Clinical Aerospace Cardiovascular Medicine
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CHAPTER 13 Clinical Aerospace Cardiovascular Medicine James R. Strader, Jr., Gary W. Gray, and William B. Kruyer I was gratified to be able to answer promptly. I said, ‘‘I don’t know’’. —Mark Twain Cardiovascular diseases (CVDs) will always be a major con- 6. Other aeromedical endpoints not considered in the second cern for aeromedical disposition and aircrew standards step should be assessed. because they are a major health problem worldwide and 7. And finally, consider the impact of medical therapy for a leading cause of mortality and morbidity in industrialized the diagnosis being addressed. nations. Cardiac diagnoses are frequent causes of loss or re- striction of licensure for all categories of civilian and military In this process, aeromedical decisions are based on flying. Most requests for special issuance to fly with a car- percent per year event rates at 1 to 3 years to address diac disorder are for cases of coronary artery disease (CAD), short-term safety and possibly at 5 to 10 years to address the including coronary revascularization (e.g., bypass surgery, longer-term likelihood of a continued aviation career. Data stent). Cardiac dysrhythmias and valvular disorders are also from aircrew populations and carefully selected populations common causes for medical review of flying eligibility. from the clinical literature would be used. Within the Rapid advancements in cardiology present both chal- selected threshold (e.g., 1% per year), sudden and complete lenges and benefits to aeromedical applications. This chapter incapacitation (sudden cardiac death, syncope) is of key can neither cover all cardiac diagnoses nor cover any in great importance but all events that may negatively affect proper detail. Topics of key aeromedical relevance will be discussed, performance of flying duties should be considered. including disposition of various electrocardiographic find- The earlier process and the following discussions of select ings, CAD and CAD intervention, valvular disorders, and cardiac disorders address applications to aviation, especially tachyarrhythmias. These discussions should also serve as military and commercial aviation. This process applies read- an example of an aeromedical approach to other cardiac ily to other special environments such as space flight while diagnoses. taking into consideration potentially different risk thresholds A seven-step process for aeromedical decision making of due to length of the space mission, isolation, and so on. cardiac diagnoses has been previously proposed and is briefly Aeromedical decision making may involve aircrew with summarized and discussed as follows (1): symptomatic, clinical heart disease. For this, helpful clinical 1. Establish a threshold of acceptable risk for aeromedically literature is usually available. However, aeromedical decision pertinent cardiac events. Annual event rates greater than making must often consider aircrew with asymptomatic, sub- threshold would be unacceptable for continued flying. clinical disease for which helpful literature may be lacking 2. Select appropriate aeromedical events for the cardiac or incomplete. And at times, a disease is not under con- diagnosis under consideration. sideration, but rather an abnormal test suggesting presence 3. Determine annual event rates for these selected events. of disease [e.g., electrocardiogram (ECG) or graded exercise 4. Address any special considerations, such as high +Gz or test]. The aeromedical issue then becomes estimating the risk single-pilot operations. of underlying heart disease and deciding to what extent this 5. If continued flying is a consideration, a recertification risk should prudently be pursued with further testing. These policy must be formulated. challenges are the bedrock of aerospace cardiology. 318 CHAPTER 13 CLINICAL AEROSPACE CARDIOVASCULAR MEDICINE 319 DISPOSITION OF aviators, has not been associated with increased risk of ELECTROCARDIOGRAPHIC FINDINGS progressive conduction system disease or other cardiac prob- lems in aviator populations (1,2). Echocardiography may be A resting 12-lead ECG is required for routine surveillance aeromedically prudent to exclude structural heart disease. of many aircrew positions but is somewhat of an enigma. If normal, unrestricted civilian and military flying duties Some ECG findings [e.g., left axis deviation (LAD), ST-T may be allowed, including entry into military flying training. wave changes, and ventricular ectopy] are correlated with Periodic reassessment does not appear to be indicated. advancing age and an increased incidence of CAD and hypertension,andmayhavesomepredictivevalue.Yet, Left Bundle Branch Block these same findings are often nonspecific, not reflective Reported in 0.01% to 0.1% of military aviators, the preva- of underlying pathology, and often not evaluated in a lence of left bundle branch block (LBBB) increases with age clinical scenario. The aeromedical dilemma is to balance as does the prevalence of CAD and hypertension. Rare in avi- the pursuit of underlying disease against the unnecessary ators aged 35 years or younger, LBBB became more common performance of tests, which themselves may prompt further with advancing age older than 35 years (1,2). Aeromedical testing. concerns are the association of LBBB with CAD and dilated When a minor ECG abnormality presents, comparison to cardiomyopathy. In the absence of underlying heart disease, priortracingsisoftenveryhelpfultodetermineaeromedical LBBB does not present a significant risk for cardiac events, disposition. An ECG finding that has been present and stable especially in the relatively young, healthy aviator population. for several years may not require evaluation, whereas an Evaluation of underlying disease is required, but accuracy of abrupt, new finding compared to prior ECG tracings may exercise testing and nuclear myocardial perfusion imaging is warrant thorough investigation. The diagnostic criteria for limited by the LBBB itself. ECG ST-segment response during each of these findings are not discussed; rather the reader is graded exercise testing is not interpretable in the presence referred to standard ECG textbooks. of LBBB, and myocardial perfusion imaging is often ab- Many ECG findings occur with such frequency and be- normal in the anteroseptal region. Conventional coronary nignity that they may be considered normal variants, which angiography remains the gold standard for definitely exclud- do not require further evaluation. A list of suggested nor- ing underlying CAD, but is associated with inherent risks. mal variants is in Table 13-1. This is not intended to be an Depending on the aircrew position, computed tomographic all-inclusive list. Moreover certainly for individual cases, the (CT) angiography might be considered to exclude most sig- aeromedical practitioner may choose to further evaluate any nificant coronary lesions. However, approximately 25% of of these findings. lesions may be incorrectly assessed by this method. Detection of coronary calcification should be as useful for screening as Conduction Disturbances in other populations, although data are not available regard- Right Bundle Branch Block ing its efficacy in LBBB. Detection of coronary calcification Incomplete right bundle branch block (RBBB) is a common is discussed later in this chapter. ECG finding and is considered a normal variant (Table 13-1). Experience with United States Air Force (USAF) aviators Complete RBBB, reported in 0.2% to 0.4% of military has revealed underlying CAD in approximately 10%, twice the estimated background incidence. Licensing authorities must consider whether initial assessment of LBBB should TABLE 13-1 include invasive or noninvasive coronary angiography. For many years, the USAF has returned aviators with LBBB to Normal Variant Electrocardiographic Findings unrestricted flying, if coronary angiography and noninvasive Sinus Bradycardia Right Axis Deviation testing are normal. Periodic noninvasive reassessment is Sinus tachycardia Indeterminate axis appropriate, especially if coronary angiography is not Sinus arrhythmia Early repolarization ST segment performed during initial evaluation. LBBB can be an early elevation manifestation of dilated cardiomyopathy reinforcing the Sinus pause of 3 s or less Nonspecific interventricular conduc- importance of regular follow-up. tion delay with QRS width <0.12 s Ectopic atrial rhythm Terminal conduction delay (wide S wave) Nonspecific Intraventricular Conduction Delay Wandering atrial Incomplete right bundle branch block Nonspecific intraventricular conduction delay (IVCD) is pacemaker considered a normal variant in otherwise healthy subjects Junctional rhythm RSR pattern in leads V1 and/or V2 if the QRS interval is less than 120 ms. If the QRS interval Idioventricular rhythm R wave taller than S wave in V1 is 120 ms or greater, the IVCD is considered abnormal but First-degree atrioven- Supraventricular or ventricular escape the risk of underlying disease and prognosis are unclear. tricular (AV) block beats Reported prevalence in military aviators is similar to RBBB. Mobitz I (Wenckebach) Rare supraventricular or ventricular If underlying cardiac disease is present, cardiomegaly is often AV block ectopy a feature. Evaluation with echocardiography and, at least in older aviators, graded exercise testing with nuclear or 320 CLINICAL echocardiographic stress imaging, should suffice to exclude healthy aviators and is felt to be due to increased resting vagal underlying disease. In the absence of underlying cardiac tone. Evaluation is unnecessary