INCREASINGLY, more marathoners are doing pre-participation health assessments for underlying heart disease. A seasoned marathoner with sub three-hour runs, Ms A, decided on a heart assessment when she became more breathless during exercise. To her surprise, she had an inherited condition in which a segment of her major heart artery was deeply tunnelled into the heart muscle (myocardial bridging) resulting in constriction by the heart muscle with each heartbeat.

Another physical enthusiast, Mr B, was preparing for his annual physical fitness assessment but felt unusually breathless during physical exertion, and decided to have his heart assessed. He had abnormal positioning of his heart arteries (anomalous coronary arteries), causing one of his major heart arteries to be “squashed” between the main artery of the body (aorta) and the main lung artery, which can result in decreased blood flow to the heart muscle. Both understood that the underlying conditions could cause sudden death (SD) and made adjustments to their lifestyles.

Besides marathoners, another category of young individuals who come for health screening are those embarking on competitive sports or those about to enrol in National Service.

Pre-participation screening

Studies published on the Italian mandatory pre-participatory screening programme for all youths participating in competitive sports showed that the programme reduced the incidence of SD in the young by 90 per cent. While SD in the young is often unexpected, autopsy studies have shown that the majority have an underlying heart condition. Hence, SD can potentially be prevented if the underlying heart disease is detected early.

Adaptable hearts

Understanding how the heart adapts to physical exercise will help those participating in competitive sports make decisions on the type and intensity of exercise. The heart adapts differently to the type of exercise to which it is exposed to.

Exercises can broadly be divided into two main categories:

• Endurance exercise, which include cross-country running, marathon, football, basketball and swimming;

• Strength-building exercise, which include weight-lifting, wrestling or shot put.

Exercises such as cycling and rowing have elements of both.

During endurance exercises, the body adapts to the significantly increased oxygen demand by increasing the blood volume pumped out by the heart to increase oxygen circulation throughout the body. Over a prolonged period, the heart chambers will adapt to the increased blood volume by enlargement of the heart chambers, a finding seen in almost 50 per cent of highly trained athletes. Occasionally, this may be accompanied by an increase in the thickness of the heart wall. Fortunately, these changes in the heart may be reversed when they cease the exercise programme.

In contrast, strength-building exercises increase body oxygen usage and blood volume pumped by the heart minimally, with less impact on the size and thickness of the heart-pumping chambers.

The athletes that show the most significant changes in the heart size or wall thickness are top athletes in the areas of long-distance running, cycling, swimming, rowing and skiing. In about 2 per cent of these athletes, the left upper heart chamber can be substantially enlarged and in less than one per cent, atrial fibrillation – an abnormal rhythm associated with progressive enlargement of the left upper heart chamber and increased risk of stroke – can occur.

Abnormal patterns

In about 40 per cent of the top athletes, the changes in the heart are accompanied by abnormal patterns on their electrocardiogram (ECG), a recording of the electrical heart pattern. An abnormal ECG should alert the person to the need for more detailed assessment of his heart. These investigations may include 24-hour continuous ambulatory ECG (Holter) monitoring and, in these top athletes, Holter monitoring has shown serious life-threatening heart rhythms (ventricular tachycardia) associated with SD. Some studies have also reported evidence of a transient heart muscle injury and impairment of the heart function immediately after vigorous endurance exercises such as triathlons and marathons.

In a large number of these individuals, these changes are reversible. However, it has been reported that for ultra-marathon runners, frequent marathon running over a prolonged period may be associated with permanent scarring of the heart.

Underlying condition

Vigorous exercise increases the risk of SD in teenagers and young adults by almost three-fold. The majority of SD victims have an underlying undetected heart condition which predisposes them to the development of life-threatening heart rhythms (ventricular tachycardia and fibrillation) that are triggered by vigorous exercise.

In the US, hereditary thickening of the heart muscles (hypertrophic cardiomyopathy or HCM) has been reported to be the commonest cause of SD in young athletes. Other inherited conditions include underlying anomalies of the heart arteries, myocardial bridging, degenerative heart muscle disease (arrhythmogenic right ventricular dysplasia or ARVD), and premature narrowing of the heart arteries. In Italy, the commonest cause of sudden death in the young is ARVD. In 2 per cent of these SD victims, the heart was normal on autopsy and death was caused by hereditary abnormal heart rhythm syndromes (long QT syndrome, Brugada syndrome and Wolff-Parkinson-White syndrome). In the large majority, the underlying mechanism of death is the sudden onset of life-threatening abnormal heart rhythms arising from the lower heart chambers (ventricular tachycardia or fibrillation).

Another mechanism of death is blunt trauma to the neck or chest. Blunt trauma to the neck causing near-instantaneous death is best illustrated by injury inflicted on the neck by a puck projectile being hurled at high speed during ice hockey, resulting in sudden backwards bending of the neck causing a tear of an artery (vertebral artery) traversing into the brain at the site where it passes through an access opening in the spine bone. The resulting tear results in bleeding into the brain and death. The more common mechanism is blunt trauma to the front of the chest without any damage to the bone or heart muscle, resulting in life-threatening ventricular fibrillation (commotio cordis). The blunt force may result from projectiles (such as a hockey puck or a baseball) or body contact (such as martial arts or physical collision between two players). Experimental studies have shown that blunt trauma over the heart area during a specific window of the heart electrical cycle (when the electrical system is recovering after the completion of one heart beat) can trigger the onset of ventricular fibrillation. About 85 per cent of those with commotio cordis do not survive; survivors are those with immediate access to resuscitation and defibrillator machines.

Inexpensive ECG

Those embarking on competitive sports or endurance events such as marathons should consider getting themselves checked. Besides assessing for the presence of risk factors for heart disease, a simple and inexpensive test is an ECG which will be helpful in detecting underlying heart diseases. If there should be suspicion of heart disease, a 24-hour Holter ECG test will be useful for detecting rhythm abnormalities and an ultrasound scan of the heart (echocardiogram) will be useful for detecting heart chamber enlargement or heart muscle abnormality. These two simple and easily available tests cannot detect those with abnormal heart arteries. For the young where X-ray radiation should always be avoided, magnetic resonance imaging (MRI) scanning of the heart arteries is an option as it can diagnose those with myocardial bridging (as in Ms A) and anomalous coronary arteries (as in Mr B) without the need for any injection or any X-ray radiation. MRI of the heart is also extremely useful for confirming the presence of the two commonest causes of SD in the young, namely HCM and ARVD. In top athletes where changes in the heart are common, the challenge for physicians is to determine whether the abnormal findings are a result of extreme exercise or underlying heart diseases. In countries where there are significant economic incentives for top athletes, making the right diagnosis is imperative as disqualification from competitive sports will impact the health positively but may have significant detrimental financial implications.