Luca Weltert

Current trends in cannulation and neuroprotection during surgery of the aortic arch in Europe

OBJECTIVESnTo conduct a survey across European cardiac centres to evaluate the methods used for cerebral protection during aortic surgery involving the aortic arch.nnnMETHODSnAll European centres were contacted and surgeons were requested to fill out a short, comprehensive questionnaire on an internet-based platform. One-third of more than 400 contacted centres completed the survey correctly.nnnRESULTSnThe most preferred site for arterial cannulation is the subclavian-axillary, both in acute and chronic presentation. The femoral artery is still frequently used in the acute condition, while the ascending aorta is a frequent second choice in the case of chronic presentation. Bilateral antegrade brain perfusion is chosen by the majority of centres (2/3 of cases), while retrograde perfusion or circulatory arrest is very seldom used and almost exclusively in acute clinical presentation. The same pumping system of the cardio pulmonary bypass is most of the time used for selective cerebral perfusion, and the perfusate temperature is usually maintained between 22 and 26°C. One-third of the centres use lower temperatures. Perfusate flow and pressure are fairly consistent among centres in the range of 10-15 ml/kg and 60 mmHg, respectively. In 60% of cases, barbiturates are added for cerebral protection, while visceral perfusion still receives little attention. Regarding cerebral monitoring, there is a general tendency to use near-infrared spectroscopy associated with bilateral radial pressure measurement.nnnCONCLUSIONSnThese data represent a snapshot of the strategies used for cerebral protection during major aortic surgery in current practice, and may serve as a reference for standardization and refinement of different approaches.

Use of the Valsalva graft and long-term follow-up.

OBJECTIVEnThe Valsalva graft is a specifically designed Dacron graft that, on implantation and pressurization, generates pseudosinuses of Valsalva. We reviewed a multicenter experience of the reimplantation procedure with the Valsalva graft in patients with aneurysms involving the aortic root.nnnMETHODSnA total of 278 patients underwent valve-sparing aortic root replacement using the Valsalva graft at 4 different Italian cardiac surgery centers and were studied by clinical assessment and echocardiography. Of the 278 patients, 220 were men (79%), with a mean age of 56 ± 15 years. Of the patients, 42 (15%) had Marfan syndrome, 31 (11%) had a bicuspid aortic valve, 13 (5%) had acute aortic dissection, and 136 (49%) had grade 3 or 4+ aortic insufficiency. Concomitant cardiac procedures were performed in 78 patients (28%). Additional aortic leaflet repair was necessary in 25 patients (9%). The mean crossclamp time was 120 ± 27 minutes.nnnRESULTSnThere were 5 (1.8%) operative and 5 (1.8%) late deaths. The mean follow-up was 52 ± 28 months (range, 2-112 months) and was 100% complete. The cumulative actuarial survival was 95.2% (268 patients). A total of 32 patients (11%) had grade 3 to 4+ aortic insufficiency, and 17 of these required late aortic valve replacement (range, 3-78 months). At 10 years of follow-up, the freedom from aortic valve reoperation rate was 91%, and the rate of freedom from residual aortic insufficiency not needing reoperation was 88%.nnnCONCLUSIONSnThe reimplantation type of valve-sparing procedure can be facilitated by the use of the Valsalva graft and can be performed with satisfactory perioperative and midterm results. How an optimal root reconstruction will affect the second decade of follow-up has yet to be determined.

Hemodynamics of the aortic valve and root: implications for surgery

The aortic valve divides the left ventricular outflow tract (LVOT) from the ascending aorta and its normal or abnormal function has a great impact on regulating physiological hemodynamic parameters. It is well known that the presence of aortic valve stenosis or insufficiency results in impaired hemodynamics with direct and dire consequences on the left ventricle. On the other hand, when normal, the valve and the root have long been perceived as a type of passive gate dividing the left ventricle from the ascending aorta and preventing any reversal of flow, with minimal effect on valve hemodynamics. However, two points need to be stressed. First, the aortic valve has to be considered a complex unit along with the other components of the aortic root, the sinuses and the sino-tubular (ST) junction (1). Second, the particular shape of the aortic root, with its narrowing at the ST junction and the direct continuity of the sinus wall with the valve leaflets, makes perfect control of the closing mechanism of the aortic cusps possible. It is well known that the vortices forming inside the sinuses due to the narrowing of the ST junction are of paramount importance in regulating the closing mechanism of the valve leaflets (2). Although Leonardo da Vinci understood and illustrated these vortices long ago (3,4), only quite recently has the sophisticated relationship among the various components of the aortic root in controlling valve motion been demonstrated experimentally (5). During isovolumetric contraction of the left ventricle, pressure is transmitted through the inter-leaflet triangle up to the commissure in such a way that the valve starts to open even before forward flow has started. Next, as soon as the blood exits the ventricle, the regions of flow closer to the wall, being slower, curl down into the sinuses and already start closing the aortic valve. The main result of all these complex mechanisms is to keep the stress on the valve leaflet to a minimum (1), allowing a life-long valve durability. n nAlthough almost everything with regard to the diastolic function of the aortic root is known, much less is clear about its systolic function or about the possibility that the aortic root, with its particular shape, might also regulate the opening of the aortic valve (6). This year our group was able to shed some light on the role of the aortic root in regulating the systolic function of the aortic valve (7). More specifically, we were able to show, for the first time, that the shape of the root, namely the presence of the sinuses, coupled with the pulsatility of the flow, was important in guaranteeing complete opening of the valve and thereby absence of a trans-valvular gradient. In this respect, root compliance seemed to be less important. n nThese in-vitro experiments were conducted by first creating two silicon roots with the same compliance, either with or without sinuses, containing the same biological stentless valve sutured inside following the remodeling technique (Figure 1, with permission). The two samples were then tested with simulated circulation to measure the pressure drop across the value, therefore calculating the effective orifice area at different cardiac outputs. The main finding of this simple experiment was that when the cardiac output was increased above 5 L/min the pressure drop significantly increased in the sample without sinuses of Valsalva. The results were identical when the portion of the aorta above the valve (the root) was replaced with either a straight Dacron graft (no sinuses) or with a Valsalva Dacron graft (with sinuses) (Figure 2, with permission): the pressure drop increased only in the sample without sinuses. This last finding appears to rule out compliance in having a role in modulating pressure drops across the valve. In fact, it was the shape, more than the compliance, which was responsible for the different findings (Figure 3, with permission). It was evident that in the presence of sinuses the valve was able to reach its full opening position; if the sinuses were absent complete opening was prevented. n n n nFigure 1 n nThe two root silicon models with the same compliance, but either with or without sinuses. A stentless valve was sutured inside following the remodeling techniques. (Reprinted from J Thorac Cardiovasc Surg, Elsevier, with permission) n n n n n nFigure 2 n nThe silicon models where the upper part was substituted with a straight or a Valsalva Dacron graft to minimize the role played by root compliance. (Reprinted from J Thorac Cardiovasc Surg, Elsevier, with permission) n n n n n nFigure 3 n nPressure drop across the valve in both roots, with and without sinuses, either made out of silicon (standard compliance) or made out of Dacron (minimized compliance). Note that independent of root compliance, the absence of sinuses increased the pressure ... n n n nTo further elucidate this aspect and to find a reasonable explanation for this different behavior, a second series of experiments was planned (8). In this series we aimed to ascertain if the pulsatility of flow played a role in generating fluid dynamics that could explain the differences in terms of the aortic valve pressure drop between the two different root configurations. We hypothesized that the interaction between the particular characteristics of pulsatile flow and the sinuses of Valsalva could be responsible for the superior hydrodynamic performance of the aortic valve. n nThe same two Dacron roots and valve models were prepared as described above: one with and one without sinuses (Figure 2, with permission). The hydrodynamic performance of the two assembled models was investigated in pulsatile and in laminar steady state flow regimes by using two dedicated test benches. Pressure drop and effective orifice area were measured at different flow rates. During the laminar steady state flow regime, it was evident that the hydrodynamic performance of the aortic valve was not markedly affected by the presence or absence of the sinuses. n nInterestingly, from a comparison of the hydrodynamic test performed using a standard reference nozzle, in steady state flow regime, no difference was found in terms of pressure drop, either in the presence or absence of the sinuses, up to a cardiac output of 15 L/min (Figure 4). This observation shows the absence of any interaction between aortic root geometry and low-turbulence steady state flow regimes on hydrodynamic performance of the aortic valve. On the contrary, as shown in the previous study, the results acquired in pulsatile flow regimes showed significantly different behavior between the two root models. This implies that only in the presence of pulsatile flow do the sinuses of Valsalva play a role in modulating the pressure drop across the valve. n n n nFigure 4 n nPressure drop across the valve in both Dacron roots, with and without sinuses, compared with a standard nozzle. Note that when steady flow becomes turbulent (i.e., around 15 L/min) the presence of sinuses helps to maintain a low pressure drop across the ... n n n nMore specifically, when comparing the results of the two aortic root configurations operating under different flow regimes, it can be seen that the hydrodynamic performance of the aortic valve is markedly affected by the presence of pulsatile flow conditions. In this setting it appears that the interaction between aortic root geometry and pulsatile flow influences the opening of the aortic valve. Pulsatile flow is, by definition, turbulent flow; it is therefore likely that in the straight graft model and in the presence of pulsatile flow, the turbulence acts as a functional obstruction preventing complete opening of the aortic leaflets. On the contrary, in presence of appropriate space and architecture (represented by the sinuses of Valsalva), aortic leaflets are free to achieve complete valve opening with low-pressure drops, even in the presence of turbulent flow. This phenomenon could possibly be caused by the systolic vortices forming above the aortic valve. These vortices find a natural home in the sinuses expansion, which has an immediate effect both on the location and on the size of the vena contracta. The importance of flow turbulence in determining the effects described above was further confirmed by the finding that in steady conditions, when the flow was increased above 15 L/min (when it starts to become turbulent) (Figure 4) the same pressure drop across the valve started to build, but now in the absence of sinuses. n nIn conclusion, this series of experiments demonstrated that in the presence of turbulent flow (i.e., pulsatile flow), the particular shape of the aortic root and its sinuses are important in regulating proper opening of the aortic valve. In the absence of sinuses the turbulence of flow causes suboptimal opening of the valve with the consequent presence of a pressure drop and reduced effective orifice area. n nHow this finding might have implications for surgical technique is less clear. Although various techniques that do not provide sinuses reconstruction have proved to be equally effective in term of satisfactory valve function (9), it is already well established that in the absence of sinuses the valve closing mechanisms are impaired and reduced valve durability is to be expected (10). The observation that the presence of sinuses is also important in regulating valve opening, especially evident at higher cardiac output, contributes to the notion that in active, young and sportive patients the surgeon should strive to achieve an anatomical reconstruction of the aortic root.

Evaluation of prosthetic-valved devices by means of numerical simulations

The in vivo evaluation of prosthetic device performance is often difficult, if not impossible. In particular, in order to deal with potential problems such as thrombosis, haemolysis, etc., which could arise when a patient undergoes heart valve replacement, a thorough understanding of the blood flow dynamics inside the devices interacting with natural or composite tissues is required. Numerical simulation, combining both computational fluid and structure dynamics, could provide detailed information on such complex problems. In this work, a numerical investigation of the mechanics of two composite aortic prostheses during a cardiac cycle is presented. The numerical tool presented is able to reproduce accurately the flow and structure dynamics of the prostheses. The analysis shows that the vortical structures forming inside the two different grafts do not influence the kinematics of a bileaflet valve or the main coronary flow, whereas major differences are present for the stress status near the suture line of the coronaries to the prostheses. The results are in agreement with in vitro and in vivo observations found in literature.

The role of neo‐sinus reconstruction in aortic valve‐sparing surgery

The aim of this study was to evaluate the clinical and echocardiographic results and the predictors of outcomes in patients undergoing valve‐sparing operation (VSO) at two aortic centers. In addition, we sought to evaluate the potential effect of recreation of the sinuses of Valsalva (SV) on the outcome of valve‐sparing procedures.

Early clinical outcome after aortic root replacement using a biological composite valved graft with and without neo-sinuses

OBJECTIVES: This study was conceived to compare the results of aortic root replacement using a composite biological valved graft with or without neo-sinuses of Valsalva. METHODS: We compared the early clinical outcomes of 421 patients who underwent aortic root replacement using a handmade biological composite valved graft with or without neo-sinuses (198 and 223 patients, respectively). Propensity matching based on the most important preoperative clinical variables resulted in a cohort of 210 patients (105 pairs) with comparable baseline variables. RESULTS: No difference in early clinical outcome was found between the unmatched groups. At a mean follow-up of 28.8 months, 11 patients required reoperation on the aortic valve (2.6%). Seven of the cases of reoperation were in the group without neo-sinuses (P = 0.83). In the propensity-matched groups, the type of graft used did not affect early and late clinical outcome and incidence of reoperations. CONCLUSIONS: The early clinical outcome of patients submitted to aortic root replacement using a handmade biological composite valved graft is equally good in the presence and in the absence of neo-sinuses.

Annular dilatation and loss of sino-tubular junction in aneurysmatic aorta: implications on leaflet quality at the time of surgery. A finite element study

OBJECTIVESnIn the belief that stress is the main determinant of leaflet quality deterioration, we sought to evaluate the effect of annular and/or sino-tubular junction dilatation on leaflet stress. A finite element computer-assisted stress analysis was used to model four different anatomic conditions and analyse the consequent stress pattern on the aortic valve.nnnMETHODSnTheoretical models of four aortic root configurations (normal, with dilated annulus, with loss of sino-tubular junction and with both dilatation simultaneously) were created with computer-aided design technique. The pattern of stress and strain was then analysed by means of finite elements analysis, when a uniform pressure of 100 mmHg was applied to the model. Analysis produced von Mises charts (colour-coded, computational, three-dimensional stress-pattern graphics) and bidimensional plots of compared stress on arc-linear line, which allowed direct comparison of stress in the four different conditions.nnnRESULTSnStresses both on the free margin and on the belly of the leaflet rose from 0.28 MPa (normal conditions) to 0.32 MPa (+14%) in case of isolated dilatation of the sino-tubular junction, while increased to 0.42 MPa (+67%) in case of isolated annular dilatation, with no substantial difference whether sino-tubular junction dilatation was present or not.nnnCONCLUSIONSnAnnular dilatation is the key element determining an increased stress on aortic leaflets independently from an associated sino-tubular junction dilatation. The presence of annular dilatation associated with root aneurysm greatly decreases the chance of performing a valve sparing procedure without the need for additional manoeuvres on leaflet tissue. This information may lead to a refinement in the optimal surgical strategy.

Aortic flow after valve sparing root replacement with or without neosinuses reconstruction

Objectives This study applied advanced 4‐dimensional flow magnetic resonance imaging processing to assess differences in aortic flow dynamics after valve sparing root replacement, with and without reconstruction of the Valsalva sinuses. Methods We enrolled patients after valve sparing root replacement with a straight tubular prosthesis (n = 10) or with a prosthesis with Valsalva neosinuses (n = 10); age‐matched subjects without cardiovascular diseases served as controls (n = 10). 4‐Dimensional flow magnetic resonance imaging acquisitions were performed on a 3.0T magnetic resonance imaging unit. In‐house processing was used to segment the aortic lumen and extract the volumetric 4‐dimensional flow velocity field. Velocity flow streamlines were computed to compare the amount of rotational flow and wall shear stress. Occurrence of abnormal wall shear stress (WSS) was estimated within the descending aorta of each surgical group. Results Physiologic‐like sinus vortices were visible in the aortic root when using the prosthesis with neosinuses, whereas straight tubular graft revealed localized intrados malrotations (P = .003 for organized vortical structures vs neosinuses graft and P < .001 vs control). In the ascending aorta, recreation of the sinuses resulted in significantly lower velocity and WSS than in the straight tubular graft (P < .001) and controls (P < .001), these alterations were attenuated in the mid‐descending aorta. Incidence of abnormal WSS was markedly higher in the straight tube grafts than neosinus of Valsalva grafts. Conclusions Re‐creation of the sinuses of Valsalva during valve‐sparing root replacement is associated with more physiologic flow and significantly lower WSS in the aortic root. Lower WSSs in the distal thoracic aorta is a novel finding with potential implications on distal aortic remodeling. Graphical abstract Figure. No Caption available.

Biological solutions to aortic root replacement: valve-sparing versus bioprosthetic conduit‡

OBJECTIVESnValve-sparing operations and root replacement with a biologic composite conduit are viable options in aortic root aneurysm. This study was conceived to compare the early and mid-term results of these 2 procedures.nnnMETHODSnFrom September 2002 to November 2015, 749 consecutive patients underwent either a valve-sparing operation or a root replacement with a biologic composite conduit at 2 institutions. Propensity score matching was used to compare similar cohorts of patients in the overall population and in theu2009≤u200955 andu2009≥u200965-year age groups.nnnRESULTSnOverall operative mortality was 0.4%, mean age 57.4u2009±u200914.3 years, 84.6% were male. Individuals in the biologic composite conduit group were older and had worse preoperative risk profiles [chronic pulmonary disease (5.5% vs 0.9%; P u2009=u20090.001), diabetes (6.4% vs 1.5%; P u2009=u20090.001) and NYHAu2009>u20092 (25.2% vs 5.2%; P u2009<u20090.001)]. Mean follow-up was 27.5u2009±u200928.4 months. In the unmatched population, there was no difference in in-hospital deaths (0 in the valve-sparing versus 3 in the biologic composite conduit group; P u2009=u20090.12). These findings were confirmed in the propensity-matched populations. During follow-up, more patients in the biologic composite conduit group underwent reoperation on the aortic valve (2.6% vs 1.5%; P u2009=u20090.026) resulting in a freedom from reoperation of 97.4% vs 98.5%, respectively. Separate analysis for patients stratified by age revealed no difference in outcomes.nnnCONCLUSIONSnIn case of aortic root aneurysm, both valve-sparing operations and root replacement with a biologic composite conduit provide excellent outcomes. However, at mid-term follow-up the use of biologic composite conduit is associated with a higher risk of reoperation.