The Five-Box Thoracoscopic Maze Procedure

As performed at The Ohio State University, the five-box thoracoscopic maze is a closed-chest, beating-heart, truly minimally invasive procedure. This innovative surgical treatment approach is teamed with comprehensive testing to assure that all potential causes are completely treated. Outcomes in patients who have had the five-box thoracoscopic maze procedure compare very favorably to those who have undergone catheter ablation or other types of maze surgery such as the Wolf Mini-Maze. In the heirarchy of atrial fibrillation treatment, the five-box thoracoscopic maze procedure represents an advanced treatment with a cure rate in excess of 95%.

To begin the procedure, the patient is asleep and placed in the supine position, with a soft roll placed between the spine and the left scapula to elevate the left chest . Four tiny incisions of half an inch in length or less are made on each side of the chest. The pericardium, or fibrous sac enclosing the heart, is opened away from the phrenic nerve, which is responsible for innervating the diaphragm. In this, as in every maneuver of the operation, the thoracoscope provides clear, magnified visualization of all key anatomic structures. This technology enhances both the safety and precision of every maneuver. No computer-enhanced imaging is necessary, since all treated regions of the heart are seen in great detail with the thoracoscope.

If you would like more information about the five-box thoracoscopic maze surgery performed by Dr. John Sirak at The Ohio State University, request a phone consultation or call Dr. Sirak's appointment phone at (866) 486-9149 .

The Five-Box Thoracoscopic Maze Operation in Detail

The five-box thoracoscopic maze consists of six major technical components which are all verified in real time, thereby systematically addressing all mechanisms responsible for atrial fibrillation.

Bilateral Pulmonary Vein Isolation

A wide ablation of the inlets of the pulmonary veins into the left atrium isolates the most common source of abnormal electrical stimuli which may trigger atrial fibrillation. However, since this ablation is performed using a quadripolar, bidirectional clamp, the treated tissue is safely in the left atrium itself, away from the delicate pulmonary veins. This feature eliminates the risk of pulmonary vein stenosis, while achieving a complete, durable electrical isolation of the entire pulmonary vein complex.

Mapping and Ablation of Epicardial Autonomics

The autonomic nervous system is a part of the central nervous system responsible for the unconscious regulation of numerous bodily processes, including temperature, thirst, sweating, and heart rate. Nerve fibers from the autonomic system enter the external surface of the heart in localized areas which are easily accessible to the five-box thoracoscopic maze. In many patients with atrial fibrillation, abnormal impulses from the epicardial autonomics produce a shortened refractoriness, or resting period between firings, in the atrial muscle. The result is a lowered threshold at which the atrium sustains fibrillation.

In the five-box thoracoscopic maze, all abnormal epicardial autonomics are located using a high-frequency stimulation probe. The probe elicits an immediate, temporary slowing of heart rate, providing safe, definitive identification of all abnormal nerve fibers. The abnormal autonomics are ablated until all positive testing signals are extinguished.

Contiguous Left Atrial Compartments Connecting to the Mitral Valve Annulus and Isolating the Posterior Left Atrium

Particularly in advanced atrial fibrillation, structural changes in the left atrium involving atrial stretch or fibrosis result in uneven conduction across the atrial muscle. This differential in the rates of conduction in contiguous atrial muscle allows for the formation of adjacent electrical circuits which propagate around the annulus of the mitral valve at different rates. Thus, with the different rates of conduction, the adjacent circuits may auto-trigger one another, resulting in the establishment of persistent atrial fibrillation in the left atrium. The key anatomy in the left atrium for perpetuating atrial fibrillation is the annulus of the mitral valve, which serves as the hub for the random, circular movement of fibrillatory current. Any anti-arrhythmia procedure which omits verified ablations to the mitral annulus is inadequate for the treatment of atrial fibrillation. Even patients with paroxysmal atrial fibrillation suffer a significant drop in cure rates when a comprehensive treatment of the left atrium is not performed.1

The five-box thoracoscopic maze addresses the left atrium specifically with two contiguous compartments isolating both the mitral annulus as well as the posterior left atrium. First, transesophageal echocardiography identifies the anterior trigone of the mitral annulus in real time. Ablations from the mitral annulus connect at two points to a line of ablation between the superior pulmonary veins, resulting in an enclosed triangle on the roof of the left atrium. Second, the line of ablations between the superior pulmonary veins forms one side of a four-sided box—consisting of the two pulmonary antral isolations and a connecting line of ablations between the inferior pulmonary veins. The result is complete electrical isolation of the posterior left atrium - a large area of the substrate supporting fibrillation - from the remainder of the heart.

The net effect is a complete interruption of peri-mitral macro re-entry in two perpendicular planes relative to the mitral annulus. No other currently performed procedure—whether surgical or catheter-based—is able to replicate this biplanar compartmentalization of the mitral annulus and floor of the left atrium. Numerous clinical studies have demonstrated that omission of either step results in a significant drop in cure rates.

Isolation of the Superior Vena Cava and Distal Coronary Sinus

The junctions of the superior vena cava and coronary sinus with the right atrium are well known potential sources of ectopic stimuli capable of initiating atrial fibrillation. The superior vena cava is quickly isolated just proximal to the right atrium with a quadripolar clamp device. The isolation of the distal coronary sinus is incorporated by connecting ablations into the box isolating the posterior left atrium described above.

Both of these ablations are included in the five box paradigm, allowing for real-time verification intraoperatively using bidirectional block, as is explained below.

Ligation of the Left Atrial Appendage

The last component of the operation consists of closing the left atrial appendage. The purpose for this maneuver is to reduce the risk of stroke. 90% of the potentially stroke-causing clots found in the heart in association with atrial fibrillation are located in the left atrial appendage. The appendage is an otherwise useless structure which is quickly closed using an endoscopic stapler. Real-time echocardiography confirms complete ligation of the appendage.

Real-Time Five-Box Verification of All Procedure Goals

Numerous procedures using a variety energy sources claim to treat atrial fibrillation. Without meticulous real-time testing to confirm all ablations, procedural efficacy is compromised. Further, incomplete ablation lines left behind in the absence of testing potentially subject the patient to even more malignant arrhythmias. Thus, rigorous intraoperative testing of all ablations is absolutely necessary to assure superior outcomes.

As performed at The Ohio State University, the clear distinguishing feature of the five-box thoracoscopic maze over all other anti-atrial fibrillation procedures is verification of all technical components with the most rigorous standards - nothing is assumed concerning the effectiveness of any given maneuver.

Diagram of heart with five electrical compartments

Using a novel five-box verification technique pioneered at The Ohio State University, electrical isolation of all potential sources of atrial fibrillation is confirmed in real time for each patient. Separate testing of the five electrical compartments enables immediate identification of areas for additional treatment in case a leak is detected. As a final test, at the end of the procedure, all patients are checked for spontaneous conversion to normal sinus rhythm after being placed into atrial fibrillation with high frequency stimulation of the untreated atrium. This non-inducibility of atrial fibrillation further confirms complete treatment of all sources of fibrillation in any given patient.

The complete five-box lesion pattern encompasses four contiguous compartments: the two pulmonary antra, the posterior left atrium, and an enclosed triangle on the dome of the left atrium incorporating the connection the anterior trigone of the mitral annulus, as well as the superior vena cava. Additional linear lesions connect both the left pulmonary antrum and the transmitral line to the base of the left atrial appendage, and the right pulmonary antrum to the coronary sinus.

1. Han F et al. Results of a minimally invasive surgical pulmonary vein isolation and ganglionic plexi ablation for atrial fibrillation: single-center experience with 12-month follow up. Circulation: Arrhythmia and Electrophyiology 2009;2;370-377.