Aortopulmonary fistula

# Overview
Aortopulmonary fistula occur when there is a communication between aorta and adjacent pulmonary artery. It is a rare but has been thought to be uniformly fatal if not treated surgically. In the earlier experiences with this entity, a chronic infectious process arising in the lung (pneumonitis or abcess or aorta), mycotic aneurysm  was the most frequent cause. In recent decades, the reported aortopulmonary fistulas have occurred most frequently as the result of erosion and/or rupture of a degenerative or false aneurysm of the distal aortic arch or descending thoracic aorta into the left lung. It can occur either in the acute or chronic phase of aortic dissection, either with or without previous cardiovascular surgery. Hemoptysis is the most common presentation of aortopulmonary fistula after cardiac surgery. The reported interval between the time of operation and the onset of hemoptysis ranges from 3 weeks to 25 years.  Aortopulmonary fistula subsequently leads to several complications such as rapid left-to-right shunt and right heart failure. Diagnostic examinations are often unable to directly visualize a fistula. Aortography is the gold standard. Indication for surgical or endovascular repair mostly relies on clinical suspicion and nonspecific diagnostic features. Aortobronchopulmonary fistulas are uniformly fatal if untreated. The overall surgical mortality rate is 15.3%.

# Pathophysiology and Etiology
Aortopulmonary fistula usually occurs when there is damage to the wall of aorta or pulmonary artery which causes a communication between these two adjacent anatomic structures. Most of the time it happens in an event of aortic dissection, aortic aneurysm, any surgery that causes damage to wall of aorta or pulmonary artery, pulmonary hypertension and extremely high flow through aorta or pulmonary artery. This can also occur if walls of aorta are fragile as they can be in an event of atherosclerosis, aortitis or any other cause of inflammation of aorta and Marfan's syndrome. The fistula leads to rapid left to right shunting and can have severe consequences. This causes the oxygen saturation of the blood to fall and it can present with signs and symptoms of congestive heart failure and pulmonary edema. 

# Risk Factors
Some of the risk factors for aortopulmonary fistula are given below:
- Complication of surgery or thoracic aortic graft 
- Indwelling chest tube, spinal fixation device, or foreign body
- Congenital 
- Repair of coarctation of aorta
- Use of Dacron draft for aortic repair surgery
Elective thoracic endovascular aortic repair is comparatively a safer option
- Elective thoracic endovascular aortic repair is comparatively a safer option
- Bentall operation 
- Marfan's syndrome
- Atherosclerotic inflammation
- Hypertension
- Blunt chest trauma
- Transcatheter pulmonary valve placement
- Ross procedure 
- Pulmonary angioplasty
- Truncus arteriosus repair
- Atrial switch operation
- High output heart failure
- Neoplasm
- Bicuspid aortic valve
- Erosion and/or rupture of a degenerative or false aneurysm of the distal aortic arch or descending thoracic aorta into the lung. Possible reasons of true or false aneurysms:
- True aneurysm
- Infectious aortitis
- Aortic dissection
- Traumatic aortic tear
- Aortic suture line breakdown

# Signs And Symptoms
The most frequent symptoms of an aortopulmonary fistula are chest pain and hemoptysis, but often shortness of breath, fever, and/or other respiratory symptoms are present. It can also presents with dyspnea, orthopnea, chest discomfort on exertion, dizziness, cool extremities, edema, hypothermic circulatory arrest, right ventricular dysfunction and other symptoms of congestive heart failure.

# Examination
Usually the first clue to an aortopulmonary fistula is unstable vitals. A person can have tachycardia, bounding pulse and increased respiratory rate. Sudden lipothymia and anemia can also indicate aortopulmonary fistula. A person can have prominent precordium, palpable thrill and murmur. There could be crackles and ronchi heard on auscultating lungs.

# Post Operation Care
In repair of aortopulmonary fistula, patient should be rigorously followed and an eye should be kept on his cardiac health. Few patients who went through aortopulmonary fistula repair showed signs of class one heart failure with in one year of post operation course. During any aortic surgical repair, use of prosthesis should be avoided because it can lead to greater chances of recurrent infection. Use of pulmonary allograft should also be made available and should be implanted when necessary.

# Complications
Aortopulmonary fistula can be very lethal. Mediastinitis and other infection can be one of the complication if recurrent infection occur after surgical repair. Sudden death can occur if immediate surgical intervention is not made at an appropriate time. The risk factors associated with early death after surgical repair are:
- Old age
- Congestive cardiac insufficiency
- Angina
- Dissection
- Aortic arch management and co-morbidities
Factors like chronic obstructive pulmonary disease, systemic arterial hypertension and peripheral vascular insufficiency in addition to coronary artery insufficiency can also dictate the course of disease.

# Diagnosis
It is very crucial to diagnose aortopulmonary fistula at the appropriate time. Timely diagnosis and intervention can save life. There are countless diagnostic modalities which can help in diagnosing aortopulmonary fistula. Aortography is the gold standard to diagnose it. It is very important to know the exact location and dimension of fistula before any surgical intervention can be done.

## Chest x-ray
Chest x-rays help to confirm pulmonary infiltrates. It can show widened mediastinum with pulmonary plethora. It can also show signs of pulmonary edema bt all these findings are non specific and can happen in many other cardiac and pulmonary pathologies.

## Echocardiogram
Echocardiogram can show dilation of aorta and increased flow of pulmonary artery. It can also show other features like enlarged chambers of heart. It might or might not not show the location of fistula.

## Cardiac Catheterization
Cardiac catheterization can show elevated pressure in pulmonary artery. The pressures can be as high as that of aorta which supports the idea of a communication between aorta and pulmonary artery. It can also reveal a step up in oxygen saturation on right sided chamber and vessels of heart but it does not show the location of fistula.

## EKG
Electrocardiogram can show tachycardia on the EKG strip. Usually there are no ST segment changes but ST segment changes can show up  in case of ischemia of heart walls.ia o

## CT

## Bronchoscopy
Bronchoscopy during an episode of hemoptysis can document its lobar origin.

## Aortography
Aortography is a gold standard of diagnosing of aortopulmonary fistula. Subtraction technique may help to obtain additional information.
Following things should be considered before doing this est
- Renal function tests
- Allergy to dyes
- Breast feeding and pregnancy
- Metal implants
Aortography can tell us about the exact location and dimension of aortopulmonary fistula.

# Treatment
Once the diagnosis is confirmed, prompt surgical or percutaneous interventions are indicated.
The indications for urgent treatment are given below
- Hemoptysis
- History of previous cardiac or aortic operation
- presence of lung infiltrates on the chest roentgenogram
- lung hemorrage on the computed tomographic scan,
- visualization of a pseudoaneurysm.
The main focus of treatment should be to control the right to left shunting, resolve the edema in lungs and minimize the signs of heart failure. This can be achieved if following goals are met
- Restoring single lumen continuity to the ascending aorta and excluding the aortic tear
- Separating the pulmonary circulation from systemic blood flow
- Restoring adequate coronary circulation through native coronary ostia and surgical bypass grafts
Immediate surgery is required to meet all these goals. Various surgical otions are on table to choose from and it can vary from one individual to another.
- Endovascular stenting  
- Surgery 
- percutaneous amplatzer septal occluder 
- Amplatzer occulder using antegrade venous approach might decrease the risk of subsequent cardiac surgery as well.
- Conventional elephant trunk implantation
- pericardial patc closure and tube graft
- percutaneous closure with an atrial septal occlusion devise
- Endovascular occlusion devise
- Retroperitoneal aortotomy with intravascular insertion of an expandable stainless steel stent covered by a polyester graft
Other options which are still under trial includes
- Amplatzer occlude via percutaneous catheterization
- pulmonary artery catheterization with thoracotomy