Sudden Cardiac Arrest Causes

Greg Scott

Greg Scott

CDE Medical

*To take the corresponding CDE quiz, visit the College of Emergency Dispatch.*

Since heart attacks (complete blockages of arteries supplying blood to the heart muscle) are such a common occurrence in our modern world, we may get the impression that heart attacks cause nearly all sudden cardiac arrests (SCAs)—the condition where the heart abruptly stops beating effectively to sustain life. However, things are not nearly that simple.

For starters, recall that respiratory arrest—when breathing stops or is ineffective—is a common reason for causing the heart to stop unless effective breathing can be restored quickly. Respiratory arrest can be due to many causes—an overdose, an acute asthma attack, severe head trauma, serious chest injuries, extreme toxic exposure, drowning, and positional asphyxia (unconsciousness with the airway compressed and closed), to name some common ones.

Even after accounting for respiratory arrests, there are other less common but clinically well-known heart conditions that can cause SCA in the absence of a heart attack. Let’s look at some of these heart conditions that can get reported by emergency callers and learn how to consider them within the Medical Priority Dispatch System™ (MPDS®).

Hypertrophic cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is a disease that causes the heart muscle to enlarge. 

Over time, this enlargement can cause life-threatening changes to the heart, including restricting regular blood flow through the heart chambers, as it pumps blood to the rest of the body.1

Hypertrophic cardiomyopathy is the most common cause of SCA in younger persons, often young athletes, many of whom do not realize they have this  condition.2,3 In the United States, the estimated incidence of HCM is 1 in every 500 persons, although many of these cases are milder forms of the disease.

Common signs and symptoms include chest pain (often with strenuous physical activity), shortness of breath (also with strenuous activity), fatigue, abnormal heart rhythms, fainting, dizziness, and swelling in the abdomen or lower extremities.4

Wolff-Parkinson-White syndrome
Wolff-Parkinson-White (WPW) syndrome is a heart condition that causes the heart to beat abnormally fast for (generally brief) periods of time. The cause is an extra electrical connection in the heart. This heart condition is present at birth (congenital), although symptoms sometimes develop only later in life. Many cases are diagnosed in otherwise healthy young adults.

WPW syndrome can cause episodes where the heart suddenly starts racing, then stops or slows down abruptly. This rapid heart rate is called supraventricular tachycardia (SVT). Episodic symptoms include fainting, a pounding or fluttering heartbeat (palpitations), dizziness or lightheadedness, chest pain, and shortness of breath.5

Long QT syndrome
Long QT syndrome (LQTS) is a heart-signaling disorder that can cause fast, chaotic heartbeats (arrhythmias). In long QT syndrome, the heart's electrical system takes longer than usual to recharge between beats. Fainting (syncope) is the most common symptom of long QT syndrome. While fainting from LQTS can occur suddenly, other cases include warning signs such as blurred vision, lightheadedness, pounding heartbeats (palpitations), and weakness.

Long QT syndrome has been linked to unexplained sudden death in children and young adults, including fainting, drownings, and seizures.6

Commotio cordis
Commotio cordis is an SCA caused by a sudden blunt impact to the chest in the absence of cardiac damage, resulting in ventricular fibrillation. This can happen by getting hit hard in the chest just as the lower heart chambers (the ventricles) are relaxing after a contraction. The force of the blow can make the ventricles contract when they’re supposed to be resting.7,8

If you’re an American football fan, you may have seen Damar Hamlin of the Buffalo Bills football team have an SCA on national television recently—which resulted in a dramatic resuscitation where Hamlin received immediate CPR and defibrillation by emergency responders right on the playing field. He eventually made a full recovery after being admitted to the Intensive Care Unit (ICU) of the University of Cincinnati Medical Center. Commotio cordis is considered the likely cause of his SCA.9

Unlike other heart conditions mentioned here, commotio cordis is based on a one-time event, so any single patient will virtually never have a history of commotio cordis. Therefore, it is especially important that the EMD be aware of the very specific circumstances in which it occurs—namely an athletic event where the patient receives a hard, direct blow to the chest. In such cases, the SCA will be handled as a cardiac arrest, as opposed to a respiratory arrest, in the MPDS Dispatch Life Support (DLS) protocols.

Brugada syndrome
According to the Mayo Clinic, “Brugada (brew-GAH-dah) syndrome is a rare but potentially life-threatening heart rhythm condition (arrhythmia) that is sometimes inherited. People with Brugada syndrome have an increased risk of irregular heart rhythms beginning in the lower chambers of the heart (ventricles). Some people with Brugada syndrome need a medical device called an implantable cardioverter-defibrillator (ICD).” Signs and symptoms include dizziness, fainting, irregular heartbeats, extremely fast and chaotic heartbeat, and seizures. Brugada syndrome may be caused by a structural problem in the heart, which may be hard to detect; an imbalance in electrolytes (chemicals that help send electrical signals through the body); or use of some prescription medications or cocaine.10

The EMD’s role
The primary role of the EMD is to consider first any caller-mentioned heart conditions when selecting the Chief Complaint. The “Okay, tell me exactly what happened” query plays a key role, since callers may describe one of these conditions in their initial response. Protocol 19 (Heart Problems/A.I.C.D.) handles most  heart conditions in a conscious patient where heart attack symptoms are not reported initially (note that Protocol 10 handles all heart-attack symptoms).11

Second, the EMD must record these heart conditions in the Key Questions section of the ProQA® system, particularly when using Protocols 10, 19, and 31 [Chest Pain/Chest Discomfort (Non-Traumatic), Heart Problems/A.I.C.D., Unconscious/Fainting (Near), respectively]. In these protocols, the existence of any of the above-mentioned heart conditions results in a higher-priority Determinant Level and/or Determinant Code assignment than would otherwise be assigned to a case where no other higher-level symptoms are present. For example, consider a fainting case with a patient in her sixties, now awake and breathing normally with no color change. In Key Questions, it is discovered the patient has a history of long QT syndrome:












In this case, the patient’s history of a known heart condition (long QT syndrome) yields a Determinant Code of 31-C-2: 

As another example, consider a 31-year-old female, 1st party caller, with heart palpitations (a fast, pounding heartbeat) as her Chief Complaint and a history of Wolff-Parkinson-White syndrome. She has taken her own heart rate and states it is 124 beats per minute. While this would otherwise be a 19-A-1 in the absence of a history of heart problems, the patient receives a 19-C-4 Determinant Code assignment because of her reported heart condition:

Remember that some patients with these unusual heart conditions may be worsening or unstable, and for them, the risk of SCA is higher. In those cases, it is extremely important to keep the caller on the line for as long as possible—preferably until the field responders arrive. Of course, when SCA risk is at its highest, patients will likely have at least one Priority Symptom (decreased level of consciousness, difficulty breathing, or chest pain), generating a DELTA-level response on various Chief Complaint protocols. But for some, these symptoms don’t happen until SCA is imminent. Early EMD recognition and proper DLS and response lead to better patient care and outcomes.

Finally, in the rare case where commotio cordis is suspected, the EMD should manage it as a cardiac-caused arrest and use the compressions-first/compressions-only DLS pathway, as opposed to the respiratory arrest pathway (used for trauma cases).

By following protocol, listening carefully to the answers given to all Case Entry queries and Key Questions, then recording all information in the ProQA system, the EMD will be able to identify serious heart conditions that may cause SCA in some patients, assign the correct Determinant Code, generate the correct field  response, provide the most effective DLS instructions, and facilitate a better patient outcome for each of these potentially serious conditions.

1. “Hypertrophic Cardiomyopathy.” Cleveland Clinic. my.clevelandclinic.org/health/diseases/17116-hypertrophic-cardiomyopathy (accessed Feb. 6, 2023).
2. Mayo Clinic Staff. “Hypertrophic cardiomyopathy.” Mayo Clinic. mayoclinic.org/diseases-conditions/hypertrophic-cardiomyopathy/symptoms-causes/syc-20350198# (accessed Feb. 7, 2023).
3. American Heart Association editorial staff. “Hypertrophic Cardiomyopathy (HCM).” American Heart Association. heart.org/en/health-topics/cardiomyopathy/what-is-cardiomyopathy-in-adults/hypertrophic-cardiomyopathy (accessed Feb. 7, 2023).
4. See notes 1, 2, and 3.
5. “Wolff-Parkinson-White syndrome.” NHS. nhs.uk/conditions/wolff-parkinsonwhite-syndrome/#:~:text=Wolff%2DParkinson%2DWhite%20(WPW, develop%20until%20later%20in%20life (accessed Feb. 7, 2023).
6. Mayo Clinic Staff. “Long QT syndrome.” Mayo Clinic. mayoclinic.org/diseasesconditions/long-qt-syndrome/symptoms-causes/syc-20352518 (accessed Feb.
8, 2023).
7. Link MS. “Commotio Cordis: Ventricular Fibrillation Triggered by Chest Impact-Induced Abnormalities in Repolarization.” AHA Journals. Circulation: Arrhythmia and Electrophysiology. 2012; April 1. ahajournals.org/doi/full/10.1161/circep.111.962712 (accessed Feb. 9, 2023).
8. “Commotio Cordis.” Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/24572-commotio-cordis. (accessed Feb. 10, 2023).
9. Camero K. “Damar Hamlin May Have Had Commotio Cordis, Cardiologists Say. Here’s What To Know About The Rare Event.” BuzzFeed News. 2023; Jan. 5.
buzzfeednews.com/article/katiecamero/commotio-cordis-damar-hamlin-what-to-know (accessed Feb. 13, 2023).
10. Mayo Clinic Staff. “Brugada syndrome.” Mayo Clinic. mayoclinic.org/diseasesconditions/brugada-syndrome/symptoms-causes/syc-20370489 (accessed Feb. 8, 2023).
11. Scott G, Olola C, Miko M, Patterson B, Quigg J, Davis C, Lindfors R, Tidwell J, Pagenkop K, Lofgren J, Fox J, Clawson J. “9-1-1 Caller-Described Heart Attack Symptoms.” Prehosp Disaster Med. 2022; July. doi.org/10.1017/S1049023X22001017