The heart is surrounded by the pericardial sac, a loose layer of tissue, which may be visualized and retracted from the heart in an open chest. Retracting the pericardial sac from the heart creates the pericardial space, a space between the heart and the pericardial sac. U.S. Pat. No. 6,162,195 issued to Igo, et al. describes the pericardial sac as surrounding the heart like a glove enfolds a hand, and the pericardial space as naturally fluid-filled. The normal pericardium functions to prevent dilatation of the chambers of the heart, lubricates the surfaces of the heart, and maintains the heart in a fixed geometric position. The normal pericardial space is small in volume and the fluid film within it is too thin to functionally separate the heart from the pericardium. See Shabetai R: Pericardial and cardiac pressure, Circulation 77:1, 1988
Many cardiac surgical procedures invade the pericardial sac leaving it torn with no detrimental effect. Various approaches may be used to access the pericardial sac and the outside of the heart including a median sternotomy, a thoracotomy, a thoracoscope, a sub-xiphoid route and a transvenous route. The median sternotomy is a chest surgical technique using an incision of the skin and sternum between the xiphoid process and the suprasternal notch. The thoracotomy is a chest surgical technique using an incision of the chest wall and may include removal of a portion of a rib. The thoracoscope approach generally involves three puncture wounds to the chest, placement of ports for access with light, camera and instruments. The sub-xiphoid route uses a puncture inferior to the xiphoid process and the xiphoid process may or may not be removed. Transvenous approaches to the outside of the heart generally involve venous access on the right side of the heart and a puncture through the right atrium, right atrial appendage or superior vena cava.
Access to the outside of the heart may be useful for revising the circulation of the heart as in coronary artery bypass grafting (CABG), the delivery of pharmaceutical agents, the revision of the heart structure in support of cardiac valvular function, the placement of electrodes for pacing, sensing, monitoring, cardioverting or defibrillating, the ablation of tissue for the prevention of arrhythmias, or other structural modification. Implantable stimulation of the heart has been in clinical use since the early 1960's when electrodes were implanted on the outside of the heart, the epicardium. Insulated wires connecting the electrodes to an implantable pulse generator called “leads” were implanted by a surgical procedure.
Approaches that involve an intact chest such as the sub-xiphoid do not provide space for accessing and retracting the pericardial sac. To access the outside of the heart without unintentional perforation, incision or damage to the heart requires retraction of the pericardial sac. U.S. Pat. No. 6,315,774 issued to Daniel et al. discloses a thoracoscopic approach to access the space around the heart by the use of a pair of graspers and scissors, then grabbing and opening the pericardial sac by making a stem to stern type of incision. The pericardial sac is pulled away from the heart and may be suspended.
U.S. Pat. No. 7,597,698 issued to Chin describes creating an opening through a pericardial reflection, a fold in the pericardium but is quick to point out that dissection is hazardous because of important large blood vessels in the vicinity of the reflection. Grasping and forming a hole in the superior vena cava, for example, would be disastrous. U.S. Pat. Nos. 4,181,123 and 4,319,562 to Crosby, and 5,033,477 to Chin et al. disclose methods for placing electrodes in contact with the heart muscles from within the pericardial space without the need for thoracotomy via a sub-xiphoid route which involves penetrating the chest wall below the xiphoid process. However, Waxman, in U.S. Pat. No. 5,968,010, describes the sub-xiphoid route as so small that it is difficult to penetrate the sac without also puncturing, and thereby, damaging the heart itself. U.S. Pat. No. 4,991,578 issued to Cohen discloses distending the pericardium from the heart by injecting a small volume of fluid into the pericardium, puncturing the pericardium with a needle, passing a guide wire through the needle into the pericardium and then removing the needle. Adding fluid between the beating heart and the pericardial sac decreases the volume to which the heart may fill. Caution must be taken to avoid the extreme of this situation called tamponade in which the output of the heart is so restricted that systemic circulation is impaired.
U.S. Pat. No. 6,237,605 issued to Vaska, et al. describes devices and methods that may be utilized through a small access port in the chest, preferably through a subxiphoid penetration, and positioned within the pericardium and around the pulmonary veins without cutting or puncturing the pericardial reflections.
Cryogenic techniques applied to the heart demonstrate reversible changes to the myocardium. U.S. Pat. No. 5,733,280 issued to Avitall describes the cooling of cardiac cells and rewarming the tissue resulting in total recovery of the tissue without damage. U.S. Pat. No. 5,147,355 issued to Friedman, et al. discloses a catheter having a fluid flow passage for directing a flow of cryogenic fluid to the tip of the catheter.
Stabilization with devices applied to a beating heart is recognized in U.S. Pat. No. 6,960,205 issued to Jahns, et al., incorporated herein in its entirety by reference, describing devices that use vacuum or suction force to hold tissue. Apparatus for visualization and access is described in U.S. Pub. No. 2007/0293724 to SAADAT, et al. wherein tissue can be engaged using a vacuum or a cryo-probe. Creation of an ice-ball at the catheter tip that stabilizes the tip relative to a tissue is described in U.S. Pub. No. 2007/0116921 by Sherman, et al.
The use of suction for accessing an anatomical space of the body, and particularly for penetrating the epicardium to access pericardial space and the epicardial surface of the heart is described in U.S. Pat. No. 6,890,295 issued to Michels et al., incorporated herein in its entirety by reference. The use of suction requires a relatively large diameter apparatus to achieve sufficient retention force applied to the pericardial surface as compared to the diameter of cardiac rhythm leads.
U.S. Pat. No. 3,737,579 issued to Bolduc, incorporated herein in its entirety by reference, describes electrical leads for myocardial implantation with a rigid helix on the distal end of the lead serving as an electrode screwed into body tissue. U.S. Pat. No. 4,142,530 issued to Wittkampf, describes the screw-in type of electrode as requiring sufficient room to approach the heart wall from a direction that is more of less normal or perpendicular to the surface to allow the helix to be screwed into the heart muscle.
For applications where it is desired to access the epicardial surface of the heart, what is needed is a procedure that does not have significant morbidity, does not compromise the patient during the procedure, only requires a small wound and carries little risk of perforating the heart or other major blood vessels.