i bc27f85be50b71b1 (15 page)

minute(s) of infusion. This image can then be compared to baseline

recordings.33 If needed, atropine is occasionally added to facilitate a

greater HR response for the test.33 Low-dose DSE has the capacity

to evaluate the contractile response of the impaired myocardium.

Bellardinelli et al." have demonstrated that improvements in functional capacity after exercise can be predicted by low dose DSE.

Patients with a positive contractile response to dobutamine were

more likely to increase their Vo,max after a 1 0-week exercise program. Having a positive contractile response on the low-dose DSE

had a positive predictive value of 84% and a negative predictive

value of 59%.35 With research such as this study beginning to demonstrate the prognostic value of certain medical tests for determining functional prognosis, physical therapists will need to be prepared to critically assess this area of literature in order to assist

the medical team in determining the level of rehabilitative care for a

patient during his or her recovery.

Exercise Testing

Exercise testing, or stress testing, is a noninvasive method of

assessing cardiovascular responses to increased activity. The use of

exercise testing in cardiac patients can serve multiple purposes,

which are not mutually exclusive. The most widespread use of

exercise testing is as a diagnostic tool for the presence of coronary

artery disease. Other uses include determining prognosis and

severity of disease, evaluating the effectiveness of treatment, early

34 ACUTE CARE HANDBOOK FOR I'HYSICAl THERAPISTS

deteclion of labile hypertension, evalualion of CHF, evalualion of

arrhythmias, and evaluation of functional capacity.33 Exercise testing involves the systematic and progressive increase in intensity of activity (e.g., treadmill walking, bicycling, stair climbing, arm

ergometry). These lests are accompanied by simultaneous ECG

analysis, BP measurements, and subjective reports, commonly

using Borg's Rating of Perceived Exertion ( RPE).36,37 Occasionally,

the use of expired gas analysis can provide useful information

about pulmonary function and maximal oxygen consumption.33

Submaximal tests, such as the 12- and 6-minute walk leSlS, can be

performed to assess a patient's function. For further discussion of

the 6-minute walk test, refer to Appendix IX.

Submaximal tests differ from maximal tests because the patient is

not pushed to his or her maximum HR; instead, the test is terminated at a predetermined end point, usually at 75% of Ihe palient's predicted maximum HR J8 For a comparison of rwo widely used

exercise test protocols and funclional activities, refer to Table ·1 - 12.

For a more thorough description of submaximal exercise testing, the

reader is referred to Noonan and Dean.38

Contraindications 10 exercise testing include the following39;

• Recent MI (less Ihan 48 hours earlier)

• Acute pericarditis

•

Unstable angina

•

Ventricular or rapid arrhythmias

•

Untreated second- or third-degree heart block

•

Decompensated CHF

• Acute illness

Exercise test results can be used for the design of an exercise

prescription. Based on the results, the patient's actual or extrapolated maximum HR can be used 10 delermine the patient's target HR range and a safe aClivity intensity. RPE with symptoms during

the exercise test can also be used to gauge exercise or activity

intensilY. (Especially in subjects on beta-blockers-please refer to

Ihe Physical Therapy Intervention section of this chapter for a discussion on the use of RPE.)

CARDIAC SYSTEM

35

Table 1-12. Comparison of Exercise Test Protocols and Functional Tasks

Energy Demands

Oxygen

Require-

Treadmill:

Bike Ergometer:

mems (ml

Metabolic

Bruce PrOtocol

for 70 kg of

O,Jkr/

EquivaJenrs

Functional

3·Min Stages

Body Weight

min)

(METS)

Tasks

(mph/elevation)

(kr/min)

52.5

1 5

49.5

14

45.5

1 3

4.2/16.0

1,500

42.0

1 2

1,350

38.5

1 1

1,200

35.0

10

jogglg

j 3.4114.0

1,050

3 1 .5

9

900

28.0

8

750

24.5

7

S t

2.5112.0

21.0

6

talr

600

climbing

17.5

5

1 .7/10.0

450

14.0

4

w1kJg

300

(level

Surfre)

10.5

3

150

7.0

2

Bed exer-

cise (arm

exercises

in supine

or sining)

Sources: Data from Amencan Heart Association, Comminee on Exercise. Exercise Testing

and Traimng of Apparently Healthy Individuals: A Handbook for Physicians. Dallas, 1972;

rcse

and GA Brooks, TO Fahey, TP Whlre (eds). Exe i Physiology: Human Bioenergetics and

Its Applications (2nd ed). Mountain View, CA: Mayfield Publishmg, 1 996.

36 ACUTE CARE HANDBOOK FOR PHYSICAL THERAPISTS

Clinical Tip

Synonyms for exercise tests include exercise tolerance test

and graded exercise test.

Thallium Stress Testing

Thallium stress testing is a stress test that involves the injection of a

radioactive nuclear marker for the detection of myocardial perfusion.

The injection is typically given (via an intravenous line) during peak

exercise or when symptoms are reported during the Stress test. After

the test, the subject is passed under a nuclear scanner to be evaluated

for myocardial perfusion by assessment of the distribution of thallium

uptake. The subject then returns 3-4 hours later to be re-evaluated

for myocardial reperfusion. This test appears to be more sensitive

than stress tests without thallium for identifying patients with coronary artery �isease. 12

Persantine Thallillm Stress Testing

Persantinq thallium stress testing is the use of dipyridamole (Persantine) to dilate coronary arteries. Coronary arteries with atherosclerosis do not dilate; therefore, dipyridamole shunts blood away from these areas. It is typically used in patients who are very unstable,

deconditioned, or unable to ambulate or cycle for exercise-based

stress testing.33 Patients are asked to avoid all food and drugs containing methylxantines (e.g., coffee, tea, chocolate, cola drinks) for at least 6 hours prior to the test as well as phosphodiesterase drugs, such

as aminophyline, for 24 hours. While the patient is supine, an infusion of dipyridamole (0.56 ml/kg diluted in saline) is given intravenously over 4 minutes (a large-vein intracatheter is used). Four minutes aftet the infusion is completed, the perfusion marker (thallium) is injected, and the patient is passed under a nuclear scanner to be evaluated for myocardial perfusion by assessment of rhe disrriburion of rhallium uprake."

Cardiac Catheterization

Cardiac catheterization, classified as either right or left, is an invasive

procedure that involves passing a flexible, radiopaque catheter into

the heart to visualize chambers, valves, coronary arteries, great vessels, cardiac pressures and volumes to evaluate cardiac function (estimate EF, CO).