Sudden Cardiac Arrest (SCA) doesn’t discriminate against anyone. From healthy to unhealthy, young to old, the unexpected cessation happens in an instant. Affecting more than 356,000 people per year with a 90% fatality rate, it is one of the leading causes of death among people over 40.

Individuals determined to be at risk—those with previous heart attacks, coronary artery disease, and heart rhythm disorders—may be fitted with a battery-powered device called an implantable cardioverter defibrillator. It is placed under the skin and tracks heart rate. If an abnormal heart rhythm is detected, the device delivers an electric shock to restore a normal heartbeat.

About 20% of SCAs have no risk factors and strike people in the prime of their lives. In most cases, death is instant, with survival possible if CPR or an electric shock to the heart is delivered within minutes. In this issue, we’ll take a closer look at SCA and highlight a molecular diagnostic test in the works to identify people at risk for this silent killer.

SCA is an electrical problem—the heart stops beating due to an electrical malfunction. Sometimes, victims of SCA have warning signs such as fatigue, fainting, blackouts, dizziness, chest pain, shortness of breath, weakness, palpitations, or vomiting, typically within 24 hours of cardiac arrest. In others, there are no warning signs.

A heart attack is a plumbing problem— the heart is still beating, but a blocked artery prevents blood from reaching a section of the heart. The longer the flow of blood is cut off, the more severe the damage to the affected area. It is imperative to start treatment with anti-clotting medications or a cardiac catheter as soon as possible to reduce the clot and free up the artery.

Chicago-based 3PrimeDx is developing a molecular diagnostic to identify those at risk for SCA based on silent genetic factors. The test borrows from research demonstrating that people who express a shortened version of the protein SCN5A are at greater risk for SCA. Since expression levels of different SCN5A variants in white blood cells mirror expression levels in cardiac tissue, the test can be done via a simple blood draw.

The variants in SCN5A expression arise due to a process called “alternative splicing,” wherein various parts of the RNA produced from the SCN5A gene are spliced together differently in at-risk individuals. This splicing pattern is not necessarily constant throughout life, but studies suggest that the detection of aberrant splice variants in white blood cells can be used to predict increased SCA risk.

SCN5 is a sodium channel—a protein embedded in cardiac muscle cell membranes to let positively charged sodium ions enter and exit. Proper control of ion flow is critical to maintaining consistent heart rhythm, so it makes sense that defects in this protein are correlated with SCA.

The best treatment for SCA is immediate defibrillation or the delivery of a therapeutic dose of electrical current to the heart. This essentially “resets” the heart, allowing a normal rhythm to be re-established. Automated external defibrillators (AED) are available in hospitals, ambulances, and some public places; however, time is of the essence in cases of SCA.

For those at known risk for SCA, implantable cardioverter defibrillators (ICDs) are a potentially lifesaving option. These devices have the ability to detect and correct life-threatening cardiac arrhythmias, including SCA. With 3PrimeDx’s diagnostic test aiming to identify those at risk for SCA, ICD placement could be the next step after diagnosis. 3PrimeDX’s test is currently in development.

Sudden Cardiac Arrest (SCA) is a formidable health challenge, striking indiscriminately and often without warning. It’s a leading cause of death in people over 40 and poses a significant risk even to those in their prime years, who may show no previous symptoms or risk factors. The good news is that advancements are being made in early detection and treatment options. With the development of 3PrimeDx’s molecular diagnostic test based on SCN5A expression levels, the promise is to identify those at high risk for SCA through a simple blood draw. This test could revolutionize how we approach this silent killer, making implantable cardioverter defibrillators (ICDs) a more targeted and effective preventive measure. While there is no one-size-fits-all solution for combating SCA, strides are being made in understanding its underlying causes, differentiating it from other heart conditions like heart attacks, and advancing technologies that may significantly reduce its devastating impact.

1. What is Sudden Cardiac Arrest (SCA)?

SCA is an abrupt loss of heart function caused by an electrical malfunction in the heart. The heart stops beating, and blood flow to the organs, including the brain, ceases.

2. How is SCA different from a heart attack?

SCA is an electrical problem where the heart stops beating altogether, while a heart attack is a “plumbing” issue where a blocked artery prevents blood from reaching a section of the heart. The heart continues to beat during a heart attack.

3. Who is at risk for SCA?

Individuals with previous heart attacks, coronary artery disease, and heart rhythm disorders are at higher risk. However, about 20% of SCAs strike people with no identifiable risk factors.

4. What are the symptoms of SCA?

Symptoms may include fatigue, fainting, blackouts, dizziness, chest pain, shortness of breath, weakness, palpitations, or vomiting. However, in some cases, there may be no warning signs.

5. What is 3PrimeDx’s molecular diagnostic test?

3PrimeDx is developing a test identifying those at risk for SCA based on their SCN5A protein expression levels. The test uses a simple blood draw and aims to revolutionize how we identify and treat individuals at high risk for SCA.

6. How do implantable cardioverter defibrillators (ICDs) work?

ICDs are battery-powered devices placed under the skin that monitor heart rate. If an abnormal heart rhythm is detected, the device delivers an electric shock to restore a normal heartbeat.

7. What is SCN5A, and how does it relate to SCA?

SCN5A is a sodium channel protein critical for maintaining consistent heart rhythm. Defects in this protein are correlated with an increased risk for SCA.

8. What is immediate defibrillation?

Immediate defibrillation involves the delivery of an electric current to the heart using an Automated External Defibrillator (AED) to restore normal heart rhythm. This is currently the most effective treatment for SCA.

9. Where can I find AEDs?

AEDs are usually available in hospitals, ambulances, and some public places like airports and schools.