In this chapter the relevance and different forms of cardiovascular diseases in seafaring are discussed, including diagnosis and treatment. The special features of laymen medical care at sea - often far away from professional medical aid - are taken into account. During the last century, cardiovascular disease (CVD) has developed to a leading cause of morbidity and mortality worldwide. By 2020 it is projected that CVD will have surpassed infectious disease as the worlds leading cause of death and disability (1).
Epidemiology of CVD
Ehara et al. (2) analysed the Japanese disease statistics for seamen over fifteen years (from 1986 to 2000) and found that CVD (11.6%) were the third most frequent diseases aboard. It has been repeatedly described that seafaring belongs to the high risk occupations of ischemic heart diseases (3,4,). Jaremin and Kotulak (5) performed a retrospective study from 1985 to 1994 based on a population of 11,325 Polish seafarers and deep-sea fishermen. They found more than 70% of the documented mortalities at sea were caused by myocardial infarction. Also other mortality studies confirmed CVD as an important cause of seafarer’s deaths (mortality rate between 30 and 45 per 100.000 seafarer-years) (6,7,8).
In recent years, due to rising economic pressure and shipboard organizational changes with elevated individual responsibility an increase of physical and psychical stress and consequently a higher risk of CVD among seamen have been assumed. Compatible with this assumption, CVD are becoming increasingly important for naval disablement among seamen. At the beginning of the 90s the naval disablement in Germany was related in 13% to 14% to CVD, whereas the current proportion is higher than 18% (9).
CVD risk in different seafarers’ groups
In a German cross-sectional study 161 seafarers operating on German-flagged vessels were examined. This study showed that Europeans compared with non-Europeans were about twice as likely to have more than 3 cardiac risk factors after adjusting for age (OR 2.4 (95% CI 1.01 - 4.55) (10); especially engine room officers (43.3%) and the galley/ operating staff (57.1%) showed a higher CVD risk judged by the number of risk factors (in contrast to 33.3% of deck officers, 24.4% of crew ranks on deck, 20.0% of crew ranks in the engine room).
Individual CVD risk factors
Besides genetic and ethnical determinants, CVD risk is generally influenced by independent coronary risk factors, namely age, LDL cholesterol, smoking, HDL cholesterol, systolic blood pressure, family history of a premature myocardial infarction, diabetes, and triglycerides, as well as dependent risk factors, i. e. overweight, lack of exercise, high-fat diet and alcohol (11).
Some of these risk factors are modifiable and related to the specific conditions aboard so that a high frequency of independent CVD risk factors respective contributing factors in seafarers has been repeatedly described (12). For example, the crew has scarcely an influence on the usually unbalanced and high-fat diet aboard (13) contributing to high cholesterol, high triglicerides and obesity. Hyperlipidemia is often observed in crews, e.g. among 40% of investigated Chinese seafarers (14); high cholesterol was measured in 80% and high glucose in 30% of Croatian seamen (15). Among Lithuanian mariners 44.9% showed age-standardized a clinically significant elevation of blood pressure (compared to 53% of the general population of Lithuania (4); the leading risk factors encompassed increased body mass index (66.5% had a BMI higher than 25 kg/m2), smoking (55.2% smokers) and alcohol use
(82.5%). Among seafarers of German-flagged vessels the most prominent CVD risk factors in seafarers were shown to be hypertension (49.7%), high triglycerides (41.6%), older age (39.8%), and smoking (37.3%) (10). The seafarer’s cigarette consumption as an important CVD risk factor is higher than in the general population (10,4,16).
Besides the mentioned parameters, also psychosocial work factors such as stress pose a contributing CVD risk factor. Kivimäki et al. (17) observed in their broad meta-analysis of prospective cohort studies that stress at work increased the CVD risk by 50% on average. It is described that seafaring constitutes a high psychophysical stress for crews (18). Not only emergency events but also the shipboard routine often result in a high level of stress. Restricted leisure time facilities on board often lead to a lack of exercise and consequently to overweight. Owing to the unique unity of workplace and limited leisure area on board - frequently lasting for months - seafarers are exposed to stress to an exceptional degree and consequently to a higher CVD risk (19).
Considering the presence of multiple CVD risk factors in seamen specific occupational preventive measures (such as smoking cessation, weight control and use of anti-stress techniques) should be performed, especially in older seafarers. They should be extensively informed about their lifestyle related CVD risk and motivated to omit unhealthy behavior. Presence of cardiovascular risk factors contributes to an increased risk of ischemic heart disease as well as cerebrovascular illnesses.
CVD risk assessment in seafarers
Nowadays, several population-based risk scores exist to assess the individuals’ CVD risk, e.g. for a 10-year period. On account of the usually multinational crews and consequently the obviously different basic risk, a coronary risk assessment by applying only one population-specific risk score is not possible. Thus, to assess the seafarers’ 10-year CVD risk, a stratification of their country of origin is mandatory.
German seafarers compared with the German population of the PROCAM study working ashore showed a similar predicted 10-year CVD risk; taking into account the healthy-worker-effect due to the periodical test for nautical fitness a higher coronary risk of the seafarers can be assumed (10). The application of such CVD-risk scores can be easily implemented in the fitness examinations for nautical service and would probably help to reduce the frequency of dangerous CVD incidents at sea (12).