Atrial Fibrillation

Background

EarlyStages keyAtrial fibrillation, a form of irregular heartbeat, occurs when the electrical signals that control the upper chambers of the heart (atria) become out of sync with the two lower chambers of the heart (ventricles). This causes poor blood flow throughout the body and increases the risk for blood clots, stroke and heart failure. Episodes of atrial fibrillation can be intermittent or permanent.

Atrial fibrillation affects more than 3 million people in the United States, and accounts for 460,000 hospitalizations and 80,000 deaths each year. The frequency of atrial fibrillation increases with age, and other risk factors include high blood pressure, diabetes, heart disease, and heavy alcohol use.

Current Treatment

Anti-arrhythmic medications can be used to convert the heart back into normal rhythm and can also be prescribed to maintain a normal heart rhythm following an episode of atrial fibrillation. Beta-blockers and calcium-channel blockers can be prescribed to control heart rate and blood thinners can protect against the formation of blood clots. In more severe cases, an electric shock can be given through paddles or patches attached to the chest to reset the heart and return it to normal rhythm.

In cases where neither medication nor electrical shock is effective, a procedure called ablation can be performed. A catheter fitted with electrodes is inserted through the groin and up into the heart where radiofrequency energy, extreme cold or heat is used to destroy the heart tissue that is causing the abnormal rhythm. This procedure, if successful, prevents the need for further medication or implantable devices.

However, if the arrhythmia is not resolved, AV node ablation is an option. This procedure is a specific form of catheter ablation in which the electrical pathway between the atria and ventricles is destroyed. The atria continue to fibrillate but they can no longer adversely affect the ventricles. Further medication and a permanent pacemaker are needed to keep the ventricles beating properly.

Focused Ultrasound

Recent preclinical studies have examined the feasibility of cardiac ablation with focused ultrasound using a transesophageal approach. These studies have shown that focused ultrasound is able to create lesions in the left atrium to potentially treat atrial fibrillation. Further studies are needed to investigate the safety and efficacy of this treatment modality before research can progress to the clinical stages.

Notable Papers

Constanciel E, N'Djin WA, Bessière F, Chavrier F, Grinberg D, Vignot A, Chevalier P, Chapelon JY, Lafon C. Design and evaluation of a transesophageal HIFU probe for ultrasound-guided cardiac ablation: simulation of a HIFU mini-maze procedure and preliminary ex vivo trials. IEEE Trans Ultrason Ferroelectr Freq Control. 2013 Sep;60(9):1868-83.

Jiang CX, Yu RH, Ma CS. Cardiac ablation by transesophageal high intensity focused ultrasound. Chin Med J (Engl). 2010 Sep;123(17):2451-3.

Villamizar NR, Crow JH, Piacentino V 3rd, DiBernardo LR, Daneshmand MA, Bowles DE, Groh MA, Milano CA. Reproducibility of left atrial ablation with high-intensity focused ultrasound energy in a calf model. J Thorac Cardiovasc Surg. 2010 Dec;140(6):1381-7.e1.

Werner J, Park EJ, Lee H, Francischelli D, Smith NB. Feasibility of in vivo transesophageal cardiac ablation using a phased ultrasound array. Ultrasound Med Biol. 2010 May;36(5):752-60.

Yu R, Ma C, Dong J, Liu X, Kang J. Transesophageal high intensity focused ultrasound ablation of left atrium posterior wall: new method for treating atrial fibrillation. Med Hypotheses. 2008;70(3):654-6.

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