Maulik Shah and Reza Ardehali Department of Internal Medicine, Division of Cardiology, Stanford University School of Medicine, Stanford, CA, USA
Cardiovascular disease (CVD) remains the leading cause of death in industrialized nations and its incidence is increasing in developing countries. The lifetime risk for the development of coronary heart disease (CHD) for men at age 40 remains at nearly 50%. Given this large risk, clinical and public health approaches to combat the development of CVD are essential. CVD accounts for over 800000 deaths each year in the United States alone, with the majority resulting from coronary artery disease (CAD). In addition, over 17 million Americans have known or asymptomatic CHD. As the annual economic costs associated with heart disease morbidity and mortality exceed $500 billion, strong efforts are required for adequate screening and prevention.
Prevention of Coronary Heart Disease
• As the prevalence of CHD is high worldwide, the prevention of even a small proportion of disease has an enormous effect.
• Primary prevention refers to risk reduction in a population without known heart disease.
• Secondary prevention refers to risk reduction in a population with known heart disease.
• Understanding CHD risk factors has allowed for better screening guidelines and preventive measures.
• There are four major categories of risk factors (Table 1.1):
• Predisposing factors (e.g. age, sex)
• Risk-modifying behaviors (e.g. smoking, exercise)
• Metabolic risk factors (e.g. hyperlipidemia, diabetes)
• Disease markers (e.g. coronary calcium score).
Smoking
Cigarette smoking accounts for nearly 400000 deaths annually. There are nearly 1 billion smokers worldwide. Even one to four cigarettes a week can increase the risk of myocardial infarction (MI) and all-cause mortality. Smoking increases risk by several mechanisms including:
• Increasing blood pressure (BP)
• Increasing sympathetic tone
• Reducing myocardial oxygen supply
• Elevating the level of oxidized low-density lipoprotein (LDL) cholesterol
• Impairing endothelium-dependent coronary artery vasodilation
• Increasing inflammation, platelet aggregation, and thrombosis.
Smoking cessation is the single most important intervention in preventive cardiology. Reductions in smoking improve outcomes, including reducing risk of MI and cardiovascular mortality.
Physicians should assess smoking status in all patients, recommend quitting smoking to all smokers, and offer support and referral to smoking cessation programs.
Bupropion, varenicline, and nicotine replacement therapy (NRT) have all been shown to increase success rates for quitting.
Hypertension
Hypertension (HTN) is an often-overlooked and silent risk factor for heart disease. Over 70 million Americans have HTN (see Chapter 3).
Most epidemiologic studies have indicated that both systolic and diastolic BP elevation contribute to an increased risk of heart disease. This risk is especially important in elderly patients and patients with a known history of CHD.
HTN, as defined by the Joint National Committee on Prevention, Detection, Evaluation and Treatment of Hypertension in its seventh report, is:
• Two or more BP readings above 140/90
• Readings must be done on two or more separate office visits.
Each increment in systolic BP of 20mmHg or in diastolic BP of 10mmHg doubles the cardiovascular risk.
Hyperlipidemia
Several clinical trials have established that lipid-lowering measures are effective in reducing cardiovascular morbidity and mortality (see Chapter 2).
The goals for lipid therapy (Table 1.2) are based on the presence or absence of CHD, as well as the number of risk factors present for the development of CHD.
Diabetes Mellitus
• Diabetic patients have a two- to eight-fold increased risk for cardiovascular events as compared to age-matched nondiabetic individuals.
• Diabetes leads to both macro- and micro-vascular complications in cardiovascular patients.
• Insulin resistance and the metabolic syndrome are also associated with increased mortality and cardiovascular risk, even long before the onset of clinical diabetes.
• By age 40, CHD is the leading cause of death in both diabetic men and women.
• Data suggest that tight glycemic control can prevent microvascular complications in diabetics (i.e. diabetic retinopathy).
• However, there are very few data suggesting that glycemic control in diabetics can control macrovascular complications.
• Recommendations:
• For diabetics a multifactorial approach involving diet, exercise, and medications is essential.
• Target BP is <130/80mmHg as per the American Diabetes Association (ADA) guidelines.
• Favored medications for HTN include angiotensin-converting enzyme inhibitors (ACE-Is), beta-blockers, and diuretics.
• Goal LDL is <100mg/dL given that diabetes is considered a CHD equivalent.
Specific Medications
• Aspirin:
• Secondary prevention. Meta-analyses demonstrate that ASA reduces the rate of cardiovascular events by 25% in patients with existing heart disease. This group includes those with a history of MI, coronary artery bypass graft (CABG), angina, stroke, percutaneous coronary intervention (PCI), and peripheral vascular disease.
– All patients with known CHD should be on ASA
– For patients with an ASA allergy, other antiplatelet agents should be used.
• Primary prevention. The data for ASA in primary prevention are mixed. It is now thought that those patients without known heart disease, but with a 10-year risk of CHD estimated at >6%, should be on ASA.
• Beta-blockers:
• A number of trials have shown that beta-blockers are effective at reducing cardiovascular events in patients with known CHD.
• The more effective the beta-blocker is at reducing heart rate, the more effective it is at reducing cardiovascular events.
• ACE-Is:
• ACE-Is reduce the risk of CHD events in patients with known heart disease.
• This risk reduction is magnified in patients with known left ventricular (LV) dysfunction and in diabetics. In fact, in patients with LV dysfunction, ACE-I treatment reduces total mortality by 26% at 30 days.
• Statins:
• Statin therapy is indicated in any patient with CVD regardless of LDL level.
Physical Activity
• One of the most modifiable risk factors for CHD.
• The importance of physical activity should be addressed in clinic visits, for both primary and secondary prevention purposes.
• Energy expenditure of 1000kcal/week is associated with a nearly 30% reduction in all-cause mortality.
• Exercise improves CHD risk by:
• Increasing HDL
• Decreasing LDL
• Reducing BP
• Decreasing triglycerides
• Increasing insulin sensitivity
• Improving endothelial function.
• Primary prevention. The United States Surgeon General recommends at least 30min/day of moderate-intensity exercise on "most" days (150min/week).
• Secondary prevention. American College of Cardiology (ACC)/AHA guidelines recommend at least 30–60min of moderate-intensity aerobic exercise on most days.
• Walking is sufficient exercise for most patients and has the fewest barriers to successful adoption.
• Cardiac rehabilitation program use is associated with significant lowering of recurrent event rates and can be a critical resource for practitioners.
Weight Loss
• Obesity continues to be an epidemic in the United States, with a growing proportion of the population now considered to be overweight (BMI 25 29.9) or obese (BMI 30 or higher).
• Obesity may have a small independent association with cardiovascular risk over many years but contributes to risk most strongly by influencing other risk factors.
• Weight loss of only 510% can result in significant improvements in BP and lipid profiles.
• Weight loss recommendations should be given to any patient with a BMI >25 according to the North American Association for the Study of Obesity.
These involve:
• Caloric restriction
• Behavioral therapy
• Physical activity.
Alcohol Consumption
• Moderate alcohol consumption is associated with reduced risk of MI, stroke, sudden cardiac death, and cardiac death (relative risk reduction of 20% according to meta-analyses of several studies).
• No clinical trial has established that alcohol use causes this association.
• Excess alcohol consumption is related to increased mortality and morbidity.
• Alcohol also has effects, often deleterious, on several other organ systems, including increased BP in some and increased breast cancer risk in women.
• Therefore, recommendations on alcohol use should be individualized to each patient; alcohol intake should not be recommended to non-users for medical purposes.
• Moderate alcohol consumption is classified as 1–2 drinks daily in men and 1 drink daily in women.
• In the absence of a history of alcohol problems, this level of intake can be acceptable in patients who report alcohol use.
Diet
• Six decades of observational and metabolic studies have found an association between diet and risk for CHD, either directly or, more often, through effects on risk factors.
• Dietary effects on CVD risk are complex and can depend on the metabolic context, particularly obesity and the amount of exercise.
• There are few large trials studying the impact of dietary changes and CHD, in part due to design challenges.
• The current consensus recommendation based on all these studies is to promote a diet that is rich in unprocessed foods, including greater intake of fresh fruits and vegetables, whole grains, and fish, with limited amounts of meat and high-fat dairy products.
• Though there are no large clinical trials studying trans-fat and the risk of heart disease, there is observational evidence that trans-fat intake is associated with higher rates of heart disease; trans-fats are found mainly in highly-processed convenience and snack foods.
• No diet program can be applied to all patients. An individualized approach, with possible involvement of a nutritionist, may prove most beneficial.
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Excerpted from A Practical Approach to Cardiovascular Medicine Copyright © 2011 by Blackwell Publishing Ltd.. Excerpted by permission of John Wiley & Sons. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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