Prevention Of Coronary Artery Disease

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Prevention Of Coronary Artery Disease

 

CAD prevention usually begins with reversal of modifiable risk

factors. Smoking cessation is of primary importance. Additional

strategies include dietary modification, achievement of appropriate

weight for height, proper management of stress, and regular

exercise.

 

Physicians should treat coexisting disorders associated with

increased risk, such as hypertension (see Ch. 199),

hypercholesterolemia, diabetes (see Ch. 13), or hypothyroidism (see

Ch. .

 

 

 

DIETARY MODIFICATION

Fats: The average U.S. diet contains 37% of total calories as fat.

The American Heart Association recommends that the proportion be

reduced to 30%, yet a reduction to < 10% may be needed to have a

major effect on CAD risk.

 

The type of dietary fat is also important; there are three kinds

(Table 202-1): saturated, monounsaturated, and omega-3 and omega-6

PUFAs. The ideal proportion of each of these fats is unknown.

 

However, diets high in saturated fats are clearly atherogenic, and

those high in monounsaturates or omega-3 oils are less so.

 

U.S. studies failed to show a decreased incidence of angina or MI in

persons eating diets high in omega-3 oils, although such diets were

associated with decreased risk of sudden cardiac death.

 

Persons eating the most fish consumed an average of 0.58 g/day of

omega-3 oils, but much higher intakes of omega-3 oils are probably

needed for demonstrable risk factor reduction. For example, omega-3

oil supplementation with two or three divided doses of

eicosapentaenoic acid 1.8 to 6 g/day and docosahexaenoic acid 0.75

to 2.5 g/day lowers elevated serum triglyceride levels.

 

These doses are up to 10 times the amounts consumed by the fish

eaters in the U.S. studies.

 

For patients at high risk of CAD and especially for those with

evidence of CAD, it is reasonable to recommend a 20 g/day fat diet

consisting of 6 to 10 g of PUFAs with equal proportions of omega-6

and omega-3 oils, <= 2 g of saturated fat,

and the remainder as monounsaturates.

 

Fruits and vegetables: Five servings/day of fruits and vegetables,

which are rich in phytochemicals, seems to decrease the risk of CAD

and some cancers. However, populations eating a high phytochemical

diet also tend to consume less saturated fat, more fiber, and more

vitamin C and E, making the role of phytochemicals less clear.

 

One group of phytochemicals called flavonoids (found in red and

purple grapes, red wine, black teas, and dark beers) appear

particularly protective against CAD. High intake of flavonoids in

red wine may help explain why French populations have a relatively

low incidence of CAD, despite using more tobacco and consuming more

fat than Americans do.

 

Fiber: Americans eat relatively little fiber, of which there are two

kinds: soluble fiber (found in oat bran and psyllium), which

decreases total cholesterol and may have a beneficial effect on

glucose and insulin levels, and insoluble fiber (eg, cellulose,

lignin).

Fiber is not without adverse effects, however, such as interfering

with the absorption of certain minerals and vitamins. In general,

foods rich in phytochemicals and vitamins are also rich in fiber.

 

Vegetable proteins: Consumption of vegetable proteins (eg, soy,

tempeh, seitan) seems to decrease CAD risk.

 

DIETARY SUPPLEMENTATION

Dietary supplementation with vitamins remains controversial. There

are data to justify supplementation with vitamin E, vitamin C, folic

acid, and Ca but less convincing data to support the use of vitamin

B6 and B12.

 

Vitamin E decreases the oxidation of serum LDL-C and thus appears to

reduce its capability for vascular damage. Serum vitamin E levels

are inversely correlated with incidence of cardiovascular mortality,

and supplementation with vitamin E 800 IU/day has been shown to

decrease the incidence of MI.

 

A recent study among nurses showed that diets higher in vitamin E

were associated with lower death rates from heart disease but failed

to show a specific benefit of vitamin E supplementation, possibly

because of problems with study design and data collection. Further

studies are underway.

 

Although it has not been shown to decrease the risk of heart

disease, supplementation with vitamin C 250 to 500 mg bid increases

the antioxidant properties of vitamin E.

 

Folic acid 0.8 mg bid prevents CAD by lowering elevated levels of

homocysteine. Vitamins B6 and B12 also lower homocysteine levels,

but evidence justifying their use in general prevention is scanty.

 

EXERCISE

Recent studies have shown that increased levels of physical activity

and fitness are associated with a decreased incidence of heart

disease and hypertension. However, there have been no controlled

trials on the optimal intensity, duration, frequency, or type of

exercise. Also, the question of whether people with healthy hearts

choose more active lifestyles or whether active lifestyles lead to

healthier hearts remains unanswered. Several controlled but small

studies demonstrated beneficial effects of exercise on BP and on CAD

risk.

 

Comprehensive cardiac rehabilitation, of which exercise is an

important part, decreases long-term morbidity and mortality after

MI. It is equally beneficial in patients with angina and in those

who have undergone bypass surgery or angioplasty. Cardiac

rehabilitation involves the same principles used in the primary

prevention of CAD. However, most patients and physicians pay little

attention to aggressive prevention of heart disease until signs of

CAD appear.

 

Pre-exercise evaluation should consist of a history and physical

examination to exclude such conditions as valvular heart disease,

ventricular hypertrophy, dangerous arrhythmias, hypertension,

exercise-induced asthma, hemoglobinopathies, and musculoskeletal

disease. In adolescents or young adults without abnormal findings,

no further workup is generally needed. Evaluation is more extensive

in older persons and those who are sick or at increased risk of

disease (including those with poorly controlled diabetes, heart

disease, hypertension, or obesity).

Ideally, such people should have an exercise stress test (see Ch.

198).

 

Further evaluation (eg, by a physical therapist for patients with

musculoskeletal problems) should be considered before the start of

resistive strength training. Patients with elevated cholesterol

levels should have lipoprotein analysis, body fat estimation, and

dietary evaluation.

 

Obese patients should have dietary analysis, thyroid function tests,

and determinations of blood glucose; insulin levels (both fasting

and following oral glucose) and resting metabolic rates may be

evaluated in research studies.

 

There are three kinds of exercise programs: those that promote

endurance, muscle strength, and flexibility. Endurance and muscle

strength have a clear role in CAD prevention. Any complete exercise

program should include all three kinds. The American College of

Sports Medicine has established minimum exercise recommendations for

healthy men and women of all ages to develop and maintain

cardiorespiratory fitness, healthy body composition, and muscular

strength and endurance (see Table 202-2).

 

Components of endurance exercise include duration, frequency, type,

and intensity. Endurance training should last >= 40 min/day at least

three times/wk. Each session includes a 5-min warm-up, 30 min of

training, and a 5-min cooldown. Endurance exercises can be performed

on various machines. Home use of machines that mimic the actions of

bicycling (particularly those that also include arm movements),

stair climbing, rowing, or cross-country skiing can be effective for

aerobic exercise as can running or jogging, fast walking, bicycling,

rowing, or kayaking.

 

Exercise should be at an intensity that provokes a training heart

rate appropriate for each person's specific health and fitness

goals. In general, after a 5-min warm-up, healthy people should

exercise to the heart rate they attain at 70 to 85% of their

VO2peak. If maximum attained heart rate (HRmax) has not been

measured, it can be calculated as:

 

 

 

However, in the elderly, this formula can be significantly

inaccurate; illness and the use of certain medications can further

complicate the relationship between age and heart rate. A patient

with heart or lung disease should use less intense exercise, with

the training heart rate being that attained at 60 or even 50% of

VO2peak.

 

Resistive strength training has recently been shown to reduce CAD

risk, decrease resting BP, increase HDL-C, and decrease insulin

resistance. However, if not done correctly, such training carries

the risk of injury, acute elevation of BP, cardiac arrhythmias, and

exacerbation of hemodynamic dysfunction in patients with certain

valvular heart abnormalities. Despite these risks, resistive

strength training can be done safely in selected elderly patients

using correct breathing and exercise techniques to promote

cardiovascular health, prevent osteoporosis, and maintain function.

 

The prescription for resistive strength training includes the type,

intensity, and frequency of the exercise. Muscle groups can be

effectively worked using free weights or weight-training machines,

although free weights are harder to use properly and are therefore

more likely to cause injury.

 

Machines ideally should allow limitations to be set on the range of

motion for any given exercise, and resistance to be added in small

increments. There is little agreement about the best exercise

intensity. Moderate resistance with frequent repetitions is safer

than heavy resistance with few repetitions, although it may provide

less stimulus for muscle adaptation. Resistance is typically set so

that patients can perform each exercise for three sets of 10

repetitions using good technique. Good technique increases the

training stimulus and reduces the risk of injury, as does avoidance

of exercises that might damage already injured or weakened joints or

muscles. Once a patient can perform three sets of 12 to 15

repetitions with good technique, resistance is increased slightly,

but never enough to prevent at least three sets of 10 repetitions.

Proper breathing during the exercise is important, particularly to

prevent Valsalva maneuver and thus avoid dangerously high BP levels.

Proper breathing can be taught by exercise physiologists.

 

All exercisers should be instructed in a good stretching routine

that includes all major muscle groups. Stretching should be slow and

steady without bouncing and should never be painful. Ideally,

stretching should be incorporated into the start and finish of each

exercise session.

 

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