Exercise as it relates to Disease/Exercise and sudden cardiac death

Background
Sudden Cardiac Death (SCD)is defined as an unexpected death due to a cardiac cause occurring in a short period of time, in a person with, or without, a pre-existing heart condition. It is estimated that up to 80,000 people die from sudden cardiac death each year in Australia and New Zealand. The most common cause is cardiac arrhythmia.

In Athletes
SCD in athletes although well documented and publicised, is actually very rare, with an incidence rate of only 1:20,000 competitors. SCD in athletes can occur for many reasons. The following list was obtained from the Department of Cardiological Sciences.

General Population
Sudden cardiac death is uncommon in young people, and is often during physical activity. As well as the previous list of conditions, it can be caused due to inflammation of the heart from an illness or virus and very rarely it can be caused by a blow to the chest from a tackle or ball. There is a loss of flow out of the aortic valve due to obstruction of flow, caused by hypertrophic obstructive cardiomyopathy (HOCM), which is categorized as a thickening of the muscle just inferior to the opening of the aortic valve, known as the left ventricular outflow tract (LVOT). Often this goes undiagnosed until it is too late, a simple and easy way to test for this would be to do screening echocardiograms on all teens. Commotio cordis, causes ventricular fibrillation if it strikes the heart at a precise time in the electrical cycle. The majority is in older adults, which is still only 0.1-0.2% of the United States population.[2]

Explanation
Although sometimes a lack of symptoms in SCD, evidence shows that a well-constructed prescreening will help identify population groups that may be at risk. Protocols could initially include a physical examination, both personal and family history of the athlete and a twelve-lead electrocardiogram (ECG). Additional screening tools like echocardiography and other exercise testing are usually only indicated if the tests results in a positive initial assessment. These prescreening tools along with medical advice can assist individuals with making their decisions as to whether they will participate in sporting activities or not. [6]One protocol will not definitely detect every condition related to SCD [6], but can identify many. Evidence suggests that thorough physical assessment and history will detect 2-6% of underlying cardiac abnormalities, and with the addition of the ECG the sensitivity is increased by 50%. It is important to remember not all conditions related to SCD can be identified by prescreening including an ECG. [7] In Italy a twelve-lead ECG is used as a part of pre-participation screening since 1982. It has decreased the rate of SCD in Italian athletes by 80%. [7] An ECG is not yet routine for pre-participation screening in America. Some argue it is "not feasible"[7] because of minimal trained physicians, large population that is eligible and lower prevalence of SCD.[7] However, there is debate about "mandatory exclusion of athletes"[6] if a positive result is obtained. This can lead to complications with life insurance and future contracts for the athlete,[6] not to mention a major effect on their wellbeing and pressures of competing.[6] This controversial topic has not yet been resolved.

Risk Factors
Coronary heart disease is seen in 80% of SCD episodes[2] and remains the biggest risk factor. Underlying heart conditions like hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, coronary abnormalities etc. prove to predispose a person to SCD.[7] Males seem to have greater risk of SCD than females (75%)[2] and the risk of SCD increases with age. [8]Other risk factors include hypertension, intraventricular conduction block, elevated serum cholesterol, glucose intolerance, decreased vital capacity, smoking, relative weight and heart rate.[3] In the ongoing Framingham Heart Study in Massachusetts, Smoking increased the annual incidence of sudden cardiac death by more than double than that of the non-smoking population present with other risk factors. Warning signs to seek medical attention include but are not limited to: unexplained fainting, shortness of breath, excessive unexplained exertional chest pain, discomfort or fatigue, prior recognition of a heart murmur, elevated systemic blood pressure and any family history of sudden cardiac death.[12]There are little to no risks associated with using ECG as protocol preparticipation screening. It is non-invasive and no evidence yet supports that it is harmful to patients. The biggest risk associated with ECG is the possibility of a false positive. [7]

Recommendations
Physical exercise is beneficial to cardiovascular health, and has been shown to decrease risk of coronary artery disease and sudden cardiac death. However, a small but significant proportion of athletes have a possible increased risk of SCD because of exercise, but it often just serves as a trigger to an underlying cardiac disease. Although the process is costly and time-consuming, a gene test can determine if a gene abnormality for a person is SCD related. Ideally, every athlete should be screened for their cardiovascular health. The American heart association disagrees with mass screening using 12 lead EGC's or echocardiography due to the high number of the population who do not have any underlying problem, the posibility of too many false positives being indentified and that not all conditions causing sudden cardiac death have ECG findings Other possibilities to decrease the risk of death would be a general increase in CPR training and more defibrillation devices available so that should a sudden cardiac event take place, the person can be revived quickly. Alternatively, people who are considered high risk or have had cardiac abnormalities revealed should consider an implantable cardioverter deﬁbrillator (ICD). These devices are becoming more accessible, and the increase in their use should continue.