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Ann Thorac Surg 2002;73:81-87
© 2002 The Society of Thoracic Surgeons

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Original article: cardiovascular

Apico-aortic conduits in children with severe left ventricular outflow tract obstruction

^a Division of Cardiothoracic Surgery, Medical College of Georgia, Augusta, Georgia, USA

* Address reprint requests to Dr Anstadt, Division of Cardiothoracic Surgery, Medical College of Georgia, BA 4300, 1120 15th St, Augusta, GA 30912, USA
e-mail: manstadt{at}mail.mcg.edu

Presented at the Forty-seventh Annual Meeting of the Southern Thoracic Surgical Association, Marco Island, FL, Nov 9–11, 2000.

	Abstract

Top Abstract Introduction Material and methods Results Comment Discussion References

 
Background. Infrequently, congenital heart defects are complicated by left ventricular outflow tract obstruction (LVOTO) not amenable to conventional reconstruction. Apico-aortic conduits provide a means of palliating such patients until definitive repair is possible. The purpose of this study was to review a single institution’s current experience with apico-aortic conduits.

Methods. The medical records of pediatric patients receiving apico-aortic conduits were reviewed. Demographics, operative techniques, preoperative and postoperative physiologic variables, morbidity, mortality, and functional class were recorded. Off-pump and on-pump procedures were categorized for comparison.

Results. Ten cases of apico-aortic conduits for left ventricular outflow tract obstruction were identified. Indications included congenital aortic stenosis, aortic atresia, and subaortic stenosis. Six procedures were performed off-pump and four required median sternotomy with cardiopulmonary bypass as necessitated by concomitant procedures. There was one operative death. The remaining patients demonstrated hemodynamic improvements and are all alive to date. One patient required conduit valve replacement. All patients are in New York Heart Association classification I or II at the time of last follow-up.

Conclusions. Apico-aortic conduits provide a safe and effective treatment alternative for select cases of left ventricular outflow tract obstruction. Off-pump techniques are feasible in the majority of cases. This valuable adjunct should be considered whenever conventional repair of left ventricular outflow tract obstruction is considered prohibitive.

	Introduction

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Congenital and acquired obstruction of the left ventricular outflow tract (LVOT) is usually managed satisfactorily with conventional repairative techniques such as valvulotomy, subaortic membrane resection, supravalvular tunnel augmentation, and the Ross/Ross-Konno procedure. Not infrequently, reconstruction of left ventricular outflow tract obstruction (LVOTO) is associated with suboptimal results requiring reoperation. Other factors that can complicate LVOTO include perivalvular obstruction, cavitary stenoses, and a small left ventricular (LV) cavity. Hemodynamic changes salient to LVOT defects include elevated LV pressures and impaired systemic perfusion. If satisfactory repair is not achieved, left ventricular hypertrophy, angina, congestive heart failure, and even sudden cardiac death are potential secondary consequences.

In 1910, Alexis Carrel [1] used a vein graft as a conduit between the left ventricle and thoracic aorta to experimentally bypass left-sided obstructive lesions. Since that time, numerous innovative modifications have been employed to create physiologically suitable relief of LVOTO [2–5]. The modern day apico-aortic conduit (AAC) evolved from an autogenous vein graft to a synthetic graft containing a bioprosthetic valve. These conduits are an alternative treatment for cases of LVOTO defects not amenable to conventional reconstructive techniques. The purpose of this study was to examine the outcome of those pediatric patients selected for this unique therapy.

	Material and methods

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After internal review board approval, the medical records of pediatric patients receiving AAC from November 1979 to August 1999 were reviewed. Demographics, indications for surgery, operative techniques, preoperative and postoperative hemodynamics, perioperative events, subsequent cardiac procedures, mortality, and functional status were recorded. Echocardiograms or cardiac catheterizations closest to the date of last follow-up were used to evaluate long-term patency and function of the conduit. Aortic annulus size was measured with echocardiography using the continuity equation, and findings were correlated with cardiac catheterization analysis. Patients were also grouped according to the operative technique utilized for the AAC implantation (left thoracotomy/off-pump versus median sternotomy/cardiopulmonary bypass).

From November 1979 to August 1999, 10 patients underwent implantation of an AAC at the Medical College of Georgia for complex LVOTO. The indication for conduits in these patients was the presence of severe left ventricular hypertrophy, a small ventricular cavity, or diffuse septal thickening that would compromise conventional repair. Patients ranged in age from 7 days to 8 years. All patients were followed in the pediatric cardiology clinic and had serial echocardiograms and cardiac catheterizations performed. Duration of follow-up ranged from 2 to 21 years (mean 85 months). The analysis of these patients (8 male and 2 female) is the subject of this report (Table 1). Six of the 10 patients had undergone previous interventions to alleviate the symptoms of their congenital pathologies (Table 2). Underlying etiologies included isolated aortic stenosis [4], annular and subvalvular aortic stenosis associated with Shone’s syndrome [2], Type B interrupted aortic arch [1], combined aortic and mitral valvular stenosis [1], subvalvular aortic stenosis with coarctation [1], and valvular and supravalvular stenosis with anomalous coronary anatomy [1]. Seven of the 10 patients had undergone previous interventions to alleviate their obstructive pathology.

View larger version (70K): [in this window] [in a new window]   Fig 1. Schematic illustration of the off-pump technique for implantation of the apico-aortic conduit. (A) Via a left thoracotomy, the distal anastomosis is completed to the descending thoracic aorta with a valved conduit, and a pericardiotomy is made anterior to the phrenic nerve. Four pledgeted sutures are placed circumferentially in the ventricular apex. (B) The left ventricle apex is resected over a Foley catheter (dotted lines). (C) The ventricular stent is guided over the Foley catheter and anchored using the pledgeted sutures. (D) Air is removed and the two grafts are anastomosed.

The pericardium is incised anterior to the phrenic nerve, exposing the apex of the left ventricle. The terminal branch of the left anterior descending (LAD) coronary artery is an important anatomic landmark for identifying the LV apex. Four pledgeted, nonabsorbable sutures are positioned circumferentially at the LV apex. A stab incision is centered between the sutures, and a balloon-tipped Foley catheter is inserted into the LV cavity. The balloon is inflated and placed on traction to secure it within the ventricle. A circular knife is then inserted over the Foley catheter and the central core of tissue is carefully excised. The circular knife is removed and the proximal graft is placed over the Foley catheter. The four sutures are next passed through the sewing ring of the graft and tied, securing it in place. The Foley catheter is then removed. Additional interrupted sutures may be required to achieve hemostasis. The operation is completed by anastomosing the tailored ends of the prosthetic grafts together in a running fashion. The valved conduit is de-aired and the distal clamp is removed. Figure 2 depicts the angiographic appearance of the conduit after implantation.

View larger version (83K): [in this window] [in a new window]   Fig 2. Anteroposterior (Top) and lateral (Bottom) views of a completed apico-aortic conduit. Radiolucent ring identifies the location of the porcine valve.

	Results

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Ten patients underwent placement of AACs for complex LVOTO during the study period. Off-pump techniques were the preferred approach at the authors’ institution in cases where concomitant procedures were not required. Six of the 10 patients underwent successful conduit implantation without cardiopulmonary bypass (CPB) using techniques modified from that described by Brown and associates [6]. The remaining 4 patients required CPB in order to address associated pathology (one aortocoronary bypass graft and three mitral valve replacements). Conversion to CPB when off-pump implantation procedure was planned did not occur in any case.

There was one death, for an overall mortality of 10%. The death occurred in a patient with Shone’s syndrome accompanied by annular and subvalvular aortic stenosis who was taken emergently to the operating room. The patient required extracorporeal oxygenation and nitric oxide therapy for postoperative respiratory insufficiency. She subsequently expired on the fourth postoperative day secondary to respiratory failure. The remaining 9 patients are alive at the time of this report. Three patients required either a Konno or Ross-Konno procedure after initial palliation with the apico-aortic conduit. Two of these patients underwent conduit removal during the aortic-root operation, whereas the other had the conduit closed via a percutaneous approach (Amplatz Closure Device; Becton Dickenson, Franklin Lakes, NJ). The conduits provided effective palliation and did not negatively impact the outcome in these cases.

Postoperatively, all patients demonstrated immediate hemodynamic improvement with significant reduction in left ventricle-aortic pressure gradients (mean gradient: 75.4 mm Hg ± 4.3 [preoperative] versus 18.1 mm Hg ± 3.3 [postoperative], p <0.001) (Fig 3). Patients experienced fewer symptoms and improved exercise performance as reflected by postoperative changes in functional status. Left ventricular end diastolic pressure (LVEDP) trended downward postoperatively (mean LVEDP: 15.3 mm Hg ± 1.7 [preoperative] versus 12.4 ± 2.1 mm Hg [postoperative], p = 0.318) (Fig 4). Finally, it is noteworthy that all patients experienced progressive increases in aortic annular size after implantation of AAC (8.4 mm ± 1.1 [preoperative], versus 13.3 mm ± 1.3 [postoperative], p = 0.015) (Fig 5).

View larger version (16K): [in this window] [in a new window]   Fig 3. Left ventricular-aortic pressure gradients in 7 of 10 patients (*p < 0.001, preoperative versus postoperative).

View larger version (13K): [in this window] [in a new window]   Fig 4. Left ventricular end diastolic pressure: preimplantation and postimplantation of apico-aortic conduit in 6 of 10 patients (p = 0.318, preoperative versus postoperative).

View larger version (14K): [in this window] [in a new window]   Fig 5. Preconduit and postconduit placement aortic annulus size in 6 of 10 patients (*p = 0.015, preoperative versus postoperative).

	Comment

Top Abstract Introduction Material and methods Results Comment Discussion References

 
The treatment of congenital LVOTO has evolved significantly over the past 20 years. Today, most patients can be managed successfully with conventional techniques. However, severe left ventricular hypertrophy, small ventricular cavities, and diffuse septal thickening can significantly compromise the adequacy of repair. In these circumstances, AACs provide an alternative approach.

Some salient points regarding the technique deserve further discussion. The balloon-tipped catheter in the LV cavity not only facilitates the off-pump insertion of the conduit, but also prevents injury of intracavitary structures. The mitral complex and papillary muscles are displaced laterally, preventing any inadvertent harm during the ventriculotomy. Gentle traction anchors the catheter during the excision phase, and prevents beveling of the endocardium as the knife penetrates the myocardial wall. Should the balloon rupture, the ventriculotomy can be controlled with the operator’s finger. The conduit is then placed over the ventriculotomy and secured quickly using the four previously placed sutures. These technical aspects can be important considerations for the success of the off-pump techniques.

The AAC is generally regarded as a palliative treatment for LVOTO; however, it may serve as a long-term treatment if definitive treatment of the underlying pathology is not feasible. Growth and development after successful palliation may better enable subsequent definitive repairs. In the present series, most patients had prior surgical treatment to alleviate symptoms (n = 4) or repair-associated congenital abnormalities (n = 3). AACs were later employed when these patients presented with critical LVOTO.

The presentation of LVOTO in neonates is often associated with severe obstruction, and many patients die within days to weeks if therapy is not provided [17]. Infants with critical LVOTO develop progressive congenital heart failure with poor peripheral perfusion and failure to thrive. Less severe lesions, if left untreated, result in left ventricular remodeling and functional impairment. AACs can effectively relieve pressure gradients of LVOTO and prevent further myocardial dysfunction. Symptoms are alleviated and systemic blood flow maintained, which facilitates growth and development. In patients with complex LVOTO who have had prior surgical interventions, AAC implantation can circumvent the difficult dissection associated with reoperative surgery. In other circumstances, the AAC preserves a "virgin" sternum for future definitive repair. The procedure can be effectively performed without the use of CPB if additional cardiac repair is not necessary. Avoiding CPB may reduce the risks of bleeding, coagulopathy, and neurologic complications.

Long-term follow-up in the present series has demonstrated that apico-aortic conduits allow clinical improvement and continued growth. Hemodynamic analyses reveal significant reductions in LV pressure gradients and LVEDP. Whereas changes in LVEDP did not reach statistical significance, they likely impacted favorably on clinical outcome. Small reductions in LVEDP may have important implications on myocardial development and the prevention of remodeling. Importantly, this form of palliation does not preclude subsequent treatment with more complex aortic root enlargements (aortoventriculoplasty) or replacement procedures (Ross-Konno).

AACs have been a valuable adjunct in the authors’ management of LVOTO. They provide a reliable and predictable alternative to complex, aortic root reconstruction in select patients when definitive repair is deemed too difficult. In particular, AACs provide an effective alternative to Ross-Konno procedures when applied to neonates with isolated LVOTO. This achieves palliation without precluding a Ross procedure or mechanical valve replacement at a later date in the larger child. The operative technique can generally be performed without the use of cardiopulmonary support. Otherwise, it may be performed in conjunction with open-heart procedures when treating multiple defects as seen in Shone’s complex. The conduit serves as a bridge to future therapy or as a definitive repair depending upon the complicating circumstances. Continued use of these conduits in adults receiving ventricular assist devices further substantiates their feasibility for such treatment strategies. [7–16]

	Discussion

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DR JOHN W. BROWN (Indianapolis, IN): That is a beautiful series of patients with apico-aortic conduits. It is interesting how things in medicine repeat in 20-year cycles. In the 1970s and 1980s, in Ann Arbor and also in Indianapolis, we implanted 60 or 70 of these conduits in children and adults. We continue to implant apico-aortic conduits in elderly adult patients with porcelain ascending aortas or mediastinums that you do not want to enter from the front: patients with previous sternal wound infections or patients with multiple coronary bypass grafts. We no longer use the apico-aortic conduit for aortic stenosis in children. Since the late 1980s and early 1990s, we utilize the Ross or Ross-Konno procedure for complex left ventricular outflow obstruction in children. When would the authors use the Ross or Ross-Konno over the apico-aortic conduit in children?

My second question is a technical one. After I looked at your drawings, I could not quite figure out how you got the plug of muscle out of the apex before you put the stent in. How do you get the LV muscle plug out?

I very much enjoyed the presentation and applaud your results.

DR KHANNA: Thank you Dr Brown. To answer your first question, we still do utilize this procedure in the neonatal and pediatric population. We have reserved the more definitive or the more formal repairs for a later date when these kids grow up to an age of 7 or 8 usually, and do the formal Ross or Ross-Konno at that time. So in the neonatal population, specifically in patients with complex, left ventricular obstructive pathologies, we do continue to use the apico-aortic conduits, be it a small subset of patients.

Regarding the technical question, as you mentioned, the point where you take out the core of ventricular apex and insert the graft is probably the bloodiest point of the entire operation, the key point being that you keep the circular knife anchored on top of the Foley catheter, and as soon as it hits the balloon, you take the knife out and then remove the core of apex at that time.

DR CONSTANTINE MAVROUDIS (Chicago, IL): Congratulations on a very nice study and very nice presentation. I only have a small question dealing with the left ventricular hypertrophy. I noticed that you did not mention this issue in some of the postoperative data. It would be interesting to know whether the technique of apico-aortic conduit helps to provide left ventricular hypertrophy regression more than the other more conventional Ross and Ross-Konno operations.

DR KHANNA: In the pediatric population, we usually get to these patients before the development of the left ventricular remodeling and ventricular hypertrophy and dilatation, so that is certainly not seen preoperatively. It does not appear to enhance or increase the ventricular hypertrophy postimplantation. So it is certainly not a factor in this study.

DR. BROWN: One additional comment. A word of caution. We did several apico-aortic conduits in young babies. We noticed that about two-thirds of the outflow from the left ventricle went out through the conduit: most of it went to the abdominal aorta. What happened in some of those babies is the intrathoracic descending aorta didn’t grow as you would expect it, and so that prompted us to go back earlier, rather than later, and do the Ross or Ross-Konno to get flow down the descending thoracic aorta so it would grow and there would not be a late problem.

I guess a second comment is that many times it is not necessary to go take this apico-aortic conduit out when you do a definitive repair. On three of four occasions we have just ligated it through a mini thoracotomy. Interventional cardiologists these days would be able to balloon occlude the conduit. It does not seem to cause any long-term problems, and it is quite a chore to dig it out of the left thorax if you try to excise it.

Thank you for allowing me to make those additional comments.

DR KHANNA: I think those are very good points. In fact, that is pretty much what we have done. In one revision case we ligated the conduit during a Ross-Konno operation. In a third case, the conduit was left in place and a percutaneous closure device used to occlude it.

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