Читать книгу The SAGE Encyclopedia of Stem Cell Research - Группа авторов - Страница 455

The Centers for Disease Control and Prevention (CDC) estimates that roughly 600,000 people die of heart disease every year. By the numbers, cardiovascular disease is the leading cause of death in the United States. Immeasurable leaps have been made in combating the disease over the past 25 years, and with the help of better prognostic tools, outcomes have steadily become more and more positive. However, the prevalence of the disease will increase in the coming years. Similar to diabetes, cardiovascular disease is a disease of affluence. As medicine progresses and effectively reduces the mortality rates of many acute communicable diseases, the fight against chronic illnesses comes to the forefront.

Cardiovascular disease is a term that refers to any disease that involves the heart and/or the blood vessels. The leading causes of cardiovascular disease are atherosclerosis and hypertension. Atherosclerosis is a term used to describe the thickening of arterial walls by the accumulation of cholesterol and triglycerides, ultimately leading to a full occlusion of the vessel. In laymen’s terms, hypertension is simply high blood pressure found within the arteries. If it is not addressed appropriately, hypertension places an undue amount of strain on the heart, culminating in heart disease.

As is indicative of other diseases of affluence, cardiovascular disease and its direct causes are a result of a sedentary lifestyle. Therefore, it should come as no surprise that the most immediate prevention for the onset of the disease is the adoption of healthier living habits. A daily regimen of exercise and a diet filled with foods low in fat are all positive means to prevent the occurrence of cardiovascular disease.

However, genetics is also a huge factor in the onset of cardiovascular disease. It is well known that thousands of seemingly healthy individuals are struck by heart attacks every year. Therefore, more research is warranted on the environment within the body post–myocardial infarction (MI). Prevention can only do so much. Sometimes a heart attack is inevitable, but it no longer is a death sentence.

In the world of interventional cardiologists, “Time is muscle.” From the moment of the initial heart attack, every second matters. Breakthroughs in the field of catheterization have allowed physicians to enter the heart and clear a path through the most occluded of vessels. However, no matter how early a heart attack is addressed, ischemic damage will always result.

Ischemia is a term used to describe any situation where the blood flow to a particular part of the body is impaired. A heart attack results in ischemia of the heart. The size and extent of the ischemic damage done to the heart is dependent upon the severity of the heart attack itself and the amount of time that transpires prior to any form of intervention being administered. A prolonged absence of oxygen to the myocardium will ultimately result in diminished heart function, and herein lies the major component in the fight against cardiovascular disease.

The diminished function of the heart seen after a heart attack does not improve over time. One indicator of heart function that sheds a great deal of light on the overall integrity and efficiency of the heart is the ejection fraction (EF). Simply put, it is the ratio of the volume of blood pumped out of the left and right ventricles during each heartbeat. A normal EF has a range of roughly 55–70 percent. In the event of a heart attack, that range can severely dip. Currently, there are no practical means to reverse the trend in ischemic damage. Management with medication will lead to a somewhat normal lifestyle, but the risk of congestive heart failure (CHF) always surrounds any heart attack victim.

Stem cells provide a revolutionary means to reinvigorate dead myocardium to a point of functionality that nearly mirrors the state of the heart pre-MI. The ability of stem cells to differentiate into nearly any cell line allows for innumerable opportunities of intervention, especially in the case of cardiovascular disease. Two specific types of stem cells have been linked to improved function in the heart post-MI in murine models. Those types are hematopoietic and umbilical cord blood stem cells.

Hematopoietic stem cells are derived from bone marrow deposits, while umbilical cord blood stem cells are derived from the cord blood of infants. In early murine models, both types of these stem cells have shown to be able to differentiate into adult cardiac cells. The administration of these newly derived cardiac cells into ischemic regions of the heart has shown to produce an increase in the ejection fraction of mice.

A novel clinical study performed by cardiologists at Cedars-Sinai Hospital in 2009 has provided the scientific community with some of the first tangible results of a stem cell therapy for cardiovascular disease. The study was revolutionary in scale and also in simplicity. Healthy cardiac progenitor cells were extracted from heart attack patients via a minimally invasive catheter procedure. This small portion of cells was then allowed to grow outside the body in a cultured dish. After roughly 20 to 25 days of growth, the cells were deemed confluent, after which the cells were reintroduced into the hearts of the patients, and the patients were monitored over the course of six months. All in all, the patients showed an increase in heart functionality. Outcomes were good, with no real signs of adverse effects. This particular study is the beginning of an entire field of research that will utilize stem cells and the possibility of directly infusing them into zones of ischemia within the infarcted heart.

The effects of ischemia on the heart have long been deemed irreversible. Although a heart attack is no longer viewed as a death sentence, the quality of life post-MI is still rife with complications. The ability to ameliorate the damage caused by a heart attack will drastically improve the quality of life for heart attack victims. A great deal of research still lies ahead. However, novel clinical trials provide a sense of optimism that the future is not too far away. The course of care for heart victims may soon no longer be deemed as solely management. Stem cells are giving physicians the opportunity not only to halt the severe damage caused by heart attacks but to even reverse it completely.