Sudden Cardiac Death

What is Sudden Cardiac Death?

Cardiac arrest is when your heart suddenly stops working, leading to a collapse in blood flow throughout your body. Sudden cardiac death (SCD) refers to a death expected to be heart-related that happens within one hour of new heart symptoms appearing, or within 24 hours from when the person was last seen healthy and alive. Sometimes, an autopsy can reveal that a heart issue was the cause of death, but not always. SCD can often be the first sign of heart disease and is responsible for half of all heart-related deaths.

SCD is more common as people age and is more likely to happen in men compared to women of the same age. Cases of SCD are quite low early in life, but they can go up to 200 in 100,000 people per year for those in their 80s.

Coronary artery disease (CAD), a condition that blocks the heart’s main blood vessels, causes over 75% of SCD cases in developed countries. The number of CAD cases has been going up over the last few decades. But, luckily, the number of deaths from heart disease has been coming down. The best way to prevent SCD is to treat CAD early. Sometimes, a person can have a heart attack or reduced blood flow to the heart (ischemia) as the first sign of CAD, especially if they have a genetic risk. To minimize the risk of cardiac arrest and SCD, it’s crucial to identify CAD early and manage risk factors for heart disease that results from artery hardening (ASCVD). Early cardiopulmonary resuscitation (CPR), which is a process to restore heart function and breathing, can effectively prevent SCD in individuals with recorded cardiac arrest.

In young people with genetic heart rhythm issues, identifying and correctly treating the underlying condition can effectively stop SCD. The only way to avoid SCD in most inherited heart rhythm disorders is using an implantable cardioverter-defibrillator (ICD), a device that can correct abnormal heart rhythms.

Your heart is a muscular organ found in your chest, a bit to the left of the middle. Its job is to move blood around, carrying oxygen and nutrients to other parts of your body. Your heart has four sections: two on top (atria) and two on bottom (ventricles). Deoxygenated blood comes back to your heart from your body into your right atrium via two large veins. Oxygenated blood comes from your lungs into your left atrium through the pulmonary veins. Blood moves from the atria to the ventricles through two valves. When the ventricles contract, they force blood out to the rest of your body through two other valves.

Coronary arteries supply your heart muscle with oxygen-rich blood. The left coronary artery sprouts two main arteries that supply different parts of the heart. The right coronary artery also supplies different regions. These arteries make sure your heart gets plenty of fresh blood to keep up with its high demands.

The heart has a special system of cells that create and send the electrical signals directing the heart’s pace and how it contracts. The sinoatrial node, in your right atrium, is the heart’s natural pacemaker. These signals then move through your atria, causing them to squeeze, then they go to the atrioventricular (or AV) node, which connects the atria and ventricles. From the AV node, the signals move through pathways that cause the ventricles to contract and send blood to your lungs and the rest of your body.

What Causes Sudden Cardiac Death?

Sudden cardiac arrest (SCA) and sudden cardiac death (SCD) can be caused by several health factors. Common risk factors include problems connected to the arteries, heart structure, and heart rhythm. Smoking greatly increases the risk of SCD. For example, the Framingham study found that people who smoked were 2.5 times more likely to experience SCD every year compared to non-smokers.

Studies have found that the SCA and SCD risk is higher for people with structural heart diseases and artery-related issues. Meanwhile, populations with lower rates of these problems have a lower risk of SCD.

The causes can change as we age, but coronary artery disease (CAD – a disease that restricts the flow of blood to the heart due to build-up of substances in the arteries) causes most cases of SCD. Among younger people, inherited heart rhythm disorders, inherited heart muscle diseases, myocarditis (inflammation of the heart muscle), and abnormal coronary arteries are common causes. In fact, up to half of SCD cases in people in their 40s are due to acute coronary syndrome (ACS – sudden reduced blood flow to the heart). Some less common causes include drug toxicity, coronary artery spasm (sudden tightening of the muscles within the arteries), and heart trauma.

Research indicates that 40% to 80% of those who survive a heart attack have more than 70% blockage in at least one of their major arteries. Autopsy studies have found blood clots blocking the artery in up to 64% of SCD patients, along with unstable artery plaque, splitting or bleeding, and non-blocking artery blood clots.

In older patients, CAD is often the cause of SCD. Other reasons include non-ischemic heart muscle diseases and abnormal heart valves. Inherited heart rhythm disorders are relatively rare for older people.

Causes of SCD related to the heart can be grouped into several categories:

Coronary Artery-Related Causes:

* Limited or blocked blood supply to the heart
* Abnormal origin of the coronary artery
* Coronary spasm
* Inflammations of the blood vessel
* Heart muscle bridging

Primary Heart Rhythm Disorders:

* Long and Short QT syndromes
* Brugada syndrome
* Early repolarization syndrome
* Catecholaminergic polymorphic ventricular tachycardia (CPVT)
* Idiopathic ventricular fibrillation
* Congenital heart blocks
* Wolf-Parkinson-White syndrome

Heart Muscle Diseases:

* Hypertrophic cardiomyopathy
* Arrhythmogenic right ventricular cardiomyopathy (ARVC)
* Myocarditis (inflammation of the heart muscle)
* Unknown cause dilated cardiomyopathy (issue with the heart’s structure and function)
* Noncompaction cardiomyopathy
* Infiltrating cardiomyopathy (abnormal thickening of the heart walls)
* Restrictive cardiomyopathy
* Alcohol-related cardiomyopathy
* Peripartum cardiomyopathy (heart failure towards the end of pregnancy or after delivery)
* Tokatsubo cardiomyopathy

Heart Failure Causes:

* Heart failure with reduced ejection fraction (heart’s lower ability to pump blood)
* Heart failure with preserved ejection fraction (heart’s inability to fill with enough blood)

Valve-Related Heart Diseases:

* Aortic stenosis (narrowing of the main heart valve)
* Mitral valve prolapse (the valve between the left heart chambers malfunctions)

Congenital (Present From Birth) Heart Diseases:

* Tetralogy of Fallot (a rare condition caused by a combination of four heart defects)
* Transposition of the great arteries, Fontan circulation
* Ebstein anomaly, Eisenminger syndrome
* Single ventricular physiology
* Coarctation of aorta
* Double-outlet right ventricle
* Interrupted aortic arch
* Tricuspid atresia
* Pulmonary atresia
* Total anomalous pulmonary venous connection

Other Causes:

* Cardiac tamponade (pressure from fluid accumulation in the heart)
* Aortic dissection (a tear in the aorta, the big blood vessel leading from the heart)
* Ruptured aortic aneurysm (burst blood-filled bulge in the aorta)
* Pulmonary embolic (a blockage in the lungs’ artery)
* Left atrial myxoma (a rare heart tumor)

Risk Factors and Frequency for Sudden Cardiac Death

Every year, about 0.1% of people in the United States and Europe have a sudden out-of-hospital cardiac arrest (OHCA), commonly assessed by medical services. This condition is considered sudden cardiac death (SCD) and makes up 10% to 20% of all deaths in Europe. In the US, SCD often affects those between ages 66 and 68, and men are more likely to develop it than women.

Some groups have a higher risk of SCD. For example, black individuals have a higher risk than white people, especially among women. This discrepancy could be because of differences in income, education, and other factors that can raise the risk of heart and blood vessel disease. SCD risk increases with age and is greatest in people in their 80s.

There are various reasons why SCD occurs. Younger people usually experience SCD due to inherited heart rhythm disorders, heart muscle diseases, and anomalies in the arteries supplying the heart. On the other hand, coronary artery disease is the most common cause of SCD in older patients. Additionally, SCD is the leading cause of non-accidental death among young athletes. In fact, the incidence of sudden death from sports is between 0.5 and 2.1 per 100,000 people per year. The risk is higher among elite athletes, with a reported incidence of 1 in 8,253 per year for those in the National Collegiate Athletic Association. Basketball players in the NCAA Division I have an incidence of 1 in 5,200.

The occurrence of SCD varies based on the time of day and is highest between 6 am to 12 pm. This fluctuation through the day is linked to the body’s regulation of adrenaline and other hormones. Some drugs can decrease the risk of SCD in the early morning. Interestingly, it’s also been found that SCD happens most frequently on Mondays.

Sudden cardiac arrest (SCA) can sometimes be the initial medical issue a person experiences before SCD. Finding people who have a high risk of SCA in the general population is beneficial for preventing SCD and reducing related health complications. The global occurrence of SCD is approximately 100 cases per 100,000 people each year, with almost 2 million reported cases annually worldwide. These numbers and the related death and health issues make SCA and SCD significant public health concerns globally.

Signs and Symptoms of Sudden Cardiac Death

People suffering from Sudden Cardiac Arrest (SCA) are often found unconscious, with no heartbeat or breathing. Immediate medical attention is necessary for such individuals. Medical practitioners need to rapidly assess their airway, breathing, heartbeat, physical and environmental condition, and start treatment without delay. Attending details can be further looked into once the person’s condition has stabilized.

Some individuals may experience symptoms such as palpitations, dizziness, or near loss of consciousness before experiencing SCA. However, around half of those experiencing SCA do not display any warning signs before passing out. Some other potential signs of SCA can include:

• Chest pain, discomfort, or pressure, particularly during activity
• Tiredness, shortness of breath, or palpitations when exercising
• Previously identified heart murmur
• High blood pressure
• Hearing loss which could be a clue to Long QT Syndrome (LQTS)

When taking a patient’s history, it’s important to inquire about any past incident of cardiac-related fainting or SCA and whether there’s a family history of sudden cardiac death or inherited heart rhythm disorders. More details might include:

• Previous restrictions from participating in sports
• Past cardiac tests ordered by a doctor
• Family history of heart disease deaths below the age of 40
• Close relatives under 50 with heart disease
• Family history of cardiomyopathy, LQTS, Marfan syndrome, or other heart conditions

Physical examination of a person having SCA would typically show no responsiveness, no pulse, with no blood pressure and cardiac activity. Breathing could be infrequent or even absent, with the skin often appearing bluish and cold. Eyes may show dilated pupils not reacting to light, and there might be a loss of muscle stiffness, with the possibility of loss of bladder and bowel control. The heart monitor might show abnormal rhythms.

In contrast, patients with myocardial ischemia, another heart condition, may show various physical symptoms. For instance, they might sweat profusely and look pale. They might display an S3 or S4 heart sound, a sign of heart failure. Heart failure could be noticeable due to a swollen neck vein, crackles in the breath sound, fluid in the abdomen, swelling in both lower limbs and variations in heart rates. EKG might show abnormal readings. Besides, sudden cardiac arrest survivors might display neurological symptoms due to insufficient oxygen in the brain during the cardiac arrest incident.

Finding certain symptoms during physical examination might help identify the underlying cause of the cardiac arrest. An existing heart murmur, systemic cyanosis (a blueish discoloration of the skin), existing murmurs, and skin signs suggestive of sarcoidosis (a type of inflammation) could be helpful. It’s important to check heart murmurs in lying and standing positions. Pulse in the groin area should be checked for abnormalities. Similarly, blood pressure measurements on both arms could be helpful.

Testing for Sudden Cardiac Death

If you experience a sudden cardiac arrest (SCA), it might be the first sign that you have coronary artery disease (CAD) or another heart condition. For anyone who survives this event, a thorough check of the heart’s health is needed. Doctors use several different tests to understand what might have caused the SCA and what the best treatment might be.

Here’s what those tests are:

– Electrocardiogram (ECG): This test measures the electrical activity in your heart to see if there are signs of a heart attack or inherited issues that affect the heart’s electrical system.

– Echocardiogram: This ultrasound of your heart helps determine whether you have any pre-existing heart conditions. It evaluates heart function and looks for conditions like heart failure, issues with the heart muscle or valves, or congenital cardiac abnormalities (issues present since birth).

– Coronary angiography: This is an X-ray examination that uses a special dye and high-speed imaging to see how blood is flowing through the heart. This helps the doctor spot blockages in the heart’s blood vessels that could indicate coronary artery disease, abnormalities, or spasms in the heart vessels.

– Exercise tests: In some patients, exercise can trigger abnormal rhythms in the heart or decreased blood flow to the heart muscle. This test helps doctors see these changes.

– Electrophysiology test: This is a test that measures the electrical activity of the heart to find where an arrhythmia (abnormal heartbeat) is coming from.

– Cardiac MRI: This imaging test provides detailed images of the heart and can help doctors diagnose conditions that affect the heart muscle and estimate the risk of sudden cardiac death.

– Genetic testing: If the doctor suspects you might have an inherited heart condition like ARVC (Arrhythmogenic right ventricular cardiomyopathy), Brugada syndrome, CPVT (catecholaminergic polymorphic ventricular tachycardia), or LQTS (long QT syndrome), genetic testing can confirm this. This testing could also be recommended if an echo or angiogram doesn’t show a specific reason for the cardiac arrest. The results from this test can provide crucial information about treatment, condition progression, and the risk for other family members.

Remember, the goal of these tests is to fully understand what caused the SCA so the doctor can recommend the best possible treatment for you. The more the medical professionals know about your heart, the better they can help ensure it stays healthy. Recent advances in genetic testing have also allowed doctors to more effectively identify different heart conditions, which are crucial for achieving the most favorable outcome.

Treatment Options for Sudden Cardiac Death

Immediate response is essential when someone experiences Sudden Cardiac Arrest (SCA), a sudden and unexpected loss of heart function. This involves procedures known as Basic Life Support (BLS) and Advanced Cardiac Life Support (ACLS), carried out by trained healthcare professionals. Their aim is to restore heart function and increase chances of survival.

Treatment for SCA begins with rapidly recognizing a cardiac arrest, swiftly starting CPR (Cardiopulmonary Resuscitation), and using a defibrillator. CPR involves chest compressions and possibly rescue breaths, while a defibrillator delivers a shock to try and restart the heart. The sooner CPR and defibrillation are done, the better the chances of survival. If you see someone experiencing cardiac arrest, immediately starting CPR and quickly using a defibrillator can greatly improve their chances of survival.

Survival after in-hospital cardiac arrest can be high if CPR and defibrillation are done swiftly. However, survival rates for out-of-hospital cardiac arrest decline rapidly – by five minutes, less than 25% survive, and nearly no one survives after ten minutes.

Using epinephrine every 3 to 5 minutes can improve the odds of successful CPR. This drug causes vasoconstriction – narrowing of the blood vessels – which boosts blood flow to the heart and brain during CPR. After three unsuccessful attempts to revive the patient with a defibrillator, the drug amiodarone can increase the chances of successful resuscitation. However, it does not improve the rates of survival to hospital discharge.

Once a patient’s heart starts beating on its own again after cardiac arrest, healthcare professionals will evaluate them for possible causes. This will include assessing the patient’s airway, heartbeat, mind, as well as a 12-lead ECG, blood tests, chest X-ray, EKG, and brain imaging. After cardiac arrest, many bodily functions are affected. An experienced team of healthcare professionals is needed to give post-cardiac arrest care and improve survival and brain function outcomes.

If heart attack symptoms are observed, immediate heart artery test followed by revascularization can be done. Revascularization is a procedure to restore blood flow to the heart. If significant coronary artery disease (CAD) is found, this procedure can be done to improve survival rates after cardiac arrest. However, if the patient doesn’t have any signs of heart attack, immediate heart artery test and revascularization don’t seem to provide any additional benefits.

It’s crucial to avoid low blood pressure, lack of oxygen, and low blood sugar levels after cardiac arrest as these can worsen brain injury. Therefore, it’s important to maintain sufficient blood pressure and avoid conditions that can damage body tissues. If the patient is not alert after cardiac arrest, body temperature is often lowered for 24 hours to protect the brain, which can improve brain function and survival outcomes.

Long-term care for patients who survive SCA aims to reduce the risk of another cardiac arrest, look at overall prognosis, and address potential underlying causes or contributing factors. This involves a team approach to optimize patient outcomes and enhance their quality of life.

Preventing another SCA is crucial after surviving one. Patients are at a high risk of experiencing another SCA, especially if they have structural heart diseases. While antiarrhythmic drugs (medication to maintain the regular rhythm of the heart) have limited use in preventing SCD, beta-blockers (medications that reduce heart rate and blood pressure) can improve survival and reduce SCD risk in patients with left ventricular systolic dysfunction or previous heart attack events.

Implantable cardioverter defibrillators (ICDs) can effectively prevent SCD and improve survival in patients who survive SCA. These are small devices placed in the chest to regulate an abnormal heart rhythm. ICD placement is recommended for patients who survive SCA due to abnormal heart rhythms, without an identified reversible cause.

Surviving SCA can cause anxiety, depression, and post-traumatic stress, as well as physical and cognitive impairment. A structured post-cardiac arrest rehabilitation program is recommended, which should include psychological support for both patients and their families. A detailed discharge plan should be provided, with instructions on daily routines.

What else can Sudden Cardiac Death be?

When a medical professional is determining whether someone has had a sudden cardiac arrest (SCA) or sudden cardiac death (SCD), there are many other potential diagnoses that they need to consider. These include causes of unconsciousness (syncope) and irregular heartbeats, such as too slow (bradyarrhythmias) or too fast (tachyarrhythmias). Conditions that may present with similar symptoms include:

• Heart attack (Acute myocardial infarction)
• Narrowing of the aortic heart valve (Aortic stenosis)
• Arrhythmogenic right ventricular cardiomyopathy, a heart muscle disease
• Interrupted electrical signals in the heart (Atrioventricular block)
• Brugada syndrome, a serious heart condition
• Catecholaminergic polymorphic ventricular tachycardia, a type of irregular heartbeat
• Dilated cardiomyopathy, where the heart becomes enlarged and cannot pump blood effectively
• Ebstein anomaly, a rare heart defect
• HCM (hypertrophic cardiomyopathy), where the heart muscle becomes thickened
• Idiopathic ventricular fibrillation, an irregular heartbeat with no known cause
• Long QT syndrome (LQTS), a heart rhythm condition
• Narrowing of the mitral valve in the heart (Mitral stenosis)
• Mitral valve prolapse, where the heart valve doesn’t close properly
• Blood clot in the lungs (Pulmonary embolism)
• Short QT syndrome (SQTS), a rare genetic heart condition
• Tetralogy of Fallot, a type of heart defect
• Wolff-Parkinson-White syndrome, a condition that causes a rapid heartbeat

Obtaining an accurate diagnosis for SCA allows the medical team to understand if there are any underlying heart conditions that require specific treatment to prevent recurrence. A thorough medical evaluation and diagnostic examination can help distinguish SCA and SCD from other conditions.

What to expect with Sudden Cardiac Death

The chances of surviving a cardiac arrest depend on various factors. Globally, the survival rate for out-of-hospital cardiac arrests (OHCA) is quite low. Only 22% of people who experience an OHCA manage to reach the emergency department, and sadly, only 8.8% survive until they are discharged from the hospital. The 1-year survival rate of OHCA is less than 8% in developed countries.

Survival of sudden cardiac arrest (SCA) can be improved with quick action such as immediate resuscitation, bystander performing cardiopulmonary resuscitation (CPR), and access to a defibrillator, which is a device used to restore the heart’s normal rhythm, in public places.

Regular training and education of public officials and community members on the importance of bystander CPR and early defibrillation play a significant role in increasing the survival rates of OHCA.

Possible Complications When Diagnosed with Sudden Cardiac Death

Complications from SCA, or sudden cardiac arrest, often involve brain injury due to lack of oxygen and malfunction of multiple body organs.

Another issue that isn’t often talked about is the impact on mental health. Both survivors of sudden cardiac arrest and their families can experience mental health problems. Research indicates that a large proportion of patients who survive sudden cardiac arrest go on to struggle with mental health issues like anxiety, depression, and post-traumatic stress disorder (PTSD).

Some statistics quoted include:

• Depression rates in survivors as high as 45%
• Anxiety rates in 6% to 15% of survivors
• Up to 27% of survivors diagnosed with PTSD

Preventing Sudden Cardiac Death

Sudden Cardiac Arrest (SCA) can often be fatal, so it’s paramount to identify and treat individuals who may be most susceptible to it. SCA frequently results in Sudden Cardiac Death (SCD), especially when it’s associated with an uncontrolled rapid heartbeat, also known as ventricular fibrillation.

A method to prevent SCA involves preventing Atherosclerotic Cardiovascular Disease (ASCVD), as it can lead to SCD due to heart attacks or damaged heart muscles caused by insufficient blood supply (ischemic cardiomyopathy). This prevention strategies can include: restoring blood flow as quickly as possible, providing the most effective treatments for heart failure, and if suitable, introducing a device to correct the timing of your heartbeats or “cardiac resynchronization therapy”. For patients displaying signs of unsynchronized left ventricular function, often measured by a low “ejection fraction” or the fraction of blood pumped out of the heart with each beat, these strategies are especially important.

Moreover, a specialized device called an Implantable Cardioverter-Defibrillator (ICD) can be placed in patients who have a significantly reduced ejection fraction (35% or less) which is a condition often seen in heart failure patients; as well as those with non-ischemic cardiomyopathy. However, those with other severe health conditions that limit their life expectancy should not undergo ICD placement.

SCD can also occur when the left ventricle’s function is normal, and in these cases, patients are often found to have conditions that lead to irregular heart rhythms. These conditions could be Hypertrophic Cardiomyopathy (HCM, a type of heart disease where the heart muscle thickens and makes it harder for the heart to pump blood), arrhythmogenic right ventricular cardiomyopathy, and inherited abnormal heart rhythm conditions.

Features such as a family history of premature SCD, episodes of temporary loss of consciousness (syncope), and evidence of a certain kind of irregular heart rhythm (arrhythmia) can help predict the risk of SCD in these patients. For these individuals, ICD placement is recommended.

Patients with these inherited heart rhythm conditions and irregular heart muscle diseases need to closely follow the treatment plans given by their heart doctor. Particularly, those with arrhythmias, a family history of SCD, and symptomatic ventricular arrhythmias would most benefit from ICDs. Genetic testing for family members can identify those unaware that they carry a mutation causing the condition, which can help prevent future instances. Having closely related parents can increase the risk of inheriting arrhythmias, making genetic counseling an extremely important tool.

As for secondary prevention, meaning prevention after the first event, those who have already suffered from SCA or SCD should adhere to long-term strategies. This can involve treating underlying heart diseases and specific irregular heart rhythms using medications such as beta-blockers, which have been shown to be effective in preventing recurrence.

For individuals with heart muscle diseases or left ventricular systolic dysfunction, the medication improves survival and can significantly reduce the SCD rates. ICD placement is also the best approach to prevent recurrence due to ventricular tachyarrhythmias – a rapid and irregular heart rhythm.

Lastly, mental health issues can lead to physical stress responses that boost the risk of arrhythmias or other heart events. Thus, providing mental health support and interventions can be key to preventing a recurrence of SCA.