Cardiac arrhythmias, such as atrial fibrillation, are a commonly occurring disorder characterized by erratic beating of the heart. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering caused by chaotic conduction of electrical signals through the upper chambers of the heart. While medication can be an effective treatment for some cases, many patients are not responsive to medical therapies and require alternative treatment. As an alternative to medication, a surgical technique, known as the Maze technique, requires open chest surgery to strategically incise the atrial wall, and subsequently repair the incisions by suturing. The result of this surgery is to create scar tissue located along the incision lines and extending through the atrial wall to block electrical conductivity from one segment to another.
While the Maze procedure has proven effective in restoring normal sinus rhythm, it requires considerable prolongation of cardiopulmonary bypass and aortic crossclamp time, especially when performed in combination with other open heart procedures. Over the last decade, more simplified techniques have been proposed which replace surgical incisions with ablations, or scars, formed in the heart tissue. The various energy sources used in ablation technologies include cryogenic, radiofrequency (RF), laser, and microwave energy. The ablation devices are used to create tissue lesions in an affected portion of the heart in order to block electrical conduction.
One common ablation technique employs the use of a catheter that is introduced into the heart (e.g., intravascularly) to direct RF energy at specific areas of heart tissue found to be the source of the irregular rhythms. An electrophysiology (EP) study is first performed to discover the location and characteristics of the arrhythmia and, once the specific location is identified and mapped, RF energy is delivered to the tissue to ablate the tissue, thus forming a lesion that blocks electrical conduction. While minimally invasive techniques are usually preferred, the procedure is often performed in combination with other open heart procedures as a prophylactic to prevent post-operative onset of atrial fibrillation.
RF ablation techniques are typically successful in treating atrial fibrillation, however the lesions must be well defined within the heart to be effective. The lesion must have a sufficient length, continuity and/or depth to interrupt or to block electrical conduction across the affected portion of the heart. This can be difficult to achieve without forming an incision in the atrium. In addition, if the energy is not uniformly transmitted to the target site, hot spots can form, possibly leading to severe tissue damage or blood coagulation (clots).
Accordingly, there exists a need for ablation instruments and procedures that produce uniform ablations on a retracted atria.