The access to the human heart has always been a source of active research especially recently with the advancement in technology that has led to improved management of cardiovascular pathology. Heart disease is the leading cause of death connected to all age groups in the United States. The esophagus has a close proximity to the heart and posterior mediastinum, which has allowed the use of transesophageal fine needle aspiration and transesophageal biopsy techniques to be used extensively in recent years to obtain tissue samples. Most of the posterior mediastinal tissues are accessible for biopsy including the lungs and lymph nodes. The technique has proven to be safe and reproducible with minimal complications. The microbial flora of the human esophagus is similar to that in the pharynx, which results in no bacteria with transesophageal puncture using needles up to 1 mm in diameter in many studies. The esophagus has never been used to access the human heart, but rather to perform procedures related to the heart due to the close anatomical proximity. A number of trials have been described as in U.S. Pat. No. 6,120,442 for transesophageal intracardiac pressure measurement, in U.S. Pat. No. 5,417,713 for using a transesophageal defibrillating system, and in U.S. Pat. No. 5,179,952 for the use of a transesophageal electrocardial stimulator. Some trials were made to use the trachea for monitoring the heart as in U.S. Pat. No. 5,080,107 that describes the use of an endotracheal sensor for cardiac monitoring.
Access to the heart has always been the main determinant of the form, degree and invasiveness of therapy, which determines the ultimate success of the treatment modality. The left side of the heart is more systemically important and much less accessible than the right side for its anatomic location and the high blood pressure it generates in the systemic circulation. The spectrum of disease states that can be assessed diagnostically or therapeutically are generally more reflected on the left side of the heart. This is evident clinically in a wide range of cardiovascular pathology e.g. congestive heart failure. There is no known non-invasive method that can directly measure the pressure in any chamber of the heart. All current methods either use speed of blood flow as a non-invasive reflection of chamber pressure or they measure the pressure invasively via a catheter inside or near the chamber. The most common technique to measure the left atrial pressure is the pulmonary catheter wedge pressure method. The left atrium is a low-pressure, left-sided structure that has a special importance with regard to its mechanical and electrical properties. Unfortunately, there is no simple non-invasive way of directly measuring the left atrial pressure. Even with invasive measurement as in pulmonary artery catheterization, the measured value reflects an indirect estimation of the left atrial pressure, and thus can be inaccurate in many instances. The left atrium is also important in terms of electrophysiological mapping and ablation. The current techniques access the left atrium using a catheter indirectly from the right atrium across the inter atrial septum or in a retrograde approach through the aorta. Both techniques have their inherent side effects and complications. Thus, access to the left atrium is a described objective in order to treat a large subset of patients, such as congestive heart failure patients.
A second subset of cardiac patients in which the access to the heart is the main determinant of interventions and management are patients with congenital cardiac defects like ASD, VSD and PDA. The main pathology in most congenital cardiac defects is the presence of an unnatural conduit that shunts the blood from the right to left heart or the reverse. This overloads the side with lower pressure and any tissue or vascular bed in the shunted circuit. The pulmonary vascular bed is commonly affected by blood overflow that may lead to reversible or late irreversible pulmonary vascular hypertension. The invasiveness of the current techniques limits the early implementation of a shunt closure especially in children, which is a curative intervention if done before irreversible vascular changes. Other techniques use the catheter transvascular approach with limited success due to lack of control and torque at the end of a long flexible, narrow catheter used in the procedure.
In a third group of patients, cardiac arrhythmias are responsible for a high percentage of morbidity and mortality. Atrial fibrillation is a common and chronic disease with a prevalence of 2-3% in the United States. The disease is longstanding and mandates chronic anticoagulation as part of the treatment to prevent any embolic disease especially to the brain. Chronic anticoagulation in itself carries serious risk of internal bleeding added to the toxicity of chronic anti-arrhythmic medications used to stabilize atrial fibrillation. Recently, surgical curative techniques have been described in the literature to treat atrial fibrillation. Access to the heart has been a main determinant in the use of any of these techniques. The invasiveness of the open chest approach has limited the number of the Maze-like procedures used to radically prevent the fibrillation impulses from being conducted to the ventricles. Also, the catheter-based approach is inaccurate, tedious, time consuming (up to 12 hours) and not definitive in creating enough linear ablations to prevent impulse conduction. The thoracoscopic approach is easier than the catheter-based transvascular approach but the side access to the posterior heart limits the linearity of ablation especially around the entrance of the pulmonary veins, which results in incomplete Maze, and recurrence of disease.
The three known accesses to the heart namely, the open chest, the catheter-based transvascular, and the thoracoscopic approaches suffer from serious limitations and complications which, in turn, limit the therapeutic options for most of patients. The limitations of the current three known accesses to the human heart can be classified as follows:
1—The Open-Chest Technique:
Most cardiovascular procedures are performed by opening the chest wall either by gross sternotomy or by lateral thoracotomy. The sternotomy approach is more common than the lateral thoracotomy as it allows a greater field for the surgeon to introduce surgical devices, to control target tissues and to clamp and catheterize the aorta for induction of cardioplegia and bypass. It involves opening the sternum using a saw to cut through the bony structure. It also involves arresting the heart by cardioplegic techniques. The circulation is switched to cardiopulmonary bypass for preserving tissue perfusion. The above advantages of the sternotomy approach are offset by serious disadvantages. First, the risk of stopping the circulation with the possibility of causing marked decrease in tissue perfusion or ischemic damage that may involve vital tissues like the brain, heart or kidneys. Second, the risk of embolization of dislodged tissues in the aorta due to aortic manipulation including clamping and catheterization. The dislodged emboli can cause acute brain or peripheral ischemia. Brain damage may be permanent after an embolic event during open sternotomy approach. Even without any embolic or gross brain injury, psychometric analysis shows definite changes and cognitive defects in young healthy individuals after open-heart surgery. Third, opening the chest wall by cutting through all layers including the bony sternum with great force applied for rib retraction produces significant pain after the surgery with post surgical morbidity and, if severe, mortality. The post surgical wound care and pain may require rehabilitation in complicated cases with longer hospital stays and increased expenses. Fourth, concomitant morbid states or age extremes may adversely increase all of the above-mentioned risks.
The other two methods to access the heart are the transvascular and the thoracoscopic approaches. Both have the advantageous difference from the conventional open-chest approach in not requiring gross thoracotomy. The thoracoscopic approach may or may not involve cardioplegia and cardiopulmonary bypass. Again, these procedures have fundamental disadvantages.
2—The Transvascular Approach:
For the transvascular approach to the treatment of heat defects, the disadvantages are inherent in the fact that the procedural tools have to go through and stay in a blood vessel or a cardiac chamber. Thus, the tools can only be long, narrow, flexible catheters. This affects the controllability and the force generation at the tip of the catheter which, in turn, decreases the accuracy and precision of the procedure. The access to the heart is mainly from the right side and rarely through an aortic retrograde approach. To reach the left heart, a septostomy opening is made in the interatrial septum that decreases the control over the catheter and makes the manipulation of the catheter tip more difficult as the catheter has to pass through the narrow right atrium and the small septostomy opening. Another main limitation is the caliber of the lumen of peripheral vessels through which the catheter has to travel. This is even a more limiting factor in young children whose smaller vessels raise the risk of vessel injury that may be acute, such as intimal dissection, or chronic such as major vascular obliteration and fibrosis. In the elder population, the occurrence of peripheral fat embolization is another risk for manipulations of a catheter in the aortic lumen for procedures like coronary angiography. This may result in temporary acute or chronic ischemia to the lower or upper extremities.
In addition to vascular injury, some techniques like intracardiac mapping and ablation require the passage of large catheters to be able to deliver large energy output through large electrodes. These ablative techniques are useful in cardiac dysrhythmias as ventricular or supraventricular tachycardias and atrial fibrillation. A number of trials to apply mapping and ablation technique through the use of the transvascular approach have been described as in U.S. Pat. Nos. 4,960,134, 4,573,473, 4,628,937, and 5,327,889. In U.S. Pat. No. 6,047,218, a technique for ablation and visualization of the intracardiac chamber through the transvascular approach is described. The small size of the vessels limits the size of catheters used in ablation techniques. That limitation gives rise to a lack of control and positionability due to the flexibility, increased distance and decreased force at the tip of such catheters.
The transvascular approach has a limited use in surgical procedures like septa defect repair by using an introductory device due to the above-mentioned limitations. A number of trials to use the transvascular approach to deliver a patch from a vein via the right heart to close a septal defect have been contemplated; see e.g. U.S. Pat. Nos. 3,874,388; 5,334,217; 5,284,488; 4,917,089, and 4,007,743. In addition to the above-mentioned limitations, the use of patches to close a septal defect using the transvascular approach with lack of distal force at the delivery tip may result in inadequate fixation of the patch to the defect plus the inability of patch repositioning after its application to the defect site. The detachment of the patch from the defect site may lead to serious patch embolization and failure of repair. In some cases this may, in turn, require an open sternotomy to correct the failed transvascular repair.
3—The Thoracoscopic Approach:
The thoracoscopic approach provides more advantages over the transvascular approach in terms of having more control over the procedure tools, and increased precision in positioning the catheter tip to perform intracardiac procedures. The disadvantages of such an approach can be considered. The inaccessibility of the posterior aspect of the heart to the rigid scopes passed from either side of the heart, which is mandatory to create an atriostomy opening in the posterior aspect of the atrium, is a problem. This may be solved by applying a stitch to the pericardium and pulling the pericardium to rotate the heart and expose the posterior aspect. The stitch should be applied from an anterior, not side, position to have enough rotation force on the pericardium. However, due to the narrow intercostals spaces in the anterior rib aspect, it is difficult to make such a stitch which makes the posterior aspect of the heart a difficult area to access. Another limitation is the need to have a second monitoring system to assess catheter position and convey accurate measurements as the procedure is not performed under direct visual examination. Such monitoring devices make the approach more complicated, may lack accurate precision, and may need to be invasive, e.g. removal of the fourth rib for visualization, or add a potential risk of ionizing radiation exposure with CT scanning, or be cumbersome and slow with MRI scanning, adding to the complexity of the technique. Second, the limited windows between the ribs as a limiting border from above and below the access, the surrounding intercostals muscles and underlying vital structures including the lungs, pleura, nerves, and great vessels can limit the access especially in young children with narrow intercostals spaces, and patients with deformities.
The need to access multiple intercostal openings to use a plurality of thoracoscopes counteracts the main objective of the technique to be minimally invasive and may turn out to be more invasive and cause significant tissue damage as it may also require removal of the fourth rib. The need to deflate the lung to widen the surgical field adds to the invasiveness and increases the complication potential of the procedure. The inability to explore the posterior mediastinum and related structures on the posterior aspect of the heart as the catheter is advanced from an anterior position makes procedures involving the posterior aspect of the heart less accessible as in ablation around the entrance of the four pulmonary veins in the left atrium. Indeed, the thoracoscopic approach has been criticized lately by a number of studies that show numerous post-surgical complications. A number of trials to perform surgical intracardiac procedures from the thoracoscopic approach have been described, e.g. in U.S. Pat. Nos. 5,980,455; 5,924,424; 5,855,614; 5,829,447; 5,823,956; 5,814,097; 5,797,960; 5,728,151; 5,718,725; 5,713,951; 5,613,937, and 5,571,215. Closed chest coronary bypass surgery using the thoracoscopic approach is described in U.S. Pat. No. 6,123,682.
None of the currently available techniques directly accesses the posterior aspect of the heart and coronary circulation or the posterior mediastinum. Recently, there has been heightened interest in minimally invasive methods of cardiac surgery that allow intracardiac or extracardiac procedures and avoid the need to crack the rib cage or stop the heart.
What are needed, therefore, are devices and methods to enable a new access to the human heart that is easily accessible, that allows access to both the interior and exterior of the heart simultaneously, with enough force and control over the procedure tools, that causes minimum tissue injury, and that can be applied to the heart, while still beating, without the need for general anesthesia. This access should allow the performance of surgical procedures like septal defect repairs, treatment of cardiac dysrhythmias and treatment of various cardiac pathology such as valvular manipulations with a degree of success similar to the open approaches, while avoiding the complications and limitations of the above-mentioned prior techniques.
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