Catheter Ablation

Pulmonary Vein Isolation

The initial approach to ablation based treatment of atrial fibrillation attempts to isolate the pulmonary veins from the body of the left atrium. Electrical signals that originate between the entrance of the pulmonary vein and the left atrium have been shown to trigger atrial fibrillation. Using ablation to isolate the veins by creating a line of scar around each vein has been shown to reduce the frequency of atrial fibrillation. There are two commonly used catheter based techniques to achieve pulmonary vein isolation.

• Radiofrequency Ablation
  With this technique, catheters are advanced into the left atrium from the femoral vein in the groin. Radiofrequency (RF) energy is used to heat the tissue around the pulmonary veins in a point by point fashion to create a circular scar around each vein, or around groups of veins (antral isolation). Testing is then performed to ensure that each vein is effectively isolated from the body of the left atrium. Additional lesions can be provided to treat other arrhythmias in either the right or left atrium dependent on the clinical presentation. 
• Cryoablation
  In this technique, a single catheter is advanced into the left atrium from the femoral vein in the groin. The tip of the catheter has a balloon that contains a refrigerant. The tip is advanced into the entrance of each vein. The balloon is then inflated, and the refrigerant is frozen. This effectively freezes the tissue that is in contact with the balloon in a circumferential fashion. In contrast to radiofrequency energy, which uses heat to create scar, cryoablation uses freezing to create scar. Electrical isolation of the pulmonary veins tested. In addition, other arrhythmias noted during the procedure may be treated using a radiofrequency catheter.

Surgical Ablation for Atrial Fibrillation

A number of techniques have been developed since the initial open chest procedures for atrial fibrillation devised by Dr. James Cox in the 1980s (Cox-Maze, Cox-Maze II). This technique involved creating a myriad of scars or lesions throughout the left atrium to prevent fibrillatory conduction. Open chest procedures may be performed in association with planned coronary bypass/or cardiac valve replacement. The original "cut and sew" approaches have been supplanted with surgical ablation tools which may use radiofrequency, or cryothermal, energy sources to create scar. These techniques may be referred as Cox-Maze III-IV procedures. Several minimally invasive techniques have been devised as stand-alone procedures.

• Mini Maze
  This technique utilized 3-5 small incisions along the front and side of the chest to insert special tools. Once the surgeon has accessed the surface of the heart, he/she will be able to use surgical ablation tools to perform isolation of the pulmonary veins, and treat other triggers for atrial fibrillation. The recovery from these procedures is much shorter than with open chest procedures. 
• Hybrid Ablation
  Hybrid ablation combines two procedures to stop the erratic electrical signals that cause atrial fibrillation (AFib). This involves the creation of lesions inside the heart (endocardial) and outside the heart (epicardial). The cardiac surgeon accesses the heart through a small incision underneath the sternum (breastbone) and advances the catheter to deliver energy to the outside surface of the heart. Inside the heart, the electrophysiologist (EP) advances catheters into the left atrium through the femoral vein. 

Isolation of the pulmonary veins is considered the hallmark of atrial fibrillation ablation, and is the first line treatment for atrial fibrillation based on more than two decades of research and experience. In some selected cases, other "substrates" of atrial fibrillation may be targeted for ablation.

• Rotors
  The left atrium is a complex structure, and individuals with persistent atrial fibrillation may have triggers independent of the pulmonary veins. Rotors are regions within the left atrium that demonstrate complex electrical activity. Recently these areas have been targeted for ablation with RF catheters and specialized mapping catheters to identify rotors. The technique may be called FIRM at some centers (Focal Impulse and Rotor Modulation).
   
• CFAE
  CFAE stands for Complex Fractionated Atrial Electrograms. These CFAEs are detected by mapping systems employed in catheter ablation. These areas in the left atrium are felt to be triggers for atrial fibrillation, and may be targeted for RF ablation.
   
• Ganglionated Plexi
  These are regions in the left atrium that are rich in autonomic innervation. Autonomic nerve fibers are involved in the human body's  "flight or fight" responses, and can affect the heart rate. These regions have also been targeted for ablation with RF catheters in those patients with persistent atrial fibrillation.

In some patients, the chances for restoration of normal sinus rhythm with either catheter or surgical methods are felt to be very low. This may be due to the long standing presence of atrial fibrillation, severe other medical problems, or prior failed ablations. RF ablation of the AV node and pacemaker implantation allows regularization of the heart rate (the rapid irregular impulses of atrial fibrillation are no longer transmitted to the lower chambers or ventricles of the heart) but results in pacemaker dependence.

Catheter ablation for supraventricular tachycardia is usually accomplished utilizing radiofrequency energy. In a small number of cases, treatment may require using cryo-energy due to the proximity of the ablation site to critical structures of the normal electrical conduction system. These catheters are advanced via the femoral veins in the groin to the right and/or left atrium.

Ventricular tachycardia usually presents in the structurally abnormal heart. RF ablation has been widely utilized to treat ventricular tachycardia. In addition, there are individuals with a structurally normal heart that present with ventricular tachycardia. These arrhythmias are very amenable to treatment with RF ablation.