Cardiac events (ILO/IMO Guidelines Appendix E I20-25)

Definition

'Cardiac events' include: myocardial infarction, ECG evidence of past myocardial infarction or newly recognised left bundle branch block, angina, cardiac arrest, coronary artery bypass grafting, coronary angioplasty

Impairment and risks

Ischaemic vascular disease is a common cause of incapacity and death. Its most frequent manifestations are angina and myocardial infarction. The conditions classified as cardiac events are almost always a consequence of such vascular disease.

Risk factors are well established and include the same condition in near relatives, smoking, the metabolic syndrome of obesity, hyperlipidaemia and type 2 diabetes, hypertension and type 1 diabetes.

This group of conditions are the commonest causes both of deaths at sea and of failure by middle aged seafarers to meet current medical fitness standards.

After episodes of ischaemic vascular disease caused by atheroma there may be a loss of functioning heart muscle, limiting exercise capacity

Defects of heart rhythm may develop, themselves causing episodic incapacity.

There is an increased risk of recurrence of both the same form and of other manifestations of the pathological processes of arterial blockage.

Early specialist treatment can greatly reduce the risk from any recurrence of a cardiac event. As this will not be available at sea the risk of death from a recurrence will be higher than it would be on shore.

Lifestyle related preventative measures (risk factor modification) and medical interventions (treatment of predisposing factors, surgical procedures to remove blockages) can reduce or delay recurrences but do not reduce the risk to the same as that of those without the condition.

Rationale and justification

There is little direct evidence about risks in seafaring but the considerable body of work that relates to driving and to flying is relevant.

Sudden death at sea

• there have been case reports of deaths of lone watchkeepers leading to collision but these are rare and do not appear in many large series of marine accident reports.
• mortality studies show that sudden death that was subsequently attributed to cardiac causes was the predominant non-accidental cause of death (>80%) while at sea.

Sudden death
Evidence from vehicle driving

• Sudden death at the wheel is a rare event (from under 1% to 3.5% of crash records).
• Post-mortem data (14 studies) show that more than 80% have cardiovascular disease and more than 70% show evidence of coronary artery disease. In one study more than 90% had cardiac hypertrophy.
• Injury to others was rare in early studies but more recent investigations show an increase in passenger deaths –possibly a consequence of increased road speeds or traffic density.
• Prodromal symptoms before the final journey had been reported to others by 25-40% of those dying.
• The only evidence on warning of event prior to incapacitation is indirect. One study showed that in only 2 out of 44 deaths were there signs of braking prior to death. However, the most commonly noted site for an at-wheel fatality to be found is in the car halted at the side of the road, suggesting some warning and a response to it.
• The role of stressful situations as initiators of sudden events is uncertain. One study showed that, whilst there were no ECG changes while driving in those without cardiovascular disease 17% of those with coronary artery disease did show significant changes.

Recurrence of cardiac events

• Recurrence rates will indicate the likelihood of an emergency at sea. They can also be used as a proxy to stratify the risk of sudden incapacitation. However measures of recurrence such as death or hospital admission have only limited predictive value for sudden events.
• Most evidence comes from large population studies. Most of these data are old and the frequency of recurrence has fallen markedly as a result of the use of better therapy. Most recent studies are of highly selected patient groups participating in studies on intervention. It is not possible to extrapolate in a valid way from their recurrence rates to the generality of seafarers.
• The older studies identified predictors of recurrence such as poor exercise ECG performance, reduced ventricular ejection fraction, presence of type 2 diabetes and a failure to reduce risk factors.
• A cardiac event makes impairment from vascular disease elsewhere, e.g. intermittent claudication, stroke or transient ischaemic attacks, more likely because the pathological processes are the same. Similarly, ischaemic disease elsewhere increases the probability of a cardiac event.

Clinical assessment and decision taking

Assessment principles

In terms of fitness for work at sea cardiovascular conditions can be viewed simply in terms of their impairing effects. Assessment needs to address the following:

1. Are there continuing limitations of exercise tolerance – lack of ability to increase pumping action of heart as needed? Particularly relevant to ability to undertake normal and emergency duties needing physical effort
2. Is there an increased risk of sudden incapacity – rapid reduction in output of blood from heart? May be from arrhythmia or from a new episode of infarction. Incapacity is normally a consequence of reduction in blood flow to the brain causing loss of consciousness as the brain uses up the available oxygen. Important as vessel safety depends on performance of watch-keeping crew, also a risk if working in dangerous places, such as at heights or if working alone
3. Is there risk of recurrence of an existing condition or of a condition which is already apparent in one part of the body presenting elsewhere? Early treatment of many vascular conditions, such as myocardial infarction can be lifesaving. The treatments are complex and rarely available at sea. Recurrence will result in direct excess risk for the individual but can also require diversion of crew to act as carers, the risks of medevac from a vessel or the costs and quality of care problems from diversion and treatment away from home country. May determine whether the person can only work close to healthcare facilities
4. Is there a foreseeable risk of the condition progressing? Do the treatments used need regular check- ups to ensure that they are working or that there are no complications? This may determine the timing of future medical assessments and hence the duration of tours of duty
5. Are there levels of risk factors such that there is an unacceptably high level of risk that a new vascular condition will arise? Concurrently present risk factors such as smoking, high/poorly controlled blood pressure, obesity/diabetes/hyperlipidaemia may create entirely foreseeable risks. Certification of unfitness in the absence of disease may not be acceptable. Compliance with a regime of treatment or lifestyle modification can be considered with sanctions for non-compliance.
6. Is there additional information available from additional clinical investigations such as angiogram results or ventricular ejection fraction measurements? These results should be considered on a case by case basis with advice from a cardiologist on their implications for risk assessment when appropriate.

In all these situations quantification of risk should be used where possible to determine the borderline between fitness and unfitness. Large studies on shore based populations can provide such information but these are necessarily historic and if there are changes in patterns of disease, such as the reducing incidence of myocardial infarction in many countries or the increased effectiveness of angioplasty now that stents are used then this data will overestimate risk. Similarly if risk factors such as obesity are increasing in frequency and there is recognition of a new alignment of risks associated with the metabolic syndrome then the information on subsequent disease may not have recognised all the potentially impairing consequences.

Important and relevant quantification includes:

• The increased risk of vascular events associated with different levels of blood pressure, smoking, lipids, obesity, exercise alone and in combination with each other
• The prognosis after cardiac events in terms of early and subsequent mortality, morbidity, sudden incapacitation and recurrence.
• Stratification of this data by the results of various predictive tests using relevant measures of cardiac function such as Bruce protocol exercise EGC, echocardiography, ejection fraction.
• Prognosis after coronary artery narrowing as seen on angiogram with information on the extent to which it is modified and for how long by the procedures used for angioplasty
• Cardiac events at sea – proportion fatal, location, scope for first aid intervention or medevac

Decision aid

Advice to seafarers

Advice on prevention of recurrence needs to be given and recorded. This may include: risk factor screening (weight, smoking, blood pressure, lipids, exercise, diet, diabetes) at medical - dietary and lifestyle advice. Advice to cease smoking.
Seafarers returning post 'cardiac event' to be made aware of limited treatment facilities at sea and hence increased risk in the event of recurrence. Compliance with risk reduction (e.g. weight control, smoking cessation) measures may be made a condition of re-certification.