Abstract
Civil aviation authorities worldwide consider cardiovascular disease (CVD) an important medical condition because it can cause sudden pilot incapacitation. This group of related conditions is the most common reason for loss of flying licence. The aims of this thesis are the following: to assess the performance of the current practice regarding cardiovascular risk assessment in airline pilots, to evaluate the efficacy of cardiovascular investigations of pilots with excessive cardiovascular risk, and to investigate potential cardiovascular tests which can be employed in proposing a more accurate cardiovascular risk assessment algorithm.
Over a 16-year study period, 15 cases of cardiovascular events were identified, most of which were manifest with sudden clinical presentation of symptoms. Using a matched case-control study, the accuracy of the New Zealand cardiovascular risk charts (NZ-CRC) was found to be only moderate; despite appropriate cut-off points, the risk assessment tool had a low sensitivity and was unable to predict almost half of the events. A case-series study examining cardiovascular investigations of 29 pilots with a 5-year CVD risk of ≥10% revealed that the current approach in New Zealand to investigate excessive cardiovascular risk relied heavily on exercise electrocardiogram as a diagnostic test. Further analysis of pilots who had coronary angiograms demonstrated that nearly half of them had either trivial disease or normal coronary arteries, indicating that the current screening approach may not be optimal either to detect disease or to protect pilots from unnecessary invasive procedures.
A systematic review of guidelines was then performed to investigate potential tests that can be used to improve CVD risk assessment in asymptomatic adults. This study identified that coronary artery calcium score (CACS) measurement was the most frequently suggested test to be utilised for CVD risk stratification in asymptomatic people with intermediate risk (5-year risk of 5-10% and 10-15%). In a following study, it was shown that the diagnostic accuracies of CACS in classifying New Zealand asymptomatic patients with and without CVD were good (AUC >0.80). There were statistically significant differences in the AUC between CACS and the NZ-CRC (0.20 in all patients and 0.22 in male patients). The reclassification analyses showed that CACS properly reclassified a considerable proportion (35%) of asymptomatic patients into correct risk categories. The most noticeable improvement was found in those with a 5-year CVD risk of 5-15%.
Risk factor modification is one of important parts in the cardiovascular risk assessment of airline pilots, especially among those with intermediate-high risk without proven significant disease. A systematic review of clinical trials was performed, and results allowed presentation of optimum thresholds for initiating pharmacologic interventions in managing hyperlipidaemia, hypertension and hyperglycaemia. Finally, supported by findings from the present studies, a new approach in cardiovascular risk assessment has been proposed. The new algorithm focuses on the utilisation of CACS to reclassify cardiovascular risks. It was highlighted that the benefits of cardiovascular tests involved in the new screening pathway outweigh the risks. While considerably more research is required in the broader ongoing process of establishing the validity and effectiveness of the cardiovascular risk screening tools, this thesis provides support for the feasibility of the proposed new system and consideration for use in clinical practice.