Surgery – Cardiac augmentation – With condition responsive means
Patent
1996-06-04
1998-01-13
Lewis, William
Surgery
Cardiac augmentation
With condition responsive means
606191, 623 3, A61B 1700, A61H 700
Patent
active
057073368
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Several forms of heart failure can be treated by ventricular assistance, such as by closed chest compression (an aspect of cardio-pulmonary resuscitation), manual heart massage, or mechanical ventricular assistance. Closed chest compression, coupled with medication, must be stopped and replaced by some other treatment if effective rhythm and adequate blood flow are not restored expeditiously. Similarly, while manual heart message can be performed for an indefinite period, it is impractical to do so. Manual message also requires a thoracotomy, with its own morbidity, high cost, and potential complications.
Direct mechanical ventricular assistance has been the subject of considerable research for many years. The requirements for highly specialized equipment and major surgery for implantation has limited widespread applicability, especially in emergency situations.
Maintenance of blood circulation by a failing heart can also be provided by removing blood from the ventricles and pumping it back to the aorta. Indirect mechanical ventricular assistance, like direct assistance, requires extensive surgery. It also involves direct contact between the blood and the apparatus. Blood can clot in areas of the apparatus where flow rates are low, and clots can break away and cause a stroke.
Direct mechanical ventricular assist devices have been described in the medical literature and in patents, the following being exemplary:
"First Successful Bridge to Cardiac Transplantation Using Direct Mechanical Ventricular Actuation," J. E. Lowe et al., Ann Thorac Surg 1991; 52:1237-45
"Direct Mechanical Ventricular Actuation: A Review," M. P. Anstadt et al., Resuscitation, 1991; 21:7-23
All of the devices proposed heretofore for direct mechanical ventricular actuation are implaced by performing a thoracotomy, opening the pericardium, and placing a cup-like squeezing element over the ventricles. The squeezing element typically has a rigid or semi-rigid outer cup and two chambers, one for each ventricle, formed by panels of an extensible material attached and sealed to the outer cup. The chambers are periodically inflated with a gas under pressure supplied through a tube leading from a mechanical pump to squeeze the ventricles and discharge blood (systole) and then deflated by evacuation by the mechanical pump to draw blood from the atria (diastole).
The squeezing action of the chambers requires that the outer non-extensible cup-like wall member of the squeezing device sustain the reaction loads of the pressure applied to the heart. That means, in turn, that the element must be sized and shaped to fit the heart snugly. Inasmuch as the exact size of the patient's heart is often not known in advance, it is necessary to have a range of sizes of squeezing elements on hand for selection and use after access to the heart has been obtained. While the need to maintain an inventory of squeezing elements and for measuring the heart and selecting an element of the right size is by no means an insurmountable impediment to clinical use of such devices, it is an inconvenience and delays the operative procedure. In an emergency situation, such as heart arrest during surgery, time is critical. The sooner that normal or near normal blood flow can be restored, the lower is the probability of irreversible damage to the patient due to temporary loss of cardiac function.
Because the ventricular portion of the heart is roughly conical, the squeezing action of the squeezing element against the ventricles tends to push the element away from the heart. Thus, it is necessary to hold the element in place. Anstadt et al. (referred to above) provide retention of the element by applying a vacuum within the squeezing element. Snyders (also referred to above) provides retention by suturing the squeezing element to the pericardium.
In addition to the requirement for highly invasive surgery for implanting the device and the need for closing the pericardium window and the thoracotomy wound if the device is to be left in place for a signif
REFERENCES:
patent: 3730186 (1973-05-01), Edmunds, Jr. et al.
patent: 4192293 (1980-03-01), Asrican
patent: 5098369 (1992-03-01), Heilman et al.
Cardassist Incorporated
Lewis William
LandOfFree
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