The Artificial Heart Prototypes, Policies, and Patients (1991) / Chapter Skim
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4. Clinical Effectiveness and Need for Long-Term Circulatory Support
4. Clinical Effectiveness and Need for Long-Term Circulatory Support
Pages 65-84
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From page 65... ...
Currently, heart disease in all its forms is the leading cause of death in the United States, but transplantation is the only effective treatment for the substantial portion of all heart disease that results in heart failure. For some types of heart failure, pharmaceuticals can reduce symptom levels, postpone death, or both, but most patients either experience sudden cardiac death or deteriorate to end-stage disease, from which they now die if unable to qualify for and receive a transplant.
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From page 66... ...
) MCSS, mechanical circulatory support system; TAH, total artificial heart.
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From page 67... ...
In more than 400 instances, tethered assist devices have been used to support life in conjunction with cardiac transplantation (Miller et al., 1990b) ; there has been additional experience with these devices during cardiogenic shock following cardiac surgery or acute myocardial infarction (Miller et al., 1990a)
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From page 68... ...
Additionally, some patients who are candidates for heart transplantation, faced with a long waiting period during which their activity and comfort levels are sharply restricted, might choose more immediate relief through the use of a device that will not categorically exclude the possibility of a subsequent transplant. In the upcoming Novacor VAD trial, candidates selected for device use will probably not compete with other transplant candidates, because of the need for the study to make the maximum possible contribution to scientific knowledge, an unlikely outcome if some VAD recipients subsequently received a transplant.
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From page 69... ...
RELATING CLINICAL EFFECTIVENESS AND DEVICE USE Given the current uncertainty about MCSS effectiveness, one approach to estimating the potential patient populations for their long-term use is to explicitly relate a range of projected device characteristics and likely patient outcomes to the number of potential patients under each circumstance. Estimates made today in this manner can be used by the National Heart, Lung, and Blood Institute (NHLBI)
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From page 70... ...
Such a device nonetheless has the potential to improve a heart failure patient's condition from moribund or partially disabled to a reasonable level of functioning, notwithstanding a long-term mortality risk. · A category C device is one that would likely be used only by patients whose survival is in doubt and for whom transplantation is not available or carries a risk of death during the waiting period that is too great.
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From page 71... ...
OTHER INFLUENCES ON THE USE OF CIRCULATORY SUPPORT DEVICES Other factors besides anticipated device performance affect the number of potential patients for MCSS use. The Impact of Other Heart Disease Treatment Technologies In the United States and some other industrialized countries, both the incidence (the rate at which new cases appear)
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From page 72... ...
Even heart transplantation does not completely free patients from the possibility of heart failure. Indeed, the anticipated fate of 20 to 30 percent of all transplant patients is failure of the transplanted organ.
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From page 73... ...
examines more EPIDEMIOLOGICAL PROJECTIONS Previous Studies Several previous studies have attempted to determine the number of endstage heart disease patients whose lives might be prolonged by an effective cardiac support or replacement device. Estimates based on mortality statistics, disease incidence, and life expectancy have ranged from 6,000 to 66,000 annually in the United States alone (NHI, 1969; NHLI, 1973; NHLBI, 1980;
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From page 74... ...
Researchers at the Mayo Clinic performed a population study in which they reviewed all deaths in Olmsted County, Minnesota, using restrictive criteria for age, associated disease, and time limitations between the onset of life-limiting illness and potential MCSS use. Based on key assumptions that the devices would be offered only to patients under age 70 who are free of major comorbidities and who survive the initial cardiac episode by at least two hours, they projected 11,000 to 23,000 potential users of an effective MCSS device per year nationwide (Kottke et al., 19901.
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From page 75... ...
This study took into account sudden deaths and serious comorbidities, but it did not consider the nature of the device to be implanted. This range of sizes for the primary group of potential MCSS candidates encompasses the upper limit of the findings from previous studies of the artificial heart program.
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From page 76... ...
Currently, the limit placed on heart transplantation by the supply of donor hearts is so stringent that no consideration can be given to transplants for patients other than those seriously disabled by their end-stage disease. Pressure to perform transplants at an early stage in the course of patients' illness would thus have been to no avail.
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From page 77... ...
Additional Potential Patients At some point, probably not before the 2020s, MCSSs likely will be used in limited numbers with two additional patient groups. One group is persons less disabled by their heart failure than those in our secondary group.
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From page 78... ...
At present, it is generally accepted that patients are more likely to require biventricular support if they are unable to survive without an MCSS and have as the precipitating factor acute ischemia induced by operation and/or acute myocardial infarction. In contrast, others who are less likely to require biventricular support include individuals with advancing chronic illness manifest by left ventricular failure and characteristically suffering from ischemic heart disease.
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From page 79... ...
On the other hand, operative risks increase each time openheart surgery is performed, so any doubt as to the patient's need for biventricular support is likely to be resolved in favor of using a TAH. Experience with early VAD clinical trials will provide considerable additional information to assist in determining the need for long-term biventricular support.
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From page 80... ...
· There is very little knowledge of comorbidity in end-stage heart dis· Hospitalization information is based on discharge data instead of using unique patient identifiers in order to track multiple hospitalizations. · Hospital discharge diagnostic codes and death certificate entries lack clarity in such respects as the mutual exclusiveness of terms such as coronary heart disease, congestive heart failure, and atherosclerotic heart disease.
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From page 81... ...
The committee recognizes the considerable uncertainty inherent in these estimates, which cannot be resolved until many long-term VADs have been implanted for several years and the patients' outcomes reported. If resources are made available to meet the demand from the primary group, indications for MCSS use may gradually broaden into a larger secondary group of patients, those not yet disabled by their heart failure.
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From page 82... ...
1985. Right ventricular function in an operating room model of mechanical left ventricular assistance and its effects in patients with depressed left ventricular function.
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From page 83... ...
1990b. Combined Registry for the Clinical Use of Mechanical Ventricular Assist Pumps and the Total Artificial Heart in conjunction with heart transplantation: Fourth official report 1989.
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From page 84... ...
1989. Heart transplantation may not improve quality of life for patients with stable heart failure.
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