Triggering a heart attackBMJ 1996; 312 doi: https://doi.org/10.1136/bmj.312.7029.459 (Published 24 February 1996) Cite this as: BMJ 1996;312:459
Compensation may be justified after physical exertion but not emotional upset
Headlines such as “Shopkeeper dies while chasing thieves” and the ever increasing volume of letters from solicitors to cardiologists testify to the fact that the press and public are convinced that heart attacks are triggered by events. For bereaved relatives, sadness and grief may turn to loneliness and bitterness, and increasingly today to a desire to blame something or someone. The sympathetic solicitor in his office in the hospital foyer lends a willing ear and seeks expert advice. Employers and insurers also want an answer to the question of what triggers a heart attack.
The suspicion that vigorous physical effort might provoke myocardial infarction was raised some 60 years ago.1 Emotional distress has likewise been incriminated.2 More recent studies have corroborated these findings. The MILIS (Multicenter Investigation of Limitation of Infarct Size) investigators, for example, found that antecedent physical activity was present in 14.1% of 849 cases and emotional upset in 18.4%.3 One American4 and one German study,5 using the novel epidemiological method known as case crossover, have suggested respectively a sixfold and twofold increase in risk of myocardial infarction in the hour after heavy physical exertion such as slow jogging, shovelling snow, swimming, pushing a lawnmower, or heavy gardening. The German study suggested further that there was an increased risk in the hours after waking or emotional upset.5 The suspicion that ventricular fibrillation and sudden cardiac death also occur more often than would be expected by chance during vigorous physical effort enjoys support from exercise testing laboratories and elsewhere.6 Only one small and rather overlooked report of 100 sudden deaths from coronary disease seems to have been undertaken in Britain, and this hinted at “acute psychological stress” as an important trigger.7 The difficulty in defining what constitutes emotional upset or acute psychological stress hardly needs emphasis; one person's stimulus is another's stress.
One event that can certainly trigger a heart attack is chest trauma. Closed chest trauma in a road traffic accident, for example, can precipitate myocardial infarction and sudden death by a variety of mechanisms. Direct myocardial contusion is usually suspected on admission from the nature of the injuries and is confirmed by electrocardiographic and cardiac enzyme changes. More often, however, cardiac damage is suspected later, when arrhythmias or heart failure are detected in an intensive care unit. Further investigation may then confirm myocardial infarction, which in turn may be due to coronary arterial trauma, but such cases are rare.
The idea that physical effort or emotional upset might trigger a heart attack is attractive because it is biologically plausible. Our current understanding of the pathology of coronary artery disease allows us to speculate that sudden effort in particular might trigger rupture or fissuring of an atheromatous plaque, with resultant platelet activation and aggregation, thrombus formation, coronary arterial occlusion, and hence myocardial infarction or sudden cardiac death.8 Alternatively, sympathetic stimulation might provoke ventricular fibrillation or simply induce a crescendo of myocardial ischaemia leading to infarction or pump failure in people with critical coronary artery disease. The notion that adrenergic mechanisms may be important in the initiation of a heart attack is also supported by observations on the timing of myocardial infarction and sudden death, which exhibit circadian variation. The start of symptoms peaks in the morning, or shortly after waking for those on shift work.9 This parallels changes in other relevant biological variables such as circulating catecholamines, blood viscosity, and fibrinolytic factors. Interestingly, β blockade abolishes the morning increases in sudden cardiac death and myocardial infarction and attenuates some of the biological variables.10
Lawyers and doctors who are familiar with social security law will be aware that certain occupational diseases entitle the victim to benefit payments. Ischaemic heart disease is not one of these. But an accident—defined as “an un-looked for mishap or untoward event” associated with “fresh pathological change … caused or materially contributed to, by the claimant's employment”11—may confer benefits, and myocardial infarction occurring at work may be regarded as an accident.
No trigger is found in most cases
Myocardial infarction may therefore occasionally entitle the victim to benefit payments. This custom stems from an important decision by Britain's social security commissioner in 1967 about a 46 year old furniture remover. The commissioner “held that the myocardial infarction resulted from the effort required of the Claimant to lift a wardrobe and that he accordingly suffered personal injury by accident arising out of and in the course of his employment.”11 Also noteworthy in that case was that reports “from two eminent cardiologists” were included in the evidence. Since then, the lay officials who adjudicate over claims arising from accidents in the workplace have generally accepted that unaccustomed strenuous work may cause the accident of a myocardial infarct, although there are continuing areas of uncertainty.11 Knowledge of this precedent may account for the increasing number of attempts under common law to claim damages for victims of heart attacks that seemed to result from severe physical effort. No such case law exists for those who suffer myocardial infarction after emotional distress.
The central problem is that naturally occurring heart attacks are extremely common—22 deaths an hour from this cause in Britain alone.12 Some are therefore bound to occur after a physical or emotional crisis. In the studies quoted above no trigger was found in most cases. Moreover the fundamental pathology in the coronary artery is an atheromatous plaque that has developed slowly from a fatty streak. The sequence of events leading to plaque rupture may begin at any time. Current thinking, which owes much to the work of Davies and his colleagues (M J Davies, personal communication), suggests that some plaques are stable (those with a thick fibrous cap and plenty of collagen, for example) whereas other plaques may be unstable and liable to rupture (for example those with a thin cap, rich lipid core, and inflammatory cells). Hence a more potent trigger for a heart attack might be a change in plaque composition, which might have more to do with lipid metabolism than physical effort, although this is speculative.
Absolute risk is extremely small
A further difficulty over the relation between physical exertion and a heart attack is that the apparent causation is based on the epidemiological concept of relative risk. In the American study, for example, only 4% of victims (5 out of 1228 patients) were actually engaged in heavy physical exertion in the hour before the myocardial infarct.4 The absolute risk of a healthy middle aged man developing a myocardial infarct as a result of physical exertion is very small indeed. The failure of the lay press to appreciate this difference between relative and absolute risk has led to misunderstanding and accusations of scaremongering.13 Small wonder that the victim of a myocardial infarct starts thinking about a claim if he or she is aware of others enjoying social security benefit after suffering a myocardial infarction at work and reads in newspapers that the risk of a heart attack is increased sixfold by physical exertion.
But what should those in authority—judges, lawyers, adjudication officers—believe? Clearly, in cases of direct trauma to the heart a claim should be settled. Claims based on emotional distress are unlikely to succeed, partly because of the difficulty in defining distress and partly because the supporting evidence is too insubstantial. But claims that a heart attack was triggered by physical exertion have to be examined more carefully. Those faced with the decision must remember that the latest supporting evidence is based on the epidemiological concept of relative risk and that the absolute risk is very small. Also the underlying disease process, which will often be the major factor in permitting the development of a heart attack, will have been present for many years. But if sudden cardiac death or myocardial infarction occurs within one hour or so of unaccustomed physical effort then a claim may be justified and may succeed.