Sudden Arrhythmic Death Syndrome
Dr. Simon Modi – Consultant Cardiologist/Electrophysiologist, Dr. Robert Cooper –
Cardiology Specialist Registrar, Suzanne Kelly – Heart Rhythm Specialist Nurse
Liverpool Heart and Chest Hospital
Sudden Arrhythmic Death Syndrome (or SADS) is the term used to describe a group of
medical conditions that lead to sudden, unexpected and life threatening instability of the
heart’s rhythm. In various forms it is also known as Sudden Cardiac Arrest (SCA), Sudden
Cardiac Death (SCD), Sudden Infant Death (SID) or Sudden Unexplained Death (SUD). We
will use the term Sudden Cardiac Arrest (SCA) for the purpose of this website.
In the majority of cases the unstable heart rhythm (arrhythmia) that develops is a rhythm
called Ventricular Fibrillation (VF), where the main pumping chambers of the heart (the
ventricles) lose all rhythm and regularity and start beating at heart rates in excess of 250
beat per minute. Ventricular fibrillation is incompatible with life and will cause sudden
collapse, seizure like activity and cardiac arrest (total loss of heart function). If diagnosed
quickly then cardiac massage (CPR) and a shock from a defibrillator can quickly restore the
normal rhythm of the heart and signs of life.
Sudden Cardiac Arrest is uncommon in young people. In the general population the chance
of SCA is highest in people with known angina, heart attacks or furred arteries but because
these conditions are rare in the under 35’s sudden cardiac arrest in the young tends to be
caused by other diseases.
What is the Difference between a Heart Attack and Sudden Cardiac Arrest?
Heart Attacks occur when the blood supply to the heart (coronary arteries) suddenly blocks
or narrows. It will commonly cause chest, throat or arm pain, heaviness or tightness.
Disruption to the blood supply will lead to damage to the muscle and cells of the heart. This
can lead to heart failure (loss of strength of the heart’s pump due to weak heart muscle) and
rarely can lead to disturbance of the heart rhythm. This can be in the form of slowing of the
heartbeat, quickening of it or cardiac arrest. Most people who have heart attacks do not
develop sudden cardiac arrest.
In contrast sudden cardiac arrest (SCA) relates purely to a sudden life threatening rhythm
disturbance of the heart (usually ventricular fibrillation) but does not need problems with
the arteries to be present. In particular, when SCA occurs in younger people, the chances of
it being caused by blocked arteries is much lower because blocked arteries are generally a
disease of the over 35’s (particularly male smokers with diabetes, high blood pressure, high
cholesterol or blocked arteries in the family). In the younger age group, SCA tends to be
causes more commonly by underlying diseases of the heart muscle or diseases of the
electric circuits in the heart.
How Common is SCA in the under 35’s?
Due to a number of factors it is difficult to know exact numbers. Several facts are known:
1. SCA occurs in approximately 3 in 100000 12-35 year olds competing regularly in
sport
2. Competing regularly in sport increases your chance of cardiac arrest by nearly 3 fold
3. Screening for cardiac conditions with a medical consultation and an ECG (EKG)
significantly reduces rates of SCA in the young.
4. Prompt resuscitation with CPR and defibrillation improves outcomes significantly
5. SCA in the young is undoubtedly more difficult for families, friends and communities
to adjust to than in older populations.
6. Some estimates suggest that SCA occurs in approximately 10 people under the age
of 35 every week in the UK
What Causes SCA?
Conditions causing SCA can be split into 4 main categories; abnormalities of the heart blood
supply, the heart muscle and the heart’s electrics. The 4th category includes ‘other
conditions’ that although not specifically heart conditions can have a ‘knock on’ effect on
the heart’s function. All conditions have a single common feature, that of the ability to
suddenly destabilize the heart’s rhythm and cause SCA.
Blood Supply
The heart is kept nourished by a series of arteries (coronary arteries) supplying its muscle
and electrical circuits. Sudden blockage of these arteries (as in heart attack) can destabilize
either heart pumping strength or heart rhythm as previously described. Blocked arteries
tends to be a disease of the over 35’s. It is more common in males, smokers and people
with a strong family history of blocked arteries (angina, stents or bypass surgery).
Conditions such as sugar diabetes, high blood pressure and high cholesterol also cause
blocked arteries.
Other than blockages, disruption to heart arteries can also occur in the form of spasm
(sudden narrowing of arteries reducing blood supply), sudden rupture and congenital
abnormalities of the origin of the arteries (can lead to compression of the blood supply). All
can cause SCA but are very rare.
Other than SCA, coronary artery disease can cause chest pain (chest, shoulder, throat, arm,
jaw or upper abdomen) or tightness on exertion. It can sometimes cause excessive
belching, shortness of breath or clamminess. Rest will often cause symptomatic relief
within 5-10 minutes.
Heart Muscle Diseases
Diseases of the heart muscle (cardiomyopathies) are the commonest cause of SCA in the
young. Two conditions Hypertrophic Cardiomyopathy and Arrhythmogenic Right Ventricular
Cardiomyopathy are the commonest causes of sports field related deaths (approx. 95%).
Other conditions such as Dilated Cardiomyopathy, Myocarditis and Infiltrative
Cardiomyopathies are also known to cause SCA.
Many of these conditions will be silent (i.e. no symptoms before SCA) however exertional
dizziness, faints, shortness of breath or chest pain can occur.
All of these conditions disrupt the muscle structure of the heart thereby disturbing the
normal passage of electricity though the heart. Under certain circumstances (e.g. illness,
extreme exertion) this can lead to SCA.
Electrical Diseases
Electrical diseases relate to the way in which the heart is ‘wired’ or the way in which the
heart cells manage electricity. Wiring problems that can lead to SCA relate predominantly
to a condition called Wolff-Parkinson-White syndrome in which an extra wire exists
connecting the top and bottom chambers of the heart (atria and ventricles). Other
‘electrical’ diseases alter the way in which each heart beat electrical signal is generated,
conducted and re-generated and under certain circumstances can lead to SCA. These
conditions include Long QT syndrome (LQT), Catecholaminergic Polymorphic VT (CPVT),
Brugada syndrome (BS), Early Repolarization Syndrome (ERS), Short QT syndrome (SQT) and
idiopathic ventricular fibrillation (IVF).
Most of these conditions can cause dizziness or faints but will largely go unrecognized until
SCA occurs. Certain triggers for fainting (other than exertion) such as large meals, fever,
swimming, alarm clocks, sleep and use of antibiotic or antihistamine medication can raise
suspicion of the presence of one of these conditions.
Other Causes
In certain sports, sudden impact to the chest (e.g. ball or physical contact) that happens at a
specific time during a normal heart rhythm can cause SCA. This happens even when no
underlying heart problems are present (i.e. completely healthy muscle, arteries and
electrics). This condition, called Commotio cordis, has been seen most commonly in sports
with high speed, small, solid balls (e.g. baseball). It cannot be medically screened for but
can be avoided by the use of impact protecting vests.
Other conditions that lead to SCA are rare and may have no direct relation to the heart.
These can include conditions such as the rupture of major blood vessels (aortic dissection),
to epilepsy & bleeding in the brain or imbalance of salts and minerals in the body. All these
conditions can alter the way in which oxygen and minerals are delivered to the heart or
brain leading to a ‘knock-on’ effect of SCA.
Screening
Screening, in the form of a medical consultation and an ECG has been in place for Italian
athletes since 1982. Italian death rates in 12-35 year olds competing regularly in sport
appear to have dropped significantly and now are approximately the same as those of nonathletes of the same age. This has become Italian law. Currently no regulations exist in the
UK sporting arena.
Graph showing decline in SCA of under 35 year old Italian athletes since the introduction
of a national screening programme in 1982. (Corrado D, Basso C, Pavei A, Michieli P,
Schiavon M, Thiene G. Trends in sudden cardiovascular death in young competitive
athletes after implementation of a preparticipation screening program. Journal of the
American Medical Association 2006;296:1593–1601.)
Medical consultations focus on the presence of abnormal symptoms during exertion
(dizziness, excess fatigue, faints, chest pain or palpitations) as the majority of athletes
having SCA will have had some prior warning signs, however subtle. The medical
consultation should also look for a ‘sinister’ history in the athlete’s family. This could
include something as obvious as SADS in the family, to more subtle signs such as
unexplained drowning or single vehicle car accidents, uncontrolled seizures despite
medication, cot death or recurrent miscarriages. Each of these features has been linked
with SADS.
ECGs are quick and easy tests to perform. They can be performed in less than 5 minutes by
sticking 10 leads across the patient’s chest and limbs and recording the heart’s electrical
activity. In athletic people a normal ECG is highly likely to represent a normal heart. An
abnormal ECG however may represent either a normal variant or underlying heart or
electrical disease.
Screening of all athletes is controversial mainly due to the rarity of SCA in the young and the
potential difficulty of distinguishing ECG changes in the ‘normal athlete’ from those in an
‘abnormal’ heart. Nevertheless, continued and advancing knowledge in this area seeks to
change these opinions slowly.