The treadmill is used in exercise testing. - File

This week's special guest columnist is Professor Charles E. Denbow. This is the third of his four-part series on various tests used to investigate problems in the heart. Parts one and two appeared on November 15 and 22, respectively.

EXERCISE TESTING

Exercise testing involves the recording of the electrocardiogram before, during and after exercise. This procedure provides the cardiologist with valuable information regarding blood circulation to the heart and patient prognosis, which is not provided by the 'ordinary' resting 12-lead electrocardiogram (discussed earlier in this series).

The exercise is usually provided (in North America and Jamaica) by having the patient walk on a motorised treadmill utilising an exercise protocol involving specific speeds and angles of the treadmill belt with continuous monitoring of the blood pressure, pulse, cardiac rhythm and patient's symptoms. In Europe, the exercise is usually supplied by a bicycle.

Exercise testing may be basic, stress echo (combined with Echocardiography) or nuclear (combined with radioisotope injection).

BASIC

The basic treadmill exercise test (which does not involve any additional imaging) remains an extremely useful test in the diagnostic armamentarium of the modern cardiologist. It is especially useful in the patient whose resting ECG is normal or near normal where significant changes in the ECG precipitated by exercise may allow significant coronary artery blockages to be diagnosed indirectly in 65-70 per cent of patients with this condition. The fact that 30-35 per cent of patients with significant coronary disease may be missed by this test is a disadvantage which is counterbalanced by its wide availability and reasonable cost (compared to stress echo and nuclear stress testing).

In addition, an extremely important feature of the basic treadmill exercise test is its very powerful prediction of patient prognosis. Large numbers of scientific studies have shown that completion of a certain number of minutes of this test indicates a low coronary risk (regardless of other considerations).

Some indications for this test include :

1. Diagnosis of coronary artery disease.

2. Assessment of prognosis after myocardial infarction (heart attack).

3. Post-coronary artery angioplasty/surgery.

4. Monitoring of medical therapy for coronary artery disease.

5. Pre-testing of patients before starting an exercise programme.

6. Obtaining an objective assessment of a patient's exercise capacity.

AVAILABILITY

Cardiology Associates; Cardiology Unit - University Hospital of the West Indies; Cardiotechnics Limited; Heart Institute of the Caribbean and Montego Bay Hope.

COST CODE .....

STRESS ECHO

This utilises the same principle as the basic treadmill, but echocardiographical images of the heart are obtained at rest and during exercise. These images are then compared to ascertain if there is evidence of a change in the motion of any segment of the heart muscle. If such a reduction were to be visualised, then the conclusion reached would be that this represented an exercise-induced reduction in the circulation to that part of the heart muscle.

Stress echocardiography is somewhat more sensitive than basic treadmill testing in the diagnosis of coronary artery disease, diagnosing 75-80 per cent of cases (compared to 65-70 per cent), but is more costly.

AVAILABILITY

Cardiology Associates and Heart Institute of the Caribbean.

COST CODE .....

NUCLEAR STRESS TEST

This utilises the same principle as the basic stress test and stress echo as described above, except that an image of the heart is produced before exercise by the intravenous injection of a special radiosensitive compound (radioisotope). This image is produced when pictures are taken with a special camera.

The patient is then subjected to exercise in the usual manner and at peak exercise more radioisotope is injected followed by repeat pictures. Comparison of the pictures obtained will allow the cardiologist or radiologist to detect any exercise-induced circulation defects.

Like the stress echo, this test improves the sensitivity for the diagnosis of coronary artery disease to 75-80 per cent. It is, however, considerably more expensive than the basic treadmill.

AVAILABILITY

Cardiotechnics Limited; X-Ray and Diagnostic Ultrasound Consultants and Heart Institute of the Caribbean.

COST CODE

PHARMACOLOGIC STRESS TEST

In some patients who are unable to exercise due to orthopaedic (bone and joint) problems in their lower limbs, stress testing may be done by injecting medication which will increase the heart rate or dilate the coronary arteries, and in so doing allow assessments which are similar to the exercise tests.

Charles E. Denbow is Professor of Medicine and consultant cardiologist at the University of the West Indies (Mona).

COST CODE IN J$

CHEAP