Medicine

Sudden Cardiac Arrest in Young Athletes

Sudden Cardiac arrest in the young may seem uncommon (2 deaths per 100,000 people) but is a fatal end for many passionate athletes. These tragedies appear to be unexpected as they are asymptomatic leading fans and spectators to wonder how a perfectly ‘healthy’ football player could suddenly collapse.

Athletes under the age of 35 predominantly have structural heart disease. This means that the defect or deformity is inherited or congenital. Whilst athletes over the age 35 usually have ischemic heart disease, meaning that the blood supply to their heart muscles is reduced.

According to a large study on 1866 deaths among athletes in the USA the most frequent causes are:

Hypertrophic Cardiomyopathy (HCM)

This is when the heart muscle (myocardium) becomes abnormally thick (hypertrophied) subsequently causing a difficulty for the heart to pump blood. Abnormal inherited genes usually cause the disease. Along with HCM these genes cause an abnormal arrangement of heart muscle cells called myofibre disarray. This disarray of muscle cells can lead to arrhythmia (abnormal heart beat) in some people. The majority of people with HCM have a form of the disease in the septum between the ventricles causing it to become enlarged and impede blood flow out of the heart (this condition can be called obstructive hypertrophic cardiomyopathy). Occasionally the HCM occurs without significant blockage of blood flow, nevertheless the left ventricle may become stiff. This limits the amount of blood the ventricle can hold and consequently the amount of blood pumped out to the body with each heartbeat (this condition can also be called non-obstructive cardiomyopathy)

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Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
This is a disorder causing the myocardium to break down over time, increasing the risk of arrhythmia and sudden death.
ARVC is a result of the mutation of at least 8 genes. The majority of these genes are involved in the function of desmosomes (structures that connect muscle cells to one another). Desmosomes strengthen the myocardium and contribute to signaling between neighboring cells.
The mutations in the genes that result in ARVC often disable the desmosomes causing the muscle cells to detach from one another and subsequently die, especially when the heart muscle is under stress such as during vigorous exercise. The damaged myocardium (around the right ventricle) is gradually replaced by fat and scar tissue, which in turn stretch the wall of the ventricle preventing the heart from pumping blood normally. These changes can also alter the electrical signals that regulate the heartbeat, which can lead to arrhythmia. This arrhythmia may also lead to ion channelopatheis meaning that the muscle fibers no longer function normally due to an abnormal amount of ions.

Dilated Cardiomyopathy

This disease affects both the hearts ventricles and atria. It often begins in the left ventricle (the hearts main pumping chamber) and is when the myocardium begins to stretch and become thinner (dilate). This causes the chamber to enlarge meaning that the heart can no longer contract normally, thus cannot pump blood very well. Over time the problem usually spreads to the right ventricle and eventually the atria as the problem worsens. Furthermore the heart becomes weaker and the probability of heart failure increases exponentially. Dilated cardiomyopathy may also lead to heart valve problems, arrhythmias and blood clots in the heart caused by stagnant blood.

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Wolff-Parkinson-White Syndrome
Those with this congenital syndrome have an extra electrical pathway between their atria and ventricles, which results in a rapid heartbeat (tachycardia).
A normal heart possesses a sinus node (a mass of tissue in the right atrium) that produces electrical impulses that generate a heartbeat. These electrical impulses pass across the atria resulting in muscle contractions that pump blood in the ventricles. The impulses then arrive at a cluster of cells known as the atrioventricular node (AV node), this is the only bridge for the signals to travel from the atria to the ventricles. The AV node slows down the signal before passing it to the ventricles, this in turn creates a slight delay which allows the ventricle to fill with blood. Eventually when the electrical impulses reach the ventricle, muscle contractions pump the blood to the rest of the body.
However the heart of a person affected by WPW has an extra electrical pathway between the atria and ventricles, allowing the electrical impulses to bypass the AV node. When the electrical impulses travel through the extra pathway they are not slowed down thus the ventricles are activated too early (pre-excitation).
-Looped electrical impulses – In WPW the heart’s electrical impulses travel down one pathway and up another. This results in an electrical loop of signals called AV reentrant tachycardia, which sends impulses to the ventricles at a rapid rate causing them to pump very quickly, causing rapid heartbeat.
-Deorganized electrical impulses – If the electrical impulses don’t begin correctly in the right atrium, they may cross the atria in a disorganized way. This results in the atria beating quickly and not in time with each other (atrial fibrillation). These disorganized signals coupled with an extra pathway can cause ventricles to beat faster subsequently not allowing enough time for the ventricles to fill up with blood. As a result not enough blood is pumped to the body.

HCM, ARVC and DCM can all be diagnosed using a magnetic resonance imaging (MRI) scanner. Additionally WPW syndrome can be detected using an electrocardiography (ECG).

In conclusion all these conditions are diagnosable and the many sudden deaths caused by them could have been avoided if thorough cardiac screening was given to these athletes.

http://www.mayoclinic.org/diseases-conditions/hypertrophic-cardiomyopathy/symptoms-causes/dxc-20122103

http://ghr.nlm.nih.gov/condition/arrhythmogenic-right-ventricular-cardiomyopathy

http://www.heart.org/HEARTORG/Conditions/More/Cardiomyopathy/Dilated-Cardiomyopathy_UCM_444187_Article.jsp#.Vl4ZAGThAy4

http://www.mayoclinic.org/diseases-conditions/wolff-parkinson-white/basics/causes/con-20043508

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