Apicoaortic Conduit (AAC), also known as Aortic Valve Bypass (AVB), is a cardiothoracic surgical procedure that alleviates symptoms caused by blood flow obstruction from the

left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...

of the heart. Left ventricular outflow tract obstruction (LVOTO) is caused by narrowing of the

aortic valve The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. Th ...

(

aortic stenosis Aortic stenosis (AS or AoS) is the narrowing of the exit of the left ventricle of the heart (where the aorta begins), such that problems result. It may occur at the aortic valve as well as above and below this level. It typically gets worse ov ...

) and other valve disorders. AAC, or AVB, relieves the obstruction to blood flow by adding a bioprosthetic valve to the circulatory system to decrease the load on the aortic valve. When an apicoaortic conduit is implanted, blood continues to flow from the heart through the aortic valve. In addition, blood flow bypasses the native valve and exits the heart through the implanted valved conduit. The procedure is effective at relieving excessive pressure gradient across the natural valve. High pressure gradient across the aortic valve can be congenital or acquired. A reduction in pressure gradient results in relief of symptoms.

Configuration

The figure depicts a typical apicoaortic configuration with a left ventricle connector sutured to the

apex of the heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

, and a conduit containing a bioprosthetic valve anastomosed to the descending

thoracic aorta The descending thoracic aorta is a part of the aorta located in the thorax. It is a continuation of the aortic arch. It is located within the posterior mediastinal cavity, but frequently bulges into the left pleural cavity. The descending thoracic ...

. Blood exits the

either through the natural valve or the bypass conduit.

History

The concept of an apicoaortic conduit to bypass valvular

(AS) was conceived by Carrel in 1910, and performed experimentally by Sarnoff and colleagues on dogs in 1955. In 1962-63, Templeton implanted prostheses similar to those originally described by Sarnoff in five patients with severe aortic valve stenosis; one patient survived more than 10 years. In 1975, Bernhard and coworkers reported a reoperation in which a conduit was implanted between the left ventricle and the thoracic aorta. The procedure was also developed in the late 1970s as a way to treat complex left ventricular outflow tract obstructions (LVOTO) in children and young adults. AAC is no longer performed on children as the

Ross procedure The Ross procedure, also known as pulmonary autograft, is a heart valve replacement operation to treat severe aortic valve disease, such as in children and young adults with a bicuspid aortic valve. It involves removing the diseased aortic valv ...

has superseded it. Today, AAC is performed clinically on elderly

patients, and has gained in popularity in recent years. In the past 25 years, a number of case series on adults have been published. As of 2010, the estimated total number of AAC cases performed worldwide in the last 30 years is greater than 1500. The procedure has not been adopted widely because it is technically challenging and blood loss can be significant. The most difficult part of the procedure is the insertion of a left ventricle connector into the

Devices

AAC requires specialized implants and installation tools. Hancock Laboratories, now part of Medtronic (Minneapolis, MN), developed and released a set of left ventricle connectors, valved conduits, and installation

trocar A trocar (or trochar) is a medical or veterinary device that is made up of an awl (which may be a metal or plastic sharpened or non-bladed tip), a cannula (essentially a hollow tube), and a seal. Trocars are placed through the abdomen during lap ...

s in the 1970s. The Hancock left ventricle connectors, with inner diameters of 12 to 22 mm, have been used clinically for the vast majority of AAC procedures reported in the literature. For the valved conduit, surgeons have used the Medtronic Hancock Model 105 or 150 valved conduits which contain a complete porcine aortic valve. Other surgeons have constructed valved conduits on the back table using a variety of bioprosthetic valves such as the Medtronic Freestyle valve. The Hancock trocars for creating a hole in the left ventricle are rarely used clinically. Surgeons typically assemble their own tools to core and remove a plug of muscle from the left ventricular wall. In 2011, Correx (Waltham, MA) released a complete kit for AVB with an installation tool that enables coring and insertion of a left ventricle connector on a beating heart while maintaining

hemostasis In biology, hemostasis or haemostasis is a process to prevent and stop bleeding, meaning to keep blood within a damaged blood vessel (the opposite of hemostasis is hemorrhage). It is the first stage of wound healing. This involves coagulation, ...

Cardiopulmonary bypass Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a ...

(CPB) is not required. The kit is CE Marked and available in Europe. Several cases have been done in Canada under the Special Access Programme. This kit is not currently available for use or sale in the United States.

Procedure

The general procedure has evolved over the years as surgeons gained experience and improved techniques. A video of an AVB procedure performed by Dr. Jim Gammie of the University of Maryland Medical Center can be found here.

Preparation

The patient is placed on the table in the supine position. Anesthesia is induced, and the patient is intubated with a double-lumen endotracheal tube, which facilitates one-lung ventilation and allows the surgeon to work within the left chest. The patient is positioned with his or her left side up (see figure). A left anterior-lateral

thoracotomy A thoracotomy is a surgical procedure to gain access into the pleural space of the chest. It is performed by surgeons (emergency physicians or paramedics under certain circumstances) to gain access to the thoracic organs, most commonly the hea ...

is performed between the fifth and sixth ribs to expose the heart and provide access to the

descending aorta In human anatomy, the descending aorta is part of the aorta, the largest artery in the body. The descending aorta begins at the aortic arch and runs down through the chest and abdomen. The descending aorta anatomically consists of two portions o ...

. A portion of a rib may be removed to enable easier access and to minimize the chance of a rib fracture. The left lung is deflated and retracted.

Distal Anastomosis

With the descending aorta exposed, the surgeon applies a side clamp to the aorta, effectively pinching and isolating one side of the great vessel. Blood continues to flow to the body's lower half through the unisolated remainder of the aorta. A lengthwise slit is made through the pinched face, and the open end of the valved conduit is carefully sutured to the slit. Once the suture line is checked for leaks, the aortic partial side clamp is removed and the valved conduit fills with blood up to the bioprosthetic valve. The valve acts as a check valve, thereby maintaining hemostasis.

Left Ventricle Connector Installation

The surgeon next opens the

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made o ...

and exposes the

. The surgeon closely examines the surface of the heart and chooses and marks an insertion site near the apex. A ring of sutures reinforced with pledgets is installed around the insertion site. The free ends of the sutures are looped through a sewing ring on the left ventricle connector. At this point, CPB is typically initiated, although a few surgeons are able to complete the left ventricle installation off-pump (without CPB). A circular core of myocardium is cut and removed using specialized coring tools. Care must be taken to avoid damaging structures inside the left ventricle such as the

interventricular septum The interventricular septum (IVS, or ventricular septum, or during development septum inferius) is the stout wall separating the ventricles, the lower chambers of the heart, from one another. The ventricular septum is directed obliquely backwar ...

, and the

chordae tendineae The chordae tendineae (tendinous cords), colloquially known as the heart strings, are inelastic cords of fibrous connective tissue that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart. Structure The chorda ...

. The left ventricle connector is filled with sterile saline to displace any air and then inserted into the hole. The sutures are sequentially tightened and tied off to permanently secure the left ventricle connector to the apex. CPB is terminated. With blood now flowing through the bypass conduit, the left ventricular outflow tract obstruction (LVOTO) is effectively relieved. 60% to 70% of the heart's output flows through the bypass to the aorta. The load on the heart is markedly reduced, and symptoms such as

dyspnea Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...

, syncope, and chest pain disappear.

Outcomes

Patients historically referred for apicoaortic conduit surgery have been considered high risk or ineligible for conventional

aortic valve replacement Aortic valve replacement is a procedure whereby the failing aortic valve of a patient's heart is replaced with an artificial heart valve. The aortic valve may need to be replaced because: * The valve is leaky (aortic insufficiency, also known as ...

. The literature reports generally favorable outcomes for apicoaortic surgery given the age, frailty, and

comorbidities In medicine, comorbidity - from Latin morbus ("sickness"), co ("together"), -ity (as if - several sicknesses together) - is the presence of one or more additional conditions often co-occurring (that is, concomitant or concurrent) with a primary ...

of the patient population. Patients typically improve from

New York Heart Association Functional Classification The New York Heart Association (NYHA) Functional Classification provides a simple way of classifying the extent of heart failure. It places patients in one of four categories based on how much they are limited during physical activity; the limitati ...

III or IV to Class I or II. AVB effectively relieves the LVOTO caused by

. There is long-term stability of the left ventricular

hemodynamics Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

after AVB, with no further biologic progression of native aortic valve stenosis. Once the pressure gradient across the native valve is substantially reduced, the narrowing and calcification of the native valve halts. In one study of 47 patients whose average age was 82 years, the mean gradient across the native valve was reduced from 46 +/- 14 mm HG to 17 +/- 7 mm HG.

Low Incidence of Stroke

Throughout the published literature, perioperative stroke is uncommon. This is because the native valve and ascending aorta are not manipulated in any way. Calcified layers and other debris do not break free and migrate to the brain. The literature also reports that postoperative stroke is rare. Whenever a prosthetic device such as a valve is introduced into the bloodstream, there is an ongoing risk of

thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of ...

formation which can lead to an

embolism An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule (fat embolism), a bubble of air or other gas ( gas embolism), amniotic fluid (am ...

should the thrombus become mobile. Computational flow studies Balaras E, Cha KS, Griffith BP, Gammie JS. ''Treatment of aortic stenosis with aortic valve bypass (apicoaortic conduit) surgery: An assessment using computational modeling''. J Thorac Cardiovasc Surg 2009 Mar; 137(3):680-687 conclude that the presence of an aortic valve bypass conduit has no effect on cerebral blood flow. All blood flow to the brain continues to flow across the native valve. Should a thrombus form on the bioprosthetic valve in the bypass conduit, it will likely migrate to the lower half of the body and not to the brain. This fact is believed to reduce the long-term risk of cerebral thromboembolism (stroke) with AAC.

Need for Pacemakers is Uncommon

The published literature reports that the need for pacemaker after AAC is very rare as the (electrical) conduction center of the heart near the aortic valve is not disturbed in any way.

Paravalvular Leak is Impossible

AAC avoids the risk of leakage around a replacement heart valve (

aortic insufficiency Aortic regurgitation (AR), also known as aortic insufficiency (AI), is the leaking of the aortic valve of the heart that causes blood to flow in the reverse direction during ventricular diastole, from the aorta into the left ventricle. As a conseq ...

), a serious complication of alternate treatments such as

(AVR) and

percutaneous aortic valve replacement Percutaneous aortic valve replacement (PAVR), also known as percutaneous aortic valve implantation (PAVI), transcatheter aortic valve implantation (TAVI) or transcatheter aortic valve replacement (TAVR), is the replacement of the aortic valve o ...

(PAVR or TAVI). With AAC, the native aortic valve is left completely undisturbed.

Patients receiving AAC

With

(AVR) as the accepted standard of care for critical AS, patients receiving apicoaortic conduits have often been refused AVR and as such are considered "no option" patients. AAC is also sometimes chosen by surgeons and cardiologists over other treatments, such as AVR and

(PAVR or TAVI), to treat critical AS. Patients who could benefit from AAC or AVB include those who: * Have had coronary artery bypass surgery and have patent grafts * Have had mediastinal radiation or infection after a prior median sternotomy * Have elevated risk of stroke, or history of stroke * Have heavily calcified, or "porcelain" ascending aortas * Have large or small aortic annular diameters * Have low coronary ostia (these are the inlets to the left and right coronary arteries just above the aortic valve) * Have heart (electrical) conduction disorders

References

{{reflist Surgical procedures and techniques Cardiac surgery