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Sudden Cardiac Arrest: Halting a Leading Killer Dead in Its Tracks

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Sixteen-year-old Dara collapses while running on a treadmill.

At the movies with his family, 48-year-old Martin sips his soda, gasps, and blacks out.

Moments after waking up on a Saturday morning, seven-year-old Liam turns gray and stops breathing.

Three different scenarios, ending in a single, life-threatening diagnosis: sudden cardiac arrest (SCA). SCA occurs when the heart stops beating, abruptly and without warning, after electrical impulses in the heart become rapid or chaotic. Without treatment, death can occur in just minutes.

On average, an SCA occurs about every 90 seconds,1 affecting seemingly healthy individuals both young and old alike, including 7,000 children and teens each year.

Close to 500,000 Americans die from SCA each year, making it a leading cause of death in North America. Two-thirds of SCA deaths occur while at home, work, or play, while the remaining one-third of SCA-related deaths are found in hospitals.

According to the American Heart Association, nearly 90% of out-of-hospital SCAs are fatal.2

Dara, Martin, and Liam above (not their real names) are extremely fortunate. All three are alive today, thanks to quick-thinking bystanders who were trained in administering cardiopulmonary resuscitation (CPR) and the ready availability of automated external defibrillators (AEDs). An SCA is often reversible if addressed within a few minutes. The chances of surviving an SCA decrease by 10% for every minute the affected individual goes without CPR.

SCA Versus Heart Attack

SCA is not a heart attack; instead, SCA could be considered as an electrical problem, while a heart attack is a plumbing problem.1

SCA is usually triggered by ventricular fibrillation, an electrical disturbance that results in a loss of heart function. This “power failure” adversely impacts the supply of blood to the brain and other vital organs. Without treatment—consisting of the delivery of an electrical shock, either via an AED or an implantable cardioverter-defibrillator (ICD)3—death can occur within minutes.

Conversely, a heart attack, known as a myocardial infarction, occurs when the flow of blood to the heart via the arteries is interrupted or blocked, usually by plaque. This blockage, similar to a backup in a plumbing line, must be “unclogged” with drugs or surgery in order to avoid damage to the heart or other adverse occurrences.

Importantly, SCA and heart attack signs and symptoms vary widely. Signs of SCA, if they occur at all, include sudden collapse, lack of pulse or breathing, and a loss of consciousness. One-quarter of adults treated by emergency responders for SCA had no prior symptoms.2

In comparison, heart attack symptoms such as chest pressure or pain, nausea or vomiting, cold sweats, and dizziness may occur days or even weeks before a heart attack.

If either an SCA or a heart attack is suspected, emergency medical services (911) should be called immediately.

SCA Risk Factors

Because SCA strikes without warning and indiscriminately, it can be challenging to pinpoint its source and causes. However, the Heart Rhythm Society has identified certain factors clinicians can use to estimate SCA risk in patients, as follows:

  • A previous heart attack: the majority of people who die of SCA show signs of a previous heart attack
  • A family history of sudden cardiac death, heart failure, or massive heart attack
  • An abnormal heart rate or rhythm of an unknown cause
  • An unusually rapid heart rate that comes and goes
  • Episodes of fainting of an unknown cause
  • The presence of a congenital heart defect before and after a surgical repair attempt
  • A low ejection fraction: the ejection fraction is a measurement of how much blood is pumped by the ventricles with each heartbeat, with a healthy heart typically pumping 55% or more of its blood with each beat; the pumping of less than 35% indicates an elevated risk of SCA

Technology for the Early Detection of SCA Probability

Individuals suspected to be at a high risk for SCA are usually referred to cardiac specialists, who use a number of diagnostic tests and procedures4 to stratify SCA risk. These tests include electrocardiography (ECG), a simple, painless evaluation that detects and records the heart's electrical activity. The test monitors how fast the heart is beating and its rhythm (steady or irregular). ECG also records the strength and timing of electrical signals as they pass through each part of the heart, and can pinpoint evidence of heart damage or previous or current heart attack.

ECG can also be used to spot another deadly SCA red flag known as long QT syndrome (LQTS). The ECG measures the heart’s electrical impulses as a series of waves labeled with the letters P, Q, R, S, and T. During SCA risk assessments, physicians focus on the heart’s QT interval, which is the time it takes the muscle to contract and then refill with blood before the next contraction.5

LQTS is present when the heart muscle takes longer than usual to recharge between beats. LQTS patients are at a greater risk of SCA due to the threat of torsade de pointes (TdP). Translated as “twisting of points,” TdP is a life-threatening ventricular tachycardia found in LQTS patients that makes the waves on an ECG monitor appear “twisted.” 5

LQTS is either inherited (congenital) or acquired. Acquired LQTS can result from certain disease states; electrolyte imbalances; or adverse reactions to some medications including volatile anesthetics, antibiotics, antinausea drugs, and antipsychotic agents.

LQTS can be treated either with medications such as β-blockers and anti-arrhythmic medications, or, in some cases, implantable cardioverter-defibrillator (ICD) insertion.

During perioperative and critical care treatment, arenas in which many LQTS-triggering drugs are used, LQTS patients face an increased risk of developing TdP or other deadly cardiac arrhythmias, setting the stage for SCA. Therefore, monitoring of the QT interval in LQTS patients throughout the hospitalization period is recommended to reduce the likelihood of an in-hospital SCA.6

Manual calculation of the QT interval is cumbersome and therefore not feasible in the high-stress settings of perioperative and critical care. Instead, the use of equipment that provides continuous automatic monitoring of the QT interval can help to increase the safety of patients suffering from or at risk of developing LQTS during surgery or the provision of critical care.

Sudden cardiac arrest can be deadly, but it can be stopped in its tracks with proper monitoring. The display of QT interval data on the patient monitor as well as the presence of sophisticated arrhythmia alarms can go a long way toward detecting an individual’s risk of TdP and preventing SCA.


  1. Heart Rhythm Society. Sudden cardiac arrest (SCA)—who's at risk?. Available at: https://www.hrsonline.org/Patient-Resources/Heart-Diseases-Disorders/Sudden-Cardiac-Arrest-SCA/SCA-Who-s-At-Risk. Accessed May 3, 2019.
  2. Benjamin EJ, Muntner P, Alonso A, et al. Heart disease and stroke statistics—2019 update: a report from the American Heart Association. Circulation. 2019;139(10):e56–e528. DOI: 10.1161/CIR.0000000000000659. Accessed May 6, 2019.
  3. Zipes DP, Camm AJ, Borggrefe M, et al. ACC/AHA/ESC 2006 guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death—executive summary. a report of the American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Develop Guidelines for Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death). J Am Coll Cardiol. 2006;48(5):1064–1108. DOI: 10.1016/j.jacc.2006.07.008. Accessed May 6, 2019.
  4. National Heart, Lung and Blood Institute. Sudden cardiac arrest. Available at: https://www.nhlbi.nih.gov/health-topics/sudden-cardiac-arrest. Accessed May 3, 2019.
  5. Mayo Clinic. Long QT syndrome. Available at: https://www.mayoclinic.org/diseases-conditions/long-qt-syndrome/symptoms-causes/syc-20352518. Accessed May 7, 2019.
  6. Friederich P. Monitoring of the QT interval in perioperative and critical care. Available at: https://www.gehealthcare.com/en/white-paper/automated-qt-interval-monitoring. Accessed May 6, 2019.