Surgery – Cardiac augmentation
Reexamination Certificate
2002-06-11
2004-02-03
Layno, Carl (Department: 3762)
Surgery
Cardiac augmentation
C623S003110
Reexamination Certificate
active
06685621
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a system for assisting the heart and, in particular, to an extracardiac pumping system and a method for both supplementing the circulation of blood through the patient and for enhancing vascular blood mixing using a minimally invasive procedure.
BACKGROUND OF THE INVENTION
During the last decade, congestive heart failure (CHF) has burgeoned into the most important public health problem in cardiovascular medicine. As reported in Gilum, R. F.,
Epidemiology of Heart Failure in the U.S.,
126 Am. Heart J. 1042 (1993), four hundred thousand (400,000) new cases of CHF are diagnosed in the United States annually. The disorder is said to affect nearly 5 million people in this country and close to 20 million people worldwide. The number of hospitalizations for CHF has increased more than three fold in the last 15 years. Unfortunately, nearly 250,000 patients die of heart failure annually. According to the Framingham Heart Study, the 5-year mortality rate for patients with congestive heart failure was 75 per cent in men and 62 per cent in women (Ho, K. K. L., Anderson, K. M., Kannel, W. B., et al.,
Survival After the Onset of Congestive Heart Failure in Framingham Heart Study Subject,
88 Circulation 107 (1993)). This disorder represents the most common discharge diagnosis for patients over 65 years of age. Although the incidence of most cardiovascular disorders has decreased over the past 10 to 20 years, the incidence and prevalence of congestive heart failure has increased at a dramatic rate. This number will increase as patients who would normally die of an acute myocardial infarction (heart attack) survive, and as the population ages.
CHF manifests itself primarily by exertional dyspnea (difficult or labored breathing) and fatigue. Three paradigms are used to describe the causes and therapy of CHF. The first views this condition in terms of altered pump function and abnormal circulatory dynamics. Other models describe it largely in terms of altered myocardial cellular performance or of altered gene expression in the cells of the atrophied heart. In its broadest sense, CHF can be defined as the inability of the heart to pump blood throughout the body at the rate needed to maintain adequate blood flow, and many of the normal functions of the body.
To address CHF, many types of cardiac assist devices have been developed. A cardiac or circulatory assist device is one that aids the failing heart by increasing its pumping function or by allowing it a certain amount of rest to recover its pumping function. Because congestive heart failure may be chronic or acute, different categories of heart assist devices exist. Short of a heart transplant, at least two types of chronic heart assist systems have been developed. One type employs a full or partial prosthetic connected between the heart and the aorta, one example of which is commonly referred to as a LVAD—Left Ventricular Assist Device. With reference to
FIG. 1
herein, one example of a LVAD
2
is shown. The LVAD comprises a pump and associated valves
4
that draws blood directly from the apex of the left ventricle
6
and directs the blood to the aortic arch
8
, bypassing the aortic valve. In this application, the left ventricle stops functioning and does not contract or expand. The left ventricle becomes, in effect, an extension of the left atrium, with the LVAD
2
taking over for the left ventricle. The ventricle, thus, becomes a low-pressure chamber. Because the intent is to take over for the left ventricle, the LVAD operates by pumping blood at cardiac rates. With an LVAD, oxygenated blood circulation is established sufficient to satisfy the demand of the patient's organs. Under these circumstances, however, continuous flow may not be desired because the patient's arterial system is deprived of pulsatile wave flow, which is beneficial to certain parts of the patient.
Another type of chronic heart assist system is shown in U.S. Pat. No. 5,267,940 to Moulder. Moulder describes a pump implanted into the proximal descending aorta to assist in the circulation of blood through the aorta. Because it is intended to pump blood flowing directly out of the heart, it is important that the Moulder device operate in a properly timed, pulsatile fashion. If it is not operated in direct synchronization with the patient's heart, there is a risk that the pump might cause “carotid steal phenomenon” where blood is drawn away from the patient's brain through the carotid arteries when there is insufficient blood in the left ventricle.
In addressing acute CHF, two types of heart assist devices have been used. One is counterpulsatory in nature and is exemplified by an intra-aortic balloon pump (IABP). With an IABP, the balloon is collapsed during isovolumic contraction, providing a reduced pressure against which the heart must pump blood, thereby reducing the load on the heart during systole. The balloon is then expanded, forcing blood omnidirectionally through the arterial system. Another example of this first type employs one or more collapsible chambers in which blood flows passively into the chamber during systole, as is shown in U.S. Pat. No. 4,240,409 to Robinson et al. The chamber is then collapsed and the blood forcibly returned to the aorta. These devices simulate a chamber of the heart and depend upon an inflatable bladder to effectuate pumping action, requiring an external pneumatic driver. Moreover, they do not operate as a continuous flow system, operating exclusively in pulsatile fashion.
A second type of acute assist device utilizes an extracorporeal pump, such as the Biomedicus centrifugal pump, to direct blood through the patient while surgery is performed on the heart. In one example, described in U.S. Pat. No. 4,968,293 to Nelson, the heart assist system employs a centrifugal pump in which the muscle of the patient is utilized to add pulsatility to the blood flow. The Nelson device is used to bypass a portion of the descending aorta.
Another device, shown in U.S. Pat. No. 4,080,958 to Bregman et al., utilizes an inflatable and collapsible bladder to assist in blood perfusion during heart trauma and is intended to supplement a conventional heart-lung machine by imparting pulsatile actuation. In the primary embodiment disclosed in Bregman, the balloon is controlled to maintain sufficient pressure at the aortic root during diastole to ensure sufficient blood perfusion to the coronary arteries. In an alternative embodiment, a low resistance outlet from the aorta to the inferior vena cava is provided to reduce the aortic pressure during systole, thus, reducing the hemodynamic load on the left ventricle.
Other devices, such as that shown in U.S. Pat. No. 4,034,742 to Thoma, depend upon interaction and coordination with a mechanical pumping chamber containing a movable pumping diaphragm. These devices are intended primarily for application proximate the heart and within the patient's thorax, requiring major invasive surgery.
Many CHF devices are acutely used in the perioperative period. For example, U.S. Pat. No. 4,995,857 to Arnold discloses a perioperative device to pump blood at essentially cardiac rates during surgery when the heart has failed or has been stopped to perform cardiac surgery. The Arnold system temporarily replaces the patient's heart and lung and pumps blood at cardiac rates, typically 5 to 6 liters/min. Like all systems that bypass the heart and the lungs, an oxygenator is required. Of course, with any system that includes an oxygenator, such as the conventional heart-lung machine, the patient cannot be ambulatory.
With early IABP devices, a polyurethane balloon was mounted on a vascular catheter, inserted into the femoral artery, and positioned in the descending aorta just distal to the left subclavian artery. The balloon catheter was connected to a pump console that pumped helium or carbon dioxide into the balloon during diastole to inflate it. During isovolumic contraction, i.e., during the brief time that the aortic valve
Bolling Steven F.
Charhut Ken
Knobbe Martens Olson & Bear LLP
Layno Carl
Orois Medical Corporation
Webb B.
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