FEATURE EMERGENCY MEDICINE
every 80 seconds. It has been estimated that SCD claims more than 7,000,000 lives per year worldwide. Although there is no rigid data on the incidence of SCD in the Middle East, the data from Al Haram Emergency Center Registry (Kingdom of Saudi Arabia) indicates its notable occurrence and a demanding cause of mortality and morbidity in this region.
ETIOLOGY Overall, coronary heart disease (CHD) is the single most common cause of SCD in the US and Western Europe, accounting for approximately 80% of the deaths. In addition, SCA is the initial clinical manifestation of CHD in approximately 15% of the cases. The specific causes of SCA, however, vary with the population studied and patient age. The group of disorders responsible for SCD in the adolescent and young adult group is distinctly different from those in the middle-aged to the elderly group. In young adults and adolescents, coronary atherosclerosis is an uncommon cause, with myocarditis, hypertrophic cardiomyopathy, long QT syndromes, right ventricular dysplasia, anomalous coronary arteries, Brugada syndrome, and idiopathic ventricular fibrillation accounting for the majority of these deaths. In different reports, approximately 10-12% of cases of SCA among subjects under age 45 occur in the absence of structural heart disease secondary to electrical abnormality of the heart. This includes Brugada syndrome, idiopathic ventricular fibrillation (also called primary electrical disease), congenital or acquired long QT syndrome, arrhythmogenic right ventricular cardiomyopathy, familial polymorphic ventricular tachycardia (also called catecholaminergic polymorphic ventricular tachycardia), familial SCD of uncertain cause, and Wolff-Parkinson-White syndrome. In addition to the presence of the above underlying disorders, superimposed triggers for SCA appear to play a major role in the pathogenesis of this disorder. These include ischemia, electrolyte disturbances (particularly hypokalemia and hypomagnesemia), the proarrhythmic effect of some antiarrhythmic drugs, autonomic nervous system activation, and psychosocial factors. An analysis of pathophysiology of SCA reveals arrhythmia as the underlying
«SCA accounts for 63% of all cardiac deaths in the United States»
mechanism in 88% of all SCA cases among which ventricular tachycardia stands first (62%) followed by bradycardia (17%), torsades de pointes (13%), and primary ventricular fibrillation (8%).
MANAGEMENT The management of SCA patient focuses on three main principles: The initial emergency care to stabilize hemodynamic status. Investigation of the underlying cause and precipitating factors. Prevention of recurrences. Guidelines regarding the standard
resuscitation protocol have been published by the American Heart Association. When someone collapses from SCA, immediate cardiopulmonary resuscitation (CPR) and use of an automated external defibrillator (AED) are essential for any chance of recovery. For patients in ventricular fibrillation, studies show that if early defibrillation is provided within the first minute, the odds are 90% that the victim’s life can be saved. After that, the rate of survival drops 10% every minute. As many as 30-50% would likely survive if CPR and AEDs were used within five minutes of collapse. The recent proliferation of AED has expanded the availability of early defibrillation. All survivors of SCA need to be admitted in an intensive care unit with
continuous cardiac monitoring and require evaluation for etiological as well as provoking factors. The patient or/ and family should be questioned about previous diagnoses of heart disease, the use of any medication, especially antiarrhythmic agents, diuretics, or digoxin and antecedent symptoms. Any electrolyte abnormality need to be identified and corrected, serial ECGs and cardiac enzymes should be measured and structure and function of the heart should be evaluated with echocardiography. Since CHD accounts for a majority of cases, coronary angiogram is often required. An electrophysiology study is helpful in the diagnosis of number of arrhythmias including nodal dysfunction, conduction abnormalities, accessory pathways and inducibility of ventricular tachycardias. After comprehensive evaluation and treatment of the underlying problem (e.g. coronary revascularization for acute ischemia) decision to administer appropriate measure to prevent further occurrence of life threatening arrhythmias has to be made. This is called secondary prevention and is of utmost necessity as one year and two year mortality of SCA survivors is as high as 32% and 47% respectively. Currently, implantable cardioverter defibrillator (ICD) is the standard of care for all resuscitated victims of SCA which are not due to transient or reversible cause such as acute myocardial infarction or electrolyte abnormalities. The other conditions that do not require ICD insertion include episodic prolonged sinus arrest, severe
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