The role of transesophageal echocardiography in aortic valve ... - Core

i n d i a n h e a r t j o u r n a l 6 6 ( 2 0 1 4 ) 3 2 7 e3 3 3

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Review Article

The role of transesophageal echocardiography in aortic valve preserving procedures Terri Hall a,b, Pallav Shah a,b, Sudhir Wahi a,b,* a

Department of Cardiothoracic Surgery, Princess Alexandra Hospital, University of Queensland, 199 Ipswich Road, Woolloongabba, Brisbane 4102, Australia b Department of Cardiology, Princess Alexandra Hospital, University of Queensland, 199 Ipswich Road, Woolloongabba, Brisbane 4102, Australia

article info

abstract

Article history:

In selected cases of aortic regurgitation, aortic valve (AV) repair and AV sparing root

Received 5 September 2013

reconstruction viable alternatives to aortic valve replacement. Repair and preservation of

Accepted 7 May 2014

the native valve avoids the use of long-term anticoagulation, lowers the incidence of subsequent thromboembolic events and reduces the risk of endocarditis. Additionally repair has a low operative mortality with reasonable mid-term durability. The success and

Keywords:

longer term durability of AVPP has improved with surgical experience. An understanding of

Transesophageal echocardiography

the mechanism of the AR is integral to determining feasibility and success of an AVPP.

Aortic valve insufficiency

Assessment of AV morphology, anatomy of the functional aortic annulus (FAA) and the

Aortic valve repair

aortic root with transesophageal echocardiography (TEE) improves the understanding of the mechanisms of AR. Pre- and intra-operative TEE plays a pivotal role in guiding case selection, surgical planning, and in evaluating procedural success. Post-operative transthoracic echocardiography is useful to determine long-term success and monitor for recurrence of AR. Copyright ª 2014, Cardiological Society of India. All rights reserved.

1.

Introduction

In selected cases AV repair and AV sparing root reconstruction are proving to be viable alternatives for the surgical management of significant AR. These procedures, collectively known as AVPP offer additional benefits over the traditional AVR with a mechanical or bioprosthesis. Repair and preservation of the

native valve avoids the use of long-term anticoagulation, lowers the incidence of subsequent thromboembolic events and reduces the overall risk of endocarditis. Additionally, repair has a relatively low operative mortality with reasonable mid-term durability.1e4 The success rate and longer term durability of AVPP has, however, been a source of conjecture since its inception.1 Over time it has become increasingly clear that along with surgical experience, a thorough

Abbreviations: AV, aortic valve; AR, aortic regurgitation; AVPP, aortic valve preserving procedure; TEE, transesophageal echocardiogram; STJ, sino-tubular junction; AVJ, aorto-ventricular junction; FAA, functional aortic annulus; ME LAX, mid-esophageal long axis; ME SAX, mid-esophageal short axis; LVOT, left ventricular outflow tract; BAV, bicuspid aortic valve. * Corresponding author. E-mail address: [email protected] (S. Wahi). http://dx.doi.org/10.1016/j.ihj.2014.05.001 0019-4832/Copyright ª 2014, Cardiological Society of India. All rights reserved.

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understanding of the mechanism and etiology of the AR is integral to determining feasibility and success of an AVPP.5e7 Pre and post-operative TEE plays a pivotal role in guiding the surgeon with case selection, surgical planning and in evaluating procedural success. This article aims to outline the comprehensive TEE assessment needed to provide this guidance. In doing so we review aortic valve and aortic root anatomy, the classification system of AR, typical echocardiographic appearance of each lesion and the stepwise approach to postoperative evaluation of success.

2.

Anatomy of the AV and aortic root

The aortic root is a direct continuation of the left ventricular outflow tract (LVOT). It acts as a stent to support the three cusps of the aortic valve.8 The aortic root is demarcated by the sino-tubular junction (STJ) superiorly and the aortoventricular junction (AVJ) inferiorly.8 Just under half of the circumference of the aortic root is connected to the muscular septum with the remaining portion (55%) attached to a fibrous membrane.9 Part of this fibrous membrane is in direct connection with the anterior mitral valve leaflet. The aortic root comprises the sinuses of Valsalva, the leaflets, commissures and inter-leaflet triangles.10 The leaflets insert into the aorta in a semi-lunar crown-like manner. The base of attachment within the ventricular myocardium forms a virtual basal ring often termed the “aortic annulus” in echocardiography. The peripheral attachment of the leaflets marks the STJ. The point at which the ventricular components give rise to the fibro-elastic walls of the aortic sinuses marks the anatomic AVJ. Thus there are multiple “rings” rather than one true annulus within the aortic root e the virtual basal ring formed by the leaflet attachments, the AVJ, the crown-like ring of leaflet attachments and the STJ. It is this structure of rings which makes up the complex FAA (Fig. 1) as described by Piazza et al11 The three components of the aortic root e the leaflets, the annulus and the STJ are imperative for valve function and competence. All elements must be considered when evaluating the mechanism and etiology of the AR.

3.

Pre-repair TEE

TEE has been shown to provide a highly accurate anatomic assessment of all types of AR lesions and has proven to be strongly predictive of valve repairability and postoperative success.7 Pre-repair TEE imaging should focus on a combination of function and anatomy to determine feasibility of AVPP.

3.1.

Functional classification of AR

AR can be caused by either dilatation of the FAA or primary disease of the AV leaflets. Dilatation of the ascending aorta distal to the aortic root will not cause AR unless the STJ is involved.12 Primary leaflet problems include prolapse, perforation or leaflet restriction. El Khoury et al proposed a classification of AV and/or aortic root pathologies similar to the Carpentier classification for mitral valve disease (Fig. 2).5,6 A

Fig. 1 e a & b: The functional aortic annulus (FAA).

subsequent study by le Polaine de Waroux et al has shown this functional classification provided by TEE is a strong predictor of repairability and outcome (4 year freedom from >grade 2 AR, reoperation or death, p ¼ 0.04).7

3.1.1.

Type I lesions

Type 1 mechanism of AR implies regurgitation due to FAA dilatation or cusp perforation with normal leaflet motion. This pathology produces a central regurgitant jet of AR. Dilatation of the FAA causes outward displacement of the commissures and decreased coaptation. This mechanism is further categorized into four subtypes. Type 1a describes STJ enlargement and dilatation of the ascending aorta. Type 1b AR results from dilatation of the sinuses of Valsalva and the STJ. Type 1c is related to dilatation of the AVJ. Type 1d is a specific category which indicates cusp perforation.5 Type 1a lesions are usually the result of progressive atherosclerotic disease of the ascending aorta with dilatation of the STJ. They can often be associated with aneurysms of the ascending aorta.5 Surgical correction aims at restoration or refashioning of the STJ and replacing aneurysmal portions of the thoracic aorta.8 Type Ib lesions involve aneurysms of the aortic root (Fig. 3) that are frequently associated with degenerative conditions of the media such as Marfan’s or Ehlers-Danlos syndrome.13,14 Historically, surgical treatment of this pathology involved concomitant aortic root and AV replacement (Bentall procedure).15 The valve-sparing alternative exists in two main forms: AV reimplantation (David procedure) and AV remodeling (Yacoub procedure).2,16 The degree of aortic root dilatation has not been shown to be a factor in predicting repair


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Fig. 2 e Repair oriented functional classification of aortic insufficiency. Reproduced from the J Thorac Cardiovasc Surg, Volume 137 (Issue 2), Boodhwani M, de Kerchove L, Glineur D, Poncelet A, Rubay J, Astarci P, et al. Repair-oriented classification of aortic insufficiency: impact on surgical techniques and clinical outcomes. 286e294, Copyright (2009), with permission from Elsevier.

failure. However those patients with Marfan’s syndrome are more susceptible to recurrent AR than those without.17 Type Ic lesions rarely occur in isolation as the sole cause of AR. More often this lesion in found concurrently with more complex aortic root and or leaflet pathology.5 When it is the only causative factor a subcommissural annuloplasty (with or without an STJ annuloplasty) is the procedure of choice.5 Type 1d lesions refer to cusp perforation as a result of infection or trauma. They are treated with a pericardial patch closure.5

3.1.2.

Type II lesions

As in the Carpentier classification, type II lesions relate to excess leaflet tissue, in particular cusp prolapse. These lesions may occur in isolation or as a late consequence of longstanding AR secondary to a Type I phenomena.5 When cusp prolapse occurs in isolation it may be the result of degeneration secondary to age and hypertension. However there is often no identifiable cause. The definition of cusp prolapse is when the free margin of one or more aortic cusps overrides the plane of the aortic annulus.8 The subsequent regurgitant jet is eccentric and in the opposite direction to the prolapsing cusp. A prolapse of the right coronary cusp produces a posteriorly directed jet.18 In the mid-esophageal long axis view (ME LAX) the jet is directed towards the anterior mitral valve leaflet (Fig. 4). Conversely a prolapse of the left or noncoronary cusp produces an anteriorly-directed jet. On the ME LAX the posterior cusp can either be the left or noncoronary cusp depending on the plane of the ultrasound. Thus the mid-esophageal short axis (ME SAX) view or a simultaneous orthogonal view is needed to determine the origin of the jet and the prolapsing cusp. Cusp prolapse can be further described as partial, whole or flail.7 Partial cusp prolapse (Fig. 5) involves prolapse of the distal part of the cusp into the left ventricular outflow tract (LVOT). There is

frequently a clear bending of the cusp body that becomes fibrous and thickened (Fig. 5A). It is sometimes visible in the ME SAX as a fibrous band across the body of the leaflet (Fig. 5B). Whole cusp prolapse is the free edge overriding the plane of the annulus with the entire body billowing into the LVOT (Fig. 6). Unlike the partial prolapse that shows a fibrous band in the ME SAX view, whole cusp prolapse can be appreciated as a circular structure in the SAX of the LVOT immediately below the valve.8 A flail cusp is defined as tip eversion into the LVOT on the ME LAX view (Fig. 7). In some cases an eccentric AR jet is visualized without obvious evidence of cusp prolapse. In these situations the pathology may be fenestrations or small tears along the free margin of the cusp.18 Surgical correction of Type II lesions involves various techniques including plication, triangular resection, free margin re-suspension or implantation of a pericardial patch.19,20 These procedures can be performed in addition to the AV sparing techniques when concomitant aortic root or

Fig. 3 e Type 1b mechanism of AR (dilated aortic root).

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ascending aorta dilatation is present. Isolated cusp prolapse frequently requires a subcommissural annuloplasty for stabilization.6

3.1.3.

Type III lesions

The mechanism of AR in a Type III lesion is related to leaflet retraction, commissural fusion and incomplete closure. These lesions are mostly seen in rheumatic and degenerative calcific disease. The valve is often thickened, more echogenic and usually calcified. Due to the underlying mechanism of AR these valves are the most difficult to repair and are more susceptible to failure.17,18 Surgical repair may be feasible in the form of cusp shaving, decalcification or, in certain situations, patch extension.6 Bhoodhwani et al published the results of 264 patients who underwent AVPP. Freedom from recurrent AR (>grade 2) and from re-operation at 5 years was 88 3% and 92 4% for Type 1 lesions and 82 9% and 93 5% for those with a Type II mechanism. These patient cohorts had a more favorable outcome compared to those with the Type III lesions who experienced only 76 17% freedom from AR and 84 13% freedom from repeat AV surgery. These results provide encouraging data for AV repair durability and recognize the Type III mechanism as a predictor of recurrent AR e potentially requiring repeat surgery following a primary AVPP.6

3.2.

Anatomy

In addition to function, several anatomical considerations relating to the valve and aortic root are important in preoperative planning. The number of leaflets, degree of leaflet calcification and pliability, and the aortic root dimensions are considered essential in determining the mechanism of AR but also to predict long-term success of an AVPP.7

3.2.1.

Aortic root dimensions

TEE is the ultrasound modality of choice to measure the dimensions of the aortic root. High-resolution images with appropriate gain settings provide accurate and reproducible measurements.21 The most important TEE view of the aortic root and ascending aorta is the ME LAX view. At this level, diameters of the annulus, sinuses of Valsalva, STJ and the tubular ascending aorta can be obtained (Fig. 8). The annulus

Fig. 4 e Eccentric AR jet secondary to aortic valve prolapse.

Fig. 5 e Partial cusp prolapse, A: LAX view of partial cusp prolapse with mid-leaflet bending (arrow) B: SAX view of a fibrous band (arrow).

is measured between the hinge points of the AV leaflets (inner edge to inner edge) during systole.21 This point in the cardiac cycle reveals the largest aortic annular diameter. The remaining measures are taken in end diastole using a leading

Fig. 6 e Aortic valve whole cusp prolapse involving the right coronary cusp.


edge to leading edge technique. The geometry of the aortic root has been shown to be relatively consistent across anatomical studies with variations in size rather than shape.11 Aortic root diameter as measured at the level of the sinuses of Valsalva is strongly related to age and body surface area (BSA).22 According to the 2005 American Society of Echocardiography Recommendations for Chamber Quantification, dilatation of the aortic root is described as a sinus of Valsalva diameter greater than the upper limit of the 95% confidence interval of the distribution in a large reference population.22 The BSA can be used to determine the predicted trans-sinus diameter and therefore the presence of dilatation across the three age divisions. Specific to the evaluation of cusp prolapse is the measurement of the effective height. Effective height is the height to which the central free margin of the cusp rises over the aortic insertion line of the cusp (Fig. 9). Effective height should be 9e10 mm for a normal cusp. Less than 6e7 mm indicates a degree of prolapse.23

3.2.2.

Valve morphology e calcification and thickening

Calcification of the aortic leaflets can be graded according to the system commonly used in stenotic valves. It is a subjective assessment that scores the degree of calcification from 1 to 4.24 A score of 1 implies no calcification, 2 mildly calcified (small isolated spots), 3 moderately calcified (multiple large spots) and 4 heavily calcified (extensive thickening and calcification of all cusps). In general valves with a calcification score of 2 mm) on either cusp with or without restricted leaflet motion.26 Commissural thickening is defined as the presence of increased echodensity at either commissure. Nash et al performed an echocardiographic study to determine the factors most likely to predict a successful repair. On multivariate analysis following adjustment for age, the presence of an eccentric jet, absence of cusp and commissural thickening, and lack of cusp calcification were all independently associated with a greater likelihood of

Fig. 7 e Eversion of the right coronary cusp (flail).

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repair. Recognition of these features enhances patient selection and improves success rates associated with AVPP.

3.2.3.

Bicuspid aortic valves

Bicuspid AV (BAV) is the commonest congenital cardiac abnormality with an estimated prevalence of 1e2%.27 They frequently occur in association with other pathologies such as coarctation of the aorta, patent ductus arteriosus, ventricular septal defects and anomalous origins of the coronary arteries. Additionally, abnormalities in matrix metalloproteinases within the aorta lead to loss of smooth muscle within the aortic wall media and predisposes the patient to the development of an aortic aneurysm and dissection.28 Bicuspid valves have been consistently reported as more favorable for repair compared to tricuspid valves.29 A number of reasons have been suggested for this. However, the fact that there is a single coaptation line appears to contribute to increased repairability. Qualitative descriptors of the BAV have been formalized into a classification system proposed by Sievers and Schmidtke.30 The system is based on three main characteristics e the number of raphes, the spatial position of the cusps or raphes and the functional status of the valve. The main category of importance for surgical planning is the number of raphes. A “pure” BAV is one that has two cusps of equal size with no raphe e this is referred to as type 0.30 The most common form of a BAV, however, is the type 1 which has fusion of two cusps and one raphe. Fusion of the left and right cusps is most frequently seen. As the name would suggest a type 2 BAV has two raphes present. The valves can be further classified based on the orientation of the cusps. The cusps of a type 0 BAV can be oriented either antero-posteriorly or laterally. Type 1 BAV is further described according to the position of the raphe relative to the coronary sinuses. For example a type 1 BAV with the raphe positioned between the left and right coronary sinuses is correctly termed Type 1 L/R. The functional status of the valve (insufficient, stenotic or both) is the final descriptor in this classification system. Aicher et al assessed the effect valve configuration on long-term repair success.31 They demonstrated that although the different

Fig. 8 e Aortic root measurements. Measurements of the proximal aorta acquired from the ME LAX view at end diastole (in order from left to right e Sinuses of Valsalva, STJ and tubular ascending aorta).

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The importance of coaptation height, the first step in the algorithm, has been further reiterated by Pethig et al32 This study specifically looked at the AV sparing population and graded coaptation heights according to three levels e A, B or C (Fig. 10). A coaptation level within the tube graft (type A) resulted in a mean AR grade of 0.3 0.5 as compared with 2.5 0.6 for coaptation below the prosthesis (type C) (p < 0.001). Valve repair can reduce the effective opening of the leaflets and as such peak and mean transvalvular gradients should be assessed to ensure there is no significant stenosis. Generally peak and mean gradients in excess of 30 and 15 mmHg respectively are risk factors for the development of severe aortic stenosis potentially necessitating further surgery.33

Fig. 9 e Measurement of effective height. The effective height is the distance between the aortic annulus and the tip of leaflet coaptation. (Normal effective height is 9e10 mm).

cusp fusion patterns and extent of fusion (partial or complete) had no influence on repair results, the orientation of the commissures did make a difference. Truly BAV (type 0) and those with type 1 or 2 but anatomically similar to type 0 (cusp arrangement close to 180 ) seem to provide more stable longterm results.

4.

5.

Conclusion

Improved understanding of the complex aortic root and encouraging outcomes for AVPP have led to increased interest in this type of surgery. Integral to the success of this operation is case selection. TEE has shown to be an essential tool in describing the anatomy and functional classification relating to the AR. The comprehensive assessment described above allows cardiologists and surgeons to communicate in a common language specific to this pathology and facilitates planning of repair strategies and ultimately improved long term outcomes. In addition the availability of TEE for real time intraoperative imaging gives the surgeon the ability to evaluate the adequacy of repair at the time of surgery. With enhanced understanding of the imaging requirements, clinicians may be able to better recognize those patients suitable

Post-repair TEE

TEE has proven to be a valuable tool intra-operatively during mitral valve repair and accordingly has become a mainstay in assessing the adequacy of AVPPs. Le Polain de Waroux et al performed a retrospective analysis of TEE data from 186 patients who underwent valve repair for significant AR.17 Their analysis yielded a stepwise algorithm for the assessment of adequacy of repair and prediction of recurrent AR. The three strongest predictors were the level of coaptation relative to the annulus, the presence of residual AR and the leaflet coaptation length. The authors’ recommendation, as a first step, is the assessment of the leaflet coaptation relative to the annulus. The risk of recurrent AR is in the order of 71% in those patients whose coaptation falls below the annulus (where there is some degree of residual cusp prolapse). Residual cusp prolapse may be related to the primary pathology or induced by the surgeon when reducing the aortic root dimensions (particularly the STJ). The second step in the algorithm requires assessment of the presence or absence of residual AR. In the absence of residual AR, the subsequent risk of >3 þ AR at follow up was low (2%). The final step is to evaluate the coaptation length. A cutoff of 4 mm is used to predict long-term repair success. Coaptation lengths below 4 mm are associated with a 47% chance of recurrent AR as opposed to a 5% risk of repair failure in those patients with adequate coaptation (>4 mm).

Fig. 10 e Coaptation heights assessed relative to aortic graft. Type A has the coaptation point >2 mm within the graft. Type B has the coaptation close to the lower border of the graft. Type C has the coaptation >2 mm below the graft. Reproduced from the Ann Thorac Surg, Volume 73, Pethig K, Milz A, Hagl C, Harringer W, Haverich A. Aortic valve reimplantation in ascending aortic aneurysm: risk factors for early valve failure. 29e33, Copyright (2002), with permission from Elsevier.


for AVPP, and therefore potentially avoid AV replacement and the risk of prosthetic valve complications.

Conflicts of interest All authors have none to declare.

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