Introduction: Issues with Cardiovascular Screening of Athletes
There is a low incidence of cardiovascular problems in athletes. However, any untoward event in this population is disconcerting as athletes are considered to be the healthiest segment of our society. Sudden death of popular or famous athletes, especially in team sports that have a large fan following, assume a high public profile and arouse intense interest. It is always a great personal tragedy, but news about these events tends to be disproportionate to their actual impact on public health.
Athletic deaths nationally are difficult to tabulate because of the large number of athletes involved. In addition to the estimated 4.5 million school and college athletes, there are a large number of recreational athletes. Only a very small proportion of participants in organized sports in the US are at risk for death. Estimates range form 1:100,000 to 1:300,000 among high school athletes. For older athletes these range from 1:15,000 among joggers to 1:50,000 among marathon runners.
Moral, ethical and sometimes legal considerations compel and justify organizations and society as a whole to think of ways to screen athletes. However current recommendations for screening have to take into account the low prevalence of cardiovascular abnormalities and that sudden cardiac death is an infrequent event in this population. A complete, honest, careful personal and family history with a physical examination designed to identify high risk individuals is therefore recommended as the best available and practical method.
These recommendations also limit the role of non-invasive diagnostic tests, which may be more effective for detecting certain diseases. An important part of the problem is the potential for false positive results in a population with a low prevalence of detectable disease.
A false positive result can cause emotional and financial burdens for individuals, teams and institutions with the requirement for additional testing. Borderline tests cannot be completely resolved in some athletes until they stop competing for some time. False negative results occur often as the disease may not be evident or completely expressed with non diagnostic findings at the time of the test. Studies done with systematic screening of athletes with non-invasive testing only detected a few potential lethal abnormalities. These tests are therefore not warranted given the overall cost/benefit ratio.
Screening of athletes should not give a false sense of security to doctors, athletes or the general public. The standard recommendations of History & Physical cannot reliably identify many lethal cardiovascular abnormalities. Indeed, the addition of non-invasive tests may not identify all the abnormal people as detailed above. It is therefore unrealistic to assume that screening can reliably identify all asymptomatic athletes at high risk.
Echocardiography
Echocardiography is a complete ultrasonic examination of the heart. It involves imaging the heart in two dimensions to get the sizes of the ventricular cavity and the left ventricular wall. Motion of the walls and thus the function of heart can be clearly appreciated. The opening and closing of the valves can be seen and any abnormality detected. Blood flow direction across the valves can be evaluated using doppler color flow imaging. The intensity of any obstruction to the blood flow across a stenosed valve can be calculated and the area of the valve determined using doppler echocardiography.
Similarly, color flow imaging can help quantify the amount of blood leaking through an abnormal valve. Certain morphologic abnormalities like dysplasia and asymmetric hypertrophy (enlargement) of the heart can be easily documented.
The most common reason for an echo examination is referral from a physician for evaluation of an abnormal murmur detected on physical examination. A history of syncope or near syncope in an athletic individual especially in conjunction with an outflow murmur, prompts an examination to look for Idiopathic Hypertrophic Cardiomyopathy.
Referral may also be made for known family history of Hypertrophic Cardiomyopathy or history of sudden death in the family. Detecting Marfans habitus with a murmur may prompt a physician to study the aortic valve or aorta clearly. Severe fatigue with inability to work in the setting of a previous viral illness in conjunction with signs of heart failure may signify a cardiomyopathy with diminished contractility of the heart. This can be clearly seen on an echocardiogram.
Although the echocardiogram is an excellent test to see the morphology of the heart and to distinguish common causes of sudden death in athletes, it is not indicated as a screening test.
Common Abnormalities of the Heart
Aortic Stenosis
This is stenosis or narrowing of the aortic valve 0and is detected on exam with a systolic murmur heard in the aortic area. This condition in young people is usually congenital, specially with bicuspid aortic valves and is usually detected during childhood. It can sometimes be caused by rheumatic fever, which is uncommon in the US. It limits the flow of blood out of the heart and may cause symptoms of fatigue, syncope or chest pain. Occasionally it is seen in asymptomatic athletes.
The echocardiogram shows decreased mobility of the aortic valve with a small opening. The valve is often thickened and calcified. Blood flow across the valve is turbulent on color doppler with high velocities across the small orifice. These velocities reflect a large pressure gradient across the valve. The velocity can be measured by doppler and an effective area of the valve can be calculated.
Aortic Regurgitation
The aortic valve leaks blood back into the heart after each contraction as it fails to close completely. It causes a characteristic diastolic decrescendo murmur on examination. It may occur in conjunction with aortic stenosis. It is also occurs commonly after rheumatic fever. Marfans syndrome with an enlarged aortic root can also cause regurgitation.
Echocardiogram shows a large jet of blood leaking back across the valve from the aorta. The breadth of the jet at the aortic orifice gives an idea about the severity.
Mitral Stenosis
This is a rare lesion and occurs in young people after rheumatic fever. Rarely, it is congenital. In the elderly population it is usually secondary to degenerative disease. It causes exertion shortness of breath, and when severe causes heart failure. The murmur is diastolic with accentuation just before S1.
Echocardiogram shows an enlarged left atrium and thickened poorly mobile mitral valve leaflets with a small opening during diastole. The anterior leaflet assumes a characteristic J shape on opening with doming of the valve. The pulse doppler shows slow exit of blood across the valve. The area can be calculated by the slope of this trace.
Mitral Valve Prolapse
This is a very common abnormality in young people, especially in women. One study in college athletes showed a 21% incidence in women. Occasionally there may be mild mitral regurgitation with the prolapse. The cause is redundant mitral leaflet tissue with myxomatous degeneration. It is a frequent finding in patients with Marfans Syndrome. In the majority of patients the cause is unknown but it appears to be a genetically determined collagen tissue disorder.
It commonly causes a mid to systolic murmur following a mid or late systolic click from the prolapsing mitral valve. The mitral valve on closure prolapses beyond the annulus of the mitral valve into the left atrium on systole. This can be clearly seen on the echocardiogram. Prolapse of other valves may also be evident.
Patients may be asymptomatic or may have palpitations(extra beats) and atypical chest pain. This common condition rarely causes any problems. Antibiotic prophylaxis before dental procedures is recommended in those with severe prolapse or a significant murmur. Occasionally drugs to slow the heart may be used in people who have unbearable palpitations.
Mitral Regurgitation
This causes a clearly abnormal murmur at the apex of the heart that lasts throughout contraction. This can be picked up during the physical examination. The valve leaks blood back from the ventricle into the left atrium. This causes symptoms of fatigue and shortness of breath on exertion.
Rheumatic heart disease causes one third of all Mitral Regurgitation. It may also occur as a congenital anomaly or as a degenerative disease. It may occur after marked dilation of the ventricle after myocarditis. In hypertrophic cardiomyopathy the enlarged muscular wall may pull the leaflet forward and cause mitral regurgitation. Degenerative changes following mitral valve prolapse or myocardial infarction may also cause regurgitation. It may also occur following an infection of the valve.
The echocardiogram shows a large amount of blood flowing backwards into the left atrium.
Physiologic Left Ventricular Hypertrophy
This is a common finding in athletes, specially those who train at high intensities for competitive sports. The walls of the heart are thickened and the cavities are enlarged in size, out of proportion to the body size.
The heart is adapted to work at high intensities and to pump more blood than an untrained person. However contractility is normal. The diastolic property (the relaxation of the heart) is normal. This is in contrast to the diastolic properties in pathological hypertrophy, for example in hypertensive subjects. An estimate of the diastolic filling can be made by doppler blood flow across the mitral valve. This has always been shown to be normal in athletes.
It may be difficult to distinguish physiologic enlargement from Hypertrophic Cardiomyopathy.
Hypertrophic Cardiomyopathy
This is an abnormal enlargement of the heart as in left ventricular hypertrophy detailed above. It is however very important to distinguish from physiologic hypertrophy as it is associated with a high mortality. It is one of the most common causes of death in young athletes. Furthermore competitive sport is prohibited once this condition is diagnosed as it may lead to death. People with this abnormality have a propensity for going into an abnormal heart rhythm, specially during exercise, which may cause death. The abnormal muscle can obstruct blood flow out of the heart and pull on the mitral valve leaflet causing a leak across the valve, especially during forceful contractions that occur with exercise. This causes a characteristic ejection murmur at the left sternal border that increases with exercise and dehydration.
The obstruction to blood flow during contraction causes syncope or light headedness, dizziness, and a feeling of passing out on exertion. Occasionally patients may report palpitations.
This condition may be inherited and others in the family may have it. It may be a cause of unexplained death in the family at a young age. It is inherited as an autosomal dominant trait.
Distinguishing features from hypertrophy include:
- The loud systolic murmur from the obstruction to blood flow.
- A fourth heart sound
- A bizarre EKG showing severe hypertrophy and other abnormalities
- On Echocardiogram the hypertrophy is not symmetric with contiguous segments not thickened to a similar degree.
- The contour of the hypertrophic wall is irregular in contrast to smooth walls in physiologic hypertrophy.
- The maximum thickening of the left ventricular wall usually does not exceed 16 mm in physiologic hypertrophy.
- The left ventricular cavity is enlarged in physiologic hypertrophy. It is normal or reduced in size in hypertrophic cardiomyopathy.
- The diastolic doppler flow pattern is abnormal in 80% of the patients with cardiomyopathy. It is always normal in physiologic hypertrophy.
- Changes of physiologic hypertrophy show regression to normal with cessation of training, while the pathologic form shows no change.
Marfans Syndrome
This is an inherited disorder, due to a gene mutation, causing a person to present with long thin extremities, reduced vision due to dislocation of the lens of the eye and aortic aneurysms- dilation of the root of the aorta. It is important in athletes as the root of the aorta may rupture causing sudden death. Marfans can usually be diagnosed from body habitus on physical exam in conjunction with the family history.
Echocardiogram shows dilated aortic root with aortic regurgitation. Mitral valve prolapse may be seen
Myocarditis-Dilated Cardiomyopathy
Occasionally viruses may infect the heart and cause weakness of the heart muscle. The walls become thin and flabby and the cavity of the heart becomes enlarged. The heart does not contract very well.
Athletes can die, usually from an arrhythmia in this condition. They usually present with fatigue and exertional weakness.