New frontiers in aortic therapy: focus on current trials and devices in transcatheter aortic valve replacement

The first decade of clinical experience with transcatheter aortic valve replacement since 2002 saw the development of 2 main valve systems, namely the Edwards Sapien balloon-expandable valve series and the Medtronic self-expanding CoreValve. These 2 valve platforms now have achieved commercial approval and application worldwide in patients with severe aortic stenosis whose perioperative risk for surgical intervention is high or extreme. In the second decade of transcatheter aortic valve replacement, clinical experience and refinements in valve design have resulted in clinical drift towards lower patient risk cohorts. There are currently 2 major trials, PARTNER II and SURTAVI, that are both evaluating the role of transcatheter aortic valve replacement in intermediate-risk patient cohorts. The results from these landmark trials may usher in a new clinical paradigm for transcatheter aortic valve replacement in its second decade.

Major themes for 2014 in cardiothoracic and vascular anaesthesia and intensive care

There has been significant progress throughout 2014 in cardiothoracic and vascular anaesthesia and intensive care. There has been a revolution in the clinical approach to acute and chronic adult aortic diseases. Contemporary management of adult aortic disease is based on etiology, clinical presentation, extent, and integrated intervention with medical, endovascular and/or surgical measures. Further European guidelines have explored in depth the cardiovascular management in non-cardiac surgery with a thematic focus to reduce perioperative mortality from the leading offender, namely myocardial ischemia. Integrated guidelines address the management of myocardial revascularization including the percutaneous and surgical options. Despite 50 years since the first coronary artery bypass grafting procedure and impressive advances in interventional cardiology, surgical revascularization remains a gold standard for many patients with coronary artery disease. These advances in 2014 will likely further improve perioperative outcomes for our patients.

The functional aortic annulus in the 3D era: focus on transcatheter aortic valve replacement for the perioperative echocardiographer

The functional aortic annulus represents a sound clinical framework for understanding the components of the aortic root complex. Recent three-dimensional imaging analysis has demonstrated that the aortic annulus frequently is elliptical rather than circular. Comprehensive three-dimensional quantification of this aortic annular geometry by transesophageal echocardiography and/or multidetector computed tomography is essential to guide precise prosthesis sizing in transcatheter aortic valve replacement to minimize paravalvular leak for optimal clinical outcome. Furthermore, three-dimensional transesophageal echocardiography accurately can quantify additional parameters of the functional aortic annulus such as coronary height for complete sizing profiles for all valve types in transcatheter aortic valve replacement. Although it is maturing rapidly as a clinical imaging modality, its role in transcatheter aortic valve replacement is seen best as complementary to multidetector computed tomography in a multidisciplinary heart team model.

Extracellular matrix determinants and the regulation of cancer cell invasion stratagems

During development, wound repair and disease-related processes, such as cancer, normal, or neoplastic cell types traffic through the extracellular matrix (ECM), the complex composite of collagens, elastin, glycoproteins, proteoglycans, and glycosaminoglycans that dictate tissue architecture. Current evidence suggests that tissue-invasive processes may proceed by protease-dependent or protease-independent strategies whose selection is not only governed by the characteristics of the motile cell population, but also by the structural properties of the intervening ECM. Herein, we review the mechanisms by which ECM dimensionality, elasticity, crosslinking, and pore size impact patterns of cell invasion. This summary should prove useful when designing new experimental approaches for interrogating invasion programs as well as identifying potential cellular targets for next-generation therapeutics.

Assessing natural and disturbed population structure in European grayling Thymallus thymallus: melding phylogeographic, population genetic and jurisdictional perspectives for conservation planning

Natural and human-mediated population structure of European grayling Thymallus thymallus was assessed in primarily Austrian reaches of the Danube River catchment. Data on phylogeographic structure based on mitochondrial DNA (mtDNA) were combined with variation found across 13 microsatellite loci to assess introgression stemming from stocking activities. Populations north of the Alps generally showed no signs of long-term introgression from allochthonous stocks, although one population comprised two distinct genotypic groups, one of which may stem from recently stocked material. South of the Alps, levels of introgression with stocks from the north were extensive and only one of six populations is believed to represent a reference state. Allelic diversity and expected heterozygosity were positively correlated with mtDNA admixture supporting more recent introgression and that there is little or no reproductive barrier between these two major lineages north and south of the Alps. A third unrelated mtDNA lineage is described from the Lafnitz, a tributary of the Raab drainage. The high lineage diversity in the upper Austrian Danube is not concordant with an existing model of T. thymallus evolutionarily significant units in Europe. Caveats in naming such units or following a strict hierarchical conservation unit structure for broadly distributed species with complex phylogeographic distributions stretching over various jurisdictions are discussed. The necessity of using both phylogeographic and population genetic approaches in evaluating the history and conservation value of populations in a conservation context is additionally highlighted.

The effect of surgical and transcatheter aortic valve replacement on mitral annular anatomy

BACKGROUND

The effect of aortic valve replacement on three-dimensional mitral annular geometry has not been well described. Emerging transcatheter approaches for aortic valve replacement employ fundamentally different mechanical techniques for achieving fixation and seal of the prosthetic valve than standard surgical aortic valve replacement. This study compares the immediate impact of transcatheter aortic valve replacement (TAVR) and standard surgical aortic valve replacement (AVR) on mitral annular anatomy.

METHODS

Real-time three-dimensional echocardiography was performed in patients undergoing TAVR using the Edwards Sapien valve (n = 10 [Edwards Lifesciences, Irvine, CA]) or AVR (n = 10) for severe aortic stenosis. Mitral annular geometric indexes were measured using Tomtec EchoView (Tomtec Imaging Systems, Munich, Germany) to assess regional and global annular geometry.

RESULTS

Mixed between-within analysis of variance showed no differences between TAVR and AVR groups in any of the mitral annular geometric indices preoperatively. However, postoperative analysis did demonstrate an effect of AVR on geometry. Patients undergoing open AVR had significant decrease in annular height, septolateral diameter, mitral valve transverse diameter, and mitral annular area after valve replacement (p ≤ 0.006). Similar changes were not noted in the TAVR group.

CONCLUSIONS

Mitral annular geometry is better preserved by TAVR than by AVR. Thus, TAVR may be a more physiologic approach to aortic replacement.

Saddle-shape annuloplasty increases mitral leaflet coaptation after repair for flail posterior leaflet

BACKGROUND

The primary goal of surgical mitral repair is the reestablishment of normal leaflet coaptation. Surgical techniques that maintain or restore leaflet geometry promote leaflet coaptation. Recent 3-dimensional (3D) echocardiographic studies have shown that saddle-shaped annuloplasty has a salutary influence on leaflet geometry. Therefore we hypothesized that saddle-shaped annuloplasty would improve leaflet coaptation in cases of repair for flail posterior leaflet segments.

METHODS

Sixteen patients with flail posterior segment and severe mitral regurgitation had valve repair using standard techniques. Eight patients received saddle-shaped annuloplasty and 8 patients received flat annuloplasty. Real-time 3D transesophageal echocardiography was performed before and after repair. Images were analyzed using custom software to calculate mitral annular area (MAA), septolateral dimension (SLD), intercommissural width (CW), total leaflet area (TLA), and leaflet coaptation area (LCA).

RESULTS

Postrepair MAA (flat, 588.6±26.5 mm2; saddle, 628.0±35.3 mm2; p=0.12) and TLA (flat, 2198.5±151.6 mm2; saddle, 2303.9±183.8 mm2; p=0.67) were similar in both groups. Postrepair LCA was significantly greater in the saddle group than in the flat group (226.8±24.0 mm2 and 154.0±13.0 mm2, respectively; p=0.02).

CONCLUSIONS

Real-time 3D echocardiography and novel imaging software provide a powerful tool for analyzing mitral leaflet coaptation. When compared with flat annuloplasty, saddle-shaped annuloplasty improves LCA after mitral valve repair for severe mitral regurgitation secondary to flail posterior leaflet segment. Use of saddle-shaped annuloplasty devices may increase repair durability.

Ischemic mitral regurgitation: a quantitative three-dimensional echocardiographic analysis

BACKGROUND

A comprehensive three-dimensional echocardiography based approach is applied to preoperative mitral valve (MV) analysis in patients with ischemic mitral regurgitation (IMR). This method is used to characterize the heterogeneous nature of the pathologic anatomy associated with IMR.

METHODS

Intraoperative real-time three-dimensional transesophageal echocardiograms of 18 patients with IMR (10 with anterior, 8 with inferior infarcts) and 17 patients with normal MV were analyzed. A customized image analysis protocol was used to assess global and regional determinants of annular size and shape, leaflet tethering and curvature, relative papillary muscle anatomy, and anatomic regurgitant orifice area.

RESULTS

Both mitral annular area and MV tenting volume were increased in the IMR group as compared with patients with normal MV (mitral annular area=1,065±59 mm2 versus 779±44 mm2, p=0.001; and MV tenting volume=3,413±403 mm3 versus 1,696±200 mm3, p=0.001, respectively). Within the IMR group, patients with anterior infarct had larger annuli (1,168±99 mm2) and greater tenting volumes (4,260±779 mm3 versus 2,735±245 mm3, p=0.06) than the inferior infarct subgroup. Papillary-annular distance was increased in the IMR group relative to normal; these distances were largest in patients with anterior infarcts. Whereas patients with normal MV had very consistent anatomic determinants, annular shape and leaflet tenting distribution in the IMR group were exceedingly variable. Mean anatomic regurgitant orifice area was 25.8±3.0 mm2, and the number of discrete regurgitant orifices varied from 1 to 4.

CONCLUSIONS

Application of custom analysis techniques to three-dimensional echocardiography images allows a quantitative and systematic analysis of the MV, and demonstrates the extreme variability in pathologic anatomy that occurs in patients with severe IMR.

Quantitative mitral valve modeling using real-time three-dimensional echocardiography: technique and repeatability

BACKGROUND

Real-time three-dimensional (3D) echocardiography has the ability to construct quantitative models of the mitral valve (MV). Imaging and modeling algorithms rely on operator interpretation of raw images and may be subject to observer-dependent variability. We describe a comprehensive analysis technique to generate high-resolution 3D MV models and examine interoperator and intraoperator repeatability in humans.

METHODS

Patients with normal MVs were imaged using intraoperative transesophageal real-time 3D echocardiography. The annulus and leaflets were manually segmented using a TomTec Echo-View workstation. The resultant annular and leaflet point cloud was used to generate fully quantitative 3D MV models using custom Matlab algorithms. Eight images were subjected to analysis by two independent observers. Two sequential images were acquired for 6 patients and analyzed by the same observer. Each pair of annular tracings was compared with respect to conventional variables and by calculating the mean absolute distance between paired renderings. To compare leaflets, MV models were aligned so as to minimize their sum of squares difference, and their mean absolute difference was measured.

RESULTS

Mean absolute annular and leaflet distance was 2.4±0.8 and 0.6±0.2 mm for the interobserver and 1.5±0.6 and 0.5±0.2 mm for the intraobserver comparisons, respectively. There was less than 10% variation in annular variables between comparisons.

CONCLUSIONS

These techniques generate high-resolution, quantitative 3D models of the MV and can be used consistently to image the human MV with very small interoperator and intraoperator variability. These data lay the framework for reliable and comprehensive noninvasive modeling of the normal and diseased MV.

Discriminated response and incentive processes in operant conditioning: a two-factor model of stimulus control

Understanding stimulus control generated in instrumental learning requires the direct investigation of discriminated response and reinforcer (incentive) processes acquired exclusively through the response-reinforcer contingencies operating on complex (multicomponent) baselines. Two series of stimulus-compounding studies accomplished this direct investigation. In one series, the independent variable was the relative reinforcement between schedule components; in the second series, it was relative response rate between components. Stimulus-compounding tests revealed that response and incentive processes enhanced each other when in agreement, counteracted each other when in opposition, and produced intermediate results when only one factor was operating. This pattern of results led to the conclusion that these factors were algebraically combining and to the development of a response/incentive matrix reflecting these dynamics. This two-factor analysis was extended to the peak-shift effect in stimulus generalization experiments and to the generation of inhibitory control. Two decades of stimulus compounding and peak-shift research were organized within this two-factor framework, extending this traditional approach to learning to active research areas heretofore not systematically considered in these terms.

The effect of reinforcement differences on choice and response distribution during stimulus compounding

In Experiments I and II, rats were trained to respond on one lever during light and another during tone. The absence of tone and light controlled response cessation. In the multiple schedule of Experiment I, all reinforcements were received for responding in tone or light; in the chain schedule of Experiment II, all reinforcements were received in no tone + no light for not responding. Experiment I subjects, for which tone and light were associated with response and reinforcement increase, responded significantly more to tone-plus-light than to tone or light alone (additive summation). Experiment II subjects, for which tone and light were associated with response increase and reinforcement decrease, responded comparably to tone, light, and tone + light. Thus, additive summation was observed when stimulus-response and stimulus-reinforcer associations in tone and light were both positive, but not when they were conflicting. All subjects in both experiments responded predominantly on the light-correlated lever during tone + light, even when light intensity was reduced in testing. Furthermore, when a light was presented to a subject engaged in tone-associated responding, all subjects immediately switched the locus of responding to the light-correlated lever. No change in locus occurred when a tone was presented to a subject engaged in light-associated responding, irrespective of the stimulus-reinforcer association conditioned to tone. The light-lever preference in tone + light indicates that the heightened responding observed in Experiment I was not the summation of tone-associated behavior with light-associated behavior. Rather, it appears to be the result of a facilitation of one operant (light-associated responding) by the reinforcement-associated cue for the other.

Generalization peak shift in rats under conditions of positive reinforcement and avoidance

Rats were trained to discriminate between two click frequencies. One frequency was associated with either variable-interval food reinforcement (Experiment 1) or free-operant avoidance (Experiment 2). The other frequency was associated with the absence of food in Experiment 1 and the absence of shock in Experiment 2. On a click frequency generalization test, the rats in both experiments showed positive peak shift with the shape of the relative gradients being very similar. This is the first reported instance of peak shift in rats when responding was maintained by an avoidance contingency. Nondifferentially trained controls showed that this shift was due exclusively to associative processes, with nonassociative stimulus factors in themselves apparently making no contribution to increased rates at particular stimulus values. These results show the comparability of appetitive and aversive control and support the position that gradient differences do not result from approach versus avoidance per se.

Discrimination training and stimulus compounding: consideration of non-reinforcement and response differentiation consequences of S

In Exp. 1, four rats were trained on a two-component multiple schedule with tone and light each associated with different variable-interval schedules. Extinction in light-out no-tone, common to previous studies reporting additive summation to compounded discriminative stimuli, was omitted from training. In testing, the simultaneous presentation of tone and light controlled a response rate intermediate between that controlled by these stimuli presented singly. In Exp. 2, animals were trained on three-ply multiple schedules. While tone and light were each associated with variable-interval schedules for both groups, light-out no-tone signalled extinction for one and differential-reinforcement-of-behavior-other-than-bar-pressing for the other. This permitted response reduction during light-out no-tone to be viewed independently of non-reinforcement. Responding of both groups showed summation to tone plus light in testing, with the effect clearly larger for extinction-trained subjects. These experiments indicate that: (1) discrimination training afforded by extinction has been integral to additive summation previously reported, (2) response differentiation and non-reinforcement consequences of extinction training contribute to the magnitude of summation, and (3) summation and peak shift might be functionally related phenomena.