Doppler-Normwerte der biologischen Aortenklappenprothesen von Edwards SAPIEN und CoreValve nach perkutanem Aortenklappenersatz

Abstract

Die Aortenklappenstenose ist heutzutage das häufigste therapiebedürftige Herzklappenvitium bei erwachsenen Patienten in den industrialisierten Ländern. Die verkalkte trikuspide Aortenklappenstenose betrifft dabei vor allem ältere Patienten. Der perkutane Aortenklappenersatz (TAVI) ist ein neuer therapeutischer Ansatz für die Behandlung einer hochgradigen Aortenklappenstenose bei multimorbiden oder alten Patienten mit hohem OP- Risiko. Derzeit sind zwei bioprothetische Aortenklappen für die kathetergestützte Aortenklappenimplantation verfügbar: Die Edwards-Sapien- Prothese (Rinderperikardklappe) und die selbstexpandierende CoreValve-Prothese (Schweineperikardklappe). Mit der zunehmenden Anzahl durchgeführter TAVI besteht die Notwendigkeit der echokardiographischen Nachbeobachtung und Beurteilung dieser neuen Klasse von bioprothetischen Klappen. Die Doppler- Echokardiographie ist dabei die Methode der Wahl bei der Untersuchung der Patienten mit prothetischen Herzklappen. Die bisher veröffentlichten TAVI- Studien, die Doppler-Daten präsentierten, bezogen sich nicht auf Klappengröße und Klappenart, darüberhinaus wurden auch Patienten mit peri-prozeduralen Komplikationen eingeschlossen, was einen wichtigen Unterschied zu unserer Studie darstellt. Unsere Studie konnte Doppler-Normwerte sowie die effektive Öffnungsfläche für die bioprothetischen perkutanen Aortenklappenprothesen vom Typ Edwards Sapien und CoreValve etablieren. Dies wird zukünftig erlauben, diese neue Art von Bioprothesen nach der Implantation besser zu beurteilen. Wir haben die früheste Echokardiographie (median 8 ± 20 Tagen) von 110 klinisch stabilen Patienten nach perkutanem Aortenklappenersatz ausgewertet. Es wurden die maximalen und mittleren Druckgradienten sowie die maximale systolische Geschwindigkeit ermittelt. Die effektive Öffnungsfläche wurde anhand der Kontinuitätsgleichung berechnet. Des weiteren wurden die linksventrikuläre Ejektionsfraktion und das Schlagvolumen bestimmt. In den meisten Publikationen über die Normwerte für chirurgische Klappenprothesen hingegen fehlen diese Werte. Patienten mit postinterventionellen hochgradigen Aortenklappen- oder Mitralklappenregurgitationen waren ein Ausschlusskriterium. Die mittlere LVEF betrug 53.5 ± 11.7% und das Schlagvolumen 73.9 ± 21.4 ml. Die maximale systolische Geschwindigkeit über der Klappenprothese für alle Klappenprothesen war 2.0 ± 0.4 m/s (1.0-3.4 m/s). Der maximale (peak) Druckgradient betrug 16.9 ± 7.2 mmHg (4-46 mmHg), der mittlere Gradient 9.2 ± 4.2 mmHg (3-26 mmHg). Die mittlere Aortenöffnungsfläche war 1.84 ± 0.42 cm2 (1.1-3.4 cm2) mit einer AVAIndex von 1.0 ± 0.3 cm2/m2 (0.5-2.0 cm2). Der mittlere Doppler velocity index (DVI) betrug 0.54 ± 0.13 (0.2-0.8). Die multivariate Analyse zeigte, dass es nur bei den CoreValve 26 mm Prothesen, verglichen mit Edwards Sapien 23 mm eine signifikant niedrigere peak velocity (1.9 ± 0.4 vs. 2.3 ± 0.4; p = 0.03) vorliegt. Auch der maximale Gradient (15.3 ± 6.4 vs. 22.6 ± 6.6; p = 0.02), und der mittlere Gradient (8.4 ± 3.9 vs. 12.4 ±3.8; p = 0.03) waren bei CoreValve 26 mm Prothesen signifikant niedriger. Darüber hinaus konnte nachgewiesen werden, dass CoreValve 29 mm Prothesen eine signifikant größere effektive Öffnungsfläche haben als Edwards Sapien 23 mm Prothesen (1.81 ± 0.37 cm2 vs. 1.50 ± 0.08 cm2; p = 0.03). Werden aber die indizierten Öffnungsflächen verglichen, konnten keine signifikanten Unterschiede zwischen den untersuchten Klappenarten gefunden werden. 20,9% unserer Patienten wiesen nach TAVI eine signifikante AI auf. Diese waren meistens paravalvuläre, halbmondförmige Regurgitationen. Hier besteht in der Literatur kein Konsens über die exakte Quantifizierung mittels 2D-Echokardiografie. Verglichen mit publizierten hämodynamischen Daten chirurgisch implantierter Aortenklappenprothesen, zeigen die perkutan implantierten Aortenklappenprothesen vergleichbare effektive Klappenöffnungsflächen, aber niedrigere maximale Geschwindigkeiten und Druckgradienten.

Percutaneous valve implantation is an evolving new approach for the over 30% of all symptomatic patients with severe aortic stenosis who cannot undergo surgical treatment due to relevant comorbiditie. As the non-inferiority of TAVI compared with surgical treatment was recently shown percutaneous treatment of severe aortic stenosis will likely become a standard method. Therefore and due to increasing experience with this technique the number of implantations will rise and the need for non-invasive evaluation will become even more necessary than it is already today. While assessment of symptomatic patients after valve repair should always start with physical examination, differentiation of symptoms caused by prosthetic valve dysfunction and other conditions needs specific diagnostic tools. Echocardiography and Doppler assessment are the method of choice also in patients after TAVI and, therefore, normal Doppler values have to be established. The present study determines the normal range for Doppler hemodynamics and EOA of two types of percutaneously implanted bioprosthetic valves (i.e. Edwards SAPIEN and CoreValve) after successful TAVI. As mild paravalvular regurgitation is common, especially in patients with CoreValve prostheses, only patients with severe aortic (or mitral) regurgitation were excluded due to alteration of forward-flow hemodynamics. In our experience the classification of paravalvular regurgitation is even more challenging in percutaneous valves than in conventional surgically implanted prostheses since the regurgitation jet is often eccentric and crescent-shaped. Moreover, measurement of the vena contracta is frequently not feasible. One limitation of our study is the fact that transesophageal echocardiography (TEE) was not routinely performed after TAVI. This modality shows higher sensitivity in AR evaluation than transthoracic echocardiographic studies in patients with a poor acoustic window and may help to identify posterior paravalvular leaks. In patients with treated severe aortic stenosis, the rate of deceleration of the diastolic regurgitant jet and the derived pressure half-time are not helpful in evaluation of AR since they are more depending on the LV compliance and pressure then on the AR itself. As recommended we used an integrative approach with an emphasis on the flow profile in the thoracic and abdominal aorta since a holodiastolic flow reversal in the descending thoracic aorta indicates an at least moderate AR. The strength of the presented data are the additionally considered hemodynamic parameters like LVEF and SV since their consideration is required for an adequate interpretation of Doppler data due to the flow dependence. In most of the published literature about normal values for Doppler gradients this crucial information is missing. However, a preserved LVEF does not rule out impaired systolic function and a paradoxical low flow situation resulting in low gradients. In consequence, the SV has a greater significance for the flow profile than LVEF alone. Importantly, our study population has normal mean flow hemodynamics with a mean SV of over 70 ml and a SVI of 40 ml/m2. In case of treating patients with low flow hemodynamic situation, our normal values have to be used with caution but the EOA and the DVI should still be valid. In patients with aortic prostheses and narrow LV outflow due to LV hypertrophy, the velocity proximal to the prosthesis may be elevated and should be included in the Bernoulli equation to derive the pressure gradients more accurately. But there is still a good correlation between pressure gradients derived from the simplified Bernoulli equation and hemodynamically measured gradients. The present publication was neither designed as a comparison between the different available percutaneous aortic valves nor between other surgically implanted aortic prostheses. Rather, it describes the hemodynamic performances of the Edwards Sapien and the CoreValve transcatheter aortic valves in a large cohort of patients. We performed only non-invasive evaluation of the different valves and no corresponding invasively measured hemodynamic values were obtained. Yet, a good correlation between continuous wave Doppler data and catheter-based hemodynamics has been shown for prostheses in the aortic position and routinely follow-up examinations will be performed non-invasively for the majority of the patients. Although our four patient groups are not matched, there were no significant differences regarding LVEF, heart rate and SV between the different valves. CoreValve 26 mm prostheses were found to have significantly lower mean peak velocities as well as lower peak and average mean gradients. Furthermore, the CoreValve 29 mm prosthesis had, on average, a significantly greater EOA compared to the Edwards Sapien 23 mm. These findings are consistent with previous studies on aortic prostheses which reported an inverse correlation between valve size and flow velocities. Although the CoreValve 26 mm had the greatest orifice area indexed to the patient’s body surface area no significant difference could be found compared with the other valve types. To describe the function of prosthesis using the indexed EOA is more reasonable since it better reflects the combination of valve function and condition of each patient present. The EOA has to be proportionate to the patient’s body size to keep the hemodynamic parameters low. Hence, the indexed orifice area was shown to be the only parameter with impact on the clinical outcome. Taken together, no percutaneous valve can be considered superior regarding to hemodynamic function. Therefore, the decision, which valve to implant should be driven by the aortic annulus diameter and the optimal interventional access for each patient. In comparison to previously published hemodynamic data of mostly stented surgically implanted bioprosthetic aortic valves the percutaneous valves tend to have lower mean peak velocities and pressure gradients. Even the normal values of some stentless valves seem higher than the tested percutaneous valves. The EOA is similar compared with previously published data of surgically implanted stented bioprosthetic aortic valves. It is not possible to compare the indexed EOA since this parameter is generally not given in the available literature. Our results appear all the more surprising because the diseased and often severely calcific leaflets of the native valve are only crushed against the supporting valvular sinuses during the valvuloplasty and the following valve implantation and are not surgically resected. Accordingly, recoil could be expected leading to reduction of the orifice area and an increase of the transvalvular pressure gradients. The frequent paravalvular regurgitation could enhance the hemodynamic effects additionally. Since the vast majority of index echocardiographic examinations took place in the first month, no information is available about mid-term alterations. However, in a subgroup analysis, no significant differences regarding the EOA and the indexed EOA in patients examined more than one month after TAVI could be detected. Importantly, since our study did not include patients after conventional therapy our comparison with surgically implanted valves is only based on previously published data. In conclusion, Doppler echocardiography is the preferred non-invasive modality for the follow-up evaluation of prosthetic valve function. This study establishes normal Doppler values for Edwards Sapien and CoreValve transcatheter aortic valves but the comparison with the individual baseline values should be considered if feasible.