Encyclopedia of Heart Diseases

M. Gabriel Khan

• Éditeur: Academic Press
• Année: 2005
• ISBN:
  9780080454818
• Sujet: Medicina
• Sous-sujet: Farmacologia

The Encyclopedia of Heart Diseases is an accurate and reliable source of in-depth information on the diseases that kill more than 12 million individuals worldwide each year. In fact, cardiovascular diseases are more prevalent than the combined incidence of all forms of cancer, diabetes, asthma and leukemia. In one volume, this Encylopedia thoroughly covers these ailments and also includes in-depth analysis of less common and rare heart conditions to round out the volume's scope. Researchers, clinicians, and students alike will all find this resource an invaluable tool for quick reference before approaching the primary literature.* Coverage of more than 200 topics, including: applied pharmacology of current and experimental cardiac drugs, gene therapy, MRI, electron-beam CT, PET scan put in perspective, cardiac tests costs and justification, and new frontiers in cardiovascular research* More than 150 helpful figures and illustrations!* Dr. Khan is a well-published and respected expert in heart and heart diseases

Aging and the Heart

I. The Size of the Problem

II. Effects of Aging on the Heart and Vascular System

III. Cardiovascular Therapy in the Elderly

IV. Research Implications

GLOSSARY

coronary heart disease obstruction of the coronary arteries with symptoms such as chest pain, angina, or heart attacks.

coronary thrombosis obstruction of a coronary artery by blood clot.

heart failure a failure of the heart to pump sufficient blood from the chambers into the aorta; inadequate supply of blood reaches organs and tissues.

hypertension high blood pressure.

hypertrophy increase in thickness of muscle.

myocardial infarction death of an area of heart muscle due to blockage of a coronary artery by blood clot and atheroma; medical term for a heart attack or coronary thrombosis.

myocardium the heart muscle.

I. THE SIZE OF THE PROBLEM

In the year 2000 there were approximately 35 million people in the United States who were 70 years and older. In the year 2030, the number will be approximately 70 million. The world population of the elderly is approximately 610 million and will grow to approximately 2 billion by 2050. There is an epidemic of heart failure in this aging population. In the United States, heart failure is the most common diagnostic related group in the population over 65. Coronary heart disease and stroke are very common. More than 60% of these individuals have hypertension, which is an important underlying cause of heart failure. Atrial fibrillation, a serious abnormal heart rhythm, is common in the age group 70 to 85; this condition requires treatment with a blood thinner, warfarin, to prevent strokes. The main underlying cause for atrial fibrillation is hypertension.

The prevention of morbidity and mortality in this age group requires the aggressive management of hypertension. Heart failure has several causes including hypertension, and the prevention and management of heart failure with old and new remedies require a concerted effort and relevant new research.

II. EFFECTS OF AGING ON THE HEART AND VASCULAR SYSTEM

A. Gross Anatomy

Aging causes decreased elasticity and compliance of the aorta and great arteries arterial stiffness. This results in higher systolic arterial pressures and increased impedance of the propagation of blood from the left ventricle through the arterial system and the delivery of blood to organs and tissues. Mild left ventricular hypertrophy also occurs.

B. Histological Changes

These changes in the heart muscle include decreased mitochondria and altered mitochondrial membranes. Increased collagen degeneration and interstitial fibrosis with increased lipid and amyloid deposition causes the left ventricular muscle mass to become stiffer. Because of this stiffness, after the systolic contraction of the ventricle it takes longer for the ventricular mass to relax in diastole. This defect in relaxation and an abnormal dispensability causes the ventricle to fail. Thus insufficient blood to meet the demands of the tissues is propelled into the arterial system and heart failure ensues. This condition is referred to as diastolic heart failure. The exact underlying causes for diastolic heart failure require further study. More knowledge will improve today’s unsatisfactory therapy for this condition.

Heart failure is commonly caused by systolic dysfunction of the ventricle. The ventricular muscle mass is weakened by scarring from heart attacks and other cardiac diseases. Failure of the muscle pump causes insufficient blood to be expelled from the ventricle into the arteries. Treatment for systolic heart failure has improved considerably since 2000.

C. Biochemical Changes

These changes include decreased protein elasticity, changes in enzyme content that affect metabolic pathways, decreased catecholamine synthesis, and diminished responsiveness to beta-adrenergic stimulation.

D. Electrical Conduction System

Substantial loss of pacemaker cells in the sinus node cause a fall in heart rate and finally failure. This condition is called sick sinus syndrome and is the most common reason for implanting an electronic pacemaker. Increased fibrosis and calcification of the conduction system and loss of specialized cells in the His bundle and bundle branches can result in failure of the electrical impulse to reach the ventricles. This condition is called heart block and requires a pacemaker. (See the chapter Pacemakers.)

E. Valvular Changes

These changes include fibrosis, thickening and calcification of heart valves which leads to degenerative valvular disease. Calcified aortic stenosis may require valve surgery but the statins, cholesterol-lowering agents, have been shown to decrease the rate of stenosis and may delay surgical intervention. Mitral annular calcification occurs commonly and occasionally causes mitral regurgitation, atrial arrhythmia, heart block, and infective endocurditis.

Fibroproliferative lesions producing mitral regurgitation has occured in elderly patients treated with anti-parkinsonian dopamine receptor agonist pergolide.

III. CARDIOVASCULAR THERAPY IN THE ELDERLY

A. Thrombolytic Therapy

Patients 70 years or older with an acute myocardial infarct are at high risk for serious events. Thrombolytic therapy may prevent death and further morbidity. Unfortunately, in patients older than 75 there is an increased risk of intracranial bleeding. This excessive risk must be balanced against any possible benefit derived from thrombolytic therapy. The incidence of intracranial hemorrhage in this age group is greater than 1.5% for alteplase (tissue plasminogen activator, t-PA) and tenectaplase, but greater than 0.5% for streptokinase.

Although intracranial hemorrhage incidence is lower with streptokinase, it is not the drug of choice in North America. Fortunately, in the UK, Europe, and worldwide the less expensive agent streptokinase is still the most widely used pharmacologic reperfusion therapy. Thrombolytic agents that are effective but cause less intracranial bleeding than alteplase and tenectaplase in the elderly would be important additions to the therapeutic armamentarium.

B. Percutaneous Intervention

Because thrombolytic therapy carries a major risk of intracranial hemorrhage and stroke in patients over age 75, randomized clinical trials have confirmed the beneficial effects of primary coronary angioplasty with intracoronary stents. PCI is superior to thrombolytic therapy and is preferred if skilled cardiologists and facilities are readily available.

In a randomized study of 87 patients older than 75 with acute myocardial infarction, the composite of death, reinfarction, or stroke at 30 days occurred in 4 (9%) patients in the percutaneous intervention (PCI) group as compared with 12 (29%) in the patients receiving streptokinase intravenously (p = 0.01). Patients older than 75 years of age with acute myocardial infarction or unstable angina obtain beneficial results with placement of a stent in the culprit coronary artery, blocked by atheroma and thrombosis.

C. Beta-Blocker Therapy

Beta-adrenergic blocking drugs, beta-blockers, have proven beneficial and save lives in patients with acute myocardial infarction regardless of age. Some caution is required because the elderly over ...