Complications of exercise Part 2
Last week I talked about the risk of sudden death during exercise. Though well known, this is an extremely rare complication of exercise – it is far more common in non-exercisers than in exercisers. Exercise is very safe. Indeed it is much safer to be an exerciser than an idler. It has been recommended that people in middle to later life should get their doctor’s advice before embarking on an exercise programme. Piffle! It is those who are not considering such a step who should seek medical advice.
Apart from sudden death there are some other cardiac problems which are rarely the result of exertion.
Atrial Fibrillation (AF)
Atrial fibrillation (AF) is a very common condition of later life. AF is similar to ventricular fibrillation (VF – See last week’s blog) but involving the ‘ante-chambers’ of the heart, the atria, which can no longer contract and propel blood into the ventricles, the main pumping chambers of the heart.The illustration above shows the ECG pattern of AF (upper trace) compared with normal sinus rhythm (lower trace).
Since the atria are not necessary for the heart to pump out blood, AF is not fatal but it does reduce the heart’s efficiency. The heart beats irregularly and more rapidly. The main risk from AF is the development of blood clots in the atria. These can be dislodged and end up in the brain, causing a stroke. It is important that most people with AF take blood thinners to prevent this.
AF affects about 7 in 100 people over the age of 65 and becomes gradually more common with increasing age. Cardiovascular Disease risk factors such as obesity, hypertension and diabetes all increase the chance of developing AF. High levels of physical fitness are protective. The fitter the individual, the lower the risk. Increasing physical fitness also lessens the risk associated with other factors, particularly obesity.
It has been suspected that excessive exercise can reverse this effect in men. A large UK study showed a more pronounced risk reduction with activity for women than for men, as well as a protective effect over the entire range of physical activity levels examined. The same study suggested that higher levels of exercise in men might reverse this effect. This has subsequently been denied by a study of 460,000 US Veterans given a symptom-limited treadmill test. During follow up of a mean of 9.8 years, 42,639 individuals developed AF. Exercise capacity was inversely related to AF risk through the full range of fitness levels, the risk being 11% lower for each 1-MET increase in exercise capacity.
So if you do develop AF, which is a common cardiac rhythm disturbance in later life, don’t blame your exercise programme. Indeed if you are not an exerciser, this is the time to get more active.
The management of AF is complicated. For a start it usually requires blood thinners – anticoagulants – to protect against the risk of stroke. Some people can have normal rhythm restored by drug treatment or by “cardioversion” which is the use of an electric shock to stop the heart which should then restart in normal rhythm. These measures may not work or the AF may recur after a short time. For these people, “ablation” may be a possibility. This is achieved by passing a catheter from a peripheral vein into the heart and zapping the electrical pathways responsible for allowing this arrhythmia.
If AF persists, there are drugs which slow the heart rate thus reducing some of the ill-effects of AF. These ill-effects include the sensation of palpitations and a reduction in the efficiency of the heart as a pump. This can cause light-headedness and breathlessness and reduced exercise tolerance.
Exercising with AF
AF is often often intermittent, so called paroxysmal AF. Most people are aware of the change from normal “sinus” rhythm to AF when it happens – they notice the associated palpitations and sometimes other symptoms like breathlessness and faintness. Such individuals should avoid vigorous exercise during periods of AF but only exert themselves when in normal rhythm. Those who are unaware of their periods of AF need not change their usual exercise habits. Rarely, periods of AF are precipitated by exercise and such individuals should avoid the exertions responsible.
People in permanent AF cannot use their pulse rate to monitor their exercise. They need to rely on how hard the exercise feels and exert themselves to a level which makes them short of breath but not uncomfortably so. This level of exercise is likely to be lower than before they went into AF.
Other cardiac problems
It has also been suggested that excessive exercise, particularly in older athletes, may damage heart muscle. There is no good evidence for this. Towards the end of very long bout of exercise there may be some fall-off in the performance of the left ventricle. This is the so called ‘exercise-induced cardiac fatigue’, but reverses itself within 48 hours. Some electrocardiographic changes are also found in endurance athletes, such as evidence of a thicker than normal heart muscle wall, but again there is no evidence that this is harmful.
Older athletes do have a higher prevalence of calcium in their coronary arteries, but this is not associated with an increased risk of heart attacks. One study of ‘extreme exercise’ examined 22,000 healthy men aged 40–80 and compared their activity levels with their risk of death during the period of study. The most active men had half the risk of death of the least active, and those taking 8 or more hours per week at 10 METS or more were 23 per cent less likely to die than their less active peers. Other studies have confirmed the direct relationship between very high levels of both physical activity and cardiorespiratory fitness with high coronary artery calcification – without any increase in adverse cardiac effects.
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