Surgery – Cardiac augmentation – With condition responsive means
Reexamination Certificate
2000-03-02
2002-06-18
Evanisko, George R. (Department: 3762)
Surgery
Cardiac augmentation
With condition responsive means
Reexamination Certificate
active
06406422
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ventricular-assist method and apparatus and, more particularly, to a ventricular-assist device (VAD) which can assist especially a failing heart and delay the development of end-stage heart failure and the point at which a heart transplant may be required. The invention also relates to a method of sustaining the failing heart utilizing a ventricular-assist device and an algorithm for operating a ventricular-assist device.
BACKGROUND OF THE INVENTION
The normal cardiac output, normalized by total body surface, is around 3.5 liter per minute per one square meter (1/min/m
2
). In general, cardiac assist is necessary whenever a patient's cardiac output drops below the adequate blood supply needed to sustain proper blood perfusion, which is 1.8-23 1/min/m
2
. Failure to supply adequate flow is defined as “systolic failure”. However, more than 50% of the patients over 60 display inadequate ventricle filling and tissue congestion, which is defined as “diastolic failure”. Cardiac assist is used to treat patients suffering from heart failure at a stage where conventional drug therapy proves ineffective.
Congestive Heart Failure (CHF) is a chronic disorder that develops over time, manifested clinically by an enlarged heart and symptoms and signs of low cardiac output and tissue congestion. The low cardiac output leads to decreased blood perfusion to vital organs (liver, kidney and brain). The CHF is also characterized by lung congestion (recurrent pulmonary edema) which threatens life and requires hospitalization. CHF is associated with profound symptoms that limit daily activities, is a debilitating disease with poor quality of life. CHF is the most common cause of hospitalization of patients over 60 years of age.
CHF has various etiologies, including cardiovascular disease (diseases which affect blood flow to the myocard), chronic hypertension (high blood pressure), incompetent values, inflammation of the heart muscle or the valves, substance accumulation (amyloid) and congenital heart problems.
Cardiovascular diseases (CVD) represent the leading cause of death in the industrialized world. CVD claimed 960,592 lives in the US in 1995 (41.5% of all deaths for that year). According to the US National Heart Lung and Blood Institute (NHLBI) and the American Heart Association there are approximately 5 million patients who suffer from Congestive Heart Failure (CHF) in the US and between 400,000 and 500,000 newly diagnosed patients each year. Long-term survival rates are low and the 5 year mortality rate for patients with CHF is 75% in men and 62% in women, while in patients with decompensated heart failure the mortality rate is 60% per year.
Patients suffering from Congestive Heart Failure (CHF) are initially treated with medication. While conventional drug therapy may delay the progress of CHF, it is not curative. Cardiologic intervention (such as Angioplasty and Stenting), surgery (Heart by-pass surgery, Cardiomyoplasty, Partial Ventriculectomy known as Batista's procedure), and mechanical devices are often considered when drug therapies prove ineffective or inadequate. Electrical disturbances of the heart that threaten or impair the quality of the patient's life have been treated effectively with pacemakers and implantable defibrillators. However, congestive heart failure has not been addressed effectively. Currently, the only available method of treating end-stage CHF is a heart transplant.
The demand for temporary and permanent cardiac-assist devices is remarkably large; in 1993 between 40,000 to 70,000 patients needed life-sustaining assist devices or a total artificial heart, and an additional 80,000 to 200,00 patients needed quality of life improvements by surgery (Cardiomyoplasty or Heart Booster).
Ventricular-assist devices are needed for:
Bridge-to-Recovery—cardiac assist for patients whose heart has sustained serious injury, but can recover if adequately supported. This includes the use of a cardiac-assist device after surgery in order to provide support until the heart regains its ability to pump. Temporary cardiac support is intended primarily to prevent or reduce damage from cardiac failure or to support adequate blood circulation.
Bridge-to-Transplantation—patients awaiting heart transplants and who are not scheduled and when the heart failure is unresponsive to medical treatment.
Existing temporary mechanical cardiac devices are divided into three groups:
1. Temporary cardiac assist for several hours, as the intra-aortic balloon that is frequently utilized for patients with heart failure after open-heart surgery due to failure to wean from the cardiopulmonary bypass.
2. Long-term (days, weeks, months) Ventricular Assist Device (VAD), as a bridge to heart transplantation.
3. Permanent support by Total Artificial Heart (TAH).
Intra Aortic Balloon Pump (ABP). The IABP has been in clinical use for over 20 years. The IABP consists of a balloon (30-50 ml) that is inserted into the descending aorta and is inflated during the diastole and deflated during the systole. The IAB increases the cardiac output by less than 0.5 1/min/m
2
.
Consequently, although it was designed to assist a failing heart by improving blood perfusion, it requires a certain threshold level of cardiac output and cannot take over the pumping function of the heart. As a result, it can only be utilized in treatment of patients who require mild levels of mechanical assistance (unless there is a supplemental assisting heart device). The device reduces the energy consumption and allows the heart to recover. However, the IABP is used only for short-term circulatory assist due to high risk of severe thromboembolic complications.
Ventricular Assist Devices (VAD)—VADs take over the complete pumping function of one or both sides of a failing heart. They unload the assisted ventricle. Left Ventricular Assist Devices have been approved for use by the FDA as bridge-to-heart transplantation, to keep patients alive who are awaiting a donor heart. These devices have also been approved for use by patients whose hearts are in failure but may be able to recover by reducing the myocardial work (unloading), including patients in post-surgical life-threatening heart failure.
More than a dozen companies (listed below) are developing devices, ranging from left-ventricular assist products to total artificial hearts, that offer CHF patients either longer-term support with an alleviation of symptoms, and/or an alternative to heart transplant. Some of these (Thermo CardioSystems, Thortec, Abiomed and Baxter Healthcare) have ventricular assist products on the U.S. market. Ventricular-assist devices are generally employed on a temporary basis, with treatment periods ranging from a few hours to a few weeks, or at most, a limited number of months. However, some devices have been designed for long-term use and can be considered lifetime support systems. To date, such lifetime support is still in developmental and experimental stages and was not approved by the FDA.
There are five major types of VAD: Roller pumps, Centrifugal pumps, Pneumatic devices, Electrical devices and direct mechanical actuators. These devices differ in the design, indications and duration.
Roller and Centrifugal Pumps are approved for short-term (i.e. hours) support of patients undergoing heart surgery. These devices generate a non-pulsatile blood flow which severely restricts the time patients can safely remain on support. They also require additional medical personnel to provide constant monitoring and ensure that the pump is operating correctly.
Transplant bridging, and possibly long-term cardiac assistance may also be accomplished with implantable axial flow and centrifugal pumps. Examples of companies pursuing cardiac-pumping technology include: Jarvik Research, Medtronic Inc., 3M Corporation Inc., Kirton Medical, Micromed Technology and Cardiac Assist Technologies.
A high-speed pump has been developed recently by Micromed in co-development with the National Aeronautics and Space Administration
Dubno Herbert
Evanisko George R.
Levram Medical Devices, Ltd.
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