Causes of SADS
The conditions for which we screen fall under two categories: cardiomyopathies and channelopathies. Cardiomyopathies are diseases that primarily affect the heart muscle. Diseases that affect the microscopic channels that mediate
and regulate the heart's electrical signals are known as channelopathies.
What are Cardiomyopathies
Cardiomyopathies are diseases, which affect the muscle of the heart. They can either cause the heart muscle to become abnormally thick (such as in hypertrophic cardiomyopathy), or to become abnormally thin, causing the heart to
dilate or enlarge (as in dilated cardiomyopathy). There are many causes of cardiomyopathy, which are not inherited, and these include cardiomyopathy due to high blood pressure, cardiomyopathy due to coronary artery disease, and cardiomyopathy due to viral
infections. However, if your doctor has diagnosed you with a hypertrophic cardiomyopathy ("HCM" or "HOCM"), or if you have a dilated cardiomyopathy with no clear cause, it may be appropriate for your family to come for family screening. Your cardiology doctor
can help advise you on this.
Another type of cardiomyopathy preferentially affects the right side of the heart, and can cause arrhythmias (abnormal heart rhythms which can lead to symptoms and / or collapse). This is arrhythmogenic right ventricular cardiomyopathy (ARVC or ARVD), and this
condition is usually only diagnosed at specialist centres. Family screening is advised for ARVC.
Symptoms of cardiomyopathies can range from hardly any or no symptoms, to breathlessness, chest pain, palpitations, and collapse or near-collapse.
What are Channelopathies
Channelopathies are inherited diseases that affect the microscopic channels, which regulate the heart cell's electrical impulses. These impulses are the means by which the cells send coordinated information through the heart
muscle. They tell the heart muscle when to contract and therefore when to pump blood about the body. If the pattern of the electrical impulses are abnormal due to a channelopathy, such as the long QT syndrome or the Brugada syndrome, you may be more likely to
develop arrhythmias, and to have collapses or black outs. In between collapses or black outs, you may have no symptoms at all.
Many SADS deaths are thought to be due to channelopathies. Because the changes in the heart cells are so tiny, channelopathies cannot be diagnosed on a standard post mortem evaluation. The diagnosis can only be made by examining family members, by examining ECGs
that the person may have had before they died, or by sending a tissue sample from the person for genetic testing.
What are arrhythmias
Although the heart is a very complex organ, its fundamental function is to pump blood to the lungs and to the body's other organs. This blood brings oxygen to the organs, to allow them to function properly. The heart therefore is
made up of a lot of tiny muscle cells, called "myocytes", which can contract together in a concerted action to create the "squeeze" of the heart. The myocytes are most numerous around the ventricles, which are the two lower chambers of the heart.
How do these myocytes know when to contract up and squeeze the heart? In fact, each myocyte can generate a small electrical current by moving sodium and potassium ions across its cell membrane. These currents are the "language" that the cells use to communicate
with each other, and such a current running through the myocytes will trigger "cardiac depolarisation" and cause the heart to pump the blood.
Therefore, small electric currents run through the heart muscle naturally, and the sequence of these currents can be thought of as the heart's "rhythm". The rhythm normally follows a set pattern though the heart. However, sometimes this rhythm can become
disrupted, and this is called an arrhythmia. Some types of changes in heart rhythm can be simply normal variants, such as occasional extra beats or "premature ventricular contractions" (PVCs). Other changes in heart rhythm can cause symptoms, and require
medication or treatment, but in themselves are not life threatening. These would include such rhythms as affect the top chambers of the heart, called the atria, such as atrial fibrillation.
Arrhythmias can also affect the heart's ventricles, which as we have said are the main pumping chambers of the heart. Ventricular tachycardia or VT occurs when the myocytes around the ventricles start to discharge electrical currents, which then form an
electrical circuit, and can cause very fast heart rates. Sometimes VT will only last for a few seconds, but a longer episode of VT can cause people to feel weak and breathless, to feel a sever chest pain, or even to collapse. Prolonged VT can lead to ventricular
fibrillation or VF. In VF, the electrical signals have become so mixed up that the heart cannot beat at all. A person with VF will collapse and will have no pulse. Unless the person is treated with a defibrillator, VF is fatal.
Arrhythmias such as VT and VF are rare. They are most common amongst older persons with coronary heart disease (caused by atherosclerotic plaque in the coronary arteries). People are more likely to get atherosclerosis if they smoke, have high blood pressure and
high cholesterol, and have diabetes. That is why it is so important to eat a healthy, low fat diet, take at least moderate exercise, and not to smoke tobacco products. However, there are some very rare conditions of the heart that can predispose to VT and VF in
people without atherosclerosis, and these conditions can cause people to collapse and even die with no warning. This is known as SADS (sudden arrhythmic death syndrome) and the Mater Misericordiae Family Heart Clinic aims to reduce these deaths through targeted
A dilated cardiomyopathy (DCM) can occur when the ventricles of the heart become enlarged and are unable to contract as efficiently as normal, leading to symptoms of breathlessness, fatigue, breathlessness on lying down flat, and
ankle or leg swelling. DCM is most often due to long-standing high blood pressure, and it can also be an after-effect of a heart attack or myocardial infarction (MI), or the result of valvular heart disease.
However, in some patients, the cause of the DCM is unclear, and in such people, family screening may show that family members also have a tendency to develop DCM. Early identification of such people will allow them take lifestyle precautions and for doctors to
closely monitor any need for medications. Screening such families is a pro active step to ensure healthier hearts, for longer.
Hypertrophic cardiomyopathy (HCM, often also called HOCM) occurs when the muscle of the ventricles hypertrophies ("hypertrophy" means to over-grow) and becomes thickened. In some people, ventricular muscle hypertrophy can happen
because of long standing high blood pressure, or because of valvular heart disease or extreme physical fitness. However, when hypertrophy occurs in the absence of these underlying causes, then it is felt to be due to HCM, a condition that is usually genetic. HCM
may be asymptomatic, but may cause such symptoms as breathlessness, chest pains, dizzy spells, palpitations and faints. It is thought that HCM affects 1 in 500 people.
People with HCM will undergo a series of tests in the Heart House (ECG, ECHO, treadmill test and sometimes a MRI of the heart). Treatment of HCM can be with regular check ups only, medications such as beta blockers, and very occasionally with pacemakers or
implantable defibrillators. Family members who have a relative with HCM should come for HCM screening, as this condition can be genetic. Genetic testing may also be considered, and this is something that you can discuss with your Heart House doctor.
Arrhythmogenic right ventricular cardiomyopathy
Arrhythmogenic right ventricular cardiomyopathy (ARVC or ARVD) is an inherited condition, which can preferentially affect the right ventricle of the heart. The muscle of the right ventricle changes gradually over time, and can
predispose the person to arrhythmia. Persons with ARVC can have subtle ECG and ECHO findings that may suggest ARVC, and the diagnosis is usually confirmed on a cardiac MRI. There are internationally agreed criteria for the diagnosis of ARVC. It is estimated that
ARVC occurs in 1 in between 1000 and 5000 persons.
ARVC is an inherited condition and therefore can run in families. Persons with ARVC may be treated with medications, and /or with an implantable defibrillator if necessary.
Long QT syndrome
The Long QT syndrome (LQTS) is an inherited ion channelopathy, which is caused by genetic mutations in the DNA, which codes for either sodium or potassium channels in the heart muscle cells ("myocytes"). This can make the heart
more vulnerable to an abnormal heart rhythm such as ventricular tachycardia (VT) of the torsades de pointes type.
The diagnostic change in LQTS is a prolongation of the QT interval, which can be measured on an ECG. Diagnostic criteria exist to help doctors classify persons who may have the long QT syndrome, and genetic testing can be very helpful also in families where the
long QT syndrome has been confirmed. Patients with Long QT syndrome will also undergo a 24-hour ECG monitor, called a Holter monitor.
People with long QT syndrome may be treated with medications such as beta blocker tablets. Certain other medications can potentially worsen the QT interval, and predispose to ventricular tachycardia in people with the Long QT syndrome. A list of these
medications is available at https://www.azcert.org/medical-pros/drug-lists/drug-lists.cfm and people with the long QT syndrome should avoid taking them. For further advice on this matter, contact your family doctor or heart specialist.
The Brugada syndrome is a rare ion channelopathy, which is characterised by either an abnormal ECG with typical Brugada changes in ECG leads V1 to V3, or by an abnormal ECG response to an Ajmaline provocation test. It was first
described as a syndrome in 1992, and knowledge of this syndrome as a cause of SADS has been increasing since then.
Patients may undergo testing for the Brugada syndrome if they have an otherwise unexplained family history of SADS, or if they have an ECG with changes suggestive of the Brugada syndrome. In the Ajmaline test, patients undergo a ten-minute infusion of an
antiarrhythmic drug called ajmaline, to see if the abnormal Brugada ECG changes will show up.
Brugada syndrome is an inherited condition. Genetic testing has not yet worked out all the genes causing the Brugada syndrome, and work is continuing on this. Patients with Brugada syndrome can be treated with medications, and in some cases, implantable
defibrillators. Recently, some of the Brugada syndrome researchers have proposed a list of medications that persons with the Brugada syndrome should avoid. These are available at the website https://www.brugadadrugs.org/
Catecholaminergic polymorphic ventricular tachycardia
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare channelopathy which can predispose patients to arrhythmia and sudden death, especially at times of physical and emotional stress. CPVT is an inherited
condition, and can run in families. CPVT has been found to be associated with a gene called the cardiac ryanodine receptor gene (RyR2) in almost half of CPVT sufferers. Patients with CPVT may be treated with medications (such as beta blockers) or may need an
Sports and the Heart
Physical exercise is important for everybody's well being. It is recommended that people should exercise for at least 30 minutes a day, at least four days a week, for optimal health. Exercise can improve cardiovascular fitness,
reduce obesity and provide a healthy outlet for stress.
Concerns can arise when a person is diagnosed with an inherited cardiac disease, which may have been associated with symptoms or even a sudden death in the family. In those cases, whilst regular healthy exercise remains important, it may be that competitive or
high intensity sports may not be advised. This should be discussed on a case-by-case basis with your heart specialist.