History and exam

Key diagnostic factors

common

patient unresponsive

Patient will be unresponsive. Airway, breathing, and circulation should be assessed.

absence of normal breathing

May have absent breathing or agonal respiration.

absence of circulation

Does not have a pulse.

cardiac rhythm disturbance

Possibilities include ventricular fibrillation, pulseless ventricular tachycardia, pulseless electrical activity, or asystole.

Risk factors

strong

coronary artery disease (CAD)

The most common cause of sudden cardiac arrest is CAD.[12] Transitively, the risk factors for myocardial infarction and ischemic heart disease also increase the risk of sudden cardiac arrest. However, given that many people with CAD do not have cardiac arrest, the degree of association of each of these risk factors with sudden cardiac arrest is unsubstantiated.[27]

left ventricular dysfunction

Strongly associated with sudden cardiac arrest, whether it is the result of ischemic heart disease or nonischemic dilated cardiomyopathy.[28] This is borne out by studies showing that the implantation of a defibrillator, without a history of sudden cardiac arrest, markedly reduces the rate of death due to ventricular arrhythmia in patients with left ventricular dysfunction.[29]

age

Advanced age is strongly associated with sudden cardiac death.[7]​ After infancy, the rate of sudden cardiac death increases exponentially with age.

hypertrophic cardiomyopathy (HCM)

Disordered myofibrils, myocardial scarring, and ischemia all likely serve as an arrhythmic substrate in patients with HCM.[30] Though the overall risk of sudden cardiac arrest in these patients is low, HCM is the number one cardiovascular cause of sudden cardiac arrest in young people.[31]

arrhythmogenic right ventricular dysplasia (ARVD)

Genetic disorder in which the right ventricular myocardium (and sometimes the left ventricular myocardium) is replaced by a fibro-fatty infiltrate. Retrospective case series in patients with ARVD estimate that almost one quarter of patients have sudden cardiac death as their presenting feature, usually before the fourth decade of life.[32]

long QT syndrome (LQTS)

Due to either the inheritance of dysfunctional cardiac ion channels or an acquired disorder due to various different medications.[24] Untreated, patients with the congenital LQTS are reported to have a risk of sudden cardiac arrest of up to 60% at 10 years.[33] The risk is markedly decreased in patients on beta-blocker treatment. High-risk features include a QT interval >500 milliseconds, certain mutations, female gender, and history of syncope.[34]

medications that prolong the QT interval or cause electrolyte disturbances

Certain medications may increase risk for prolongation of the QT interval. These include quinidine, procainamide, sotalol, amiodarone, disopyramide, dofetilide, phenothiazines, and tricyclic antidepressants. CredibleMeds: drugs that prolong the QT interval Opens in new window

Diuretic use may increase risk of electrolyte disturbances.

acute medical or surgical emergency

Potential causes of cardiac arrest include massive pulmonary embolism (PE), hypoxia, hypovolemia, hemorrhagic shock, hyper- or hypokalemia, hydrogen ion excess (acidosis), hypothermia, hypo- or hyperglycemia, trauma, tension pneumothorax, thrombus (PE, myocardial infarction), toxins (e.g., in renal failure or drug intoxication), cardiac tamponade, valvular disturbance, myocardial puncture, and intracranial pathology.

poisoning

Opioid overdose is the leading cause of cardiac arrest due to poisoning in North America.[35] Rates of out-of-hospital cardiac arrests due to opioid use have been increasing in recent years with the rising use of synthetic opioids (particularly fentanyl).[36][37] Opioids directly lead to respiratory depression and hypoxia-induced cardiac arrest. Stimulants such as cocaine may also increase the risk of arrhythmia or ischemia leading to cardiac arrest. Other substances that can lead to cardiac arrest in overdose include benzodiazepines, beta-blockers, calcium channel blockers, cyanide, digoxin and related cardiac glycosides, local anesthetics, methemoglobinemia, organophosphates and carbamates, sodium channel antagonists, and sympathomimetics.[35]

weak

Brugada syndrome

Characterized electrocardiographically by a pseudo-right bundle branch block pattern and ST-segment elevations in leads V1 through V3.[38] In a meta-analysis of 24 studies, prevalence was estimated at 0.4% worldwide.[39] The disorder is thought to be due to the autosomal dominant SCN5A gene mutation, which encodes a dysfunctional cardiac sodium channel and predisposes to arrhythmia, though the known mutations in this gene are found in only 18% to 30% of patients with the syndrome.[40]

Notably, the syndrome is estimated to cause up to 4% of sudden cardiac arrest overall, and up to 20% of sudden cardiac arrest in patients without structural heart disease.[40]

valvular heart disease

Risk of acute or chronic heart failure with history of valvular heart disease; during evaluation, specific attention should be paid to aortic and mitral stenosis.

smoking

Cigarette smoking is associated with an increased risk of sudden cardiac arrest.[41] This may be due to the nicotine-mediated effects of increased myocardial oxygen demand, induction of catecholamine release, coronary vasospasm, and related arrhythmogenicity.[42]

history of eating disorders

Due to either malnutrition or emesis, eating disorders may result in electrolyte abnormalities (such as hypokalemia and/or hypophosphatemia) that contribute to ventricular arrhythmia or cardiac failure.[43]

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