CORONARY ARTERY DISEASE

EXERCISE PRESCRIPTION FOR INDIVIDUALS WITH CORONARY ARTERY DISEASE

Physical inactivity is recognized as a risk factor for coronary artery disease. Regular aerobic physical activity increases exercise capacity and plays a role in both primary and secondary prevention of cardiovascular disease.

The known benefits of regular aerobic exercise and recommendations for implementation of exercise programs are discussed.

Exercise training increases cardiovascular functional capacity and decreases myocardial oxygen demand at any level of physical activity in apparently healthy persons and in most individuals with cardiovascular disease. Regular physical activity is required to maintain these training effects.

Myocardial work can be affected by caffeine intake, and caffeine intake has been shown to increase blood pressure response to exercise. The potential risks of physical activity can be reduced by receiving a medical evaluation, risk stratification, supervision, and education.

Exercise can help control blood lipid abnormalities, diabetes, and obesity. In addition, aerobic exercise adds an independent blood pressure–lowering effect in certain hypertensive patient groups, with a decrease of 8-10 mm Hg in both systolic and diastolic blood pressure measurements.

A direct relationship exists between physical inactivity and cardiovascular mortality, and physical inactivity is an independent risk factor for the development of coronary artery disease. A dose response relationship exists between the amount of exercise performed (from approximately 700-2000 kcal/wk [2940-8400 kJ/wk] energy expenditure) and all-cause mortality and cardiovascular disease mortality in middle-aged and elderly populations.

The greatest potential for reduced mortality is in sedentary persons who become moderately active. Most beneficial effects of physical activity on cardiovascular disease mortality can be attained through moderate-intensity activity (40-60% of maximal VQ, depending on the participant's age). The activity can be accrued through formal training programs or leisure-time physical activities.

Although most supporting data are based on studies in men, relatively recent findings show similar results for women. Results of pooled studies reveal that persons who modify their behavior after myocardial infarction to include regular exercise have improved rates of survival.

Studies have revealed that intensive multiple interventions, such as smoking cessation, blood lipid reduction, weight control, and physical activity, significantly decreased the rate of progression—and, in some cases, lead to regression—in the severity of atherosclerotic lesions in persons with coronary disease.

In addition, limited data indicate that higher-intensity exercise, compared with lower-intensity exercise, improves left ventricular ejection fractions in persons with coronary artery disease. Current activity status (eg, persons remaining physically active or having been sedentary and becoming physically active) revealed the greatest decline in coronary artery disease risk. Persons who remain sedentary have the highest risk for cardiovascular disease mortality.

Exercise intensity should approximate 40-85% of VO2 reserve (VO2 R) or HR reserve (HRR), as determined by an exercise test. If a test is not performed initially, a reasonable estimate of 20-30 beats per minute (bpm) above HR rest is generally appropriate until testing is performed.

Activities can be prescribed according to the work intensity at which the training HR is achieved after 5-10 minutes at the same workload (steady state). This may be expressed as watts on an ergometer, speed on a treadmill, or METs. If an individual cannot assess intensity, HR counting (manually or with a pulse meter or cardio tachometer) is especially useful. HR counters are widely available and generally accurate for low- to moderate-intensity exercise.

If an individual intends to walk on a level surface, activity can be prescribed as the treadmill step rate that generates the desirable HR. The step rate is the number of steps taken in 15 seconds while walking at the desired speed on the treadmill. Step rate can be counted easily because it requires less skill than counting HR. If this approach is used, caution individuals to avoid hills. Walking in shopping malls or gymnasiums allows individuals to avoid inclement weather and to exercise on a flat surface. Exercise should be supervised for the first few sessions to ensure that instructions are understood and the activity is well tolerated.

JUDGING INTENSITY OF EXERCISE

Individuals can also judge the intensity of exercise by the RPE, which can be equated with the desired HR during laboratory exercise and activities.

The original scale is a 15-grade category scale that ranges from 6-20, with a verbal description at every odd number, beginning at 7 (very, very light) and progressing to 19 (very, very hard).

RPE values should be rated as follows:

Less than 12 – Perceived as fairly light (light intensity), 40-60% of HR max

From 12-13 – Perceived as somewhat hard (moderate intensity), 60-75% of HR max

From 14-16 – Perceived as hard (high intensity), 75-90% of HR max

Activities can progress as tolerance is demonstrated. An appropriate initial intensity of training is 60-75% of HR max (moderate) or an RPE of 12-13. However, many individuals may need to begin at 40-60% of HR max (light).

After safe activity levels have been established, duration is increased in 5-minute increments each week. Later, with increased strength and as the HR response to exercise decreases with conditioning, intensities can be increased to a frequency of 3-6 times per week. At this point, limited resistive exercises can be added, which have proved both safe and effective in secondary prevention.