Intro4u2u

The small aortic annulus and the small aortic root represent one of the most vexing problems to the cardiac surgeon.  There are studies in the literature which support the belief that the size of the prosthesis inserted to replace the aortic valve has little influence on survival [1,2].  This is simply not true in our experience and many others.  When patient prosthesis mismatch (PPM) is looked at specifically one finds that it is an extremely important variable that predicts morbidity and mortality.  In a recent study by Blais, et al, PPM had a significant impact on mortality [3].  The risk of death was increased 2.1 fold in patients with moderate mismatch and 11.4 fold in patients with severe PPM (Slide 1).  All patients who died with severe PPM died of cardiac causes, low cardiac output syndrome, or myocardial infarction. Severe PPM was particularly deleterious in patients with poor LV function.  The mortality in this group of patients was 77% (Slide 2).
Slide 1

Slide 2

The significance of these findings are particularly important to analyze.  Cardiac surgeons today are faced with an ever increasing sub-population of patients with multiple co-morbidities.  Many of these, such as poor LV function, an exhausting list of complex medical problems, and advanced age, are beyond our control.  On the other hand, severe PPM is something we do have control over.  A strategy which preoperatively addresses the potential for PPM postoperatively will have a significant benefit on mortality.
Slide 3

The postoperative indexed EOA can be predicted preoperatively.  An EOA for each of the prostheses can be obtained from the literature.  Examples are in Table 1 from Blais article (Slide 3).  The indexed EOA is obtained simply by dividing the EOA by the recipient patient’s body surface area. PPM should not be clinically significant if the indexed EOA postoperatively is greater than 0.85 cm. sq./meter sq.  PPM will be moderate between 0.65 and 0.85 cm. sq./meter sq. Mismatch will be severe if the indexed EOA postoperatively turns out to be less than 0.65 cm. sq./meter sq.
Slide 4

The small aortic valve is most commonly seen in patients of small body size and is often associated with congenital heart disease.  It is in patients who have severe aortic stenosis that the adult cardiac surgeon confronts this problem.  In this situation we are asked to exchange one small valve for another.  Generally speaking, in the adult population we rarely confront an inadequate left ventricular outflow tract except in the instance of asymmetrical septal hypertrophy of the left ventricle.  This problem is easily recognized on the preoperative echocardiogram.  Turbulent flow is seen around a bulging septum on sagital view of the left ventricular outflow tract beneath the aortic valve. Measurements of the septum are significantly abnormal on echocardiography.  The cure is simply to perform a septal myomectomy after the aortic valve is removed.  The septum is incised just beneath the aortic annulus from the junction of the right and left coronary cusps to a point beneath the right coronary orifice (Slide 4).  The incision in the muscle is 2-4 mm deep and is carried towards the apex of the heart until one reaches the level of the papillary muscles.  There is no real danger of injuring the mitral valve as long as one stays on the ventricular septum.  Staying in line or to the left of the right coronary ostium keeps one away from the conduction system.  Obviously, the extent of the septal myomectomy is dependent on the degree of asymmetrical septal hypertrophy.

The smaller size traditional mechanical and bioprosthetic valves are inherently stenotic.  Under the best of circumstances they leave many patients with residual mild to moderate aortic stenosis.  Slide 5 shows the effective orifice areas for the most commonly available mechanical and bioprosthetic aortic valves.  Slide 6 shows that much of the space that these valves occupy in the LVOT is unavailable to blood flow and the flow through these valves is turbulent in nature (Slide 7).
Slide 5

Slide 6

Slide 7

The tradition has been to handle the small aortic annulus with an aortic annular enlargement procedure and the small aortic root with an aortic patch of some sort.  There are two commonly performed aortic annular enlargement techniques.  The Mannougian operation is considered the most simple and therefore the most common one utilized [4].  It is performed by cutting through the aortic annulus at the juncture of the left and right coronary cusps (Slide 8, 9).  This procedure only allows upsizing the prosthesis by 2 mm.  Any larger size would require incising too much of the anterior leaflet of the mitral valve, resulting in serious malfunction.  Upsizing by more than 2 mm requires the prosthesis to be placed on an oblique angle.  This would result in more turbulent flow patterns and thus be just as obstructive as a size smaller prosthesis.  One valve size increase is often insufficient to completely prevent PPM.
Slide 8

Slide 9

Slide 10

A much larger prosthesis can be inserted in the aortic root if one utilizes the aorto-ventriculoplasty technique described by Konno [5].  This technique requires transecting the first septal perforator artery when the ventricular septum is divided towards the apex of the heart.  The incision in the septum is initiated at the commissural junction where the right and left cusps of the aortic valve meet (Slide 10).  While this maneuver is well tolerated in children, many adults will develop a significant decline in left ventricular performance when this artery is divided.  Therefore, this may be a poor alternative for the adult patient with a small aortic annulus.
Slide 11

Pibarot and Dumesnil have evaluated many prostheses for the presence of mismatch [6,7].  They have clearly shown that natural aortic valve replacement options fare distinctly more favorably in patients with small aortic annuluses (Slide 11). Importantly, they have demonstrated that these differences are more pronounced when the patients are exercised.  The pulmonary autograft fares the best, followed by the aortic homograft and the stentless heterograft.  Some of the differences in the natural valve group may be related to the implant technique employed.  Most homografts and autografts were implanted using a free-standing root replacement technique, while most stentless heterografts were implanted as a sub-coronary implant.  We have found the root replacement technique reliable and can be performed with similar morbidity and mortality rates as a valve replacement [8].  Technique involves mobilizing the coronary arteries on buttons of aortic wall and removing excess sinus aorta.  The proximal suture line is accomplished with 28-32 simple interrupted 3-0 braided polyester sutures.  Coronary buttons are reattached with 5-0 polypropylene continuous suture and aortic continuity is re-established with a continuous 5-0 polypropylene suture (Slide 12-16).
Slide 12 | Play video

Slide 13 | Play video

Slide 14 | Play video
Slide 15a | Play video
Slide 15b | Play video

Slide 16 | Play video

Slide 17 | Play video

The armamentarium of natural valve substitutes available to the cardiac surgeon today make the Manougian operation and the Konno operation in the adult patient, with a small aortic annulus, an antiquated procedure.  Use of these valve substitutes will give larger EOAs, lower postoperative gradients, and more hemodynamically efficient laminar flow patterns than will upsizing with an aortic annular enlarging procedure. The most hemodynamically efficient way to implant a natural valve (stentless heterograft, cryopreserved aortic allograft, or a pulmonary autograft) is to use a free standing total aortic root replacement.  A stentless heterograft should be selected one size larger than the size of the left ventricular outflow tract.  When this is done, all the blood flow from the left ventricle sees is aortic valve leaflets and thus there is no impedance to flow (Slide 17).

In summary, PPM can largely be avoided today with a good preoperative strategy.  Eliminating PPM postoperatively will improve postoperative morbidity and mortality, particularly in patients with severe mismatch and/or depressed left ventricular performance.  If PPM is anticipated by preoperative predictions with a standard valve substitute, a natural valve substitute should be selected.  After one makes certain there are no obstructing lesions in the left ventricular outflow tract, an additional aortic annular enlarging procedure should not be necessary. Hemodynamic performance is best optimized by using a natural valve substitute (stentless heterograft, cryopreserved aortic allograft, pulmonary autograft) implanted with a total root replacement technique.