Aorto Atrial Fistula - A Bizzare Connection

Introduction:

Aorto atrial fistula is a complex condition in which abnormal communication occurs between the aorta and the atrium. Aorto atrial fistula usually occurs secondary to an underlying pathological condition that affects the cardiac structures. Aorto atrial fistula causes various life-threatening complications, including heart failure. The following article gives insight into the particulars of aorto atrial fistula.

What Does Aorto Atrial Fistula Mean?

A fistula refers to an abnormal or surgically created communication between two body parts, such as a blood vessel or an organ and another body structure. A fistula can also occur as a result of an infection, inflammation, or injury. It can occur in any part of the body, including the heart and its blood vessels. Aorto atrial fistula refers to an abnormal connection between the aorta and the right or left atrium. Aorta is the large blood vessel that transports blood away from the heart to the rest of the body. Aorta originates from the heart's left lower chamber (ventricle) and extends down to the abdomen. The atrium refers to the upper chamber of the heart and is divided into the right and the left atria. In the aorta atrial fistula, abnormal communication occurs between the aorta and one of the atriums, resulting in abnormal blood flow between the aorta and the atria.

What Are the Causes of the Aorto Atrial Fistula?

Aorto atrial fistula can be caused by congenital or acquired cases. It usually occurs as a result of an underlying pathological condition affecting the cardiac structures. Aorta atrial fistula occurs secondary to conditions such as endocarditis, aortic dissection, valve replacement surgeries, or iatrogenic causes. Secondary causes result in the weakening of the cardiac wall integrity leading to the formation of fistulas, but the iatrogenic causes lead to the formation of fistulas that are traumatic in nature.

What Are the Types of Aorto Atrial Fistula?

Aorto atrial fistula can evolve in various methods, and the anatomy of each type is different.

Congenital Aorto Atrial Fistula:

Congenital aorto atrial fistula has been present since birth. The congenital aorto atrial fistula is divided into two groups, namely congenital aorto atrial tunnels and coronary camel fistulas. Congenital aortic-atrial tunnels originate above the sinotubular ridge. It is formed due to an inherited weakness in the wall of the aorta, resulting in the formation of a tunnel in one of the atria. Coronary camel fistulas develop when a shunt (passage) forms in one of the coronary arteries directly into the atria. The idiopathic aortic root is another rare anomaly, and it refers to the sinus of Valsalva. Individuals with congenital aorto atrial fistula may remain asymptomatic or show symptoms of heart failure. Early intervention is required because the symptoms worsen over time.

Acquired Aorto Atrial Fistula:

Acquired aorto atrial fistula occurs after birth and is associated with various conditions, including trauma, endocarditis, aorta dissection or aneurysms, previous cardiac surgery, iatrogenic perforation, ruptured sinus of Valsalva aneurysm, and vasculitis in conditions like Behcet's disease, and giant cell arteritis. Of all these conditions, endocarditis is the most important cause of acquired aorto atrial fistula. In endocarditis, the inflammatory process combines with the bacterial destruction of the tissues and weakens the integrity of the walls of the atria and aorta, resulting in fistula formation. A paravalvular abscess usually coincides with an aortic root infected with endocarditis and destroys the cardiac tissue, establishing a fistula. Fistula formation is common between the right atria and aorta and is less common between the left atrium and aorta due to their anatomical positions. Also, acquired aorto atrial fistula is common during aortic surgery. It can also occur in valve replacement surgeries.

What Are the Signs and Symptoms of Aorto Atrial Fistula?

The signs and symptoms of aorto atrial fistula include fever, pedal edema, regurgitative murmurs, and cardiac chamber dilatation. It results in complications like volume overload and cardiac failure. The patients present with the symptoms of cardiac failure, including chest pain, dyspnea (breathlessness), fatigue, palpitations, cough, weakness, or edema.

What Are the Effects of Aorto Atrial Fistula?

Aorto atrial fistula redirects the oxygenated blood from the aorta into one of the atriums through the fistula, resulting in volume overload and cardiac remodeling. Aorto atrial fistula can also result in distension of the atrial wall, with or without atrial fibrillation. If the blood from the aorta is redirected directly into the ventricles, volume overload can increase the ventricular strain leading to cellular remodeling. Constant volume overload on the right side increases the pulmonary pressure and causes pedal edema, resulting in right ventricular failure. Left-sided volume overload results in eccentric left ventricular hypertrophy and mitral dilation with secondary mitral insufficiency.

How Is Aorto Atrial Fistula Diagnosed?

The diagnosis of aorto atrial fistula depends on the following imaging tests:

• Echocardiography - Both transesophageal echocardiography and trans-thoracic echocardiography help in the diagnosis of aorto atrial fistula. Color Doppler transesophageal echocardiography provides high-quality images in cases where fistulas are present in the posterior aspect of the aorta. Echocardiography helps in the examination of the defect at all stages of the surgery. However, it requires high-frequency transducers with a high spatial resolution in some cases.

• Cardiac Magnetic Resonance Imaging and Cardiac Catheterization - Cardiac magnetic resonance imaging (CMR) determines the cardiac shunt fraction and the blood flow. It helps to identify the quantitative flow measurements. However, the use of gadolinium-based dye as a contrast can cause nephrogenic systemic fibrosis. Cardiac catheterization is an invasive procedure that helps assess shunt quantification, but flow measurements are less accurate than cardiac magnetic resonance imaging.

How Is Aorto Atrial Fistula Treated?

Aorto atrial fistula is corrected by performing surgical or percutaneous closure. However, small asymptomatic aorto atrial fistula can be managed with medications that reduce the cardiac afterload. Surgical correction is achieved by ligating the fistula, and percutaneous closure uses an occluder device to close the fistula.

Conclusion:

Aorto atrial fistula is a rare pathological condition. Aorta atrial fistula can be congenital or acquired, and it sometimes remains asymptomatic. Closure of the fistula is recommended, though it is asymptomatic because aorto atrial fistula can worsen over time. Early intervention is required to prevent life-threatening complications like heart failure.