, Full-Root Bioprosthesis

BACKGROUND

Management of systemic semilunar valve disease in growing, young patients is challenging. When replacement is necessary, use of a pulmonary autograft is sometimes not possible for anatomic, pathologic, or technical reasons or due to parental or patient preference. We employed a stentless, porcine, full-root bioprosthesis in this setting and report our outcomes.

METHODS

Over 9 years (2005 to 2013), 24 patients of mean age 13.1 years (range, 3 months to 20.3 years) underwent operation for mixed stenosis and insufficiency in 16 of 24 (67%), pure insufficiency in 7 of 24 (29%), and pure stenosis in 1 of 24 (4%). Twenty patients had previous interventions of repair or replacement, valvuloplasty, or multiple operations. Survival, follow-up echocardiographic findings, and outcomes were documented. All patients were maintained on daily aspirin.

RESULTS

There were no hospital deaths and no early or late deaths over a mean follow-up for 23 patients of 46.1 months (range, 14 months to 9.2 years). One patient moved abroad and was lost to follow-up. Echocardiographic follow-up (mean 34.0 months) demonstrated that no patient developed more than mild insufficiency or moderate stenosis. In total, 20 of 24 (83%) showed no insufficiency and 11 of 24 patients (46%) showed no stenosis. Near or complete normalization of left ventricular mass and dimension was demonstrated. There were no explants and no thromboembolic or bleeding events.

CONCLUSIONS

When use of a pulmonary autograft is not an option, the porcine full-root bioprosthesis appears favorable for systemic semilunar valve replacement in the pediatric and young adult population. Of note, when prosthetic degeneration does occur, stenosis predominates rather than insufficiency. Longer term studies are warranted.

Stentless aortic valve replacement: current status and future trends

Stentless aortic xenografts were introduced into clinical practice as aortic valve substitutes over a decade ago. Stentless prosthetic valves were expected to provide enhanced durability and more physiologic hemodynamic behavior when compared with stented bioprostheses. Whilst the former expectation has not been fulfilled, partly due to concomitantly improved durability of second-generation stented bioprostheses, the latter has consistently been satisfied in early and late clinical observation. Evidence is accumulating suggesting improved long-term survival due to more timely and thorough regression of ventricular hypertrophy. In addition, stentless xenografts have shown extreme versatility when adopted in a variety of complex clinical conditions associated with aortic valve disease, including small aortic anulus, ascending aortic aneurysm, endocarditis and left ventricular dysfunction. Future research in the form of prospective, multicenter, randomized trials must address the issues of very long-term durability and survival, while simplification in valve design is required to promote wider use of stentless valves.

Stentless aortic valve replacement: an update

Although porcine aortic valves or pericardial tissue mounted on a stent have made implantation techniques easier, these valves sacrifice orifice area and increase stress at the attachment of the stent, which causes primary tissue failure. Optimizing hemodynamics to prevent patient–prosthetic mismatch and improve durability, stentless bioprostheses use was revived in the early 1990s. The purpose of this review is to provide a current overview of stentless valves in the aortic position. Retrospective and prospective randomized controlled studies showed similar operative mortality and morbidity in stented and stentless aortic valve replacement (AVR), though stentless AVR required longer cross-clamp and cardiopulmonary bypass time. Several cohort studies showed improved survival after stentless AVR, probably due to better hemodynamic performance and earlier left ventricular (LV) mass regression compared with stented AVR. However, there was a bias of operation age and nonrandomization. A randomized trial supported an improved 8-year survival of patients with the Freestyle or Toronto valves compared with Carpentier–Edwards porcine valves. On the contrary, another randomized study did not show improved clinical outcomes up to 12 years. Freedom from reoperation at 12 years in Toronto stentless porcine valves ranged from 69% to 75%, which is much lower than for Carpentier–Edwards Perimount valves. Cusp tear with consequent aortic regurgitation was the most common cause of structural valve deterioration. Cryolife O’Brien valves also have shorter durability compared with stent valves. Actuarial freedom from reoperation was 44% at 10 years. Early prosthetic valve failure was also reported in patients who underwent root replacement with Shelhigh stentless composite grafts. There was no level I or IIa evidence of more effective orifice area, mean pressure gradient, LV mass regression, surgical risk, durability, and late outcomes in stentless bioprostheses. There is no general recommendation to prefer stentless bioprostheses in all patients. For new-generation pericardial stentless valves, follow-up over 15 years is necessary to compare the excellent results of stented valves such as the Carpentier–Edwards Perimount and Hancock II valves.

Aortic valve replacement: choice between mechanical valves and bioprostheses

BACKGROUND

The choice between a mechanical or bioprosthetic valve replacement device is not always clear, although patient age is most often the determining factor. We reviewed our experience with patients undergoing aortic valve replacement (AVR) in order to assess and compare long-term outcomes between patients receiving a mechanical valve and those receiving a bioprosthesis.

METHODS

Three hundred fifty-two patients underwent AVR with or without coronary artery bypass between 1993 and 2004: 189 received a mechanical valve and 163 a bioprosthesis. Events included: late mortality, thrombo-embolic events, stroke, bleeding events, valve thrombosis, endocarditis, reoperation, and coronary catheterization.

RESULTS

Patients in the bioprosthesis group were older (71 +/- 11 vs. 65 +/- 13) than in the mechanical group (p < 0.0001). There was no difference in operative mortality (6.8%) or morbidity. Follow-up (61 +/- 40 months) was available in 87%. For mechanical valves and bioprostheses, respectively: 3-, 5-, and 10-year survival was 92%, 86%, and 69% versus 90%, 86%, and 71% (p = n.s.); and event-free survival was 79%, 68%, and 41% versus 79%, 68%, and 44% (p = n.s.). Five patients (3%) in each group required re-replacement of their aortic valve (p = n.s.). Coronary artery disease requiring bypass surgery did not affect long-term survival. Age at operation and renal failure were the only predictors for late mortality.

CONCLUSIONS

Survival and event-free survival are similar for patients receiving a mechanical or biological aortic valve substitute. Selection of a valve replacement device should be based on life expectancy, patient preference, ability to take anticoagulants, lifestyle, risk of bleeding, and risk of reoperation. Patient age alone should not be the determining factor.

Effect of surgeon on transprosthetic gradients after aortic valve replacement with Freestyle stentless bioprosthesis and its consequences: a follow-up study in 587 patients

Background

The implantation of stentless valves is technically demanding and the outcome may depend on the performance of surgeons. We studied systematically the role of surgeons and other possible determinants for mid-term survival, postoperative gradients and Quality of Life (QoL) after aortic valve replacement (AVR) with Freestyle^® stentless bioprostheses.

Methods

Between 1996 and 2003, 587 patients (mean 75 years) underwent AVR with stentless Medtronic Freestyle^® bioprostheses. Follow-up was 99% complete. Determinants of morbidity, mortality, survival time and QoL were evaluated by multiple, time-related, regression analysis. Risk models were built for all sections of the Nottingham Health Profile (NHP): energy, pain, emotional reaction, sleep, social isolation and physical mobility

Results

Actuarial freedom from aortic valve re-operation, structural valve deterioration, non-structural valve dysfunction, prosthetic valve endocarditis and thromboembolic events at 6 years were 95.9 ± 2.1%, 100%, 98.7 ± 0.5%, 97.0 ± 1.5%, 79.6 ± 4.3%, respectively. The actuarial freedom from bleeding events at 6 years was 93.1 ± 1.9%. Estimated survival at 6 years was similar to the age-matched German population (61.4 ± 3.8 %). Predictors of survival time were: diabetes mellitus, atrial fibrillation, peripheral vascular disease, renal dysfunction, female gender > 80 years and patients < 165 cm with BMI < 24. Predictive models showed characteristic profiles and good discriminative powers (c-indexes > 0.7) for each of the 6 QoL sections. Early transvalvular gradients were identified as independent risk factors for impaired physical mobility (c-index 0.77, p < 0.002). A saturated propensity score identified besides patient related factors (e.g. preoperative gradients, ejection fraction, haematological factors) indexed geometric orifice area, subcoronary implantation technique and individual surgeons as predictors of high gradients.

Conclusion

In addition to the valve size (in relation to body size), subcoronary technique (versus total root) and various patient-related factors the risk of elevated gradients after stentless valve implantation depends, considerably on the individual surgeon.

Although there was no effect on survival time and most aspects of QoL, higher postoperative transvalvular gradients affect physical mobility after AVR.

Meta-Analysis of Valve Hemodynamics and Left Ventricular Mass Regression for Stentless Versus Stented Aortic Valves

BACKGROUND

Stentless aortic bioprostheses have been advocated as being superior to conventional bioprosthetic valves, with benefits including superior left ventricular mass regression and larger effective orifice area. Several high-quality randomized studies now exist on this topic, and we sought to summarize them by meta-analysis.

METHODS

The literature was searched from 1995 to 2006, in MEDLINE, EMBASE, CRISP, metaRegister of Controlled Trials, and the Cochrane database. Experts were also contacted and reference lists searched. Studies were combined using the inverse variance fixed-effects model. Heterogeneity was assessed and a sensitivity analysis performed. Publication bias was also investigated.

RESULTS

Ten studies were identified that included 919 patients in which the Freedom (Sorin Biomedica Cardio, Via Crescentino, Italy), Freestyle (Medtronic, Minneapolis, MN), Prima Plus (Edwards Life Sciences, Irvine, CA) and the Toronto and Biocor (St Jude Medical, St. Paul, MN) valves were used. The mean aortic valve gradient was lower in the stentless groups, with a weighted mean difference (WMD) of -3.57 mm Hg (95% confidence interval [CI], -4.36 to -2.78; p < 0.01). The left ventricular mass index was significantly lower in the stentless groups at 6 months (WMD, -6.42; 95% CI, -11.63 to -1.21; p = 0.02), but this improvement disappeared after 12 months (WMD, 1.19; 95% CI, -4.15 to 6.53; p = 0.66). The weighted mean increase in cross-clamp time was 23 minutes, and the increase in bypass time was 29 minutes with a stentless valve.

CONCLUSIONS

This meta-analysis showed that stentless aortic valves provide an improved level of left ventricular mass regression at 6 months, reduced aortic gradients, and an improved effective orifice area index, at the expense of a 23-minute longer cross-clamp time and a 29-minute longer bypass time.

Impact of Stentless Aortic Valves on Left Ventricular Function and Hypertrophy: Current Best Available Evidence

Past four decades have seen a gradual evolution in aortic valve replacement surgery. The ideal valve substitute should combine central flow, low transvalvular gradient, low thrombogenicity, durability, easy availability, resistance to infection, freedom from anticoagulation, and easy implantability. Although there are several types of valves available to replace the diseased aortic valve-autograft, allograft, xenograft, mechanical, and bioprosthetic valves-none is ideal. On one end of the spectrum is the pulmonary autograft, which comes closest to achieving these goals, but creates a double valve procedure for single valve disease, while on the other end are the mechanical valves and stented tissue valves, which allow easy "off the shelf" availability as well as easy implantability but are limited by the potential drawback of causing intrinsic obstruction to some extent because of the space occupied by the stent and sewing ring. Stentless xenograft aortic valves have been developed as a compromise between these ends of the valve spectrum. Stentless aortic valves have been reported to provide more physiologic hemodynamic behavior and cause more timely and thorough regression of ventricular hypertrophy. This review article attempts to evaluate current best available evidence from randomized controlled trials to assess the impact of stentless aortic valves on left ventricular function and hypertrophy.

Heart valve replacement: which valve for which patient?

The ideal heart valve substitute would show no deterioration or thrombogenicity, offer no resistance to blood flow, and be easy to implant. However, such a valve does not exist and we must accept compromises in some of these qualities based on our patients' needs. In selection of cardiac valve prosthesis, valve-related factors such as durability, thrombogenicity, and fluid dynamics should be carefully matched to patient-related factors such as age, size, life expectancy, comorbidities, plans for pregnancy, and lifestyle. In addition, surgeon- or operation-related factors should be considered. Technical aspects of implantation, ease of reoperation, and operative mortalities may tip the risk and benefit balance in a particular direction. We review currently available heart valve prostheses and the clinical factors that are involved in selection of a heart valve substitute.

Echocardiographic and hemodynamic characteristics of reconstructed bicuspid aortic valves at rest and exercise

Repair of diseased bicuspid aortic valves has gained increasing interest as an alternative to conventional valve replacement. Hemodynamic data at exercise have not been reported before. The aim of this study was to investigate the clinical and echocardiographic status of patients after bicuspid aortic valve repair at rest and exercise. Between 03/94 and 09/02 a reconstruction of an incompetent bicuspid aortic valve was performed in 25 patients (mean age 35+/-12.1 years, group A, mean insufficiency 2.8 preoperatively). Patients were investigated clinically and echocardiographically after 2.1+/-2.4 (0.1-8.9) years at rest and exercise and compared to 20 controls (group B). Clinical followup was complete. There were no deaths, reoperations, thromboembolic or bleeding complications. At last examination 21 patients were in NYHA class I, n=4 in NYHA class II and mean aortic valve insufficiency (AI) was 1.0 with one patient having an AI>II degrees. Maximum and mean pressure gradient (dPmax/mean) across the aortic valve at rest were 14+/-5.5/7+/-2.6 mmHg for patients of group A and 7+/-2.5/3.6+/-1.1 mmHg in group B. Mean AVA at rest was 2.6+/-0.8 (group A) vs 2.9+/-0.6 cm(2) (group B, p=0.025), valvular resistance 13.4+/-4.8 (group A) vs 13.6+/-2.9 dyn x s x cm(-5) (group B, p>0.05). All individuals were stressed up to 100 W (dPmax/mean 21+/-6.8/11+/-3.6, group A vs 11+/-2.9/6+/-1.3 mmHg, group B). 56% of group A and 85% of group B could be stressed up to 175 W with dPmax/mean 24.5+/-8.3/12+/-4.2 and 16+/-3.6/8+/-1.4 mmHg, respectively (p<0. 01). Heart rate and blood pressure behavior were comparable. Left ventricular mass regression (preoperatively 369.3+/-76.4 vs 277.3+/-80.7 g at last examination, p<0.01) was significant in group A but did not reach normal values (group B, 227.8+/-71.1; p<0.01). Bicuspid aortic valve reconstruction reduces left ventricular volume load significantly. Although residual mild subclinical obstruction and incompetence were observed, the behavior of hemodynamics at exercise was comparable to controls. The clinical relevance of these findings in long term follow-up has to be evaluated.

St. Jude Medical Toronto biologic aortic root prosthesis: Early FDA phase II IDE study results

BACKGROUND

Several biological aortic root replacement techniques have distinct advantages over mechanical composite root replacement including better valvular hemodynamic characteristics and the lack of need for anticoagulation. Current biological root replacement options lack proven long-term durability or are limited by technical or practical concerns. We report the early results from a phase II multicenter clinical trial of the porcine St. Jude Toronto Bioprosthesis with BiLinx (Toronto root).

METHODS

176 Toronto roots were implanted as total aortic root replacement from August 2001 through August 2003. Concomitant cardiac procedures including coronary artery bypass grafting (31%) and ascending aortic replacement (55%) were performed in 74%. Patients were followed clinically and were examined with an echocardiogram at discharge, 6 months, 12 months, and yearly thereafter. Root sizes implanted included 29 mm in 38%, 27 mm in 30%, 25 mm in 20%, 23 mm in 10%, and 21 mm in 2.2%.

RESULTS

There are 205 patient years of follow-up through October 2003. Operative mortality was 3.9% (none were valve related) and late mortality was 4%. Operative stroke rate was 1.1% and late stroke rate was 0.6%. Endocarditis developed in 1 patient. Freedom from aortic regurgitation is to date 100% at discharge, 6 months, and 1 year postimplant. Reoperation of the aortic valve/root was not required in any patient. Six-month mean transvalvular gradients for 21-29 mm valves were 12.8, 8.8, 5.3, 4.9, and 4.7 mm Hg, respectively.

CONCLUSIONS

Aortic root replacement with the Toronto root is safe and provides superb transvalvular hemodynamics with freedom from anticoagulation. The Toronto root seems widely applicable for all types of aortic root pathology and these early data offer very encouraging results. Long-term follow-up is required.

Complications of prosthetic heart valves

Treatment of native valvular heart disease has resulted in an increasing number of patients with prosthetic valves. Although an improvement over the diseased native valve removed at surgery, prosthetic valves have suboptimal hemodynamics; mechanical valves require anticoagulation and tissue valves wear out over time. Serious complications of prosthetic valves occur at a rate of about 2% to 3% per patient-year. Complications include thromboembolism, prosthesis-patient mismatch, structural valve dysfunction, endocarditis, and hemolysis. Prosthetic valve endocarditis is a lethal disease with mortality rates of 50% to 80% even with appropriate therapy. Echocardiography now provides detailed information on valve function and hemodynamics, allowing early detection of complications. Many of these complications can be prevented by choosing the optimal valve at the time of surgery, rigorous control of anticoagulation and adherence to established anticoagulation guidelines, dental hygiene and endocarditis prophylaxis, and periodic echocardiographic monitoring by a cardiologist.

Further insights into normal aortic valve function: role of a compliant aortic root on leaflet opening and valve orifice area

BACKGROUND

This study aims to find the fundamental differences in the mechanism of opening and closing of a normal aortic valve and a valve with a stiff root, using a dynamic finite element model.

METHODS

A dynamic, finite element model with time varying pressure was used in this study. Shell elements with linear elastic properties for the leaflet and root were used. Two different cases were analyzed: (1) normal leaflets inside a compliant root, and (2) normal leaflets inside a stiff root.

RESULTS

A compliant aortic root contributes substantially to the smooth and symmetrical leaflet opening with minimal gradients. In contrast, the leaflet opening inside a stiff root is delayed, asymmetric, and wrinkled. However, this wrinkling is not associated with increased leaflet stresses. In compliant roots, the effective valve orifice area can substantially increase because of increased root pressure and transvalvular gradients. In stiff roots this effect is strikingly absent.

CONCLUSIONS

A compliant aortic root contributes substantially to smooth and symmetrical leaflet opening with minimal gradients. The compliance also contributes much to the ability of the normal aortic valve to increase its effective valve orifice in response to physiologic demands of exercise. This effect is strikingly absent in stiff roots.