In many jurisdictions, including the United States, an annual medical incapacitation risk of one percent per annum in two-pilot public transportation is used in assessing pilot fitness to fly for many medical conditions. This rule is known as the one percent rule and is applied in evaluating pilot cardiovascular fitness to fly.
When a cardiovascular issue is identified, the Federal Aviation Administration (FAA) may require a cardiovascular evaluation for aircrew.
This assessment should be performed within 90 days. It should include a personal and family medical history, a clinical cardiac and general physical examination, and an evaluation and statement regarding the applicant's medication. Furthermore, it should include evaluation of functional capacity and modifiable cardiovascular risk factors, a prognosis for incapacitation, and a blood chemistry (fasting blood sugar, current blood lipid profile to include total cholesterol, HDL, LDL, and triglycerides).
Aeromedical Disposition of Pilot Electrocardiographic Findings
Depending on a pilot's age and class of medical certificate, a resting 12 Lead ECG is typically required for initial license application and routine medical surveillance of aircrew in most jurisdictions. For example, the FAA requires an EKG for first-class medical applicants at the first application after reaching the 35th birthday and on annual basis after reaching the 40th birthday.
ECG findings for the aircrew population in both military and civilian aviation are somewhat inexplicable especially for aircrew younger than 30 years old.
Boos CJ, et al. investigated abnormalities in medically screened ECGs of 868 healthy military aircrews with an average age of 39.6 years. In 46.3% of the ECGs, results were classified as normal; however, 53.7% were classified as abnormal. Common training-related ECG findings were sinus bradycardia, first-degree AV block, and incomplete right bundle branch block. These findings are considered normal variance in young, healthy aircrew, and further investigations are not required.
Hampton JR, reports that minor abnormalities of the ST segment and T wave are seen in one percent of the normal population. In epidemiological studies, these findings are associated with increased risk of death, and such findings in aircrew during medical assessments for fitness needs to be investigated further with a stress test especially in aviators older than 35 years old. Abnormal ECG findings of aircrew should always be compared with previous ECGs, if available, before making aeromedical decisions.
Issues of Concern
Common Cardiac Arrhythmias
Aeromedical concerns with regards to cardiac arrhythmias in aviators are the risk of sudden incapacitation, hemodynamic symptoms, recurrences, and treatment modality.
Bradycardia (less than 50 bpm)
For all classes of medical, FAA certification requires documentation of history and findings, cardiovascular events, and any test deemed appropriate. A medical certificate may be issued by the aeromedical examiner if no evidence of coronary artery disease is documented.
Wolff-Parkinson-White Syndrome (WPW) and ECG Pattern
The Wolff-Parkinson-White pattern is ECG findings without supraventricular tachycardia. Wolff-Parkinson-White syndrome is ECG findings with supraventricular tachycardia.
The aeromedical concern with Wolff-Parkinson-White Syndrome is sudden cardiac death. Sudden cardiac death is due to the occurrence of malignant arrhythmias from rapid anterograde action potential conduction in the setting of atrial fibrillation. Pappone et al. reports that sudden cardiac death occurs in 0.0 to 0.8% per year or 1.4% over a five-year period in patients with Wolff-Parkinson-White Syndrome, and reports that sudden cardiac death cannot be predicted. Other studies determined predictors of SCD as young age, male gender, inducible AVRT, multiple accessory pathways, and short refractory period of the pathway.
According to the United States Air Force waiver guide, Wolff-Parkinson-White Syndrome pattern is disqualifying for all classes. A waiver is possible after non-invasive testing shows low risk with annual follow-up. It is important to note that these guidelines continue to change and it's imperative to refer to the waiver guide for current aeromedical disposition.
Catheter ablation for Wolff-Parkinson-White Syndrome in an aviator requires a three-month grounding period and further evaluation by a cardiologist to stratify risk. 
Left and Right Bundle Block for all Classes of Medical Certification
LBBB will not occur in aircrew younger than 25 years of age. It is rare in aircrew 25 to 35 years old. Most occur in aircrew older than 35 years old.
Right Bundle block is a normal variant in young aircrew, and further investigation is not required.
The FAA requires cardiovascular evaluation as above, as well as, a graded exercise test (GXT). If there is no evidence of coronary artery disease, a medical certificate can be issued. Otherwise, deferral to the FAA is required.
Paroxysmal atrial fibrillation is of greater concern aeromedically than chronic atrial fibrillation.
In military aviation, rate control medications for atrial fibrillation are not compatible with the +Gz environment.
Chronic and paroxysmal atrial fibrillation requires an FAA decision.
Valvular Heart Disease
In a study by Strader JR and Kruyer WB, et al., regarding the efficacy of echocardiographic screening of Pilot Applicants, 20,208 screening echocardiogram were analyzed, and 294 or 1.45% were initially read as disqualifying for flight duties. The most common diagnosis was bicuspid aortic valve with mild or less aortic insufficiency 154 (0.76%), mitral valve prolapse with mild mitral regurgitation 51 (0.25%) and trileaflet aortic valve with mild aortic insufficiency 58 (0.29%).
About 70% of patients with bicuspid aortic valve develop aortic valve insufficiency and or aortic stenosis in their lifetime.
Pilots with healthy functioning bicuspid aortic valve are fit for unrestricted flying but periodic echocardiography to monitor complications is required. Aircrew with mitral valve prolapse with mild mitral regurgitation may be allowed to continue flying duties with regular surveillance for complications.
Coronary Heart Disease and Interventions
Usually disqualifying and requires FAA decision. A six-month grounding period is required by the United Kingdom CAA before a cardiologist assessment. In the United States Air Force guidelines, a pilot with history of previous myocardial infarction or revascularization has a potential to return to flying with a waiver on a case by case basis if he or she has no residual ischemia with normal cardiac function. The return to fly status is dependent on how much coronary artery disease is appreciated and the pilot is likely restricted to multiple-pilot aircraft. Coronary artery calcium (CAC) scoring is a useful screening criteria in asymptomatic patients, and is a much more effective tool than a treadmill stress test or functional cardiac imaging as these have poor positive predictive value. It even mirrors the results seen in invasive angiography. A CAC score of 10-99 was associated with a cardiac event of roughly 1%, so the current criteria to not need a waiver for flying in USAF standards is a CAC of <10.
The FAA’s acceptable blood pressure limit is a systolic blood pressure of less than or equal to 155 mmHg and diastolic blood pressure less than or equal to 95 mmHg.
The United States Aeromedical Consultation Service: hypertension for aeromedical purposes is defined as a three-day average systolic blood pressure greater than 140 mmHg or diastolic blood pressure greater than 90 mmHg.
Treatment of hypertension reduces the risk of stroke by 35 to 40%, myocardial infarction by 20 to 25%, and heart failure by 50%.
In aviators younger than 35 years old, causes of secondary hypertension like alcohol, drugs, obesity, and renal problems should be considered.
Modifiable risk factors should be considered as first-line treatment in aviators.
The FAA acceptable medications are alpha-adrenergic blockers, ACE inhibitors, beta-blockers, calcium channel blockers, angiotensin II receptor antagonist, direct renin inhibitors, and diuretics.
Unacceptable medications are centrally acting: clonidine, guanabenz, guanfacine, methyldopa, nitrates, and reserpine.
The USAF acceptable medications are hydrochlorothiazide (thiazide diuretic), chlorothiazide (thiazide diuretic), triamterene (potassium sparing diuretic), Lisinopril, Ramipril, Losartan, and Telmisartan (ARA).
Unacceptable medications in military aviation are beta-blockers, calcium channel blockers, and alpha-blockers. Atenolol, Nifedipine, and Amlodipine may be allowed on a restricted basis for a flight crew that does not operate in high +Gz environments.