Complications of exercise – the heart.
Before launching into my usual stuff about exercise, my apologies to those of you who had a problem accessing last week’s blog. Some recipients of the weekly information found that when they clicked on the link they were taken to the previous week’s blog. Still not sure why but the answer is to click on the “Blog” button across the top of the webpage and that will take you to the most recent edition. For the whole post click on the “Read More” button.
I sincerely hope that the same error does not recur this week but if it does please follow the same steps.
The complications of exercise:
The only exercise I take is acting as pall-bearer to my friends who have indulged in strenuous exercise! ~Author unknown, quoted in “Play Safe in Taking Physical Exercise” by Royal S. Copeland, 1926
Despite Copeland’s concerns, exercise is extremely safe – even strenuous and prolonged exercise rarely produces more than muscle and joint strains and sprains. Not exercising is far more dangerous than exercising. However there are some complications produced by any physical activity and I will start with the most significant, also the rarest, and work backwards.
Congenital heart disease
Sudden death is the best known, but by far the most uncommon, complication of exercise. The incidence is about one per 50,000 in professional athletes in whom the usual cause is a congenital abnormality of the heart.
Sudden death is nearly always caused by a disturbance of heart rhythm known as ventricular fibrillation (VF). The muscle fibres of the main heart chambers, the ventricles, lose their rhythmic coordinated control and each muscle fibre contracts and relaxes independently of all the other fibres. As a result the ventricles stop pumping and death follows swiftly if normal heart rhythm is not restored. Definitive treatment is “defibrillation”, the application of an electric shock to the chest of the victim using a defibrillator. If a defibrillator is not immediately available, the victim can be kept viable by external cardiac massage until one can be acquired. Automatic external defibrillators (AEDs) are carried by all emergency ambulances and by many “first responders”. They are also widely spread in community facilities and public places. It is not unreasonable for all concerned citizens to learn how to perform external cardiac massage and acquaint themselves with the way to use an AED. Being automatic the AED does make its use easy enough to allow completely untrained individuals to apply it successfully. St John Ambulance Brigades offer resuscitation courses across the country.
The most usual cause of VF in young people is an inherited abnormality of the heart – hypertrophic cardiomyopathy (HCM). This is inherited as an autosomal dominant gene which means that on average half the offspring of a sufferer will have the condition. All the children of HCM patients should be screened for the condition and if found to be positive will usually be fitted with an implanted defibrillator which delivers a defibrillating shock if the heart goes into VF.
Screening for HCM
It has been suggested that all professional sports people should be screened for HCM. Unfortunately screening has a high false negative rate – six out of eight deaths in one study of sudden death in young footballers had normal previous screening results. So screening is generally not thought to be a cost effective endeavour and may also lead to a range of psychological, ethical and legal problems.
In middle and later life sudden death from VF is usually caused by coronary heart disease, either at the onset of a heart attack or as a result of severe heart damage from previous heart attacks. There is a widespread belief that sudden death from a heart attack is a result of “massive” cardiac damage. In fact VF is an electrical accident unrelated to the extent of cardiac injury. Those who are successfully resuscitated have the same prognosis as those who have not suffered this complication.
VF can be triggered by exercise – the rate of VF during competitive sports is about one per 130,000 person years. During triathlons it is about one per 60,000 (mostly during the swim section) and during marathon running about one per 50,000 person hours.
The risk of exercise-related VF in fit exercisers is far lower than in unfit non-exercisers.
When the risk of sudden death during exercise is compared with the benefits of being a regular exerciser, the latter wins hands down. There is always a small risk with vigorous exercise but the reduction in the death rate resulting from being physically fit easily outweighs the dangers of vigorous exercise.
Other cardiac rhythm disturbances
These include atrial fibrillation (AF), a very common condition of later life. AF is similar to VF but involving the “ante-chambers” of the heart. Since the atria are not necessary for the heart to pump out blood, AF is not fatal but does reduce the heart’s efficiency. The heart beats more rapidly and irregularly. The main complication is the development of blood clots in the atria. These can be dislodged and end up in the brain causing a stroke. It important that people with AF should take blood thinners to prevent this.
AF affects about seven in 100 people over the age of 65 and becomes gradually more common with increasing age. It is also related to physical fitness. The fitter you are the lower the risk except in those who take excessive amounts of exercise. Above a level of about 1500MET-mins (equivalent to about five hours of moderately vigorous exertion) per week AF becomes more common. With appropriate management, this should not cause serious problems.
There is no good evidence that even very prolonged vigorous exercise is harmful to the heart. Towards the end of very long bout of exercise there may be some fall off in the pumping efficiency of the heart, so called “exercise induced cardiac fatigue” but this self-reverses within 48 hours. There are also some electrocardiographic changes 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.
Other cardiac problems:
It has been suggested that excessive exercise, particularly in older athletes, may damage the heart. 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 to 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 eight or more hours per week at 10 METS or more were 23% less likely to die than their less active peers.
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