EXERCISE POST-MI

Risk classification It is very helpful if patients are stratified by risk level before starting exercise training.

High risk Large or multiple infarcts, poor cardiac output, low exercise tolerance, perhaps with residual ischaemia and/or a tendency for irregular electrical heart activity.

Medium risk Medium infarcts with moderately reduced exercise tolerance and patients with residual ischaemia.

Low risk Small infarcts with good exercise tolerance and no residual ischaemia or ventricular arrhythmias.

Exercise advice

Exercise training can start four weeks after the heart attack for low and medium risk patients, but should be delayed for a further two to four weeks for those in the high risk group.

Supervised circuit training is the most popular choice of exercise in nearly all cardiac rehabilitation programmes. It is easy to supervise, can involve large numbers in one venue, trains many different muscle groups, and avoids the boredom of single exercise sessions such as the bicycle ergometer or treadmill. It is usual to include a mix of aerobic (eg. step-ups, trampoline jogging, cycling, treadmill) and muscular strength and endurance exercises (eg. dumbells, static exercise machines, therabands).

Exercise should be performed at least three times weekly for 30 to 60 minutes to an intensity which pushes the pulse rate to the level decided by the exercise test (see Box 1).

Low and medium risk patients can perform much of their exercise at home using a similar circuit to that used at the rehabilitation centre. High risk patients should be more closely monitored. All patients should be encouraged to include a regular, brisk, two mile walk in their home programme.

The programme should last four to six weeks for low risk patients, at least 10 weeks for medium risk patients, and up to five months for high risk patients although this will depend on individual circumstances and available resources.

At the end of the programme it is helpful to repeat the exercise test to check the effectiveness of the training and measure the increase in fitness achieved.

The benefits of exercise training for cardiac patients

1 Increased physical fitness

During the first three months after a heart attack physical fitness improves spontaneously by about 10% as the heart recovers and as the patient’s activities increase. A course of exercise at this stage has been shown to increase this figure to between 25% and 30%.

Most patients can be restored to a level of fitness which is greater than before the heart attack unless the amount of damage to the heart has been great. Even if such an outcome is not possible an extremely worthwhile degree of improvement can be achieved, even in patients with heart failure.

The mechanism for the effect of exercise in coronary patients is different to that

in people with normal hearts. Usually exercise training has two effects – central and peripheral.

The central effects result in an increased output of blood from the heart at each contraction meaning oxygen delivery to the body can be achieved at a lower heart rate for a given effort. This is achieved by increases in stroke volume, ejection fraction and force of contraction of the left ventricle together with lowered sympathetic tone during exercise.

The peripheral effects are a more efficient distribution of blood volume and a greater capacity of the working muscles to extract oxygen from the blood supplied to them.

The central and peripheral effects lead to an increase in the ability of the heart to work effectively at a lower heart rate for any given exercise level or cardiac output.

During the first few months after a cardiac illness, only the peripheral effects and the lowered sympathetic tone can be obtained. But if training is continued for a year or more and is sufficiently strenuous, the central effects of the improved heart output can also be achieved.

2 Reduced angina

Improved fitness means a lowered demand on the heart for any activity level, an extremely important result for patients with angina. Nearly all controlled trials of exercise for angina sufferers have shown a great reduction in this symptom and its complete resolution in some.

3 Enhanced coronary blood flow

In several controlled trials patients with angina who have been ‘treated’ by physical training have shown the ability to exercise to a greater oxygen demand from the heart muscle before developing either angina or ST segment depression.

Research using thallium scanning has shown that patients with angina have better oxygen perfusion of the heart muscle during exercise after physical training.

SportEX 15