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stasis of the blood. Patients with a PT greater than 2.5 times the reference range should not undergo physical therapy because of the potential for spontaneous bleeding. Likewise, an international normalized ratio of more than 3 warrants asking the physician if treatment

should be withheldP

Blood Lipids

Elevated total cholesterol levels in the blood are a significant risk

factor for atherosclerosis and therefore ischemic heart disease.29

Measuring blood cholesterol level is necessary ro determine the risk

for development of atherosclerosis and to assist in patient education, dietary modification, and medical management. Normal values can be adjusted for age; however, levels of more than 240 mg/dl are

generally considered high, and levels of less than 200 mg/dl are considered normal.

A blood lipid analysis categorizes cholesterol into high-density

lipoprotiens ( HDLs) and low-density lipoproteins (LDLs) and provides an analysis of triglycerides.

HDLs are formed by the liver and are considered beneficial because

they are readily transportable and do nOt adhere to the intimal walls

CARDIAC SYSTEM

29

of the vascular system. People with higher amounts of HDLs are at

lower risk for coronary artery disease.27,29 HDL levels of less than 33

mg/dl carry an elevated risk of heart disease, and a more important

risk for heart disease is an elevated ratio of total cholesterol to HDL

Normal toral cholesterol to HDL ratios range from 3 to 5."

LDLs are formed by a diet excessive in fat and are related to a

higher incidence of coronary artery disease. Low-densiry lipoproteins

are nOt as readily transportable, because they adhere to intimal walls

in the vascular system .21 Normal LDLs are below 100 mg/dl,"

Triglycerides are fat cells that are free floating in the blood, When

not in use, they are stored in adipose tissue. Their levels increase after

eating foods high in fat and decrease with exercise. High levels of triglycerides are associated with a risk of coronary heart diseaseP

Clinical Tip

Cholesterol levels may be falsely elevated after an acute

MI; therefore, pre-infarction levels (if known) are used to

guide risk factor modification. Values will not return to

normal until at least 6 weeks post-M!.

Biochemical Markers

After an initial myocardial insult, the presence of tissue necrosis can

be determined by increased levels of biochemical markers. Levels of

biochemical markers, such as serum enzymes (creatine kinase [CK),

lactate dehydrogenase [LDHJ) and proteins (myoglobin, troponin I

and T), can also be used to determine the extent of myocardial death

and the effectiveness of reperfusion therapy, In patients presenting

with specific anginal symptoms and diagnostic ECG, these biochemical markers assist with confirmation of the diagnosis of an M I (Table 1-1 1). Enzymes play a more essential role in medical assessment of

the many patients with nonspecific or vague symptoms and inconclusive ECG changes,30 Such analysis also includes evaluation of isoenzyme levels as wel1,31 Isoenzymes are different chemical forms of the same enzyme that are tissue specific and allow differentiation of damaged tissue (e,g" skeletal muscle vs, cardiac muscle), CK (formally called creatille phosphokinase) is released after cell

injury or cell death. CK has three isoenzymes. The CK-MB isoenzyme

is related to cardiac muscle cell injury or death, The most widely used

30 AClITE CARE HANDBOOK FOR PHYSICAL THERAPISTS

Table 1 - 1 1 . Biochemical Markers

Onset

Enzyme or

Normal

of Rise Time of

Return to

Marker

Isoenzyme

Value

(hrs)

Peak Rise

Normal

Creatine kinase

55-7 1

3-6

1 2-24 hrs 24-48 hrs

(CK)

IU

CK-MB

0-3%

4-8

1 8-24 hrs 72 hrs

Lactate

1 27 1U

1 2-24

72 hrs

5- 1 4 days

dehydrogenase

LDH-I

14-26%

24-72

3-4 days

1 0- 1 4 days

Troponin T

<0.2 �g/

2-4

24-36 hrs

10-14 days

(cTnT)

liter

Troponin I

d . 1 pg/

2-4

24-36 hrs

10- 1 4 days

(cTnl)

liter

Myoglobin

3 1-80

1-2

6-9 hrs

24-36 hrs

ng/ml

Sources: Data from RH Christenson, HME Azzazy. Biochemical markers oC Ihe acute

coronary syndromes. Clin Chern 1 998;44: 1855-1 864; and AK Kratz, KB Leq:md

Rawski. Normal reference laboratory values. N Engl ] Med 1 998;339: 1 063-1072.

value is the relative

( 100%[CK-MBrrotal CKj).30 Temporal

measurements of the CK-MB relative index help physicians diagnose

MI, estimate the size of infarction, evaluate the occurrence of reperfusion as well as possible infarct extension. An early CK-MB peak with rapid clearance is a good indication of reperfusion.'2 Values may

increase from skeletal muscle trauma, cardiopulmonary resuscitation,

defibrillation, and open-heart surgery. Postoperative coronary artery

bypass surgery tends to elevate CK-MB levels secondary to crossclamp time. Early postoperative peaks and rapid clearance seem to indicate reversible damage, whereas la[er peaks and longer clearance

times with peak values exceeding 50 Ulliter may indicate an ML 12

Treatment with thrombolytic therapy, such as streptokinase or a tissue plasminogen activaror (tPa), has been shown to falsely elevate the values and may create a second peak of CK-MB, which strongly suggests successful reperfusion.'2•30

Troponins are essential contractile proteins found in both skeletal