The heart in endurance performance: How robust is this machine ?

Myocarditis is one of major threats to the heart of an endurance athlete

If we consider how long a heart is able to beat without taking a break, this muscle can be called robust without any doubt. But during a life time this muscle is exposed to many risk factors beside the fact that congenital defects of different extent may play a crucial role in initiating cardiac issues sooner or later in life. Basically, a good life style of which physical activity is one pillar, is strengthening and securing your heart’s condition, but if the muscle is stressed too much and you overlook the early symptoms of overreaching, then the consequences may be serious or even lethal. The following chapter is meant to give an idea about the heart’s robustness on the one hand, and its fragility on the other.

The heart is a complex machinery that cannot be thoroughly explained and presented in a blog post. It is important to know that the heart is not only a muscle but an organ with a very sophisticated network of nerves, that makes it beat the way it does, and a net of vessels that supplies it. The heart pumps supplies into the body, and it has to care for its own supplies likewise. As a hard working engine the heart muscle reacts very sensitive, if the supplies (e.g. oxygen) for itself are not sufficient. A deficit in supplies regardless of the cause quickly leads to symptoms such as chest pain or breathlessness, that make you cut down on your performance. Usually, the scariness of these symptoms lets you slow down before permanent lesions afflict the heart. As a rule of thumb for you as an athlete, the skeletal muscle shuts down before the respiratory muscles and the heart muscle shut down. This is one mode how the heart is protected.

The heart is secured – let’s put it this way – by several safety belts

These safety limits function perfectly as long as the heart is healthy, in the case of a sick heart the situation changes. The difficulty is to differentiate between the symptoms that – due to the integrated safety margins of the healthy heart – make you feel your performance limits and the symptoms that a sick heart presents and may lead to a detrimental outcome, if interventions don’t happen in time or are inadequate. After arduous exercise breathlessness, dizziness, tachycardia, collapse or minor ECG anomalies may be harmless in most cases, in rare cases they may be not.

Before we dive into some pathophysiology around myocarditis,
some probabilities that may be of interest for you.

There are no reliable statistics around cardiac issues among endurance athletes. Most of the athletes dying of sudden cardiac death are under 20 years old, and autopsies have shown that this was due to congenital structural muscle failures or deformities that have not been detected until it was too late. The data from the US also suggests that the death rate among young athletes due to sudden cardiac arrest is higher than among sedentary youngsters. Stress factors such as strenuous workouts on the young heart with undiscovered structural muscle defects appear earlier in athletes than in non-athletes, even so the figures are tiny. The picture changes as athletes grow older and acquired heart problems may become an issue such as arrhythmias, atherosclerosis and dilated or hypertrophic cardiomyopathies etc. Cardiac death due to cardiac infarction and/or affected coronaries may occur in the late thirties already and increases with age.

Be it as it may, many an endurance athlete worries about his/her heart condition as being aware of the fact that stress and workload on their heart muscle are quite enormous. Nevertheless serious heart diseases in young athletes such as sudden cardiac arrest are rare. But the heart can be affected on the long run, if you are not listening to the early, still benign signs of a sick heart such as drop in performance combined with arrhythmic heart beats. This is where myocarditis comes in, an illness that often slowly creeps in and is very difficult to diagnose precisely, and if finally diagnosed, it may be too late and force you into a long break. Myocarditis is the most common acquired cardiac disease in the young population. 52% of the cases occur in young adults (20 to 39 years). Susceptibility declines with increasing age.

Myocarditis – a sneaky disease difficult to diagnose

Myocarditis may be responsible for cardiac dysfunctions such as arrhythmias, congestive heart failure (the heart muscle is dilated and cardiac output is inefficient) or even sudden death. This inflammatory disease can be acute or chronic, focal or attack the muscle diffusely. What you have to keep in mind that even if mended the scars that a myocarditis leaves behind can cause fatal arrhythmia. This is the reason why the inflammation needs to be controlled as fast as possible. This can be achieved by strengthening immunity, or in case of a bacterial infection with antibiotics. Usually a myocarditis is one of the sequelae of an infection such as teeth, upper respiratory tract, tonsils or appendicitis etc. that have not been treated properly or neglected.
The diagnostics are by far not trivial. Clinical manifestations of myocarditis in athletes may range from asymptomatic to focal inflammation to severe congestive heart failure. Myocarditis can be the cause of atrial or ventricular arrhythmias. The heart may appear normal in ECG, sonography or x-ray or it may mimic a myocardial infarction with the typical precordial chest pain. A drop in performance may be the only sign of an ongoing myocarditis. Blood testing for viruses or bacteria often remain obscure and unspecific, and even MRI is lacking the diagnostic accuracy. Syncope or sudden death after strenuous exercise may then be the sad first sign of the deleterious disease.

I think that listening carefully to an athlete’s history that led to a drop in performance may help to or rule out or diagnose a myocarditis in time, and spare the athlete a endomyocardial biopsy which is considered as the gold standard for diagnosing myocarditis.

Myocarditis has to be suspected, if the athlete presents fatigue, dyspnoea, palpitations, precordial discomfort, especially if their is a recent history of flu-like symptoms.

Exercise for the good or bad?

Generally spoken, physical exercise is the most healthy approach avoiding illnesses of all kinds. It boosts immunity and makes you more stress resistant. But if you overdo it then either a single bout of exhausting exercise or a persistent overtraining can increase your susceptibility for a broad spectrum of infections, and if ignored they finally may lead to a protracted infection. Infections of this kind increase the probability to come down with a myocarditis. If an infectious agent* remains active in your body, the heart may become affected as the immune system is not able to contain the process, the microbes spread, the local immune response turns into a smoldering inflammatory process. A strong immunity thus is one of the prerequisites to prevent this disease.

*some microbes of which we know that they preferably involve the heart: Adenovirus, Cocksackie virus. Epstein-Barr virus, Respiratory syncytial virus, Varicella virus, Arbovirus; bacteria such as Clostridia, Salmonella, Staphylococcus; but also fungi and spirochetes such as borrelia may affect the heart.