Sudden cardiac death definitions and diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Edzel Lorraine Co, DMD, MD[3] Nehal Eid, M.D.[4]

Overview

• The diagnosis of sudden cardiac arrest (SCA) is made when the following diagnostic criteria are met: the absence of a palpable pulse of the heart due to abrupt cessation of pump function, absent carotid pulse,gasping respiration or no respiration, loss of consciousness due to cerebral hypoperfusion.

Definitions and Diagnosis

• The case definitions of sudden cardiac death vary based on the use of death certificates, reviews of EMS or hospital records, or whether the cases met the criteria of epidemiological definitions (eg, World Health Organization),society definitions (eg, Cardiac Arrest Registry to EnhanceSurvival [CARES]), outcomes of clinical trials, or the definition required in pathology-based studies.
• Sudden cardiac death is typically presumed to be of cardiac etiology because most individuals who died from sudden cardiac death do not have autopsies to confirm the underlying cause.
• A person resuscitated from an out-of-hospital cardiac arrest to hospitalization is classified as having resuscitated out-of-hospital cardiac arrest,regardless of subsequent in-hospital death or survival to discharge, the latter of whom are sudden cardiac arrest survivors.

• The diagnosis of SCA is made when the following diagnostic criteria are satisfied:

• Absence of a palpable pulse of the heart due to cessation of pumping function whether with prompt intervention will be reversible
• Absent carotid pulse
• Gasping respiration or no respiration
• Loss of consciousness due to cerebral hypoperfusion

Components	Assessment and findings
Symptoms	Symptoms related to arrhythmia Palpitations, lightheadedness, syncope, dyspnea, chest pain, cardiac arrest Symptoms related to underlying heart disease: Dyspnea at rest or on exertion, orthopnea, paroxysmal nocturnal dyspnea, chest pain, edema Precipitating factors: Exercise, emotional stress
Past medical history	Heart disease: Coronary, valvular (mitral valve prolapse), congenital heart disease Thyroid disease Acute kidney injury Chronic kidney disease Electrolyte abnormalities  Stroke,embolic events  Lung disease  Epilepsy (arrhythmic syncope can be misdiagnosed as epilepsy)  Alcohol, illicit drug use  Use of over-the-counter medications caused QT prolongation and torsades de pointes  Unexplained motor vehicle accident
Medications	Antiarrhythmic medications  Medication with QT prolongation and torsades de pointes effect Cocaine,amphetamines Anabolic steroids  Medication-medication interaction that could cause QT prolongation and torsades de pointes
Family history	SCD, SCA, unexplained drowning in a first-degree relative SIDS, repetitive spontaneous pregnancy losses concerning cardiac channelopathies  IHD  Cardiomyopathy: Hypertrophic,dilated, ARVC Congenital heart disease  Cardiac channelopathies: Long QT, Brugada, Short QT, CPVT  Arrhythmias: conduction disorders, pacemakers/ICDs Neuromuscular disease associated with cardiomyopathies  Muscular dystrophy Epilepsy

• Following an initial diagnosis of cardiac arrest, healthcare professionals further categorize the diagnosis based on the ECG rhythm.
• There are 4 rhythms that result in a cardiac arrest. Ventricular fibrillation (VF) and Pulseless Ventricular tachycardia (VTach) are both responsive to a defibrillator and so are colloquially referred to as Shockable rhythms, whereas Asystole and Pulseless Electrical Activity (PEA) are non-shockable.
• The nature of the presenting heart rhythm suggests different causes and treatment and is used to guide the rescuer as to what treatment may be appropriate (see Advanced Life Support and Advanced Cardiac Life Support, as well as the causes of arrest (below))
• The table below provides information on the differential diagnosis of sudden cardiac death in terms of ECG appearance:

Disease Name	Causes	ECG Characteristics	ECG view
Ventricular tachycardia	Ischemic heart disease Illicit drug use such as cocaine and methamphetamine Structural heart diseases Electrolyte disturbances Congestive heart failure Myocarditis Obstructive sleep apnea Pulmonary artery catheter Long QT syndrome	Ventricular tachycardia (VTach originates from a ventricular focus. Lasts more than 30 seconds. Broad QRS complexes: rate of >90 BPM.
Ventricular fibrillation	Acute coronary ischemia Cardiomyopathies Congenital heart disease Myocardial infarction Heart surgery Electrolyte abnormalities	Poorly identifiable QRS complexes and absent P waves The heart rate is >300 BPM Rhythm is irregular
Ventricular flutter	Electrolyte disturbances Medications such as: Disopyramide Quinidine	The ECG shows: A typical sinusoidal pattern Frequency of 300 bpm
Asystole	Hypovolemia Hypoxia Acidosis Hypothermia Hyperkalemia or Hypokalemia Hypoglycemia Cardiac Tamponade Tension pneumothorax Thrombosis Myocardial infarction Thrombosis Pulmonary embolism Cardiogenic shock Degeneration of the sinoatrial or atrioventricular nodes Ischemic stroke	There is no electrical activity in the asystole
Pulseless electrical activity	Hypovolemia Hypoxia Hydrogen ions (Acidosis) Hypothermia Electrolyte disturbances Hypoglycemia Tablets or Toxins (Drug overdose) such as beta blockers, tricyclic antidepressants, or calcium channel blockers Tamponade Tension pneumothorax Thrombosis (Myocardial infarction) Thrombosis (Pulmonary embolism) Trauma (Hypovolemia from blood loss)	Several ppattern are possible including: Normal sinus rhythm Sinus tachycardia, with discernible P waves and QRS complexes Bradycardia, with or without P waves
Torsade de Pointes	*Electrolyte disturbances Medications such as: Amiodarone Azithromycin Clozapine Famotidine Flecainide Foscarnet Levofloxacin Lithium Mirtazapine Quetiapine Risperidone Tacrolimus Tamoxifen Ziprasidone	Paroxysms of VTach with irregular RR intervals. A ventricular rate between 200 and 250 beats per minute. Two or more cycles of QRS complexes with alternating polarity. Changing the amplitude of the QRS complexes in each cycle in a sinusoidal fashion. Prolongation of the QT interval. Is often initiated by a PVC with a long coupling interval, R on T phenomenon. There are usually 5 to 20 complexes in each cycle.